Download or read book A Nonlinear Wave Load Model for Extreme and Fatigue Responses of Offshore Floating Wind Turbines written by Sungho Lee (Ph. D.) and published by . This book was released on 2012 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean energy is one of the most important sources of alternative energy and offshore floating wind turbines are considered viable and economical means of harnessing ocean energy. The accurate prediction of nonlinear hydrodynamic wave loads and the resulting nonlinear motion and tether tension is of crucial importance in the design of floating wind turbines. A new theoretical framework is presented for analyzing hydrodynamic forces on floating bodies which is potentially applicable in a wide range of problems in ocean engineering. The total fluid force acting on a floating body is obtained by the time rate of change of the impulse of the velocity potential flow around the body. This new model called Fluid Impulse Theory is used to address the nonlinear hydrodynamic wave loads and the resulting nonlinear responses of floating wind turbine for various wave conditions in a highly efficient and robust manner in time domain. A three-dimensional time domain hydrodynamic wave-body interaction computational solver is developed in the frame work of a boundary element method based on the transient free-surface Green-function. By applying a numerical treatment that takes the free-surface boundary conditions linearized at the incident wave surface and takes the body boundary condition satisfied on the instantaneous underwater surface of the moving body, it simulates a potential flow in conjunction with the Fluid Impulse Theory for nonlinear wave-body interaction problems of large-amplitude waves and motions in time domain. Several results are presented from the application of the Fluid Impulse Theory to the extreme and fatigue wave load model: the time domain analysis of nonlinear dynamic response of floating wind turbine for extreme wave events and the time domain analysis of nonlinear wave load for an irregular sea state followed by a power spectral density analysis.
Download or read book Wave Loads on Offshore Wind Turbines written by and published by . This book was released on 2015 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean energy is one of the most important sources of alternative energy and offshore floating wind turbines are considered viable and economical means of harnessing ocean energy. The accurate prediction of nonlinear hydrodynamic wave loads and the resulting nonlinear motion and tether tension is of crucial importance in the design of floating wind turbines. A new theoretical framework is presented for analyzing hydrodynamic forces on floating bodies which is potentially applicable in a wide range of problems in ocean engineering. The total fluid force acting on a floating body is obtained by the time rate of change of the impulse of the velocity potential flow around the body. This new model called Fluid Impulse Theory is used to address the nonlinear hydrodynamic wave loads and the resulting nonlinear responses of floating wind turbine for various wave conditions in a highly efficient and robust manner in time domain. A three-dimensional time domain hydrodynamic wave-body interaction computational solver is developed in the frame work of a boundary element method based on the transient free-surface Green-function. By applying a numerical treatment that takes the free-surface boundary conditions linearized at the incident wave surface and takes the body boundary condition satisfied on the instantaneous underwater surface of the moving body, it simulates a potential flow in conjunction with the Fluid Impulse Theory for nonlinear wave-body interaction problems of large amplitude waves and motions in time domain. Several results are presented from the application of the Fluid Impulse Theory to the extreme and fatigue wave load model: the time domain analysis of nonlinear dynamic response of floating wind turbine for extreme wave events and the time domain analysis of nonlinear wave load for an irregular sea state followed by a power spectral density analysis.
Download or read book An Integrated Nonlinear Wind Waves Model for Offshore Wind Turbines written by Enzo Marino and published by Firenze University Press. This book was released on 2010 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents a numerical model capable of simulating offshore wind turbines exposed to extreme loading conditions. External condition-based extreme responses are reproduced by coupling a fully nonlinear wave kinematic solver with a hydro-aero-elastic simulator. First, a two-dimensional fully nonlinear wave simulator is developed. The transient nonlinear free surface problem is formulated assuming the potential theory and a high-order boundary element method is implemented to discretize Laplace's equation. For temporal evolution a second-order Taylor series expansion is used. The code, after validation with experimental data, is successfully adopted to simulate overturning plunging breakers which give rise to dangerous impact loads when they break against wind turbine substructures. Emphasis is then placed on the random nature of the waves. Indeed, through a domain decomposition technique a global simulation framework embedding the numerical wave simulator into a more general stochastic environment is developed. The proposed model is meant as a contribution to meet the more and more pressing demand for research in the offshore wind energy sector as it permits taking into account dangerous effects on the structural response so as to increase the global structural safety level.
Download or read book Offshore Wind Turbine Nonlinear Wave Loads and Their Statistics written by Yu Zhang (Ph.D.) and published by . This book was released on 2019 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the large influence of lateral flexible vibrations on offshore wind turbine foundations and the higher natural frequencies of the offshore wind turbine foundation relative to the dominant frequencies of the linear wave load model, the modeling of the dynamic behavior of the foundation under nonlinear wave loads and analysis of their statistical characteristics have become an important issue for offshore wind turbine design. This thesis derives an approximate model of the nonlinear wave loads in the time domain by Fluid Impulse Theory, verifies it with a boundary element method software WAMIT and validates it with experimental measurements. The load level crossing rates and the load power spectral density is obtained in multiple sea states. The simulated nonlinear wave loads are applied as the forcing mechanism on the offshore wind turbine and its foundation, and the mudline bending moments are computed and compared with experimental measurements. The system identification is conducted by fitting the model with the experimental data using linear regression method. The analytical extreme and fatigue prediction of the offshore wind turbine system are derived and evaluated in waters of finite depth and in multiple seastates. Key words: Nonlinear wave loads, nonlinear wave loads statistics, system identification, extremes and fatigue
Download or read book Modeling Nonlinear Stochastic Ocean Loads as Diffusive Stochastic Differential Equations to Derive the Dynamic Responses of Offshore Wind Turbines written by David F. H. Larson and published by . This book was released on 2016 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: A procedure is developed for modeling stochastic ocean wave and wind loads as diffusive stochastic differential equations (SDE) in a state space form to derive the response statistics of offshore structures, specifically wind turbines. Often, severe wind and wave systems are highly nonlinear and thus treatment as linear systems is not applicable, leading to computationally expensive Monte Carlo simulations. Using Stratonovich-form diffusive stochastic differential equations, both linear and nonlinear components of the wind thrust can be modeled as 2 state SDE. These processes can be superposed with both the linear and nonlinear (inertial and viscous) wave forces, also modeled as a multi-dimensional state space SDE. Furthermore, upon implementing the ESPRIT algorithm to fit the autocorrelation function of any real sea state spectrum, a simple 2-state space model can be derived to completely describe the wave forces. The resulting compound state-space SDE model forms the input to a multi-dimension state-space Fokker-Planck equation, governing the dynamical response of the wind turbine structure. Its solution yields response, fatigue and failure statistics-information critical to the design of any offshore structure. The resulting Fokker-Planck equation can be solved using existing numerical schemes.
Download or read book Fatigue and Extreme Wave Loads on Bottom Fixed Offshore Wind Turbines written by Signe Schløer and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stochastic Dynamics of Marine Structures written by Arvid Naess and published by Cambridge University Press. This book was released on 2013 with total page 425 pages. Available in PDF, EPUB and Kindle. Book excerpt: For students and professionals, this covers theory and methods for stochastic modelling and analysis of marine structures under environmental loads.
Download or read book DTU Wind Energy PhD written by Signe Schløer and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Wind energy Methods for computation of wave forcing and the resulting motion of a slender offshore floating structure written by Olga Glöckner and published by GRIN Verlag. This book was released on 2018-07-19 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Academic Paper from the year 2014 in the subject Engineering - Civil Engineering, grade: 1,0, University of Hannover (A&M University Texas, Ludwig-Franzius-Institut für Wasserbau, Ästuar- und Küsteningenieurwesen), language: English, abstract: This thesis investigates how wave loads act on an OC3 Hywind spar-buoy. The author analyzes the resulting motions of the support platform. This work also contains a detailed presentation of the topic with useful additional information and graphics. Unlike fossil fuels (like oil, coal and natural gas), wind energy is a renewable energy resource. Since winds at sea are stronger and more consistent than onshore winds, the demand for offshore wind turbines has increased over the last years. As energy can be produced more efficient in deeper water, several floating offshore wind turbine constructions, such as the OC3 Hywind spar-buoy, have been proposed. The design of floating wind turbines depends on the simulation of the system behavior caused by exciting forces. A general overview of regular and irregular waves as well as hydrostatic and hydrodynamic loads acting on floating structures is given in chapter 2. Furthermore, essential formulations for calculating motions of FOWTs are given at the end of this chapter. Since all simulations carried out in this thesis are based on the OC3 Hywind concept, detailed information about this floating wind turbine model are given in chapter 3. Three different methods are used for the estimation of wave induced loads and motions. Section 4 describes a modified Morison formulation in the time domain which is applied by the commercially available software MATLAB. On the basis of the diffraction theory the commercial offshore software package SESAM simulates wave excitation forces and responding motions which are presented and discussed in chapter 5. The third method is the open source code FAST that computes wave induced loads and motions based on the first-order potential theory and Kane’s equation of motion. Basic formulations used in FAST and essential hydrodynamic results are shown in chapter 6. The comparisons between the simulations of the three programs are represented and the individual results are analyzed in chapter 7.
Download or read book A comparison of methods for computation of wave forcing written by Olga Glöckner and published by GRIN Verlag. This book was released on 2018-05-17 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diploma Thesis from the year 2014 in the subject Engineering - Civil Engineering, grade: 1,0, University of Hannover (A&M University Texas, Ludwig-Franzius-Institut für Wasserbau, Ästuar- und Küsteningenieurwesen), language: English, abstract: Unlike fossil fuels (for example oil, coal and natural gas), wind energy is a renewable energy resource. Since winds at sea are stronger and more consistent than onshore winds, the demand for offshore wind turbines has increased over the last years. As energy can be produced more efficient in deeper water, several floating offshore wind turbine constructions, such as the OC3 Hywind spar-buoy, have been proposed. The design of floating wind turbines depends on the simulation of the system behavior caused by exciting forces. This thesis deals with the comparison between different methods for calculating wave forces and resulting platform motions of a floating offshore wind turbine. On the one hand, wave exciting loads computed with Morison’s equation are compared to the hydrodynamic forces simulated by the open source code FAST on the basis of the diffraction theory. On the other hand, response motions of the floating structure are simulated by the commercial offshore software SESAM in the frequency domain and compared with the motions calculated by FAST in the time domain.
Download or read book Floating Offshore Wind Energy written by Joao Cruz and published by Springer. This book was released on 2016-08-20 with total page 345 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a state-of-the-art review of floating offshore wind turbines (FOWT). It offers developers a global perspective on floating offshore wind energy conversion technology, documenting the key challenges and practical solutions that this new industry has found to date. Drawing on a wide network of experts, it reviews the conception, early design stages, load & structural analysis and the construction of FOWT. It also presents and discusses data from pioneering projects. Written by experienced professionals from a mix of academia and industry, the content is both practical and visionary. As one of the first titles dedicated to FOWT, it is a must-have for anyone interested in offshore renewable energy conversion technologies.
Download or read book MARE WINT written by Wiesław Ostachowicz and published by Springer. This book was released on 2016-08-30 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a holistic, interdisciplinary overview of offshore wind energy, and is a must-read for advanced researchers. Topics, from the design and analysis of future turbines, to the decommissioning of wind farms, are covered. The scope of the work ranges from analytical, numerical and experimental advancements in structural and fluid mechanics, to novel developments in risk, safety & reliability engineering for offshore wind.The core objective of the current work is to make offshore wind energy more competitive, by improving the reliability, and operations and maintenance (O&M) strategies of wind turbines. The research was carried out under the auspices of the EU-funded project, MARE-WINT. The project provided a unique opportunity for a group of researchers to work closely together, undergo multidisciplinary doctoral training, and conduct research in the area of offshore wind energy generation. Contributions from expert, external authors are also included, and the complete work seeks to bridge the gap between research and a rapidly-evolving industry.
Download or read book Structural Reliability of Offshore Wind Turbines written by Puneet Agarwal and published by . This book was released on 2008 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: Statistical extrapolation is required to predict extreme loads, associated with a target return period, for offshore wind turbines. In statistical extrapolation, "short-term" distributions of the load random variable(s) conditional on the environment are integrated with the joint probability distribution of environmental random variables (from wind, waves, current etc.) to obtain the so-called "long-term" distribution, from which long-term loads may be obtained for any return period. The accurate prediction of long-term extreme loads for offshore wind turbines, using efficient extrapolation procedures, is our main goal. While loads data, needed for extrapolation, are obtained by simulations in a design scenario, field data can be valuable for understanding the offshore environment and the resulting turbine response. We use limited field data from a 2MW turbine at the Blyth site in the United Kingdom, and study the influence of contrasting environmental (wind) regimes and associated waves at this site on long-term loads, derived using extrapolation. This study also highlights the need for efficient extrapolation procedures and for modeling nonlinear waves at sites with shallow water depths. An important first step in extrapolation is to establish robust short-term distributions of load extremes. Using data from simulations of a 5MW onshore turbine model, we compare empirical short-term load distributions when two alternative models for extremes--global and block maxima--are used. We develop a convergence criterion, based on controlling the uncertainty in rare load fractiles, which serves to assess whether or not an adequate number of simulations has been performed. To establish long-term loads for a 5MW offshore wind turbine, we employ an inverse reliability approach, which is shown to predict reasonably accurate long-term loads, compared to a more expensive direct integration approach. We show that blade pitching control actions can be a major source of response variability, due to which a large number of simulations may be required to obtain stable tails of short-term load distributions, and to predict accurate ultimate loads. We address model uncertainty as it pertains to wave models. We investigate the effect of using irregular nonlinear (second-order) waves, compared to irregular linear waves, on loads for an offshore wind turbine. We incorporate this nonlinear irregular wave model into a procedure for integrated wind-wave-response analysis of offshore wind turbines. We show that computed loads are generally somewhat larger with nonlinear waves and, hence, that modeling nonlinear waves is important is response simulations of offshore wind turbines and prediction of long-term loads.
Download or read book Assessment and Nonlinear Modeling of Wave Tidal and Wind Energy Converters and Turbines written by Madjid Karimirad and published by . This book was released on 2020-09-04 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Special Issue "Assessment and Nonlinear Modeling of Wave, Tidal, and Wind Energy Converters and Turbines" contributes original research to stimulate the continuing progress of the offshore renewable energy (ORE) field, with a focus on state-of-the-art numerical approaches developed for the design and analysis of ORE devices. Particularly, this collection provides new methodologies, analytical/numerical tools, and theoretical methods that deal with engineering problems in the ORE field of wave, wind, and current structures. This Special Issue covers a wide range of multidisciplinary aspects, such as the 1) study of generalized interaction wake model systems with elm variation for offshore wind farms; 2) a flower pollination method based on global maximum power point tracking strategy for point-absorbing type wave energy converters; 3) performance optimization of a Kirsten-Boeing turbine using a metamodel based on neural networks coupled with CFD; 4) proposal of a novel semi-submersible floating wind turbine platform composed of inclined columns and multi-segmented mooring lines; 5) reduction of tower fatigue through blade back twist and active pitch-to-stall control strategy for a semi-submersible floating offshore wind turbine; 6) assessment of primary energy conversion of a closed-circuit OWC wave energy converter; 7) development and validation of a wave-to-wire model for two types of OWC wave energy converters; 8) assessment of a hydrokinetic energy converter based on vortex-induced angular oscillations of a cylinder; 9) application of wave-turbulence decomposition methods on a tidal energy site assessment; 10) parametric study for an oscillating water column wave energy conversion system installed on a breakwater; 11) optimal dimensions of a semisubmersible floating platform for a 10 MW wind turbine; 12) fatigue life assessment for power cables floating in offshore wind turbines.
Download or read book Sloshing written by Odd M. Faltinsen and published by Cambridge University Press. This book was released on 2014-03-06 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents sloshing with marine and land-based applications, with a focus on ship tanks. It also includes the nonlinear multimodal method developed by the authors and an introduction to computational fluid dynamics. Emphasis is also placed on rational and simplified methods, including several experimental results. Topics of special interest include antirolling tanks, linear sloshing, viscous wave loads, damping, and slamming. The book contains numerous illustrations, examples, and exercises.
Download or read book Wind Wave Misalignment in the Loads Analysis of a Floating Offshore Wind Turbine written by and published by . This book was released on 2014 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Wind resources far from the shore and in deeper seas have encouraged the offshore wind industry to look into floating platforms. The International Electrotechnical Commission (IEC) is developing a new technical specification for the design of floating offshore wind turbines that extends existing design standards for land-based and fixed-bottom offshore wind turbines. The work summarized in this paper supports the development of best practices and simulation requirements in the loads analysis of floating offshore wind turbines by examining the impact of wind/wave misalignment on the system loads under normal operation. Simulations of the OC3-Hywind floating offshore wind turbine system under a wide range of wind speeds, significant wave heights, peak-spectral periods and wind/wave misalignments have been carried out with the aero-servo-hydro-elastic tool FAST [4]. The extreme and fatigue loads have been calculated for all the simulations. The extreme and fatigue loading as a function of wind/wave misalignment have been represented as load roses and a directional binning sensitivity study has been carried out. This study focused on identifying the number and type of wind/wave misalignment simulations needed to accurately capture the extreme and fatigue loads of the system in all possible metocean conditions considered, and for a down-selected set identified as the generic US East Coast site. For this axisymmetric platform, perpendicular wind and waves play an important role in the support structure and including these cases in the design loads analysis can improve the estimation of extreme and fatigue loads. However, most structural locations see their highest extreme and fatigue loads with aligned wind and waves. These results are specific to the spar type platform, but it is expected that the results presented here will be similar to other floating platforms.
Download or read book Model Development and Loads Analysis of a Wind Turbine on a Floating Offshore Tension Leg Platform written by and published by . This book was released on 2010 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents results of the analysis of a 5-MW wind turbine located on a floating offshore tension leg platform (TLP) that was conducted using the fully coupled time-domain aero-hydro-servo-elastic design code FAST with AeroDyn and HydroDyn. Models in this code are of greater fidelity than most of the models that have been used to analyze floating turbines in the past--which have neglected important hydrodynamic and mooring system effects. The report provides a description of the development process of a TLP model, which is a modified version of a Massachusetts Institute of Technology design derived from a parametric linear frequency-domain optimization process. An extensive loads and stability analysis for ultimate and fatigue loads according to the procedure of the International Electrotechnical Commission offshore wind turbine design standard was performed with the verified TLP model. Response statistics, extreme event tables, fatigue lifetimes, and selected time histories of design-driving extreme events are analyzed and presented. Loads for the wind turbine on the TLP are compared to those of an equivalent land-based turbine in terms of load ratios. Major instabilities for the TLP are identified and described.
