Passive Isolation System Research Articles

Fuzzy Logic Controlled Semi-Active Floating Raft Vibration Isolation System

A warship may be detected in hostile waters because of its unique acoustic signature. A typical two-stage passive vibration isolation system used on ships and submarines to isolate onboard machinery is the floating raft isolation system. The passive isolation system, though robust, may result in substantially high transmission of forces to the foundation at certain excitation frequencies, adversely affecting the ship's stealth. This paper highlights the results of a simulation study aimed at the design of a semi-active floating raft vibration isolation system with the objective of mitigating the acoustic signature of a warship by minimising the transmission of forces, resulting from operation of onboard machinery, to the foundation. A semi-active control scheme with variable damping has been proposed for the floating raft, the variable damping being achieved by means of an electrorheological (ER) damper. A fuzzy logic controller has been designed to achieve the best isolation effect by analysing the characteristics of the frequencies in the excitation signal. The designed semi-active control system is subjected to a time-varying signal, each time-segment corresponding to a different optimal damping ratio. The MATLAB simulation results indicate that the proposed fuzzy logic control method is more effective in vibration isolation than the passive method thereby indicating the potential of the designed semi-active control system in reducing a ship's acoustic signature.

Combined primary–secondary system approach to the design of an equipment isolation system with High-Damping Rubber Bearings

Isolating acceleration-sensitive equipment from the motion of the supporting structure represents an effective protection from earthquake damage. In this paper, a passive equipment isolation system composed of High-Damping Rubber Bearings (HDRB) is designed by adopting a coupled approach in which the supporting structure and the isolated equipment are considered as parts of a combined primary–secondary system and analyzed together. This allows for taking into account their dynamic interaction when significant and non-negligible according to the mass ratio and to the frequency ratio. The design methodology is developed by resorting to a reduced-order 2-DOF model of the combined system, a linear visco-elastic constitutive model of the isolation system and to a modal damping constraint depending upon the damping properties of the HDRB and their rubber compound. A 1:5 scale experimental model, consisting of a two-storey steel frame and a heavy block-type mass isolated from the second floor, is subsequently used to exemplify the design methodology and to perform shaking table tests. The dynamic properties of the experimental model are identified and the seismic performance of the equipment isolation system is discussed under a wide selection of seismic inputs, both artificial and natural.

Retrofitting A Passive Vibration Isolation System with Zero-Compliance Modules

A vibration isolation module with zero-power magnetic suspension is developed to retrofit a passive vibration isolation system to improve the performance against direct disturbance. In the module, the zero-power magnetic suspension mechanism is connected in series with a normal spring through a middle mass. This structure can generate zero compliance to direct disturbance while the transmitted vibration is still reduced. Such zero- compliance module was actually designed and fabricated. The characteristics of the fabricated module were studied experimentally. A passive vibration isolation system using air springs were retrofitted with four modules. It was demonstrated that the performance against direct disturbance was improved significantly.

Passive Vibration Isolation by Compliant Mechanism Using Topology Optimization

Compliant mechanisms have been designed for various types of applications to transmit desired forces and motions. In this paper, we explore an application of compliant mechanisms for passive vibration isolation systems. For this, a compliant isolator is used to cancel undesired disturbances, resulting in attenuated output amplitude. A compliant mechanism is equipped with an isolator, while a compliant mechanism also functions as a transmission of force and controls the amount of displacement that is transmitted from it. It can be used as passive vibration isolation. Here, by introducing compliance into the connection, the transmission of applied forces is reduced at some frequencies at the expense of increasing transmission at other frequencies. While transmitted force is the key parameter from the receiver’s perspective, motion at the isolated machine is uninteresting. The force transmissibility is numerically identical to the motion transmissibility. The structural optimization approach is focused on the determination of the topology, shape, and size of the mechanism. The building blocks are used to optimize a structure for force transmission. The flexible building blocks method is used for the optimal design of compliant mechanisms. This approach is used to establish the actuator model of the block and its validation by commercial finite element software. A library of compliant elements is proposed in FlexIn. These blocks are limited in number, and the basis is composed of 36 elements. The force transmitted to the rigid foundation through the isolator is reduced in order to avoid the transmission of vibration to other machines. The preliminary results of FEA from ANSYS demonstrate that compliant mechanism can be effectively used to reduce the amount of force transmitted to the surface.

Design and experimentation on passive vibration isolation systems using PZT- PDMS composite and a shape memory alloy wire integrated mechanism

Abstract Passive use of smart materials for vibration isolation of dynamic systems is drawing wide attention due to its flexibility, vast applicability and effectiveness in aerospace and automobile applications. In the present work, we design and investigate experimentally, the application of two vibration isolation systems based on such passive smart materials. First, a smart composite based on Lead Zirconate-Titanate (PZT) and Poly-dimethylsiloxane (PDMS) is considered as a conventional system. Further, a Shape Memory Alloy (SMA) wire integrated four bar linkage mechanism is chosen as a novel system for this study. In the first phase, vibration response of a single stage isolation system is obtained for a low frequency range from 10-70 Hz. The vibration isolation system comprises of neoprene rubber tubes as a spring element. Experiments are carried out with neoprene rubber blocks and piezoelectric (PZT)-PDMS composite. Finally, the piezoelectric damper is replaced by a new four bar linkage incorporating pre-stressed SMA wire in order to determine its efficiency of vibration isolation. The SMA wire undergoes pseudoelastic transformation at a temperature higher than austenite finish temperature due to loading and unloading upon induction of transverse vibrations from electro-dynamic shaker. Frequency responses and transmissibility of the proposed device are also analyzed. The experimental results project that SMA wire based passive damping system could be a very effective solution for vibration isolation. Future work will investigate the improvement of the design of SMA wire based vibration isolation system.

Researches on Nonlinear Hybrid Vibration Isolation System

In this paper, the dynamics of nonlinear hybrid vibration isolation system is carried out for a qualitative analysis, based on the algorithm of synovial variable structure the control model of hybrid vibration isolation system is designed, and then the validity of the control model is verified by relevant examples in the condition of nonlinear stiffness. Moreover, the simulation results show that: the control performance of nonlinear hybrid vibration isolation is better than passive vibration isolation and linear vibration isolation system, and the introduction of nonlinear stiffness can effectively reduce the force transmited to foundation. The control methods studied in this paper has an important guiding significance to design the nonlinear hybrid vibration isolation system in the practical engineering.

다목적 유전자알고리즘을 이용한 첨단기술산업 시설물의 스마트 미진동제어

Reduction of microvibration is regarded as important in high-technology facilities with high precision equipments. In this paper, smart control technology is used to improve the microvibration control performance. Mr damper is used to make a smart base isolation system amd fuzzy logic control algorithm is employed to appropriately control the MR damper. In order to develop optimal fuzzy control algorithm, a multi-objective genetic algorithm is used in this study. As an excitation, a train-induced ground acceleration is used for time history analysis and three-story example building structure is employed. Microvibration control performance of passive and smart base isolation systems have been investigated in this study. Numerical simulation results show that the multi-objective genetic algorithm can provide optimal fuzzy logic controllers for smart base isolation system and the smart control system can effectively reduce microvibration of a high-technology facility subjected to train-induced excitation.

Multiaxial active isolation for seismic protection of buildings

Passive isolation has been widely accepted as an effective means for the protection of structures against seismic hazards. The isolation bearings, typically placed at the base of the structure, increase the flexibility of the structure and shift its fundamental frequency away from the dominant frequency of seismic excitations, resulting in significantly reduced interstory drifts and floor accelerations. During severe earthquakes, the performance of passive isolation systems is usually achieved at the expense of having large base displacements. Alternatively, active isolation combines isolation bearings with adaptive actuators to effectively mitigate the base displacements, while maintaining reasonable interstory drifts and floor accelerations. Despite successfully theoretical proof documented in previous studies, most experimental implementations only verified active isolation with unit-axial actuators under unidirectional excitations. Earthquakes are intrinsically multidimensional, resulting in out-of-plane responses such as torsional responses. Therefore, the focus of this paper is the development and experimental verification of active isolation strategies for multistory buildings subjected to bidirectional earthquake loadings. First, a model building is designed to be dynamically similar to a representative full-scale structure. The selected isolation bearings feature low friction and high vertical stiffness, providing stable behavior. In the context of the multidimensional response control, three custom-manufactured and appropriately scaled actuators are employed to mitigate both in-plane and out-of-plane responses. In addition, the structure is subjected to multi-directional earthquake ground motion. To obtain a high-fidelity model of the active isolation systems, the authors propose a hybrid identification approach, which combines the advantages of the lumped mass model and nonparametric methods. Control-structure interaction is also included in the identified model to further enhance the control authority. By employing the H2/LQG control algorithm, the controllers for the hydraulic actuators are shown to offer high performance and good robustness. Active isolation is found to possess the ability to reduce base displacements and produce comparable accelerations and interstory drifts to passive isolation. The proposed active isolation strategies are validated experimentally for a six-story building tested on the six-degree-of-freedom shake table in the Smart Structures Technology Laboratory at the University of Illinois at Urbana-Champaign. Copyright © 2013 John Wiley & Sons, Ltd.

Design of a vibration isolation system using eddy current damper

This article aims at modeling, analysis and design of a passive vibration isolation system using a magnetic damper with high efficiency and compactness. The experimental set-up was developed for a single degree-of-freedom vibration isolation system, where the damper consists of two elements: an outer stationary conducting tube made up of copper and a moving core made up of an array of three ring-shaped neodymium magnets of Nd–Fe–B alloy separated by four block cylinders made of mild steel that are fixed to a steel rod. The generation of eddy currents in the conductor and its resistance causes the mechanical vibration to dissipate heat energy. The vibration response of the system is obtained starting from a low-frequency range. The proposed magnetic damper achieves a maximum transmissibility value less than two for a natural frequency that is less than 10 Hz and the excitations at higher frequencies are successfully isolated. Numerical and experimental studies were carried out for a range of system parameters which show that isolators based on magnetic damping could be very effective for passive vibration isolation. Further, a theoretical model for an active isolation system is proposed in order to reduce the transmissibility at resonance. It is envisaged that the combined active–passive eddy current damper could be effectively used for vibration isolation.

Seismic performance evaluation of an MR elastomer-based smart base isolation system using real-time hybrid simulation

Recently, magneto-rheological (MR) elastomer-based base isolation systems have been actively studied as alternative smart base isolation systems because MR elastomers are capable of adjusting their modulus or stiffness depending on the magnitude of the applied magnetic field. By taking advantage of the MR elastomers’ stiffness-tuning ability, MR elastomer-based smart base isolation systems strive to alleviate limitations of existing smart base isolation systems as well as passive-type base isolators. Until now, research on MR elastomer-based base isolation systems primarily focused on characterization, design, and numerical evaluations of MR elastomer-based isolators, as well as experimental tests with simple structure models. However, their applicability to large civil structures has not been properly studied yet because it is quite challenging to numerically emulate the complex behavior of MR elastomer-based isolators and to conduct experiments with large-size structures. To address these difficulties, this study employs the real-time hybrid simulation technique, which combines physical testing and computational modeling. The primary goal of the current hybrid simulation study is to evaluate seismic performances of an MR elastomer-based smart base isolation system, particularly its adaptability to distinctly different seismic excitations. In the hybrid simulation, a single-story building structure (non-physical, computational model) is coupled with a physical testing setup for a smart base isolation system with associated components (such as laminated MR elastomers and electromagnets) installed on a shaking table. A series of hybrid simulations is carried out under two seismic excitations having different dominant frequencies. The results show that the proposed smart base isolation system outperforms the passive base isolation system in reducing the responses of the structure for the excitations considered in this study.

Control design of ultra-quiet spacecraft platform

Precision payloads require the spacecraft platform to provide an ultra-quiet working environment. Vibration isolators can be used for disturbance rejection purpose but may result in undesirable impact to the spacecraft attitude control performance. This paper studies the issues in relation to isolator-control interactions and proposed guidelines for selection of key parameters of a passive isolation system. An integrated design and analysis environment developed for high-fidelity control performance assessment is also introduced.

스마트 최상층 면진시스템의 중약진지역 적용성 평가

Because a smart isolation system cannot be used as a base isolation system for tall buildings, top-story or mid-story isolation systems are required. In this study, adaptability of a smart top-story isolation system for reduction of seismic responses of tall buildings in regions of low-to-moderate seismicity has been investigated. To this end, 20-story example building structure was selected and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes generated based on design spectrum of low-to-moderate seismicity regions are used for structural analyses. Based on numerical simulation results, it has been shown that a smart top-story isolation system can effectively reduce both structural responses and isolation story drifts of the building structure in low-to-moderate seismicity regions in comparison with a passive top-story isolation system.

Seismic attenuation system for the AEI 10 meter Prototype

Isolation from seismic motion is vital for vibration sensitive experiments. The seismic attenuation system (SAS) is a passive mechanical isolation system for optics suspensions. The low natural frequency of a SAS allows seismic isolation starting below 0.2 Hz. The desired isolation at frequencies above a few hertz is 70–80 dB in both horizontal and vertical degrees of freedom. An introduction to the SAS for the AEI 10 m Prototype, an overview of the mechanical design and a description of the major components are given.

Optimized Fuzzy Neural Networks Control of a Magnetic Suspension Vibration Isolation System

Active vibration isolation technology can overcome the defects of passive vibration isolation technology that the poor vibration isolation performance in low and resonant frequencies. Compared with other active vibration isolation technologies, magnetic suspension isolation technology has shown useful characteristics, such as wide response frequency range, fast response, high reliability and long-life. However, the control of MSVI is still one of the areas that require further investigation. This paper presents a Fuzzy Neural Networks(FNN) control algorithm for a magnetic suspension isolation vibration system, which is optimized by improved Genetic Algorithm(GA). The output force responses of the FNN and passive vibration isolation system under same excitation are simulated. The simulation results show that the fuzzy control system has much better performance in vibration isolation.

A comparison of two nonlinear damping mechanisms in a vibration isolator

The vibration transmissibility characteristics of a single-degree-of-freedom (SDOF) passive vibration isolation system with different nonlinear dampers are investigated in this paper. In one configuration, the damper is assumed to be linear and viscous, and is connected to the mass so that it is perpendicular to the spring (horizontal damper). The vibration is in the direction of the spring. The second configuration is one in which the damper is in parallel with the spring but the damping force is proportional to the cube of the relative velocity across the damper (cubic damping). Both configurations are studied for small amplitudes of excitation, when some analysis can be conducted based on analytical expressions, and for large amplitudes of excitation, where the analysis is based on numerical simulations. It is found that the two nonlinear systems can outperform the linear system when force transmissibility is considered. However, for displacement transmissibility, the system with the horizontal damper exhibits some desirable properties, but the system with cubic damping does not.

열차진동하중을 받는 첨단시설물의 스마트 면진시스템을 이용한 미진동제어

정밀한 공정을 요구하는 반도체 및 TFT-LCD와 같은 첨단 기술산업 공장의 미진동 문제는 제품의 성능에 영향을 주는 주요한 인자로서 정밀기기 및 부품의 제조공정에 있어서 중요시 되어왔다. 본 논문에서는 이러한 첨단시설물의 미진동 문제를 해결하기 위하여 기초면진시스템의 미진동제어성능을 검토하였다. 이를 위하여, 기차에서 유발되는 인공지반운동을 생성하여 시간이력해석을 수행하였고 3층 예제구조물을 사용하였다. 수치해석을 통하여 수동 기초면진 및 스마트 면진시스템의 미진동제어성능을 고정기초구조물과 비교하였다. 그 결과 스마트 면진시스템이 미진동제어에 있어서 우수한 제어성능을 나타내는 것을 확인하였다. Microvibration problem of high-technology facilities, such as semi-conductor plants and TFT-LCD plants, has been considered as important factors that affects the performance of products and thus it is regarded as important in facilities with high precision equipments. In this paper, various base isolation control systems are used to investigate their microvibration control performance. To this end, train-induced ground acceleration is used for time history analysis and three-story example building structure is employed. Microvibration control performance of passive and smart base isolation systems have been investigated in this study. Based on numerical simulation results, it has been verified that smart base isolation system can control microvibration of a high-technology facility subjected to train-induced excitation.

Design of Axially Loaded Helical Spring Isolation Systems

Engineering metals have a desirable property of absorbing energy especially when they are manufactured into helical springs. This ability has been utilized favorably in the design of isolation systems. The material and spring behavior prolongs the time period of excitation thereby decreasing the frequency and acceleration of the shock into the structure. This paper presents the design and behavioral response of a steel spring isolation system subjected to shock excitation as experienced in real world applications. The isolation discussed is for the support motion where the shock excitation originates outside the structure. In particular the focus is on undamped single degree of freedom (SDOF) systems. The goal is to design a passive isolation system in the form of helical steel springs. The system must limit the instance of high acceleration energy transferred into the structure in a very short time frame. A transmissibility algorithm is developed and presented. A test case is designed and manufactured based upon the design data simulated from the algorithm. A comparative study is presented to validate the accuracy of the algorithm and isolation system against empirical results from the test case using a drop testing apparatus. The shock response spectra commonly used in problems of shock excitation to a half sine wave is presented.

The research of passive vibration isolation system with broad frequency field

A passive vibration isolator with broad frequency field (zero dynamic stiffness system) is designed in this paper, whose mathematics model is built applying a mathematics method. Then the static and dynamic analysis of the isolator is conducted with ADAMS software. The zero dynamic system is developed based on theoretic study and simulation analysis. Moreover, the experimental validation of modal and frequency field is acquired. The modal experiment shows that the natural frequency of the isolator has dropped from 11.715 Hz to 2.5421 Hz because of importing negative stiffness mechanism. The result of the frequency field experiment is that the isolator has a better vibration reduction effect between 3 and 100 Hz.

Research on hybrid isolator technique

This paper presents a new hybrid isolator technique that composes of passive vibration device and active actuator. It contains the advantages of both active and passive isolation system. During the optimization design, the passive vibration isolator as cylindrical rubber is designed, then the active actuator is designed as electromagnetic actuator with advantages of compact construction and larger forces. After manufacturing the prototype designed, the vibration active control experiment is carried out, which can verify the hybrid isolator's performance. During the mono-layer active control experiment, vibration of the upper layer mass reduced about 29dB~40dB. In the two-stage experiment, it has gained a good effect in both single and double frequency excitation. It means that the hybrid isolator technique designed has good performance of anti-vibration in practical application.

Development and simulation evaluation of a magnetorheological elastomer isolator for seat vibration control

Driver fatigue is one of the leading factors contributing to road crashes. Environmental stress, such as unwanted seat vibration, is a key contributor to fatigue. This article presents the design and development of a magnetorheological elastomer isolator for a seat suspension system. By altering the magnetorheological elastomer isolator’s stiffness through a controllable magnetic field and selecting suitable control strategy, the system’s natural frequency can be changed to avoid resonance, which consequently reduce the vehicle’s vibration energy input to seat, and thus suppress the seat’s response. Experimental results show that the developed magnetorheological elastomer isolator is able to reduce vibration more when compared with the passive isolation system, indicating the significant potential of its application in vehicle seat vibration control.