scholarly journals Aeroelastic stability of idling wind turbines

2017 ◽  
Vol 2 (2) ◽  
pp. 415-437 ◽  
Author(s):  
Kai Wang ◽  
Vasilis A. Riziotis ◽  
Spyros G. Voutsinas
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Operation Mode ◽  
Nonlinear Effects ◽  
Eigenvalue Stability ◽  
Out Of Plane ◽  
Aeroelastic Simulations ◽  
The Time Domain ◽  
Work Done ◽  
Nonlinear Time Domain

Abstract. Wind turbine rotors in idling operation mode can experience high angles of attack within the post-stall region that are capable of triggering stall-induced vibrations. The aim of the present paper is to extend the existing knowledge on the dynamics and aerodynamics of an idling wind turbine and characterize its stability. Rotor stability in slow idling operation is assessed on the basis of nonlinear time domain and linear eigenvalue analyses. The aim is to establish when linear analysis is reliable and identify cases for which nonlinear effects are significant. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First, the flow conditions that are likely to favor stall-induced instabilities are identified through nonlinear time domain aeroelastic simulations. Next, for the above specified conditions, eigenvalue stability analysis is performed to identify the low damped modes of the turbine. The eigenvalue stability results are evaluated through computations of the work done by the aerodynamic forces under imposed harmonic motion following the shape and frequency of the various modes. Nonlinear work characteristics predicted by the ONERA and Beddoes–Leishman (BL) dynamic stall models are compared. Both the eigenvalue and work analyses indicate that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the nonlinear work analysis and the time domain simulations.

scholarly journals Aeroelastic Stability of Idling Wind Turbines

2016 ◽  
Author(s):  
Kai Wang ◽  
Vasilis A. Riziotis ◽  
Spyros G. Voutsinas
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Linear Time ◽  
Operation Mode ◽  
Time Domain Analysis ◽  
Eigenvalue Analysis ◽  
Eigenvalue Stability ◽  
Non Linear ◽  
Aeroelastic Simulations ◽  
The Time Domain

Abstract. Wind turbine rotors in idling operation mode can experience high angles of attack, within the post stall region that are capable of triggering stall-induced vibrations. In the present paper, rotor stability in slow idling operation is assessed on the basis of non-linear time domain and linear eigenvalue analyses. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First, the flow conditions that are likely to favour stall induced instabilities are identified through non-linear time domain aeroelastic simulations. Next, for the above specified conditions, eigenvalue stability simulations are performed aiming at identifying the low damped modes of the turbine. The eigenvalue stability results are evaluated through computations of the work of the aerodynamic forces under imposed harmonic motion following the shape and frequency of the various modes. Eigenvalue analysis indicates that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the non-linear work analysis and the time domain analysis.

On the Parallelization of a Harmonic Balance Compressible Navier-Stokes Solver for Wind Turbine Aerodynamics

2011 ◽  
Author(s):  
Adrian Jackson ◽  
M. Sergio Campobasso ◽  
Mohammad H. Baba-Ahmadi
Keyword(s):  
Flow Field ◽  
Domain Decomposition ◽  
Wind Turbine ◽  
Time Domain ◽  
Harmonic Balance ◽  
Unsteady Aerodynamics ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Navier Stokes ◽  
The Time Domain

The paper discusses the parallelization of a novel explicit harmonic balance Navier-Stokes solver for wind turbine unsteady aerodynamics. For large three-dimensional problems, the use of a standard MPI parallelization based on the geometric domain decomposition of the physical domain may require an excessive degree of partitioning with respect to that needed when the same aerodynamic analysis is performed with the time-domain solver. This occurrence may penalize the parallel efficiency of the harmonic balance solver due to excessive communication among MPI processes to transfer halo data. In the case of the harmonic balance analysis, the necessity of further grid partitioning may arise because the memory requirement of each block is higher than for the time-domain analysis: it is that of the time-domain analysis multiplied by a variable proportional to the number of complex harmonics used to represent the sought periodic flow field. A hybrid multi-level parallelization paradigm for explicit harmonic balance Navier-Stokes solvers is presented, which makes use of both distributed and shared memory parallelization technologies, and removes the need for further domain decomposition with respect to the case of the time-domain analysis. The discussed parallelization approaches are tested on the multigrid harmonic balance solver being developed by the authors, considering various computational configurations for the CFD analysis of the unsteady flow field past the airfoil of a wind tubine blade in yawed wind.

Whipping Response of Vessels With Large Amplitude Motions

2006 ◽  
Author(s):  
Nuno Fonseca ◽  
Eduardo Antunes ◽  
Carlos Guedes Soares
Keyword(s):  
Time Domain ◽  
Large Amplitude ◽  
Nonlinear Effects ◽  
Regular Waves ◽  
Structural Dynamic ◽  
Highly Nonlinear ◽  
Large Amplitude Motions ◽  
Structural Dynamic Characteristics ◽  
The Time Domain ◽  
Equations Of Motions

The paper presents a time domain method to calculate the ship responses in heavy weather, including the global structural loads due to whipping. Since large amplitude waves induce nonlinear ship responses, and in particular highly nonlinear vertical structural loads, the equations of motions and structural loads are solved in the time domain. The “partially nonlinear” time domain seakeeping program accounts for the most important nonlinear effects. Slamming forces are given by the contribution of two components: an initial impact due to bottom slamming and flare slamming due to the variation of momentum of the added mass. The hull vibratory response is calculated applying the modal analysis together with direct integration of the differential equations in the time domain. The structural dynamic characteristics of the hull are modeled by a finite element representation of a Timoshenko beam accounting for the shear deformation and rotary inertia. The calculation procedure is applied to a frigate advancing in regular waves. The contribution of whipping loads to the vertical bending moments on the ship structure is assessed by comparing this response with and without the hull vibration.

The Time Domain Analysis of the Flutter of Wind Turbine Blade Combined with Eigenvalue Approach

2013 ◽  
Vol 860-863 ◽  
pp. 342-347
Author(s):  
Hao Wang ◽  
Jiao Jiao Ding ◽  
Bing Ma ◽  
Shuai Bin Li
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Wind Turbine Blade ◽  
Eigenvalue Approach ◽  
Characteristic Roots ◽  
Eigenvalue Method ◽  
The Time Domain

The aeroelasticity and the flutter of the wind turbine blade have been emphasized by related fields. The flutter of the wind turbine blade airfoil and its condition will be focused on. The eigenvalue method and the time domain analysis method will be used to solve the flutter of the wind turbine blade airfoil respectively. The flutter problem will be firstly solved using eigenvalue approach. The flutter region, where the flutter will occur and anti-flutter region, where the flutter will not occur, will be obtained directly by judging the sign of the real part of the characteristic roots of the blade system. Then the time domain analysis of flutter of wind turbine blade will be carried out through the use of the four-order Runge-Kutta numerical methods, the flutter region and the anti-flutter region will be gotten in another way. The time domain analysis can give the changing treads of the aeroelastic responses in great detail than those of the eigenvalue method. The flap displacement of wind turbine blade airfoil will change from convergence to divergence, and change from divergence to convergence extremely suddenly. During the flutter region, the flutter of wind turbine blade will occur extremely dramatically. The flutter region provided by the time domain analysis of the flutter of the blade airfoil accurately coincides with the results of eigenvalue approach, therefore the simulation results are reliable and credible.

Analysis of Brief Tension Loss in TLP Tethers

1988 ◽  
Vol 110 (1) ◽  
pp. 43-47 ◽  
Author(s):  
J. N. Brekke ◽  
T. N. Gardner
Keyword(s):  
Time Domain ◽  
Large Diameter ◽  
Nonlinear Effects ◽  
Response Analysis ◽  
Bending Stress ◽  
Large Wave ◽  
Wave Trough ◽  
Design Selection ◽  
The Time Domain ◽  
Selection Of

The avoidance of “slack” tethers is one of the factors which may establish the required tether pretension in a tension leg platform (TLP) design. Selection of an appropriate safety factor on loss of tension depends on how severe the consequences may be. It is sometimes argued that if tethers go slack, the result may be excessive platform pitch or roll motions, tether buckling, or “snap” or “snatch” loading of the tether. The results reported here show that a four-legged TLP would not be susceptible to larger angular motions until two adjacent legs lose tension simultaneously. Even then, this analysis shows that a brief period of tether tension loss (during the passage of a large wave trough) does not lead to excessive platform motion. Similarly, momentary tension loss does not cause large bending stress in the tether or significant tension amplification as the tether undergoes retensioning. This paper presents TLP platform and tether response analysis results for a representative deepwater Gulf of Mexico TLP with large-diameter, self-buoyant tethers. The time-domain, dynamic computer analysis included nonlinear effects and platform/tether coupling.

Numerical modeling of wind turbine aerodynamic noise in the time domain

2013 ◽  
Vol 133 (2) ◽  
pp. EL94-EL100 ◽  
Author(s):  
Seunghoon Lee ◽  
Seungmin Lee ◽  
Soogab Lee
Keyword(s):  
Numerical Modeling ◽  
Wind Turbine ◽  
Time Domain ◽  
Aerodynamic Noise ◽  
The Time Domain

scholarly journals Solution of the Burgers Equation in the Time Domain

10.14311/340 ◽  
2002 ◽  
Vol 42 (2) ◽  
Author(s):  
M. Bednařík ◽  
P. Koníček ◽  
M. Červenka
Keyword(s):  
Saddle Point ◽  
Time Domain ◽  
Acoustic Waves ◽  
Burgers Equation ◽  
Nonlinear Effects ◽  
Finite Amplitude ◽  
Theoretical Description ◽  
Saddle Point Method ◽  
Order Of Accuracy ◽  
The Time Domain

This paper deals with a theoretical description of the propagation of a finite amplitude acoustic waves. The theory based on the homogeneous Burgers equation of the second order of accuracy is presented here. This equation takes into account both nonlinear effects and dissipation. The method for solving this equation, using the well-known Cole-Hopf transformation, is presented. Two methods for numerical solution of these equations in the time domain are presented. The first is based on the simple Simpson method, which is suitable for smaller Goldberg numbers. The second uses the more advanced saddle point method, and is appropriate for large Goldberg numbers.

A Complex Frequency Domain Model of Wind Turbine Structures

1995 ◽  
Vol 117 (4) ◽  
pp. 311-317 ◽  
Author(s):  
P. So̸rensen ◽  
G. C. Larsen ◽  
C. J. Christensen
Keyword(s):  
Wind Turbine ◽  
Frequency Domain ◽  
Time Domain ◽  
Domain Model ◽  
Horizontal Axis ◽  
Complex Frequency ◽  
Horizontal Axis Wind Turbine ◽  
The Time Domain

The present paper describes a frequency domain model of the structure of an operating horizontal axis wind turbine with three or more blades. The frequency domain model is implemented along with an analogous time domain model in a PC code. This PC code is used to verify the frequency domain model comparing loads on the structure calculated with the frequency domain model both to loads calculated with the time domain model and to measured loads.

scholarly journals Transient Response Estimation of an Offshore Wind Turbine Support System

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 891 ◽  
Author(s):  
Fushun Liu ◽  
Xingguo Li ◽  
Zhe Tian ◽  
Jianhua Zhang ◽  
Bin Wang
Keyword(s):  
Wind Turbine ◽  
Frequency Domain ◽  
Transient Response ◽  
Time Domain ◽  
Initial Conditions ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Domain Method ◽  
The Time Domain ◽  
External Loads

To obtain reliable estimations of the dynamic responses of high-rising marine structures such as offshore wind turbines with obvious nonzero initial conditions, traditional frequency-domain methods cannot be employed because they provide only steady-state results. A novel frequency-domain transient response estimation method for offshore wind turbines is presented in this paper. This method builds upon a recent, significant theoretical development, which found that expressions of external loads in the frequency domain can be obtained by discretizing their eigenvalues and corresponding complex coefficients rather than directly by discrete Fourier transform (DFT) analysis, which makes it possible to deal with nonzero conditions in the frequency domain. One engineering advantage of this approach is its computational efficiency, as the motion equations of the system can be solved in the frequency domain. In order to demonstrate this approach, a case of a monopile-supported wind turbine with nonzero initial conditions was investigated. The numerical results indicate that the approach matches well with the time-domain method, except for a small, earlier portion of the estimated responses. A second case study of a sophisticated, jacket support wind turbine, involving practical issues such as complex external loads and computation efficiency, is also discussed, and comparisons of the results with the time-domain method and traditional frequency-domain method using the commercial software ANSYS are included here.

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