Effect of Second-Order and Fully Nonlinear Wave Kinematics on a Tension-Leg-Platform Wind Turbine in Extreme Wave Conditions

2017 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Henrik Bredmose
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Second Order ◽  
Surface Elevation ◽  
Tension Leg Platform ◽  
Fully Nonlinear ◽  
Wave Kinematics ◽  
Wave Basin ◽  
Definition Of ◽  
The Impact

In this study, we assess the impact of different wave kinematics models on the dynamic response of a tension-leg-platform wind turbine. Aero-hydro-elastic simulations of the floating wind turbine are carried out employing linear, second-order, and fully nonlinear kinematics using the Morison equation for the hydrodynamic forcing. The wave kinematics are computed from either theoretical or measured signals of free-surface elevation. The numerical results from each model are compared to results from wave basin tests on a scaled prototype. The comparison shows that sub and superharmonic responses can be introduced by second-order and fully nonlinear wave kinematics. The response at the wave frequency range is better reproduced when kinematics are generated from the measured surface elevation. In the future, the numerical response may be further improved by replacing the global, constant damping coefficients in the model by a more detailed, customizable definition of the user-defined numerical damping.

scholarly journals A study on fully nonlinear wave load effects on floating wind turbine

2019 ◽  
Vol 88 ◽  
pp. 216-240 ◽  
Author(s):  
Kun Xu ◽  
Yanlin Shao ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wave Load ◽  
Fully Nonlinear ◽  
Floating Wind Turbine ◽  
Load Effects

scholarly journals Numerical modeling and preliminary validation of drag-based vertical axis wind turbine

2015 ◽  
Vol 36 (1) ◽  
pp. 19-38 ◽  
Author(s):  
Tomasz Krysiński ◽  
Zbigniew Buliński ◽  
Andrzej J. Nowak
Keyword(s):  
Wind Turbine ◽  
Vertical Axis ◽  
Boundary Layer Separation ◽  
Complex Nature ◽  
Vertical Axis Wind Turbine ◽  
Preliminary Validation ◽  
Definition Of ◽  
Key Aspects ◽  
Simulation Parameters ◽  
The Impact

Abstract The main purpose of this article is to verify and validate the mathematical description of the airflow around a wind turbine with vertical axis of rotation, which could be considered as representative for this type of devices. Mathematical modeling of the airflow around wind turbines in particular those with the vertical axis is a problematic matter due to the complex nature of this highly swirled flow. Moreover, it is turbulent flow accompanied by a rotation of the rotor and the dynamic boundary layer separation. In such conditions, the key aspects of the mathematical model are accurate turbulence description, definition of circular motion as well as accompanying effects like centrifugal force or the Coriolis force and parameters of spatial and temporal discretization. The paper presents the impact of the different simulation parameters on the obtained results of the wind turbine simulation. Analysed models have been validated against experimental data published in the literature.

scholarly journals Mitigating impact of spatial variance of turbulence in wind energy applications

2020 ◽  
Vol 5 (2) ◽  
pp. 439-450
Author(s):  
Jonas Kazda ◽  
Jakob Mann
Keyword(s):  
Wind Turbine ◽  
Random Error ◽  
Wind Farm ◽  
Second Order ◽  
Mitigation Measures ◽  
Order Moment ◽  
Spatial Variance ◽  
Turbine Performance ◽  
The Difference ◽  
The Impact

Abstract. For the first time an analytical solution for the quantification of the spatial variance of the second-order moment of correlated wind speeds was developed in this work. The spatial variance is defined as random differences in the sample variance of wind speed between different points in space. The approach is successfully verified using simulation and field data. The impact of the spatial variance on three selected applications relevant to the wind energy sector is then investigated including mitigation measures. First, the difference of the second-order moment between front-row wind turbines of Lillgrund wind farm is investigated. The variance of the difference ranges between 25 % and 48 % for turbulence intensities ranging from 7 % to 10 % and a sampling period of 10 min. It is thus suggested to use the second-order moment measured at each individual turbine as input to flow models of wind farm controllers in order to mitigate random error. Second, the impact of the spatial variance of the measured second-order moment on the verification of wind turbine performance is investigated. Misalignment between the mean wind direction and the line connecting the meteorological mast and wind turbine is observed to result in an additional random error in the observed second-order moment of wind speed. In the investigated conditions the random error was up to 34 %. Such a random error adds uncertainty to the turbulence intensity-based classification of the fatigue loads and power output of a wind turbine. To mitigate the random error, it is suggested to either filter the measured data for low angles of misalignment or quantify wind turbine performance using the ensemble-averaged measurements of the same wind conditions. Third, the verification of sensors in wind farms was investigated with respect to the impact of distant reference measurements. In the case of a misalignment between the wind direction and the line connecting sensor and reference, an increased random error will hamper the comparison of the measured second-order moments. The suggested mitigation measures are equivalent to those for the verification of turbine performance.

scholarly journals EXPERIMENTAL STUDY ON THE LOADING AND SCOUR OF THE JACKET TYPE OFFSHORE WIND TURBINE FOUNDATION

2011 ◽  
Vol 1 (32) ◽  
pp. 25
Author(s):  
Ray-Yeng Yang ◽  
Hsin-Hung Chen ◽  
Hwung-Hweng Hwung ◽  
Wen-Pin Jiang ◽  
Nian-Tzu Wu
Keyword(s):  
Wind Turbine ◽  
Water Depth ◽  
Fixed Bed ◽  
Offshore Wind ◽  
Scale Model ◽  
Offshore Wind Turbine ◽  
Wave Flume ◽  
Wave Basin ◽  
Scour Protection ◽  
The Impact

A 1:36 scale model tests were carried out in the Medium Wave Flume (MWF) and Near-shore Wave Basin (NSWB) at the Tainan Hydraulics Laboratory (THL) with the jacket type offshore wind turbine foundation located in the test area. The loading of typhoon wave with current on the jacket type offshore wind turbine foundation was investigated in the MWF with fixed bed experiment. Meanwhile, the scour around the jacket type offshore wind turbine foundation exposed to wave and current was conducted in the NSWB with the moveable bed experiment. Two locations (water depth 12m and 16m) of the foundations are separately simulated in this study. Based on the analysis from the former NSWB experimental results, the suitable scour protection of a four-layer work around the foundation is also proposed to the impact of scour. Finally, a four-layer scour protection is tested and found to be effective in preventing scour around jacket type foundation of offshore wind turbines at water depth 12m and 16m.

scholarly journals Water wave diffraction by a cylinder array. Part 1. Regular waves

2001 ◽  
Vol 442 ◽  
pp. 1-32 ◽  
Author(s):  
C. O. G. OHL ◽  
R. EATOCK TAYLOR ◽  
P. H. TAYLOR ◽  
A. G. L. BORTHWICK
Keyword(s):  
Free Surface ◽  
Diffraction Theory ◽  
Second Order ◽  
Surface Elevation ◽  
Circular Cylinders ◽  
Regular Waves ◽  
Wave Basin ◽  
Measured Time ◽  
Field Radiation ◽  
Offshore Wave

Diffraction of regular waves by arrays of vertical bottom-mounted circular cylinders is investigated using theoretical, computational, and experimental methods. Experiments in an offshore wave basin are designed to measure free surface elevation η at multiple locations in the vicinity of a multi-column structure subjected to regular waves of frequency 0.449 < ka < 0.524 and steepness 0.122 < kA < 0.261, where k is the wavenumber, a the cylinder radius and A the wave amplitude. Results from regular wave data analysis for first-order amplitudes are compared with those from analytical linear diffraction theory, which is shown to be accurate for predicting incident waves of low steepness. Second- and third-order terms are also estimated from the measured time series, and the effects near a second-order near-trapping frequency are compared to semi-analytical second-order diffraction theory. Linear diffraction theory is shown to be very accurate at predicting the global surface elevation features, even for waves of high steepness. However, violent events and significant nonlinear interactions, including breaking induced by wave scattering, have been observed. Furthermore, second-order near-trapping was observed to affect the magnitude of local free surface oscillations as well as scattered far-field radiation.

Using Nonlinear Wave Kinematics to Estimate the Loads on Offshore Wind Turbines in 3-Hour Sea States

2018 ◽  
Author(s):  
Tim Bunnik ◽  
Erik-Jan de Ridder
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wind Turbines ◽  
Wave Model ◽  
Breaking Waves ◽  
Model Tests ◽  
Offshore Wind ◽  
Wave Loads ◽  
Offshore Wind Turbines ◽  
Wave Basin

The effects of operational wave loads and wind loads on offshore mono pile wind turbines are well understood. For most sites, however, the water depth is such that breaking or near-breaking waves will occur causing impulsive excitation of the mono pile and consequently considerable stresses, displacements and accelerations in the monopile, tower and turbine. As has been shown in earlier, recent publications, Computational Fluid Dynamics (CFD) can be used to accurately analyze wave impacts on offshore wind turbines. However, it is not yet well suited to study the statistical variability of wave impact loads in long-duration sea states, and thus estimate the ULS and ALS loads for which a wind turbine has to be designed. An alternative, simplified approach, is the use of a Morison model in which the kinematics (water particle velocities and accelerations) from a nonlinear wave model are used. For long-crested waves the nonlinear wave model can be run in a 2D mode and is therefore relatively cheap. In this paper model tests for steep and breaking waves on an offshore wind turbine are compared with results from the Morison model. First, a deterministic comparison is made between the wave loads from the model tests and the simulation model (simulating the same 3-hour wave realization as in the basin), which turns out to be difficult because of differences between wave reflections in the wave basin (a physical beach) and the numerical wave model (absorbing boundary condition). Second, a statistical comparison is made by comparing with different wave realizations measured in the wave basin.

scholarly journals Mitigating Impact of Spatial Variance of Turbulence in Wind Energy Applications

2019 ◽  
Author(s):  
Jonas Kazda ◽  
Jakob Mann
Keyword(s):  
Wind Turbine ◽  
Random Error ◽  
Wind Farm ◽  
Second Order ◽  
Mitigation Measures ◽  
Order Moment ◽  
Spatial Variance ◽  
Turbine Performance ◽  
The Difference ◽  
The Impact

Abstract. The first analytical solution for the quantification of the spatial variance of the second-order moment of correlated wind speeds was developed in this work. The spatial variance is defined as random differences in the sample variance of wind speed between different points in space. The approach is successfully verified using simulation and field data. The impact of the spatial variance on three selected applications relevant to the wind energy sector is then investigated including mitigation measures. First, the difference of the second-order moment between front-row wind turbines of Lillgrund wind farm is investigated. The variance of the difference ranges between 25 % and 48 % for turbulence intensities ranging from 7 % to 10 % and a sampling period of 10 min. It is thus suggested to use the second-order moment measured at each individual turbine as input to flow models of wind farm controllers in order to mitigate random error. Second, the impact of the spatial variance of the measured second-order moment on the verification of wind turbine performance is investigated. Misalignment between the mean wind direction and the line connecting the meteorological mast and wind turbine is observed to result in an additional random error in the observed second-order moment of wind speed. In the investigated conditions the random error was up to 34 %. Such random error adds uncertainty to the turbulence intensity-based classification of the fatigue loads and power output of a wind turbine. To mitigate the random error it is suggested to either filter the measured data for low angles of misalignment, or to quantify wind turbine performance using the ensemble averaged measurements of the same wind conditions. Third, the verification of sensors in wind farms was investigated with respect to the impact of distant reference measurements. In case of a misalignment between the wind direction and the line connecting sensor and reference, an increased random error will hamper the comparison of the measured second-order moments. The suggested mitigation measures are equivalent to those for the verification of turbine performance.

scholarly journals Second Order Ideal-Ward Continuity

2014 ◽  
Vol 2014 ◽  
pp. 1-4
Author(s):  
Bipan Hazarika
Keyword(s):  
Second Order ◽  
Order Ideal ◽  
Convergence Of Sequences ◽  
Definition Of ◽  
The Impact

The main aim of the paper is to introduce a concept of second order ideal-ward continuity in the sense that a function f is second order ideal-ward continuous if I-limn→∞Δ2f(xn)=0 whenever I-limn→∞Δ2xn=0 and a concept of second order ideal-ward compactness in the sense that a subset E of R is second order ideal-ward compact if any sequence x=(xn) of points in E has a subsequence z=(zk)=(xnk) of the sequence x such that I-limk→∞Δ2zk=0 where Δ2zk=zk+2-2zk+1+zk. We investigate the impact of changing the definition of convergence of sequences on the structure of ideal-ward continuity in the sense of second order ideal-ward continuity and compactness of sets in the sense of second order ideal-ward compactness and prove related theorems.

scholarly journals The determination of nonlinear forces of the second order during the longitudinal motions of the ship

2020 ◽  
Author(s):  
В.Ю. Семенова ◽  
Д.А. Альбаев
Keyword(s):  
Three Dimensional ◽  
Nonlinear Boundary Conditions ◽  
Second Order ◽  
Heading Angle ◽  
Deep Fluid ◽  
Definition Of ◽  
The Impact ◽  
National Practice ◽  
Good Agreement

В статье рассматривается определение нелинейных сил, возникающих при продольной качке судов (продольно-горизонтальной, вертикальной и килевой) на основании трехмерной потенциальной теории. Для нахождения нелинейных сил, требуется определение потенциалов второго порядка малости. Решение основано на методах малого параметра, интегральных уравнений и функций Грина для случая глубокой воды и ограниченной глубины (при H→∞). При определении потенциалов второго порядка учитываются нелинейные граничные условия на свободной поверхности жидкости и на смоченной поверхности судна. На основании изложенного метода разработаны две программы, использующие разные функции Грина.. Приводятся результаты расчетов сил и моментов для двух разных судов. Показано практически полное согласование результатов при использовании различных функций Грина. Приведено сравнение с результатами по двумерной теории. Проведены расчеты нелинейных сил на различных курсовых углах. Показано влияние курсового угла на отдельные составляющие нелинейных сил. Показано значительное влияние потенциалов второго порядка в образовании нелинейных сил, возникающих при всех видах продольных колебаний. The article deals with the definition of nonlinear forces arising in the surge, heave and pitch motions of the ships on the basis of three-dimensional potential theory. To determine them, it is necessary to calculate the potentials of the second order of smallness. The presented solution in national practice is new. The solution of the problem is carried out on the basis of small parameter methods, integral equations and Green’s functions: for an infinitely deep fluid and a fluid of limited depth (when H→∞).During the determination of the second order potentials, nonlinear boundary conditions on the free surface of the liquid and on the wetted surface of the ship are taken into account On the basis of methods two programs were developed, using different Green functions. The results of calculations of the forces and moments for two different ships are presented. Good agreement between the results for different functions is shown. The calculations are presented in comparison with the calculations according to the two-dimensional theory. calculations were made for nonlinear forces at various heading angles. The impact of heading angle is shown.A significant influence of second-order potentials in the formation of nonlinear forces arising from all types of longitudinals motions is shown

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