Response Of Wind Turbine Research Articles

Evaluation of different wind fields for the investigation of the dynamic response of offshore wind turbines

AbstractAs the size of offshore wind turbines increases, a realistic representation of the spatiotemporal distribution of the incident wind field becomes crucial for modeling the dynamic response of the turbine. The International Electrotechnical Commission (IEC) standard for wind turbine design recommends two turbulence models for simulations of the incident wind field, the Mann spectral tensor model, and the Kaimal spectral and exponential coherence model. In particular, for floating wind turbines, these standard models are challenged by more sophisticated ones. The characteristics of the wind field depend on the stability conditions of the atmosphere, which neither of the standard turbulence models account for. The spatial and temporal distribution of the turbulence, represented by coherence, is not modeled consistently by the two standard models. In this study, the Mann spectral tensor model and the Kaimal spectral and exponential coherence model are compared with wind fields constructed from offshore measurements and obtained from large‐eddy simulations. Cross sections and durations relevant for offshore wind turbine design are considered. Coherent structures from the different simulators are studied across various stability conditions and wind speeds through coherence and proper orthogonal decomposition mode plots. As expected, the standard models represent neutral stratification better than they do stable and unstable. Depending upon the method used for generating the wind field, significant differences in the spatial and temporal distribution of coherence are found. Consequently, the computed structural design loads on a wind turbine are expected to vary significantly depending upon the employed turbulence model. The knowledge gained in this study will be used in future studies to quantify the effect of various turbulence models on the dynamic response of large offshore wind turbines.

Extended Environmental Contour Methods for Long-Term Extreme Response Analysis of Offshore Wind Turbines1

AbstractEnvironmental contour method is an efficient method for predicting the long-term extreme response of offshore structures. The traditional environmental contour is obtained using the joint distribution of mean wind speed, significant wave height, and spectral peak period. To improve the accuracy of traditional environmental contour method, a modified method was proposed considering the non-monotonic aerodynamic behavior of offshore wind turbines. Still, the modified method assumes constant wind turbulence intensity. In this paper, we extend the existing environmental contour methods by considering the wind turbulence intensity as a stochastic variable. The 50-year extreme responses of a monopile-based offshore wind turbine are compared using the extended environmental contour methods and the full long-term method. It is found that both the environmental contour method and the modified environmental contour method, with the wind turbulence intensity included as an individual variable, give more accurate predictions compared with those without. Using the full long-term method as a benchmark, this extended approach could reduce the nonconservatism of the environmental contour method and conservatism of the modified environmental contour method. This approach is effective under wind-dominated or combined wind-wave loading conditions, but may not be as important for wave-dominated conditions.

Applying multiple tuned mass dampers to control structural loads of bottom-fixed offshore wind turbines with inclusion of soil-structure interaction

Using structural control methods to suppress structural loads of offshore wind turbines is an economical and feasible solution. Note that the dynamic responses of offshore wind turbines are generally analyzed under the parked condition, and the blades are usually modeled with a lumped mass. Actually, the geometrical properties and rotational speed of blades can significantly affect the wind turbine performances. Therefore, these simplifications may result in inaccurate evaluation for the wind turbine dynamic responses, and then further influence the evaluation of the load mitigation effect of a control system. Moreover, the vibration behaviors and structural responses of the wind turbine can be influenced by soil-structure interaction. In this work, the structural responses of a bottom-fixed offshore wind turbine that suffers combined wind and wave excitations are explored. The blade model is explicitly established and soil-structure interaction is also taken into account. The dynamic responses of the wind turbine as well as the vibration mitigation effects of a single tuned mass damper (STMD) and a multiple TMDs (MTMD) system are examined. Furthermore, the sensitivity analysis for the TMD tuning frequency and the robustness of the MTMD system are investigated under the assumption that some TMDs in MTMD do not work properly.

Responses of vertical axis wind turbines to gusty winds

Gust is a common atmospheric condition encountered by wind turbines. Despite the presence of a vast amount of literature on this topic, few of them involve lateral gust influence. Due to this motivation, this paper presents an investigation on the effects of sinusoidal gusts on a three-bladed vertical axis wind turbine under varying gust parameters including gust direction, velocity amplitude, and frequency. The chimera mesh technique is used to model the real rotation of the rotor, as well as the resolved gust approach model in the DLR (German Aerospace Center) TAU code for gust simulation. Both the general aerodynamic computational fluid dynamics model and the gust model are validated before the following simulations. Numerous new flow phenomena and physics are revealed. The influences of gust on the rotor power output and flowfield characteristics are discussed and analyzed in detail. The findings in this study may be helpful for some practical wind engineering applications, such as atmospheric influence evaluation and field site selection.

Tuned mass dampers in wind response control of wind turbine with soil-structure interaction

The efficiency of tuned mass dampers (TMDs) in along-wind response mitigation of a wind turbine with consideration of blade coupling and soil-structure interaction (SSI) is investigated. The wind turbine tower is modeled as a multi-degree of freedom (MDOF) with three blades are connected as a MDOF system to the tower. The along-wind drag forces are generated using Shinozuka method. The effect of SSI is considered using frequency independent parameters. The equation of motion for the coupled system is numerically solved in time domain using the Newmark Beta method. In order to observe the changes in response of the system, the blades are subjected to rotating wind field to include the effects of the blade-tower interaction and rotor movement. The peak displacement, peak acceleration, root mean square (RMS) displacement, RMS acceleration, and power spectral density (PSD) of the wind turbine are the response quantities considered for comparative studies. Single TMD (STMD) and distributed multiple TMDs (d-MTMDs) are used to mitigate the wind response of the tower. Parametric studies are conducted to find the most suitable parameters (such as mass ratio, frequency bandwidth, and damping ratios) of the TMD schemes to increase the effectiveness of the strategy in the mitigation of the wind response of wind turbine with/without consideration of SSI. It is concluded that wind response of the wind turbine is amplified with inclusion of the SSI, blade-tower interaction, and rotor movement. In addition, it is concluded that the d-MTMDs are more effective and robust in wind response control of the wind turbine as compared to the STMD.

Effects of inflow turbulence on structural response of wind turbine blades

A better understanding of the intense interaction between the turbulent inflow and rotating wind turbine components is critical to accelerating the path towards larger wind turbines. The present investigation provides the first field characterization of the influence of turbulent inflow on the blade structural response of a utility-scale wind turbine, using the unique facility available at the Eolos Wind Energy Research Station. A representative dataset under a stable atmosphere is selected for the characterization, including the inflow turbulent data measured from the meteorological tower, high-resolution blade strain measurement at different circumferential and radiation positions along the blade, and the wind turbine operational conditions. The results indicate that the blade response to turbulence shows distinct trends under three scale ranges. The blade structure responds strongly to the turbulent inflow in the lower and intermediate ranges, while it is primarily dominated by the rotation effect and other high-frequency characteristics of the turbine in higher frequencies. Moreover, the blade structural behaviors at different azimuth angles, circumferential and radial locations along the blade are compared, suggesting the comparatively high possibility of structural failure at certain positions. Further, the present study uncovers the linkage between the turbulent inflow and blade structural response using temporal correlation.

Offshore Wind Turbine Coupled Motion in Regular Waves

AbstractThis study aims to accurately predict the hydrodynamic performance and motion responses of offshore wind turbines on the basis of computational fluid dynamics (CFD) theory. Continuous and Navier-Stokes (N-S) equations are employed as control equations, and the k-ε model is used as a turbulence model. The finite difference method is utilized to discretize the equation. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm is applied to solve the control equation, and the volume-of-fluid (VOF) method is used to capture the free surface. The numerical wave tank of irregular wave is also established. The hydrodynamic performances and motion responses of the offshore wind turbines under regular waves are studied. First, we assume a floating foundation without the influence of a rotational fan and examine its motion responses and wave force in three typical sea conditions, namely, Levels 5, 6, and 7. Thereafter, we use a series of force and torque acting on the rotating center of the offshore to substitute for the influence of the rotational fan on the floating foundation. Then, we study the hydrodynamic performance influenced by blade rotation of the floating foundation in various sea conditions and three wind speeds, namely, 5, 8, and 11 m/s. Research results can provide usable theoretical principle and technical support for the investigation of the hydrodynamic performance and motion responses of similar offshore wind turbines.

A Linear Inertial Response Emulation for Variable Speed Wind Turbines

A torque limit-based (TLB) method was proposed in literature in order to emulate inertial response of variable speed wind turbines (VSWTs). In this paper, this conventional TLB scheme is firstly modified by considering a finite ramp rate for inertial power of the VSWT. It is exposed that the maximum values of the VSWT's inertial power and kinetic energy released by its rotor have a non-linear relationship with its operation point. Then, a linear TLB scheme is proposed to make the inertia emulation more flexible by customizing its key parameters based on the VSWT's operating point. Accordingly, the released kinetic energy and power ramp rate can be selected in proportion of the VSWT's power, rotor speed and/or its reserved kinetic energy. The derived scheme offers a significant reduction of the mechanical tensions on the turbine compared to the conventional one. In addition, when the parameters of the proposed strategy is designed according to the VSWT's power, the inertial response of the corresponding wind farm can be exactly estimated only by deploying its total generation, regardless of its wind turbines’ installed capacities and operating points. Furthermore, a new approach is projected to estimate the VSWT's inertial response during the deceleration period using an analytical closed-form function. This facilitates large scale system studies. Finally, the efficiency of derived linear inertia emulation is evaluated through a typical grid with various levels of the wind power penetration.

Predicting loads and dynamic responses of an offshore wind turbine in a nonlinear mixed sea

ABSTRACT In this article the loads and dynamic responses of an offshore wind turbine (OWT) operating in a nonlinear multidirectional mixed sea have been rigorously investigated. It has been demonstrated that nonlinearly simulated realistic waves with bottom effects should be utilised as inputs in the stochastic time domain simulation in order to design an un-conservative support structure for the offshore wind turbine. In order to further improve the simulation efficiency, a novel transformed linear simulation method based on a Hermite transformation model has been first proposed in this article for generating equivalent waves as those obtained from the nonlinear simulation method. The predicted results of the loads and dynamic responses of the offshore wind turbine have been rigorously analysed and systematically compared, and the advantages of using our proposed novel method have been convincingly substantiated.

Ancillary services from wind turbines: automatic generation control (AGC) from a single Type 4 turbine

Abstract. Wind turbines possess the technical ability to provide various ancillary services to the electrical grid. Despite this, renewable generators such as wind and solar have traditionally not been allowed to provide significant amounts of ancillary services, in part due to the variable and uncertain nature of their electricity generation. Increasing levels of renewable generation, however, continue to displace existing synchronous generation and thus necessitate new sources of ancillary or system services. This work is part of an ongoing project that seeks to provide empirical evidence and an examination of how ancillary services can be provided from commercially available wind turbines. We focus specifically on providing secondary frequency response (automatic generation control or AGC) and demonstrate that wind turbines have the technical capability to provide this service. The algorithms used are intentionally simple so as to evaluate the capabilities and limitations of the turbine technology. This work presents results from a single, 800 kW, International Electrotechnical Commission (IEC) Type 4 wind turbine. A total of 10 % of rated power is offered on the regulation market. We do not separate up- and downregulation into individual services. Upregulation is offered through a 5 % constant power curtailment. The AGC update interval is 4 s, to mimic real-world conditions. We use performance scoring methods from the Pennsylvania–Jersey–Maryland (PJM) operator and the National Research Council (NRC) of Canada to quantify the wind turbine's response. We use the calculated performance scores, annual site wind data, and 2017 PJM market price data to estimate income from providing secondary frequency regulation. In all cases presented, income from the regulation market is greater than the energy income lost due to curtailment.

Typhoon-induced vibration response and the working mechanism of large wind turbine considering multi-stage effects

The typhoon-induced vibration characteristics of large wind turbines are significantly different in different travelling stages of typhoons due to the structural complexity of typhoons. Influences of multi-stage typhoon-induced effects on structural safety of wind turbines have not been studied yet. The objective of this paper is to investigate the vibration characteristics of wind turbines in different stages of the typhoon as well as the influencing rules of the structural design standards. For this purpose, a framework was established for predicting multi-stage typhoon-induced effects of large wind turbines, which includes a new typhoon-induced multi-stage wind field simulation method and an advanced multi-body model for large wind turbines. On this basis, aerodynamic loads and dynamic response of large wind turbines during different travelling stages of typhoon were analyzed systematically based on the blade element momentum, multi-body dynamic methods, spectral analysis and data statistics. The working mechanisms of multi-stage effects on vibration characteristics of the large wind turbine were revealed. Finally, an evaluation method of vibration amplification effects for large wind turbines with considerations to multi-stage effects was established. Research results demonstrate that the proposed method can predict vibration characteristics of large wind turbines considering the multi-stage effects efficiently. The multi-stage typhoon-induced effects can influence the value of peak factor and the extremum of wind-induced force and vibration responses of large wind turbines significantly. Conversely, the wind vibration coefficient of structural design was affected slightly. Instead of using a uniform structural design standard for large wind turbines, the influence rule of multi-stage effects on anti-typhoon safety performance was summarized in this paper.

Aeroelastic response of a multi-megawatt upwind horizontal axis wind turbine (HAWT) based on fluid–structure interaction simulation

Abstract. With the increasing demand for greener, sustainable, and economical energy sources, wind energy has proven to be a potential sustainable source of energy. The trend development of wind turbines tends to increase rotor diameter and tower height to capture more energy. The bigger, lighter, and more flexible structure is more sensitive to smaller excitations. To make sure that the dynamic behavior of the wind turbine structure will not influence the stability of the system and to further optimize the structure, a fully detailed analysis of the entire wind turbine structure is crucial. Since the fatigue and the excitation of the structure are highly depending on the aerodynamic forces, it is important to take blade–tower interactions into consideration in the design of large-scale wind turbines. In this work, an aeroelastic model that describes the interaction between the blade and the tower of a horizontal axis wind turbine (HAWT) is presented. The high-fidelity fluid–structure interaction (FSI) model is developed by coupling a computational fluid dynamics (CFD) solver with a finite element (FE) solver to investigate the response of a multi-megawatt wind turbine structure. The results of the computational simulation showed that the dynamic response of the tower is highly dependent on the rotor azimuthal position. Furthermore, rotation of the blades in front of the tower causes not only aerodynamic forces on the blades but also a sudden reduction in the rotor aerodynamic torque by 2.3 % three times per revolution.

Hurricane eyewall winds and structural response of wind turbines

Abstract. This paper describes the analysis of a wind turbine and support structure subject to simulated hurricane wind fields. The hurricane wind fields, which result from a large eddy simulation of a hurricane, exhibit features such as very high gust factors (>1.7), rapid direction changes (30∘ in 30 s), and substantial veer. Wind fields including these features have not previously been used in an analysis of a wind turbine, and their effect on structural loads may be an important driver of enhanced design considerations. With a focus on blade root loads and tower base loads, the simulations show that these features of hurricane wind fields can lead to loads that are substantially in excess of those that would be predicted if wind fields with equally high mean wind speeds but without the associated direction change and veer were used in the analysis. This result, if further verified for a range of hurricane and tropical storm simulations, should provide an impetus for revisiting design standards.

Inerter-based Passive Structural Control for Barge Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWT) stand as a promising concept to expand the wind energy generation into the more productive deep-water areas, where conventional bottom-fixed turbines are infeasible. Barge-type floating wind turbines experience an inverted pendulum effect which produces a coupling with the wind turbine response, resulting in large structural loads. In this paper, the authors investigate passive structural control to mitigate the tower fatigue, in the form of a tuned mass damper (TMD) installed in the nacelle. The study focuses on evaluating the benefits of adding a parallel-connected inerter device to the TMD. Based on a reduced dynamics model for the barge-type offshore wind turbine identified using the FAST-SC synthetic reference data, an optimization of the TMD and the inerter parameters is carried out. To that end, genetic algorithms were used taking the tower fatigue as a fitness function, derived from the tower top displacement. The results confirm that the inerter has limitations when installed in a traditional TMD, but show signifcant benefits when the TMD stroke is constrained by stops. It is found that the improved performance including the inerter is dependent on the stroke limitation with respect to the ideal TMD stroke without stops. Therefore, the use of the inerter is especially useful to enhance performances for both mass and stroke constrained applications. The load reduction for the selected baseline model improved up to 6 % over the TMD with stops and 12 % over the TMD without stops.

Simulating the response of a small horizontal-axis wind turbine during wind gust using FAST

Small wind turbines are often erected close to their load and in urban environments where the mean velocity is lower than ideal, and the turbulence level is high. Urban environments experience wind gust events with published results indicating the number of gust events greatly exceeding the number of events assumed in International Electrotechnical Commission (IEC) standard IEC 61400.2-2013. The work presented in this paper has analysed detailed wind measurements from a site in an urban environment to identify wind gust events and has used these wind gust events as an input into a FAST model of a 5 kW horizontal-axis wind turbine. The FAST model predicted the turbine power extracted from the measured gusts are lower than the power extracted during the assumed IEC gust. The maximum energy extracted by the turbine during a gust is at least 36% lower for a measured gust event than for the assumed ideal gust event.

Effect of shape parameters on stability and transient response of cylinder blade wind turbine driven by longitudinal vortex

Effect of shape parameters on stability and transient response of cylinder blade wind turbine driven by longitudinal vortex

Numerical Simulation of the Aeroelastic Response of Wind Turbines in Typhoons Based on the Mesoscale WRF Model

A new simulation method for the aeroelastic response of wind turbines under typhoons is proposed. The mesoscale Weather Research and Forecasting (WRF) model was used to simulate a typhoon’s average wind speed field. The measured power spectrum and inverse Fourier transform method were coupled to simulate the pulsating wind speed field. Based on the modal method and beam theory, the wind turbine model was constructed, and the GH-BLADED commercial software package was used to calculate the aerodynamic load and aeroelastic response. The proposed method was applied to assess aeroelastic response characteristics of a commercial 6 MW offshore wind turbine under different wind speeds and direction variation patterns for the case study of typhoon Hagupit (2008), with a maximal wind speed of 230 km/h. The simulation results show that the typhoon’s average wind speed field and turbulence characteristics simulated by the proposed method are in good agreement with the measured values: Their difference in the main flow direction is only 1.7%. The scope of the wind turbine blade in the typhoon is significantly larger than under normal wind, while that under normal operation is higher than that under shutdown, even at low wind speeds. In addition, an abrupt change in wind direction has a significant impact on wind turbine response characteristics. Under normal operation, a sharp variation of the wind direction by 90 degrees in 6 s increases the wind turbine (WT) vibration scope by 27.9% in comparison with the case of permanent wind direction. In particular, the maximum deflection of the wind tower tip in the incoming flow direction reaches 28.4 m, which significantly exceeds the design standard safety threshold.

Uncertainty assessment for the extreme hydrodynamic responses of a wind turbine semi-submersible platform using different environmental contour approaches

This paper aims to assess the uncertainty on the extreme responses of a semi-submersible wind turbine using two environmental contour approaches. The approaches are based on the inverse First Order Reliability Method and the direct Monte Carlo Simulation with different sample sizes. The long-term sea states are described by a 3-parameters Weibull distribution for the significant wave height and a conditional log-normal distribution for the zero-up crossing period. Two extreme sea states are extracted from each environmental contour, which are associated with the maximum significant wave height and maximum zero-upcrossing period. A 3-h time domain simulation for each sea state is conducted by adopting a validated numerical model. The root mean square for all the response spectra are estimated and compared to each other. It is observed that despite the small deviation between the significant wave heights resulting from adopting different environmental contour approaches, the deviation between the resulting responses is much more significant. The Gumbel and the generalized extreme value distributions are fitted to the maximum extreme response values for each sea state and unified fitted parameter are obtained.

Consensus-Based Demand Response of PMSG Wind Turbines With Distributed Energy Storage Considering Capability Curves

This article proposes a distributed consensus-based demand response control for permanent magnet synchronous generator (PMSG)-based wind turbines using standalone distributed battery energy storage systems (BESSs). The proposed controller cooperatively regulates the output power of individual wind turbines and BESSs in a wind farm to deliver active and reactive powers to the load in varying wind speed conditions. Capability curves of the wind turbines and BESSs are considered in the design. In addition, a virtual leader is designed to regulate the voltage and frequency of the combined PMSG-BESS units at the point of common coupling. Simulations on modified IEEE 14-bus power system are performed to validate the proposed design.

Wind Field-Based Short-Term Turbine Response Forecasting by Stacked Dilated Convolutional LSTMs

Predicting a wind turbine's responses that correspond to a complex wind field is challenging because the responses are caused by the complex interaction between a dynamically operating mechanical system and a spatially and temporally coupled stochastic wind field. We propose a physics-inspired, data-driven prediction model called stacked dilated convolutional LSTMs (SDCL) that uses a sequence of wind fields (snapshots) as an input to predict future wind turbine responses. A SDCL is composed of a set of dilated convolutional neural networks (CNNs) combined with a long short-term memory (LSTM) to capture the spatial and temporal evolution of the turbulence structure in the input wind field. Notably, a dilated CNN with different dilation ratios along with a corresponding LSTM module, a single component of SDCL, is designed to capture the evolution of an eddy of a certain size in the turbulent wind field. Then SDCL effectively models the evolution of multiple eddies of different sizes. Through a simulation study, we have demonstrated that such a physics-inspired network architecture is effective in processing a complex wind field and thus predicting two representative future wind turbine responses, energy generation and blade root out-of-plane bending moment, more accurately than other standard deep learning architectures.