An adjustable low frequency vibration isolation with high-static-stiffness low-dynamic-stiffness property using a novel negative stiffness element

Nonlinear isolators with high-static-low-dynamic-stiffness have received considerable attention in the recent literature due to their performance benefits compared to linear vibration isolators. A quasi-zero-stiffness (QZS) isolator is a particular case of this type of isolator, which has a zero dynamic stiffness at the static equilibrium position. These types of isolators can be used to achieve very low frequency vibration isolation, but a drawback is that they have purely hardening stiffness behavior. If something occurs to destroy the symmetry of the system, for example, by an additional static load being applied to the isolator during operation, or by the incorrect mass being suspended on the isolator, then the isolator behavior will change dramatically. The question is whether this will be detrimental to the performance of the isolator and this is addressed in this paper. The analysis in this paper shows that although the asymmetry will degrade the performance of the isolator compared to the perfectly tuned case, it will still perform better than the corresponding linear isolator provided that the amplitude of excitation is not too large.

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Modelling the Quasi-Zero Stiffness Property of Shape Memory Alloy Spring for Ultra-Low Frequency Vibration Isolation

Electrical Engineering and Automation ◽

10.1142/9789813220362_0078 ◽

2017 ◽

Author(s):

Ting Wu ◽

Lin-xiang Wang

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Vibration Isolation ◽

Low Frequency ◽

Stiffness Property ◽

Low Frequency Vibration

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Dynamically variable negative stiffness structures

Science Advances ◽

10.1126/sciadv.1500778 ◽

2016 ◽

Vol 2 (2) ◽

pp. e1500778 ◽

Cited By ~ 30

Author(s):

Christopher B. Churchill ◽

David W. Shahan ◽

Sloan P. Smith ◽

Andrew C. Keefe ◽

Geoffrey P. McKnight

Keyword(s):

Vibration Isolation ◽

Dynamic Stiffness ◽

Low Frequency ◽

Variable Stiffness ◽

Negative Stiffness ◽

Load Bearing ◽

Vibration Isolators ◽

Wide Range ◽

Engineered Systems ◽

Tunable Stiffness

Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness–based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators.

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An Air Spring Vibration Isolator Based on a Negative-Stiffness Structure for Vehicle Seat

Applied Sciences ◽

10.3390/app112311539 ◽

2021 ◽

Vol 11 (23) ◽

pp. 11539

Author(s):

Cong Hung Nguyen ◽

Cong Minh Ho ◽

Kyoung Kwan Ahn

Keyword(s):

Vibration Isolation ◽

Dynamic Stiffness ◽

Low Frequency ◽

Negative Stiffness ◽

Vibration Isolator ◽

Air Spring ◽

Nonlinear Force ◽

Mechanical Spring ◽

Negative Stiffness Mechanism ◽

Vehicle Seat

This research introduces an air spring vibration isolator system (ASVIS) based on a negative-stiffness structure (NSS) to improve the vehicle seat’s vibration isolation performance at low excitation frequencies. The main feature of the ASVIS consists of two symmetric bellows-type air springs which were designed on the basis of a negative stiffness mechanism. In addition, a crisscross structure with two straight bars was also used as the supporting legs to provide the nonlinear characteristics with NSS. Moreover, instead of using a vertical mechanical spring, a sleeve-type air spring was employed to provide positive stiffness. As a result, as the weight of the driver varies, the dynamic stiffness of the ASVIS can be easily adjusted and controlled. Next, the effects of the dimension parameters on the nonlinear force and nonlinear stiffness of ASVIS were analyzed. A design process for the ASVIS is provided based on the analytical results in order to achieve high static–low dynamic stiffness. Finally, numerical simulations were performed to evaluate the effectiveness of the ASVIS. The results obtained in this paper show that the values of the seat displacement of the ASVIS with NSS were reduced by 77.16% in comparison with those obtained with the traditional air spring isolator without NSS, which indicates that the design of the ASVIS isolator with NSS allows the effective isolation of vibrations in the low-frequency region.

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Modeling a Mechanical Molecular Spring Isolator with High-Static-Low-Dynamic-Stiffness Properties

Shock and Vibration ◽

10.1155/2020/8853936 ◽

2020 ◽

Vol 2020 ◽

pp. 1-9

Author(s):

Zhanyong Li ◽

Qian Chen ◽

Fengshou Gu ◽

Andrew Ball

Keyword(s):

Vibration Isolation ◽

Dynamic Properties ◽

Piecewise Linear ◽

Dynamic Stiffness ◽

Low Frequency ◽

Isolation System ◽

Isolation Technique ◽

Piston Cylinder ◽

Low Frequency Vibration ◽

Stiffness Model

A mechanical molecular spring isolator (MMSI) is proposed for the purpose of isolating the low-frequency vibration of a heavy payload. The MMSI is a passive vibration isolation technique mimicking molecular spring isolator characteristics of high-static-low-dynamic stiffness (HSLDS). An MMSI consists of a piston-cylinder container filled with the liquid and some hydraulic spring accumulators. The piston would support a lump of mass and be subjected to a specific external vibration excitation force. Those accumulators can get intercommunication by the liquid to produce the transformation from high static stiffness to low dynamic stiffness. The stiffness model of the MMSI with several identical accumulators is established based on the hydrostatic law. After that, some parameters that significantly influence the stiffness characteristics are studied. Results show that the stiffness property of this kind of MMSI demonstrates a piecewise linearity of three segments. It applies the averaging method to acquire amplitude-frequency and phase-frequency relationships of the piecewise linear vibration isolation system. An inevitable jump phenomenon may occur when the exciting force reaches the critical value. The vibration isolation performance is evaluated by energy transmissibility. Finally, an experimental prototype was designed to carry out quasi-static and dynamic experiments to verify the stiffness model and the dynamic properties as an HSLDS vibration isolator.

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The design of negative stiffness spring for precision vibration isolation using axially magnetized permanent magnet rings

Journal of Vibration and Control ◽

10.1177/1077546319866035 ◽

2019 ◽

Vol 25 (19-20) ◽

pp. 2667-2677 ◽

Cited By ~ 1

Author(s):

Zhenhua Zhou ◽

Shuhan Chen ◽

Dun Xia ◽

Jianjun He ◽

Peng Zhang

Keyword(s):

Vibration Isolation ◽

Dynamic Stiffness ◽

Low Frequency ◽

Design Procedure ◽

Air Gap ◽

Negative Stiffness ◽

Linear Component ◽

Vibration Isolator ◽

Stiffness Characteristic ◽

Isolation Performance

A negative stiffness element is always employed to generate high-static–low-dynamic stiffness characteristic of the vibration isolator, reduce the resonance frequency of the isolator, and improve the vibration isolation performance under low and ultra-low frequency excitation. In this paper, a new compact negative stiffness permanent magnetic spring (NSPMS) that is composed of two axial-magnetized permanent magnetic rings is proposed. An analytical expression of magnetic negative stiffness of the NSPMS is deduced by using the Coulombian model. After analyzing the effect of air-gap width, air-gap position, height difference between the inner ring and outer ring on the negative stiffness characteristic, a design procedure is proposed to realize the negative stiffness characteristic with a global minimum linear component and uniformity stiffness near the equilibrium position. Finally, an experimental prototype is developed to validate the effectiveness of the NSPMS. The experimental results show that combining a vibration isolator with the NSPMS in parallel can lower the natural frequency and improve the isolation performance of the isolator.

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Dynamic characterization of controlled multi-channel semi-active magnetorheological fluid mount

Mechanical Sciences ◽

10.5194/ms-12-751-2021 ◽

2021 ◽

Vol 12 (2) ◽

pp. 751-764

Author(s):

Zhihong Lin ◽

Mingzhong Wu

Keyword(s):

High Frequency ◽

Optimization Design ◽

Vibration Isolation ◽

Dynamic Stiffness ◽

Low Frequency ◽

Vehicle Model ◽

Mr Fluid ◽

Unbalanced Force ◽

Low Frequency Vibration ◽

Engine Mount

Abstract. In this paper, a novel structure of a controlled multi-channel semi-active magnetorheological (MR) fluid mount is proposed, including four controlled channels and one rate-dip channel. Firstly, the magnetic circuit analysis, rate-dip channel optimization design, and MR fluid mount damping analysis are given. Secondly, the mathematical model of the controlled multi-channel semi-active MR fluid mount is constructed. We analyze the effect of controlled multi-channel closing on the dynamic characteristics of the mounts and the effect of the presence or absence of the rate-dip channel on the low-frequency isolation of the mount. Finally, the controlled multi-channel semi-active MR fluid mount was applied to the 1/4 vehicle model (a model consisting of an engine, a single engine mount, a single suspension and a vehicle frame), with the transmissibility of the engine relative to the vehicle frame at low frequency and the transmissibility of the engine reciprocating unbalanced force to the vehicle frame magnitude at high frequency as the evaluation index. Numerical simulation shows the following points. (1) The controllable multi-channel semi-active MR fluid mount can achieve adjustable dynamic stiffness and damping with applied 2 A current to different channels. (2) With known external excitation source, applied currents to different controllable channels can achieve the minimum transmissibility and meet the mount wide-frequency vibration isolation requirement, while adding a rate-dip channel can improve the low-frequency vibration isolation performance of the MR fluid mount. (3) Switching and closing different controllable channels in the 1/4 vehicle model can achieve the minimum transmissibility of low-frequency engine vibrations relative to the vehicle frame and high-frequency engine vibrations reciprocating an unbalanced force to the vehicle frame. Therefore, the design of the controllable multi-channel semi-active MR fluid mount can meet the wide-frequency isolation.

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Nonlinear Dynamic Study of Oscillation System Featuring Quasi-Zero and Asymmetric Stiffness

10.21203/rs.3.rs-190067/v1 ◽

2021 ◽

Author(s):

Thanh Danh Le ◽

Minh Ky Nguyen ◽

Ngoc Yen Phuong Vo

Keyword(s):

Vibration Isolation ◽

Sliding Friction ◽

Dynamic Stiffness ◽

Low Frequency ◽

Force Model ◽

Oscillation System ◽

Time Dynamic ◽

Bifurcation Phenomenon ◽

Low Frequency Vibration ◽

Approximate Polynomial

Abstract This paper will broaden our previous works about the asymmetric and quasi-zero stiffness oscillator named AQZSO. In this paper, the dynamic stiffness of the AQZSO will be investigated. Then, the condition for which the minimum dynamic stiffness is quasi-zero around the equilibrium position is also determined. By using Multi-Scale method, the fundamental resonance response of the AQZSO subjected to the vibrating base is analyzed, in which the dynamic stiffness is expressed as a fifth-order approximate polynomial through expanding Taylor series. The stability of the response is then found out via nonlinear Routh-Herwitz criterion. Moreover, because of existing the sliding friction between the cylinder and piston, the nonlinear and varying-time dynamic characteristics, the complex dynamic response of the AQZSO is the need for discovery by performing direct integration of the original dynamic equation through using 5th-order Runge-Kutta algorithm. In this work, the friction force model of cylinder will be identified through virtual prototyping technique and genetic algorithm. Additionally, the Poincáre map is also employed to analyze the bifurcation phenomenon, coexistence of multiple solutions. The traction basin of the period-1, period-2 and period-3 solution is determined, indicating that the attractor basin is influenced by the asymmetric of the stiffness curve. This research will offer a useful insight to design low frequency vibration isolation systems.

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Design and Theoretical Analysis of High-Static-Low-Dynamic Stiffness Torsion Vibration Isolator Based on Oblique Springs

Journal of Physics Conference Series ◽

10.1088/1742-6596/2101/1/012028 ◽

2021 ◽

Vol 2101 (1) ◽

pp. 012028

Author(s):

Zhirong Yang ◽

Lintao Li ◽

Jiacheng Yao ◽

Qingkai Wang

Keyword(s):

Harmonic Balance ◽

Vibration Isolation ◽

Dynamic Stiffness ◽

Low Frequency ◽

Vibration Isolator ◽

Torsion Vibration ◽

Low Frequency Vibration ◽

Torsion Stiffness ◽

Ihb Method ◽

Peak Value

Abstract A torsion vibration isolator composed of oblique springs with high-static-low-dynamic stiffness (HSLDS) is proposed to attenuate the transmission of torsion vibration along the shipping shaft in this paper. It is good at in low frequency vibration isolation as it can significantly reduce the resonance frequency of the system with the same load capability. Firstly, the model of HSLDS torsion vibration isolator is introduced in this paper. Secondly, the non-dimensional torsion stiffness is formulated using mechanics theory, and the HSLDS characteristic of designed torsion vibration isolator is verified. Finally, the torque transmissibility is analyzed using the Increment Harmonic Balance (IHB) method, and the effects of the system parameters on it are analyzed. The results show that the resonant frequency increases accordingly as the stiffness ratio and the excitation torque are increased. However, the peak value of the torsion transmissibility is decreased as the damper ratio increasing.

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