Dynamic Response Of Wind Turbine Research Articles

An experimental study on the influence of wind-wave-current coupling effect on the global performance of a 12 MW semi-submersible floating wind turbine

Investigating the coupling effect between different marine environmental conditions is essential to understand the dynamic response of wind turbines. This paper presents the study findings from the model tests conducted in a wave basin, exploring the coupling effect of wind, waves, and currents on the global performance of a 1:70 scale model 12 MW semi-submersible floating wind turbine (FWT). A multi-blade large-scale wind generation system with a rectifier network was improved and fabricated to provide a reliable wind field for the experiment. The stiffness-matched and geometry-matched tower models were designed and fabricated, achieving an accurate simulation of the tower's flexibility and windward areas and their impact on the global dynamic response. Following the calibration of marine environmental conditions and the characterization of the model FWT system, the study focused on the operational and extreme responses of the FWT concept. The aerodynamic damping effect of wind in pitch and surge motions is remarkable, especially in pitch motion, primarily manifesting by reducing the standard deviation of motions. Mooring load responses are predominantly induced by the hydrodynamic effect, with the wave-frequency response gradually becoming dominant as wave parameters increase. Tower-top load responses are primarily induced by the hydrodynamic effect of waves and the aerodynamic load effect of wind. Furthermore, the phenomenon where the action of current strengthens the aerodynamic damping effect of wind is observed. The coupling effect between wind and current amplifies surge motion while diminishing pitch motion, effectively reducing the tower-top and tower-base load responses.

Dynamic analysis of a 5 MW Barge-type FOWT with two-mooring failure of wind-wave misalignment scenarios

A floating offshore wind turbine (FOWT) experiencing two mooring failure can substantially escalate the risk of persistent damage to the remaining moorings. Industry standards mandate that FOWTs must demonstrate the capability of maintaining self-sustainability even in the occurrence of dual mooring failure. Therefore, it is importance to investigate the dynamic response of wind turbines in the case of two mooring line failure. In this study, a novel coupling method of FAST and AQWA was used to analyze the dynamic response of a 5 MW FOWT installed on a barge platform when two mooring lines fail at the same corner. The time-domain response processes of rated and extreme sea conditions were simulated for different failure time intervals (0s, 60s, and 1500s), and the dynamic response of the platform and the change of mooring line tension at each stage are regularly explored. The results indicate that a shorter interval between two mooring line failures results in a more unstable FOWT state. The center of gravity of the wind turbine presents an irregular spiral trajectory, and the platform response exhibits varying characteristics at each stage of the failure process. The transient effect is smaller as the wind turbine approaches the motion limit state.

Dynamic response of OWTs under wind-wave loads considering 3D water-pile-soil interactions

A new three-dimensional (3D) integrated model of offshore wind turbine (OWT) is proposed, which considers the soil-monopile-water interactions and the accumulative deformation of foundations under cyclic loads. The effects of three different modelling methods on the dynamic response of wind turbine are discussed, where three modelling methods are the new WOT model, OWT model with a 3D soil-pile medium without a seawater domain and OWT model with API's spring-type foundation. The numerical results show that the use of API's soil spring may overestimate the fundamental frequency of OWT by up to 32.2%. This leads to inaccurate structural resonance. Meanwhile, a significant displacement drift of the tower top of the new model is observed due to the ratcheting effect, and the OWT with API's spring cannot correct this phenomenon. Consequently, the API method should be used with care in assessing dynamic performance under wind-wave loads. The added mass method considers only the water-structure interaction and excludes the soil-water interaction, and it may underestimate the responses of the tower, blades and monopile, which can render the design of wind turbines unsafe. Additionally, assumption of the parked condition underestimates the structural response, and the frequency of the blades may change during operation.

Time Domain Nonlinear Dynamic Response Analysis of Offshore Wind Turbines on Gravity Base Foundation under Wind and Wave Loads

The third-generation gravity base foundation, which consists of a concrete-based structure with infill aggregates, is designed for water depths greater than 20 m. In this study, a simplified method in the time domain for predicting the nonlinear dynamic response of the offshore wind turbine supported on the third-generation gravity base foundation is proposed. The results obtained by the proposed method are compared with 3D finite element simulations, and the consistency of the results verifies the reliability of the simplified method. In addition, the dynamic response of the wind turbine supported on GBF under wind and wave loads is investigated. The results indicate that the lateral dynamic responses of the GBF are more affected by the thrust force than by the distributed force when the wind loads are only considered; the maximum dynamic displacement of the GBF caused by the drag force is almost the same as that of the GBF caused by the inertia force when the wave loads are only considered, and the dynamic response of the GBF under combined wind and wave loads show a similar trend to that of the GBF under the wind loads only, especially the existence of a large displacement on the horizontal direction at the beginning of the loading.

Analysis of Dynamic Response Characteristics for 5 MW Jacket-type Fixed Offshore Wind Turbine

This study aims to evaluate the dynamic responses of the jacket-type offshore wind turbine using FAST software (Fatigue, Aerodynamics, Structures, and Turbulence). A systematic series of simulation cases of a 5 MW jacket-type offshore wind turbine, including wind-only, wave-only, wind & wave load cases are conducted. The dynamic responses of the wind turbine structure are obtained, including the structure displacement, rotor speed, thrust force, nacelle acceleration, bending moment at the tower bottom, and shear force on the jacket leg. The calculated time-domain results are transformed to frequency domain results using FFT and the environmental load with more impact on each dynamic response is identified. It is confirmed that the dynamic displacements of the wind turbine are dominant in the wave frequency under the incident wave alone condition, and the rotor thrust, nacelle acceleration, and bending moment at the bottom of the tower exhibit high responses in the natural frequency band of the wind turbine. In the wind only condition, all responses except the vertical displacement of the wind turbine are dominant at three times the rotor rotation frequency (considering the number of blades) generated by the wind. In a combined external force with wind and waves, it was observed that the horizontal displacement is dominant by the wind load. Additionally, the bending moment on the tower base is highly affected by the wind. The shear force of the jacket leg is basically influenced by the wave loads, but it can be affected by both the wind and wave loads especially under the turbulent wind and irregular wave conditions.

Modal decomposition of the dynamic response of wind turbine during one year of continuous monitoring

Modal decomposition of the dynamic response of wind turbine during one year of continuous monitoring

Foundations, Design, and Dynamic Performance of Wind Turbines: Overview and Challenges in Sudan

Sudan is one of the developing countries that suffers from a lack of electricity, where the national electrification rate is estimated at 38.5%. In order to solve this problem, it is possible to use renewable energy sources such as wind energy. Beside many aspects to be considered at the design of wind turbine foundations, more attention should be given to the geotechnical part. There are many types of foundations for wind turbines. The foundation must satisfy two design criteria: 1) It should be safe against bearing failure in soils under design loads and settlements during the life of the structure must not cause structural damage; 2) In addition to static loads, wind turbine foundations loads are extremely eccentrically and the loading is usually highly dynamic. Therefore, the selection of foundation type should consider these two criteria taking into account the nature and magnitude of these loads. This paper presents a review of different types of wind turbine foundations of focusing on on-shore wind turbine foundation types and the dynamic response of wind turbine. The paper also demonstrate experimentally the dynamic response of the wind turbines using wind tunnel facility test on a scaled model.  

A general frequency adaptive framework for damped response analysis of wind turbines

Dynamic response analysis of wind turbine towers plays a pivotal role in their analysis, design, stability, performance and safety. Despite extensive research, the quantification of general dynamic response remains challenging due to an inherent lack of the ability to model and incorporate damping from a physical standpoint. This paper develops a frequency adaptive framework for the analysis of the dynamic response of wind turbines under general harmonic forcing with a damped and flexible foundation. The proposed method is founded on an augmented dynamic stiffness formulation based on a Euler-Bernoulli beam-column with elastic end supports along with tip mass and rotary inertia arising from the nacelle of the wind turbine. The dynamic stiffness coefficients are derived from the complex-valued transcendental displacement function which is the exact solution of the governing partial differential equation with appropriate boundary conditions. The closed-form analytical expressions of the dynamic response derived in the paper are exact and valid for higher frequency ranges. The proposed approach avoids the classical modal analysis and consequently the ad-hoc use of the modal damping factors are not necessary. It is shown that the damping in the wind turbine dynamic analysis is completely captured by seven different physically-realistic damping factors. Numerical results shown in the paper quantify the distinctive nature of the impact of the different damping factors. The exact closed-form analytical expressions derived in the paper can be used for benchmarking related experimental and finite element studies and at the initial design/analysis stage.

Geometric nonlinear dynamic response of wind turbines with different power performance

As the size of wind turbine blades increases, the influence of geometric nonlinearity on aerodynamic, structural and design of blades becomes more and more serious. In this work, the efficient aero-elastic calculation of large flexible blades is studied. In order to solve the problem of efficient aeroelastic caculation of large flexible blades, this work applied the geometrically exact beam theory based on Legendre spectral finite element and coupled with the blade element momentum theory to establish the aero-elastic analysis model of large flexible blades. This model can efficiently calculate the deformation and load on the blade under aerodynamic loading and fully consider the influence of geometric nonlinearity caused by deformation on aeroelastic ability. Taking NREL 5MW and IEA 15MW wind turbines as examples, the linear and nonlinear dynamic responses of these two wind turbine blades are calculated. The result shows that the neglect of nonlinear effect will bring error. From 5MW wind turbine to 15MW wind turbine, the numerical error increased by 27.88%. The influence of geometric nonlinearity of blades on dynamic responses is analysed, which is of great significance to improve the design level of large-scale wind turbines.

Analysis on dynamic interaction between flexible bodies of large-sized wind turbine and its response to random wind loads

Analysis of structural dynamic response of wind turbine is one of important issues to assess its structural integrity and safety during operation process. As the output power of wind turbine increasingly gets larger, the structural flexibility of the elastic components, such as rotor blades and supporting tower, of wind turbine gets larger owing to larger structural size, and, consequently, the dynamic interaction between these flexible bodies become more profound or, even, may have a significant impact on the dynamic response of the wind turbine. In this study, the integrated finite element model of a 5-MW wind turbine is developed so as to carry out dynamic response analysis, in terms of both time history and frequency spectrum, of the large wind turbine including multiple elastic bodies and their dynamic interactions. In order to have a deeper insight into the impact and mechanism of the dynamic interaction, the load transmission along its transmitting route and mechanical energy distribution during dynamic response under random wind loads are studied. And, the influences of the stiffness and motion of the supporting tower on the integrated system response are discussed.Our numerical results show that the dynamic interaction between the elastic bodies may be significant during dynamic response. The response of the tower top becomes around 15% larger than that of the simplified model mainly due to the elastic deformation and dynamic vibration (called inertial-elastic effect) of the flexible blade; On the other hand, the elastic deformation may additionally consume around 10% energy (called energy-consuming effect) coming from external wind load, and, consequently, it could decrease the displacement of the tower. Therefore, there is a competition between the energy-consuming effect and inertial-elastic effect of the flexible blade on the overall dynamic response of the wind turbine. As for the blade response, the displacement of the blades gets up to 20% larger than that without blade-tower interaction, because the elastic-dynamic behaviors of the tower principally provides a more flexible and vibrating supporting base, which can significantly change the natural mode shape of the integrated wind turbine and can decrease the natural frequency of the blade.

Experimental and computational dynamic response comparison of hybrid and mono windmill towers considering soil–structure interaction

In countries like India, wind turbine heights are rapidly increasing to harvest more wind energy at a given location. In recent years, due to increase in hub height of windmill likelihood, soil lying below foundation may influence dynamic response of wind turbines. By increasing the height of the conventional monopole supporting system, it becomes slender and dynamically sensitive under the influence of soil below foundation; therefore, in the present investigation, hybrid supporting system is proposed to avoid slenderness effect of monopole system. A 1:40 scaled model of 78-m-high conventional monopole windmill and hybrid windmill comprised of nacelle, rotor mass and supporting tower are prepared in the laboratory. To study the behavior of both the towers under operational dynamic loads of rotor, laboratory tests were conducted on scaled model considering soil below foundation. Simulations of experimental analysis are presented for multi-degree of freedom turbine structure subjected to dynamic loading of rotor considering soil stiffness below base. It is examined in terms of displacement in time domain, shear at base of tower and response spectra. From laboratory tests and its simulation, it can be concluded that hybrid supporting system are recommended for windmill towers with higher hub heights considering soil stiffness below foundations.

Smart Rotor With Trailing Edge Flap Considering Bend–Twist Coupling and Aerodynamic Damping: Modeling and Control

Aerodynamic damping and bend–twist coupling significantly affect the dynamic response of wind turbines. In this paper, unsteady aerodynamics, aerodynamic damping, and bend–twist coupling (twist-towards-feather) are combined to establish a smart rotor model with trailing edge flaps (TEFs) based on a National Renewable Energy Laboratory (NREL) 5 MW reference horizontal-axis wind turbine. The overall idea is to quantitatively evaluate the influence of aerodynamic damping and bend–twist coupling on the smart rotor and to present the control effect of the TEFs under normal wind turbine operating conditions. An aerodynamic model considering the dynamic stall and aerodynamic damping as well as a structural bend–twist coupling model with the influence of gravity and centrifugal force are incorporated into the coupling analysis. The model verification shows that the present model is relatively stable under highly unsteady wind conditions. Then, a robust adaptive tracking (RAT) controller is designed to suppress fluctuations in both the flapwise tip deflection and output power. The simulations show an average reduction of up to 63.86% in the flapwise tip deflection power spectral density (PSD) of blade 1 at the 1P frequency, with an average reduction in the standard deviation of the output power of up to 34.33%.

Self-optimizing Pitch Control for Large Scale Wind Turbine Based on ADRC

Since wind turbine is a complex nonlinear and strong coupling system, traditional PI control method can hardly achieve good control performance. A self-optimizing pitch control method based on the active-disturbance-rejection control theory is proposed in this paper. A linear model of the wind turbine is derived by linearizing the aerodynamic torque equation and the dynamic response of wind turbine is transformed into a first-order linear system. An expert system is designed to optimize the amplification coefficient according to the pitch rate and the speed deviation. The purpose of the proposed control method is to regulate the amplification coefficient automatically and keep the variations of pitch rate and rotor speed in proper ranges. Simulation results show that the proposed pitch control method has the ability to modify the amplification coefficient effectively, when it is not suitable, and keep the variations of pitch rate and rotor speed in proper ranges

Dynamic analysis of wind turbines including nacelle–tower–foundation interaction for condition of incomplete structural parameters

Considering the complexity structure of wind turbines, it is difficult to establish an accurate model for wind turbines. This article proposed an improved model based on the vibration signal analysis to investigate the onshore wind turbine dynamic behavior. The model is formulated using the Euler–Lagrangian approach in which the dynamic interaction effects between the nacelle and the tower and the effects between the tower and the foundation are considered. The nacelle is assumed as a mass with 2 degrees of freedom at the top of a flexible tower. And the tower is considered as a beam with elastic end support. The foundation stiffness can influence the dynamic response of wind turbines due to the soft soils surrounding the tower base. A rotational spring and a lateral spring derived from the foundation are used to reflect the interaction between the tower and the foundation. Finally, a comparison with existing National Renewable Energy Laboratory 5-MW baseline wind turbine model is performed. And a field experiment has been implemented to validate the model. The vibration signal of the nacelle and the tower is analyzed to determine the model parameters. Results show that the proposed model is accurate and practical for dynamic property analysis of wind turbine.

The Influence of Soil-Structure-Interaction on the Fatigue Analysis in the Foundation Design of Onshore Wind Turbines

The growth of wind turbine size entails the necessity of research and advances in foundation design. To increase the efficiency of alternative energy resources wind turbines also need to be designed for longer life-spans. Because of this it is inevitable to gain deeper understandings of the continuous stress in the foundation and the influence of the soil-structure interaction (SSI) effects on the dynamic response of wind turbines, especially when grounded on soft or inhomogenous soil. Current standards emphasise the need of the SSI analysis during the whole design phase of the turbine, the tower and the foundation as well as the need of detailed fatigue design.In this study the foundation design of a wind turbine is carried out regarding to the current standards, also including SSI via state of the art methods. Major influences on the wind turbine foundation design are the overturning moment, the bending of the foundation and the connection of the tower to the foundation. Nevertheless, the special focus of this study lies on the detailed fatigue design of the concrete in the foundation using the rainflow algorithm. However, fatigue design can lead to the necessity of stronger concrete and a higher rate of reinforcement steel. The main objectives of this study are: (1) to determine the influence of state of the art SSI in the foundation design on the fatigue load design via the different soil parameters and the arising foundation geometry and material properties. (2) to show how the fatigue design differs while considering standard SSI or more detailed calculation methods.

FAST Simulation Tool Containing Methods for Predicting the Dynamic Response of Wind Turbines

FAST Simulation Tool Containing Methods for Predicting the Dynamic Response of Wind Turbines

Microgrid dynamic responses enhancement using artificial neural network‐genetic algorithm for photovoltaic system and fuzzy controller for high wind speeds

AbstractThe microgrid (MG) is described as an electrical network of small modular distributed generation, energy storage devices and controllable loads. In order to maximize the output of solar arrays, maximum power point tracking (MPPT) technique is used by artificial neural network (ANN), and also, control of turbine output power in high wind speeds is proposed using pitch angle control technic by fuzzy logic. To track the maximum power point (MPP) in the photovoltaic (PV), the proposed ANN is trained by the genetic algorithm (GA). In other word, the data are optimized by GA, and then these optimum values are used in ANN. The simulation results show that the ANN‐GA in comparison with the conventional algorithms with high accuracy can track the peak power point under different insolation conditions and meet the load demand with less fluctuation around the MPP; also it can increase convergence speed to achieve MPP. Moreover, pitch angle controller based on fuzzy logic with wind speed and active power as inputs that have faster responses which leads to have flatter power curves enhances the dynamic responses of wind turbine. The models are developed and applied in Matlab/Simulink. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of soil–structure interaction on real time dynamic response of offshore wind turbines on monopiles

Offshore wind turbines are highly dynamically loaded structures, their response being dominated by the interrelation effects between the turbine and the support structure. Since the dynamic response of wind turbine structures occurs in a frequency range close to the excitation frequencies related to environmental and parametric harmonic loads, the effects of the support structure and the subsoil on the natural vibration characteristics of the turbine have to be taken into account during the dynamic simulation of the structural response in order to ensure reliable and cost-effective designs. In this paper, a computationally efficient modelling approach of including the dynamic soil–structure interaction into aeroelastic codes is presented with focus on monopile foundations. Semi-analytical frequency-domain solutions are applied to evaluate the dynamic impedance functions of the soil–pile system at a number of discrete frequencies. Based on a general and very stable fitting algorithm, a consistent lumped-parameter model of optimal order is calibrated to the impedance functions and implemented into the aeroelastic nonlinear multi-body code HAWC2 to facilitate the time domain analysis of a wind turbine under normal operating mode. The aeroelastic response is evaluated for three different foundation conditions, i.e. apparent fixity length, the consistent lumped-parameter model and fixed support at the seabed. The effect of soil–structure interaction is shown to be critical for the design, estimated in terms of the fatigue damage 1Hz equivalent moment at the seabed. In addition, simplified foundation modelling approaches are only able to capture the dynamic response reasonably well after tuning of the first natural frequency and damping within the first mode to those of the integrated model. Nevertheless, significant loss of accuracy of the modal parameters related to the second tower modes is observed.

New Generic Model of DFG-Based Wind Turbines for RMS-Type Simulation

New requirements for the validation of simulation models based on measurements in many grid codes show that existing generic approaches for generator and converter models of doubly fed generator systems (DFG) may not be accurate enough. The authors show that by applying a detailed analysis of the generator equations and the converter control design, a reduction of the model complexity is possible while maintaining a high level of accuracy. The generator model presented in this paper allows an improved representation of the stationary and dynamic response of wind turbines equipped with DFG systems especially during grid faults and during voltage recovery. The model is designed to represent modern DFG systems independently of vendor specific hardware and software. The results of simulations are compared to measurements of a voltage dip involving wind turbines. The generator model has been proposed as extension to the WECC/IEEE generator models and has been accepted as reference for IEC TC88 working group 27 (standard IEC 61400-27-1) on modeling and model validation of wind turbines.

Dynamic analysis of wind turbines including soil-structure interaction

This paper investigates the along-wind forced vibration response of an onshore wind turbine. The study includes the dynamic interaction effects between the foundation and the underlying soil, as softer soils can influence the dynamic response of wind turbines. A Multi-Degree-of-Freedom (MDOF) horizontal axes onshore wind turbine model is developed for dynamic analysis using an Euler–Lagrangian approach. The model is comprised of a rotor blade system, a nacelle and a flexible tower connected to a foundation system using a substructuring approach. The rotor blade system consists of three rotating blades and includes the effect of centrifugal stiffening due to rotation. The foundation of the structure is modeled as a rigid gravity based foundation with two DOF whose movement is related to the surrounding soil by means of complex impedance functions generated using cone model. Transfer functions for displacement of the turbine system are obtained and the modal frequencies of the combined turbine-foundation system are estimated. Simulations are presented for the MDOF turbine structure subjected to wind loading for different soil stiffness conditions. Steady state and turbulent wind loading, developed using blade element momentum theory and the Kaimal spectrum, have been considered. Soil stiffness and damping properties acquired from DNV/Risø standards are used as a comparison. The soil-structure interaction is shown to affect the response of the wind turbine. This is examined in terms of the turbine structural displacement and also the base shear and bending moment in the tower and the foundation. The frequency domain response of the bending moment and shear force in the foundation and the tower base, for stiffer soil condition, is shown to be characterized by peaks at multiples of the wind turbine rotational speed (3P effects). The effect of dynamic soil-structure interaction on the rotation of the foundation has also been investigated.