scholarly journals Effective Method for Determining Environmental Loads on Supporting Structures for Offshore Wind Turbines

2016 ◽  
Vol 23 (1) ◽  
pp. 52-60
Author(s):  
Paweł Dymarski ◽  
Ewelina Ciba ◽  
Tomasz Marcinkowski
Keyword(s):  
Wind Turbines ◽  
Computational Method ◽  
Offshore Wind ◽  
Cfd Simulations ◽  
Drag Coefficients ◽  
Offshore Wind Turbines ◽  
Drag Forces ◽  
The Time Domain ◽  
Range Of Variation ◽  
Supporting Structures

Abstract This paper presents a description of an effective method for determining loads due to waves and current acting on the supporting structures of the offshore wind turbines. This method is dedicated to the structures consisting of the cylindrical or conical elements as well as (truncates) pyramids of polygon with a large number of sides (8 or more). The presented computational method is based on the Morison equation, which was originally developed only for cylindrically shaped structures. The new algorithm shown here uses the coefficients of inertia and drag forces that were calculated for non-cylindrical shapes. The analysed structure consists of segments which are truncated pyramids on the basis of a hex decagon. The inertia coefficients, CM, and drag coefficients, CD, were determined using RANSE-CFD calculations. The CFD simulations were performed for a specific range of variation of the period, and for a certain range of amplitudes of the velocity. In addition, the analysis of influence of the surface roughness on the inertia and drag coefficients was performed. In the next step, the computations of sea wave, current and wind load on supporting structure for the fifty-year storm were carried out. The simulations were performed in the time domain and as a result the function of forces distribution along the construction elements was obtained. The most unfavourable distribution of forces will be used, to analyse the strength of the structure, as the design load.

scholarly journals CFD Simulations on Interference Effects between Offshore Wind Turbines

2014 ◽  
Vol 524 ◽  
pp. 012143 ◽  
Author(s):  
P Weihing ◽  
K Meister ◽  
C Schulz ◽  
Th Lutz ◽  
E Krämer
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Interference Effects ◽  
Cfd Simulations ◽  
Offshore Wind Turbines

Implementation of Computational Methods to Obtain Accurate Induction Factors for Offshore Wind Turbines

2014 ◽  
Author(s):  
Anand Bahuguni ◽  
Krishnamoorthi Sivalingam ◽  
Peter Davies ◽  
Johan Gullman-Strand ◽  
Vinh Tan Nguyen
Keyword(s):  
Wind Turbines ◽  
Lift Coefficient ◽  
Offshore Wind ◽  
Cfd Simulations ◽  
Sea State ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Blade Tip ◽  
Computational Fluid Dynamics Cfd ◽  
Blade Element

Most of the wind turbine analysis softwares widely being used in the market are based on the Blade Element Momentum method (BEM). The two important parameters that the BEM codes calculate are the axial and the tangential induction factors. These factors are calculated based on the empirical blade lift coefficient Cl and drag coefficient Cd along with some loss/correction functions to account for the losses near the blade tip and the hub. The current study focusses on verifying the values of induction factors using Computational Fluid Dynamics (CFD) simulations for floating offshore wind turbines at a selected sea state. The study includes steady state calculations as well as transient calculations for pitching motions of the turbine due to waves. The NREL FAST software is used to set the simulation scenarios according to OC3 Phase IV cases. The blades are divided a number of elements in CFD calculations and the data are extracted at individual elements to have an exact comparison with the BEM based calculations.

scholarly journals Nonlinear Wave Loads on Offshore Wind Turbines: Extreme Statistics and Fatigue

2019 ◽  
Author(s):  
Yu Zhang ◽  
Paul D. Sclavounos
Keyword(s):  
Nonlinear Wave ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Wave Loads ◽  
Extreme Statistics ◽  
Support Structure ◽  
Nonlinear Load ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
The Time Domain

Abstract The development is presented of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines. Explicit expressions are derived for the time-domain and frequency-domain nonlinear exciting forces in a seastate with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed.

Towards credible CFD simulations for floating offshore wind turbines

2020 ◽  
Vol 209 ◽  
pp. 107237
Author(s):  
Simon Burmester ◽  
Guilherme Vaz ◽  
Ould el Moctar
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Cfd Simulations ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

A two-step approach to damage localization at supporting structures of offshore wind turbines

2017 ◽  
Vol 17 (5) ◽  
pp. 1313-1330 ◽  
Author(s):  
Karsten Schröder ◽  
Cristian Guillermo Gebhardt ◽  
Raimund Rolfes
Keyword(s):  
Numerical Model ◽  
Objective Function ◽  
Wind Turbines ◽  
Optimization Algorithm ◽  
Measurement Data ◽  
Offshore Wind ◽  
Mode Shapes ◽  
Damage Localization ◽  
Offshore Wind Turbines ◽  
Supporting Structures

This article introduces a new adaptive two-step optimization algorithm for finite element model updating with special emphasis on damage localization at supporting structures of offshore wind turbines. The algorithm comprises an enhanced version of the global optimization algorithm simulated annealing, the simulated quenching method that approximates an initial guess of damage localization. Subsequently, sequential quadratic programming is used to compute the final solution adaptively. For the correlation of numerical model and measurement data, both a measure based on eigenfrequencies and mode shapes and a measure employing time series are implemented and compared with respect to their performance for damage localization. Phase balance of the time signals is achieved using cross-correlation. The localization problem is stated as a minimization problem in which the measures are used in time and modal domain as the objective function subject to constraints. Furthermore, the objective function value of the adjusted model is used to distinguish correct from wrong solutions. The functionality is proven using a numerical model of a monopile structure with simulated damage and a lab-scaled model of a tripile structure with real damage.

Support Structure Optimization for Offshore Wind Turbines With a Genetic Algorithm

2014 ◽  
Author(s):  
Lucía Bárcena Pasamontes ◽  
Fernando Gómez Torres ◽  
Daniel Zwick ◽  
Sebastian Schafhirt ◽  
Michael Muskulus
Keyword(s):  
Genetic Algorithm ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Hot Spot ◽  
Offshore Wind ◽  
Support Structures ◽  
Hot Spot Stress ◽  
Offshore Wind Turbines ◽  
Structural Design Optimization ◽  
The Time Domain

This study considers the use of a genetic algorithm for the structural design optimization of support structures for offshore wind turbines. Member diameters, thicknesses and locations of nodes are jointly optimized. Analysis of each design is performed with a complete wind turbine simulation, for a load case in the time domain. Structural assessment is in terms of fatigue damage, evaluated for each joint using the hot-spot stress approach. This defines performance constraints. Designs are optimized with respect to their weight. The approach has been tested with the modified 4-legged UpWind jacket from the OC4 project. The weight is quickly reduced, convergence slows after about 100 iterations, and few changes occur after 250 iterations. Interestingly, the fatigue constraint is not active for any member, and it is the validity of stress concentration factors that determines the best design, which utilizes less than 90 percent of the available fatigue lifetime. These results of the preliminary study using the genetic algorithm demonstrate that automatic optimization of wind turbine support structures is feasible under consideration of the simplified load approach. Even for complex, multi-member structures such as the considered jacket a weight reduction was achieved.

A Conceptual Design Method for Parametric Study of Blades for Offshore Wind Turbines

2011 ◽  
Author(s):  
Lars Fro̸yd ◽  
Ole G. Dahlhaug
Keyword(s):  
Wind Turbines ◽  
Design Method ◽  
Design Procedure ◽  
Rotor Blades ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Integrated Method ◽  
Horizontal Axis Wind Turbines ◽  
Parametric Studies ◽  
The Time Domain

This article presents a simplified, integrated method for design studies of blades for offshore wind turbines. The method applies to variable speed horizontal axis wind turbines with pitch control, and allows designing the rotor blades based on a very limited set of input parameters. The purpose of the method is to allow parametric studies of different design configurations of the rotor at a reasonable effort. The resulting wind turbine models are at a level of detail suitable for preliminary design considerations using e.g. aero-elastic simulations in the time domain. The aerodynamic design is based on blade element momentum (BEM) considerations using a distribution of 2D airfoil characteristics. The structural design of the blades is based on aerodynamic forces calculated from a small number of load cases. The design procedure is facilitated by using simplified cross-section definitions and iterative approaches. The resulting blade designs are shown to compare well with data from available turbine models.

Development of an Actuator Line Model for Simulation of Floating Offshore Wind Turbines

2021 ◽  
Author(s):  
Alireza Arabgolarcheh ◽  
Ernesto Benini ◽  
Morteza Anbarsooz
Keyword(s):  
Wind Turbines ◽  
Computational Cost ◽  
Considerable Effect ◽  
Initial Position ◽  
Computational Method ◽  
Offshore Wind ◽  
Line Model ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Actuator Line Model

Abstract This study focuses on developing and applying an actuator line model (ALM) to predict the wake behind floating offshore wind turbines (FOWTs). A computational method is presented which implements an ALM, able to handle 6 Degree-of-Freedom (DOF) motion dynamics, coupled with a CFD solver. Computational grides used are cubic and do not require a boundary layer mesh. Results show that just about 300k grids are necessary for performance assessment of the NREL Phase VI case. Therefore, the proposed method leads to significantly lower computational cost and easier preprocessing compared to high-order methods used for solving RANS. On the other hand, coupled aerodynamic and motion analyses showed that pitch and surge motions have the most considerable influence on turbine performance due to their inherent effect on 3D local wind inclination in the relative frame. The peak power happened when the platform is in its initial position, where the platform motion velocity is maximum. Finally, it is shown that the wind turbine movement has a considerable effect on its wake characteristics. The gap distances between wake rings can also change wake interactions, and, for the case with platform pitch motion, the condition of the wake is even more complicated as such distance is not the same in all azimuthal sectors. The results show that the applied ALM method is beneficial for simulating the wake behind offshore wind turbines and the complex phenomena in the wake due to platform oscillation.

scholarly journals Iterative Frequency-Domain Response of Floating Offshore Wind Turbines with Parametric Drag

2018 ◽  
Vol 6 (4) ◽  
pp. 118 ◽  
Author(s):  
Frank Lemmer ◽  
Wei Yu ◽  
Po Cheng
Keyword(s):  
System Dynamics ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Domain Model ◽  
Offshore Wind ◽  
Viscous Drag ◽  
Drag Coefficients ◽  
Reduced Order ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Methods for coupled aero-hydro-servo-elastic time-domain simulations of Floating Offshore Wind Turbines (FOWTs) have been successfully developed. One of the present challenges is a realistic approximation of the viscous drag of the wetted members of the floating platform. This paper presents a method for an iterative response calculation with a reduced-order frequency-domain model. It has heave plate drag coefficients, which are parameterized functions of literature data. The reduced-order model does not represent more than the most relevant effects on the FOWT system dynamics. It includes first-order and second-order wave forces, coupled with the wind turbine structural dynamics, aerodynamics and control system dynamics. So far, the viscous drag coefficients are usually defined as constants, independent of the load cases. With the computationally efficient frequency-domain model, it is possible to iterate the drag, such that it fits to the obtained amplitudes of oscillation of the different members. The results show that the drag coefficients vary significantly across operational load conditions. The viscous drag coefficients converge quickly and the method is applicable for concept-level design studies of FOWTs with load case-dependent drag.

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