Active Vibration Control of Wind Turbine Using Virtual TMD Algorithm Based on Aerodynamic-Structure-Servo Coupling Model

High-rise buildings and wind turbines under dynamic environmental loads experience excessive vibrations. Excessive vibration in tall buildings can exceed both strength and serviceability limit states, leading to structural damage and occupant discomfort. In contrast, unwanted vibration in wind turbines can have adverse effects on energy generation, fatigue life, and initial cost. The current research investigates two high-rise buildings and a 5 MW wind turbine from the National Renewable Energy Laboratory (NREL) numerically and experimentally to single out the optimal vibration mitigation techniques under diverse environmental loads. A performance-based design of viscous dampers with magnifying mechanism was employed to mitigate the vibration in 76 story benchmarks building under seismic and wind loads. Displacement, acceleration, inter-story drift ratio, shear force, and base bending moment are considered along with other concise sets of system-level performance criteria that are easily understood by decision-makers and/or stakeholders of diverse technical backgrounds. The results suggest viscous dampers as a viable solution for vibration attenuation in high-rise buildings. Viscous dampers can reduce structural and nonstructural damage by counteracting multi-hazard forces in real-time. We proposed a robust pendulum-pounding tuned mass damper (PTMD) to attenuate vibration in wind turbines. The NREL wind turbine equipped with the pendulum PTMD was modeled following the Lagrangian method to facilitate the numerical study. The results reveal that the optimum frequency ratio of the pendulum PTMD can be far different from the corresponding tuned mass damper (TMD) frequency ratio. The pendulum PTMD exhibits higher performance over the corresponding TMD, in terms of robustness and capabilities to reduce maximum accelerations and displacements under earthquakes. We verified the numerical results using a shake table experiment under several earthquake excitations. We carried out dynamic analysis investigations of a 42-story timber-hybrid building, along with a comparative control performance study of three mass dampers: (1) pendulum pounding tuned mass damper (PTMD), (2) tuned mass damper inerter (TMDI), and (3) tuned mass damper (TMD) under the earthquake excitations. Coupling the inerter with TMD to form TMDI can impact the optimal frequency ratio and damping ratio of TMD, resulting in reduced performance. Compared to TMD/TMDI, the pendulum PTMD was more robust, with a higher potential to reduce building responses under seismic loads. We performed aerodynamic investigations of a large-scale high-rise building model at a high Reynolds number (~1 million) to evaluate wind pressure distribution and wind loads. To demonstrate, aerodynamic testing of a 1:50 scale test model was executed with two aspect

In this chapter, a review of the optimum design of passive and active tuned mass dampers for structures is presented. Metaheuristics have been often used in the optimum design of tuned mass dampers. As an example, an improved harmony search algorithm is presented for the optimum design of active tuned mass dampers (ATMDs) using proportional integral derivative type controllers. The ATMD was also compared via passive tuned mass damper (TMD) and the optimum design results are presented for a 10-story structure with multiple cases of the time delay of the controller and stroke capacity of ATMD. ATMD is better than TMD in the reduction of displacements up to 32.01%.

Vibration mitigation in offshore wind turbines via tuned mass damper

A semiactive control strategy for the vibration control of structures using a stiffness varying tuned mass damper (TMD) with application of bang-bang control force to TMD is proposed. The control strategy involves a combination of controlling the response of structure using bang-bang control with a control force applied to the TMD, and the use of the principle of minimizing the maximum value of the frequency response function (FRF) for the coupled structure-variable stiffness TMD system. The optimal tuning parameter and damping ratio for the TMD are obtained based on this principle. When the control force is applied to the TMD, the TMD is simultaneously retuned (by varying the stiffness) in real time to achieve the minimax principle for the desired level of response reduction. When the active control is ineffective or is turned off, the damper system acts as a passive TMD. The performance of the control strategy is examined under harmonic excitations and is compared to previous results on bang-bang control and minimax shaping of the FRF when the TMD is not retuned in real time. In order to examine the robustness of the controller, a wind excitation obtained from the Davenport spectrum is applied to a structure with low natural frequency. The control strategy is shown to achieve substantial response reduction with relatively low control force requirements.

This paper studies the feasibility of self-powered active vibration control of structures with Tuned Mass Dampers (TMDs). Without consuming external energy, the proposed self-powered vibration control strategy can provide better performance than the passive TMD in mitigating the vibration of buildings induced by wind load. the vibration-dissipative element of TMD is replaced with an electromagnetic machine, which serves as actuator and harvester at the same time. First, the desired force is obtained by adopting Linear Quadratic Regulator (LQG) optimal control. Then, the self-powered active control strategy is designed based on the essence of the desired force, which can be passive or active types. The energy of the vibration can be harvested as electricity in energy harvesting mode, and pumped back into the mechanical system when instant active force is required. Switch based circuits with capability of bi-directional power flow are presented for the implementation of self-powered active TMDs. With taking the efficiency of the harvesting and driving circuits into account, numerical simulations are carried out based on a tall building with a TMD under random and harmonic excitations. The results indicate the feasibility and effectiveness of self-powered active TMDs.

Compared to the onshore wind turbines, the offshore floating wind turbines experience larger loads and displacements due to combined effects of the wind and waves. Suppressing the structural vibration of floating wind turbines with a passive tuned mass damper (TMD) device has the potential to be an effective and economical method. In this study, a barge-type floating wind turbine is chosen as the research object. The SIMPACK multi-body dynamics software is employed to establish the detailed model of the wind turbine. For achieving considerable load reduction performance, the spring stiffness, damping coefficient, and mass of the TMD system are optimized based on a simplified mathematical model. Furthermore, the genetic algorithm (GA) is used to achieve global optimal TMD parameters. To investigate the effect of the detailed drivetrain model on the wind turbine performances and comprehensively evaluate the structural vibration inhibition effect of the designed TMD, a coupled aero-hydro-servo-elastic model is constructed and simulated for different load cases. The time-domain and frequency-domain analysis of simulation results are performed. Moreover, a robustness study for TMD parameters obtained by the GA is also performed. Analysis results indicate that the flexibility and gear contact within the drivetrain has a noticeable effect on the wind turbine performances, and the designed TMD can significantly inhibit the structural loads and stabilize the electrical output power.

A numerical simulation of adaptive feedforward control of building structures under seismic inputs is presented. The control actuator is an active tuned mass damper (ATMD) located on the last floor of an eight-story shear type building. The properties of the tuned mass damper (TMD) are selected for optimum performance as a passive device, i.e. the natural frequency of the device is nearly the same as the fundamental frequency of the building. The feedforward compensator is implemented with a finite impulse response (FIR) filter. The ground acceleration is sensed and fed forward into the compensator to generate the control input. The adaptive algorithm updates in “real time” the compensator’s weights such that a critical response, referred as the error signal, is minimized. The relative displacement of the first floor, which is monitored with an error transducer, is the error signal to be minimized. The ground motion used for the computer simulation includes various real accelerograms. The passive TMD is able to attenuate the peak and root mean square (rms) responses by an average of 14.6 and 16.6%, respectively. The attenuation achieved for the hybrid passive/active control approach was 44.4 and 51.2%, respectively, which clearly demonstrates that the adaptive controller improves the effectiveness of the passive TMD to attenuate both the maximum and root-mean-square responses. The numerical simulation also shows that the algorithm adapts in “real time” for uncertainties and modeling errors in the system.

The paper discusses some of the recent developments in vibration control strategies for wind turbines, and in this context proposes a new dual control strategy based on the combination and modification of two recently proposed control schemes. Emerging trends in the vibration control of both onshore and offshore wind turbines are presented. Passive, active and semi-active structural vibration control algorithms have been reviewed. Of the existing controllers, two control schemes, active pitch control and active tendon control, have been discussed in detail. The proposed new control scheme is a merger of active tendon control with passive pitch control, and is designed using a Pareto-optimal problem formulation. This combination of controllers is the cornerstone of a dual strategy with the feature of decoupling vibration control from optimal power control as one of its main advantages, in addition to reducing the burden on the pitch demand. This dual control strategy will bring in major benefits to the design of modern wind turbines and is expected to play a significant role in the advancement of offshore wind turbine technologies.

Many developed and developing countries are investing a huge amount of resources to tap the potential of offshore wind energy. It has advantages over onshore wind farms in many aspects as it neither uses landmass nor creates noise problem to the human habitat. Continuous wind availability and better wind quality are some other advantages of offshore wind farms. With the advancement of offshore technology, deep draft floating platforms like spar have been developed recently. These deepwater floating-type platforms experience extreme marine environmental forces such as wind and waves. Floating offshore structures that are form-dominant types resist the dynamic wind and wave loads by means of displacement responses. Platform tower fore-aft, platform surge, and platform pitch movements/vibrations are the dominant responses among them. The dynamic tower fore-aft displacement reduces the power generation efficiency of the turbines and causes fatigue failure at the tower base. Hence, these movements need to be controlled to increase the performance of the wind turbines. Tuned mass damper is one of the commonly adopted damper systems to mitigate such unintended dynamic movements. Several studies with tuned mass damper on offshore structures reported that it can reduce the unintended dynamic structural responses positively. The present study intends to review the free vibration responses (to review the basic dynamic characteristics of the structure) of the spar platform with and without tuned mass damper (placed at the tower nacelle). The OC3 Hywind spar platform (benchmark) developed by National Renewable Energy Laboratory (NREL) is taken as the study structure. The benchmark study wind turbine structure incorporated OpenFAST software work frame is used for the evaluation. For the vibration response control, tuned mass damper properties (mass, stiffness, and damping) are evaluated corresponding to different mass ratios (tuned mass to tower mass). Initially, free vibration analyses are carried out in OpenFAST to find the natural frequencies in the respective degrees of freedom. Similarly, for free vibration control analysis, fore-aft initial displacement conditions are set, and corresponding free vibration tests are carried out with and without tuned mass dampers and the resulting responses are evaluated.KeywordsFloating offshore wind turbinesFore-aft displacementTuned mass damper

This paper is a comprehensive study of series tuned mass damper (TMDs) for vibration mitigation in passive, active, and semi-active manners. Recently, the authors proposed a novel configuration of TMD with multiple auxiliary absorbers connected to the primary structure in series, and proved that passive series TMDs are more effective and robust than other types of TMDs. Here we further extend the study to active and semi-active controls using LQG and clipped algorithms. The advantages of series TMDs are further highlighted in comparison with the classic TMD. Numerical simulations based on the parameters of Taipei 101 tower are carried out. It is founded that in the passive implementation we can reduce the total mass requirement by 40%, and decrease the damping coefficient to 1/30. We also found that in the active and semi-active manners, the requirement of actuation force is reduced to only 1/4 while achieving the same or better performance.

Offshore wind turbines suffer from severe wind and wave conditions which generate heavy fluctuating loads and vibrations leading to fatigue of turbine towers. We employ tuned mass dampers (TMDs) as passive structural vibration control method to reduce fluctuating loads acting on the tower. We obtain a discretized state space model from the coupled non-uniform NASA SCOLE (Spacecraft Control Laboratory Experiment) and TMD system, which represents a monopile wind turbine tower with a TMD system atop it, using spectral element method. The parameters of the TMD are optimized by minimizing the frequency-limited ℋ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> norm of the transfer function of the discretized state space model with force and torque as inputs and tower-top displacement as output. In addition to control design, our model can also be used for fast & accurate simulation for the dynamics of the wind turbine tower. Other advantages of our model and method over previous work are also analyzed. Verifications are conducted against FAST (Fatigue, Aerodynamics, Structures, and Turbulence) simulation.

The active control of a tall building, using tendons, is offered as an alternative control mechanism to that using an active tuned mass damper as this has been done in the Citicorp Center of New York City. It is shown that the tendon control system, when applied to a building subjected to self‐excited wind forces, provides more efficient control than a tuned mass damper system. However, tendon control may need larger forces than the tuned mass damper control. The paper shows systematically, with a numerical example, how to design the optimal control forces for both active tendons and active tuned mass dampers in order to introduce active damping to a tall building, even under nonlinear structural behavior, and the paper provides a comparison between two schemes of control.

Semi-active control of monopile offshore wind turbines under multi-hazards

Under the excitation of strong mainshock (MS), the structure will enter the nonlinear stage, whose hysteretic characteristic can be well-simulated by the Bouc–Wen (BW) model. The accompanying aftershock (AS) may increase structural damage and cause the safety problem, therefore, the advanced structural control technology is worthy of being applied to nonlinear structure under MS–AS sequences. The tuned mass damper (TMD) is a popular vibrational absorber, however, it is sensitive to the frequency deviation and may lose its effect for nonlinear dynamic response control in this issue. To protect the nonlinear tall building under MS–AS sequences effectively, a semi-active TMD (STMD) is investigated in this study, which can vary its frequency and damping in real time simultaneously. It can adapt to structural nonlinear behavior in each time segment through varying its stiffness according to the wavelet transform (WT) based algorithm, and meanwhile, enhance the energy dissipation through switching its damping coefficient in real time. A 10-story nonlinear tall building is proposed as a case study and for comparison, a passive TMD (PTMD) is used. Nine MS–AS sequences are elected and nonlinear structural control performance of STMD is highlighted. Results show that STMD can control structural displacement responses and base shear effectively and performs better than PTMD in reducing the plastic development of the structure as well. Further, energy analysis is proposed and it is verified that STMD has an excellent effect in decreasing the structural input energy from MS–AS sequences and dissipating more energy than PTMD. Especially, it is found that a strong AS may cause a larger response to the nonlinear structure than MS, while the nonlinear control effect of STMD is still significant in that case.

Tremor is a semirhythmic oscillatory movement of a body part caused by alternating simultaneous contractions of an antagonistic muscle group. Medical and surgical treatments used to reduce the symptoms of involuntary tremor can cause negative side effects. This study examined the ability of passive vibration absorbers in reducing the amplitude of postural tremor (PT). Inertial measurement unit (IMU) was used to record PT signals at the forearm and hand of a patient. IMU signal was used to excite an upper limb modeled to represent the flexion-extension vibrational motion at the joints. Equations of motion were solved numerically to obtain a response that fits the measured tremor signal. Passive tuned mass damper (TMD) was modeled as a cantilever beam and a screw placed along its length, at a position reflecting its operational frequency. Natural frequency of the TMD was derived for different mass positions and validated numerically and experimentally. Modal damping ratio of the TMD, for each mass position, was also estimated. Mass position and damping coefficient of the TMD were optimized depending on the minimization in the power spectral density (PSD) of angular displacement amplitude at the wrist joint. Optimized three-TMD system of 28.64 g total effective mass with the estimated modal damping ratio reduced 83.1% of the PSD of the angular displacement amplitude. This study showed the performance ability of a lightweight passive absorber in controlling the involuntary tremor of a system excited by the measured tremor signal of a patient.