Passive Isolation Research Articles

Mechanisms with Negative Stiffnesses for Simplified Designs of Broad Band Passive Vibration Isolation

Mechanisms with Negative Stiffnesses for Simplified Designs of Broad Band Passive Vibration Isolation

Study on Decoupling Control Strategy of Redundant Parallel Hybrid Vibration Isolation Platform

Background: The vibration isolation platform (VIP) can greatly reduce the risk of damage to dynamic equipment caused by external vibration interference and provide the most stable and reliable working environment for dynamic equipment. Objective: Aiming at the problems of small vibration isolation dimension, low bearing capacity, serious motion coupling, and narrow vibration isolation bandwidth in the field of vibration isolation of dynamic load equipment, a hydraulic redundant six degrees of freedom parallel vibration isolation platform (PVIP) with active and passive composite vibration isolation support is proposed. Methods: The dynamic coupling model of active and passive hybrid vibration isolation (APHVI) of redundant PVIP is established, and the matrix diagonal decoupling control strategy and fuzzy PI control theory are combined. Analysis of passive vibration isolation performance and APHVI performance of VIP is done. Results: The simulation results show that the effect of APHVI based on fuzzy PI decoupling control is better than that of passive vibration isolation and matrix diagonal decoupling control. Conclusion: Fuzzy PI control can effectively attenuate more than 98 % of the disturbance, significantly improve the vibration isolation performance and decoupling effect of the platform, and expand the effective vibration isolation bandwidth.

A cryogenic torsion balance using a liquid-cryogen free, ultra-low vibration cryostat.

We describe a liquid-cryogen free cryostat with ultra-low vibration levels, which allows for continuous operation of a torsion balance at cryogenic temperatures. The apparatus uses a commercially available two-stage pulse-tube cooler and passive vibration isolation. The torsion balance exhibits torque noise levels lower than room temperature thermal noise by a factor of about four in the frequency range of 3-10 mHz, limited by residual seismic motion and by radiative heating of the pendulum body. In addition to lowering thermal noise below room-temperature limits, the low-temperature environment enables novel torsion balance experiments. Currently, the maximum duration of a continuous measurement run is limited by accumulation of cryogenic surface contamination on the optical elements inside the cryostat.

Human Comfort Assessment of Vibration Behaviour of Office Floors: Before and After Strengthening Using the Laminated Elastomeric Bearing

Vibration issues of floor areas in relation to human comfort perception in an open working space are very common. This paper discusses the results of a human comfort assessment before and after strengthening of a a post-tensioned reinforced concrete flooring structure. All floors experience structural vibration, which arises from various sources inside and outside of the building. This paper investigated the vibration issue of a problematic flooring slab area on Level 3 of a four storey building, which vibrations induced by people walking through the working station area. Two types of tests were conducted, namely a (1) shaker test and a (2) walking test. Accelerometers were attached to the floor according tothe sensor points and recorded all acceleration responses on the floor system. The highly sensitive KS 48C accelerometer was used in this study. The accelerometers were placed at the same locations for both shaker and walking tests. The floor slab which was initially reported as problematic structure on Level 3 was found that its peak acceleration exceeded the recommended human comfort limitation. A passive vibration isolation technique was used in order to tackle the vibration issue. A laminated elastomeric bearing was chosen as one of the methods in passive vibration isolation. The natural frequency for both results before and after strengthening remained as low-frequency floor classes. However, peak acceleration excitation was reduced after the strengthening work was completed.

Vibration isolation of machine foundations by topology optimization of wave barriers

ABSTRACT Vibrations generated from rotary machines can cause problems to the nearby buildings and their residents. Screening the generated waves using barriers is a common solution for mitigating these vibrations. This paper presents a coupled finite element-genetic algorithm methodology to study the efficiency of scattered barriers to alleviate the surface vibrations of machine foundations by focusing on their installation pattern. Additionally, the effect of other parameters including loading frequency of the machine, barrier material, soil layering, and so on is also investigated. The efficacy of these barriers is also compared to the vertical concrete walls, which are easier to be placed in the soil. The results of the analyses showed that using a soft material for the barrier instead of concrete can double the mitigation capacity of the system. Additionally, passive isolation was shown to be the best approach with up to about 27% and 28% vibration reduction in homogeneous and layered soil profiles, respectively. Furthermore, by proper placement, scattered barriers can reduce the vibrations by more than twice as much as the vertical columns. Finally, the optimal pattern at higher frequencies (i.e. 51–60 Hz) was shown to be 10 times as effective as the one at lower frequencies (i.e. 1–10 Hz).

Hybrid isolation system with wire‐rope isolators and magnetorheological dampers for the isolation of blast‐induced vibration

The aim of this research is to improve the isolation performance and energy dissipation characteristics of the widely used passive isolation (PI) system with wire-rope isolators (WRIs) under the excitation of various blast-induced vibration loads through the use of a semi-active control system. A hybrid isolation (HI) system composed of WRIs and an innovative magnetorheological (MR) damper equipped with a motion controller is proposed, which can protect sensitive equipment and nonstructural elements by attenuating their dynamic response. The designs of the MR damper's magnetic circuit and control system were validated by establishing an electromagnetic field finite element model and a motion controller simulation model, respectively. A series of quasi-static and shock table tests were conducted on models using three types of isolation: (1) a PI with WRIs, (2) an HI without a motion controller, and (3) an HI alone. The results show that the proposed MR damper can effectively restrain the tensile vibration of WRIs, significantly increase the isolation rate, and provide greater energy dissipation in HI systems with different weights of static loading subjected to various blast-induced vibration loads.

Random vibration, exported vibration, and passive isolation testing of the Ricor K508N cryocooler

The Ricor K508N is a rotary Stirling Cryocooler whose predecessor, the K508, has extensive flight heritage. The K508N has significant potential as a low-cost option for CubeSat infrared electro-optical payload applications. This paper will explore the work done by the ATA project on the exported vibration characterization of a set of standard K508N cryocoolers (35 atm) and the implementation and performance comparison of several passive vibration isolation and damping technologies to help mitigate the jitter effect of COTS cryocoolers. Kistler Force dynamometers and accelerometers were used to measure the K508N’s body and cold tip Multicomponent Exported Forces and Torques (EFT). Wire rope and Pyrolytic Graphite Sheet thermal straps are used as vibration isolation technologies. The K508N also underwent sine sweep resonant and peak profile testing as well as random vibration testing to GEVS launch loads in a NanoRacks soft stow configuration.

Active isolation tests of metamaterial-based barriers and foundation

This study investigates the performance of novel metamaterial-based barriers and foundation on mitigating waves transmitting from a vibrational source to the surrounding soil. An active isolation system is a wave barrier built close to the vibration source to reduce the wave radiating from the source of vibration on the structure to surrounding soil. This research reports the efficacy of the proposed isolation system using an active excitation field test, thereby expanding the applicability of such wave barriers beyond passive isolation. The test barrier is a trench barrier infilled with a layered periodic metamaterial that is composed of alternating layers of polyurethane and reinforced concrete (RC). Tests are also conducted on an empty trench for comparison. A mobile shaker mounted on top of a steel frame is utilized to simulate an active vibration source. By mechanically reorienting the shaker, active isolation tests can be conducted in all three directions (vertical, horizontal inline, and horizontal crossline). Motions on the ground surface, periodic barrier, foundation, and steel frame are monitored using three-dimensional (3D) geophones and 3D accelerometers. The effects of the barrier length, the infilled material, and the total number of barriers on the isolation behavior at various exciting frequencies, and excitation directions are investigated. Tests also include the scenario where the wave barrier is used along with a metamaterial-based periodic foundation. Experimental studies show that vibrations generated from the shaker mounted on top of the steel frame are effectively restrained by a metamaterial-based foundation. The performance of the periodic barriers is better than that of an empty trench within certain frequency ranges. The wave isolation performance is enhanced with the increasing barrier length. This research provides the benchmark for the future design of periodic barriers and periodic foundations in buildings or other vibration-sensitive facilities.

Study on Electrical Parameter Matching of Piezoelectric Stack Periodic Strut for Helicopter Cabin Noise Control

The gear meshing noise generated by the helicopter main reducer is one of the important sources of noise in the helicopter cabin. By improving the isolation performance of the struts supporting reducer to the gear meshing vibration, the purpose of reducing the gear meshing noise in the helicopter cabin can be achieved. Piezoelectric stack periodic strut (PSPS) composed of piezoelectric stacks and passive materials periodically arranged is an original type of strut with active and passive hybrid isolation characteristics. Piezoelectric stacks and passive materials form a periodic structure, which makes PSPS have a unique stopband characteristic. The propagation of elastic waves in the stopband frequency range is attenuated, which can improve the broadband passive vibration isolation capability of the PSPS; The piezoelectric stacks can adjust the elastic wave propagation in the PSPS and improve the single-frequency or multifrequency active isolation performance of the PSPS. Since the driving voltage and current range of the piezoelectric stacks significantly affect the isolation performance of the PSPS, this article focuses on the relationship between the isolation performance of the PSPS and the voltage and current required by the piezoelectric stacks. Firstly, based on the passive material periodic structure transfer matrix model, the driving voltage and current of the piezoelectric stacks are introduced into the model, and a PSPS electromechanical coupling model based on the transfer matrix form is established. Secondly, the correctness of the model is verified by the finite element software. Based on the model, the design process of PSPS parameters is proposed. The optimal isolation performance of PSPS is predicted under the limitation of maximum driving voltage and current. The effects of damping loss factor, exciting force, period number and passive material on the requirements of electrical parameters for active control are studied. A three-period PSPS strut composed of piezoelectric stack actuator and PV strut is used for experimental research, and the matching of electrical parameters of this PSPS in the test is analyzed.

Lightweight and Flexible Graphene Foam Composite with Improved Damping Properties.

As an elastomer, PDMS can effectively suppress vibration in various fields in a certain temperature range by its viscoelastic behavior in the vitrification transition region, but the vibration isolation effect is poor at high temperature. In this paper, a three-dimensional graphene oxide (GO) foam is fabricated by solution processing method and freeze-drying techniques. After sequential infiltration synthesis, a GO-foam-reinforced PDMS nanocomposite (GO/PDMS) is fabricated with improved damping ability. By adjusting the content of GO, the micros-tructure of GO foam can be sensitively changed, which is crucial to the damping properties of composites. In this paper, by the dynamic mechanical analysis (DMA) of pure PDMS and five kinds of GO/PDMS composites, it is proved that the GO/PDMS composites developed in this work have reliable elasticity and viscoelasticity at 25 °C, which is 100 °C higher than the applicable temperature of pure PDMS. The storage modulus can reach 3.58 MPa, and the loss modulus can reach 0.45 MPa, which are 1.87 times and 2.0 times of pure PDMS, respectively. This GO-based nanocomposite is an ideal candidate for damping materials in passive vibration isolation devices.

Finite-Element Simulation of a Resonant Frequency-Tunable Vibration Isolator Based on Shape Memory Alloy Wire

BackgroundThe resonant-frequency-tunable vibration isolator based on Shape Memory Alloys (SMAs) combines the priority of passive and active vibration isolators, expands its engineering application, and improves the efficiency of vibration isolation. However, the special characteristics of SMAs and the complexity of the resonant-frequency-tunable vibration isolator result in the difficulty in finite-element analysis.MethodsThis article employs the ABAQUS subroutine and presents the finite-element analysis for this resonant-frequency-tunable vibration isolator, which simulates the thermomechanical responses of SMA wires and the mechanical behaviors of the vibration isolator.ResultsThe pseudoelasticity characteristics of SMA wires were simulated and validated. The mechanical characteristics of the vibration isolator, such as the temperatures, martensitic volume fractions, displacements, and equivalent stresses, were obtained and verified.ConclusionsThe results show that the finite-element analysis method presented is appropriate for simulating mechanical behaviors of the resonant-frequency-tunable vibration isolator. The analysis results reveal in detail the mechanical characteristics of the vibration isolator.

Numerical studies regarding the behaviour a large span roof under seismic load when using anti-seismic devices

Abstract The study presents the data obtained on a large span structure equipped with passive seismic isolators, placed at roof level, when subjected to multiple seismic loads. Three distinct passive isolation systems are taken into consideration to reduce the seismic response of the structure. The first case uses Friction Pendulum Systems (FP), the second uses a combination of High Damping Rubber Bearing (HDRB) and low friction pot-bearing systems, and the third implies the use of Lead Rubber Bearings (LRB) and low friction pot-bearing systems. Using seven sets of accelerograms, recorded and generated, the values for the main seismic response parameters are extracted in to underline the efficiency of the proposed systems. The results obtained in terms of natural vibration period, accelerations, bending moment, base shear are compared.

Development of a near-5-Kelvin, cryogen-free, pulse-tube refrigerator-based scanning probe microscope.

We report the design and performance of a cryogen-free, pulse-tube refrigerator (PTR)-based scanning probe microscopy (SPM) system capable of operating at a base temperature of near 5 K. We achieve this by combining a home-made interface design between the PTR cold head and the SPM head, with an automatic gas-handling system. The interface design isolates the PTR vibrations by a combination of polytetrafluoroethylene and stainless-steel bellows and by placing the SPM head on a passive vibration isolation table via two cold stages that are connected to thermal radiation shields using copper heat links. The gas-handling system regulates the helium heat-exchange gas pressures, facilitating both the cooldown to and maintenance of the base temperature. We discuss the effects of each component using measured vibration, current-noise, temperature, and pressure data. We demonstrate that our SPM system performance is comparable to known liquid-helium-based systems with the measurements of the superconducting gap spectrum of Pb, atomic-resolution scanning tunneling microscopy image and quasiparticle interference pattern of Au(111) surface, and non-contact atomic force microscopy image of NaCl(100) surface. Without the need for cryogen refills, the present SPM system enables uninterrupted low-temperature measurements.

Novel magnetic levitation systems for the vibration control of lightweight structures and artworks

This work designs, models, and experimentally validates novel magnetic levitation systems for the vibration isolation of lightweight structures and artworks. 2D and 3D passive vibration isolators are studied, making use of easy-to-assemble 3D-printed components and neodymium magnets. An optimized design of the number of magnets and the 3D printing process of the stabilizing parts allows us to finely tune the resonant frequencies and the vibration isolation performances. Ratios between the maximum horizontal and vertical accelerations, exhibited by the floating bodies, and the maximum horizontal acceleration applied to the base of the system are provided, for varying excitation frequencies. With these outputs, we show that it is possible to optimize the main design parameters of the isolation system, by targeting the desired frequency window, for a given payload.

Field experimental investigation on broadband vibration mitigation using metamaterial-based barrier-foundation system

Both periodic barriers and periodic foundations can be used as passive isolation measures to reduce the unfavorable vibrations affecting the protected superstructure. Under a certain direction of excitation, the frequency band gaps provided by the periodic barriers and periodic foundations are usually distinguishable due to the different orientations of these subsurface structures. In this study, a series of field tests are conducted to assess the combined usage of the periodic barrier and periodic foundation in a manner to achieve better wave isolation effect. Both periodic barrier and periodic foundation used in this study are made of one-dimensional (1-D) layered periodic material. Using the state-of-art hydraulic mobile shaker (T-Rex), the excitation with various types of input signals can be applied in all the three orthogonal directions at the desired location. The arrangement of motion sensors allows for recording the response of the ground surface and the protected superstructure in all the three directions. The screening effectiveness, quantified as Frequency Response Function (FRF), of the periodic barrier and periodic foundation are discussed separately, followed by an overall evaluation of the wave isolation performance of the system composed of both periodic barrier and periodic foundation. The results show that the filtering capability of the periodic barrier and the periodic foundation is complementary to each other, and the combined usage of the periodic barrier and the periodic foundation is beneficial to mitigating the vibration of the protected superstructure. ∙ A novel large-scale field tests reported on wave isolation of periodic barriers and periodic foundations. ∙ State-of-art shaker (T-Rex) is adopted to apply triaxial excitation and triaxial soil velocity are collected. ∙ The composite isolation effect of periodic barrier-periodic foundation system is first reported. ∙ Various excitations lead to similar isolation results for the periodic barrier and periodic foundation. ∙ The addition of periodic foundation will not adversely affect the performance of periodic barrier.

Enhanced design of the quasi-zero stiffness vibration isolator with three pairs of oblique springs: Theory and experiment

Quasi-zero stiffness vibration isolators have been extensively studied due to superior passive vibration isolation performance. As the quasi-zero stiffness region of the isolators is generally small, the research on their responses to the excitation with high amplitude is currently quite limited. This paper presents an improved design of the quasi-zero stiffness isolator with three pairs of oblique springs to increase the amplitude of the excitation. Theoretical formulations are derived for stiffness and force, and then the influences of three independent parameters on the quasi-zero stiffness region are studied to obtain optimal design parameters. A prototype is fabricated and tested for displacement excitations with amplitudes of 5 mm, 10 mm, and 15 mm in a frequency range of 1.5–10 Hz. The absolute displacement transmissibility of the enhanced quasi-zero stiffness isolator is theoretically and experimentally compared with that of the corresponding linear isolator and that of the previous isolators with three pairs of oblique springs using the same parameter conditions of the loaded mass, the horizontal length of oblique springs, and the vertical spring. The experimental results show that the enhanced design of the quasi-zero stiffness isolator with three pairs of oblique springs can achieve lower displacement transmissibility and deal with the displacement excitation with higher amplitude.

An asymmetric quasi-zero stiffness vibration isolator with long stroke and large bearing capacity

A novel passive asymmetric quasi-zero stiffness vibration isolator (AQZS-VI) comprising two linear springs acting in parallel with one negative stiffness element (NSE) is proposed, of which the NSE is mainly constructed by the combination of cantilever plate spring and L-shaped lever (CPS-LSL). The static model of the isolator is deduced considering the geometrical nonlinearity of the NSE and the bending deformation of plate spring. The nonlinear stiffness properties of the CPS-LSL and the AQZS-VI, as well as the nonlinear damping properties of the AQZS-VI, are discussed. The absolute displacement transmissibility of the AQZS-VI under base displacement excitation is obtained using harmonic balance method, and the effects of different excitation amplitudes and damping factors on the vibration isolation performance are analyzed. Better than other quasi-zero stiffness vibration isolators (QZS-VI) whose NSEs do not provide supporting force at zero stiffness point, the NSE of the AQZS-VI provides more supporting force than the parallel connected linear springs, which is very beneficial for improving the bearing capacity of the isolator. Compared with a typical symmetric QZS-VI with same damping property, the AQZS-VI has longer stroke with low stiffness and lower peak value of displacement transmissibility. The prototype experiments indicate that the AQZS-VI outperforms the linear counterpart with much smaller starting frequency of vibration isolation and lower displacement transmissibility. The proposed AQZS-VI has great potential for applying in various engineering practices with superior vibration isolation performance.

Study on Buckling Characteristics of a Convex Tape-Shaped Ti-Ni Shape Memory Alloy Element for Application to Passive Vibration Isolator Devices and Force Limit Devices

The tape-shaped Ti-Ni shape memory alloy (SMA) shows negative or quasi-zero stiffness during post-buckling deformation, and this characteristic can be applied to passive vibration isolator devices and force limit devices. Design calculation of the buckling load and the negative stiffness gradient after buckling of tape-shaped SMA element are required to apply the SMA element to these devices. When the cross-section of the SMA element is convex tape shaped, an improvement in buckling properties is expected. In this study, the effects of the curvature of the cross-section on the buckling characteristics of convex tape-shaped SMA elements were investigated by the 3D finite element method (3D-FEM) and material testing. The results of the study indicate that the buckling load and negative stiffness gradient of convex tape-shaped SMA elements tend to increase with increasing curvature of the cross-section. Furthermore, when the convex tape-shaped SMA elements buckled in the convex direction of the cross-section, the loading stress was approximately equivalent to that of buckling a flat tape-shaped SMA elements. Therefore, the convex tape-shaped SMA element is considered to be more suitable for device application compared to the flat tape-shaped SMA element, because the buckling characteristics of convex tape-shaped SMA elements can be controlled by adjusting the curvature of the cross-section without changing the dimensions.

Correlation of design parameters of lattice structure for highly tunable passive vibration isolator

The purpose of this study is to correlate the influence of multiple size-based design parameters of lattice structure, namely, the unit cell (UC) and strut diameter (SD) through the static and dynamics analyses for passive vibration isolation application. The lattice structures were prepared by utilizing the fused deposition modeling (FDM) additive manufacturing (AM). The samples were designed to retain lattice structure’s unique advantages while also conserving material consumption to fulfill the energy and cost demand. Through the static test, the crush behavior, failure mechanism, and mechanical properties were determined. The stiffness of lattice structure exhibited an increasing relationship with the unit cell and strut diameter where smaller unit cell and bigger strut diameter produced higher strength, and with that, higher load can be sustained. Through the dynamic vibration transmissibility test, it was found that the dynamic vibration results follow closely the trend in the static analysis. Lattice structure with larger unit cell and smaller strut diameter showed larger effective isolation region due to lower natural frequency value. The trade-off limit between stiffness for a lower natural frequency of the proposed design parameters was determined from the two parts analyses. The results suggest that most lattice isolators from the pool of design parameter combinations in this study have sufficient strength to withstand the predefined mass load and provide the most region for vibration isolation. The two proposed design parameters can later be used for a major or minor tuning of lattice isolators for other specific applications.

Vibration Reduction in a Pulse Tube-Cooled High Purity Germanium Detector

High-purity germanium (HPGe) is a vibration-sensitive, high-resolution detector. It has been found that microphonic noise induced by vibration and electromagnetic interference from EMC causes energy resolution degradation in HPGe detectors. In this paper, to enhance the energy resolution of a pulse tube-cooled high purity germanium detector, a passive vibration isolation system for the portable pulse tube cooler (PTC) was employed and investigated. In order to evaluate the performance of the vibration isolation system, micro-vibration tests of the compressor with a vibration isolation kit and detector mounting interface were performed. Meanwhile, detector energy resolution and detector signal noise were tested, respectively, under the PTC, with the isolation system switched to either an on or off condition. The test results indicate that the effectiveness of passive vibration isolation techniques is confirmed, and no degradation was induced by PTC vibration on detector energy resolution.