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Paul Fromme - One of the best experts on this subject based on the ideXlab platform.
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Modelling wind turbine tower-rotor interaction through an Aerodynamic Damping matrix
Journal of Sound and Vibration, 2020Co-Authors: Chao Chen, Philippe Duffour, Paul FrommeAbstract:Abstract Current wind turbine modelling packages mainly adopt a complex methodology in which Aerodynamic forces are coupled with the motion of the wind turbine components at every time step. This can result in long simulation run times, detrimental for the large number of simulations required for fatigue or reliability analyses. This contribution presents an efficient wind turbine modelling methodology based on blade element momentum theory and a linearization of the Aerodynamic forces. This allows the wind-rotor interaction to be reduced to static forces applied at the tower top, with additional terms proportional to the tower velocities expressed as an Aerodynamic Damping matrix. This Aerodynamic model was implemented as part of a finite element model of the tower and was successfully verified against the fully-coupled modelling package FAST. The Damping matrix components explain key features of the coupling between fore-aft and side-side vibrations of the wind turbine. This coupling causes energy transfers between the two directions, complicating Aerodynamic Damping identification. The Aerodynamic Damping matrix offers novel insights and an efficient method to describe the Aerodynamic Damping of wind turbines.
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Identification of Aerodynamic Damping matrix for operating wind turbines
Mechanical Systems and Signal Processing, 2026Co-Authors: Chao Chen, Philippe Duffour, Kaoshan Dai, Ying Wang, Paul FrommeAbstract:Abstract Accurate knowledge of wind turbine tower vibration Damping is essential for the estimation of fatigue life. However, the responses in the fore-aft and side-side directions are coupled through the wind-rotor interaction under operational conditions. This causes energy transfers and complicates Aerodynamic Damping identification using conventional Damping ratios. Employing a reduced two-degree of freedom wind turbine model developed in this paper, this coupling can be accurately expressed by an unconventional Aerodynamic Damping matrix. Simulated time series obtained from this model were successfully verified against the outputs from the wind turbine simulation tool FAST. Based on the reduced system obtained, a matrix-based identification method is proposed to identify the Aerodynamic Damping for numerically simulated wind turbine tower responses. Applying harmonic excitations to the tower allowed the frequency response functions of the wind turbine system to be obtained and the Aerodynamic Damping matrix to be extracted. Results from this identification were compared to traditional operational modal analysis methods including standard and modified stochastic subspace identification. The Damping in the fore-aft direction was successfully identified by all methods, but results showed that the identified Damping matrix performs better in capturing the Aerodynamic Damping and coupling for the side-side responses.
Søren Nielsen - One of the best experts on this subject based on the ideXlab platform.
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online dwt algorithm for identification of Aerodynamic Damping in wind turbines
Mechanical Systems and Signal Processing, 2021Co-Authors: Bei Chen, Zili Zhang, Xugang Hua, Biswajit Basu, Zhouquan Feng, Zhengqing Chen, Søren NielsenAbstract:Abstract A new online identification method for estimating the time-varying Aerodynamic Damping of a wind turbine is proposed. Through a combination of measured aeroelastic response data and an aeroelastic wind turbine model, the time-varying Aerodynamic Damping matrix can be identified with the aid of the real-time Discrete Wavelet Transform (DWT) technique. The proposed method is validated by means of a 13-DOF aero-servo-elastic wind turbine model, which is used to mimic the in situ aeroelastic response of the NREL 5 MW wind turbine. A measurement noise sensitivity survey is conducted. Results from current DWT-based estimation method are compared with those from previously proposed Continues Wavelet Transform (CWT)-based estimation method and found to be superior in terms of accuracy and efficiency.
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Identification of Aerodynamic Damping in wind turbines using time-frequency analysis
Mechanical Systems and Signal Processing, 2017Co-Authors: Bei Chen, Zili Zhang, Xugang Hua, Biswajit Basu, Søren NielsenAbstract:Abstract The paper presents a wavelet-based linearization method for evaluating Aerodynamic Damping of a wind turbine during operation. The method is used to estimate the Aerodynamic Damping solely from actual measurements of the dynamic response of the operating wind turbine due to ambient excitation from air turbulence and control forces. Based on the response measurements the generalised displacement, velocity and acceleration vectors related to a given aeroelastic model and an available aeroelastic code are estimated by a state observer. Then, the external generalised load vector, depending on the generalised velocity vector, is obtained from the aeroelastic code. Next, the external generalised load vector is linearized into two parts: a quasi-static load vector independent on the generalised velocity vector and a first order term linearly proportional to the velocity vector indicating the Aerodynamic Damping matrix. Filtering technique is applied to evaluate the quasi-static load vector from the actual measurements of the structural stiffness force, made up as a product of the time-dependent stiffness matrix and the estimated generalised displacement vector. Finally, the time-dependent Aerodynamic Damping matrix has been evaluated by wavelet analysis at each time step. Unlike other inverse-based approaches, this wavelet-based method can avoid calculating the inverse of the velocity vector covariance matrix, which is singular. The proposed method has been illustrated by a reduced 13-DOF aeroelastic model, which is used to mimic the in situ response measured on the wind turbine.
Bei Chen - One of the best experts on this subject based on the ideXlab platform.
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online dwt algorithm for identification of Aerodynamic Damping in wind turbines
Mechanical Systems and Signal Processing, 2021Co-Authors: Bei Chen, Zili Zhang, Xugang Hua, Biswajit Basu, Zhouquan Feng, Zhengqing Chen, Søren NielsenAbstract:Abstract A new online identification method for estimating the time-varying Aerodynamic Damping of a wind turbine is proposed. Through a combination of measured aeroelastic response data and an aeroelastic wind turbine model, the time-varying Aerodynamic Damping matrix can be identified with the aid of the real-time Discrete Wavelet Transform (DWT) technique. The proposed method is validated by means of a 13-DOF aero-servo-elastic wind turbine model, which is used to mimic the in situ aeroelastic response of the NREL 5 MW wind turbine. A measurement noise sensitivity survey is conducted. Results from current DWT-based estimation method are compared with those from previously proposed Continues Wavelet Transform (CWT)-based estimation method and found to be superior in terms of accuracy and efficiency.
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Identification of Aerodynamic Damping in wind turbines using time-frequency analysis
Mechanical Systems and Signal Processing, 2017Co-Authors: Bei Chen, Zili Zhang, Xugang Hua, Biswajit Basu, Søren NielsenAbstract:Abstract The paper presents a wavelet-based linearization method for evaluating Aerodynamic Damping of a wind turbine during operation. The method is used to estimate the Aerodynamic Damping solely from actual measurements of the dynamic response of the operating wind turbine due to ambient excitation from air turbulence and control forces. Based on the response measurements the generalised displacement, velocity and acceleration vectors related to a given aeroelastic model and an available aeroelastic code are estimated by a state observer. Then, the external generalised load vector, depending on the generalised velocity vector, is obtained from the aeroelastic code. Next, the external generalised load vector is linearized into two parts: a quasi-static load vector independent on the generalised velocity vector and a first order term linearly proportional to the velocity vector indicating the Aerodynamic Damping matrix. Filtering technique is applied to evaluate the quasi-static load vector from the actual measurements of the structural stiffness force, made up as a product of the time-dependent stiffness matrix and the estimated generalised displacement vector. Finally, the time-dependent Aerodynamic Damping matrix has been evaluated by wavelet analysis at each time step. Unlike other inverse-based approaches, this wavelet-based method can avoid calculating the inverse of the velocity vector covariance matrix, which is singular. The proposed method has been illustrated by a reduced 13-DOF aeroelastic model, which is used to mimic the in situ response measured on the wind turbine.
John H G Macdonald - One of the best experts on this subject based on the ideXlab platform.
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aeroelastic stability of a 3dof system based on quasi steady theory with reference to inertial coupling
Journal of Wind Engineering and Industrial Aerodynamics, 2017Co-Authors: John H G MacdonaldAbstract:Abstract This paper investigates the galloping stability of a two-dimensional three-degree-of-freedom (3DOF) system with an eccentric shape, such as an iced cable or power transmission line, incorporating inertial coupling along with the Aerodynamic Damping. The inertial coupling is a result of the offset of the centre of mass with respect to the elastic centre. A theoretical model is firstly constructed for the derivation of the Aerodynamic Damping matrix, based on quasi-steady theory, as well as the inertial coupling components in the mass matrix. The model is then employed to investigate the effects on the aeroelastic stability of the system of incorporating the inertial coupling and the results are compared with both dynamic test results and predictions from previous models. The comparisons indicate that even small eccentricity can lead to significant change of the stability of the system, for both detuned and perfectly tuned natural frequencies of the different degrees of freedom. For a system with perfectly tuned natural frequencies, and neglecting structural Damping, analytical solutions of the eigenfrequencies and eigenvectors allowing for the inertial coupling, are derived for the case of no wind. Subsequently, an approximate solution is found for the prediction of the galloping stability of a system coupled by the Aerodynamic Damping as well as the inertial coupling. Finally, the approximate solution is verified against numerical results using examples with two cross-section shapes, showing excellent agreement.
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An analytical solution for the galloping stability of a 3 degree-of-freedom system based on quasi-steady theory
Journal of Fluids and Structures, 2016Co-Authors: Mingzhe He, John H G MacdonaldAbstract:The Aerodynamic forces on a two-dimensional three-degree-of-freedom (3DOF-heave, sway and torsion) body of arbitrary cross-section are considered, for arbitrary wind direction relative to the principal structural axes. The full 3DOF Aerodynamic Damping matrix is derived, based on quasi-steady theory, using the commonly-used concept of an Aerodynamic centre to represent the effect of the torsional velocity on the Aerodynamic forces. The Aerodynamic coefficients are assumed to be consistent functions of only the relative angle of attack. It is shown that the determinant of the quasi-steady Aerodynamic Damping matrix is always zero. The galloping stability of the Aerodynamically coupled system is then addressed by formulating the eigenvalue problem, for which analytical solutions are derived for the case of perfectly tuned structural natural frequencies. The solutions define a non-dimensional effective Aerodynamic Damping coefficient, indicating how stable the system is. A trivial solution always exists, with zero effective Aerodynamic Damping, corresponding to rotation about the Aerodynamic centre, and relatively simple exact closed-form solutions are derived for the other one or two solutions, the minimum solution defining the stability of the system. Example results are presented and discussed for square, rectangular (aspect ratio 3) and equilateral triangular sections and a lightly iced cable, and they are compared with results using previous solutions for 2DOF translational and 1DOF pure torsional galloping. For the shapes considered it is found that the stability of the 3DOF system is normally close to that of the 2DOF translational system, with a relatively small influence of the stability of the torsional degree of freedom, although in some instances, especially at the critical angles of attack, it can significantly affect the stability.
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a unified approach to Aerodynamic Damping and drag lift instabilities and its application to dry inclined cable galloping
Journal of Fluids and Structures, 2006Co-Authors: John H G Macdonald, G L LaroseAbstract:Inclined cables of cable-stayed bridges often experience large amplitude vibrations. One of the potential excitation mechanisms is dry inclined cable galloping, which has been observed in wind tunnel tests but which has not previously been fully explained theoretically. In this paper, a general expression is derived for the quasi-steady Aerodynamic Damping (positive or negative) of a cylinder of arbitrary cross-section yawed/inclined to the flow, for small amplitude vibrations in any plane. The expression covers the special cases of conventional quasi-steady Aerodynamic Damping, Den Hartog galloping and the drag crisis, as well as dry inclined cable galloping. A nondimensional Aerodynamic Damping parameter governing this behaviour is proposed, which is a function of only the Reynolds number, the angle between the wind velocity and the cable axis, and the orientation of the vibration plane. Measured static force coefficients from wind tunnel tests have been used with the theoretical expression to predict values of this parameter. Two main areas of instability (i.e. negative Aerodynamic Damping) have been identified, both in the critical Reynolds number region, one of which was previously observed in separate wind tunnel tests on a dynamic cable model. The minimum values of structural Damping required to prevent dry inclined cable galloping are defined, and other factors in the behaviour in practice are discussed.
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separation of the contributions of Aerodynamic and structural Damping in vibrations of inclined cables
Journal of Wind Engineering and Industrial Aerodynamics, 2002Co-Authors: John H G MacdonaldAbstract:Abstract Large amplitude cable vibrations have occurred on several major cable-stayed bridges. Complex mechanisms including rain-wind excitation and possibly cable–deck interaction have been responsible, but the extremely low level of Damping of bridge cables has been an important contributory factor. Measurements of cable Damping have been undertaken on several cable-stayed bridges, but previously, the full contribution of Aerodynamic Damping, which could be a significant proportion of the total measured Damping, has not been considered. To address this issue, theoretical expressions for the Aerodynamic Damping are proposed for the general case of an inclined cable and an arbitrary wind velocity, for both in-plane and out-of-plane vibrations. Damping estimates from cable vibration tests during construction of the Second Severn Crossing cable-stayed bridge, with varying wind velocity, have shown the expression for in-plane cable vibrations to give good estimates of the actual Aerodynamic Damping. The remaining contribution from structural Damping is also determined and the effects of the injection of corrosion prevention wax into the cable sheaths, temperature, and interaction with other cables are considered.
Xiong Liu - One of the best experts on this subject based on the ideXlab platform.
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effects of Aerodynamic Damping on the tower load of offshore horizontal axis wind turbines
Applied Energy, 2017Co-Authors: Xiong Liu, Ajit R Godbole, Yan ChenAbstract:Aerodynamic Damping has an important effect on the dynamic response of offshore Horizontal Axis Wind Turbines (HAWTs). In this paper, an analysis of the loads on offshore HAWTs is presented. The analysis combines the Aerodynamics, hydrodynamics and structural dynamics of the structure, and includes the effects of Aerodynamic Damping. The aim is to better understand the role of Aerodynamic Damping during the interaction of wind and wave and the structure, and to quantitatively evaluate the effects of Aerodynamic Damping on the lifetime fatigue load on offshore HAWT towers. The Aerodynamic loads are estimated using the Blade Element-Momentum (BEM) theory, including the effects of dynamic inflow and dynamic stall. The wave dynamics is estimated assuming ‘random sea state’ described by the JONSWAP spectrum, with wave loads calculated using Morison’s equation and water kinematics modelled using linear wave theory. Two Aerodynamic Damping models are proposed: (1) a model based on the analysis of the rotor Aerodynamics incorporating the tower-top motion of a constant-speed wind turbine, which is then modified for variable-speed wind turbines by introducing a correction factor; and (2) a model based on Salzmann and van der Tempel’s method (Salzmann and van der Tempel, 2005) to calculate the Aerodynamic Damping as the increase in the thrust per unit increase in the wind speed. The models are incorporated into a transient load analysis. The effects of Aerodynamic Damping on the lifetime fatigue loads of the tower are then investigated through load analysis of a 5MW offshore HAWT. In addition, the influence of different Aerodynamic Damping calculation methods on the prediction of fatigue loads is studied.