Response Of Wind Turbine Research Articles

Evolution of the Seismic Response of Monopile-Supported Offshore Wind Turbines of Increasing Size from 5 to 15 MW including Dynamic Soil-Structure Interaction

As a result of wind power’s expansion over the globe, offshore wind turbines (OWTs) are being projected in seismic prone areas. In parallel, the industry develops increasingly larger and more powerful generators. Many of the seismic response analyses of wind turbines conducted so far only consider smaller units. In this paper, a finite element substructuring model in frequency domain is used to compute the seismic response of four reference OWTs from 5 to 15 MW founded on monopiles embedded in several homogeneous soil profiles with shear wave velocities from 100 to 300 m/s and subjected to different accelerograms. The foundation behaviour is obtained through a continuum model including kinematic and inertial interaction. The relevance of soil-structure interaction and main trends of the seismic response of OWTs are inferred from the presented results. Although the seismic maximum bending moments increase with the size of the OWT system, their relevance with respect to the ones produced by design loads decreases as the turbine gets bigger. The same effect is observed for the shear forces if the soil is soft enough. The inclusion of SSI effects almost duplicates the seismic response when compared to the rigid base scenario.

Design of an Active Damping System for Vibration Control of Wind Turbine Towers

The vibration of wind turbine towers is relevant to the reliability of the wind turbine structure and the quality of power production. It produces both ultimate loads and fatigue loads threatening structural safety. This paper aims to reduce vibration in wind turbine towers using an active damper named the twin rotor damper (TRD). A single degree of freedom (SDOF) oscillator with the TRD is used to approximate the response of wind turbines under a unidirectional gusty wind with loss of the electrical network. The coincidence between the wind gust and the grid loss is studied to involve the maximum loading on the structure. The performance of the proposed damping system under the maximum loading is then evaluated on the state-of-the-art wind turbine NREL 5 MW. The effectiveness of the TRD is compared to a passive tuned mass damper (TMD) designed with similar requirements. The numerical results reveal that, at the 1st natural mode, the TRD outperforms the passive TMD by three to six times. Moreover, the results show that the TRD is effective in reducing ultimate loads on wind turbine towers.

Parametric study of the quasi-static response of wind turbines in downburst conditions using a numerical model

Many research studies were conducted on wind turbine towers subjected to either seismic loads or synoptic wind loading, such as: hurricanes, typhoons, and tropical cyclones. However, the behavior of wind turbines under localized high-intensity wind events (HIW), such as downbursts, is not well-understood. The localized nature of downbursts makes the prediction of critical loads on wind turbines quite challenging. In the current study, a numerical model is developed and validated to investigate the effect of downburst wind loading on wind turbines. This model incorporates a previously developed Computational Fluid Dynamics (CFD) model for the downburst wind field coupled with a newly developed wind turbine structural model. The numerical model is capable of predicting the effect of downbursts on wind turbines taking into consideration the different downburst parameters such as the jet velocity, the size of the downburst and its location relative to the wind turbine. The model also accounts for the change in the pitch angle of the blades, which is a parameter typically used to control the blades rotation and the power generation. An extensive parametric study is conducted using the developed numerical model to determine the peak moments at the tower base and the roots of the blades considering a large number of downburst configurations and different blade pitch angles. Downburst critical configurations for different pitch angles are obtained and the optimum pitch angle which minimizes the downburst effect on the wind turbine is recommended.

Optimal Charging/Discharging Control of Electric Vehicle Charging Station Considering Grid Resiliency

Management and control of charging/discharging of Electric vehicles (EVs) with the aim of profitability for the Distribution System Operator (DSO) and the private sector is one of the challenges in operating Electric vehicles Charging Stations (EVCS). This paper proposes a novel methodology for optimal planning of charging/discharging of the hybrid wind- EVCS which on the one hand, lead to correction of the load curve and on the other hand, improves the grid resilience in extreme weather conditions. In the proposed methodology, since the weather-based outages lead to consumer interruptions, the idea of profit-sharing between DSO and EVCS owners is proposed to incentivize the owner to implement the obtained charging/discharging schedule. To this end, firstly, a Monte-Carlo based stochastic framework for forecasting the probability of weather-based line outages and also modelling uncertainties is devised. Then, a resilience-oriented multi-objective optimization algorithm is presented that, while coordinating the operation of the wind turbine, EV management and Demand Response Programs (DRP), the profits of both EVCS and DSO are maximized during daily operation planning. The resiliency improvement of the proposed method is evaluated by using metrics. The obtained optimal results prove the effectiveness of the proposed method in increasing resiliency and benefits for all players.

Provision of Frequency Response from Wind Farms: A Review

Renewable sources of energy play a key role in the process of decarbonizing modern electric power systems. However, some renewable sources of energy operate in an intermittent, non-dispatchable way, which may affect the balance of the electrical grid. In this scenario, wind turbine generators must participate in the system frequency control to avoid jeopardizing the transmission and distribution systems. For that reason, additional control strategies are needed to ensure the frequency response of variable-speed wind turbines. This review article analyzes diverse control strategies at different levels which are aimed at contributing to power balancing and system frequency control, including energy storage systems.

Loads on a Jacket-Supported Wind Turbine During Hurricane Sandy Simulation

Abstract The dynamic response of a jacket-supported offshore wind turbine under coupled wind, wave, and current fields during Hurricane Sandy is the subject of this study. To illustrate the detailed procedure related to the response evaluation of a 5-MW offshore wind turbine with a jacket support structure, we consider a single site where the water depth is 50 m. Loads are computed using two simulation tools, fast and abaqus, with partial coupling. Aerodynamic loads on the turbine rotor are first evaluated using a wind turbine model in fast with a fixed base; then, these rotor aerodynamic loads are applied as point loads at the top of a model of a tower that is supported by a jacket structure in abaqus. On the basis of stochastic simulations, we discuss the applicability of the abaqus jacket modeling and describe the characteristics and comparisons of the aerodynamic and hydrodynamic effects on loads on the jacket members. Details related to the structural model and soil–pile interaction model employed in the analyses are also discussed.

Comparative study of load simulation approaches used for the dynamic analysis on an offshore wind turbine jacket with different modeling techniques

In this paper, the influences of different load simulation approaches and jacket models on the loading and the structural responses of offshore wind turbine (OWT) jackets are investigated. In the first part, the effect of three load simulation approaches used for the dynamic analysis in OWT simulation is compared under different wind and wave conditions. One is the uncoupled method, the second is the sequentially coupled approach and the final one is the fully integrated (coupled) approach. The fully integrated method is with strong coupling and is considered as the reference. The comparison with the other two methods is conducted based on an OWT jacket, which is modeled with pure beam elements. For the comparison of load simulation approaches, the results show that the simulation results of the sequentially coupled approach are mostly in good agreement with those of the fully coupled approach. The uncoupled approach may lead to big errors in the extreme responses of dynamic analysis. Based on this numerical investigation, the sequentially coupled approach is chosen for the following study. In the second part, the influences of the different jacket models on the structural responses are also studied, because the OWT jackets are often modeling with beam elements, which will over/underestimate the responses of the jackets. Two numerical models of the jacket are developed. One is with pure beam elements (Beam model), while the second is with more advanced modeling by using super-elements (Super-element model). The sequentially coupled load simulation approach is applied for both the two jacket models. For the comparison between the two jacket models, the responses of the super-element model are different from those of the beam model, especially in the jacket displacement. Hence, from this study, the fully and sequentially coupled approaches are recommended for offshore load calculations and the super-element model is recommended for better modeling the jacket behaviors.

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.

Influence of variability and uncertainty of wind and waves on fatigue damage of a floating wind turbine drivetrain

This study investigates the effect of variability and uncertainty of wind and wave conditions on the short-term fatigue damage of a 10-MW floating wind turbine drivetrain. Global dynamic responses of a semi-submersible wind turbine are calculated by aero-hydro-servo-elastic simulations in various environmental conditions. Then, rotor and generator loads, as well as nacelle motions from the global analysis are provided to a drivetrain model to investigate its dynamics. One-hour fatigue damage of the drivetrain bearings is calculated based on the bearing loads and speeds, and the effect of uncertainties related to wind and waves is assessed. The results indicate that the variations of mean wind speed, turbulence intensity and wind shear have great effects on the studied drivetrain. The effect of uncertainties of irregular waves on the drivetrain fatigue damage is small. Five wind and wave random samples are sufficient for dynamic analysis of the drivetrain to achieve accurate results at a reasonable computational cost. Among the drivetrain components, the main bearings are generally most sensitive to the investigated environmental variables. Finally, this study discusses the variation of environmental variables in terms of their relative importance for drivetrain analysis. The results provide a basis for establishing improved design standards and engineering practice for design and analysis of floating wind turbine drivetrains.

Simulations of 10MW wind turbine under seismic loadings

In this study, a shell-based finite element model based on Technical University of Denmark 10MW reference wind turbine (DTU 10 MW RWT) is used to study its dynamic responses under seismic loads. The natural vibration frequencies of blades and wind turbines from this study and the results from the literature Bak et al. (2013) are compared. The difference in natural vibration frequencies of the blades arises from simple assigned orientation in composites blades in Bak et al. (2013). The differences in natural vibration frequencies of the wind turbines are suggested to be due to shell elements used in this study whereas beam elements are used in Bak et al. (2013). The built shell-based finite element model of DTU 10MW reference Wind Turbine is then subject to artificially generated earthquake converted from codes of European union earthquake response spectrum. The simulation results show that the foundation has a significant impact on the responses of DTU 10 MW RWT. That is, the DTU 10 MW RWT suffers less stress in the flexible foundation than in the more rigid foundation . The results also show that neglecting the self-weight effect could significantly underestimate the dynamic responses of wind turbines under seismic loadings. This study suggests that shell-element based model should be used in company in the process for certification.

A remedial action framework against cyberattacks targeting energy hubs integrated with distributed energy resources

Operation of modern power systems integrated by distributed energy resources is only possible if information/communication technologies are leveraged in the system. This results in cyber-physical power systems which are vulnerable to malicious cyberattacks. Hence, it is crucial to propose practical solutions to enhance the resilience of smart grids against cyberattacks. Targeting energy hubs integrated by distributed energy resources, a cyberattack based on min–max formulation is presented in this paper. A remedial action scheme, which changes status (i.e., connection/disconnection) of the energy hub components, is proposed to mitigate the economic effect of the aforementioned cyberattack. The electricity/heat demands of the energy hub are supplied by electricity/gas networks and the energy hub components including combined heat and power, wind turbine, electrical/thermal storages, boiler, and demand response. The attacker utilizes the energy hub components to increase the associated costs. However, the system operator controls the costs by changing the status of the energy hub devices. Obtained results verify that the proposed framework leads to an effective mechanism to proactively mitigate the economic-related consequences of cyberattacks on energy hubs. The simulation results demonstrate that: 1) disconnection of the energy hub from electricity networks under the cyberattack mitigates the increased cost by 40%, 2) disconnection of the energy hub from boiler and connection of thermal storage to the system under the experienced cyberattack reduce the imposed cost by 76%.

Mechanisms of dynamic near-wake modulation of a utility-scale wind turbine

The current study uses large eddy simulations to investigate the transient response of a utility-scale wind turbine wake to dynamic changes in atmospheric and operational conditions, as observed in previous field-scale measurements. Most wind turbine wake investigations assume quasi-steady conditions, but real wind turbines operate in a highly stochastic atmosphere, and their operation (e.g. blade pitch, yaw angle) changes constantly in response. Furthermore, dynamic control strategies have been recently proposed to optimize wind farm power generation and longevity. Therefore, improved understanding of dynamic wake behaviours is essential. First, changes in blade pitch are investigated and the wake expansion response is found to display hysteresis as a result of flow inertia. The time scales of the wake response to different pitch rates are quantified. Next, changes in wind direction with different time scales are explored. Under short time scales, the wake deflection is in the opposite direction of that observed under quasi-steady conditions. Finally, yaw changes are implemented at different rates, and the maximum inverse wake deflection and time scale are quantified, showing a clear dependence on yaw rate. To gain further physical understanding of the mechanism behind the inverse wake deflection, the streamwise vorticity in different parts of the wake is quantified. The results of this study provide guidance for the design of advanced wake flow control algorithms. The lag in wake response observed for both blade pitch and yaw changes shows that proposed dynamic control strategies must implement turbine operational changes with a time scale of the order of the rotor time scale or slower.

Large scale wind turbine TMD optimization based on Blade-Nacelle-Tower-Foundation Coupled Model

Taking large-scale offshore wind turbines as the research object, introducing tuned mass dampers (TMD), through multi-body dynamics theory, considering pile-soil coupling and the flexibility of key components, a method based on Blade-Nacelle-Tower-Foundation Coupled Model's TMD parameter optimization model is proposed. According to the artificial fish swarm algorithm (AFSA) parameter optimization research is carried out on the dynamic response of offshore wind turbine results revealed that When considering the pile-soil coupling, vibration frequency in the fore/art direction can be reduced from 0.26 Hz to 0.235 Hz realizing suppression rate of 68.77% under emergency shutdown condition. Compared with unconsidered pile-soil structure, the suppression efficiency is increased by 7.08%.

Analysis of turbulence models fitted to site, and their impact on the response of a bottom-fixed wind turbine

This study compares a wind field recommended by the wind turbine design standards to more realistic wind fields based on measurements. The widely used Mann spectral tensor model with inputs recommended by the standard, is compared to FitMann, the Mann model with inputs fitted to measurements and TIMESR; using measured time series combined with the Davenport coherence model. The Mann model produces too low energy levels at the lowest frequencies of the wind spectra, while the wind spectra generated by FitMann approaches the measured values. TIMESR reproduces the measured spectral values at all frequencies. The different models give similar vertical coherence, while the Mann and FitMann models give lower horizontal coherence than TIMESR. Investigating the wind loads on a bottom-fixed 10-MW wind turbine, the spectra for the tower bottom fore-aft and blade root flapwise bending moment follow the shape of the wind spectra closely at low frequencies. The low-frequency range is important for the blade root and in particular the tower bottom bending moment. Thus, the TIMESR model, followed by FitMann, is assumed to give the most accurate fatigue estimates. For the specific situation analysed in this study, the FitMann model gives only 18 and 5 % lower estimates than TIMESR of the tower bottom and blade root damage equivalent bending moments, while the Mann model gives 27 % and 12 % lower estimates. The tower top yaw and fore-aft bending moments depend on the wind coherence. For the specific situation analysed in this study, the FitMann model gives 9 and 5 % higher estimates of the tower top yaw and tower top damage equivalent (bending) moments compared to TIMESR, while the Mann model gives 23 % and 18 % higher estimates. Since only measurements of the vertical coherence are available, it is not clear which model is superior for the tower top moments. However, the importance of a proper coherence model is documented.

Site-specific response of a 5 MW offshore wind turbine for Gujarat Coast of India

In India, the coastline of Gujarat is known to have a high potential for offshore wind energy. However, the region is highly seismically active with large magnitude earthquakes experienced in the past. The aim of the work is to investigate the site-specific response of an offshore wind turbine (OWT) for assessment of suitability of installation of OWT along the Gujarat coast. Seismic hazard analyses of 44 sites are performed using deterministic approach and response spectrum matched acceleration time histories at all these sites are obtained. Monopile for the wind turbine is designed considering a two-layered soil profile. As per specifications of National Renewable Energy Laboratory (NREL), three-dimensional finite element model of 5 MW OWT along with the soil domain is developed in the software ABAQUS considering material nonlinearity. Earthquake time histories combined with wind and wave load are being employed for the analyses. It is observed that the sites lying between Kachchh and Saurashtra regions are most vulnerable whereas sites along the western coast of Saurashtra are found to be least vulnerable. Further, seismic fragility curves for the OWT are derived for different damage states in order to evaluate the probability of damage under various seismic scenarios.

Seismic performance of offshore wind turbine in the vicinity of seamount subduction zone

The presence of seamount on the subducting interface of oceanic and continental tectonic plates has potential to alter the characteristics of ground motion due interface earthquakes. In this study, we address the influence of seamount presence on offshore wind turbine response, through a finite element simulation of earthquake and subsequently applying the recorded shaking from earthquake simulation as input to offshore wind turbines. The wind turbine response is computing by incremental dynamic analysis and fragility curves are derived for serviceability and ultimate limits of wind turbines. The effect of hypocenter being above or below the seamount, on the offshore wind turbine fragility is also addressed.

Sensitivity Study of the Influence of Blade Sectional Stiffness Parameters on the Aeroelastic Response of Wind Turbines

With the development of wind turbines as a result of large-scale and offshore trends, the wind turbine size is becoming increasingly larger. The passive control technique is used to alleviate the increasing loads on the blade for the sake of improving the durability of the wind turbine. The ply design of shells considering the coupling effect of bending and torsion is one of the passive control techniques. The bending torsion coupling stiffness is one of the parameters of the blade section stiffness matrix. In order to fully understand the influence of each blade stiffness parameter on the aeroelastic responses of wind turbines and to consider the influence of structural characteristics on the aeroelastic responses in blade design, the influences and sensitivity of each stiffness parameter in the 6 × 6 stiffness matrix of the blade sections on the aeroelastic responses of the wind turbines are systematically studied under steady wind condition. The aerodynamic forces in the aeroelastic model are calculated by an AeroDyn module based on blade element momentum theory, and the structural dynamic responses of the blade are calculated using generalized Timoshenko beam theory and geometric exact beam theory. The NREL baseline 5 MW wind turbine and blade properties are used in this study, where the diagonal stiffness parameters and non-diagonal stiffness parameters of the matrixes of each blade section are scaled according to certain principles. The results show that the axial stiffness, the flap-wise stiffness, and the torsional stiffness in the diagonal are sensitive to the root loads and tip displacement of the blade. The flap-wise bending torsion coupling stiffness, the flap-wise shear-torsion coupling stiffness, and the edge-wise shear-torsion coupling stiffness in the non-diagonal are also sensitive to the aeroelastic responses. For completeness, the effects of other stiffness parameters on the aeroelastic responses are also analyzed and discussed.

Dynamic analysis of two-rotor wind turbine on spar-type floating platform

The dynamic response of a two-rotor wind turbine mounted on a spar-type floating platform is studied. The response is compared against the baseline OC3 single-rotor design. Structural design shows how the two-rotor design may lead to a mass saving of about 26% with respect to an equivalent single-rotor configuration. Simulations predict significant platform yaw response of the two-rotor floating wind turbine — about 6 deg standard deviation at the rated operating wind speed. It is shown how the platform yaw response is directly caused by the turbulence intensity at the hub coupled with the transversal distribution of thrust loads on the structure. A coupled control strategy for the rotor-collective blade pitch controller is proposed, in which a simple proportional control mitigating platform yaw motion is superimposed to the baseline OC3 PI controller. Numerical simulations show how platform yaw response is reduced by about 60%, at the cost of mean power loss at below-rated wind speeds of about 100 kW and maximum increase of the rotor-collective blade-pitch angles standard deviation of about 2 deg. Parametric analysis of mooring lines design shows how an equivalent mass density of the line of at least 190 kg/m is needed to avoid vertical loads at the anchors.

Static analysis of wind turbine blade using 1D FE model

The study presents a unique technique to determine the static response of wind turbine (WT) blade. A 1D Finite element (FE) beam model of WT blade is developed using thin-walled beam theory coupled with PreComp tool used to compute crosssectional stiffness with elastic coupling effects. A realistic 9.2 m long, WT blade is developed using different aerofoils with fourth order polynomial variation for twisting angle of blade span. Three different aerfoil sections NREL S818, NREL S825, and NACA 2412 are employed in the current study. For validation, the results of 1D model developed using MATLAB are compared with that of 3D WT blade model which is analyzed in ANSYS using NuMAD..

Dynamic behaviors of wind turbines under wind and earthquake excitations

The dynamic behaviors of wind turbines subjected to combined wind-earthquake loading were investigated. Numerical simulations were performed to examine the influence of wind speed and earthquake intensity on the dynamic behaviors of wind turbines after evaluating the influence of randomness of wind. Subsequently, the effect of start time and input angle of earthquakes on seismic responses of wind turbines was evaluated to explore the temporal and spatial combinations of wind and earthquake loads. It is noted that the wind increases and decreases the response amplitude of the wind turbine under weak and strong earthquake excitations, respectively. Consequently, the most unfavorable seismic load conditions are represented by the wind–earthquake combination in the former scenario and by only the earthquake case in the latter scenario. Because the start time of earthquakes can significantly affect the dynamic response of the wind turbine, sufficient wind samples must be generated to obtain the mean of the response amplitudes. Moreover, the input angle of earthquakes influences the seismic response of wind turbines, owing to the asymmetry of aerodynamic damping and blade stiffness. Consequently, the combination of wind and earthquake excitations in the space domain must be considered prudently.