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1
Easom, Gary. "Improved turbulence models for computational wind engineering." Thesis, University of Nottingham, 2000. http://eprints.nottingham.ac.uk/10113/.
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The fundamental errors in the numerical modelling of the turbulent component of fluid flow are one of the main reasons why computational fluid dynamics techniques have not yet been fully accepted by the wind engineering community. This thesis is the result of extensive research that was undertaken to assess the various methods available for numerical simulation of turbulent fluid flow. The research was undertaken with a view to developing improved turbulence models for computational wind engineering. Investigations have concentrated on analysing the accuracy and numerical stability of a number of different turbulence models including both the widely available models and state of the art techniques. These investigations suggest that a turbulence model, suitable for wind engineering applications, should be able to model the anisotropy of turbulent flow as in the differential stress model whilst maintaining the ease of use and computational stability of the two equation k-e models. Therefore, non-linear expansions of the Boussinesq hypotheses, the quadratic and cubic non-linear k-e models, have been tested in an attempt to account for anisotropic turbulence and curvature related strain effects. Furthermore, large eddy simulations using the standard Smagorinsky sub-grid scale model have been completed, in order to account for the four dimensional nature of turbulent flow. This technique, which relies less heavily on the need to model turbulence by utilising advances in computer technology and processing power to directly resolve more of the flow field, is now becoming increasingly popular in the engineering community. The author has detailed and tested all of the above mentioned techniques and given recommendations for both the short and longer term future of turbulence modelling in computational wind engineering. Improved turbulence models that will more accurately predict bluff body flow fields and that are numerically stable for complex geometries are of paramount importance if the use of CFD techniques are to gain wide acceptance by the wind engineering community.
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Bajoria, Ankur. "Computational wind engineering using finite element package ADINA." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43891.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references (leaves 61-64).
Design of tall and long span structures is governed by the wind forces. Inadequate research in the field of wind dynamics has forced engineers to rely on design codes or wind tunnel tests for sufficient data. The present work uses a computational wind dynamics method to compare the coefficient of pressure (Cp) for the different aerodynamic shapes. ADINA, a finite element package, contains an inbuilt turbulence model which will be used to construct four different shapes for comparison. Results are verified with the experimental and simulation data. The effect of increase in the Reynolds number on the flow has been studied. Graphs for the pressure, velocity and turbulence energy distribution have been developed to assist the engineers in design.
by Ankur Bajoria.
M.Eng.
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Zoumprouli, Argyro. "Wind farm and environmental aerodynamics assessment using computational engineering." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7212.
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The aim of this thesis is the application of computational engineering software for the study of wind resource assessment of a wind farm as well as for establishing the range of influence of different numerical and physical parameters, including turbulence modeling , surface roughness and wakes.
Simulations were performed for a wind farm which is in operation since 2006, called Panachaiko, located at the west part of Greece and encompassing an energy capacity of 34.85 MW. Simulations were performed using three variants of the k-ε model. Moreover, the effects of surface roughness and wake on the efficiency of wind farm operation were investigated. Comparisons were performed between linear and non-linear computational fluid dynamics (CFD) modeling, in the framework of the available engineering (commercial) software. Both qualitative and quantitative assessment of the results is presented.
The study revealed the dependence of the results on the CFD (linear vs non-linear) model employed. The results of the present study provide useful guidance regarding the applicability of CFD models for wing resource assessment.
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Chinchore, Asmita C. "Computational Study of Savonius Wind Turbine." Cleveland State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=csu1389795972.
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Irshad, Wahid. "Wind resource assessment : statistical and computational fluid-dynamic analysis." Thesis, Edinburgh Napier University, 2012. http://researchrepository.napier.ac.uk/Output/5329.
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Wind is an important source of renewable energy and is widely available, despite the changing condition. In recent years a growing number of manufacturers have produced small wind turbines suitable for utilisation by individual householders or small businesses. These systems are designed to install in towns or cities. This raises the question about the potential of wind energy resource in build-up areas. This thesis sets to investigate the wind energy resource implication in the build-up areas by understanding the wind climatology of urban areas. As well as the overall mean wind speed, knowledge of the wind speed distribution (due to the non-linear relationship between wind speed and wind power) and the wind-direction distribution for optimum turbine siting is required. Other areas that have been considered are short-duration fluctuations in both speed and direction as these can affect the efficiency of the turbine. The aims of this research are to study the local wind conditions and estimate the available wind resource for the wind-energy driven generation of electricity in Edinburgh by taking into account of its climate, wind data and topographical effects. To achieve these aims eleven years of Met office data was investigated in addition to analysis of the data collected from locally installed weather station. Diurnal effect on wind condition was studied and found to be more pronounced in Edinburgh's rural area than its urban conurbation. It was also found that the available wind energy in the urban area is 30% less than that of the rural area. Turbulence in wind speed and direction of flow was also investigated. Careful consideration of all the parameters defining and affecting the prevailing wind revealed the wind resource in Edinburgh's urban area to be insufficient for viable generation of wind energy through the available technology of micro WEC (wind energy converter) systems. A CFD analysis was also performed to determine wind resource differences because of different mounting locations of wind equipment over the building under consideration. As a part of the project, a commercially available wind turbine was installed and monitored to investigate its performance in urban area. The research study finally suggests that the available grid connected micro WEC system cannot provide a cost effective contribution to urban Edinburgh's renewable energy generation.
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Anbreen, Faiqa. "Design of airborne wind turbine and computational fluid dynamics analysis." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=1606691.
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Wind energy is a promising alternative to the depleting non-renewable sources. The height of the wind turbines becomes a constraint to their efficiency. Airborne wind turbine can reach much higher altitudes and produce higher power due to high wind velocity and energy density. The focus of this thesis is to design a shrouded airborne wind turbine, capable to generate 70 kW to propel a leisure boat with a capacity of 8-10 passengers. The idea of designing an airborne turbine is to take the advantage of higher velocities in the atmosphere.
The Solidworks model has been analyzed numerically using Computational Fluid Dynamics (CFD) software StarCCM+. The Unsteady Reynolds Averaged Navier Stokes Simulation (URANS) with K-ϵ turbulence model has been selected, to study the physical properties of the flow, with emphasis on the performance of the turbine and the increase in air velocity at the throat. The analysis has been done using two ambient velocities of 12 m/s and 6 m/s. At 12 m/s inlet velocity, the velocity of air at the turbine has been recorded as 16 m/s. The power generated by the turbine is 61 kW. At inlet velocity of 6 m/s, the velocity of air at turbine increased to 10 m/s. The power generated by turbine is 25 kW.
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HORVAT, MARKO. "Computational Wind Engineering simulations for design of Sand Mitigation Measures and performance assessment." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2872324.
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Paetzold, Joachim Meinert. "A Wind Engineering Analysis of Parabolic Trough Concentrating Solar Power." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15256.
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This thesis aims at improving the understanding of the effects of the wind on parabolic trough Concentrating Solar Power technology. Parabolic trough power plants are often located in areas that are subjected to high wind speeds, as an open terrain without any obstructions is beneficial for the plant performance. The wind impacts both the structural requirements and the performance of the plant. The aerodynamic loads from the wind impose strong requirements on the support structure of the reflectors, and they also impact the tracking accuracy. On a thermal level the airflow around the glass envelope of the receiver tube cools its outer surface through forced convection, thereby contributing to the total heat loss of the system. The influence of the shape and design of the trough is studied with the aim to minimise wind loads and thermal losses and, thus, contribute to making parabolic trough technology more efficient and hence reduce the cost of the generated electricity. Starting with an investigation on the level of a single row of collectors, the influence of different trough depths on the wind effects — the aerodynamic loads, as well as the thermal effects — is analysed via numerical simulations that are validated against experimental data from wind tunnel tests. While a deeper trough geometry leads to higher forces than a shallow one, it also significantly reduces the wind speed around the receiver and hence the thermal loss on its outer surface. Based on these results alterations to the standard trough design of a continuous parabolic shape are undertaken, analysed in numerical simulations, and validated in wind tunnel experiments. A staggered reflector layout with different focal lengths in different sections of the trough is found to be able to reduce the wind loads by up to 24%,while some designs also retain the sheltering effect on the receiver. Various numerical simulation approaches for an adequate representation of the wind effects on individual rows of collectors, as well as in a solar field are investigated and compared. For the simulation of a solar field, time-averaged simulations of a large domain with several collector rows are compared with a transient simulation with stream-wise periodic boundary conditions. At the level of an individual collector row, the performance and results of a transient scale resolving simulation are compared with those of a simulation using synthetic turbulence generation at the inlet boundary.
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Alexeev, Timur. "Computational aeroelasticity study of horizontal axis wind turbines with coupled bending - torsion blade dynamics." Thesis, University of California, Davis, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3614169.
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With the increasing size of wind turbines and the use of flexible and light materials in aerodynamic applications, aeroelastic tailoring for power generation and blade stability has become an important subject in the study of wind turbine dynamics. To this day, coupling of bending and torsion in wind turbine rotor blades has been studied primarily as an elastic mechanism due to a coupling laminate construction. In this report, inertial coupling of bending and torsion, due to offset of axis of elasticity and axis of center of mass, is investigated and numerical simulations are performed to test the validity of the constructed model using an in-house developed aeroelastic numerical tool. A computationally efficient aeroelastic numerical tool, based on Goldstein's helicoidal vortex model with a prescribed wake model and modal coupling of bending and torsion in the blades, is developed for 2-bladed horizontal axis wind turbines and a conceptual study is performed in order to argue the validity of the proposed formulation and numerical construction. The aeroelastic numerical tool, without bending-torsion coupling, was validated (Chattot 2007) using NREL Phase VI wind turbine data, which has become the baseline model in the wind turbine community. Due to novelty of the proposed inertial bending-torsion coupling in the aeroelastic model of the rotor and lack of field data, as well as, other numerical tools available for code to code comparison studies, a thorough numerical investigation of the proposed formulation is performed in order to validate the aeroelastic numerical tool Finally, formulations of geometrically nonlinear beams, elastically nonlinear plates and shells, and a piecewise linear, two degree of freedom, quasi steady, aerodynamic model are presented as an extension for nonlinear wind turbine aeroelastic simulations. Preliminary results of nonlinear beams, plates, shells, and 2 DOF NACA0012 aeroelastic model are presented.
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Collins, Carl. "Development and application of a computational model for scour around offshore wind turbine foundations." Thesis, University of Hull, 2017. http://hydra.hull.ac.uk/resources/hull:16530.
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There is a constant requirement to understand scour especially regarding its prevention, due to the potential impact and disastrous consequences. The installation of offshore wind turbines is haunted by scour mitigation and at the start of the offshore wind turbine boom in the early 2000’s this was achieved using overzealous amounts of rock armour. However, as investment and cost efficiency has increased, protection methods have been refined, but, there remains significant room for improvement. Research into offshore sediment dynamics has benefited greatly by computational advancements providing a greater understanding of processes and the driving mechanisms; leading to protection method improvements and reductions in environmental impact. The premise of this study is to push this knowledge further, by developing and validating a novel scour model within CFD software that can be used to simulate and analyse offshore scour; specifically, the scour around complex, new offshore wind turbine foundation geometries.
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Drofelnik, Jernej. "Massively parallel time- and frequency-domain Navier-Stokes Computational Fluid Dynamics analysis of wind turbine and oscillating wing unsteady flows." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8284/.
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Increasing interest in renewable energy sources for electricity production complying with stricter environmental policies has greatly contributed to further optimisation of existing devices and the development of novel renewable energy generation systems. The research and development of these advanced systems is tightly bound to the use of reliable design methods, which enable accurate and efficient design. Reynolds-averaged Navier-Stokes Computational Fluid Dynamics is one of the design methods that may be used to accurately analyse complex flows past current and forthcoming renewable energy fluid machinery such as wind turbines and oscillating wings for marine power generation. The use of this simulation technology offers a deeper insight into the complex flow physics of renewable energy machines than the lower-fidelity methods widely used in industry. The complex flows past these devices, which are characterised by highly unsteady and, often, predominantly periodic behaviour, can significantly affect power production and structural loads. Therefore, such flows need to be accurately predicted. The research work presented in this thesis deals with the development of a novel, accurate, scalable, massively parallel CFD research code COSA for general fluid-based renewable energy applications. The research work also demonstrates the capabilities of newly developed solvers of COSA by investigating complex three-dimensional unsteady periodic flows past oscillating wings and horizontal-axis wind turbines. Oscillating wings for the extraction of energy from an oncoming water or air stream, feature highly unsteady hydrodynamics. The flow past oscillating wings may feature dynamic stall and leading edge vortex shedding, and is significantly three-dimensional due to finite-wing effects. Detailed understanding of these phenomena is essential for maximising the power generation efficiency. Most of the knowledge on oscillating wing hydrodynamics is based on two-dimensional low-Reynolds number computational fluid dynamics studies and experimental testing. However, real installations are expected to feature Reynolds numbers of the order of 1 million and strong finite-wing-induced losses. This research investigates the impact of finite wing effects on the hydrodynamics of a realistic aspect ratio 10 oscillating wing device in a stream with Reynolds number of 1.5 million, for two high-energy extraction operating regimes. The benefits of using endplates in order to reduce finite-wing-induced losses are also analyzed. Three-dimensional time-accurate Reynolds-averaged Navier-Stokes simulations using Menter's shear stress transport turbulence model and a 30-million-cell grid are performed. Detailed comparative hydrodynamic analyses of the finite and infinite wings highlight that the power generation efficiency of the finite wing with sharp tips for the considered high energy-extraction regimes decreases by up to 20 %, whereas the maximum power drop is 15 % at most when using the endplates. Horizontal-axis wind turbines may experience strong unsteady periodic flow regimes, such as those associated with the yawed wind condition. Reynolds-averaged Navier-Stokes CFD has been demonstrated to predict horizontal-axis wind turbine unsteady flows with accuracy suitable for reliable turbine design. The major drawback of conventional Reynolds-averaged Navier-Stokes CFD is its high computational cost. A time-step-independent time-domain simulation of horizontal-axis wind turbine periodic flows requires long runtimes, as several rotor revolutions have to be simulated before the periodic state is achieved. Runtimes can be significantly reduced by using the frequency-domain harmonic balance method for solving the unsteady Reynolds-averaged Navier-Stokes equations. This research has demonstrated that this promising technology can be efficiently used for the analyses of complex three-dimensional horizontal-axis wind turbine periodic flows, and has a vast potential for rapid wind turbine design. The three-dimensional simulations of the periodic flow past the blade of the NREL 5-MW baseline horizontal-axis wind turbine in yawed wind have been selected for the demonstration of the effectiveness of the developed technology. The comparative assessment is based on thorough parametric time-domain and harmonic balance analyses. Presented results highlight that horizontal-axis wind turbine periodic flows can be computed by the harmonic balance solver about fifty times more rapidly than by the conventional time-domain analysis, with accuracy comparable to that of the time-domain solver.
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Li, Huaxia. "An integrated multibody dynamics computational framework for design optimization of wind turbine drivetrains considering wind load uncertainty." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2240.
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The objective of this study is to develop an integrated multibody dynamics computational framework for the deterministic and reliability-based design optimization of wind turbine drivetrains to obtain an optimal wind turbine gear design that ensures a target reliability under wind load and gear manufacturing uncertainties. Gears in wind turbine drivetrains are subjected to severe cyclic loading due to variable wind loads that are stochastic in nature. Thus, the failure rate of drivetrain systems is reported to be relatively higher than the other wind turbine components. It is known in wind energy industry that improving reliability of drivetrain designs is one of the key issues to make wind energy competitive as compared to fossil fuels. Furthermore, a wind turbine is a multi-physics system involving random wind loads, rotor blade aerodynamics, gear dynamics, electromagnetic generator and control systems. This makes an accurate prediction of product life of drivetrains challenging and very limited studies have been carried out regarding design optimization including the reliability-based design optimization (RBDO) of geared systems considering wind load and manufacturing uncertainties.
In order to address these essential and challenging issues on design optimization of wind turbine drivetrains under wind load and gear manufacturing uncertainties, the following issues are discussed in this study: (1) development of an efficient numerical procedure for gear dynamics simulation of complex multibody geared systems based on the multi-variable tabular contact search algorithm to account for detailed gear tooth contact geometry with profile modifications or surface imperfections; (2) development of an integrated multibody dynamics computational framework for deterministic and reliability-based design optimization of wind turbine drivetrains using the gear dynamics simulation software developed in (1) and RAMDO software by incorporating wide spatiotemporal wind load uncertainty model, pitting gear tooth contact fatigue model, and rotor blade aerodynamics model using NREL AeroDyn/FAST; and (3) deterministic and reliability-based design optimization of wind turbine drivetrain to minimize total weight of a drivetrain system while ensuring 20-year reliable service life with wind load and gear manufacturing uncertainties using the numerical procedure developed in this study.
To account for the wind load uncertainty, the joint probability density function (PDF) of 10-minute mean wind speed (V₁₀) and 10-minute turbulence intensity (I₁₀) is introduced for wind turbine drivetrain dynamics simulation. To consider wide spatiotemporal wind uncertainty (i.e., wind load uncertainty for different locations and in different years), uncertainties of all the joint PDF parameters of V₁₀, I₁₀ and copula are considered, and PDF for each parameter is identified using 249 sets of wind data. This wind uncertainty model allows for the consideration of a wide range of probabilistic wind loads in the contact fatigue life prediction. For a given V₁₀ and I₁₀ obtained from the stochastic wind model, the random time-domain wind speed data is generated using NREL TurbSim, and then inputted into NREL FAST to perform the aerodynamic simulation of rotor blades to predict the transmitted torque and speed of the main shaft of the drivetrain that are sent to the multibody gear dynamics simulation as an input.
In order to predict gear contact fatigue life, a high-fidelity gear dynamics simulation model that considers the detailed gear contact geometry as well as the mesh stiffness variation needs to be developed to find the variability of maximum contact stresses under wind load uncertainty. This, however, leads to a computationally intensive procedure. To eliminate the computationally intensive iterative online collision detection algorithm, a numerical procedure for the multibody gear dynamics simulation based on the tabular contact search algorithm is proposed. Look-up contact tables are generated for a pair of gear tooth profiles by the contact geometry analysis prior to the dynamics simulation and the contact points that fulfill the non-conformal contact condition and mesh stiffness at each contact point are calculated for all pairs of gears in the drivetrain model.
This procedure allows for the detection of gear tooth contact in an efficient manner while retaining the precise contact geometry and mesh stiffness variation in the evaluation of mesh forces, thereby leading to a computationally efficient gear dynamics simulation suited for the design optimization procedure considering wind load uncertainty. Furthermore, the accuracy of mesh stiffness model introduced in this study and transmission error of gear tooth with tip relief are discussed, and a wind turbine drivetrain model developed using this approach is validated against test data provided in the literature.
The gear contact fatigue life is predicted based on the gear tooth pitting fatigue criteria and is defined by the sum of the number of stress cycles required for the fatigue crack initiation and the number required for the crack to propagate from the initial to the critical crack length based on Paris-Erdogan equation for Mode II fracture. All the above procedures are integrated into the reliability-based design optimization software RAMDO for design optimization and reliability analysis of wind turbine drivetrains under wind load and manufacturing uncertainties.
A 750kW GRC wind turbine gearbox model is used to perform the design optimization and the reliability analysis. A deterministic design optimization (DDO) is performed first using an averaged joint PDF of wind load to ensure a 20-year service life. To this end, gear face width and tip relief (profile modification) are selected as design variables and optimized such that 20-year fatigue life is ensured while minimizing the total weight of drivetrains. It is important to notice here that an increase in face width leads to a decrease in the fatigue damage, but an increase in total weight. On the other hand, the tip relief has almost no effect on the total weight, but it has a major impact on the fatigue damage. It is shown in this study that the optimum tip relief allows for lowering the greatest maximum shear stresses on the tooth surface without relying heavily on face width widening to meet the 20-year fatigue life constraint and it leads to reduction of total drivetrain weight by 8.4%. However, if only face width is considered as design variable, total weight needs to be increased by 4.7% to meet the 20-year fatigue life constraint.
Furthermore, the reliability analysis at the DDO optimum design is carried out considering the large spatiotemporal wind load uncertainty and gear manufacturing uncertainty. Local surrogate models at DDO optimum design are generated using Dynamic Kriging method in RAMDO software to evaluate the gear contact fatigue damage. 49.5% reliability is obtained at the DDO optimum design, indicating that the probability of failure is 50.5%, which is as expected for the DDO design. RBDO is, therefore, necessary to further improve the reliability of the wind turbine drivetrain.
To this end, the sampling-based reliability analysis is carried out to evaluate the probability of failure for each design using the Monte Carlo Simulation (MCS) method. However, the use of a large number of MCS sample points leads to a large number of contact fatigue damage evaluation time using the 10-minute multibody drivetrain dynamics simulation, resulting in the RBDO calculation process being computational very intensive. In order to overcome the computational difficulty resulting from the use of high-fidelity wind turbine drivetrain dynamics simulation, intermediate surrogate models are created prior to the RBDO process using the Dynamic Kriging method in RAMDO and used throughout the entire RBDO iteration process. It is demonstrated that the RBDO optimum obtained ensures the target 97.725 % reliability (two sigma quality level) with only 1.4 % increase in the total weight from the baseline design with 8.3 % reliability. This result clearly indicates the importance of incorporating the tip relief as a design variable that prevents larger increase in the face width causing an increase in weight. This, however, does not mean that a larger tip relief is always preferred since an optimum tip relief amount depends on stochastic wind loads and an optimum tip relief cannot be found deterministically. Furthermore, accuracy of the RBDO optimum obtained using the intermediate surrogate models is verified by the reliability analysis at the RBDO optimum using the local surrogate models. It is demonstrated that the integrated design optimization procedure developed in this study enables the cost effective and reliable design of wind turbine drivetrains.
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Sangoor, Abbas Jarullah. "Experimental and Computational Study of the Performance of a New Shroud Design for an Axial Wind Turbine." Youngstown State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1433503872.
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Li, Yuwei. "Coupled computational fluid dynamics/multibody dynamics method with application to wind turbine simulations." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/4681.
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A high fidelity approach coupling the computational fluid dynamics method (CFD) and multi-body dynamics method (MBD) is presented for aero-servo-elastic wind turbine simulations. The approach uses the incompressible CFD dynamic overset code CFDShip-Iowa v4.5 to compute the aerodynamics, coupled with the MBD code Virtual.Lab Motion to predict the motion responses to the aerodynamic loads. The IEC 61400-1 ed. 3 recommended Mann wind turbulence model was implemented in this thesis into the code CFDShip-Iowa v4.5 as boundary and initial conditions, and used as the explicit wind turbulence for CFD simulations. A drivetrain model with control systems was implemented in the CFD/MBD framework for investigation of drivetrain dynamics. The tool and methodology developed in this thesis are unique, being the first time with complete wind turbine simulations including CFD of the rotor/tower aerodynamics, elastic blades, gearbox dynamics and feedback control systems in turbulent winds.
Dynamic overset CFD simulations were performed with the benchmark experiment UAE phase VI to demonstrate capabilities of the code for wind turbine aerodynamics. The complete turbine geometry was modeled, including blades and approximate geometries for hub, nacelle and tower. Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Detached Eddy Simulation (DES) turbulence models were used in the simulations. Results for both variable wind speed at constant blade pitch angle and variable blade pitch angle at fixed wind speed show that the CFD predictions match the experimental data consistently well, including the general trends for power and thrust, sectional normal force coefficients and pressure coefficients at different sections along the blade.
The implemented Mann wind turbulence model was validated both theoretically and statistically by comparing the generated stationary wind turbulent field with the theoretical one-point spectrum for the three components of the velocity fluctuations, and by comparing the expected statistics from the simulated turbulent field by CFD with the explicit wind turbulence inlet boundary from the Mann model.
The proposed coupled CFD/MBD approach was applied to the conceptual NREL 5MW offshore wind turbine. Extensive simulations were performed in an increasing level of complexity to investigate the aerodynamic predictions, turbine performance, elastic blades, wind shear and atmospheric wind turbulence. Comparisons against the publicly available OC3 simulation results show good agreements between the CFD/MBD approach and the OC3 participants in time and frequency domains. Wind turbulence/turbine interaction was examined for the wake flow to analyze the influence of turbulent wind on wake diffusion.
The Gearbox Reliability Collaborative project gearbox was up-scaled in size and added to the NREL 5MW turbine with the purpose of demonstrating drivetrain dynamics. Generator torque and blade pitch controllers were implemented to simulate realistic operational conditions of commercial wind turbines. Interactions between wind turbulence, rotor aerodynamics, elastic blades, drivetrain dynamics at the gear-level and servo-control dynamics were studied, showing the potential of the methodology to study complex aerodynamic/mechanic systems.
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Abodonya, Ahmed [Verfasser], Kai-Uwe [Akademischer Betreuer] Bletzinger, Riccardo [Gutachter] Rossi, Bert [Gutachter] Blocken, and Kai-Uwe [Gutachter] Bletzinger. "Verification Methodology for Computational Wind Engineering Prediction of Wind Loads on Structures / Ahmed Abodonya ; Gutachter: Riccardo Rossi, Bert Blocken, Kai-Uwe Bletzinger ; Betreuer: Kai-Uwe Bletzinger." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1215293232/34.
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Smith, Jason Allan. "California Polytechnic State University Wind Resource Assessment." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/629.
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Wind resource assessment at California Polytechnic State University shows there is potential for wind power generation on Cal Poly land. A computational fluid dynamics model based on wind data collected from a campus maintained meteorological tower on Escuela Ranch approximately 5 miles northwest of campus suggests there are areas of Cal Poly land with an IEC Class III wind resource at a height of 80 meters above ground. In addition during the daytime when the campus uses the most energy there are large portions of land with annual average daytime wind speeds above 6.9m/s. These areas have been identified by analyzing the wind speed and directional data collected at the meteorological tower and using it to create the boundary conditions and turbulence parameters for the computer model. The model boundary conditions and turbulence parameters have been verified through comparison between data collected at Askervein hill in Scotland during the 1980’s and the results of a simulation of Askervein hill using the same model. Before constructing a wind farm for power generation, additional meteorological towers should be constructed in Poly Canyon to further confirm the wind resource prediction.
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Pierce, Warrick Tait. "Evaluation and performance prediction of a wind turbine blade." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1791.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009.The aerodynamic performance of an existing wind turbine blade optimised for low wind speed conditions is investigated. The aerodynamic characteristics of four span locations are determined from surface pressure measurements and wake surveys with a traversed five-hole probe performed in a low speed wind tunnel for chord Reynolds numbers ranging from 360,000 - 640,000. Two-dimensional modelling of the wind tunnel tests is performed with the commercial computational fluid dynamics code FLUENT. The predictive accuracies of five eddy-viscosity turbulence models are compared. The computational results are compared to each other and experimental data. It is found that agreement between computational and experimental results varies with turbulence model. For lower Reynolds numbers, the Transitional-SST turbulence model accurately predicted the presence of laminar separation bubbles and was found to be superior to the fully turbulent models considered. This highlighted the importance of transitional modelling at lower Reynolds numbers. With increasing angles of attack the bubbles were found to move towards the leading edge and decrease in length. This was validated with experimental data. For the tip blade section, computations implementing the k-ε realizable turbulence model best predicted experimental data. The two-dimensional panel method code, XFOIL, was found to be optimistic with significantly higher lift-to-drag ratios than measured. Three-dimensional modelling of the rotating wind turbine rotor is performed with the commercial computational fluid dynamics code NUMECA. The Coefficient of Power (Cp) predicted varies from 0.440 to 0.565 depending on the turbulence model. Sectional airfoil characteristics are extracted from these computations and compared to two-dimensional airfoil characteristics. Separation was found to be suppressed for the rotating case. A lower limit of 0.481 for Cp is proposed based on the experimental data.
Centre for Renewable and Sustainable Energy Studies
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Boyd, Robert Raymond. "An Experimental and Computational Investigation on the Effect of Transonic Flow in Hypersonic Wind Tunnel Nozzles, Including Filtered Rayleigh Scattering Measurements /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu148793364864785.
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Tingey, Eric Blaine. "The Development of a Vertical-Axis Wind Turbine Wake Model for Use in Wind Farm Layout Optimization with Noise Level Constraints." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6553.
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This thesis focuses on providing the means to use vertical-axis wind turbines (VAWTs) in wind farms as an alternative form of harnessing wind energy in offshore and urban environments where both wake and acoustic effects of turbines are important considerations. In order for VAWTs to be used in wind farm layout analysis and optimization, a reduced-order wake model is needed to calculate velocities around a turbine quickly and accurately. However, a VAWT wake model has not been available to accomplish this task. Using vorticity data from computational fluid dynamic (CFD) simulations of VAWTs and cross-validated Gaussian distribution and polynomial surface fitting, a wake model is produced that can estimate a wake velocity deficit of an isolated VAWT at any downstream and lateral position based on nondimensional parameters describing the turbine speed and geometry. When compared to CFD, which takes over a day to run one simulation, the wake model predicts the velocity deficit at any location with a normalized root mean squared error of 0.059 in about 0.02 seconds. The model agrees with two experimental VAWT wake studies with a percent difference of the maximum wake deficit of 6.3% and 14.6%. Using the actuator cylinder model with predicted wake velocities of multiple turbines, aerodynamic loads can be calculated on the turbine blades to estimate the power production of a VAWT wind farm. As VAWTs could be used in urban environments near residential areas, the noise disturbance coming from the turbine blades is an important consideration in the layout of a wind farm. Noise restrictions may be imposed on a wind farm to limit the disturbance, often impacting the wind farm's power producing capability. Two specific horizontal-axis wind turbine farm designs are studied and optimized using the FLORIS wake model and an acoustic model based on semi-empirical turbine noise calculations to demonstrate the impact a noise level constraint has on maximizing wind farm power production. When a noise level constraint was not active, the average power production increased, up to 8.01% in one wind farm and 3.63% in the other. Including a noise restriction in the optimization had about a 5% impact on the optimal average power production over a 5 decibel range. By analyzing power and noise together, the multi-modality of the optimization problem can be used to find solutions were noise impact can be improved while still maximizing wind farm power production.
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Haglund, El Gaidi Sebastian. "Partially Parabolic Wind Turbine Flow Modelling." Thesis, KTH, Mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-226309.
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Climate change is an evermore urging existential treat to the human enterprise. Mean temperature and greenhouse gas emissions have in-creased exponentially since the industrial revolution. But solutions are also mushrooming with exponential pace. Renewable energy technologies, such as wind and solar power, are deployed like never before and their costs have decreased significantly. In order to allow for further transformation of the energy system these technologies must be refined and optimised. In wind energy one important field with high potential of refinement is aerodynamics. The aerodynamics of wind turbines constitutes one challenging research frontier in aerodynamics today. In this study, a novel approach for calculating wind turbine flow is developed. The approach is based on the partially parabolic Navier-Stokes equations, which can be solved computationally with higher efficiency as compared to the fully elliptic version. The modelling of wind turbine thrust is done using actuator-disk theory and the torque is modelled by application of the Joukowsky rotor. A validation of the developed model and force implementation is conducted using four different validation cases. In order to provide value for industrial wind energy projects, the model must be extended to account for turbulence (and terrain in case of onshore projects). Possible candidates for turbulence modelling are parabolic k-ε and explicit Reynolds stress turbulence models. The terrain could possibly be incorporated consistently with the used projection method by altering the finite difference grid layout.
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Gonzales, Howell B. "Aerodynamics of wind erosion and particle collection through vegetative controls." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/20382.
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Doctor of PhilosophyBiological & Agricultural Engineering
Mark E. Casada
Ronaldo G. Maghirang
Wind erosion is an important problem in many locations, including the Great Plains, that needs to be controlled to protect soil and land resources. This research was conducted to assess the effectiveness of vegetation (specifically, standing vegetation and tree barriers) as controls for wind erosion. Specific objectives were to: (1) measure sand transport and abrasion on artificial standing vegetation, (2) determine porosity and drag of a single row of Osage orange (Maclura pomifera) barrier, (3) assess effectiveness of Osage orange barriers in reducing dust, (4) predict airflow through standing vegetation, and (5) predict airflow and particle collection through Osage orange barriers. Wind tunnel tests were conducted to measure wind speed profiles, relative abrasion energies, and sand discharge rates for bare sand and for two vegetation heights (150 and 220 mm) at various densities of vegetation. Results showed that vegetation density was directly related to threshold velocity and inversely related to sand discharge. The coefficient of abrasion was adversely affected by saltation discharge but did not depend on wind speed. Field tests measured the aerodynamic and optical porosities of Osage orange trees using wind profiles and image analysis, respectively, and an empirical relationship between the two porosities was derived. Vertical wind profiles were also used to estimate drag coefficients. Optical porosity correlated well with the drag coefficient. Field measurements also showed a row of Osage orange barrier resulted in particulate concentration reduction of 15 to 54% for PM2.5 and 23 to 65% for PM10. A computational fluid dynamics (CFD) software (OpenFOAM) was used to predict airflow in a wind tunnel with artificial standing vegetation. Predicted wind speeds differed slightly from the measured values, possibly due to oscillatory motions of the standing vegetation not accounted for in the CFD simulation. OpenFOAM was also used to simulate airflow and particle transport through a row of Osage orange barrier. Predicted and measured wind speeds agreed well. Measured dust concentration reduction at two points (upwind and downwind) were also similar to the predicted results.
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McDonald, William J. "Design and computational analysis of aerodynamics in an annular cascade." Honors in the Major Thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1112.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering and Computer Science
Aerospace Engineering
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Joubert, Eugene Christiaan. "A computational fluid dynamics study of the near surface wind patterns over a desert dune and the effect on seed dispersion." Thesis, Stellenbosch : Stellenbosch University, 2010. http://hdl.handle.net/10019.1/4357.
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Thesis (MScEng)--Stellenbosch University, 2010.ENGLISH ABSTRACT: This project originated when a team of scientists at the Gobabeb training and research and centre observed seed accumulation sites on the slope of sand dunes in the Namib Desert. Seeds that accumulate on the slip face of a sand dune provide food for small desert creatures that in turn attract larger animals, resulting in a small ecosystem on the side of the dune. Since wind is the primary transport of seeds throughout the Namib Desert it is of interest to investigate wind patterns over the dune. In this project it is therefore desired to look at seed dynamics and deposition as a result of near surface wind patterns around a three-dimensional dune geometry using computational fluid dynamics. The project is a joint venture between the University of Stellenbosch and the University of Namibia. This document presents the South African MScEng thesis part. The literature review shows the dominant winds in the Namib Desert to be from the south to westerly direction. Previous studies on air flow over dunes focussed on sand movement and were often limited to simplified two-dimensional geometries and steady state simulations. From these studies the basic flow features associated with dunes can be identified. Lastly, factors that influence particle dynamics around dune geometries are looked at. These particle studies mostly involve the movement of sand rather than seeds but still provide valuable insight. The project methodology is explained and includes the equipment used, the considerations taken into account, the simplifications made as well as the procedure followed when conducting field work and simulations. A section of an actual Namibian linear dune is mapped in order to obtain a geometry for the simulations. Flow measurements are carried out with a wind mast to obtain velocity profile inlet conditions for the simulations. Furthermore, seed sampling is done by the collaborating Namibian team of which the data is used to obtain an effective seed particle model. Lastly, simulations are carried out using primarily OpenFOAM-1.5. The simulations look at general near surface wind patterns, time dependant flow features and particle movement and seed deposition around and on the linear dune. The results show different wind profiles for different wind direction. It is also possible to see how the profile changes as the flow accelerates up the dune slope. Two-dimensional results provide the opportunity to compare results with previous studies as well as to provide the basis for looking at aspects such as differencing schemes, turbulence models and parallel computing before three-dimensional simulations are carried out. The importance of higher order differencing schemes are confirmed in the two-dimensional results. The turbulence models, however, produce very similar results. The results from the two- and three-dimensional results show typical flow features associated with dunes. Transient flow features and separation vortex structures can be identified from time dependant simulations. Furthermore, particle simulations reveal how particles tend to be trapped in the recirculation regions. The conclusions explain how the project objectives were achieved and provide recommendations for future studies related to this project.
AFRIKAANSE OPSOMMING: Die projek het ontstaan toe naforsers areas van saad akumulasie op die hellings van duine in Namibë opgelet het. Hierdie akumulasie van plant materiaal verskaf die voedsel vir klein diere op die duin wat ‘n klein ekosisteem tot gevolg het. Aaangesien die primêre vervoermiddel vir sade in die woestyn wind is beoog die projek om deur die wind patrone oor die duin beter te verstaan die saad verspreiding te beskryf. Die doel is dus om saad verspreiding en akumulasie te beskryf deur die wind patrone te bekyk wat die verspreiding tot gevolg het deur gebruik te maak van numeriese vloei dinamika. Die projek is ‘n saamgestelde projek tussen die Universiteit van Stellenbosch en die Universiteit van Namibië. Hierdie dokument behels die Suid Afrikaanse MScIng gedeelte van die projek. Deur die hersiening van literatuur word daar gesien dat die domineerende wind rigtings as suid tot wes beskryf kan word. Vorige studies wat verband hou met wind vloei oor duine wys dat die meeste op twee-dimensionele eenvoudige geometrië gefokus het met tyd onafhankike simulasies. Dit is egter moontlik om die resultate te gebruik om karakteristieke vloei patrone te identifiseer wat met duin wind patrone geassosieer kan word. Laastens word daar gekyk na die faktore wat partikel beweeging beïnvloed, maar hierdie studies sluit hoofsaaklik sand partikels in eerder as sade. Die motodologie beskryf die toerusting, oorwegings en prosedures wat gevolg is tydens veld werk asook simulasies. Tydens die veld werk is ‘n gedeelte van ‘n Namib lineêre duin gemeet en so gebruik om ‘n geometrie te maak wat vir simulasie doeleindes gebruik kan word. Daar is ook wind meetings gedoen met ‘n wind mas om wind profiele vir inlaat kondisies vir die simulasies te kry. Verder het saad bestudeering die nodige data verskaf om ‘n voledige saad partikel model op te stel wat in die simulasies gebruik kan word. Laastens kyk die simulasies veral na algemene vloei patrone, tyd afhanklike vloei effekte en ook partikel beweging in die vloei veld. Die resultate wys hoe wind profiele verskil wat van verskillende rigtings af waai. Dit is ook moontlik on te wys hoe die wind profiele verander soos die wind versnel teen die duin op. Tweedimensionele simulasies verskaf die geleentheid om te kyk na die effek van verkillende numeriese modelle, turbulensie modelle en ook multi-prosesseerder verwerking. Tydens die twee-dimensionele simulasies is die belangrikheid van hoër orde numeriese metodes besef. Die verkillende turbulensie modelle het egter klein verkille gewys. Alby die twee- en driedimensionele resultate wys karakteristieke vloei patrone wat met duine geasosieer kan word. Verder het tyd afhanklike simulasies gewys hoe wind patrone verander met tyd. Die partikel simulasies wys ook die beweging van partikels deur die wind en hoe dit neig om te akumuleer in die hersirkulasie gebied agter die duin. Die gevolgtrekkings wys dat al die doelstellings bereik is en maak voorstelle vir toekomstige studies wat met hierdie studie verband hou.
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Rogers, Daniel R. "Design of a Three-Passage Low Reynolds Number Turbine Cascade with Periodic Flow Conditions." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2684.pdf.
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Yifan, Wang, and Huang Yizhang. "Urban Wind and Thermal Environment Simulation - A Case Study of Gävle, Sweden." Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-16605.
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As urbanization and industrialization progressed during the last decades, Urban Heat Island (UHI) has become a major environmental issue to many cities around the world. The effect of UHI differs from area to area due to varying urban scale, population density, construction of urban surface layer, the level of industrialization and type of climate. Researchers have made great efforts in investigating various approaches to Urban Heat Island studies. Monitoring technologies have been widely used in this field, especially Geographic Information System (GIS) and remote sensing technology. Computational Fluid Dynamics (CFD) simulations are also actively applied in wind engineering, which can provide details of air flow over urban areas. The combined application of these technologies can provide the monitoring and simulation of urban wind corridor and thermal environment that can produce relevant information at a lesser time.A research using GIS, remote sensing technology and CFD simulation was done in this project to obtain a holistic view of the urban thermal environment and wind flow for Gävle City. With GIS and remote sensing the thermal image of the city was presented. The temperature data, which were collected from MODIS satellite were transferred and processed by ArcGIS and Global Mapper. The wind flow above the city was simulated through constructing geometric and mathematical model with OpenFOAM. The outcomes of the modeling and simulation identified that the temperature in the city center could possibly reach 35℃ during summers, which can cause the Urban Heat Island to form. Ventilation was also poorer in the city centre, and neither the river nor the green area in the southwest could help ventilate the city. The study result also suggested that certain sites in the city had relatively high wind flow for urban wind turbines to work.This study had used method of Urban Heat Island study with remote sensing and CFD technologies. The model produced from simulation could also be used to further study Gävle city's thermal and wind environment to produce more accurate results.
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Piccoli, Guilherme Luiz. "Análise numérica na Engenharia do Vento Computacional empregando computação de alto desempenho e simulação de grandes escalas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2009. http://hdl.handle.net/10183/17561.
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O presente trabalho tem como objetivo o desenvolvimento de um sistema voltado à solução de problemas relacionados à Engenharia do Vento Computacional. Para o tratamento das estruturas turbulentas, a Simulação das Grandes Escalas é empregada. Esta metodologia resolve diretamente as estruturas que governam a dinâmica local do escoamento (grandes escalas) e utiliza modelos para resolver as escalas com características mais universais (pequenas escalas). Neste estudo, os efeitos sub-malha são obtidos a partir do modelo clássico de Smagorinsky. Na análise numérica, o método dos elementos finitos é avaliado a partir da utilização de elementos hexaédricos e uma formulação baseada nas equações governantes de escoamentos quase-incompressíveis. Para reduzir o requerimento de memória computacional, esquemas explícitos para solução de sistemas de equações são empregados. O primeiro aspecto a ser abordado para o desenvolvimento do sistema proposto é a redução do tempo de processamento. Partindo do algoritmo desenvolvido por [Petry, 2002], desenvolvese um estudo a cerca de técnicas computacionais de alto desempenho visando acelerar o processamento dos problemas. Assim, apresenta-se um comparativo entre alocações estática e dinâmica de vetores e matrizes, juntamente a implementação do paralelismo de memória compartilhada utilizando diretivas OpenMP. A verificação do aumento da velocidade de processamento é desenvolvida simulando o escoamento em um domínio contendo um corpo imerso aerodinamicamente rombudo. As técnicas utilizadas permitiram a obtenção de um aumento de aproximadamente cinco vezes em relação ao código originalmente avaliado. Uma importante dificuldade na avaliação de escoamentos externos está na solução numérica de problemas advectivo-dominantes. O esquema de Taylor-Galerkin explícito-iterativo, originalmente presente no código e validado para escoamentos internos, mostrou-se inadequado para avaliação do escoamento externo proposto, apresentando perturbações no campo de pressões e não convergindo para a solução correta do problema. Estas instabilidades persistiram em uma versão alternativa desenvolvida, a qual utilizava funções de interpolação de igual ordem para solução da pressão e velocidade. Para uma análise de escoamentos não confinados, é implementado o esquema temporal de dois passos utilizando funções de interpolação para velocidade e pressão de mesma ordem. Esta configuração apresentou resultados físicos de boa qualidade e importante redução no tempo de processamento. Após a identificação da alternativa que permitiu a avaliação dos resultados sem a presença de perturbações, apresenta-se a análise do escoamento sobre um prisma quadrado bidimensional, privilegiando o monitoramento da velocidade, pressão e energia cinética total da turbulência na linha central do domínio e nas proximidades do obstáculo. Esta avaliação é efetuada em malhas com configurações uniformes e irregulares para um número de Reynolds igual a 22000.Development of a system to solve problems related to Computational Wind Engineering is the main aim of this work. In order to treat turbulent structures, Large Eddy Simulation is employed. This methodology compute directly scales governing local flow dynamics (large eddies) and it use models to solve those with universal character (small eddies). In this study, the sub-grid effects are considered using the standard Smagorinsky model. In the numerical analysis, hexahedral finite elements are used and a formulation based on the governing equations of quasi-compressible flows. To reduce the computational memory request, explicit schemes to solve the equations system are used. In order to reduce CPU time, an algorithm developed by [Petry, 2002] is evaluated and high-performance techniques aiming to accelerate the problem solution are studied. Thus, it is showed a comparison between dynamic and static allocations of vectors and matrices associated to the implementation of shared-memory parallelization using OpenMP directives. The speed up verification is developed simulating the flow around an immersed bluff body. As a consequence of the techniques employed here, an acceleration of approximately five times with respect of the original computational code is obtained. An important difficulty in the external flow evaluation is the numerical solution of convection dominated flows. The Taylor-Galerkin explicit-iterative scheme, (originally used by the program), which was validated for confined flows, did not present good results for external flows simulations and pressure field perturbations were observed. These instabilities were persevered even in an alternative version, where interpolations functions with the same order were used to compute velocity and pressure (in the original version, constant pressure field at element level were employed). To analyze unbounded flows accurately, a two-step explicit scheme using velocity and pressure interpolation functions with the same order was implemented. This configuration presented physical results with good quality and achieve an important reduction in the processing time. After identification of the best alternative without perturbations of the pressure field, the numerical simulation of the flow around a two-dimensional square cylinder was investigated favoring velocity, pressure and total kinetic energy evaluations along the mid line of the domain and in the obstacle vicinity. These evaluations were effectuated with uniform and stretched meshes for a Reynolds number equal to 22000.
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Bertani, Gregorio. "Wind loading on elongated structures characterized by bluff sections: comparison between 2D and 3D simulations." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22291/.
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The flow around bluff-bodies is characterized by specific flow features (e.g. flow separations, flow re-attachments and vortex shedding) which clearly differentiate it from flows over aerodynamic bodies, such as aerofoils or turbine blades. Due to the lack of analytical solutions, bluff-body aerodynamics relies on experimental measurements and, increasingly, on Computational Fluid Dynamics (CFD), which involves the solution of fluid flow equations by means of numerical methods. However, since the computational cost for Direct Numerical Simulations (DNS) is often prohibitive, the use of turbulence models is essential for the application of CFD to engineering problems. Such models can be developed in various ways. In particular, Reynolds Averaged Navier-Stokes (RANS) models are derived by Favre-averaging Navier-Stokes equations, whereas Large Eddy Simulations (LES) rely on their spatial filtering. The major drawback in the use of such models is the loss of flow details, which may however have a strong influence on the flow field development. The resulting flow can, indeed, be remarkably different from DNS and experimental measurements. This is particularly true for RANS models, especially when used in a two-dimensional (2D) framework. In fact, in cases for which the time-averaged flow is approximately two-dimensional, the use of 2D RANS models appears to be an extremely convenient and widely adopted solution. However, such simplification can lead to strong inaccuracies.
The aim of this thesis is to explore and assess the accuracy of 2D RANS models for the prediction of the aerodynamic coefficients for the wind loading of elongated structures characterized by bluff sections. Results show an overall tendency to overestimate drag due to the impossibility to generate three-dimensional structures in the wake zone. Additional LES simulations confirm the obtained results.
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Perkins, Hugh Douglas. "Development and Demonstration of a Computational Tool for the Analysis of Particle Vitiation Effects in Hypersonic Propulsion Test Facilities." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1227553721.
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Owen, Michael Trevor Foxwell. "A numerical investigation of air-cooled steam condenser performance under windy conditions." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4101.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: This study is aimed at the development of an efficient and reliable method of evaluating the performance of an air-cooled steam condenser (ACSC) under windy conditions, using computational fluid dynamics (CFD). A two-step modelling approach is employed as a result of computational limitations. The numerical ACSC model developed in this study makes use of the pressure jump fan model, amongst other approximations, in an attempt to minimize the computational expense of the performance evaluation. The accuracy of the numerical model is verified through a comparison of the numerical results to test data collected during full scale tests carried out on an operational ACSC. Good correlation is achieved between the numerical results and test data. Further verification is carried out through a comparison to previous numerical work. Satisfactory convergence is achieved for the most part and the few discrepancies in the results are explained. The effect of wind on ACSC performance at El Dorado Power Plant (Nevada, USA) is investigated and it is found that reduced fan performance due to distorted flow at the inlet of the upstream fans is the primary contributor to the reduction in performance associated with increased wind speed in this case. An attempt is subsequently made to identify effective wind effect mitigation measures. To this end the effects of wind screens, solid walkways and increasing the fan power are investigated. It is found that the installation of an appropriate wind screen configuration provides a useful means of reducing the negative effects of wind on ACSC performance and an improved wind screen configuration is suggested for El Dorado. Solid walkways are also shown to be beneficial to ACSC performance under windy conditions. It is further found that ACSC performance increases with walkway width but that the installation of excessively wide walkways is not justifiable. Finally, increasing the fan power during periods of unfavourable ambient conditions is shown to have limited benefit in this case. The model developed in this study has the potential to allow for the evaluation of large ACSC installations and provides a reliable platform from which further investigations into improving ACSC performance under windy conditions can be carried out.
AFRIKAANSE OPSOMMING: Hierdie studie is daarop gemik om die ontwikkeling van 'n geskikte en betroubare metode van evaluering van die verrigting van ’n lugverkoelde stoom-kondensator (air-cooled steam condenser, ACSC) onder winderige toestande, met behulp van numeriese vloei-dinamika. ’n Twee-stap modelleringsbenadering is aangewend as gevolg van rekenaar beperkings. Die numeriese ACSC-model wat in hierdie studie ontwikkel is, maak gebruik van die druksprong waaier model, asook ander benaderings, in ’n poging om die berekeningskoste van die verrigting-evaluering te verminder. Die akkuraatheid van die numeriese model is bevestig deur middel van ’n vergelyking van die numeriese resultate met toetsdata ingesamel tydens die volskaal toetse uitgevoer op ’n operasionele ACSC. Goeie korrelasie is bereik tussen die numeriese resultate en toetsdata. Verdere bevestiging is uitgevoer deur middel van ’n vergelyking met vorige numeriese werk. Bevredigende konvergensie is in die algemeen bereik en die paar verskille in die resultate word verduidelik. Die effek van wind op ACSC verrigting by El Dorado Power Plant (Nevada, VSA) is ondersoek, en daar is bevind dat verlaagde waaierverrigting, as gevolg van vervormde vloei by die inlaat van die stroomop waaiers, die primêre bydraer is tot die afname in ACSC werkverrigting geassosieer met verhoogde windsnelheid in hierdie geval. ’n Poging word dan aangewend om effektiewe wind-effek velagingsmaatreëls te identifiseer. Windskerms, soliede wandelvlakke en die verhoging van die waaierkrag word gevolglik ondersoek. Daar is bevind dat die installasie van ’n toepaslike windskerm-opset ’n nuttige middel tot ’n vermindering van die negatiewe effekte van wind op ACSC verrigting bied, en ’n verbeterde windskerm opset is voorgestel vir El Dorado. Soliede wandelvlakke word ook aanbeveel as voordelig vir ACSC verrigting onder winderige toestande. Dit is verder bevind dat die ACSC prestasie verhoog met wandelvlak breedte, maar dat die installasie van ’n te ruim wandelvlak nie regverdigbaar is nie. Ten slotte, word bewys dat die verhoging van die waaierkrag tydens periodes van ongunstige omgewingsomstandighede ’n beperkte voordeel in hierdie geval het. Die model wat ontwikkel is in hierdie studie het die potensiaal om voorsiening te maak vir die evaluering van groot ACSC- installasies en bied ’n betroubare platform vanwaar verdere ondersoeke tot die verbetering van ACSC verrigting onder winderige toestande uitgevoer kan word.
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Kaya, Halil. "Aerodynamic Analysis Of Long-span Bridge Cross-sections Using Random Vortex Method." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615072/index.pdf.
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In this thesis, two dimensional, incompressible, viscous flow past bluff bodies and a bridge section, in which strong vortex shedding and unsteady attribute of flow are generally found, is simulated by means of random vortex method.
The algorithm and method are described in detail. The validation and applicability of the developed numerical implementation to general wind engineering problems is illustrated by solving a number of classical problems, such as flow past circular and square cylinders. An application of the numerical implementation in the area of computational wind engineering is performed by analyzing a bridge deck section. Moreover, all results are compared with experimental and numerical studies in literature.
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Moravej, Mohammadtaghi. "Investigating Scale Effects on Analytical Methods of Predicting Peak Wind Loads on Buildings." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3799.
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Large-scale testing of low-rise buildings or components of tall buildings is essential as it provides more representative information about the realistic wind effects than the typical small scale studies, but as the model size increases, relatively less large-scale turbulence in the upcoming flow can be generated. This results in a turbulence power spectrum lacking low-frequency turbulence content. This deficiency is known to have significant effects on the estimated peak wind loads.
To overcome these limitations, the method of Partial Turbulence Simulation (PTS) has been developed recently in the FIU Wall of Wind lab to analytically compensate for the effects of the missing low-frequency content of the spectrum. This method requires post-test analysis procedures and is based on the quasi-steady assumptions. The current study was an effort to enhance that technique by investigating the effect of scaling and the range of applicability of the method by considering the limitations risen from the underlying theory, and to simplify the 2DPTS (includes both in-plane components of the turbulence) by proposing a weighted average method. Investigating the effect of Reynolds number on peak aerodynamic pressures was another objective of the study.
The results from five tested building models show as the model size was increased, PTS results showed a better agreement with the available field data from TTU building. Although for the smaller models (i.e., 1:100,1:50) almost a full range of turbulence spectrum was present, the highest peaks observed at full-scale were not reproduced, which apparently was because of the Reynolds number effect. The most accurate results were obtained when the PTS was used in the case with highest Reynolds number, which was the1:6 scale model with a less than 5% blockage and a xLum/bm ratio of 0.78. Besides that, the results showed that the weighted average PTS method can be used in lieu of the 2DPTS approach. So to achieve the most accurate results, a large-scale test followed by a PTS peak estimation method deemed to be the desirable approach which also allows the xLum/bm values much smaller than the ASCE recommended numbers.
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Guimarães, da Silva Jôse Lorena. "Computational sound propagation models: An analysis of the models Nord2000, CONCAWE, and ISO 9613-2 for sound propagation from a wind farm." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331752.
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The recent goals from some countries to become renewable energy based and reduce carbon dioxide emissions have caused the wind industry to grow. Together, the size of the wind farms and the noise emission have grown, while the noise emission regulations have to be fulfilled. Numerical simulations based on engineering approaches are in many cases a fast alternative that may supplement actual sound measurements at the site on question. However, the sound propagation models have many assumptions and estimations, as different variants can affect the resulting sound propagation. The accuracy of the sound propagation models Nord2000, CONCAWE, and ISO 9613-2 are investigated in this research by comparing the predicted to the measured sound pressure levels from a wind farm in northern Sweden. Different parameters were investigated in each model, as wind speed and direction, roughness length, ground class, temperature gradient, and receiver height. The computational calculations were run on SoundPLAN software for a single point, the nearby dwelling. For the different parameters investigated, the settings were defined and inputted in the software, and the calculations were run. The equivalent sound pressure level results from the computational models were compared to the equivalent sound pressure level of the sound measurements filtered from background noise. The results indicate that the model ISO 9613-2 did not perform well for the specific site conditions at the wind farm. On the other hand, the CONCAWE and Nord2000 showed high accuracy, for downwind conditions at 8 m/s. For upwind conditions at 8 m/s, Nord2000 is more accurate, as the refraction of the sound rays are better calculated on this model. For the variants investigated on the Nord2000 model, the results that better approximate to the sound levels of the sound measurements are the roughness length 0.3, ground class D, and temperature gradient 0.05 K/m. Thus, these settings would be recommended for calculations with Nord2000 for noise assessment in a permit process.
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Lee, Jin Woo. "Multi-level Decoupled Optimization of Wind Turbine Structures Using Coefficients of Approximating Functions as Design Variables." University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1501003238831086.
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H, N. Akshay Jamadagni. "Simulations of complete vehicles in cold climate at partial and full load driving conditions." Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-170181.
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In this study, CFD simulations of a complete truck are carried out to investigate the effect of altered simulation settings at cold climatic conditions. The aim of this study is to obtain knowledge through CFD simulations performed on a selected driving condition namely at a vehicle speed of 93 kph, an ambient temperature of -20 °C and for an engine operating at 25 % load. Data from measurement carried out in a climatic wind tunnel is available and utilized as boundary conditions for the simulations.The simulations are performed under steady state conditions utilizing the commercial software STAR-CCM+. The first simulation case (reference simulation case) is constructed through java macro-scripts as per the standard VTM settings at Scania. The results from the simulations are compared with the measurement data utilizing temperature validation probes. These probes are located around the engine and measure the air temperature in the underhood engine compartment. The results from the first simulation case show that the temperature of each probe located in front of the engine and above the engine agrees well with the measured probe temperatures. But the temperature of the remaining probes show larger differences with the measured probe temperatures. To investigate the larger differences in probe temperatures, additional simulations are carried out by changing specific simulation settings. For instance, this is achieved by including thermal radiation in the physics continua. Finally, a simulation of engine load of 100 % is carried out and the results from the simulation are compared with the measurement from the same engine load as well as the results from the measurement and simulation of 25 % engine load. The results from all the simulations indicate that additional boundaryconditions and/or different methodologies need to be explored to better replicate the cold climatic conditions in the simulations.
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Agsarlioglu, Ekin. "Numerical Investigations Of Lateral Jets For Missile Aerodynamics." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613585/index.pdf.
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In this thesis, effects of sonic lateral jets on aerodynamics of missiles and missilelike
geometries are investigated numerically by commercial Computational Fluid
Dynamics (CFD) software FLUENT. The study consists of two parts. In the first
part, two generic missile-like geometries with lateral jets, of which experimental data
are available in literature, are analyzed by the software for validation studies. As the
result of this study, experimental data and CFD results are in good agreement with
each other in spite of some discrepancies. Also a turbulence model study is
conducted by one of test models. It is also found out that k-&epsilonturbulence model is the most suitable model for this kind of problems in terms of accuracy and ease of convergence. In the second part of the thesis, parametric studies are conducted on a generic supersonic missile, NASA TCM, to see the effect of jet parameters on missile and component force and moments in pitch plane. Variable parameters are jet location, jet mass flow rate and angle of attack. As a result, it was found out that downstream influence zone of jet exit is more than the upstream influence zone. Normal force occurring by the interaction of the free stream and jet plume are amplified whenever the jet exit is located between lifting surfaces. Greater pitching moments are obtained when the jet exit moment arm with respect to moment reference center or jet mass flow rate is increased.
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Cantoni, Lorenzo. "Load Control Aerodynamics in Offshore Wind Turbines." Thesis, KTH, Kraft- och värmeteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291417.
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Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.
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Asghari, Mooneghi Maryam. "Experimental and Analytical Methodologies for Predicting Peak Loads on Building Envelopes and Roofing Systems." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1846.
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The performance of building envelopes and roofing systems significantly depends on accurate knowledge of wind loads and the response of envelope components under realistic wind conditions. Wind tunnel testing is a well-established practice to determine wind loads on structures. For small structures much larger model scales are needed than for large structures, to maintain modeling accuracy and minimize Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel meaning that it is not possible to simulate the low frequency end of the turbulence spectrum. Such flows are called flows with Partial Turbulence Simulation.
In this dissertation, the test procedure and scaling requirements for tests in partial turbulence simulation are discussed. A theoretical method is proposed for including the effects of low-frequency turbulences in the post-test analysis. In this theory the turbulence spectrum is divided into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in a quasi-steady manner. The joint probability of load resulting from the two processes is derived from which full-scale equivalent peak pressure coefficients can be obtained. The efficacy of the method is proved by comparing predicted data derived from tests on large-scale models of the Silsoe Cube and Texas-Tech University buildings in Wall of Wind facility at Florida International University with the available full-scale data.
For multi-layer building envelopes such as rain-screen walls, roof pavers, and vented energy efficient walls not only peak wind loads but also their spatial gradients are important. Wind permeable roof claddings like roof pavers are not well dealt with in many existing building codes and standards. Large-scale experiments were carried out to investigate the wind loading on concrete pavers including wind blow-off tests and pressure measurements. Simplified guidelines were developed for design of loose-laid roof pavers against wind uplift. The guidelines are formatted so that use can be made of the existing information in codes and standards such as ASCE 7-10 on pressure coefficients on components and cladding.
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Mousaviraad, Sayyed Maysam. "CFD prediction of ship response to extreme winds and/or waves." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/559.
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The effects of winds and/or waves on ship motions, forces, moments, maneuverability and controllability are investigated with URANS computations.
The air/water flow computations employ a semi-coupled approach in which water is not affected by air, but air is computed assuming the free surface as a moving immersed boundary. The exact potential solution of waves/wind problem is modified introducing a logarithmic blending in air, and imposed as boundary and initial conditions. The turbulent air flows over 2D water waves are studied to investigate the effects of waves on incoming wind flow. Ship airwake computations are performed with different wind speeds and directions for static drift and dynamic PMM in calm water, pitch and heave in regular waves, and 6DOF motions in irregular waves simulating hurricane CAMILLE. Ship airwake analyses show that the vortical structures evolve due to ship motions and affect the ship dynamics significantly. Strong hurricane head and following winds affect up to 28% the resistance and 7% the motions. Beam winds have most significant effects causing considerable roll motion and drift forces, affecting the controllability of the ship.
A harmonic wave group single run seakeeping procedure is developed, validated and compared with regular wave and transient wave group procedures. The regular wave procedure requires multiple runs, whereas single run procedures obtain the RAOs for a range of frequencies at a fixed speed, assuming linear ship response. The transient wave group procedure provides continuous RAOs, while the harmonic wave group procedure obtains discrete transfer functions, but without focusing. Verification and validation studies are performed for transient wave group procedure. Validation is achieved at the average interval of 9.54 (%D). Comparisons of the procedures show that harmonic wave group is the most efficient, saving 75.8% on the computational cost compared to regular wave procedure. Error values from all procedures are similar at 4 (%D). Harmonic wave group procedure is validated for a wide range of Froude numbers, with satisfactory results.
Deterministic wave groups are used for three sisters rogue waves modeling. A 6DOF ship simulation is demonstrated which shows total loss of controllability with extreme ship motions, accelerations and structural loads.
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Madalozzo, Deborah Marcant Silva. "Simulação numérica da dispersão de poluentes em zonas urbanas considerando efeitos térmicos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/55435.
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O objetivo deste trabalho é estudar, dentro da Engenharia do Vento Computacional (EVC), a dispersão de poluentes em zonas urbanas, empregando-se um modelo numérico baseado em técnicas da Dinâmica dos Fluidos Computacional para escoamentos incompressíveis, não isotérmicos e com transporte de massa. Um esquema explícito de dois passos é usado para a discretização temporal das equações governantes, considerando expansões em séries de Taylor de segunda ordem para as derivadas no tempo. O processo de discretização espacial é realizado através da aplicação do Método dos Elementos Finitos (MEF), onde hexaedros de oito nós com um ponto de integração são utilizados. A turbulência é tratada numericamente através da Simulação de Grandes Escalas (LES) e os modelos clássico e dinâmico de Smagorinsky são empregados na modelagem das escalas inferiores à resolução da malha. Efeitos de temperatura sobre o escoamento são considerados na forma de forças de flutuação presentes na equação de balanço de momentum, as quais são calculadas a partir da aproximação de Boussinesq. Técnicas de paralelização em memória compartilhada (OpenMP) são também usadas a fim de melhorar a eficiência computacional do presente modelo para problemas com grande número de elementos. Exemplos clássicos de Dinâmica de Fluidos e Fenômenos de Transporte são inicialmente analisados para teste das ferramentas numéricas implementadas. Problemas de dispersão de poluentes com e sem a inclusão dos efeitos de temperatura são abordados para configurações geométricas bi e tridimensionais de street canyons, representando a unidade geométrica básica encontrada em centros urbanos de grandes cidades.The main goal of the present work is to study the pollutant dispersion in urban areas using a numerical model based on techniques developed by Computational Fluid Dynamics, where applications of Computational Wind Engineering (CWE) are analyzed considering incompressible flows with heat and mass transport. A two-step explicit scheme is adopted for the time discretization of the governing equations considering second order Taylor series expansions of the time derivative terms. Spatial discretization is performed by applying the Finite Element Method (FEM), where eight-node hexahedral elements with one-point quadrature are utilized. Turbulence is numerically analyzed by using Large Eddy Simulation (LES) with the classical and dynamic Smagorinsky’s models for subgrid scale modeling. Thermal effects on the flow field are taken into account through buoyancy forces acting on the momentum balance equation, which are calculated considering the Boussinesq approximation. Shared memory parallelization techniques (OpenMP) are also employed in order to improve computational efficiency for problems with large number of elements. Classic examples of Fluid Dynamics and Transport Phenomena are first analyzed to verify the numerical tools implemented. Problems involving pollutant dispersion with and without the inclusion of thermal effects are investigated for two and three-dimensional geometric configurations of street canyons, which represent the basic geometric unit observed in urban centers of large cities.
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Braun, Alexandre Luis. "Simulação numérica na engenharia do vento incluindo efeitos de interação fluido-estrutura." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/10592.
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O objetivo deste trabalho é estudar e desenvolver procedimentos numéricos adequados para a análise de problemas da Engenharia do Vento Computacional (EVC). O escoamento é analisado a partir das equações de Navier-Stokes para um fluido Newtoniano e de uma equação de conservação de massa considerando a hipótese de pseudo-compressibilidade, ambas em um processo isotérmico. Na presença de escoamentos turbulentos emprega-se a Simulação de Grandes Escalas (“LES”) com os modelos clássico e dinâmico de Smagorinsky para as escalas inferiores à resolução da malha. Dois modelos numéricos de Taylor-Galerkin para a análise do escoamento são estudados: o esquema explícito de dois passos e o esquema explícito-iterativo. O Método dos Elementos Finitos (MEF) é empregado para a discretização do domínio espacial utilizando o elemento hexaédrico trilinear isoparamétrico com integração reduzida das matrizes em nível de elemento. Em problemas envolvendo efeitos de interação fluido-estrutura emprega-se um esquema de acoplamento particionado com características superiores de conservação, permitindo, inclusive, o uso de subciclos entre as análises do fluido e da estrutura e de malhas não compatíveis na interface. A estrutura é considerada como um corpo deformável constituído de um material elástico linear com a presença de nãolinearidade geométrica. O MEF é também usado para a discretização da estrutura, empregando-se para tanto o elemento hexaédrico trilinear isoparamétrico com integração reduzida e controle de modos espúrios. A equação de equilíbrio dinâmico é integrada no tempo utilizando o método implícito de Newmark no contexto do método de estabilização α- Generalizado. Na presença de estruturas deformáveis, o escoamento é descrito através de uma formulação arbitrária Lagrangeana-Euleriana (ALE). Ao final, comparações com exemplos numéricos e experimentais são apresentadas para demonstrar a viabilidade dos algoritmos desenvolvidos, seguindo-se com as conclusões do trabalho e as sugestões para trabalhos futuros.Analysis and development of numerical tools to simulate Computational Wind Engineering (CWE) problems is the main goal of the present work. The isothermal flow is analyzed using the Navier-Stokes equations for viscous fluids and a mass conservation equation obtained according to the pseudo-compressibility assumption. Turbulent flows are simulated employing Large Eddy Simulation (LES) with the classical and dynamic Smagorinsky’s models for subgrid scales. Two Taylor-Galerkin models for the flow analysis are investigated: the explicit two-step scheme and the explicit-iterative scheme. The Finite Element Method (MEF) is employed for spatial discretizations using the eight-node hexahedrical isoparametric element with one-point quadrature. Fluid-structure interaction problems are analyzed with a coupling model based on a conservative partitioned scheme. The Finite Element Method (MEF) is employed for spatial discretizations using the eight-node hexahedrical isoparametric element with one-point quadrature. Fluid-structure interaction problems are analyzed with a coupling model based on a conservative partitioned scheme. Subcycling and nonmatching meshes for independent discretizations of the fluid and structure domains are also available. The structure is considered as a deformable body constituted by a linear elastic material with geometrically nonlinear effects. The FEM is used for the spatial discretization of the structure as well. Eight-node hexahedrical isoparametric elements with one-point quadrature and hourglass control are adopted in this process. The implicit Newmark algorithm within the framework of the α-Generalized method is employed for the numerical integration of the dynamic equilibrium equation. An arbitrary Lagrangean-Eulerian (ALE) description is adopted for the kinematic description of the flow when deformable structures are analyzed. Numerical and experimental examples are simulated in order to demonstrate the accuracy of the developed algorithms. Concluding remarks and suggestions for future works are pointed out in the last chapter of the present work.
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Pieterse, Jacobus Erasmus. "CFD investigation of the atmospheric boundary layer under different thermal stability conditions." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80024.
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Thesis (MScEng)--Stellenbosch University, 2013.ENGLISH ABSTRACT: An accurate description of the atmospheric boundary layer (ABL) is a prerequisite for computational fluid dynamic (CFD) wind studies. This includes taking into account the thermal stability of the atmosphere, which can be stable, neutral or unstable, depending on the nature of the surface fluxes of momentum and heat. The diurnal variation between stable and unstable conditions in the Namib Desert interdune was measured and quantified using the wind velocity and temperature profiles that describe the thermally stratified atmosphere, as derived by Monin- Obukhov similarity theory. The implementation of this thermally stratified atmosphere into CFD has been examined in this study by using Reynoldsaveraged Navier-Stokes (RANS) turbulence models. The maintenance of the temperature, velocity and turbulence profiles along an extensive computational domain length was required, while simultaneously allowing for full variation in pressure and density through the ideal gas law. This included the implementation of zero heat transfer from the surface, through the boundary layer, under neutral conditions so that the adiabatic lapse rate could be sustained. Buoyancy effects were included by adding weight to the fluid, leading to the emergence of the hydrostatic pressure field and the resultant density changes expected in the real atmosphere. The CFD model was validated against measured data, from literature, for the flow over a cosine hill in a wind tunnel. The standard k-ε and SST k-ω turbulence models, modified for gravity effects, represented the data most accurately. The flow over an idealised transverse dune immersed in the thermally stratified ABL was also investigated. It was found that the flow recovery was enhanced and re-attachment occurred earlier in unstable conditions, while flow recovery and re-attachment took longer in stable conditions. It was also found that flow acceleration over the crest of the dune was greater under unstable conditions. The effect of the dune on the flow higher up in the atmosphere was also felt at much higher distances for unstable conditions, through enhanced vertical velocities. Under stable conditions, vertical velocities were reduced, and the influence on the flow higher up in the atmosphere was much less than for unstable or neutral conditions. This showed that the assumption of neutral conditions could lead to an incomplete picture of the flow conditions that influence any particular case of interest.
AFRIKAANSE OPSOMMING: 'n Akkurate beskrywing van die atmosferiese grenslaag (ABL) is 'n voorvereiste vir wind studies met berekenings-vloeimeganika (CFD). Dit sluit in die inagneming van die termiese stabiliteit van die atmosfeer, wat stabiel, neutraal of onstabiel kan wees, afhangende van die aard van die oppervlak vloed van momentum en warmte. Die daaglikse variasie tussen stabiele en onstabiele toestande in die Namib Woestyn interduin is gemeet en gekwantifiseer deur gebruik te maak van die wind snelheid en temperatuur profiele wat die termies gestratifiseerde atmosfeer, soos afgelei deur Monin-Obukhov teorie, beskryf. Die implementering van hierdie termies gestratifiseerde atmosfeer in CFD is in hierdie studie aangespreek deur gebruik te maak van RANS turbulensie modelle. Die handhawing van die temperatuur, snelheid en turbulensie profiele in die lengte van 'n uitgebreide berekenings domein is nodig, en terselfdertyd moet toegelaat word vir volledige variasie in die druk en digtheid, deur die ideale gaswet. Dit sluit in die implementering van zero hitte-oordrag vanaf die grond onder neutrale toestande sodat die adiabatiese vervaltempo volgehou kan word. Drykrag effekte is ingesluit deur die toevoeging van gewig na die vloeistof, wat lei tot die ontwikkeling van die hidrostatiese druk veld, en die gevolglike digtheid veranderinge, wat in die werklike atmosfeer verwag word. Die CFD-model is gevalideer teen gemete data, vanaf die literatuur, vir die vloei oor 'n kosinus heuwel in 'n windtonnel. Die standaard k-ε en SST k-ω turbulensie modelle, met veranderinge vir swaartekrag effekte, het die data mees akkuraat voorgestel. Die vloei oor 'n geïdealiseerde transversale duin gedompel in die termies gestratifiseerde ABL is ook ondersoek. Daar is bevind dat die vloei herstel is versterk en terug-aanhegging het vroeër plaasgevind in onstabiele toestande, terwyl vloei herstel en terug-aanhegging langer gevat het in stabiele toestande. Daar is ook bevind dat vloei versnelling oor die kruin van die duin groter was onder onstabiele toestande. Die effek van die duin op die vloei hoër op in die atmosfeer is ook op hoër afstande onder onstabiele toestande gevoel, deur middel van verhoogte vertikale snelhede. Onder stabiele toestande, is vertikale snelhede verminder, en die invloed op die vloei hoër op in die atmosfeer was veel minder as vir onstabiel of neutrale toestande. Dit het getoon dat die aanname van neutrale toestande kan lei tot 'n onvolledige beeld van die vloei toestande wat 'n invloed op 'n bepaalde geval kan hê.
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Ivanell, Stefan S. A. "Numerical computations of wind turbine wakes." Licentiate thesis, Stockholm : Royal Institute of Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-316.
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Aguirre, Miguel Angel. "Simulação numérica de tornados usando o método dos elementos finitos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/174397.
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O presente trabalho tem como objetivo estudar escoamentos de tornados e sua ação sobre corpos imersos empregando ferramentas numéricas da Engenharia do Vento Computacional (EVC). Os tornados constituem-se atualmente em uma das causas de desastres naturais no Brasil, especialmente nas regiões sul e sudeste do país, como também em alguns países vizinhos. Os efeitos gerados são geralmente localizados e de curta duração, podendo ser devastadores dependendo da escala do tornado. Tais características dificultam a realização de estudos detalhados a partir de eventos reais, o que levou ao desenvolvimento de modelos experimentais e numéricos. A abordagem numérica é utilizada neste trabalho para a simulação de tornados, a qual se baseia nas equações de Navier-Stokes e na equação de conservação de massa, considerando a hipótese de pseudo-compressibilidade e condições isotérmicas. Para escoamentos com turbulência utiliza-se a Simulação Direta de Grandes Escalas com o modelo clássico de Smagorinsky para as escalas inferiores à resolução da malha (Large Eddy Simulation ou LES em inglês). A discretização das equações fundamentais do escoamento se realiza com um esquema explícito de dois passos de Taylor-Galerkin, onde o Método dos Elementos Finitos é empregado na discretização espacial utilizando-se o elemento hexaédrico trilinear isoparamétrico com um ponto de integração e controle de modos espúrios Na presença de corpos imersos que se movem para simular os deslocamentos dos tornados, o escoamento é descrito cinematicamente através de uma formulação Arbitrária Lagrangeana-Euleriana (ALE) que inclui um esquema de movimento de malha. Tornados são reproduzidos através da simulação numérica de dispositivos experimentais e do Modelo de Vórtice Combinado de Rankine (RCVM). Exemplos clássicos da Dinâmica dos Fluidos Computacional são apresentados inicialmente para a verificação das ferramentas numéricas implementadas. Finalmente, problemas envolvendo tornados móveis e estacionários são analisados, incluindo sua ação sobre corpos imersos. Nos modelos baseados em experimentos, a variação da relação de redemoinho determinou os diferentes padrões de escoamento observados no laboratório. Nos exemplos de modelo de vórtice, quando o tornado impactou o corpo imerso gerou picos de forças em todas as direções e, após a passar pelo mesmo, produziu uma alteração significativa na estrutura do vórtice.Analyses of tornado flows and its action on immersed bodies using numerical tools of Computational Wind Engineering (CWE) are the main aims of the present work. Tornadoes are currently one of the causes of natural disasters in Brazil, occurring more frequently in the southern and southeastern regions of the country, as well as in some neighboring countries. Effects are usually localized, presenting a short time interval, which can be devastating depending on the scale of the tornado. These characteristics difficult to carry out detailed studies based on real events, leading to the development of experimental and numerical models. The numerical approach is used in this work for the simulation of tornadoes, which is based on the Navier-Stokes equations and the mass conservation equation, considering the hypothesis of pseudo-compressibility and isothermal conditions. For turbulent flows, Large Eddy Simulation (LES) is used with the classical Smagorinsky model for sub-grid scales Discretization is performed the explicit two-step Taylor-Galerkin scheme, where the Finite Element Method is used in spatial discretization using isoparametric trilinear hexahedral elements with one-point quadrature and hourglass control. In the presence of immersed bodies that are moving in order to simulate translating tornadoes, the flow is kinematically described through a Lagrangian-Eulerian Arbitrary (ALE) formulation, which includes a mesh motion scheme. Tornadoes are reproduced using numerical simulation of experimental devices and the Rankine Combined Vortex Model (RCVM). Classical examples of Computational Fluid Dynamics are presented initially for the verification of the numerical tools implemented here. Finally, problems involving moving and stationary tornadoes are analyzed, including their actions on immersed bodies. For models based on experiments, the variation of the swirl ratio determined the different flow patterns observed in the laboratory. In the vortex model examples, when the tornado impacted on the immersed body, peaks of forces were generated in all directions and, after passing over it, a significant change in the structure of the vortex was produced.
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Wood, Dylan M. "Finite Element Modeling for Assessing Flood Barrier Risks and Failures due to Storm Surges and Waves." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595572799377091.
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Lim, Seng Chuan. "Computational investigation of flapping-wing propulsion for a micro air vehicle." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FLim%5FSeng.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Kevin Jones. "December 2006." Includes bibliographical references (p. 87). Also available in print.
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Longo, Riccardo. "Advanced turbulence models for the simulation of air pollutants dispersion in urban area." Doctoral thesis, Universite Libre de Bruxelles, 2020. https://dipot.ulb.ac.be/dspace/bitstream/2013/312254/3/thesis.pdf.
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NOWADAYS, a number of studies keep on demonstrating the existence of a strong relation between high concentrations of particulate matter (PM) and the prevalence of human morbidity and mortality. Large particles can be filtered in the nose or in the throat, while fine particles (about10 micrometer) can settle in the bronchi and lungs, leading to more serious consequences. According to Karagulian et al. the major sources of urban air pollution are traffic (25%), combustion and agriculture (22%), domestic fuel burning (20%), natural dust (18%) and industrial activities (15%).As a consequence, the detailed study of dispersion phenomena within the urban canopy becomes a target of great interest. To this end, Computational Fluid Dynamics (CFD) can be successfully employed to predict turbulence and dispersion patterns, accounting for a detailed characterization of the pollutant sources, complex obstacles and atmospheric stability classes.Despite being intrinsically different phenomena, turbulence and dispersion are closely related. It is universally accepted that, to reach accurate prediction of the concentration field, it is necessary to properly reproduce the turbulence one. For this reason, the present PhD thesis is split into two main Sections: one focused on turbulence modelling and the subsequent, centered on the dispersion modelling.Thanks to its good compromise between accuracy of results and calculation time, Reynolds-averaged Navier-Stokes (RANS) still represents a valid alternative to more resource-demanding methods. However, focusing on the models’ performance in urban studies, Large Eddy Simulation (LES) generally outperforms RANS results, even if the former is at least one order of magnitude more expensive. Stemming from this consideration, the aim of this work is to propose a variety of approaches meant to solve some of the major limitations linked to standard RANS simulation and to further improve its accuracy in disturbed flow fields, without renouncing to its intrinsic feasibility. The proposed models are suitable for the urban context, being capable of automatically switching from a formulation proper for undisturbed flow fields to one suitable for disturbed areas. For neutral homogeneous atmospheric boundary layer (ABL), a comprehensive approach is adopted, solving the issue of the erroneous stream-wise gradients affecting the turbulent profiles and able to correctly represent the various roughness elements. Around obstacles, more performing closures are employed. The transition between the two treatments is achieved through the definition of a Building Influence Area (BIA). The finalgoal is to offer more affordable alternatives to LES simulations without sacrificing a good grade of accuracy.Focusing on the dispersion modelling framework, there exists a number of parameters which have to be properly specified. In particular, the definition of the turbulent Schmidt number Sct, expressing the ratio of turbulent viscosity to turbulent mass diffusivity, is imperative. Despite its relevance, the literature does not report a clear guideline on the definition of this quantity. Nevertheless, the importance of Sct with respect to dispersion is undoubted and further demonstrated in the works of different authors. For atmospheric boundary layer flows, typical constant values range between 0.2 and 1.3. As a matter of fact, the local variability of Sct is supported by experimental evidence and by direct numerical simulations (DNS). These observations further suggest that the turbulent Schmidt number should be prescribed as a dynamic variable. Following these observations a variable turbulent Schmidt number formulation is proposed in this work. The latter stems from the same hypothesis of the variable formulation developed by Gorlé et al. Moreover, the relevant uncertain model parameters are optimized through uncertainty quantification (UQ). This formulation further increased the accuracy of the predictions, and was successfully verified by Di Bernardino et al. However, the turbulent Schmidt number resulting from this formulation is still intrinsically linked to the turbulence model employed, i.e. to the Cμ coefficient. To overcome this constraint, the nature and the dependencies of Sct were further analyzed through correlation studies and employing principal component analysis (PCA) on data obtained through the proposed ABL RANS model. Subsequently, the same data-driven technique was employed based on the high-fidelity outcomes of a delayed Detached Eddy Simulation (dDES) to derive a generalized turbulentSchmidt number formulation. The latter can be employed within a wide range of turbulence models, without limiting its variability.Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished
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Chan, Godine Kok Yan. "Computation of nonlinear hydrodynamic loads on floating wind turbines using fluid-impulse theory." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104254.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 199-202).
Wind energy is one of the more viable sources of renewable energy and offshore wind turbines represent a promising technology for the cost effective harvesting of this abundant source of energy. To capture wind energy offshore, horizontal-axis wind turbines can be installed on offshore platforms and the study of hydrodynamic loads on these offshore platforms becomes a critical issue for the design of offshore wind turbine systems. A versatile and efficient hydrodynamics module was developed to evaluate the linear and nonlinear loads on floating wind turbines using a new fluid-impulse formulation - the Fluid Impulse Theory(FIT). The new formulation allows linear and nonlinear loads on floating bodies to be computed in the time domain, and avoids the computationally intensive evaluation of temporal and spatial gradients of the velocity potential in the Bernoulli equation and the discretization of the nonlinear free surface. The module computes linear and nonlinear loads - including hydrostatic, Froude-Krylov, radiation and diffraction, as well as nonlinear effects known to cause ringing, springing and slow-drift loads - directly in the time domain and a stochastic seastate. The accurate evaluation of nonlinear loads by FIT provides an excellent alternative to existing methods for the safe and cost-effective design of offshore floating wind turbines. The time-domain Green function is used to solve the linear and nonlinear free-surface problems and efficient methods are derived for its computation. The body instantaneous wetted surface is approximated by a panel mesh and the discretization of the free surface is circumvented by using the Green function. The evaluation of the nonlinear loads is based on explicit expressions derived by the fluid-impulse theory, which can be computed efficiently.
by Godine Kok Yan Chan.
Ph. D.
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Turnock, Stephen Richard. "Prediction of ship rudder-propeller interaction using parallel computations and wind tunnel measurements." Thesis, University of Southampton, 1993. https://eprints.soton.ac.uk/48365/.
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A theoretical method has been developed to predict the forces developed due to the interaction between a ship rudder and propeller. A parallel lifting suface panel program (PALISUPAN) ha sbeen written in Occam2 which is designed to run across variable sized square arrays of transputers. thsi program forms teh basis of the theoretical method. The rudder and propeller are modelled separately. Their interaction is accounted for through an iterative process whereby their respective inflow velocity fields are modified using a circumferential average of the disturbance velcoity due to the other body. Prior to writing PALISUPAN, software techniques for the implementation of computational fluid dynamics algorithms across arrays of transputers were developed. The approach used is based on a geometric parallelism. At the outermost level on each transputer the particular CFD algorithm runs in parallel with a harness process. The harness controls teh communication across teh transputer array. to prove thsi concept an explicit finite volume solver for the two-dimensional Euler equations has been implemented. PALISUPAN itself uses a perturbation potential formulation and an explicit zero pressure loading condition is enforced at the trailing edge. Use of the communications harness greatky reduces code development time and although an implicit solver PALISUPAN gives good parallel performance. Wind tunnel tests were undertaken to derive experimental data for validation of the prediction method. These used a 3.5m x 2.5m low speed widn tunnel and a range of flow an dgeometrical parameters were tested. Total rudder forces and moments, propeller thrust and torque and quasi-steady rudder surface pressures were measured. Empirical relationships for teh prediction of rudder lift, drag and stall for use in ship manoeuvring studeis were also derived. The validated theoretical prediction for rudder-propeller interaction using PALISUPAN allows the detailed design of sjip rudder-propeller systems to be enhanced. The parallel performance of the pALISUPAN demonstrates the practicality of using transputer arrays to solve CFD problems.
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Smuts, Evan M. "A computational study of a lifting wing in close proximity to a moving ground plane." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/12129.
Full textAbstract:
Includes abstract.Includes bibliographical references (leaves 94-96).
Commercial software packages Fluent® and Gambit® were used to develop a 3D Computational Fluid Dynamics (CFD) model to determine the aerodynamic characteristics of a DHMTU lifting wing flying in ground effect. In particular, the performance of the wing in the presence of waves was of interest. But first a reliable computational model had to be developed to simulate waves flowing past the wing. Therefore the objective of this study was to develop such a model.
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Bastidas, Oscar. "Computational Study of Protein-Protein Interactions in Misfolded States." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3521.
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Protein-protein interactions (PPI’s) play important roles in biological systems. In particular, intra-protein interactions help create and maintain correctly folded protein states and mutations that result in misfolded states may be associated with significant changes in PPI behavior. Six unrelated protein systems with known structure files, each consisting of a wild-type and mutant strain, were studied using the computational algorithm OpenContact©. OpenContact© is a simple tool that can be used to rapidly identify or map interactions “hot-spots” in a protein and was, consequently, used in this study as a starting point to examine the potential or possible role of PPI’s on the behavior of mutated, misfolded proteins. Specific results include the observations of single chain protein systems exhibiting mutant strains with significantly stronger inter-atomic interactions as well as a surprising gain of secondary structure in the mutant state. These observations stood in contrast to multi-chain systems (proteins with more than two constituent chains) that appeared to display stronger inter-atomic interactions for the wild-type strains. Results also indicated a potential classification scheme for intra-protein interaction behavior in mutated states based on several criteria. It is important to note, however, that observations on PPI behavior presented need to be verified across a greater number of systems than those studied here before any such trends can be concretely established.