Performance Comparison of Different Vibration Control Strategies

In this paper, the characteristics of forces in active control systems connected to adjacent levels of a building are analyzed. The following characteristics are observed: (1) active control can provide significantly superior supplemental damping to a building, but causes a small frequency shift; (2) the linear quadratic regulator (LQR)-based control force is composed of an elastic restoring force component and a damping force component, where the damping force is almost identical to the total control force, however, the elastic restoring force is very small; and (3) the active control forces prevent motion most of the time during the entire control process. These three characteristics imply that active control systems connected to adjacent levels of a building behave like passive damping devices with adjustable parameters, namely damping characteristics in an active control, which is the mechanism used by semi-active control devices to reach similar performance as active control systems. Two indices are defined to quantify the damping characteristics of control forces in active control systems. These two indices can also be used to quantify the capacity of semi-active control to achieve the performance of active control. Based on the above observations, two principles are founded for optimization of parameters of semi-active control devices and passive dampers. The first is that the maximum output force of a semi-active or passive device to be designed is identical to an active device, called “design principle”. The other is the response equivalent principle, which states that the response of a building with semi-active or passive devices is the same as with active devices when the same maximum output force is applied. The design procedure for semi-active control devices and passive dampers is described in detail. Finally, numerical simulations of two benchmark problems is conducted to demonstrate the damping characteristics of active control and investigate the capacity of semi-active control to achieve the same performance as active control.

The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric detectors cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture consists in several stages cooled using different active coolers. These generate weak thermal fluctuations on the HFI thermal stages. Without a dedicated thermal control system these fluctuations could produce unwanted systematic effects, altering the scientific data. The HFI thermal architecture allows to minimise these systematic effects, thanks to passive and active control systems described in this paper. The passive and active systems are used to damp the high and low frequency fluctuations respectively. The results of the simulation of these active and passive control systems are presented here. These simulations based on the use of thermal transfer functions for the thermal modelling can then be used for finding the optimal working point of the HFI PID active thermal control system.

This paper presents an overview and problem definition of a benchmark problem for the response control of wind-excited tall buildings. The building considered is a 76-story 306 m concrete office tower proposed for the city of Melbourne, Australia. The building is slender with a height to width ratio of 7.3; hence, it is wind sensitive. Wind tunnel tests for such a 76-story building model have been conducted at the University of Sydney and the results of across-wind data are used in the present benchmark problem. Either active, semiactive, or passive control systems can be installed in the building to reduce the wind response, although only an active control sample problem has been worked out to illustrate the control design. In the case of active control systems, either an active tuned mass damper or an active mass driver can be installed on the top floor. In the case of passive or semiactive systems, such as viscous dampers, viscoelastic dampers, electrorheological, or magnetorheological dampers, etc., control devices can be installed in selected story units. Control constraints and evaluation criteria are presented for the design problem. A simulation program based on the linear quadratic Gaussian technique has been developed and made available for the comparison of the performance of various control strategies.

It is generally accepted that active control systems provide better structural performance when compared to their passive counterparts. On the other hand, the design of active control systems based on linear control theory is highly dependent on the structural properties. For this reason, their performance is expected to be affected more severely by variations in structural properties compared to those of passive systems. These variations can occur due to nonlinear structural behavior, or even before that due to uncertainties in the estimation of these properties and in numerical modeling. The present work is an investigation of the dependency of various control systems used for supplemental energy dissipation to the changes in structural properties. For this purpose, the performance degradations of most common control systems are studied for structures entering their nonlinear response range. The considered control systems include active control using linear quadratic regulator algorithm and passive control using viscous fluid dampers and yielding devices. These control systems are optimized separately for linear and nonlinear structures by minimizing performance indices based on inter-story drift and absolute acceleration response. It is shown that among these control systems, viscous dampers are affected the least by the alteration of structural properties, which may further support their utilization contrary to the more costly active control systems. It is also shown that the amount of performance degradation depends on the selected structural performance index, and more importantly, the severity of the earthquake excitation.

Visual Acuity Chart

In recent years, intensive research works are concentrated on the development of semi-active control devices. A semi-active control system can also be explained as a system that mainly requires a small external power source for functioning and applies the motion of the structure to generate the control forces. A semi-active control system typically begins from a passive control system, which is followed by a change to permit the flexibility of mechanical properties. The mechanical properties of the semi-active control devices may be modified depending upon the response from the excitation and/or from the calculated reaction. Magneto-rheological (MR) dampers are a type of a semi-active control device that, in the presence of Magneto-rheological (MR) fluid, responds to the applied vibrations. This type of damper has copper winding in it, forming an electronic circuit internally with a combination of MR fluids. The effectiveness of MR damper greatly depends on the command voltage to the copper winding. In the present study, the response of MR Damper to the command voltage, and the excitation frequency is experimentally evaluated. MR damper is supported by a wall mounting rigid fixture and connected to a shake table by a fixing unit. The voltage is varied from 0 V - 10 V with an interval of 2 V. Command voltages is applied to the MR damper with the help of voltage regulator and digital multi meter. The effect of excitation frequency is also studied (1 Hz – 8 Hz). While conducting the experimental work, acceleration values are obtained through the Data acquisition system. These acceleration values are integrated to get the velocity and displacement response. The relation between the displacement, velocity, acceleration of the MR damper, and the frequency of shake table and command voltage is studied. From the experimental work, it is observed that the displacement response of the damper is effectively controlled by increasing the command voltage.

Hybrid Passive/Active Control Performance in Buildings Using Robust Control Design Approaches

The strong need of verifying theories formulated for semi-active control through applications to real structures is due to the fact that theoretical research on semi-active control systems is not matched by a corresponding satisfactory experimental activity. This paper shows how a smart system including magnetorheological devices as damping elements can be implemented in a large-scale structural model, by describing in detail the kind of electronics (dedicated hardware and software) adopted during the experimental campaign. It also describes the most interesting results in terms of reduction of the seismic response (either experimental or numerical) of the semi-actively controlled structure compared to a passive operating control system, and in terms of the evaluation criteria proposed in the benchmark for seismically excited controlled buildings. The paper also explains how to derive from the classical theory of optimal control the adopted control logic, based on a clear physical approach, and provides an exhaustive picture of the time delays characterizing the control sequence.

Hybrid Control of Smart Structures Using a Novel Wavelet-Based Algorithm

The demand of seismic resistance in structures and constructions is increasing, the Vibration control techniques are gaining more attention. Many researchers have investigated different vibration control systems to reduce the response of structures in earthquakes, including passive, active, semi-active, and hybrid vibration control systems. This paper represents the historical background and development of each technique is represented. Moreover, the advantage and limits of these devices are argued. Finally, the applications and the future prospects of these techniques are discussed.

The increased prevalence of semi-active control systems is largely due to the emergence of cost effective commercially available controllable damper technology such as Magneto-Rheological (MR) devices. Unfortunately, MR dampers are highly nonlinear, which presents an often over-looked complexity to the control system designer. The well-known Skyhook Damping control algorithm has enjoyed great success for both fully active and semi-active control problems. The Skyhook design strategy is to create a control force that emulates what a passive linear damper would create when connected to an inertial reference frame. Skyhook control is device independent since it generates a desired control force command output that must be produced by the control system. For simplicity, MR dampers are often assumed to have a linear relationship between the current input and the force output at a given relative velocity. Often this assumption is made implicitly and without knowledge of the underlying nonlinearity. In this paper, we show that the overall performance of a semi-active Skyhook control system can be improved by explicitly inverting the nonlinear relationship between input current and output force. The proposed modification will work with any semi-active control algorithm, such as Skyhook, to insure that the controller performance is at least as good as the performance without the proposed modification. This technique is demonstrated through simulation on a quarter-vehicle system.

The dynamic performance of base isolation systems provides an effective means to reduce the seismic vulnerability of buildings. However, large displacements in the base isolation during seismic events pose a major challenge for this control system. Recently, novel control systems have been implemented to control and reduce the excessive displacements. This study presents an evaluation of the seismic performance of unconnected‐fiber‐reinforced elastomeric isolators (U‐FREI) and variable orifice damper (VOD) devices used together as a hybrid control system for a low‐degree‐of‐freedom reference structure by employing real‐time hybrid simulation (RTHS) testing technique. This physical cybernetic testing methodology allows a dynamic system of interest to be substructured into two components: numerical and experimental. In this study, the numerical substructure corresponds to a 2‐degree of freedom model, representing a reference structure, and an experimental substructure was formed using the hybrid control system described. To develop an interface between the two substructures, a horizontal transfer system (HTS) was implemented and coupled with a vertical transfer system (VTS). Using RTHS, the performance of the reference structure and the hybrid control system was evaluated under six seismic events: CAM, CAT, El Centro, Loma Prieta, Pizarro, and Chihuahua, at a maximum acceleration of 0.10 g (0.981 m·s−2). The experimental behavior of the hybrid control system allows the reference structure to reduce its maximum drift by more than 24% compared to the fixed structure. Finally, the performance and accuracy of the RTHS tests were calculated.

The seismic response reduction of the semi-active fuzzy control system including a newtype of piezoelectric variable-friction damper and fuzzy controller was investigated on theshaking table under various earthquake records for a building model. The performance ofthe piezoelectric actuator under different preloads was tested in advance to identify itsforce generation. The feature test of the damper under either constant or linear increasedvoltage was carried out to study its motion characteristics. Based on the experimental testsof the damper, a semi-active fuzzy control algorithm was presented for the real-timemanipulation of the damper according to the structural response. The seismicperformance of the building structural model was tested for the uncontrolled,passive-controlled and semi-active controlled cases. The semi-active control effectiveness ofthe damper was compared with other cases. Experimental results have indicatedthat the proposed semi-active control system based on the fuzzy controller andpiezoelectric variable-friction damper can be more efficient in reducing the inter-storeydrifts and accelerations of the building under various earthquake excitations.

Active vibration control using regenerated vibration energy, i.e., self-powered active control, is proposed. In the self-powered active control system, vibration energy is regenerated by an electric generator, which is called an energy regenerative damper, and is stored in the condenser. An actuator achieves active vibration control using the energy stored in the condenser. The variable-value resistance whose value can be controlled by a computer is utilized to control output force of the actuator. The authors examine the performance of the self-powered active vibration control on experiments and propose to apply this system to cab suspensions of a heavy duty truck. Through experiments, it is shown that the self-powered active vibration control system has better isolation performance than a semi-active and a passive control system. Numerical simulations demonstrate better isolation performance of the self-powered active vibration control in cab suspensions of a heavy duty truck.

In this paper, a hybrid fault tolerant control system is proposed for air–fuel ratio control of internal combustion gasoline engines based on Kalman filters and triple modular redundancy. Hybrid fault tolerant control system possesses properties of both active fault tolerant control system and passive fault tolerant control system. As part of active fault tolerant control system, fault detection and isolation unit is designed using Kalman filters to provide estimated values of the sensors to the engine controller in case of faults in the sensors. As part of passive fault tolerant control system, a dedicated proportional–integral feedback controller is incorporated to maintain air–fuel ratio by adjusting the throttle actuator in the fuel supply line in faulty and noisy conditions for robustness to faults and sensors’ noise. Redundancy is proposed in the sensors and actuators as a simultaneous failure of more than one sensor, and failure of the single actuator will cause the engine shutdown. Advanced redundancy protocol triple modular redundancy is proposed for the sensors and dual redundancy is proposed for actuators. Simulation results in the MATLAB Simulink environment show that the proposed system remains stable during faults in the sensors and actuators. It also maintains air–fuel ratio without any degradation in the faulty conditions and is robust to noise. Finally, the probabilistic reliability analysis of the proposed model is carried out. The study shows that the proposed hybrid fault tolerant control system with redundant components presents a novel and highly reliable solution for the air–fuel ratio control in internal combustion engines to prevent engine shutdown and production loss for greater profits.