Active Structural Control System Research Articles

Metaheuristic Airflow control for vibration mitigation of a hybrid oscillating water Column-Floating offshore wind turbine system

Unlike the fixed wind turbines, the structure of Floating Offshore Wind Turbines (FOWT) have the added motions of six degrees of freedom induced by the wind, wave and tidal loads. These motions lead to vibration and the degradation of the structure. This paper presents a novel approach to model and stabilize the FOWT by employing the Oscillating Water Columns (OWC) as active structural control system. The innovative concept involves designing a new floating barge-type platform with integrated OWCs on opposite sides of the platform to mitigate undesired oscillations of the system. These OWCs counteract the bending forces caused by wind on the tower and waves on the barge platform. To synchronize the opposing forces with the system’s tilting, a proposed Particle Swarm Optimization with Decreasing Inertia-based Adaptive Neuro-Fuzzy Inference System (PSODI-ANFIS) airflow control strategy is employed. Through manipulation of the barge platform’s pitch angle, the PSODI-ANFIS airflow control system adjusts the valves on either side, opening one and closing the other accordingly. Simulation results, compared with the standard FOWT as well as the Fuzzy-based airflow control system, demonstrate the effectiveness of the PSODI-ANFIS airflow control. It is shown to be superior in reducing platform pitching and the fore-aft translation of the top tower.

Improved Three-Variable Control for Electromagnetic Mass Damper System Considering Control–Structure Interaction

Current methods account for control–structure interaction (CSI) in structural control design, which may be unavailable in the preliminary design phase of actively controlled structures due to the unknown dynamic characteristic of an actuator. Therefore, it may result in significant difference in the design and evaluation of an active structural control system when ignoring or considering CSI at different phases. To eliminate the CSI effects of electromagnetic mass damper (EMD) system and thus decouple the tracking control of EMD from the control design of structure, in this paper, an improved three-variable control (ITVC) combining a signal convertor, a typical three-variable controller, and a voltage compensator is developed. The voltage compensator counteracts the influence of lower-order CSI including viscous damping force and Coulomb friction. The three-variable controller reduces the higher-order CSI effects, while the signal convertor converts all command and feedback signals to the relative coordinate system and eliminates the additional CSI effects. Performance tests and frequency response tests of the EMD system show that the CSI effects are basically eliminated by ITVC. In addition, shake table tests are performed on a one-story actively controlled structure to further verify ITVC. Experimental results suggest that ITVC can apply accurate control force on the structure and achieve ideal structural response control.

A novel active tendon pendulum tuned mass damper and its application in transient vibration control

Enhancing the performance characteristics of Tuned Mass Dampers (TMDs), in particular extending their narrow frequency band of operation, has been the subject of many researches. In the adaptive type of TMDs, the device's properties can be adjusted gradually in response to a slight alteration in the excitation characteristics and physical properties of the main structure. A novel vibration absorbing system, namely Active Tendon Pendulum TMD (AT-PTMD), is proposed in the present study. The device consists of a simple pendulum whose horizontal movement is restricted by a tendon with an adjustable tensile force which is attached to the pendulum’s rod. The device is designed and formulated, and its efficiency is assessed numerically and experimentally. For this purpose, a 3-degree of freedom structure is considered. Scrutinizing the responses of the uncontrolled, passively controlled and actively controlled structure shows the appropriate performance of the AT-PTMD in comparison with the passive TMD system in transient vibration reduction, particularly in reducing the total vibrational energy of the structure's response. Considering the achieved results, the proposed AT-PTMD system is capable of reducing the maximum displacement and acceleration of the main structure up to 43% and 37%, respectively, which substantiates its excellence over the common passive vibration absorbing devices. The case study also proves that the utilized mechanism for adjusting the equivalent stiffness of AT-PTMD increases its operating frequency range by 105% compared to common TMDs. Unlike active structural control systems, the suggested approach will not induce structural instability in any operating mode.

Energy regeneration of active pendulum system in tall buildings subjected to wind and seismic loads

High power demand of active structural control systems in tall buildings and incapability of energy storage system (ESS) in supplying the demanded power results in a power shortage which, in turn, can adversely affect their performance. Energy regeneration in active structural control systems may contribute to efficient energy management and sustainable power supply in these systems. This paper explores various aspects of energy regeneration of active pendulum system (APS) in tall buildings. A regenerative hybrid passive-active pendulum system (HPAPS) is proposed to control the wind-induced vibrations in a benchmark tall building. The vibration control system includes an APS that incorporates a fuzzy logic controller (FLC) to calculate the stabilizing torque. The regeneration system comprises an energy management system (EMS), DC-DC convertor, AC boost rectifier, ESS, and their corresponding controllers which have been carefully modeled and included in the simulations. Furthermore, the system is implemented in a laboratory-scale structure, and extensive shake table tests are carried out to examine the system's performance in the presence of seismic disturbances. The findings of this research are as follows: the proposed APS can well reduce the transmitted vibrations to the structure; the top story’s displacements and accelerations are reduced by 47 and 50 percent respectively in the benchmark model, implying the effectiveness of the active structural control system in enhancing simultaneous structural safety and inhabitants’ comfort. Moreover, the energy regeneration scheme can restore 34 percent of the APS’s power. Experimental results also verify the simulation results where a considerable drop in both the top story’s displacement and acceleration is reported for the test structure under seismic load. Furthermore, 44 percent of the active pendulum power is restored in the battery of the laboratory-scale APS.

Control-Force Spectrum Considering Both Natural Period and Damping Ratio for Active Base-Isolated Building

The active structural control (ASC) has been applied to base-isolated buildings to achieve a high-damping system. The critical step for designing an ASC system is selecting control parameters and isolation parameters that satisfy the design restrictions. However, the conventional methods are limited in theoretically estimating the maximum control force, which requires great demand for trial-and-error approaches and numerical simulations. This paper constructed the equivalent model of the feedback control system that theoretically expresses the dependence of vibration characteristics (natural period and damping ratio) of the control system on the feedback gain. Then, the control-force spectrum is proposed that estimates the maximum control force for a feedback control system, adjusting both the natural period and damping ratio of the control system. The maximum responses and control force are estimated without additional numerical simulations and trial-and-error approaches using the equivalent model and control-force spectrum. Moreover, a design method was devised for determining the allowance range of the vibration characteristics of structures (damping ratio and natural period) and controllers that satisfy the design limitations (maximum responses and maximum control force). The design method does not require trial-and-error and numerical simulations, thus simplifying the design procedure. Finally, this paper uses numerical examples and a design example to verify the validity of the control-force spectrum and design method.

Optimal stochastic compensator for time-delayed active structural control systems subjected to random excitations

Active feedback control systems confront with technical challenges when they are applied in civil engineering structures for vibration mitigation; one of which is the potential instability risk inherent in structure-control systems caused by insufficient compensation of time delay, especially in the scenario considering randomness associated with external excitations. To this end, this paper proposes an optimal stochastic compensator (OSC) to improve time-delayed active structural control systems subjected to random excitations. By extending the state vector, the OSC can be denoted as a linear combination between system state at the present time-step and control forces at the previous time-steps. According to the probabilistic criterion in function of reliability metrics of system state and control force, optimal cost-function weights of the OSC for good trade-off between control gain and control cost can be readily derived by introducing the framework of physically-based stochastic optimal (PSO) control. For verification purposes, randomly base-excited structures controlled by time-delayed active tendon systems, comprising single-degree-of-freedom, multi-degree-of-freedom and nonlinear oscillator systems, are investigated. The analysis and results reveal that the control performance is seriously degraded with increasing time delay; however, a rationally-designed OSC can be used to significantly improve control systems. Moreover, a definite relationship in cubic polynomial functions between optimal control cost-function weight of the OSC and time delay is obtained, by which the problem of time-varying delay compensation can be elegantly solved. In addition, the OSC has a good robustness, and can accommodate a larger effective time delay to linear systems than to nonlinear systems.

New spectra of responses and control force for design of equivalent-input-disturbance-based active structural control of base-isolated buildings

This paper presents new spectra of responses and control force for an active base-isolated building that uses the equivalent-input-disturbance (EID) approach for active structural control. The EID approach estimates the effect of disturbances and uses it to suppress building vibrations. This system plugs an EID estimator into a conventional state-feedback control system. Note that these kinds of disturbance-rejection systems contain both feedforward and feedback terms from disturbances to a control output. This paper describes spectra that can handle systems with such structure. The spectra can be used to simplify the design of an active structural control system. This paper illustrates the use of the spectra for control-system design and presents a design algorithm for the EID-based control system. A shear building model and 44 kinds of earthquake waves are used to demonstrate the availability of the spectra.

A spectrum for estimating the maximum control force for passive-base-isolated buildings with LQR control

The combination of passive-base-isolated (PBI) and active structural control (ASC) has been employed in many buildings globally to improve control performance. Controllers are mainly designed using the linear-quadratic-regulator (LQR) method, which minimizes the response and control force by using their weights. While the estimation of the required control force is important to select an appropriate actuator to perform ASC, previous approaches utilized trial-and-error because the dependency of the maximum control force on the natural period and the passive damper has not been expressed theoretically. To solve this problem, this paper presents a spectrum, namely a control-force spectrum, to estimate the maximum control force while considering the combination of PBI and ASC. An equivalent model of an ASC system is derived to describe the relationship between the vibration characteristics and the LQR weighting matrices. Using the equivalent model and the control-force spectrum, the maximum control force of an ASC system designed by the LQR method is estimated, and the appropriate maximum control force, natural period, and damping ratio are theoretically determined. This study also develops a design method for PBI construction with ASC that selects the natural period, passive damper, and maximum control force by using spectra without requiring trial-and-error and numerical simulations. A numerical design example validates the design method.

Online control of an active seismic system via reinforcement learning

Tuning the seismic control systems in order to achieve optimal performance is a challenging area due to the system and disturbance uncertainties. Although, model uncertainties, process time delay, and actuator dynamics can be considered as typical uncertainties, the main source of uncertainty in a seismic control system comes from the aleatory nature of earthquake disturbances. In this case, tuning of the control system based on a given seismic record may not necessarily result in optimal performance for other earthquakes. In this paper, a methodological approach is proposed for online control of active structural control systems considering seismic uncertainties. For this purpose, the concept of reinforcement learning is utilized for online tuning of an active mass drive system. The controller comprises a gain-scheduling fuzzy proportional derivative controller whose gains are tuned via an online reinforcement learning algorithm. Moreover, in order to tackle the time delays, a dynamic state predictor is utilized in conjunction with the proposed controller. To evaluate the performance of proposed controller, according to an assumed site hazard, thousand ground motion records are generated and clustered based on their spectral features using a fuzzy clustering approach. Finally, the controller is implemented in a laboratory-scale structure, and its performance is examined in the presence of the cluster centers and some real seismic records simulated on a shake table. The test results reveal successful performance of the proposed controller in tackling a wide range of seismic disturbances in the presence of time delay.

Automatic determination of LQR weighting matrices for active structural control

This paper presents a method for the automatic selection of weighting matrices for a linear-quadratic regulator (LQR) in order to design an optimal active structural control system. The weighting matrices of a control performance index, which are used to design optimal state-feedback gains, are usually determined by rule of thumb or exhaustive search approaches. To explore an easy way to select optimal parameters, this paper presents a method based on Bayesian optimization (BO). A 10-degree-of-freedom (DOF) shear building model that has passive-base isolation (PBI) under the building is used as an example to explain the method. A control performance index that contains the absolute acceleration, along with the inter-story drift and velocity of each story, is chosen for the design of the controller. An objective function that contains the maximum absolute acceleration of the building is chosen for BO to produce optimal weighting matrices. In the numerical example, a restriction on the displacement of the PBI is used as a constraint for the selection of weighting matrices. First, the BO method is compared to the exhaustive search method using two parameters in the weighting matrices to illustrate the validity of the BO method. Then, thirty-three parameters (which are automatically optimized by the BO method) in the weighting matrices are used to elaborately tune the controller. The control results are compared to those for the exhaustive search method and conventional optimal control, in terms of the control performance of the relative displacement, absolute acceleration, inter-story-drift angle, and the story-shear coefficient of each story. The damping ratio for each mode, and the control energy and power are also compared. The comparison demonstrates the validity of the method.

Effect of soil in controlling the seismic response of three-dimensional PBPD high-rise concrete structures

In the last decades, valuable results have been reported regarding conventional passive, active, semi-active, and hybrid structural control systems on two-dimensional and a few three-dimensional shear buildings. In this research, using a three-dimensional finite element model of high-rise concrete structures, designed by performance based plastic design method, it was attempted to construct a relatively close to reality model of concrete structures equipped with Tuned Mass Damper (TMD) by considering the effect of soil-structure interaction (SSI), torsion effect, hysteresis behavior and cracking effect of concrete. In contrast to previous studies which have focused mainly on linearly designed structures, in this study, using performance-based plastic design (PBPD) design approach, nonlinear behavior of the structures was considered from the beginning of the design stage. Inelastic time history analysis on a detailed model of twenty-story concrete structure was performed under a far-field ground motion record set. The seismic responses of the structure by considering SSI effect are studied by eight main objective functions that are related to the performance of the structure, containing: lateral displacement, acceleration, inter-story drift, plastic energy dissipation, shear force, number of plastic hinges, local plastic energy and rotation of plastic hinges. The tuning problem of TMD based on tuned mass spectra is set by considering five of the eight previously described functions. Results reveal that the structural damage distribution range is retracted and inter-story drift distribution in height of the structure is more uniform. It is strongly suggested to consider the effect of SSI in structural design and analysis.

Semi-active control of flexible structures using closed-loop input shaping techniques

In this research effort, a novel approach on the control of structures with magnetorheological (MR) dampers is presented, based on an appropriately adapted closed-loop version of the generic input shaping control theory. The MR damper is a very promising kind of semi-active control system (actuator), mixing the advantages of the active and passive structural control systems, hence their increasing use as attenuators that reject the effects of dynamic loads on civil engineering structures. The main contribution of this article is the application and performance evaluation of the novel ‘Linear Matrix Inequality-based’ feedback version of the input shaping control theory for the first time in the area of structural control. The need for the use of a feedback version of input shaping control stems from the design trade-off between robustness and speed of response requirements. A simulation of a benchmark three-story building with one MR damper is employed to verify the efficiency of the proposed control approach. The nonlinear behaviour of the MR damper, rigidly connected between the first floor of the structure and the ground, is captured by the well-known Bouc–Wen model. The superiority and effectiveness of the proposed scheme in reducing the responses of the structure were proved using seven quantifiable evaluation criteria and by comparing these results with those achieved by classical and well-established alternative control schemes. Copyright © 2016 John Wiley & Sons, Ltd.

Modified sliding mode control of a seismic active mass damper system considering model uncertainties and input time delay

Model uncertainties and actuator delays are two factors that degrade the performance of active structural control systems. A new robust control system is proposed for control of an active tuned mass damper (AMD) in a high-rise building. The controller comprises a two-loop sliding model controller in conjunction with a dynamic state predictor. The sliding model controller is responsible for model uncertainties and the state predictor compensates for the time delays due to actuator dynamics and process delay. A reduced model that is validated against experimental data was constructed and equipped with an electro-mechanical AMD system mounted on the top storey. The proposed controller was implemented in the test structure and its performance under seismic disturbances was simulated using a seismic shake table. Moreover, robustness of the proposed controller was examined via variation of the test structure parameters. The shake table test results reveal the effectiveness of the proposed controller at tackling the simulated disturbances in the presence of model uncertainties and input delay.

Active mass damper system using time delay control algorithm for building structure with unknown dynamics

This paper numerically investigates the feasibility of an active mass damper (AMD) system using the time delay control (TDC) algorithm, which is one of the robust and adaptive control algorithms, for effectively suppressing the excessive vibration of a building structure under wind loading. Because of its several attractive features such as the simplicity and the excellent robustness to unknown system dynamics and disturbance, the TDC algorithm has the potential to be an effective control system for mitigating the vibration of civil engineering structures such as buildings and bridges. However, it has not been used for structural response reduction yet. In this study, therefore, the active control method combining an AMD system with the TDC algorithm is first proposed in order to reduce the wind-induced vibration of a building structure and its effectiveness is numerically examined. To this end, its stability analysis is first performed; and then, a series of numerical simulations are conducted. It is demonstrated that the proposed active structural control system can effectively reduce the acceleration response of the building structure.

Multi-objective genetic algorithms for cost-effective distributions of actuators and sensors in large structures

This paper proposes a multi-objective genetic algorithm (MOGA) for optimal placements of control devices and sensors in seismically excited civil structures through the integration of an implicit redundant representation genetic algorithm with a strength Pareto evolutionary algorithm 2. Not only are the total number and locations of control devices and sensors optimized, but dynamic responses of structures are also minimized as objective functions in the multi-objective formulation, i.e., both cost and seismic response control performance are simultaneously considered in structural control system design. The linear quadratic Gaussian control algorithm, hydraulic actuators and accelerometers are used for synthesis of active structural control systems on large civil structures. Three and twenty-story benchmark building structures are considered to demonstrate the performance of the proposed MOGA. It is shown that the proposed algorithm is effective in developing optimal Pareto front curves for optimal placement of actuators and sensors in seismically excited large buildings such that the performance on dynamic responses is also satisfied.

Dynamic Sensing Performance of a Point-Wise Fiber Bragg Grating Displacement Measurement System Integrated in an Active Structural Control System

In this work, a fiber Bragg grating (FBG) sensing system which can measure the transient response of out-of-plane point-wise displacement responses is set up on a smart cantilever beam and the feasibility of its use as a feedback sensor in an active structural control system is studied experimentally. An FBG filter is employed in the proposed fiber sensing system to dynamically demodulate the responses obtained by the FBG displacement sensor with high sensitivity. For comparison, a laser Doppler vibrometer (LDV) is utilized simultaneously to verify displacement detection ability of the FBG sensing system. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is used to provide full-field vibration mode shapes and resonant frequencies. To verify the dynamic demodulation performance of the FBG filter, a traditional FBG strain sensor calibrated with a strain gauge is first employed to measure the dynamic strain of impact-induced vibrations. Then, system identification of the smart cantilever beam is performed by FBG strain and displacement sensors. Finally, by employing a velocity feedback control algorithm, the feasibility of integrating the proposed FBG displacement sensing system in a collocated feedback system is investigated and excellent dynamic feedback performance is demonstrated. In conclusion, our experiments show that the FBG sensor is capable of performing dynamic displacement feedback and/or strain measurements with high sensitivity and resolution.

Servo Control Strategy of Single Axis Shaking Table in Active Structural Control System

The purpose of this paper is to develop an approach to improve the tracking characteristics of a single axis shaking table actuation system, which is used in active structural control system. Firstly, the process of constructing analytical model of servo-hydraulic actuation system is presented. The proposed model, in the form of the total shaking table transfer function, accounts for the specific physical characteristics of the single axis shaking table. Due to low natural frequency and small hydraulic actuator damping, the single axis shaking table cannot meet the experimental requirement Therefore, three states feedback and three state feed-forward control algorithm based on pole-assignment principle is applied to extend the acceleration bandwidth. Lastly, the shaking table experiments are tested and the experimental results indicate that the controller is effective and reliable.

불확실성을 고려한 동조질량 감쇠기(TMD) 시스템의 다자유도 슬라이딩 모드 지진동 제어

지진동에 대처하기 위한 구조물의 능동제어기를 설계할 때, 모델링의 오차 및 외란의 불확실성을 무시하고 진행하면 제어성능이 크게 퇴화될 수 있다. 심지어 시스템 전체가 불안정하게 되어 제진이 불가능하게 될 가능성도 배제할 수 없다. 본 연구의 목적은 슬라이딩 모드제어기(SMC)라 불리는 비선형제어기의 제어성능을 TMD가 장착된 구조물에 설계하여 그 적용 가능성을 검토하는 것이다. 이때 가진 외란은 FFT 해석으로 탁월주파수를 분석한 3개의 지진동이다. SMC로 제어한 결과, 구조물의 질량과 강성이 <TEX>${\pm}30%$</TEX> 섭동되어도 강인성을 유지하고 있음을 확인할 수 있었다. 다만, 오버슈트가 증대되고 정정시간이 증가하는 등 과도응답성능은 다소 퇴화되는 것을 확인할 수 있었다. 전반적으로 SMC는 모델링 및 외란의 불확실성에 대해 강인함을 유지하고 지진동을 효과적으로 제어하는 능동제어법으로 TMD 구조물과 결합시켜 지진동제어에 적용해 볼 수 있는 유용한 기법이라 판단된다. The control performance in active structural control system can be drastically deteriorated when the modeling errors and the uncertainties existing in the disturbances are disregarded in the designing stage. It can even throw the control system into an unstable phase, resulting in out of control against the seismic excitations. The purpose of the study is to investigate the control effectiveness of a non-linear control system called sliding mode controller(SMC) in cooperation with a Tuned Mass Damper subjected to the three seismic excitations selected from the FFT analysis. Even though the transient performance such as settling time and overshoot were deteriorated, the robustness against the system stability was appeared from SMC when the structural masses and stiffness perturbed within the range of <TEX>${\pm}30%$</TEX>. SMC is a feasible technique for active structural control in cooperation with TMD against seismic disturbances, exhibiting robustness in perturbation of system stiffness and mass as well as uncertainties of the disturbances.

Passive structural control of offshore wind turbines

AbstractThe application of control techniques to offshore wind turbines has the potential to significantly improve the structural response of these systems. A new simulation tool is developed that can be utilized to model passive, semi‐active and active structural control systems in wind turbines. Two independent, single degree of freedom (DOF) tuned mass‐ damper (TMD) devices are incorporated into a modified version of the aero‐elastic code FAST (Fatigue, Aerodynamics, Structures and Turbulence). The TMDs are located in the nacelle of the turbine model, with one TMD translating in the fore‐aft direction, and the other in the side‐side direction. The equations of motion of the TMDs are incorporated into the source code of FAST, yielding a more realistic system for modeling structural control in wind turbines than has previously been modeled. The stiffness, damping and commanded force of each TMD are controllable through the FAST‐Simulink interface, and so idealizations of semi‐active and active control approaches can be implemented. A parametric study is performed to determine the optimal parameters of a passive single DOF, fore‐aft, TMD system in both a barge‐type and monopile support structure. The wind turbine models equipped with TMDs are then simulated and the performance of these new systems is evaluated. The results indicate that passive control approaches can be used to improve the structural response of offshore wind turbines. The results also demonstrate the potential for active control approaches. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Multiple-model structural control for seismic protection of nuclear power plant

An approach for multiple-model structural control is developed for seismic protection of nuclear power plant, based on active structural control systems. Structural control provides opportunity to realize measures for reduction of seismic vulnerability of high risk structures, like nuclear power plants. The reliability of devices and systems for seismic protection is proved after modelling and simulation of seismic structural control with strong motion real or synthetic seismic signals, maximal close to the realistic ones. In suggested multiple-model system each sub-system corresponds to different actuator or combination of actuators for structural control of different parts of reactor building. After determination of frequency, characteristics, resonances and anti-resonances, is taken decision about reconfiguration of the structural control system. Simulation results for multiple-model active structural control system are shown.