Academic literature on the topic 'Offshore structures Boundary element methods. Hydrodynamics'
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Journal articles on the topic "Offshore structures Boundary element methods. Hydrodynamics"
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Newman, J. N., and C. H. Lee. "Boundary-Element Methods In Offshore Structure Analysis." Journal of Offshore Mechanics and Arctic Engineering 124, no. 2 (April 11, 2002): 81–89. http://dx.doi.org/10.1115/1.1464561.
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Boundary-element methods, also known as panel methods, have been widely used for computations of wave loads and other hydrodynamic characteristics associated with the interactions of offshore structures with waves. In the conventional approach, based on the low-order panel method, the submerged surface of the structure is represented by a large number of small quadrilateral plane elements, and the solution for the velocity potential or source strength is approximated by a constant value on each element. In this paper, we describe two recent developments of the panel method. One is a higher-order method where the submerged surface can be represented exactly, or approximated to a high degree of accuracy by B-splines, and the velocity potential is also approximated by B-splines. This technique, which was first used in the research code HIPAN, has now been extended and implemented in WAMIT. In many cases of practical importance, it is now possible to represent the geometry exactly to avoid the extra work required previously to develop panel input files for each structure. It is also possible to combine the same or different structures which are represented in this manner, to analyze multiple-body hydrodynamic interactions. Also described is the pre-corrected Fast Fourier Transform method (pFFT) which can reduce the computational time and required memory of the low-order method by an order of magnitude. In addition to descriptions of the two methods, several different applications are presented.
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Kostecki, Stanisław. "Random Vortex Method in Numerical Analysis of 2D Flow Around Circular Cylinder." Studia Geotechnica et Mechanica 36, no. 4 (February 28, 2015): 57–63. http://dx.doi.org/10.2478/sgem-2014-0036.
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Abstract A combination of the vortex method and the boundary element method is used here to predict the two-dimensional flow field around a circular cylinder. Cylindrical structures experience strong hydrodynamic loading, due to vortex detachment from the both sides of cylinder during the flow. Thus, the practical meaning of such calculation is significant particularly in offshore oil and gas engineering as well as in the bridge and hydraulic structure engineering. This paper presents the mathematical formulation of the vortex method for the velocity and vorticity field calculation. The calculated velocity and vorticity fields are then used to predict the pressure distribution on the cylinder surface by the boundary element method. The resulting pressure on the cylinder, the Strouhal number and the length of the base recirculation zone are compared with solutions of other numerical methods and experiments, and a good agreement is achieved.
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Thomsen, Jonas Bjerg, Amélie Têtu, and Henrik Stiesdal. "A Comparative Investigation of Prevalent Hydrodynamic Modelling Approaches for Floating Offshore Wind Turbine Foundations: A TetraSpar Case Study." Journal of Marine Science and Engineering 9, no. 7 (June 22, 2021): 683. http://dx.doi.org/10.3390/jmse9070683.
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Numerical models have been used extensively in the design process of the TetraSpar floating offshore wind turbine (FOWT) foundation to optimize and investigate the influence from a number of structural and environmental conditions. In traditional offshore design, either the Morison approach or a linear boundary element method (BEM) is applied to investigate the hydrodynamic loads on a structure. The present study investigated and compared these two methods and evaluated their applicability on the TetraSpar FOWT concept. Furthermore, a hybrid model containing load contributions from both approaches was evaluated. This study focuses on motion response. In the evaluation, hydrodynamic data from BEM codes are applied, while the commercial software package OrcaFlex is utilized for time series simulations of the coupled structure. The investigation highlights the difference between the modelling approaches and the importance of particularly drag and inertia contributions. By optimizing the input coefficients, reasonable agreement between the models can be achieved.
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Sun, L., G. H. Dong, Y. P. Zhao, and C. F. Liu. "Numerical analysis of the effects on a floating structure induced by ship waves." Journal of Ship Research 55, no. 02 (June 1, 2011): 124–34. http://dx.doi.org/10.5957/jsr.2011.55.2.124.
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Ship-generated waves can make bad effects on offshore structures. A numerical model is presented for evaluating the forces exerted on a nearby floating structure by ship generated waves. The ship waves were modeled using Michell thin-ship theory (Wigley waves), the forces were computed using a boundary element method in the time domain, and the motions of the offshore structures were evaluated using the equation of motion of the floating body, and predicted using the fourth-order Runge-Kutta method. The numerical method was validated by comparing its results to those of frequency-domain methods reported in the literature. It was then applied to calculate the force of ship waves on a floating box. The ship's speed, dimensions, and distance were varied. The numerical results indicate some useful rules for varying these factors.
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Do, Hung Chien, Wei Jiang, and Jian Xin Jin. "Estimation of Ultimate Limit Statefor Stiffened-Plates Structures: Applying for a Very Large Ore Carrier Structures Designed by IACS Common Structural Rules." Applied Mechanics and Materials 249-250 (December 2012): 1012–18. http://dx.doi.org/10.4028/www.scientific.net/amm.249-250.1012.
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In advanced marine industry, the reduction in weight of hull structures for a very large object ship plays an important role as the economic efficiency is the most significant aspect. In this paper, we investigate the ultimate strength of structural ship stiffened-plates designed by International Association of Classification Societies (IACS) Common Structural Rules (CSR) methods of collapse state, by applying for ANSYS nonlinear finite element analysis (FEA). Specifically, the ultimate limit assessment methods for the outer bottom of ship structures, which have drawn a significant attention from industrial marine and offshore structures, are proposed to reduce the weight of ship structures. To solve this, we study the structures of a hypothetical Very Large Ore Carrier (VLOC) designed by pre-CSR and CSR methods. In particular, the stiffened-plates under the biaxial compression and lateral pressure loads with simply supported or/and clamped boundary condition(s), the results ultimate limit state assessment performance of Nonlinear FEA methods are shown and compared to various states.
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McKiver, W. J., G. Sannino, F. Braga, and D. Bellafiore. "Investigation of model capability in capturing vertical hydrodynamic coastal processes: a case study in the north Adriatic Sea." Ocean Science 12, no. 1 (January 15, 2016): 51–69. http://dx.doi.org/10.5194/os-12-51-2016.
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Abstract. In this work we consider a numerical study of hydrodynamics in the coastal zone using two different models, SHYFEM (shallow water hydrodynamic finite element model) and MITgcm (Massachusetts Institute of Technology general circulation model), to assess their capability to capture the main processes. We focus on the north Adriatic Sea during a strong dense water event that occurred at the beginning of 2012. This serves as an interesting test case to examine both the models strengths and weaknesses, while giving an opportunity to understand how these events affect coastal processes, like upwelling and downwelling, and how they interact with estuarine dynamics. Using the models we examine the impact of setup, surface and lateral boundary treatment, resolution and mixing schemes, as well as assessing the importance of nonhydrostatic dynamics in coastal processes. Both models are able to capture the dense water event, though each displays biases in different regions. The models show large differences in the reproduction of surface patterns, identifying the choice of suitable bulk formulas as a central point for the correct simulation of the thermohaline structure of the coastal zone. Moreover, the different approaches in treating lateral freshwater sources affect the vertical coastal stratification. The results indicate the importance of having high horizontal resolution in the coastal zone, specifically in close proximity to river inputs, in order to reproduce the effect of the complex coastal morphology on the hydrodynamics. A lower resolution offshore is acceptable for the reproduction of the dense water event, even if specific vortical structures are missed. Finally, it is found that nonhydrostatic processes are of little importance for the reproduction of dense water formation in the shelf of the north Adriatic Sea.
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de Camargo, Felipe Vannucchi. "Survey on Experimental and Numerical Approaches to Model Underwater Explosions." Journal of Marine Science and Engineering 7, no. 1 (January 15, 2019): 15. http://dx.doi.org/10.3390/jmse7010015.
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The ability of predicting material failure is essential for adequate structural dimensioning in every mechanical design. For ships, and particularly for military vessels, the challenge of optimizing the toughness-to-weight ratio at the highest possible value is essential to provide agile structures that can safely withstand external forces. Exploring the case of underwater explosions, the present paper summarizes some of the fundamental mathematical relations for foreseeing the behavior of naval panels to such solicitation. A broad state-of-the-art survey links the mechanical stress-strain response of materials and the influence of local reinforcements in flexural and lateral-torsional buckling to the hydrodynamic relations that govern the propagation of pressure waves prevenient from blasts. Numerical simulation approaches used in computational modeling of underwater explosions are reviewed, focusing on Eulerian and Lagrangian fluid descriptions, Johnson-Cook and Gurson constitutive materials for naval panels, and the solving methods FEM (Finite Element Method), FVM (Finite Volume Method), BEM (Boundary Element Method), and SPH (Smooth Particle Hydrodynamics). The confrontation of experimental tests for evaluating different hull materials and constructions with formulae and virtual reproduction practices allow a wide perception of the subject from different yet interrelated points of view.
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Hu, Zheng Zheng Hu, Derek Causon, Clive Mingham, and Ling Qian. "NUMERICAL SIMULATION OF WATER IMPACT INVOLVING THREE DIMENSIONAL RIGID BODIES OF ARBITRARY SHAPE." Coastal Engineering Proceedings 1, no. 32 (January 29, 2011): 14. http://dx.doi.org/10.9753/icce.v32.posters.14.
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As is well known, the design of coastal or offshore structures whether a ship, wave energy device or other fixed or floating structure, needs to consider its operation in a very hostile environment, including heavy storms. For example, an extremely high or steep wave impact on the bow or stern of a moored FPSO may result in a large amount of water on deck. Known as green water, this may cause severe damage to the deck house or other deckside equipment. Thus, there is great need for simulation tools to predict impact loadings and to provide more insight into the physics of local impact phenomena.
Published research or prediction work on the water impact problem has mostly related to studies in 2D. For example, Greehow& Lin (1983), Greenhow (1987), Zhao & Faltinsen (1993), Mei et al.(1999) have studied the hydrodynamics of rigid bodies entering water both theoretically and experimentally. More recently, a laboratory investigation of the pressure distribution on a free-falling wedge entering water by Yettou et al.(2006 has been compared a numerical and experimental study carried out by Campbell and Weynberg (1980). Water impact and green water loading in 3D has been simulated by Kleefsman et al. (2005) using a VOF method, which for dam break and water entry problems. In this study, we have developed the AMAZON-3D code for studies of water impact problems involving various 3D rigid solid bodies.
The in-house Cartesian cut cell approach has been used to simulate 3D water impact involving both moving rigid solid bodies and the free surface. The Cartesian cut cell method in the AMAZON-3D code is unrestricted in terms of boundary complexity or range of boundary movement. Solid objects are carved out of a background mesh, leaving a set of irregularly shaped cells aligned with the surface boundary. The advantages of the cut cell approach have been outlined previously by Causon et al. (2000, 2001) and Hu et al.(2009) including its flexibility for dealing with arbitrarily complex geometries and moving bodies. There is no requirement to re-mesh globally or even locally for the case of a moving body. All that is required is to update the cut cell data at the body contour for as long as the body motion continues.
The AMAZON-3D finite volume code solves the incompressible Navier-Stokes equations in both air and water regions simultaneously treating the free surface as a contact surface in the density field that is captured automatically in a manner analogous to shock capturing in compressible flow. A time-accurate artificial compressibility method and high Godunov-type scheme replaces the pressure correction solver used in other methods (see Qian et al. 2006).
We believe that the success of a study of water impact depends ultimately on the problem under consideration and the computer resources available and for each method there is a class of problem for which one method may perform better another. Each method has its own advantages and disadvantages and it is not possible to assert conclusively that one method is uniformly superior. However, we believe we can demonstrate that our method can be used successfully to study real local impact phenomena including the egress of an arbitrary rigid body from air to water or vice versa, the splash zone and entrapment of one fluid into the other. The code has been validated by recourse to a number of test cases including a cone undergoing forced oscillations and water impact of a rigid wedge with constant entry velocity where data and/or analytical results are available for comparison purposes. A range of results including the free surface elevation and force calculations will be presented for the water impact of various 3D rigid bodies.
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Ferrandis, José del Águila, Luca Bonfiglio, Ricardo Zamora Rodríguez, Chryssostomos Chryssostomidis, Odd Magnus Faltinsen, and Michael Triantafyllou. "Influence of Viscosity and Non-Linearities in Predicting Motions of a Wind Energy Offshore Platform in Regular Waves." Journal of Offshore Mechanics and Arctic Engineering 142, no. 6 (May 27, 2020). http://dx.doi.org/10.1115/1.4047128.
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Abstract Motion predictions of floating bodies in extreme waves represent a challenging problem in naval hydrodynamics. The solution of the seakeeping problem involves the study of complex non-linear wave-body interactions that require large computational costs. For this reason, over the years, many seakeeping models have been formulated in order to predict ship motions using simplified flow theories, usually based on potential flow theories. Neglecting viscous effects in the wave-induced forces might largely underestimate the energy dissipated by the system. This problem is particularly relevant for unconventional floating bodies at resonance. In these operating conditions, the linear assumption is no longer valid, and conventional boundary element methods, based on potential flow, might predict unrealistic large responses if not corrected with empirical viscous damping coefficients. The application considered in this study is an offshore platform to be operated in a wind farm requiring operability even in extreme meteorological conditions. In this paper, we compare heave and pitch response amplitude operators predicted for an offshore platform using three different seakeeping models of increasing complexity, namely, a frequency-domain boundary element method (BEM), a partly nonlinear time domain BEM, and a non-linear viscous model based on the solution of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations. Results are critically compared in terms of accuracy, applicability, and computational costs.
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Kuo, Kirsty A., and Hugh E. M. Hunt. "Dynamic Models of Piled Foundations." Applied Mechanics Reviews 65, no. 3 (May 1, 2013). http://dx.doi.org/10.1115/1.4024675.
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The vibration behavior of piled foundations is an important consideration in fields such as earthquake engineering, construction, machine-foundation design, offshore structures, nuclear energy, and road and rail development. This paper presents a review of the past 40 years' literature on modeling the frequency-dependent behavior of pile foundations. Beginning with the earliest model of a single pile, adapted from those for embedded footings, it charts the development of the four pile-modeling techniques: the “dynamic Winkler-foundation” approach that uses springs to represent the effect of the soil; elastic-continuum-type formulations involving the analytical solutions for displacements due to a subsurface disk, cylinder, or other element; boundary element methods; and dynamic finite-element formulations with special nonreflecting boundaries. The modeling of pile groups involves accounting for pile-soil-pile interactions, and four such methods exist: interaction factors; complete pile models; the equivalent pier method; and periodic structure theory. Approaches for validating pile models are also explored.
Dissertations / Theses on the topic "Offshore structures Boundary element methods. Hydrodynamics"
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Muthedath, Premkumar. "Numerical study of nonlinear free-surface flows." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07212009-040300/.
Full textBook chapters on the topic "Offshore structures Boundary element methods. Hydrodynamics"
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Harries, R., and A. Alexandre. "Evaluating corrections to linear boundary element method hydrodynamics accounting for mean second order forces on spar buoy wind turbine support structures." In Renewable Energies Offshore, 689–95. CRC Press, 2015. http://dx.doi.org/10.1201/b18973-97.
Full textConference papers on the topic "Offshore structures Boundary element methods. Hydrodynamics"
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Yan, Hongmei, and Yuming Liu. "Efficient Computations of Fully-Nonlinear Wave Interactions With Floating Structures." In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20412.
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We consider the problem of fully nonlinear three-dimensional wave interactions with floating bodies with or without a forward speed. A highly efficient time-domain computational method is developed in the context of potential flow formulation using the pre-corrected Fast Fourier Transform (PFFT) algorithm based on a high-order boundary element method. The method reduces the computational effort in solving the boundary-value problem at each time step to O(NlnN) from O(N2∼3) of the classical boundary element methods, where N is the total number of unknowns. The high efficiency of this method allows accurate computations of fully-nonlinear hydrodynamic loads, wave runups, and motions of surface vessels and marine structures in rough seas. We apply this method to study the hydrodynamics of floating objects with a focus on the understanding of fully nonlinear effects in the presence of extreme waves and large-amplitude body motions.
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Martin, Tobias, Arun Kamath, and Hans Bihs. "Modelling and Simulation of Moored-Floating Structures Using the Tension-Element-Method." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77776.
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The application of a discrete mooring model for floating structures is presented in this paper. The method predicts the steady-state solution for the shape of an elastic cable and the tension forces under consideration of static loads. It is based on a discretization of the cable in mass points connected with straight but elastic bars. The successive approximation is applied to the resulting system of equations which leads to a significant reduction of the matrix size in comparison to the matrix of a Newton-Raphson method. The mooring model is implemented in the open-source CFD model REEF3D. The solver has been used to study various problems in the field of wave hydrodynamics and fluid-structure interaction. It includes floating structures through a level set function and captures its motion using Newton and Euler equations in 6DOF. The fluid-structure interaction is solved explicitly using an immersed boundary method based on the ghost cell method. The applications show the accuracy of the solver and effects of mooring on the motion of floating structures.
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Li, Chengxi, and Yuming Liu. "Fully-Nonlinear Simulation of the Hydrodynamics of a Floating Body in Surface Waves by a High-Order Boundary Element Method." In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-41448.
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The objective of this work is to understand and evaluate the hydrodynamics modeling of a floating rigid body in regular and irregular ocean surface waves. Direct time-domain numerical simulation, based on the potential-flow formulation with the use of a quadratic boundary element method, is employed to compute the response of the body under the action of surface waves including fully-nonlinear wave-body interaction effects associated with steep waves and large-amplitude body motions. The viscous effect due to flow separation and turbulence is included by empirical modeling. The simulation results of body motions are compared with laboratory experimental measurements. The nonlinear effects due to body motion and wave motion are quantified and compared to the viscous effect. Their relative importance in the prediction and modeling of a rigid body motion under various wave conditions is investigated. This study may provide essential information pertaining to develop effective modeling of nonlinear wave-body interactions which is needed in design of offshore structures and wave energy conversion devices.
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Kazemi, Saeid, and Atilla Incecik. "Application of Direct Boundary Element Method to Three Dimensional Hydrodynamic Analysis of Interaction Between Waves and Floating Offshore Structures." In ASME 2004 23rd International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/omae2004-51429.
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A three-dimensional hydrodynamic analysis of interaction between a floating offshore structure and sea waves has been carried out using a novel approach which is based on the weighted residual technique and the direct boundary element method. The main advantage of the direct boundary element method is the fact that one can determine the total velocity potential directly. Direct BEM is more versatile and computationally more efficient than indirect BEM. Besides, the BEM can easily be coupled with other numerical methods, e.g. finite element method (FEM) in order to carry out structural analysis of deck of the platform due to impact. Firstly, the boundary value problem of three-dimensional interaction between regular sea waves and a semi-submersible will be described. Secondly, the direct boundary element method has been applied to predict hydrodynamic behaviour of Khazar Semi-Submersible Drilling Unit (KSSDU), which is the largest semi-submersible drilling platform under construction for a location in the Caspian Sea, North of Iran. The rigid body motion responses in six degrees of freedom of KHAZAR semi-submersible in response to encountering waves have been calculated by using the direct boundary element method. The results obtained from the direct BEM will be compared with those obtained by the results based on the conventional boundary element method (indirect BEM) which were obtained by the designers of KHAZAR semi-submersible.
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Vijay, K. G., and T. Sahoo. "Retrofitting of Floating Bridges With Perforated Outer Cover for Mitigating Wave-Induced Responses." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77054.
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An investigation has been carried out based on multi-domain boundary element method to analyze the mitigation of wave-induced hydrodynamic loads on a pair of floating rectangular bridges by retrofitting the structures with external porous plates. The study is based on the assumptions of small amplitude water wave theory in finite water depth with the characteristics of wave-body interactions remain unaltered along the bridge. Wave past porous structure is modelled using Darcy’s law. Various hydrodynamic characteristics are studied by analyzing the wave forces acting on the floating bridges and the retrofitted porous structures for different wave and structural parameters. With the introduction of a retrofit, the horizontal force on the bridge reduces irrespective of wave and structural parameters, whilst vertical force increases under certain conditions. Moreover, when the distance between the bridges is an integer multiple of half of the wavelength of the incident waves, both the bridges experience optima in horizontal and vertical wave forces, with both these forces being 180° out of phase. The present study is expected to be useful in the design of efficient bridge structures which will reduce wave-induced hydrodynamics loads on the structure and thus enhance the service life of floating bridges.
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Marino, E., C. Lugni, L. Manuel, H. Nguyen, and C. Borri. "Simulation of Nonlinear Waves on Offshore Wind Turbines and Associated Fatigue Load Assessment." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24623.
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By using a global simulation framework that employs a domain-decomposition strategy for computational efficiency, this study investigates the effects of fully nonlinear (FNL) waves on the fatigue loads exerted on the support structure (monopile) of a fixed-bottom offshore wind turbine. A comparison is made with more conventional linear wave hydrodynamics. The FNL numerical wave solver is invoked only on specific sub-domains where nonlinearities are detected; thus, only locally in space and time, a linear wave solution is replaced by the FNL results as input to the Morison equation used for the hydrodynamic loads. The accuracy and efficiency of this strategy allows long timedomain simulations where strongly nonlinear free-surface phenomena, like imminent breaking waves, are accounted for in the prediction of structural loads. The unsteady nonlinear free-surface problem governing the propagation of gravity waves is formulated using potential theory and a higher-order boundary element method (HOBEM) is used to discretize Laplace’s equation. The FNL solver is employed and associated hydrodynamic loads are predicted in conjunction with aerodynamic loads on the rotor of a 5-MW wind turbine using the NREL open-source software, FAST. We assess fatigue loads by means of both time- and frequency-domain methods. This study shows that the use of linear theory-based hydrodynamics can lead to significant underestimation of fatigue loads and damage.
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Alexandre, Armando, Ricard Buils Urbano, John Roadnight, and Robert Harries. "Methodology for Calculating Floating Offshore Wind Foundation Internal Loads Using Bladed and a Finite Element Analysis Software." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-78035.
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In the recent years, the floating offshore wind industry has developed quickly and most authors are now converging towards the need of a coupled loads analysis using aero-hydro-servo-elastic software on time domain simulations for floating foundations design. Different hydrodynamic theories still exist and their application depends on the floating platform characteristics. The Morison equation and the boundary element method (BEM, not to be confused with the Blade Element Momentum theory) theory approaches are often used in combination on the same platform model, sometimes applied to different elements of the same structure depending on their shape. When using the potential flow theory approach calculating internal distributed loads and later on transferring them to stress for hull design purposes is still a challenge due to the large ammount of load cases needed and the complexity of the structure. Furthermore, accounting for platform flexibility is also difficult in most codes using BEM theory due to the same reasons. Different approaches have been proposed by different authors, and currently there is not a single best industry practice for this. This paper presents a method for accounting for platform flexibility when using BEM theory. A range of methods for the load to stress transfer are also presented and the advantages and disadvantages between them are discussed. The choice of one or another method will depend heavily on the platform structure, and different methods might be used and combined for the same platform depending on the shape of the different elements within it. The different methods presented here involve performing coupled loads analysis using the aero-elastic software Bladed and multiple bodies to represent the floating platform in order to obtain internal loads at different points in the structure, as well as allowing for platform flexiblity modelling. Bladed can model multiple hydrodynamic bodies including the hydrodynamic effects between (e.g. coupled terms in the radiation force). The approach used in the current study is based on a platform modelled with the hydrodynamic loading distributed over independent sections, but originally computed from a single body BEM calculation. This simplification offers significant gains in computational efficiency and is expected to be valid for many types of floating structure, whist still allowing for some platform flexiblity to be modelled. The simulation resultant time series can later on be postprocessed to obtain distributed pressure forces on the platform wetted surface and transfer those onto a Finite Element code. Different options are presented here on how to perform this last step for both extreme and fatigue analysis of the hull structure. A couple of examples are shown using the OC3 spar and OC4 semisubmersible, focusing on a subsection of the structures to demonstrate the methodology.
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Sheng, Wanan, Anthony Lewis, and Raymond Alcorn. "Numerical Studies of a Floating Cylindrical OWC WEC." In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-83041.
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Oscillating water column (OWC) wave energy converters (WECs) are a popular type of wave energy devices. Generally, the OWC WECs have a simple structure and working principle, but with a high conversion efficiency, and a high reliability in power take-off due to a small torque and a high rotation speed for a certain power extraction. The OWC devices convert wave energy into pneumatic energy primarily by producing the pressured and de-pressured air (pneumatic energy) in the air chamber through the motions of the interior water surface in the water column. Conventionally, the pneumatic energy is converted into mechanical energy through an air turbine (in small scaled model, an orifice or porous membrane material is used for non-linear or linear power take-off modelling). However, these processes are very limitedly understood due to the complexities of the hydrodynamics, aerodynamics, and thermodynamics and their coupling effects. Theoretical and numerical attempts are very limited, especially when the coupling effects are included. As a result of the difficulties, in the device development, the most popular and acceptable approach may be the model tests, with different scaling factors in their corresponding development stages, as recommended by the relevant wave energy development protocols. To reduce the dependencies on the physical modelling in the OWC device development, numerical methods are very desirable to accommodate the simulation and assessment of the hydrodynamic and aerodynamic/thermodynamic performances of the OWC WECs. This is the main target of this investigation. In this numerical simulation, the hydrodynamic performances (including the motions of the structure and the interior water surface in waves) are carried out by employing a conventional boundary element method (i.e., WAMIT in this case) in frequency domain. To include the effects of the airflow passing through an orifice, its aerodynamic performance is much simplified by assuming its effects on the hydrodynamic performance through some extra damping coefficients to the motions of the floating structure and to the motion of the interior water surface. In this way, the interior water surface response can be obtained for the coupling effects of the hydrodynamics and aerodynamics of the OWC WEC. In this regard, an important issue in the numerical simulation is to seek an appropriate representation of the damping levels.
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Clauss, Gu¨nther F., Christian E. Schmittner, and Robert Stu¨ck. "Numerical Wave Tank: Simulation of Extreme Waves for the Investigation of Structural Responses." In ASME 2005 24th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2005. http://dx.doi.org/10.1115/omae2005-67048.
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For the deterministic analysis of extreme structure behavior, the hydrodynamics of the exciting wave field, i. e. pressure and velocity fields, must be known. Whereas responses of structures, e. g. motions, can easily be obtained by model tests, the detailed characteristics of the exciting waves are often difficult to determine by measurements. Therefore, numerical wave tanks (NWT) promise to be a handy tool for providing detailed insight into wave hydrodynamics. In this paper different approaches for numerical wave tanks are introduced and used for the simulation of rogue wave sequences. The numerical wave tanks presented are characterized by the following key features: a) Potential theory with Finite Element discretization (Pot/FE); b) Reynolds-Averaged Navier-Stokes Equations (RANSE) using the Volume of Fluid (VOF) method for describing the free surface. For the NWT using the VOF method three different commercial RANSE codes (CFX, FLUENT, COMET) are applied to calculate wave propagation, whereas simulations based on potential theory are carried out with a wave simulation code developed at Technical University Berlin (WAVETUB). It is shown that the potential theory method allows a fast and accurate simulation of the propagation of nonbreaking waves. In contrast, the RANSE/VOF method allows the calculation of breaking waves but is much more time-consuming, and effects of numerical diffusion can not be neglected. To benefit from the advantages of both solvers, i. e. the calculation speed (Pot/FE-solver WAVETUB) and the capability of simulating breaking waves (RANSE/VOF-solver), the coupling of both simulation methods is introduced. Two different methods of coupling are presented: a) at a given position in the wave tank; b) at a given time step. WAVETUB is used to simulate the propagation of the wave train from the start towards the coupling position (case A) or until wave breaking is encountered (case B). Subsequently, the velocity field and the contour of the free surface is handed over as boundary (case A) or initial values (case B) to the RANSE/VOF-solver and the simulation process is continued. To validate these approaches, different types of model seas for investigating wave/structure interactions are generated in a physical wave tank and compared to the numerical simulations.
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Guha, Amitava, and Jeffrey Falzarano. "Development of a Computer Program for Three Dimensional Analysis of Zero Speed First Order Wave Body Interaction in Frequency Domain." In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-11601.
Full textAbstract:
Evaluation of motion characteristics of ships and offshore structures at the early stage of design as well as during operation at the site is very important. Strip theory based programs and 3D panel method based programs are the most popular tools used in industry for vessel motion analysis. These programs use different variations of the Green’s function or Rankine sources to formulate the boundary element problem which solves the water wave radiation and diffraction problem in the frequency domain or the time domain. This study presents the development of a 3D frequency domain Green’s function method in infinite water depth for predicting hydrodynamic coefficients, wave induced forces and motions. The complete theory and its numerical implementation are discussed in detail. An in house application has been developed to verify the numerical implementation and facilitate further development of the program towards higher order methods, inclusion of forward speed effects, finite depth Green function, hydro elasticity, etc. The results were successfully compared and validated with analytical results where available and the industry standard computer program for simple structures such as floating hemisphere, cylinder and box barge as well as complex structures such as ship, spar and a tension leg platform.