Development Of Impulse Wave Load Model For Offshore Wind Turbine Foundations Induced By Nonlinear Wave Groups
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An Integrated Nonlinear Wind-Waves Model for Offshore Wind Turbines
| Author | : Enzo Marino |
| Publisher | : Firenze University Press |
| Total Pages | : 232 |
| Release | : 2010 |
| Genre | : Coastal engineering |
| ISBN | : 8866550515 |
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.
Offshore Wind Turbine Nonlinear Wave Loads and Their Statistics
| Author | : Yu Zhang (Ph.D.) |
| Publisher | : |
| Total Pages | : 91 |
| Release | : 2019 |
| Genre | : |
| ISBN | : |
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
A Nonlinear Wave Load Model for Extreme and Fatigue Responses of Offshore Floating Wind Turbines
| Author | : Sungho Lee (Ph. D.) |
| Publisher | : |
| Total Pages | : 173 |
| Release | : 2012 |
| Genre | : |
| ISBN | : |
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.
Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines
| Author | : Madjid Karimirad |
| Publisher | : |
| Total Pages | : 290 |
| Release | : 2020-09-04 |
| Genre | : |
| ISBN | : 9783039369126 |
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.
Wave Loads on Offshore Wind Turbines
| Author | : |
| Publisher | : |
| Total Pages | : 65 |
| Release | : 2015 |
| Genre | : |
| ISBN | : |
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.
Design of Foundations for Offshore Wind Turbines
| Author | : Subhamoy Bhattacharya |
| Publisher | : John Wiley & Sons |
| Total Pages | : 392 |
| Release | : 2019-03-01 |
| Genre | : Technology & Engineering |
| ISBN | : 1119128153 |
Comprehensive reference covering the design of foundations for offshore wind turbines As the demand for “green” energy increases the offshore wind power industry is expanding at a rapid pace around the world. Design of Foundations for Offshore Wind Turbines is a comprehensive reference which covers the design of foundations for offshore wind turbines, and includes examples and case studies. It provides an overview of a wind farm and a wind turbine structure, and examines the different types of loads on the offshore wind turbine structure. Foundation design considerations and the necessary calculations are also covered. The geotechnical site investigation and soil behavior/soil structure interaction are discussed, and the final chapter takes a case study of a wind turbine and demonstrates how to carry out step by step calculations. Key features: New, important subject to the industry. Includes calculations and case studies. Accompanied by a website hosting software and data files. Design of Foundations for Offshore Wind Turbines is a must have reference for engineers within the renewable energy industry and is also a useful guide for graduate students in this area.
Wind energy. Methods for computation of wave forcing and the resulting motion of a slender offshore floating structure
| Author | : Olga Glöckner |
| Publisher | : GRIN Verlag |
| Total Pages | : 151 |
| Release | : 2018-07-19 |
| Genre | : Technology & Engineering |
| ISBN | : 3668754780 |
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.
Computation of Nonlinear Hydrodynamic Loads on Floating Wind Turbines Using Fluid-Impulse Theory
| Author | : |
| Publisher | : |
| Total Pages | : |
| Release | : 2015 |
| Genre | : |
| ISBN | : |
A hydrodynamics computer module was developed for the evaluation of the linear and nonlinear loads on floating wind turbines using a new fluid-impulse formulation for coupling with the FAST program. The recently developed formulation allows the computation of linear and nonlinear loads on floating bodies in the time domain and avoids the computationally intensive evaluation of temporal 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. Computations are presented of the linear and nonlinear loads on the MIT/NREL tension-leg platform. Comparisons were carried out with frequency-domain linear and second-order methods. Emphasis was placed on modeling accuracy of the magnitude of nonlinear low- and high-frequency wave loads in a sea state. Although fluid-impulse theory is applied to floating wind turbines in this paper, the theory is applicable to other offshore platforms as well.
Comparison of methods for the computation of wave forcing
| Author | : Olga Glöckner |
| Publisher | : GRIN Verlag |
| Total Pages | : 20 |
| Release | : 2018-05-18 |
| Genre | : Technology & Engineering |
| ISBN | : 366870614X |
Presentation slides from the year 2014 in the subject Engineering - Civil Engineering, grade: 1,0, University of Hannover, language: English, abstract: Unlike fossil fuels (e.g. 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.
