Passive Isolation Research Articles

Amplification of Vibrations in High-Speed Railway Embankments by Passive Ground Vibration Barriers

The objective of the present study is to characterise the dynamic response of ballasted railway embankments subject to high-speed train loads, for the track conditions with and without inclusions of geofoam in-filled trenches next to the embankments for passive isolation of ground vibrations. Full-scale models of the ballasted railway track sections were developed for the simulation of high-speed train transit. Although vibration isolation trenches have been characterised as a suitable method for attenuation of ground-borne railway vibrations propagating away from the track, the results from the present study signify that the embankments supporting the railway track are subject to augmented levels of vibrations, due to reflection of ground vibrations from the soil–trench interface back into the embankment. In-filling of trenches with EPS (expanded polystyrene) geofoam of high buffer stiffness results in stronger reflection of ground vibrations back into the railway embankment. Augmented levels of track vibration are also estimated, when geofoam with higher densities are used for in-filling the trench. Deployment of vibration isolation trenches with higher depths result in stronger reflection of ground vibrations as well, especially when the trench is deployed at locations farther from the track. In general, amplification of vibrations in the railway embankment is higher when the trains transit at faster speeds. Reflection of vibrations by the passive vibration isolation trenches is inevitable, and hence, it is recommended that rail pads or under-sleeper pads shall be used in conjunction with the passive trenches for limiting the amplification of vibrations in the embankment.

The Design and Analysis of a Novel Passive Quasi-Zero Stiffness Vibration Isolator

This project aims to design a novel passive quasi-zero stiffness vibration isolator (QZS-VI) and analyze the static and dynamic mechanical properties of the QZS-VI. First, a novel combination of V-shaped lever, plate spring and cross-shaped structure (VL-PS-CS) vibration isolation platform is designed, and a nonlinear QZS-VI is built by parallel connecting VL-PS-CS and coil spring. Second, the static and dynamic modeling of QZS-VI are derived considering the geometrical nonlinearity of V-shaped lever and the large deflection of plate spring, and the average method is applied to obtain the displacement transmissibility. Third, the effects of different structural parameters (e.g., the lengths of long arm and short arm of V-shaped lever, the assembly angle between two arms, the thickness of plate spring) on the static mechanical and equivalent nonlinear friction properties of QZS-VI are thoroughly investigated. Finally, the vibration isolation performance of the designed QZS-VI is compared with another QZS-VI of buckled beam mechanism and traditional linear vibration isolator. The QZS-VI with VL-PS-CS fully explores the nonlinear advantages of plate spring and V-shaped lever and can achieve excellent high static and low dynamic stiffness and nonlinear friction properties. The superior static mechanical properties and nonlinear friction of QZS-VI can be tuned with different structural parameters. The designed QZS-VI exhibits much smaller resonant frequency, lower peak value and more stability property at the peak frequency than other isolators due to its special nonlinear friction and stiffness properties. The designed QZS-VI is practical, novel and suitable for low-frequency vibration isolation. The innovative structure provides novel insights into the design of passive vibration isolators and has great potential for application in engineering practice.

Applications of Nonlinearity in Passive Vibration Control: A Review

Vibration present on various levels in many engineering fields and hence vibration mitigation has become a subject of intense study. The nonlinear vibration isolation devices are effective for broad frequency bandwidth and can provide better vibration isolation than linear devices. The need for nonlinearity in stiffness and damping characteristics has motivated researchers to apply the nonlinearity found in mechanisms or materials in the passive vibration control devices. This review discusses the applications of nonlinearity in the passive vibration control devices to provide an understanding of how the nonlinearity is applied and useful in the implemented system. Further, applications for nonlinearity can also be extended in the energy harvesting devices, Nonlinear energy sink, metamaterials for the purpose of vibration isolation and energy harvesting. The need for nonlinearity also encouraged research work through inspiration from the nature called bio-inspired devices. The bio-inspired devices mimic the nonlinearity of the biological system to suppress the vibrations. The nonlinear passive isolation is effective for wide frequency bandwidth than the linear isolation system. Further, the nonlinear systems also reduce transmissibility much efficiently than the linear system. The nonlinear energy harvesting system shows a great scope to harvest energy from wide ranges of excitations. The bio-inspired devices also are proven to be effective in vibration isolation. Additionally the design of the metamaterial with nonlinearity in the microstructure, proves to be promising in the vibration suppression applications. Based on the review, the nonlinearity introduced into the systems has greater benefits than the linear systems.

Vibration Control Method of an Electromagnetic Isolation System Based on LQR and Coevolutionary NGA

An electromagnetic isolation system can dynamically adjust the output characteristic parameters of the system in real time through the active control strategy, which has strong adaptability to the external environment. In order to control the electromagnetic vibration isolation system effectively, an active control method is presented based on the linear quadratic regulator (LQR) approach and the coevolutionary niche genetic algorithm (NGA). In this paper, the dynamical equation and state equation of the electromagnetic isolation system are built, which include the nonlinear relationship between electromagnetic force and coil current and gap. The LQR approach is employed to maintain a steady state of an isolated object on the vibration isolation system. Meanwhile, a coevolutionary niche genetic algorithm is put forward to optimize the parameters in Q and R matrices. Simulation and experimental results demonstrate that the electromagnetic isolation system with the LQR approach and coevolutionary NGA can effectively isolate the vibration and maintain a steady state for an isolated object in comparison with the passive isolation system.

Development of the passive vibroacoustic isolation system for the path matched differential interferometry based fiber-optic sensors

Fiber-optic interferometric sensor arrays are very attractive for many applications. One of the common used interrogation approaches for fiber-optic sensor arrays is the path matched differential interferometry (PMDI). It allows to interrogate a large number of multiplexed fiber-optic sensors by using an auxiliary compensation interferometer (CIF). This approach with using the phase modulator allows to implement the phase-generated carrier demodulation for multiplexed fiber-optic sensors. However, this approach has the significant disadvantage, which is that environmental vibroacoustic impacts on the CIF produce undesirable phase signals from the sensor array. It leads to increasing the noise floor level of the measuring system. In this paper the development methodology and results of the experimental investigation of the passive vibroacoustic isolation system for the CIF in the PMDI-based fiber-optic interferometric sensor are presented. The proposed isolation system is implemented by using acoustic absorbing layers and the special mechanical suspension system for the CIF mounted in the single rack unit. It is shown that the proposed approach for the CIF isolation allows to reduce its sensitivity to vibroacoustic impacts by up to 30 dB in the frequency range up to 500 Hz. It is also demonstrated that potting of the CIF fiber-optic components reduces its isolation efficiency by an average value of 8.3 dB in the considered frequency range, that is not applicable for interferometric sensors. The presented methodology and obtained results might be used in PMDI-based fiber-optic interferometric sensors to improve their performance characteristics.

A bio-inspired isolator based on characteristics of quasi-zero stiffness and bird multi-layer neck

With the increasing of the accuracy requirement of data record for on-orbit instruments, it becomes a greater challenge and brings more opportunities in design of observing spacecraft to isolate micro-vibrations of low frequency and ultra-low frequency. By imitating both multi-vertebra structure of bird’s neck and gazing stability of head, a multi-layer quasi-zero stiffness (QZS) nonlinear isolator is investigated in this paper. The mathematical model with high-order coupled nonlinear ordinary differential equations is established. Its isolation performance is analyzed by the harmonic balance method (HBM) combining with the pseudo arc length method. In comparison to the corresponding linear structure, the proposed multi-layer QZS nonlinear isolator can break the limitation of poor isolation performance in low frequency and ultra-low frequency vibration for traditional linear passive isolation systems. Also, the analysis results show that its High-Static-Low-Dynamic-Stiffness (HSLDS) property may solve the traditional contradiction between large isolation frequency band and loading capacity for reducing soft stiffness. The multi-layer QZS combined system as integration is quite capable of cumulatively expanding the effective range of dynamic displacement which is too narrow for a single QZS system. The relevant conclusions are instructive to develop preferable isolation equipment to isolate low frequency and ultra-low frequency vibration in practical engineering.

A Fully Isolated N-Way Radial Power Combiner

A new passively isolated $N$ -way radial combiner design is proposed. The design incorporates low-loss partially filled radial combiners with a passive peripheral isolation network, where coaxial termination loads are used as isolation resistors. To confirm real-world performance, a 16-way combiner operating at 4 GHz was manufactured and tested. The minimum isolation measured among peripheral ports is better than 27 dB over more than 30% fractional bandwidth (BW), and the average asymmetric peripheral port input reflection is below −15 dB over 50% BW. Simulation analyses show that such excellent peripheral port isolation and matching has a significant value in improving the graceful degradation of a system utilizing such combiners. The prototype also achieves a center port reflection coefficient magnitude below −18 dB over 45% BW, and the measured signal balances are ±0.2 dB and ±2°. The structure that forms the radial cavity and PCB housing was manufactured exclusively on manually controlled machinery, so the measured 1-dB insertion loss BW is approximately 25%.

Bio-inspired polygonal skeleton structure for vibration isolation: Design, modelling, and experiment

Inspired by the safe landing of a cat falling from a high altitude, a bio-inspired polygonal skeleton (BIPS) structure is proposed, and its nonlinear characteristics are systematically studied to explore its potential application in the suppression of vibration. The polygon is formed by the skeleton structure of the cat’s entire body and the ground. The BIPS system consists of two symmetrical bionic legs with three robs (as skeleton) and four horizontal springs (as muscle). Two bionic legs are connected through the bearing platform (as spine), which could adjust the distance between the two bionic legs. A theoretical model is developed to characterize its stiffness nonlinearity through geometrical and mechanical analysis. Parameter analysis reveals that the BIPS structure has diverse stiffness, including nonlinear positive stiffness and negative stiffness. By imitating adjustment of leg posture and telescopic function of the spine (control the distance between legs), these flexible stiffness properties can be adjusted by structure parameters. In addition, the load capacity and working range can also be designed by the length of the bars, the initial angle, the mounting position, and the spring stiffness. The experimental setup is established, and the vibration isolation performance under various excitation is tested. The experimental results verify the accuracy of the dynamic model and also show that the proposed BIPS structure can suppress the vibration effectively under a variety of excitations. These peculiarities may provide potential possibility of an innovative approach to passive vibration control and isolation.

Integrated design, fabrication, and experimental study of a parallel micro-nano positioning-vibration isolation stage

• A novel parallel micro-nano positioning-vibration isolation stage (PVI stage) is proposed for sensitive load to realize the precision positioning and vibration isolation simultaneously in space environment. • The requirements of large-stroke positioning and passive vibration isolation could be achieved through combination of giant magnetostrictive actuator (GMA) and compliant amplification mechanism. • Some appurtenances are designed for preventing static deformation and ensuring assembly accuracy. • Theoretical simulation and experimental research are performed to verify the positioning and vibration isolation performances of the proposed stage. Positioning and vibration isolation are two important steps for sensitive payloads to realize precision observation in space environment. However, current base stages applied to sensitive payloads often focus on one function, thus limiting their engineering applications. This paper presents a novel parallel micro-nano positioning-vibration isolation stage (PVI stage), which could realize the two functions simultaneously. The advantages of the presented stage lie in the compactness and convenience, which determine its feasibility in limited volume. Through combination of giant magnetostrictive actuator (GMA) and compliant amplification mechanism, the requirements of large-stroke positioning and passive vibration isolation could be achieved. And three auxiliary unloading devices are designed to bear the sensitive payload for resisting the static deformations of compliant mechanism. The detailed scheme and corresponding dynamic model are constructed for showing the stage. Furthermore, finite element simulation is carried out to verify the desired performance. Finally, a prototype is fabricated and experimental tests are conducted to validate the capabilities of the stage. The test results prove that the proposed positioning-vibration isolation stage owns a compact structure and realizes micro-nano positioning and vibration isolation simultaneously, and thus shows a promising prospect in aerospace field.

Active Vibration Isolation of a Diesel Generator in a Small Marine Vessel: An Experimental Study

An active vibration isolation system is retrofitted to a diesel generator set in a tugboat to determine the effectiveness of such a system in a realistic practical environment. The system consists of six bespoke inertial actuators chosen to make minimal modifications to the machinery arrangement, and a DSP-based controller. Six accelerometers are collocated with the actuators on the top of six isolators to act as error sensors, and six accelerometers are placed below the isolators to give a measure of the global vibration of the ships structure below the generator set. A hydrophone is also placed in the water to give an indication of the underwater noise due to the generator. The control strategy employed is six-input and six-output decentralized adaptive feedforward control with the reference signal being derived from the signal from an optical tachometer on shaft between the engine and the generator. To suppress the vibration at all the dominant forcing frequencies, an electrical circuit generated the half engine orders required from the measured reference signal. The experimental results show that the combination of the active control system and the passive isolators is effective in reducing the global vibration and the acoustic pressure at the hydrophone position.

Review on Development of High-Static–Low-Dynamic-Stiffness Seat Cushion Mattress for Vibration Control of Seating Suspension System

This review focuses on studying passive vibration isolation techniques and their applications. Advantages and disadvantages of different vibration isolation techniques will be compared in order to find an innovative method to reduce seating suspension system vibration and improve the ride comfort of vehicles’ drivers. Quasi-zero stiffness (QZS) isolators of high-static–low-dynamic stiffness are found to have good application prospects in low-frequency vibration isolation. In order to improve the isolation performance of the seating suspension system, a specially made seat cushion will be studied where a quasi-zero stiffness (QZS) isolator such as a double-diamond isolator is selected as one of the cells/units/elements of the seat cushion mattress. The double-diamond isolator structure does not represent the whole seating suspension system. The transmissibility ratio of the double-diamond isolator is evaluated by analytical and simulation models and compared to that of a conventional linear spring isolator. Although the performance of the passive vibration isolation/control system is usually worse than that of the active or semi-active control system, the cost of the passive vibration isolation/control system is lower than that of the active and semi-active control system, and the relative simplicity of adding a vibration isolation cushion mattress in an existing passive seating suspension system makes it low in cost, easy to implement, and more attractive than the active and semi-active vibration control systems.

Integration of an omnidirectional self-powering component to an MRE isolator towards a smart passive isolation system

Base isolator is one of the most adopted and effective means of mitigating unwanted and harmful vibrations to protect buildings and other key civil infrastructure from seismic events. For this reason, the base isolation technology has advanced greatly in recent years, especially the magnetorheological elastomer (MRE) isolator. However, the operation of such an MRE isolator needs external power supply to be activated, which may fail due to the power outage caused by the seismic movement. To this end, this work developed an MRE base isolation system with self-powering capability. This characteristic enables the isolation system self-sufficient without relying on external power. The self-powering component is an innovative omnidirectional element and can collect vibration energy from all horizontal directions. In addition, the self-powered isolation system performs rate-dependent softening behaviour which overcomes the conflicting requirements that the stiffness is required to be hard during daily operation but soft when the earthquake happens. For this reason, this new isolation system has been built and tested, including its MRE isolator and self-powering components. Its vibration reduction capability for building is also investigated on a scaled building. The theoretical analysis and verification is also performed and the conclusions coincide with the experimental results. The experimental and simulation results demonstrate that this new isolation system is capable of generating electricity which is sufficient to power itself when it is subjected to ground motions, and that it shows a high effectiveness in reducing the floor accelerations and the relative displacement.

Active vibration isolation system based on the LADRC algorithm for atom interferometry

A new, to the best of our knowledge, method based on the linear active disturbance rejection control (LADRC) algorithm is proposed to design and build a vertical vibration isolator below ${0.1}\;{\rm Hz}$0.1Hz for cold-atom interferometry. This system combines the control system that is used to process and to reduce feedback vibrations measured by a seismometer and a voice coil that is used to cancel the motion of a commercial passive vibration isolation platform. When the feedback is on, the vertical vibration is reduced by an additional factor of up to 1000 from 0.1 to ${5}\;{\rm Hz}$5Hz, while the system has a steady oscillation with a natural period of 66 s. The experimental results show that the LADRC is an effective control algorithm for this application and performs better than the classic lag compensation filters in our case. In addition, there are fewer parameters to adjust in this method, and we only need to tune the feedback gain of the system state error for its application.

A simplified cryogenic optical resonator apparatus providing ultra-low frequency drift.

A system providing an optical frequency with instability comparable to that of a hydrogen maser is presented. It consists of a 5 cm long, vertically oriented silicon optical resonator operated at temperatures between 1.5 K and 3.6 K in a closed-cycle cryostat with a low-temperature Joule-Thomson stage. We show that with a standard cryostat, a simple cryogenic optomechanical setup, and no active or passive vibration isolation, a minimum frequency instability of 2.5 × 10-15 at τ = 1500 s integration time can be reached. The influence of pulse-tube vibrations was minimized by using a resonator designed for low acceleration sensitivity. With reduced optical laser power and interrogation duty cycle, an ultra-low fractional frequency drift of -2.6 × 10-19/s is reached. At 3.5 K, the resonator frequency exhibits a vanishing thermal sensitivity and an ultra-small temperature derivative 8.5 × 10-12/K2. These are favorable properties that should lead to high performance also in simpler cryostats not equipped with a Joule-Thomson stage.

A hybrid multi-degree-of-freedom vibration isolation platform for spacecrafts by the linear active disturbance rejection control

The hybrid vibration isolation, which takes advantages of both the passive and active approaches, has been an important solution for space missions. The objective of this paper is to design a vibration isolation platform for payloads on spacecrafts with the robust, wide bandwidth, and multi-degree-of-freedom (MDOF). The proposed solution is based on a parallel mechanism with six voice-coil motors (VCMs) as the actuators. The linear active disturbance resistance control (LADRC) algorithm is used for the active control. Numerical simulation results show that the vibration isolation platform performs effectively over a wide bandwidth, and the resonance introduced by the passive isolation is eliminated. The system robustness to the uncertainties of the structure is also verified by simulation.

Model predictive control method of a parallel electromagnetic isolation system based on the improved genetic algorithm

To improve the vibration isolation performance for a parallel electromagnetic isolation system, an improved genetic algorithm to optimize the Q and R matrices in the control objective function for a model predictive control approach is proposed. In this study, a parallel electromagnetic isolation system with two electromagnetic isolation units is designed to expand the vibration isolation range to isolate the large object. The dynamical equation and state equation of the parallel electromagnetic isolation system are built. The nonlinear relationship among electromagnetic force, coil current, and gap is calculated by COMSOL Multiphysics to design the model predictive control controller. Meanwhile, an improved genetic algorithm by the variable chromosome length coevolutionary method is presented to tackle two issues. The first issue is that the parameters of Q and R matrices in the control objective function are mainly selected by trial and error. The other issue is that the model predictive control approach needs to determine prediction steps which may lead to the model predictive control approach suffering from heavy computation or an inaccurate prediction model. Simulation and experimental results demonstrate that the parallel electromagnetic isolation system with model predictive control method based on the improved genetic algorithm can achieve better vibration isolation performance in comparison with the passive isolation system.

와이어 메쉬 재질을 이용한 하이브리드 마운트용 수동 진동 절연 요소 설계

와이어 메쉬 재질을 이용한 하이브리드 마운트용 수동 진동 절연 요소 설계

Modeling and control of magnetorheological 6-DOF stewart platform based on multibody systems transfer matrix method

A 6-DOF vibration isolation system with magneto-rheological damper (MRD) based on Stewart mechanism was designed to reduce the mechanical vibration more effectively. To make the isolation system perform well, an effective control method was also proposed. Using the linear multibody systems transfer matrix method (MSTMM), the dynamic model of the MRD 6-DOF vibration isolation system was established to obtain the dynamic characteristics. Firstly, based on the test mechanical property of magnetorheological damper, the electromagnetic coupling model of magnetorheological damper was established. Secondly, the transfer equation of 6-DOF vibration isolation system was established by linear MSTMM. And the state space equation was derived using the modal superposition method, which was based on the augmented eigenvector and body dynamics equation. Thirdly, the linear quadratic Gaussian control method of MRD 6-DOF vibration isolation system was designed. Finally, the numerical simulation was carried out. The results showed that MRD 6-DOF vibration isolation system with optimal control improved the dynamic performance of mechanical equipment effectively. Compared with passive vibration isolation system, the translation of the vibration isolation system in the X, Y, and Z directions, as well as the rotation around the X axis, Y axis and Z axis were reduced by 51.85%, 58.71%, 64.43%, 75.43%, 66.45% and 52.87%, respectively. Similarly, the percentage drops were 50.00%, 56.16%, 34.94%, 53.09%, 38.14% and 46.76% compared to the PID control based vibration isolation system, respectively. The established dynamic model and control strategy provided theoretical basis for relevant vibration isolation tests.

Passive impact/vibration control and isolation performance optimization for space noncooperative target capture

On-orbit capture is an important technique for the space debris removal, refueling, or malfunction satellite repairing. While due to the uncertainty of the motion parameters of the space noncooperative target, the impact between the capture device and the noncooperative target during the capturing process is inevitable, which may bring strong vibration perturbation to the base satellite, and potentially alter the position and the attitude of the servicing spacecraft, or even cause failure of on-orbit tasks. This article presents a new and alternative method for passive suppression of spacecraft impact and perturbation during noncooperative spacecraft capture. The passive device based on bioinspired X-shape is installed between the satellite and the capture device. In the capture process, nonlinear damping of the passive isolation structure can significantly reduce impact/vibration perturbation. For performance analysis, dynamic equations of the isolation system are established. Based on which, the relationship between structure parameters and isolation performance is systematically analyzed. Experiments are conducted for verification of the effectiveness of the proposed method. Moreover, an optimal process using the non-dominated sorting genetic algorithm II optimization method is developed to minimize impact/vibration perturbation effect, and optimal solutions can provide useful reference for the passive isolation system design.

Analysis of a passive scissor-like structure isolator with quasi-zero stiffness for a seating system vibration-isolation application

It is widely known that vibration is a mechanical motion phenomenon where a mass point oscillates around an equilibrium point. Vibrations are a source of discomfort and are extremely harmful to vehicle drivers and passengers. The motivations of this research are to develop an innovative vehicle seating suspension system to isolate vibrations transmitted to vehicle drivers and passengers and to improve ride comfort to ensure that their health is not negatively impacted and to improve the working efficiency of the driver. An innovative design of a passive multi-degree-of-freedom vibration isolator is presented in a truck seat suspension system where a Stewart platform configuration with a six-degree-of-freedom (6-DOF) isolation system is used rather than the traditional Stewart platform. A scissor-like structure (SLS) is used as one of the supporting legs to provide a nonlinear system with quasi-zero stiffness (QZS). Vibration is effectively attenuated without a loss of the system's load capacity. The effects of structural parameters in the proposed system are studied to determine how to adjust the parameters to achieve better vibration-isolation performance. The results reveal that a SLS supporting leg with a small assembly angle, more layers, a shorter link length and less spring stiffness has led to better vibration isolation and higher system stability than the conventional baseline supporting structure.