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Evans, E. M. "Tidal stream energy." Thesis, University of Plymouth, 1987. http://hdl.handle.net/10026.1/515.
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Hrushetska, I. "Tidal energy systems." Thesis, Видавництво СумДУ, 2012. http://essuir.sumdu.edu.ua/handle/123456789/26026.
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Patel, Keval. "Prospective of Tidal Energy." Thesis, Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-40592.
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Giles, Jack William. "Energy extraction from shallow tidal flows." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/361703/.
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Over the past decade within the renewable energy sector a strong research and development focus has resulted in the growth of an embryonic tidal stream energy industry. Previous assessments of the tidal stream resource appear to have neglected shallow tidal flows. This resource located in water depths of 10-30m is significant because it is generally more accessible for energy extraction than deeper offshore tidal sites and hence a good location for first generation tidal stream arrays or fences. The close proximity to shore may lead to improvements in construction feasibility and economic prospects. The objective of this project is to investigate several aspects concerning the exploitation of shallow tidal flows for energy extraction. Fundamental to this project is the importance of developing research alongside and in conjunction with industrial shallow water prototype projects. The key objectives are: (1) The development and understanding of the use of artificial flow constraint structures in the form of specifically-shaped foundations (herein described as “rampfoundations”) that constrain the flow leading to an increase in the magnitude and quality of power from marine current energy convertors (MCEC) operating in shallow tidal flows. (2) The investigation of seabed and free-surface proximity effects on the downstream wake structure of a MCEC. (3) Commercial shallow water device optimisation; utilising project results to aid with the design and development of full-scale commercial demonstrators. Through theoretical and scaled experimental modelling, and commercial collaboration the project has concluded ramp foundations could be utilised to locally increase tidal flow velocities and increase MCEC output across a tidal cycle in shallow flows. Predicted power benefits are in the region of 5-22% depending on lateral and vertical ramp channel blockage ratios. The ramp width or overall array width must therefore be tuned to the channel width to maximise power benefits. Rampfoundations will thus only be technically viable in relatively narrow channels or ideally in MCEC arrays or tidal fences. Results have shown that the downstream wake length is dependent on and varies with the vertical flow constraint and it is critical that the downstream array spacing of MCECs are tuned to the local flow depth. An optimum device height to flow depth ratio to minimise wake length has been identified. It is hoped that this ramp-foundation concept and the relationship between boundary proximity and wake length will continue to help with the development of a niche shallow tidal energy market
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Schluntz, Justine Oakley. "Tidal turbine array modelling." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:b342fda1-a311-4783-8249-9b1515e0ad62.
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Computational fluid dynamics (CFD) is used in this thesis to model wind and tidal stream turbines and to investigate tidal turbine fence performance. There are two primary objectives of this work. The first is to develop and validate an actuator line method for the simulation of wind and tidal turbines which applies the blade forces to the flow field without the need for a regularisation kernel. The second is to examine tidal fences using, in part, the newly developed actuator line method. A potential flow equivalence method for determining the relative velocity to the blade chord and flow angle at the rotor blades in the actuator line method is proposed and validated. Results for simulations using this method compare favourably with those from both experiments and alternative computational methods, although the present model’s results deviate from experimental results in the vicinity of the blade tips. A CFD-embedded blade element-momentum tool is used to design rotors for operation in infinitely wide tidal fences spanning a tidal channel. Rotors are designed for fences with several different blockage ratios, with those designed for high blockage flows having greater solidity than those designed for operation in fences with lower blockage. It is found that designing rotors for operational blockage conditions can significantly improve the power output achieved by a tidal fence. Improved power output for higher blockage conditions is achieved by the application of greater thrust to the flow. Actuator line simulations of short (up to 8 turbines) fences with varying intra-rotor spacing and number of rotors confirm that hydrodynamic performance of the rotors improves as the spacing is reduced and as rotors are added to a fence. The position of a rotor within the fence impacts its performance; rotors at the ends of a fence extract reduced power compared to those at the centre of the fence, particularly for tip speed ratios greater than the design tip speed ratio.
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Carter, Caroline Jane. "Tidal energy, underwater noise & marine mammals." Thesis, University of the Highlands and Islands, 2008. https://pure.uhi.ac.uk/portal/en/studentthesis/tidal-energy-underwater-noise-and-marine-mammals(9963d662-76e1-4e70-a3ac-e18a96b23101).html.
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Sourcing energy from renewable sources is currently a key theme in modern society. Consequently, the pace of development of these emerging technologies is likely to increase in the near future, particularly in marine renewables. However, the environmental and ecological impact of many of these new developments in the marine environment is largely unknown. My thesis has focused on one unknown area of interaction; the potential effect of tidal-stream devices on marine mammals. Collision risk is often cited as a key concern. Therefore, my premise was - for marine mammals to avoid a collision with a marine renewable device (assuming they are on a collision course) they must first detect the device. It is well understood that marine mammals use sound and hearing as their primary sense for communication, foraging, navigation and predator avoidance, so it is highly likely that the primary cue for device detection will be acoustic. However, it is not known how operational marine renewable devices might modify the acoustic landscape in these areas, or whether they will be audible to marine mammals in time to alert them to the presence of devices. It has been suggested that the high level of natural and anthropogenic background noise in tidal-stream areas may mask (drown out) the signal of the tidal devices. The acoustic characteristics of underwater noise in shallow coastal waters are currently not well known. My thesis adds data to this knowledge gap by measuring and mapping underwater noise levels in tidal-stream areas.
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Vogel, Christopher Reiner. "Theoretical limits to tidal stream energy extraction." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:68486b23-d773-44ad-a353-7efc855dc8ff.
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Tidal stream energy has gained attention as a source of predictable and renewable energy. Devices resembling underwater wind turbines, placed in fast tidal streams, have been proposed to extract this energy. Arrays of many such devices will need to be deployed to deliver a significant amount of energy to the electricity grid. One consequence of energy extraction is that the array provides a resistance to the tidal stream, which may change the local and far field hydrodynamics, which in turn affects the power available to the array. Array-scale hydrodynamic changes affect the flow presented to the devices, which in turn affects the total resistance the array provides to the flow. This thesis is concerned with the interactions between device, array, and the tidal stream resource, to better understand the power potential of turbine arrays. Linear momentum actuator disc theory is employed to describe the operation of an idealised turbine array partially spanning a wide channel. The model is comprised of two quasi-independent sub-models, an array-scale model, describing flow phenomena around the array, which provides the upstream boundary condition to the device-scale model, describing the flow around a device. The thrust applied by the array is the sum of the thrust applied by the devices, completing the sub-model coupling. The numerical simulation of arrays in depth-averaged simulations is then investigated using the two-scale concept developed in the analytic partial-array model. It is shown that the device-scale flow must be modelled with a sub-grid scale model in order to correctly describe the unresolved device-scale flow and hence estimate the power available to an idealised array. Turbulence modelling in depth-averaged simulations of turbine arrays is also discussed. Temporal variations in tidal amplitude and strength mean that generator capacity will need to be economically matched to the available resource. As device performance may consequently depart from the relationship derived in idealised models when power capping is employed, blade element momentum theory is modified to parameterise tidal turbine performance during power capping. The array-scale effect of power capping is studied in depth-averaged simulations, in which it is shown that a significant reduction in device thrust may occur during power capping, reducing the impact of energy extraction from the tidal stream.
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Broadhurst, Melanie. "The ecology of marine tidal race environments and the impact of tidal energy development." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/14450.
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Marine tidal race environments undergo extreme hydrodynamic regimes and are favoured locations for offshore marine renewable tidal energy developments. Few ecological studies have been conducted within these complex environments, and therefore, ecological impacts from tidal energy developments remain unknown. This thesis aimed to investigate the ecological aspects of marine tidal race environments in two themes, using a combination of field-based sampling techniques. I first examined the natural ecological variation of a marine tidal race environment at the spatial and temporal scale. These studies were based on the benthic and intertidal communities within the Alderney Race tidal environment, Alderney. My results suggest that both communities vary in species diversity and composition, at different spatial gradients and timescales. Species showed opportunistic or resilient life history characteristics, highlighting the overall influence of the strong hydrodynamic conditions present. I then explored the ecology of a marine tidal race environment within a renewable tidal energy development site. These studies were based within the European Marine Energy Centre’s tidal energy development site, Orkney. Here, I investigated ecological variation in terms of fish interaction and benthic assemblage structure with a deployed tidal energy device, and, the structure of intertidal communities within the overall development site. Interestingly, my results indicated species-specific interactions with the deployed tidal energy device, which was related to species’ refuge or feeding behaviour. These results also imply that different communities show varied spatial and temporal heterogeneity within a development site, associated with the complex interplay of abiotic and biotic processes. This work begins to reveal the ecological consequences of tidal energy development, with single devices acting as potential short-term artificial reef structures. Further research is recommended within these environments, with reference to how the hydrodynamic regimes directly influence these communities, and, the overall ecological consequences of future large-scale tidal energy development scenarios.
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Spurlock, Derek Scott. "Modeling Flows for Assessing Tidal Energy Generation Potential." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/35140.
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Tidal energy is a clean, sustainable, reliable, predictable source of energy. Recent developments in underwater turbines have made harvesting tidal energy feasible. Determining the power potential available in a given water body can be accomplished by using numerical hydraulic models to predict the flow velocity at a location of interest. The East River in Manhattan has been used here in an effort to develop a modeling methodology for assessing the power potential of a site. Two two-dimensional CFD models, FESWMS and TUFLOW, as well as one one-dimensional model, HEC-RAS, are used to analyze flows in the East River. Comparisons are made between the models and TUFLOW proves to best represent flows in the East River. HEC-RAS provides accurate results; however, the one-dimensional results lack the necessary detail of a two-dimensional model. FESWMS cannot produce results that mimic actual flow conditions in the East River. Using the TUFLOW model, power and energy estimates are made. These estimates show that a two-dimensional model, such as TUFLOW, can be a great tool for engineers and planners developing tidal energy projects. Using the results of this work, a methodology is developed to assess power potential at other sites using publicly available data.Master of Science
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Shah, Sunny. "Improved uncertainty analysis for tidal energy project development." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/32602.
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High investment risk is a key barrier to the commercialisation of the nascent tidal energy sector. An increase in investor confidence can unlock funding for early arrays, the lessons from which can provide further de-risking, leading to further investment. This thesis focussed on increasing investor confidence by improving the uncertainty analysis methods used to quantify the overall uncertainty in key investment decision metrics; energy yield, levelised cost of energy (LCOE) and internal rate of return (IRR). A Monte Carlo Analysis (MCA) framework for tidal energy annual yield uncertainty analysis was developed and compared to the currently recommended ISO-GUM method. It was shown that key assumptions implicit in ISO-GUM are inaccurate for most realistic projects. Crucially, the resultant error provides an overly optimistic view of a project's P90 energy yield. By modelling a range of realistic projects, it was shown that the ISO-GUM P90 yield overestimate exceeds 2% for a maximum resource uncertainty between 4% and 11%, depending on the project, with increasing uncertainty leading to larger errors. It is difficult to judge accurately where within that range a given case crosses the 2% error threshold, as it is a complex function of numerous project specific variables. This undermines confidence in ISO-GUM results, even in cases where the method may be acceptable, because it is not possible to deduce the validity for a particular project a priori. MCA does not make the same assumptions and provides consistently accurate results. A modification to the standard ISO-GUM process was also proposed as a simpler alternative to MCA, with an improvement in results compared to the standard method, but the residual error would still remain unquantified. A generic cost modelling tool for probabilistic discounted cashflow analysis using MCA was also developed. The tool accepts user specified uncertainty distributions in a multitude of flexibly defined input variables defining a project's CapEx, OpEx, yield and finances to produce distributions representing uncertainty in LCOE and IRR. It was compared to commonly used deterministic methods for a realistic tidal energy project. MCA provides highly resolved results compared to the point estimates from deterministic methods. The improved decision support provided by MCA was demonstrated and the scope for misinterpreting the deterministic outputs was highlighted. The significance of several common cost modelling assumptions was tested and the difference between probabilistic and deterministic sensitivity analysis was highlighted. A probability weighted deterministic method was suggested and shown to provide useful indicative results at a reduced effort compared to MCA. Finally, the impact of the ISO-GUM P90 yield error on the P90 LCOE and IRR was quantified for several cases by propagating the ISO-GUM and MCA yield uncertainty distributions through the cost model. MCA propagates input distributions through the functional relationship between the inputs and outputs. For any application, this reduces the unquantified approximations in the results compared to the simpler methods considered. This leads to not only more accurate results, but also a higher confidence in the results. The use of MCA is therefore recommended for annual yield and financial performance uncertainty analysis for tidal energy projects.
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Leclercq, Mathilde. "Harvesting energy from the sea." Thesis, KTH, Kraft- och värmeteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91881.
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Every marine energy source presents advantages and disadvantages. For example, they are not atthe same stage of maturity. Tidal range power is fully mature but the limited number of sitesavailable, combined with the large environmental impacts and investment costs limit itsdevelopment. The idea of artificial lagoons that will be offshore tidal range plant could create a newinterest for this technology. But for the moment, no plant of this type has been constructed yet. Tidalstream power is the next mature technology of marine energy after tidal range. Its development willrequire public subsidies but is supposed to be commercial in 2015. Systems are already indemonstration in several countries (UK, France and Canada). Wave power is less mature but it willbenefit from the development of tidal stream power and will probably be commercial in 2020. Somesystems are also in demonstration but challenges seem greater in wave power than in tidal power.Wave power conversion systems have to extract energy from the waves, even the largest ones, butat the same time resist to them. Contrary to tidal stream which has a predictable resource, waves areway less predictable and systems will have to be able to resist and valorize waves. OTEC (OceanThermal Energy Conversion) has been studied for years but it is still not mature. Its development forelectricity production needs technology research to develop cheaper and more compact systems(heat exchangers, pipes…). Air conditioning applications are developing and also require the use ofpipes and heat exchangers. Advances in this utilization could maybe help the development of OTECsystems for electricity production. Osmosis is the less mature and the most challenging technology. Atechnological breakthrough in the membrane could allow a rapid development. This breakthroughwill probably come from other sectors so it is important for the industries to get ready in order todevelop the system as soon as this technological improvement will be made.
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Lande-Sudall, David. "Co-located offshore wind and tidal stream turbines." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/colocated-offshore-wind-and-tidal-stream-turbines(72acb21d-1b88-45ad-b944-3f9664330420).html.
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Co-location of offshore wind turbines at sites being developed for tidal stream arrays has been proposed as a method to increase capacity and potentially reduce the cost of electricity compared to operating either technology independently. This research evaluates the cost of energy based on capital expenditure and energy yield. It is found that, within the space required around a single 3 MW wind turbine, co-location provides a 10-16% cost saving compared to operating the same size tidal-only array without a wind turbine. Furthermore, for the same cost of electricity, a co-located farm could generate 20% more yield than a tidal-only array. These results are based on analysis of a case-study site in the Pentland Firth. Wind energy is assessed using an eddy viscosity wake model in OpenWind, with a 3 MW rated power curve and thrust coefficient from a Vestas V90 turbine. Three years of wind resource data is from the UK Met Office UK Variable (UKV) 1.5 km numerical model and corrected against a 400 m Weather Research and Forecasting (WRF) model run over the site. Tidal stream energy is modelled using a semi-empirical superposition of self-similar plane wakes, with a generic 1 MW rated power curve and thrust based on a full-scale, fixed-pitch turbine. Coincident tidal resource data is from the Forecasting Ocean Assimilation Model (FOAM) at 7.5 km resolution and correlated with a 150 m ADvanced CIRCulation model (ADCIRC). Wave parameters are corrected from ERA-Interim data with six months of wave buoy data. Multiple tidal turbine array layouts are considered, with maximum tidal energy generated for a staggered array with spacing of 20 tidal turbine diameters, Dt , streamwise and 1.5Dt cross-stream. However, cheapest cost of electricity from the tidal-only array, was found for a single row of turbines, due to minimal wake effects. Laboratory experiments were undertaken to validate the superposition wake model for use with large, shared support structures. Two rotors mounted either side of a central tower generate a peak wake velocity deficit 70% greater than predicted by superposition. This was due to high local blockage and a complex near-wake structure, with a corresponding increase in tower drag of 9%. Further experiments evaluated the impact of oblique inflow on turbines yawed at +/-15 degrees. These results validated a theoretical cosine correction for thrust coefficient and characterised the centreline wake drift with downstream distance. Extreme environmental loads for a shared support structure, compared to structures for wind-only and tidal-only, have also been modelled. A non-linear wave model was used to represent a single wave form with 1% occurrence for each hour of time-series data. Overturning moment about the base of a shared support, with one wind and two tidal turbines, was found to be 4.5% larger than for a wind-only turbine in strong current and with turbines in different operational states. Peak loads across the tidal array were found to vary by 2.5% and so little load reduction benefit could be gained by locating a shared support in a more sheltered area of the array.
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Muchala, Subhash. "Impact of tidal turbine support structures on realizable turbine farm power." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:12db3e87-650b-4784-b68c-c81636e72118.
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This thesis discusses the importance of tidal turbine support structures through analytical and computational modelling. A head-driven analytical channel model was first developed to determine the sensitivity of the flow to the presence and type of support structures. It showed that there was a significant potential reduction in farm power output even when only considering approximate force coefficients for rotor and support structure. To confirm these findings, computational simulations were performed on a full-scale turbine to obtain more accurate force coefficients considering full rotor-support structure interactions. The flow interaction effects between the rotor and its support structure were studied using Computational Fluid Dynamics (CFD) for different support structure shapes for a range of tidal velocities including the power-capping zone. The integrated rotor force coefficients were higher in the presence of the cylindrical support structure than the elliptical support due to the higher opposing thrust from the cylinder in the channel redirecting the flow and increasing the flow velocity over the top half of the rotor. The presence of rotor caused a drop in the stream-wise forces on the support structure. The amplitude of the stream-wise sectional forces along the support structure height was lower in the case of an elliptical than a circular cylinder due to more streamlined shape of the ellipse. At device scale, the computational model was used to study the turbine performance in the power-capping zone by pitching the blades to feather. The influence of pitch-to- feather power-capping strategy was examined by studying the forces and angle of attack on the turbine blades, and the wake at three different blade pitch angles. Increasing blade pitch angle resulted in a significant drop in the average load on the blade. Also since the tidal channel flow has a shear in its velocity profile, the influence of shear on turbine performance was studied by comparing it to the same turbine in a uniform flow. The analytical channel flow model was used to investigate the characteristics of tidal stream energy extraction for large tidal farms deployed in tidal channels with specific focus on the limitations to realizable farm power due to turbine support structure drag and constraints on volume flow rate reduction. The force coefficients dataset from computational modelling was used to obtain a better estimate of the farm power output. Support structures were seen to contribute significantly to the overall resistive force in the channel and thus reduce the overall flow rates in the channel, leading to losses in realizable power. Over a wide range of channel characteristics, realistic levels of support structure drag lead to up to a 10% reduction in realizable power, and an associated reduction in the number of turbines that can be economically installed.
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Sun, Xiaojing. "Numerical and experimental investigation of tidal current energy extraction." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/2756.
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Numerical and experimental investigations of tidal current energy extraction have been conducted in this study. A laboratory-scale water flume was simulated using commercial computational fluid dynamics (CFD) code FLUENT. In the numerical model, the tidal current turbine is represented with an actuator disk, which produces a pressure drop associated with energy loss. The free water surface is considered in the model using a volume of fluid method and is allowed to deform freely. Numerical results identified that a localised wake is formed behind the tidal current turbine and there is considerable localised flow acceleration around and most especially, under the energy extraction device. A free water surface drop is visualised in the model results due to the energy extraction and this free surface drop is believed to have an impact on the recovery of turbine wake. The influence of other parameters like water depth, ambient turbulence and flow speed on the tidal current energy extraction are also testified, based on the numerical model. Numerical results demonstrated that, because of the existence of a free water surface, tidal turbine interaction with the flow is a complicated three dimensional problem. Therefore, completely using the theoretical methods of wind turbines for tidal current turbine study would be inappropriate. Two physical tests were deigned for the experimental investigation of energy extraction from tidal currents and were carried out under different testing conditions: one was in moving water using a natural open channel and the other was in still water using a towing tank. Comparing experimental and numerical results of wake velocity profiles, good qualitative agreement has been obtained, which proves that the proposed numerical model can provide essential insight into the mechanism of wake development behind tidal current turbines. Experimental results also confirmed that, although moving water is the real operational condition of tidal turbines, a towing tank is still an ideal facility for the experimental study of tidal turbines, especially at the early stages of understanding of the detailed physical processes governing the performance of rotors and turbine wake behaviour. This study is a comprehensive investigation into tidal current energy extraction at laboratory scale. Environmental impact of tidal current energy extraction is further recognized and an appropriate experimental facility for the model testing of tidal energy extraction devices is recommended.
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Fleming, Conor F. "Tidal turbine performance in the offshore environment." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:f51fd313-1589-4e9c-98cc-ae6e64c1184b.
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A three dimensional computational model of a full scale axial flow tidal turbine has been used to investigate the effects of a range of realistic environmental conditions on turbine performance. The model, which is based on the Reynolds averaged Navier-Stokes equations, has been developed using the commercial flow solver ANSYS Fluent. A 1:30 scale tidal turbine is simulated in an open channel for comparison to existing experimental data. The rotor blades are directly resolved using a body-fitted, unstructured computational grid. Rotor motion is enabled through a sliding mesh interface between the rotor and the channel boundaries. Reasonably good agreement in thrust and power is observed. The computed performance curves are offset from the measured performance curves by a small increment in rotor speed. Subsequently, a full scale axial flow turbine is modelled in a variety of conditions representative of tidal channel flows. A parametric study is carried out to investigate the effects of flow shear, confinement and alignment on turbine performance, structural loading, and wake recovery. Mean power and thrust are found to be higher in sheared flow, relative to uniform flow of equivalent volumetric flow rate. Large fluctuations in blade thrust and torque occur in sheared flow as the blade passes through the high velocity freestream flow in the upper portion of the profile and the lower velocity flow near the channel bed. A stronger shear layer is formed around the upper portion of the wake in sheared flow, leading to enhanced wake mixing. Mean power and thrust are reduced when the turbine is simulated at a lower position in a sheared velocity profile. However, fluctuations in blade loading are increased due to the higher velocity gradient. The opposite effects are observed when the turbine operates at greater heights in sheared flow. Flow misalignment has a negative impact on mean rotor thrust and power, as well as on unsteady blade loading. Although the range of unsteady loading is not increased significantly, additional perturbations are introduced due to interactions between the blade and the nacelle. A deforming surface is introduced using the volume-of-fluid method. Linear wave theory is combined with the existing free surface model to develop an unsteady inflow boundary condition prescribing combined sheared flow and free surface waves. The relative effects of the sheared profile and wave-induced velocities on turbine loading are identified through frequency analysis. Rotor and blade load fluctuations are found to increase with wave height and wave length. In a separate study, the performance of bi-directional ducted tidal turbines is investigated through a parametric study of a range of duct profiles. A two dimensional axi-symmetric computational model is developed to compare the ducted geometries with an unducted device under consistent blockage conditions. The best-performing ducted device achieves a peak power coefficient of approximately 45% of that of the unducted device. Comparisons of streamtube area, velocity and pressure for the flow through the ducted device shows that the duct limits the pressure drop across the rotor and the mass flow through the rotor, resulting in lower device power.
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Chapman, John Christopher. "Tidal energy device hydrodynamics in non-uniform transient flows." Thesis, Swansea University, 2008. https://cronfa.swan.ac.uk/Record/cronfa42229.
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Tidal energy devices convert the flow of water induced by the tidal cycle into useful energy. Presently the most common type of tidal energy device is a horizontal axis zero head turbine. Conceptually the form of these devices is similar to modern wind turbine systems. This thesis presents the development of a flexible code that models the hydrodynamic behaviour of a tidal stream turbine rotor and its supporting structure in a non-uniform, time varying flow. Blade Element Momentum Theory (BEMT) is reviewed and its implementation is discussed. Corrections to the theory are reviewed in the context of operation in an ocean environment. The completed model operates in a three-dimensional representation of the ocean and includes the calculation of supporting structure loads using Morison's equation. The flow regime either includes boundary layer effects and a calculated wave climate or can be taken from data measured with an ADCP. Specific model features are introduced that allow realistic appraisal of the system's performance and load regime as well as specific situations such as braking of the rotor. The capability of the code is then demonstrated using a non-uniform, time varying flow and the importance of this in the design of turbine systems is discussed. The novel features introduced in this thesis are; the inclusion of non rotor-normal inflow in the BEMT equations, a new, robust approach to solving the BEMT equations and a novel blade-off modelling approach. A calibrated marine tower shadow model, a novel procedure for comparing the performance of alternative device concepts and a method to input ADCP data directly to the model system were also novel steps introduced in the thesis.
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Alex, Ansu. "Tidal stream energy integration with green hydrogen production : energy management and system optimisation." Thesis, Normandie, 2022. http://www.theses.fr/2022NORMC216.
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L'objectif principal de cette thèse est de concevoir, mettre en œuvre et comparer différentes stratégies de gestion de l'énergie et approches d'optimisation pour un système hybride impliquant l'intégration de l'énergie marémotrice flottante avec la production de l'hydrogène vert. Pour atteindre les objectifs, les composants individuels du système sont d'abord modélisés. Les capacités annuelles de performance du système de la centrale d'énergie marémotrice ont ensuite été obtenues à l'aide des profils quotidiens fréquents au poste d'amarrage de Fall of Warness dans les îles Orcades. Les modes de fonctionnement transitoires des électrolyseurs à membrane échangeuse de protons, lorsqu'elles sont soumises à l'énergie de la centrale hydrolienne, ont été analysés sur la base d'une (RBA) stratégie de gestion de l'énergie basée sur des règles. Plus tard, une évaluation préliminaire du coût de production d'hydrogène est effectuée sur la base de différentes conditions de demande quotidienne d'hydrogène et de profils de marée quotidiens. En outre, une approche d'optimisation dans le but de maximiser le profit d'exploitation du système tout en assurant un fonctionnement optimal et suffisant des deux électrolyseurs sous des contraintes réelles du système, est formulée en donnant la priorité à la production d'hydrogène par l'énergie marémotrice. Le problème d'optimisation est résolu à l'aide d'un algorithme génétique basé sur un problème non linéaire à entiers mixtes. Une analyse coûts-avantages complète basée à la fois sur les coûts fixes-variables et sur les facteurs de coûts actualisés est réalisée pour analyser le fonctionnement technico-environnemento-économique optimal d'un système hybride d'énergie marémotrice-éolienne-hydrogène connecté au réseau. Les résultats ont été comparés aux résultats de l'approche basée sur des règles. Les bénéfices annuels dans l'approche d'optimisation ont été estimés supérieurs de 41,5 % par rapport à ceux de la RBA. De plus, d'un point de vue environnemental, les meilleurs résultats d'optimisation étaient supérieurs d’environ 47 % par rapport aux résultats de la RBA en termes de réduction des émissions de carbone. Un électrolyseur dynamique capable de fonctionner à deux fois sa puissance nominale pendant une durée limitée s'avère particulièrement avantageux lorsqu'il est couplé à l'énergie marémotrice qui est de nature cyclique avec des périodes prévisibles de production d'énergie élevée et faible. Enfin, il est conclu que l'approche d'optimisation des coûts fixes-variables est relativement simple dans l'estimation des coûts. Au contraire, bien que des résultats légèrement meilleurs soient obtenus dans le cas de l'approche par coût actualisé, il est nécessaire d'avoir une meilleure connaissance préalable du fonctionnement du système pour estimer finement les facteurs de coût actualisé. Le modèle proposé peut être utilisé comme un outil générique pour l'analyse de la production d'hydrogène dans différents contextes et il est particulièrement applicable dans les sites à fort potentiel d'énergie verte avec des installations de réseau limitéesThe overarching aim of this thesis is to design, implement and compare different energy management strategies and optimisation approaches for a hybrid system involving floating tidal stream energy integration with green hydrogen production. Towards reaching the objectives, the individual system components are modelled initially. The annual system performance capabilities of the tidal stream energy plant are then obtained using frequently occurring daily profiles at the Fall of Warness berth in the Orkney Islands, Scotland. The transitionary operating modes of two polymer electrolyte membrane electrolyser units, when subjected to the energy from the tidal stream plant are analysed based on a rule-based approach energy management strategy. Later, a preliminary evaluation of the hydrogen production cost is assessed based on different daily hydrogen demand and daily tidal profile conditions. Further, an optimisation approach with the objective to maximise the system operating profit ensuring optimal and sufficient operations of both the electrolyser units under real system constraints, is formulated with priority for tidal energy powered hydrogen production. The optimisation problem is solved using a genetic algorithm based on the mixed integer non-linear problem. A comprehensive cost-benefit analysis based on fixed-variable costs and levelised costs factors is performed to analyse the optimal techno-enviro-economic operation of a hybrid grid connected tidal-wind-hydrogen energy system. The outcomes are compared against the rule-based approach results. The annualised profits in the optimisation approach are estimated to be 41.5% higher compared to the rule-based approach. Further, from an environmental view, the best optimisation results are approximately 47% higher than the rule-based approach results in terms of carbon emission reductions. A dynamic electrolyser capable of working at twice of its nominal power rating for limited duration, resulted particularly advantageous when coupled with tidal energy which is cyclic in nature with predictable periods of high and low power generation. Finally, it was determined that the fixed cost (FC) optimisation approach is relatively simple in terms of cost estimation. On the contrary, while the levelised cost (LC) approach yields slightly better results, it necessitates a greater prior knowledge of system operations to reasonably estimate the cost factors. The proposed method can be used as a generic tool for electrolytic hydrogen production analysis under different contexts, with preferable application in high green energy potential sites with constrained grid facilities
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Hunter, William. "Actuator disk methods for tidal turbine arrays." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:bf8e95df-9e67-4c89-8d9d-1a608a8be0f4.
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Tidal stream energy presents challenges that will require the development of new engineering tools if designs are to harness this energy source effectively. At first glance one might imagine that tidal stream energy can be treated as wind with appropriate adjustment for fluid properties of water over air, and account taken of the harsher offshore environment; both waves and turbulence. However, it is now well accepted that the flow past turbines that are constrained by the local sea bed, sea surface, and possibly also neighbouring turbines and channel sides, will differ markedly from that of an ostensibly unblocked wind turbine. Garrett & Cummins (2007) were the first to demonstrate that operating a turbine in a non- negligibly blocked flow passage presents a different flow solution and importantly a significant opportunity to enhance the power that can be delivered by blocked turbines with the limit of power extraction exceeding the Lanchester-Betz limit for operation of unblocked wind turbines. Although it is impractical to array real turbines across the entire width of a channel it has been proposed to use short arrays of turbines making use of local constructive interference (blockage) effects; Nishino & Willden (2012) showed that although the phenomenal power limits of Garrett & Cummins are unobtainable in a real flow, a significant uplift in the limit of power extraction can be achieved for short fences of turbines arrayed normally to the flow in wide cross-section channels. However, it does not follow that rotors designed using unblocked wind turbine tools are capable of extracting any more power than they are designed for and hence the power uplift made available through blockage effects may be squandered. This thesis sets out to develop design tools to assist in the design of rotors in blocked environments that are designed to make use of the flow confinement effects and yield rotors capable of extracting some of the additional power on offer in blocked flow conditions. It is the pressure recovery condition used in wind turbine design that requires relaxation in blocked flow conditions and hence it is necessary to resort to a computational framework in which the free stream pressure drop can be properly accounted for. The tool of choice is a computational fluid dynamics embedded blade element method. As with all models with semi-empirical content it is necessary to select and test correction models that account for various simplifications inherent to the use of the blade element method over a fully blade resolved simulation. The thesis presents a rigorous comparison of the computational model with experimental data with the various correction methods employed. The tool is then used to design rotors, first for unblocked operation, with favourable comparison drawn to lifting line derived optimal Betz rotor solutions. The final objective of the study is to design rotors for operation in short fence configurations of four turbines arrayed normally to the flow. This is accomplished and it is shown that by using bespoke in situ rotor design it is possible to extract more power than possible with non-blockage designs. For the defined array layout and operating conditions, the bespoke rotor array design yields a power coefficient 26% greater than the implied Betz limit for an unblocked rotor and 4% greater than operating a rotor designed in isolation in the same array.
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Moreira, Tulio Marcondes. "Augmented Tidal Resonant System: Design for Uninterrupted Power Generation." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1462460475.
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Atwater, Joel. "Limitations on tidal-in-stream power generation in a strait." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/635.
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In the quest to reduce the release of carbon dioxide to limit the effects of global climate change, tidal-in-stream energy is being investigated as one of many possible sustainable means of generating electricity. In this scheme, turbines are placed in a tidal flow and kinetic energy is extracted. With the goal of producing maximum power, there is an ideal amount of resistance these turbines should provide; too little resistance will not a develop a sufficient pressure differential, while too much resistance will choke the flow.
Tidal flow in a strait is driven by the difference in sea-level along the channel and is impeded by friction; the interplay between the driving and resistive forces determines the flow rate and thus the extractible power. The use of kinetic energy flux, previously employed as a metric for extractible power, is found to be unreliable as it does not account for the increased resistance the turbines provide in retarding the flow.
The limits on extraction from a channel are dependant on the relationship between head loss and velocity. If head loss increases with the square of the velocity, a maximum of 38% of the total fluid power may be extracted; this maximum decreases to 25\% if head loss increases linearly with velocity. Using these values, the estimated power potential of BC's Inside Passage is 477MW, 13% of previous assessments.
If a flow has the ability to divert through a parallel channel around the installed turbines, there are further limits on production. The magnitude of this diversion is a function of the relative resistance of impeded and diversion channels.
As power extraction increases, the flow will slow from its natural rate. This reduction in velocity precipitously decreases the power density the flow, requiring additional turbine area per unit of power. As such, the infrastructure costs per watt may rise five to eight times as additional turbines are installed. This places significant economic limitations on utility-scale tidal energy production.
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Bruder, Brittany Lynn. "Assessing hydrokinetic tidal energy extraction for Rose Dhu Island, Georgia: A case study for tidal rivers with marsh environs." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53864.
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Hydrokinetic tidal power is a novel and emergent technology undergoing continuous advancement with much of the progress focused on large utility scale projects. This resource is potentially underutilized because much of the coastal United States, despite having substantial tidal currents, do not have the deep and wide environments required by most of the developing turbine technology. This dissertation includes a detailed characterization of the tidal hydrodynamics for Rose Dhu Island, Georgia used for a tidal energy resource assessment as well as a general feasibility study for tidal estuaries with extensive wetlands.
For predictions and evaluation of the estuarine hydrodynamics, data from an existing numerical model of the estuary encompassing the island is utilized. Field measurements in close proximity to the island are used to calibrate the model as well as characterize local hydrodynamic features. After the model calibration, the simulation data is used to evaluate the hydrodynamics. Wetland dominated estuaries commonly have a high degree of non-linear distortion which govern the relative durations and strengths of the tidal stages and thus the overall hydrodynamics and incoming hydrokinetic energy. The Ogeechee Estuary is characterized as ebb dominant with peak ebb and flood volume fluxes near high tide as a result of the increased storage capacity of the wetlands. Lowering the average wetland elevation in the model decreased ebb dominance and quickened the transition from flood to ebb tide. Increased domain friction in the model removed energy from the system and reduced ebb dominance. Enhanced model marsh friction reduced lateral flooding of the wetlands as well as ebb dominance. Localized measurements surrounding the island are analyzed to determine a location near the southwest coast of the island as a hydrokinetic energy hotspot. A kinematic and dynamic analysis is performed using channel transect measurements to identify key physical processes behind the hotspot formation. The hotspot forms due to sub-critical flow acceleration over a singular bump in the topography. High streamwise momentum is further concentrated at the hotspot due to secondary circulation cells across the channel. Flood tide circulation is characterized by two co-rotating cells induced by channel curvature and delineated by the bump. Ebb circulation consists of two counter-rotating cells from flow confluence of two upstream channels.
Once the hydrodynamics are understood, the theoretical and technical resource assessment of the island is completed. A sensitivity analysis of hydrokinetic energy and tidal distortion is performed on synthetic data. For a principle constituent and its first harmonic, distortion greatly changes as does the distribution of velocities and energy as the relative phase varies. While the theoretical energy remains consistent, the technical energy can greatly vary. This effect is reduced with the addition semi-lunar variation. Using a simplified analytical method, the maximum average channel power is estimated as 8.80 MW. For the hotspot it is estimated that there is 30.3 MWh available to capture yearly with an average power of 3.46 kW for a turbine with an area of 10 square meters. For the same turbine area with conservative efficiencies, the hotspot could provide a yearly technical energy of 10.9 MWh with an average power of 1.25kW for the island. Due to the complex localized hydrodynamics, both the theoretical and technical resource varies greatly across and along the channel. These considerations are more pertinent when performing a hydrokinetic energy resource assessment in a marsh estuary than for large scale bay-ocean exchange environments, the present industry focus.
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Olczak, Alexander. "The influence of waves on tidal stream turbine arrays." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/the-influence-of-waves-on-tidal-stream-turbine-arrays(3ed6653f-1cc3-4e3b-ba03-5e5094a15ecc).html.
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The aim of this research was to quantify the influence of waves on arrays of tidal turbines. Experiments measured the wake of a turbine operating in combined wave-current flows, these were found to reduce velocity deficit as opposed to current only flow. The vertical region of the wake affected was dependant on the wave depth parameter, kd.RANS-BEM and Actuator Line methods were implemented within a commercial CFD code to provide computationally efficient methodologies for the simulation of both large turbine arrays and a turbine subjected to unsteady flow. For scaled experiments thrust coefficient was within 7% and 1% of the flume experiments for the RANS-BEM and Actuator Line methods respectively. The methods were found to give good prediction of a single turbine wake at distances greater than four diameters downstream, provided values of inlet turbulence intensity and length scale were equal to those measured experimentally.An unsteady Actuator Line method was used to quantify rotor loads and wake generation for a turbine operating within combined wave-current flow. The use of a streamwise pulsatile flow was found to give similar rotor and blade loads to simulations using a wave in a two phase volume of fluid simulation. The control strategy adopted by the turbine was found to greatly influence the computed rotor loads and blade bending moments. The wake generated by an Actuator Line method showed a reduction in velocity, however this was smaller than that measured experimentally for equivalent wave conditions.The accuracy with which the RANS-BEM method computed turbine loads and wakes was quantified for a number of one, two and three row arrays. The square of the disk averaged velocity encountered by turbines downstream of a single row of five turbines was found to be predicted to within 5% and 28% for an aligned and staggered arrangement respectively. For the two row arrays, the thrust of individual turbines was within 31% of the experimental measurements. The merged wake downstream of the multiple turbines was well predicted.Measurements of the wake of five porous disks showed combined wave-current flow did not alter the wake in the same manner as a single isolated disk. Measurement of wave energy over the wake showed the downstream current field altered wave propagation, causing a reduction in wave energy over the wake but an increase over the bypass flow. The accuracy of the wave model SWAN was assessed for the calculation of this change in wave characteristics. The model gave good prediction of the lateral variation of wave height over the far wake, however discrepancies in the near wake and upstream of the disk occurred.
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Harendza, Astrid. "Benthic habitats in a tide-swept channel of the Pentland Firth and their potential responses to a tidal energy development." Thesis, University of the Highlands and Islands, 2014. https://pure.uhi.ac.uk/portal/en/studentthesis/benthic-habitats-in-a-tideswept-channel-of-the-pentland-firth-and-their-potential-responses-to-a-tidal-energy-development(f5af15f2-779a-4fa1-9ab9-467d8aa1cb2d).html.
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This thesis investigates sublittoral epibenthic assemblages, the ecological processes associated with distributions of benthic assemblages and potential ecological impacts arising from the de-ployment of tidal energy devices (TEDs) at a key tidal energy development site. An extensive field campaign was undertaken to collect fine-scale, in-situ data for local hydrodynamics, seabed structure and epibenthic assemblages. Data from a two-dimensional hydrodynamic model com- plemented in-situ flow data and provided an insight into possible changes to local tidal patterns after the deployment of a tidal array. The study revealed a highly complex tidal stream structure with maximal velocities reaching 4.2 ms1 during spring tide. The seabed was predominantly formed by scoured bedrock. Deployment of a tidal array was predicted to decrease tidal flow within and downstream of the array by up to 24 % for peak flows, whereas effects on the seabed were thought to be minor. Epibenthic assemblages were typical for tide-swept channels with a fringe of dense kelp forest along the shallow, sheltered waters of the channel, followed by a 'tran- sition zone' dominated by foliose red algae in the mid-depth ranges and animal turf assemblages in the deeper, very tide-swept waters. Multivariate analyses identified depth and bed-shear stress as being strongly associated with the distribution and composition of assemblages. In conjunction with presence-only data for epibenthic species, depth and bed-shear stress were used as predic- tor variables to develop site-specific habitat suitability models (HSMs) for a baseline and TED deployment case. Comparison of probability of occurrence values between the respective HSMs indicated a potential increase of suitable habitat for species inhabiting the deep, very tide-swept circalittoral following the deployment of TEDs, whilst assemblages along the fringes of the channel were mostly unaffected. This is the first attempt of using HSM as a tool for identification of potential changes in distributions of benthic species arising from the deployment of TEDs. The good overall performance of the models shows this tool may be valuable for for impact analysis of tidal energy development projects.
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Hooper, Tara Louise. "Evaluating the costs and benefits of tidal range energy generation." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619144.
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Tidal barrages could contribute to mitigating climate change, but their deployment is not without potential welfare costs attributable to the degradation of ecosystem services. Economic valuation of natural resources provides a common metric for quantifying the disparate costs and benefits of barrage construction in a way that provides transparency when trade-offs are considered. However, very little is currently known about the value of environmental impacts associated with tidal barrages. Using the Taw Torridge estuary in North Devon as a case study, this research proposes an Environmental Benefits Assessment methodology that supports application of the ecosystem services concept to local environmental impact appraisal, and facilitates economic valuation. This methodology is novel in that it evaluates benefits, as opposed to services, and considers a comprehensive suite of benefits in a single assessment: an approach rarely attempted in practice, but essential if ecosystem services approaches are to fully support resource management needs. The subsequent empirical valuation uses stated preference techniques to examine the different ways people use and value the estuary ecosystem, determine how strongly they rank different costs and benefits of tidal barrages, and elicit willingness to pay (WTP) to reduce the habitat loss resulting from a tidal barrage development. The study provides the first empirical valuation of UK estuarine mudflats, but makes a further contribution to the environmental economics discipline by deploying both contingent valuation and choice experiment methods. Additionally, a novel application of the Analytic Hierarchy Process (AHP) is used to examine the consistency of WTP with expressed preferences for habitat protection in relation to other barrage attributes. The alternative stated preference techniques result in comparable WTP values and the importance attached to habitat loss (as measured by the AHP) is strongly associated with WTP and also with its scope sensitivity, indicating that WTP is largely driven by environmental preferences.
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Massacand, Christophe Maurice Jean-Baptiste. "Particle production by tidal forces and the energy-momentum tensor /." [S.l.] : [s.n.], 1993. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10359.
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Foran, Derek. "Experimental and Numerical Modeling of a Tidal Energy Channeling Structure." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32387.
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Tidal power, or the use of tides for electricity production, exists in many forms including tidal barrages, which exploit tidal head differentials, and turbines placed directly in regions with large tidal current velocities. The latter is actively being investigated in many countries around the world as a means of providing renewable and wholly predictable electricity (cf. wind, solar and wave power). The expansion of the in-stream tidal industry is hindered however by several factors including: turbine durability, deployment and maintenance costs, and the lack of abundant locations which meet the necessary current velocities for turbine start-up and economic power production. A new novel type of augmentation device, entitled the ‘Tidal Acceleration Structure’ or TAS (Canadian patent pending 2644792), has been proposed as a solution to the limited number of coastal regions which exhibit fast tidal currents. In preliminary investigations, the TAS, a simple Venturi section consisting of walls extending from the seafloor to above the high water mark in an hourglass shape, was found as able to more than double current velocities entering the device. The results indicated a significant advantage over other current channeling technologies and thus the need for more in-depth investigations.
The main objective of the present study was to optimise the design of the TAS and to predict the power that a turbine placed within it could extract from flow. To do this, two principal methods were employed. Firstly, a 1:50 scale model of the TAS was tested and its shape optimised in a 1.5 m wide flume. Secondly, a 3D numerical model (ANSYS Fluent) was used for comparison with the experimental results. During the tests, a TAS configuration was found that could accelerate upstream velocities by a factor of 2.12. In separate tests, turbines were simulated using Actuator Disc Theory and porous plates. The TAS-plate combination was found to be able to extract up to 4.2 times more power from flow than the stand-alone plate, demonstrating that the TAS could provide turbines with a significant advantage in slower currents.
Though further research is needed, including the testing of a larger TAS model in conjunction with a small in-stream turbine, the results of this thesis clearly demonstrate the potential of the TAS concept to unlock vast new areas for tidal energy development.
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Toupin, Mathieu. "Scientific Validation of Standards for Tidal Current Energy Resource Assessment." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34212.
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The tidal current energy resource is challenging to assess with accuracy and precision. An accepted standard methodology is lacking, which in turn perpetuates uncertainty and hinders the industry’s development. Technical Committee 114 of the International Electro-technical Commission (IEC-TC-114) is working to develop a standard for emerging tidal energy conversion systems. The draft standard prescribes methods for determining, objectively and reliably, the scale and character of tidal current energy resources at a site. The IEC-TC-114 draft standard for tidal energy resource assessment and characterisation has not yet been tested in a real world case study. Hence, it is not yet known whether the proposed methods will yield the desired outcome.
This research has adopted the Fundy Ocean Research Center for Energy (FORCE) project in Minas Passage, Nova Scotia, for pilot application of the draft standard on tidal current resource assessment. The Bay of Fundy, located on the Atlantic coast of North America between the Canadian provinces of New Brunswick and Nova Scotia, is known for having the highest tidal range in the world and has long been recognised as an ideal stage for tidal energy development.
The thesis is presented in three main parts. Firstly, the latest peer-reviewed scientific literature is summarised and the standard is reviewed in view of lessons learned. The aim of this exercise is to establish a scientific basis for and to develop suggestions towards improving and extending future revisions of the standard. Secondly, a comprehensive assessment of the tidal current energy resource at the FORCE project site is conducted in a manner that is consistent with IEC-TC-114 protocol based on available measurements from static current profiler surveys and a two-dimensional hydrodynamic model of the upper Bay of Fundy developed for this study. Thirdly, a sensitivity analysis is performed to determine the main sources of error and uncertainty affecting resource assessment, a topic which has yet to be addressed in the literature.
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Melville, Guy T. "Hydrodynamic and economic modelling of tidal current energy conversion systems." Thesis, Robert Gordon University, 2008. http://hdl.handle.net/10059/695.
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This thesis examines the contribution of computational modelling to the development of the tidal current energy industry, against the background of increasing commercial, government, academic and public interest. It does this through the practical application of a number of computational techniques in the areas of: 1. Tidal current analysis and prediction 2. Hydrodynamic flow modelling 3. Tidal resource analysis 4. Optimised economic modelling Appropriate survey set-up is essential in gathering data. Given this, processing the data using velocity profiles; statistical techniques; and harmonic analysis can produce valuable data for site development, device design and grid management. This work developed the application of a directional and time-dependent power coefficient and demonstrates its importance in resource evaluation from tidal flow data. It further concludes that hydrodynamic flow modelling of sites prior to development is important in determining suitable sites, given the scarcity of tidal information in the areas suitable for tidal developments. The same scarcity of data, in terms of boundary conditions, interior validation points and depth does limit the accuracy of such models. The work demonstrates that using differing resource analyses can obtain dramatically different results; and develops a correlation relating energy extraction to developed energy extraction using a one dimensional channel model. In doing so it concludes that energy resource estimates may be reduced from contemporary estimates. Overall, computational modelling of tidal current energy conversion systems can have a significant contribution to their design and site development. The most significant capital costs arise from installation, decommissioning and the turbine itself, however significant reduction in the cost of energy production can result from correct placement, array size and component selection This work contributes to knowledge in a number of areas, namely: 1. It is the first published work on survey data analysis prior to deployment of a large-scale prototype tidal current energy conversion system; 2. At the time that the work was carried out, it was the first published work considering the use of the least-squared harmonic method for prediction of energy output from a tidal current energy device; 3. It is the first work to propose a directional power coefficient in the process of resource analysis for a tidal current energy conversion system; 4. The work on economic modelling was the first to produce an optimised economic model for tidal current energy conversion systems (TCECS); 5. It is the first work to use an optimised economic model for TCECSs to demonstrate the effect of device placement on the cost of energy produced; 6. It is the first work to use an optimised economic model for TCECSs to demonstrate that the cost of energy for TCECSs is minimised by maximising the rated power, given no topographical impedence; 7. It proposes a method to determine the energy resource available including energy extraction.
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Sankaran, Iyer Abhinaya. "New methodologies and scenarios for evaluating tidal current energy potential." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/6182.
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Transition towards a low carbon economy raises concerns of loss of security of supply with high penetrations of renewable generation displacing traditional fossil fuel based generation. While wind and wave resources are increasingly forecastable, they are stochastic in nature. The tidal current resource, although variable has the advantage of being deterministic and truly predictable. With the first Crown Estate leasing round complete for wave and tidal current energy, plans are in place to install 1000 MW of tidal capacity in the Pentland Firth and Orkney waters. The aim of the work presented in this thesis is to examine the role tidal current energy can realistically play in the future electricity mix. To achieve this objective it was first necessary to develop new methodologies to capture the temporal and spatial variability of tidal current dynamics over long timescales and identify metrics relevant in a tidal energy context. These methodologies were developed for project scale resource characterisation, and provided a basis for development of a national scale dataset. The creation of project and national scale tidal datasets capture spatial and temporal variability at a level beyond previous insight, as demonstrated in case studies of three important early stage tidal current energy development sites. The provision of a robust national scale dataset enabled the development of realistic scenarios for the growth of the tidal current energy sector in UK waters. Assessing the various scenarios proposed indicates that first-generation technology solutions have the potential to generate up to 31 TWh/yr (over 8% of 2009 UK electricity demand). However, only 14 TWh/yr can be sensibly generated after incorporating realistic economic and environmental limitations proposed in this study. The preceding development of methodologies, datasets and scenarios enabled statistical analysis of the matching characteristics of future tidal energy generation potential with the present UK electricity demand and trends of electricity usage. This analysis demonstrated that the UK tidal current energy resource is much more in phase than has previously been understood, highlighting the flaws in previous studies suggesting that a combined portfolio of sites around the UK can deliver firm power. As there is negligible firm production, base-load contribution is insignificant. However, the time-series generated from this analysis identifies the role tidal current energy can play in meeting future energy demand and offer significant benefit for the operation of the electricity system as part of an integrated portfolio.
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MacGillivray, Andrew John. "Economically sustainable development of wave and tidal stream energy technologies." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/25405.
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The wave and tidal energy sectors have received much interest in recent years, from policy-makers attentive to the prospect that ocean energy technologies could be capable of contributing towards meeting environmental targets; from utility companies that expressed interest in developing, constructing and operating array projects to export large quantities of clean energy from ocean based resources; and from Small to Medium Enterprises (SMEs) and large multi-national Original Equipment Manufacturers (OEMs) that were interested in undertaking technological development to commercialise wave and tidal energy converters that could successfully harness the energy contained within the ocean waves and tides. Within the existing research, development and innovation environment that has largely dominated the development of wave and tidal energy to date – rapid development of large MW-scale devices capable of utility scale power generation – technology developers have failed to reach the level of deployed capacity that was initially anticipated, despite the significant level of investment that has taken place. Indeed, the expected contribution of ocean energy in the wider energy mix, which has been written into policy documentation at both national and European level, has so far failed to materialise in the form of prolific multiple device array deployments. The research, development and innovation environment has not delivered on its intended objective of demonstrating commercial technology readiness, and the historic development trajectories for ocean energy technologies may not represent the most cost-effective route to product commercialisation. This research explores the wave and tidal energy research, development, and innovation environment through extensive stakeholder engagement within the ocean energy sector, and through application of suitable techniques from innovation theory. The purpose of this research was three-fold. Firstly, an objective analysis of the development of the wave and tidal energy sectors – building a comprehensive understanding of their development to date through extensive stakeholder engagement, and comparing wave and tidal energy technology development with that of historic energy technologies that have successfully entered into commercial operation – was necessary in order to identify whether the attempt by ocean energy technologies for rapid up-scaling of technology is consistent with the development pathway that was followed by energy technologies which have successfully transitioned from novel invention to full commercial operation. This work identified several dichotomies that are present in the nascent stages of technology development in the wave and tidal energy sectors. Secondly, the uncertainties surrounding existing capital and revenue costs, and the uncertainties within the potential future cost reductions associated with current technology trajectories, could lead to unsustainable investment requirements. Commercialisation of wave and tidal energy technology is predicated upon significant cost reduction – the current technology costs are not feasible for large scale roll out of technology. A research focus on the economic uncertainty through application of learning theory and a learning investment sensitivity analysis was anticipated to demonstrate the economic impact of minor perturbations from idealised reference assumptions. The results from this work suggest that even minor perturbations in input parameters have substantial negative impact on overall investment requirements to bring technology to a level of cost competitiveness. Thirdly, the policy landscape surrounding wave and tidal energy development has not been specifically compared and contrasted, using a number of performance metrics, to a technology which was subject to similar expectations in the form of income streams – wind energy technology. The causes and motivations for the rapid transition to large-scale technologies and ‘accelerated innovation’ within ocean energy technology were considered within this research, which suggested that a mismatch between policy support and technological readiness could misguide and misdirect the innovation pathway, harming the commercialisation prospects of ocean energy technology. In order for the successful emergence of economically sustainable wave and tidal energy technologies, a paradigm shift may be necessary, a change from the current approach that has to date dominated technological development within both the wave and tidal energy sectors. This research draws together industry consultation with academic insight to identify an optimised innovation pathway, culminating in a policy appraisal to guide and inform economically sustainable development of wave and tidal energy technologies.
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Yates, Nicholas Charles. "Tidal energy resources of the UK's estuaries and coastal waters." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.679593.
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Gay, Thomas Joseph. "Assessment of tidal stream energy potential for Marine Corps Recruit Depot Parris Island." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37293.
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The energy of the tides represents one globally existent source of renewable energy, and has the potential to play a major role in a sustainable future. An assessment of the potential for tidal energy extraction using marine current turbines at a particular location in the Beaufort River near Parris Island, South Carolina is presented. The Marine Corps Recruit Depot located on Parris Island is situated between the confluence of the Broad and Beaufort Rivers. These rivers are tidally dominated, and experience some of the largest tidal ranges in the southeastern United States, between 2.5 and 3 meters during spring tide periods. Because Parris Island already has much of the necessary land-based infrastructure in place, there is logical potential for the extraction of kinetic energy from the nearby tidal streams using underwater turbines for power production. In order to evaluate the potential of a particular location to produce significant amounts of energy using these types of devices, extensive investigations must be conducted to determine important site characteristics such as water depth, current velocity, and water level fluctuations over time. This potential was investigated using in-situ measurements in the vicinity of the pump station on Parris Island, and by developing a numerical model of the region using the Regional Ocean Modeling System (ROMS). This model was calibrated using the results from the in-situ measurements, and was then used to determine the impacts of tidal energy extraction on the local flow field.
Results from in-situ measurements indicate that tidal currents along the portion of the Beaufort River analyzed in this study are driven primarily by the semi-diurnal M2 tidal constituent. The tidal range at the study site is approximately 2 meters on average, with a mean depth-averaged current velocity magnitude of 0.57 m/s predicted for a period of one year. A mean depth-averaged current velocity magnitude of 0.59 m/s was observed over the course of the longer-term ADCP deployment from November 12 to December 17, 2009. The maximum current speed at the site is approximately 1.2 m/s at the water surface. The ROMS model applied to the coastal areas surrounding Parris Island, SC produces results that closely resemble in-situ measurements collected previously during both the boat-based survey and the longer-term ADCP deployment. In the analysis of the effects of energy extraction from the system, four separate cases were considered in which 10, 20, 30, and 60% of the total kinetic energy contained in the flow was dissipated near the location of the longer-term ADCP deployment. Minimal impacts on the local hydrodynamics were observed across the four cases considered.
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Bruder, Brittany Lynn. "Assessment of hydrokinetic renewable energy devices and tidal energy potential at Rose Dhu Island, GA." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41198.
Full textAbstract:
Current hydro-turbines aim to capture the immense energy available in tidal movements, however commonly applied technologies rely on principles more applicable in hydroelectric dams. Tidal stream currents, such as in Coastal Georgia, are not strong enough to make such turbines both efficient and economically viable. This research proposes a novel low-energy vortex shedding vertical axis turbine (VOSTURB) to combat the inefficiencies and challenges of hydro-turbines in low velocity free tidal streams.
Some of the energy in tidal streams is extracted naturally from vortex shedding; as water streams past a bluff body, such as pier, low pressure vortices form alternatively on each side, inducing a rhythm of pressure differentials on the bluff body and anything in its wake. VOSTURB aims to capture this energy of the vortices by installing a hydrofoil subsequent to the bluff body. This foil, free to oscillate, translates the vortex energy into oscillatory motion, which can be converted into a form of potential energy. The presented research will act as a 'proof of concept.' It aims to assess such foil motion, or the ability of VOSTURB to capture vortex energy, and begin to assess the amount of tidal energy that can be theoretically harnessed.
In this study a small scale model of VOSTURB, a cylindrical bluff body with a hammer shaped hydrofoil, was tested in a hydraulic flume for various mean flow speeds. Tangential accelerations of the foil's center of gravity were obtained through the use of an accelerometer. The acceleration data was analyzed utilizing Fourier analysis to determine the fundamental frequency of the wing oscillations. The available power to be harnessed from the oscillatory motion was then estimated utilizing this fundamental frequency.
Ultimately it was found that the frequency of the VOSTURB foil oscillations corresponded highly with the theoretical frequency of vortex shedding for all moderate to high flow speeds. Low speeds were found to produce inconsistent and intermittent small oscillations. This signifies at moderate to high flow speeds, VOSTURB was able to transform some vortical energy into kinetic. The maximum average power obtained 8.4 mW corresponded to the highest flow velocity 0.27 m/s. Scaled to Rose Dhu prototype conditions this represented 50 W at a flow velocity of 0.95m/s, the maximum available at Rose Dhu.
Although it was ascertained that VOSTURB could consistently capture some of the vortical energy; the percentage of which could not be calculated with certainty. Thus, the average kinetic power assessments of the foil were compared to the available power of the mean flow for each flow speed calculated by two methods: (1) over the foil's swept area; (2) the area of fluid displaced by the bluff body immediately in front of the foil. The maximum efficiency of the foil, found for the fastest flow speed was at 18% and 45% respectively. It was found that both average foil power, available flow power, and efficiency all decreased with a decrease in flow velocity.
This study can serve as only a preliminary study for the effectiveness of VOSTURB as a hydro-turbine for tidal power. In the experiments, the foil was allowed to oscillate freely with little resistance. Future testing of VOSTURB needs to observe whether the vortex energy can overcome the resistive torque introduced by a generator to induce oscillatory motion as well as further optimize the foil design. While the testing in this project assesses the kinetic energy or power of the vortex shedding, this future testing will provide insight into the actual work that can actually be converted into potential energy or power.
Complementing this research, both a Harmonic Analysis of Least Squares (HAMELS) and a Complex Empirical Orthogonal Function (CEOF) Analysis was conducted on available surface height and current velocity data separately from an available Regional Ocean Modeling System (ROMS) model of Coastal Georgia. Such analysis were conducted to observe spatial and temporal tidal patterns advantageous to a possible prototype installation of a tidal turbine such as VOSTURB. The more conventional HAMELS analysis, which isolates components of a signal with a certain frequency, identified temporal and spatial patterns attributed to tidal constituents. CEOF analysis, where major patterns of variance are identified not according to prescribed frequencies, was employed to identify any patterns possible not attributed to the tidal constituents. This study was also in part to observe whether the CEOF analysis could identify any patterns of tidal propagation that could not be resolved by the HAMELS analysis.
The CEOF and HAMELS analysis of the surface height output produced very similar results: major modes of surface height variation due to the diurnal and semidiurnal tidal constituents propagating up the estuary. The CEOF results did not produce any additional information that could not be found through the HAMELS analysis of the constituents and presented such results in an arguably more convoluted manner. In addition, the surface height analysis provided no direct insight into areas more advantageous to tidal power. The CEOF analysis of the vector current velocity data however did provide some insight. The CEOF of the current data was able to isolate patterns of variance corresponding to the tidal constituents. However, the CEOF was also able to identify local 'hotspots' of high current magnitudes not resolved by HAMELS. These local areas of high current magnitudes, most likely due to changes in hydrodynamic conditions such as channel constrictions, are advantageous for tidal power applications. These general areas could serve as a starting point for the location selection process for a possible prototype installation of VOSTURB if the area was refined more.
Ultimately for a prototype installation of VOSTURB, further experimentation and analysis is required for both the turbine design and placement, such as a power conversion methodology for the turbine and a more spatially resolute set of data to perform a CEOF analysis on. With these tasks completed, the prototype installation will be part of a larger effort between the Georgia Institute of Technology and the Girl Scouts of America to create completely sustainable "Eco-Village" on Rose Dhu Island, GA. With an extensive community outreach planned to educate the public, Rose Dhu, along with championing hydrokinetic energy, will serve as a paradigm for sustainable design and energy.
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McPeake, F. A. "Wave energy conversion using small scale floating devices." Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374227.
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Brammer, James. "Physical and numerical modelling of Marine Renewable Energy technologies, with particular focus on tidal stream and tidal range devices." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/58699/.
Full textAbstract:
The past decade has seen a significant rise in the interest of deploying Marine Renewable Energy technologies. Tidal stream technology is developing rapidly, and developers are favouring horizontal axis turbines (HAT’s). However, vertical axis turbines (VAT’s) are better suited for shallow waters, and higher efficiencies can potentially be gained by utilising shallow water blockage effects. The Severn Estuary is an ideal deployment area in this context. Additionally, due to a large tidal range the estuary has long been the subject of tidal barrage proposals. The original ebb-only STPG barrage has recently been superseded by a two-way generation scheme, therefore the need exists for renewed research into the hydrodynamic impacts of this proposal. Furthermore, little is known about the interaction between tidal range and tidal stream technologies, and if they could coexist in the Severn Estuary. This thesis uses physical and numerical modelling techniques to assess a range of MRE technologies, with particular focus on their deployment in the Severn Estuary. Physical model tests of a number of VAT’s were conducted in a recirculating flume. Device performance and the wake characteristics were assessed, and it was demonstrated that VATS’s could potentially provide competitive performance values if deployed in shallow waters. The CFD code ANSYS CFX was used to predict the unsteady turbine behaviour at the physical model scale; good agreement was achieved with the laboratory data, particularly in predicting the wake behaviour. The CFD model TRIVAST was then applied to the Severn Estuary. Comparisons were made of the Severn Barrage schemes, as well as two hypothetical HAT and VAT arrays. The model results confirmed that vertical axis turbines are better suited to the Severn Estuary, provided that the technology is feasible. Finally, whilst the Severn Barrage proposals would eradicate the HAT resource, a lesser impact on the VAT resource was observed.
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Dacre, Sarah Lynn. "The environmental impacts and developmental constraints of tidal current energy generation." Thesis, Robert Gordon University, 2007. http://hdl.handle.net/10059/649.
Full textAbstract:
The thesis discusses the environmental impacts and developmental constraints of tidal current energy. Using an iterative approach and drawing upon a number of different methodologies the thesis attempts to evaluate the development potential of tidal current energy in terms of the resource and identify the potential environmental impacts. In addition, it attempts to identify the barriers to development that may be preventing the growth of the industry. The thesis also assesses further research requirements in terms of environmental and social barriers to development, focusing on an environmental impact methodology and its importance in tidal current energy development. Over recent years there has been a significant acceleration in tidal current energy research and development. The key challenge is for technologies to reach full commercialisation. The thesis investigates present market and industrial accessibility and due to institutional and environmental barriers, concludes that commerciality will be hard to achieve if such 'barriers' are not broken. However, the skills and capability base in the UK offshore industry and indeed the renewable energy sector is significant and this should be utilised accordingly. This vision of commercialisation needs to be sustained and a culture of forward thinking needs to be continuously cultivated. In essence, the UK cannot afford to miss this opportunity, both in terms of R&D status, economic stability, energy diversity and security of supply and in time export potential. The thesis identifies key environmental issues concerning tidal current energy development using a site-specific case study and highlights the misconception that renewable energies are without environmental impact. It is clear that some are well understood within the realm of other offshore industries, however, some are relatively unique to this type of development and the need for further research is evident in these areas, in order to dispel the environmental impact uncertainties that exist. The thesis also demonstrates that there are 'process gaps' within Environmental Impact Assessment and attempts to develop an environmental impact assessment framework to aid the tidal current energy development process.
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Johnson, P. "Hydrodynamics of tidal stream energy devices with two rows of blades." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1348136/.
Full textAbstract:
Tidal stream energy is an emerging low-carbon technology which could meet 5% of UK electricity demand. Current developments use ‘axial-flow’ rotors, which are efficient but limited in size, to generate electricity from ocean currents. This thesis investigates the hydrodynamics of a previously undeveloped rotor concept which has two rows of blades and also has no inherent size limit, hence it might achieve greater economies of scale. The rotor concept, called the ‘Moonraker’, is a cross-flow device with an oval blade path in the horizontal plane. This thesis presents research into the hydrodynamic performance of the Moonraker, focussing on the forces exerted on the blades by water currents and thereby deriving the thrust on and power generated by a Moonraker. The point vortex method was used to model the Moonraker and predicted high power coefficients when compared to a conventional cross-flow turbine with a circular blade path. A lab-scale Moonraker device was built and tested in the towing tanks at UCL and QinetiQ. The device was 2 m wide, 0.5 m high, with up to six blades and was towed at up to 0.7 m/s (blade Reynolds numbers were in the range 65,000--112,000). One of the blades was instrumented with strain gauges so that two components of blade loading could be recorded. Comparisons of predictions and measurements of blade loading showed some encouraging agreement, but also some disagreement, leading to suggested improvements in the modeling of the blade forces. The vortex model was subjected to further verification and validation tests in order to explore the issue of double actuator surfaces in close proximity. The extension of this work could help optimise the spacing between the two rows of blades on a Moonraker.
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Li, Xiaorong. "Three-dimensional modelling of tidal stream energy extraction for impact assessment." Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3006766/.
Full textAbstract:
This research is themed around development of a tidal turbine simulation platform based on a three-dimensional oceanographic numerical modellling environment; more specifically, parameterization of effects of tidal turbine on flow current, turbulence, waves and sediment transport. In this context, the author adopts concepts in the current module, the turbulent module, the wave module and the sediment transport module of Finite-Volume, primitive equation Commmunity Ocean Model (FVCOM) to simulate the effects of tidal turbines. The retarding force concept is employed in the current module, working as an additional body force exerted on the water to simulate the turbine induced water deceleration. Three terms are added into the MY-2.5 turbulence closure to model turbine related turbulence generation, dissipation and turbulence length-scale interference. The built-in feature 'OBSTACLE' of the wave module is used to simulate the reduction of wave height caused by the turbine. The enhanced sediment suspension due to the turbine in motion is represented by an additional bottom shear stress term, entraining an extra portion of sediment particles from the bed into the water. Due to the fact that the bedload sediment transport module of FVCOM is not fully developed, it is not considered in this research; development of such a module is beyond the scope of this project. Coefficients of the turbine simulation terms are calibrated based on experimental data collected in the 'Total Environment Simulator laboratory flume' at the University of Hull, in which a prototype experiment was conducted. Small scale simulations carried out using ANSYS FLUENT also provided complementary calibration data. An idealized water channel model with mesh resolution fined down to the size of the simulated turbine is built to carry out the coefficient calibration. In general, the developed turbine simulation platform is capable of predicting reliable flow velocity, turbulent level, wave height and suspended sediment transport in the far wake region of the turbine, given proper values assigned to the relating coefficients. In addition, preliminary sensitivity tests are carried out to investigate the impact of these coefficients to the model's overall prediction to reveal the model's application range. Upon the satisfactory choices of the coefficients, the platform is applied to a 15m scale idealized single turbine case as well as a regional scale case based on the realistic hydrodynamics off the Anglesey coast, north-west of Wales. A series of single turbine tests are carried out with and without the turbine implementations, i.e. the coefficients represent turbine effects being switched on and off, in order to reveal the differences between the baseline case (no turbine) and case with turbine effects. Under realistic natural tidal and wave conditions, the Anglesey coast case showcases impact from a large scale turbine farm to both local and regional processes.
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Abdul, Rahman Anas. "Numerical modelling of full scale tidal turbines using the actuator disc approach." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31246.
Full textAbstract:
In recent years, the actuator disc approach which employs the Reynolds-Averaged Navier-Stokes (RANS) solvers has been extensively applied in wind and tidal energy field to estimate the wake of a horizontal axis turbine. This method is simpler to administer and requires moderate computational resources in modelling a tidal turbines rotor. Nonetheless, the use of actuator disc approximation in predicting the performance of tidal devices has been limited to studies involving an extremely small disc (e.g. rotor diameter of 0.1 meter). The drawback of a small scale actuator disc model is the overestimation of essential parameters such as the mesh density and the resolution of the vertical layers, making them impractical to be replicated in a regional scale model. Hence, this study aims to explore the methodology on implementation of the Three- Dimensional (3D) actuator disc-RANS model in an ocean scale simulation. Additionally, this study also aspires to examine the sensitivity of the applied momentum source term and its validity in representing full-size tidal devices. Nonetheless, before the effectiveness of an actuator disc in a regional model can be tested, tidal flow models for the area of interest needed to be set up first. This was essential for two reasons: (a) to ensure accurate hydrodynamic flow conditions at the deployment site were replicated, (b) to give confidence in the outputs produced by the regional scale actuator disc simulations, since in-situ turbine measurement data from a real deployment site were difficult to source. This research was undertaken in two stages; in the first stage, a numerical model which can simulate the tidal flow conditions of the deployment sites was constructed, and, in the second stage, the actuator disc method which is capable of modelling an array of real scale-sized tidal turbines rotors has been implemented. In the first stage, tidal flow simulations of the Pentland Firth and Orkney Waters (PFOW) were conducted using two distinct open-source software - Telemac3D, which is a finite element based numerical model, and Delft3D, which is a finite difference based model. Detailed methodologies in developing a 3D tidal flow model for the PFOW using both numerical models were presented, where their functionality, as well as limitations were explored. In the calibration and validation processes, both models demonstrated excellent comparison against the measured data. However, Telemac3D was selected for further modelling of the actuator disc considering the model's capability to perform parallel computing, together with its flexibility to combine both structured and unstructured mesh. In the second stage, to examine the actuator disc's accuracy in modelling a full size tidal device, the momentum source term was initially applied in an idealised channel study, where the presence of a 20-meter diameter turbine was simulated for both single and array configurations. The following parameters were investigated: (i) size of the unstructured mesh utilised in the computational domain, (ii) variation in disc's thickness, (iii) resolution of the imposed structured grid to represent turbine's enclosure, (iv) variation in the vertical layers, and (v) influence of hydrostatic and non-hydrostatic formulations on the models' outputs. It is to be noted that the turbine's support structures have not been included in the modelling. The predicted velocities and computed turbulence intensities from the models were compared against laboratory measurement data sourced from literature, where excellent agreement between the model outputs and the data from literature was observed. In essence, these studies highlighted the efficiency and robustness of the applied momentum source term in replicating the wake profiles and turbulence characteristics downstream of the disc, hence providing credence in implementing the actuator disc method for a regional scale application. Subsequently, the validated actuator disc method was applied to the Inner Sound region of the Pentland Firth to simulate arrays of up to 32 tidal turbine rotors. The wake development, flow interactions with the rotor arrays, and flow recovery at the Inner Sound region have been successfully mapped. Also, this study highlighted the importance of employing optimal numerical margins, specifically for the structured grid and horizontal planes, as both parameters were relevant in defining the disc's swept area. As published materials on the implementation of actuator disc approach within a regional scale model is still scarce, it was aspired that this work could provide some evidence, guidance and examples of suggested best practice in effort to fill the research gap in modelling tidal turbine arrays using the actuator disc approach.
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Martinez, Fabien. "Drag study of the nacelles of a tidal stream device using CFD." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/7440.
Full textAbstract:
Nowadays, renewable energy is in full growth. In particular, offshore wind farms
will be at the centre of UK energetic strategy in the coming years. However,
other types of marine renewable are still at an early development stage. That is
the case for tidal energy. Many projects have been undertaken but there is no
candidate for competitive commercial applications yet.
Deltastream is one of these numerous pioneering projects. It consists of a set of
three marine current turbines mounted on a triangular base put down onto the
seabed. The device is not moored and no harm is done to the environment.
However, that makes the structure more sensitive to water flows. And it is
important to ensure that it will remain at its location and not being carried along
with the tidal streams.
Using CFD, the present study aims to evaluate the drag on the nacelles of the
structure and come up with solutions to reduce it as much as possible.
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Merkai, Christina. "Tidal park within offshore wind parks : An analysis for the potential use of tidal kites within the Aberdeen offshore wind farm." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-240594.
Full textAbstract:
Offshore wind has proved to be one of the most reliable and clean energy sources over the last few years. The industry has experienced a significant growth, with an increase of 101% only in 2017 compared to 2016. This raises the importance of the need for more secure power supply systems, which can be used for controlling the offshore farms during disconnections from the main grid. Nowadays, diesel generators are being used to feed auxiliary services of the offshore wind turbines in situations of emergency. However, as the marine renewable energy industry evolves, tidal energy parks have the potential to replace diesel generators and provide a more sustainable and eco-friendly solution for a long-term auxiliary power system. Moreover, they have the potential to produce extra power, which can be either stored for future use or linked directly to distribution. This report demonstrates a technical, financial and environmental assessment of a potential tidal park within an offshore wind park. Comparison with alternative sources for emergency power supply is also performed. Three alternative locations with high wind speeds and large tidal resource around the UK coast and four different groups of tidal devices are evaluated and compared for the implementation of this solution with the use of ArcGIS maps and other accessible marine data. The Aberdeen wind farm and the tidal kites are selected for further investigation and cost analysis. Seven tidal kites with average power 700 kW and rated power 3.5 MW can provide adequate power to the offshore wind farm for three months without grid connection, whereas they can also provide excess of energy on daily basis when grid disconnection does not occur. The total cost for the project would be approximately 301.6 MSEK. Due to the current renewable energy market, the project is not feasible without high investment risks. However, this study should be evaluated again in the near future when the cost of the tidal device will be further decreased.Havsbaserad vind har visat sig vara en av de mest tillförlitliga och rena energikällorna under senare år. Inom denna industri har en betydande tillväxt skett, med en ökning med 101% år 2017 jämfört med 2016. Detta relaterar till behovet av säkra elförsörjningssystem, som kan användas för att styra havsbaserade vindraftverksparker under urkoppling från huvudnätet. Numera används dieselgeneratorer som reservkälla till havsvindkraftverk i nödsituationer. Men när den marina förnybara energiindustrin utvecklas, har tidvattenkraftverk potential att ersätta dieselgeneratorer och ge ett mer hållbar och miljövänlig långtidslösning. Dessutom har de potential att producera extra el, som antingen kan lagras för framtida användning eller kopplas direkt till distributionsnätet. Denna rapport erbjuder en teknisk, finansiell och miljömässig bedömning av en potentiell tidvattenkraftverkspark kopplad till en havsvindpark. Jämförelse med alternativa källor för strömförsörjning genomförs också. Tre alternativa platser med hög vindstyrka och stora tidvattenresurser längs Storbritanniens kust och fyra olika grupper av tidvattenanordningar utvärderas och jämförs med hjälp av kartor och andra tillgängliga marina data. Aberdeen vindkraftpark och tidvattendrakar väljs för ytterligare undersökning och kostnadsanalys. Sju tidvattendrakar med genomsnittlig effekt på 700 kW och nominell effekt 3,5 MW kan ge tillräckligt med el till havsvindkraftverk i tre månader utan nätförbindelse, medan de också kan ge överflöd av energi dagligen när strömavbrott inte förekommer. Den totala kostnaden för projektet skulle vara cirka 301,6 MSEK. På grund av läget idag på elmarknaden för förnybar energi, är projektet inte genomförbart utan höga investeringsrisker. Men den här studien bör utvärderas igen inom en snar framtid när kostnaden för tidvattenanordningen har minskat.
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Berry, Matthew James. "Hydrodynamic analysis of the momentum-reversal and lift tidal turbine." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/29541.
Full textAbstract:
Tidal energy has the potential to make a valuable contribution to meeting future global energy demands. Converting the energy of tidal streams into useful electricity can be achieved with use of tidal-stream turbines, such as the Momentum-Reversal and Lift (MRL) device. This turbine utilises a blade motion where each blade rotates continuously through 180° about its own axis for every 360° of turbine rotation. The aim of the design is to harness both useful lift and drag forces when rotating at relatively slow speeds. However, no detailed analysis of the time-varying fluid dynamic behaviour of the turbine has been undertaken before this study. The primary aim of this study has been to further understanding of the performance characteristics of the MRL turbine design, focusing on a laboratory- scale device. The study has analysed both the time-averaged and time-varying torque and power output, and the associated fluid-dynamic structure of flow through the turbine. A secondary aim was to generate data that can be used by other researchers who focus on the wake generation of the MRL tidal turbine. This study has used OpenFOAM to develop a time-dependent RANS CFD model and investigate the performance of the MRL turbine. To allow validation of the CFD model, experiments were firstly undertaken in order to measure the cycle-mean torque and power output of the turbine when operating in a laboratory flume. Measurements of the flow velocity at a number of upstream and downstream locations were also taken, in order to allow comparison with the CFD simulation results, where appropriate. Also, in order to allow validation of the CFD approach against time-varying data, the motion of the turbine blades was analysed. This allowed suitable experimental test cases to be identified from the literature and CFD simulation results have been compared to these. A detailed sensitivity analysis of the MRL turbine CFD model was carried out, followed by two-dimensional simulations of the turbine involving a single-blade and three-blades. Three-dimensional simulations were also undertaken, with results compared to the gathered experimental results. Finally, the effect of varying turbine solidity was investigated with the CFD model. Overall it was found that the CFD simulations successfully reproduce the rotational speed at which maximum torque and power are developed. However, the three-dimensional simulations significantly over-predict the magnitude of results in comparison to the gathered experimental results. Regardless, the two- and three-dimensional simulations have allowed detailed analysis of the flow behaviour and structures that are responsible for the development of blade forces and turbine torque.
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Krehnovi, Emily M. "Resonate Energy Conversion: Analysis of a Lunar Tide Power Plant Using a Variable Area Pipe." University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1366991503.
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Taccogna, Matthew Ryan. "Risk perceptions and marine spatial planning surrounding tidal energy in British Columbia." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57916.
Full textAbstract:
This thesis examines in-stream tidal energy (ISTE) generation technology and its potential for development, underwater within Discovery Passage, a narrow channel ocean environment near Campbell River, British Columbia, Canada. The study took place in the summer of 2014 and measured levels of support and opposition towards two separate investigative license (IL) ocean energy sites held by a BC developer. The primary approach was to interview expert marine stakeholders and First Nations persons based on their commercial, recreational and cultural usage of the Discovery Passage waterway and its foreshores near the ILs. The study measured subjects’ risk and benefit perceptions of the technology and the projects, levels of support for its development, willingness to pay for it, and any specific conflicts with the developments, both on and under the water. Interactive marine spatial planning (IMSP) and geographic information systems (GIS) were used to elicit respondents’ principle areas of marine usage within the study area, levels of value associated with these areas and seasons of usage. In addition, at the end of the interview, subjects were shown the IL sites on a map and were given the opportunity to indicate areas of perceived conflict between their organizations’ operations and the sites.
Results found respondents to be initially strongly in favour of developing tidal energy in BC, with 88% indicating a high levels of support for its development and willingness to pay small amounts for it as part of BC Hydro’s rate increases. However, once the IL sites were shown to the interviewees specifically on a map, levels of support declined and specific opposition to the sites was identified amongst 72% of respondents, indicating highly localized risk perceptions towards the projects. Perceived risks identified by stakeholders included marine traffic interference stemming from installation operations, high costs, cumulative impacts of many turbine installations and tugboat towlines and fishing gear potentially snagging underwater turbines. Identified benefits of tidal energy included local reservoir water conservation from tidal energy generation displacing hydropower water use, local economic development, displacing regional area off-grid diesel generation and achieving more localized electrical generation on Vancouver Island.Science, Faculty of
Resources, Environment and Sustainability (IRES), Institute for
Graduate
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Osalusi, Emmanuel. "Analysis of wave and current data in a tidal energy test site." Thesis, Heriot-Watt University, 2010. http://hdl.handle.net/10399/2327.
Full textAbstract:
Characterisation of a tidal stream site before device deployment is important for the marine tidal industry, in order to optimise the device design and accurately predict its performance during operation. Understanding the short-term uctuations in tidal stream velocity, resulting from turbulence and wave-current interactions, is essential for proper evaluation of the transient performance of a tidal stream turbine. Several aerodynamic models have been proposed for the design of tidal stream turbines and energy production calculation, most of which have proved to predict accurately mean quantities within the ow regime. Unfortunately, these models cannot accurately predict the instantaneous ow variation and resulting forces within the ow regime acting on tidal stream systems which is of central importance to the tidal energy industry. The reasons for this may not be unconnected to the signi cant differences between wind and tidal turbines. Given the uncertainties which exist in the assumptions of resource modelling and the need for an accurate energy capture assessment at a speci c site, accurate on-site measurements that can predict the ow velocity (and its directional component) at a given location, are needed. This thesis is devoted to characterisation of ow in a typical tidal stream site (the Fall of Warness, of the European Marine Energy Center (EMEC), Orkney) through measured data. The high-frequency Acoustic Doppler Current Pro ler (ADCP) surveys were conducted at different locations within this site by EMEC. This dataset allows for the rst time a statistical and thorough analysis of the vertical turbulence structure at the EMEC's tidal stream test site. Detailed analyses of the directional components of the wave elds using a non-phase-locked method and in uences of seabed and tidal stream on wave elds, were performed. The bulk turbulence parameters within the tidal streams were estimated using the variance method. The results suggest a signi - cant effect of directionality and short-term uctuations in stream velocity resulting from turbulence and wave-current interactions, on the hydrodynamics in a typical tidal energy test site. The results from this study can be used to validate and improve/develop proposed hydrodynamic models and can play a vital role in tidal energy resource planning.
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Brown, Alice Goward. "Simulating feedbacks between tidal stream array operation and the marine energy resource." Thesis, Bangor University, 2017. https://research.bangor.ac.uk/portal/en/theses/simulating-feedbacks-between-tidal-stream-array-operation-and-the-marine-energy-resource(418a4dee-601e-44e5-b656-1a3c4870a9e7).html.
Full textAbstract:
Tidal streams have long since been acknowledged as a reliable and predictable source of energy. For tidal energy developments to be economically viable, the arrangement of tidal devices needs to consider regional complex flow conditions. First generation tidal energy development sites are selected on their proximity to port and grid infrastructure, water depth and mean spring current velocity. The layout of tidal energy devices within an array is planned to reduce blade fatigue. The continental shelf seas around the United Kingdom have world leading levels of tidal dissipation; Tidal streaming around the coastline is further accentuated by topographic complexities. The Crown Estate has leased numerous locations around the United Kingdom's shelf seas and a spatially representative selection of these sites has been characterised using the Regional Ocean Modeling System (ROMS). Using the HPC Wales system, high resolution regional 3-D models are developed. Model results enable maps of metrics which illuminate flow features important to tidal energy extraction, which include: tidal phasing, tidal asymmetry and the misalignment of flood and ebb tidal currents. From this assessment four leased tidal development sites within the Pentland Firth are highlighted as the most dynamic of the UK's leased tidal stream sites. Three-dimensional tidal energy extraction techniques are employed within each of the sites in the Pentland Firth which enables a technical resource assessment to be carried out. Furthermore, changing the hydrodynamics has a cumulative impact on natural physical processes of the coastal system. The non-linear nature of the interaction between tidal arrays and physical processes calls for more complex numerical modelling techniques to enable a full quantification of tidal energy development on marine systems.
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Banerjee, S. "Ocean energy assessment : an integrated methodology." Thesis, Coventry University, 2011. http://curve.coventry.ac.uk/open/items/16196d0d-e671-489a-ba71-f20cdb6c8df3/1.
Full textAbstract:
The huge natural energy resources available in the world’s oceans are attracting increasing commercial and political interest. In order to evaluate the status and the degree of acceptability of future Ocean Energy (OE) schemes, it was considered important to develop an Integrated Assessment Methodology (IAM) for ascertaining the relative merits of the competing OE devices being proposed. Initial studies included the gathering of information on the present status of development of the ocean energy systems on wave, OTEC and tidal schemes with the challenges faced for their commercial application. In order to develop the IAM, studies were undertaken for the development and standardization of the assessment tools focussing on: • Life Cycle Assessment (LCA) on emission characteristics. • Energy Accounting (EA) studies. • Environmental Impact Assessment (EIA) over different environmental issues. • Resource captures aspects. • Defining economy evaluation indices. The IAM developed from such studies comprised of four interrelated well defined tasks and six assessment tools. The tasks included the identification of the modus operandi on data collection to be followed (from industry) for assessing respective OE devices, and also advancing relevant guidelines as to the safety standards to be followed, for their deployment at suitable sites. The IAM as developed and validated from case studies in ascertaining relative merits of competing OE devices included: suitable site selection aspects with scope for resource utilisation capability, safety factors for survivability, scope for addressing global warming & energy accounting, the environmental impact assessment both qualitatively and quantitatively on different environmental issues, and the economic benefits achievable. Some of the new ideas and concepts which were also discovered during the development of the IAM, and considered useful to both industry and researchers are given below: • Relative Product Cost (RPC) ratio concept- introduced in making an economic evaluation. This is considered helpful in sensitivity analysis and making design improvements (hybridising etc) for the cost reduction of OE devices. This index thus helps in making feasibility studies on R&D efforts, where the capital cost requirement data and life span of the device is not well defined in the primary stages of development. • Determination of the threshold limit value of the barrage constant - considered useful in determining the efficacy of the planning process. The concept ascertained the relative efficiency achieved for various barrage proposals globally. It could also be applied to suggest the revisions required for certain barrage proposals and also found useful in predicting the basin area of undefined barrage proposal for achieving economic viability. • Estimations made on the future possibility of revenue earnings from the by-products of various OTEC types, including the scope of chemical hubs from grazing type OTEC plants. • Determination of breakeven point- on cost versus life span of wave and OTEC devices studied, which is useful in designing optimum life of the concerned devices. The above stated multi-criterion assessment methodology, IAM, was extended leading to the development of a single criterion model for ascertaining sustainability percent achievable from an OE device and termed IAMs. The IAMs was developed identifying 7 Sustainability Development Indices (SDI) using some the tools of the IAM. A sustainability scale of 0-100 was also developed, attributing a Sustainability Development Load Score (SDLS) percentage distribution pattern over each SDIs, depending on their relative importance in achieving sustainability. The total sum of sustainability development (SD) gained from each SDI gave the IAMs (for the concerned device), indicating the total sustainable percentage achieved. The above IAMs developed, could be applied in ranking OE devices alongside the unsustainable coal power station. A mathematical model of estimating the IAMs was formulated, in order to ascertain the viability to the sustainable development of any energy device. The instruments of IAM and IAMs which have been developed would be helpful to the OE industry in ascertaining the degree of acceptability of their product. In addition it would also provide guidelines for their safe deployment by assessing the relative merits of competing devices. Furthermore, IAM and IAMs would be helpful to researchers undertaking feasibility studies on R&D efforts for material development research, ‘hybridization studies’ (as also new innovations), cost reduction, the performance improvement of respective devices, and any economic gains. With future advancements in OE systems and the availability of field data from large scale commercial applications, the specific values/data of the IAM & IAMs may be refined, but the logic of the models developed in this research would remain the same.
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Dagà, Kunze Jordi Sebastián. "Aprovechamiento Hidroeléctrico de las Mareas y su Posible Desarrollo en Chile." Tesis, Universidad de Chile, 2008. http://repositorio.uchile.cl/handle/2250/103061.
Full textAbstract:
Utilizar fuentes de energía renovable es el desafío para el mundo civilizado del siglo
XXI. Una fuente que ha sido poco explorada en Chile es la energía mareomotriz. Esta fuente
depende de factores como el efecto gravitacional de la luna y el sol, fuentes que están
aseguradas por muchos millones de años más. Además, las energías no renovables se están
encareciendo cada día más, por lo que se espera que algún día estas nuevas fuentes de
energías sean rentables. Por esto es importante estudiar el recurso de las mareas en nuestro
país, y prepararse para cuando eso suceda.
En este estudio se investiga acerca del fenómeno de las mareas y se estudia este
recurso en Chile, haciendo así un diagnóstico del potencial mareomotriz que existe en este
país. Además se analizan los lugares más propicios para el desarrollo de las diversas formas
de explotar este recurso en Chile.
Se exponen distintas tecnologías para aprovechar el potencial energético de las
mareas, tanto las que aprovechan su energía potencial como las que utilizan la energía
cinética generada por las corrientes de mareas. Se pone especial énfasis en esta última debido
a que es una forma ambientalmente muy favorable de obtener electricidad.
Para analizar la factibilidad económica de la explotación energética de este recurso
se estudia la eficiencia energética de las distintas tecnologías analizando su factor de planta y
el costo de la energía producida, se analiza la central mareomotriz más emblemática que es la
central de La Rance, Francia. Además, se diseña un posible proyecto en Chile, utilizando la
tecnología que aprovecha la energía cinética de las mareas y haciendo la evaluación
económica de él.
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Stringer, Robert. "Numerical investigation of cross-flow tidal turbine hydrodynamics." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760981.
Full textAbstract:
The challenge of tackling global climate change and our increasing reliance on power means that new and diverse renewable energy generation technologies are a necessity for the future. From a number of technologies reviewed at the outset, the cross-flow tidal turbine was chosen as the focus of the research. The numerical investigation begins by choosing to model flow around a circular cylinder as a challenging benchmarking and evaluation case to compare two potential solvers for the ongoing research, ANSYS CFX and OpenFOAM. A number of meshing strategies and solver limitations are extracted, forming a detailed guide on the topic of cylinder lift, drag and Strouhal frequency prediction in its own right. An introduction to cross-flow turbines follows, setting out turbine performance coefficients and a strategy to develop a robust numerical modelling environment with which to capture and evaluate hydrodynamic phenomena. The validation of a numerical model is undertaken by comparison with an experimentally tested lab scale turbine. The resultant numerical model is used to explore turbine performance with varying Reynolds number, concluding with a recommended minimum value for development purposes of Re = 350 × 103 to avoid scalability errors. Based on this limit a large scale numerical simulation of the turbine isconducted and evaluated in detail, in particular, a local flow sampling method is proposed and presented. The method captures flow conditions ahead of the turbine blade at all positions of motion allowing local velocities and angles of attack to be interrogated. The sampled flow conditions are used in the final chapter to construct a novel blade pitching strategy. The result is a highly effective optimisation method which increases peak turbine power coefficient by 20% for only two further case iterations of the numerical solution.
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Xu, Mingzhou. "A study of induction generator performance in a wave energy conversion system." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387930.
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