Vibration Isolation Capability Research Articles

Implementation and Experiment of a Novel Molecular Spring Isolator

A molecular spring isolator comprising ZIF-8 with hydrophobic micropores, water, and a cylinder/piston unit is introduced. Liquid water can be intruded into the micropores of ZIF-8 under critical pressure. In the meantime, mechanical energy is stored. And once the external pressure is withdrawn, spontaneous capillary evaporation will occur. The stored energy, meanwhile, is released. This behavior is similar to a coil spring. The Laplace–Washburn equation is used to describe the force equilibrium of a single water column in a micropore. After that, the result of water infiltrating a great deal of hydrophobic pores is revealed by theoretical analysis and an experiment. An averaging method is devoted to computing the primary resonance response and its accuracy is proved by the fourth-order Runge–Kutta method. Furthermore, the energy transmissibility is used to estimate its vibration isolation capability. Finally, a vibration isolation test indicated that the inherent frequency of the isolator is as low as 1.3 Hz.

On the broadband vibration isolation performance of nonlocal total-internal-reflection metasurfaces

The concept of a nonlocal elastic metasurface has been recently proposed and experimentally demonstrated in Zhu et al. (2020). When implemented in the form of a total-internal-reflection (TIR) interface, the metasurface can act as an elastic wave barrier that is impenetrable to deep subwavelength waves over an exceptionally wide frequency band. The underlying physical mechanism capable of delivering this broadband subwavelength performance relies on an intentionally nonlocal design that leverages long-range connections between the units forming the fundamental supercell. This paper explores the design and application of a nonlocal TIR metasurface to achieve broadband passive vibration isolation in a structural assembly made of multiple dissimilar elastic waveguides. The specific structural system comprises shell, plate, and beam waveguides, and can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. The study also reports the results of an experimental investigation that confirms the significant vibration isolation capabilities afforded by the embedded nonlocal TIR metasurface. These results are particularly remarkable because they show that the performance of the nonlocal metasurface is preserved when applied to a complex structural assembly and under non-ideal incidence conditions of the incoming wave, hence significantly extending the validity of the results presented in Zhu et al. (2020). Results also confirm that, under proper conditions, the original concept of a planar metasurface can be morphed into a curved interface while still preserving full wave control capabilities.

Dynamics of elastic hyperbolic lattices

The hyperbolic space affords an infinite number of regular tessellations, as opposed to the Euclidean space. Thus, the hyperbolic space significantly extends the design space lattices, potentially providing access to unexplored wave phenomena. Here we investigate the dynamic behavior of hyperbolic tessellations governed by interactions whose strengths depend upon the distances between neighboring nodes. We find eigen-modes that are primarily localized either at the center or towards the boundary of the Poincaré disk, where hyperbolic lattices are represented. Hyperbolic translations of the seeding polygon produce distorted lattices, leading to a redistribution of the eigen-modes akin to edge-to-edge transitions. The spectral flow associated with these deformed lattices reveals a rich behavior that is characterized by modes that are spatially asymmetric and localized. The strength of the localization can be predicted from the slopes of the corresponding spectral branches, suggesting a potential topological origin for the observed phenomena. The rich yet predictable spectral flow and the high modal density of these lattices, along with the propensity of their modes to be strongly localized, suggest potential applications of hyperbolic lattices as vibration sensors, which operate over a large range of frequencies and exploit the sensitivity of localized modes to perturbations. In addition, hyperbolic lattices can inform the design of architected structural components with strong vibration attenuation and isolation capabilities.

Tailored Mechanical Metamaterials with Programmable Quasi‐Zero‐Stiffness Features for Full‐Band Vibration Isolation

AbstractQuasi‐zero‐stiffness (QZS) isolators of high‐static‐low‐dynamic stiffness play an important role in ultra‐low frequency vibration mitigation. While the current designs of QZS mainly exploit the combination of negative‐stiffness corrector and positive‐stiffness element, and only have a single QZS working range, here a class of tailored mechanical metamaterials with programmable QZS features is proposed. These programmed structures contain curved beams with geometries that are specifically designed to enable the prescribed QZS characteristics. When these metamaterials are compressed, the curved beams reach the prescribed QZS working range in sequence, thus enabling tailored stair‐stepping force‐displacement curves with multiple QZS working ranges. Compression tests demonstrate that a vast design space is achieved to program the QZS features of the metamaterials. Further vibration tests confirm the ultra‐low frequency vibration isolation capability of the proposed mechanical metamaterials. The mechanism of QZS stems solely from the structural geometry of the curved beams and is therefore materials‐independent. This design strategy opens a new avenue for innovating compact and scalable QZS isolators with multiple working ranges.

An integrated nonlinear passive vibration control system and its vibration reduction properties

A novel integrated nonlinear passive vibration control system with the function of vibration isolation and absorption is proposed by applying a bio-inspired isolator and a nonlinear energy sink (NES). The designed integrated system has excellent vibration isolation capability in the low-frequency bands and can decrease the resonance amplitude simultaneously. The nonlinear dynamic model of the integrated passive vibration control system is established. The displacement transmissibility is employed to evaluate the vibration reduction performance of the integrated system by the harmonic balance method. The coupling mechanism of vibration isolation and absorption is revealed through studying the effects of the parameters on the vibration isolation and absorption performance. It is found that due to the nonlinear weak coupling between the bio-inspired isolator and the NES, they can promote each other in the vibration isolation and absorption. Experiments are conducted to validate the advantageous vibration reduction properties of the system. And the design methodology of the integrated passive vibration control system is also elaborated for practical applications. The integrated nonlinear passive vibration control system would provide an innovative method for vibration control in various engineering practice.

Synchronization analysis of the anti-resonance system with three exciters

In the petroleum exploitation industry, the vibration isolation technology of the traditional vibration screen is difficult to satisfy the security requirement of industrial production, so the anti-resonance system of three exciters is proposed in the present work. The differential motion equations of the vibrating system are established through introducing Lagrange's equation. The vibration isolation coefficient is defined to analyze the vibration isolation capability of anti-resonance system. And the synchronization condition and stability criterion are obtained by introducing the small parameters averaging method. Besides, the relation between the dynamic characteristics and structural parameters of the vibrating system is explored by numerical analyses. The simulation results are given to verify the accuracy of theoretical research. The results indicate that the optimal vibration isolation ability of the system is carried out when the excitation frequency of the vibrating system is equal to natural frequency of the system. The self-synchronization of the proposed system is independent of the mounting distance of the motors with the same mounting angle. Nevertheless, the self-synchronization is obviously influenced by the mounting distance of the motors with different mounting angle. This study can provide design ideas of the anti-resonance machine and promote the development of vibration utilization engineering.

Nonlinear dynamic response of a wire rope isolator: Experiment, identification and validation

The vibration isolation capability of a nonlinear wire rope spring is experimentally and numerically investigated. The isolated structure consists of two cantilever beams with a lumped mass at the tip. The force-displacement cycles exhibited by the isolator show a hysteretic behavior due to interwire friction and geometric nonlinearities. The restoring force possesses a distinct nonsymmetry exhibiting softening under compression and hardening under tension. The device rheological response is identified using a suitable mechanical model to fit the experimental data. Families of frequency response curves (FRCs) for increasing levels of the vertical base excitation are obtained for the standalone device and the non-isolated and isolated structures, respectively. The comparison between the FRCs of the isolated and the non-isolated structures shows a severe reduction of the transmissibility coefficient in a broad frequency range. The proposed phenomenological model of the device, in which the parameters are identified according to the static response, is employed to predict the nonlinear dynamic response which also proves to be in good agreement with the experimental response.

Computational analysis of phononic crystal vibration isolators via FEM coupled with the acoustic black hole effect to attenuate railway-induced vibration

The problem of ambient vibration caused by urban rail transit continues to be serious, but it has not been satisfactorily resolved. This study investigates the structure of a novel phononic crystal vibration isolator (NPCVI) in which the low-frequency and multi-modal features of the acoustic black hole (ABH) structure are used to create coupling vibration between the ABH rubber and steel resonator. The bandgap is widened and the vibration isolation capability of the phononic crystal vibration isolator is optimized. By establishing a finite element model, the multi-bandgap behavior of the NPCVI is discussed, and its vibration isolation capability is demonstrated via studies of the force transmission spectrum. The energy distribution in the finite element model reveals the nature of multi-bandgap formation. Finally, a train–floating slab track–tunnel coupled dynamic model is established to investigate the vibration isolation capability of the NPCVI under the excitation of various track irregularities. The results demonstrate that, under various train speeds, the NPCVI exhibits a superior vibration isolation capability as compared to that of a steel-spring vibration isolator.

Seismic metamaterials with cross-like and square steel sections for low-frequency wide band gaps

This study investigates the propagation of Lamb waves in seismic metamaterials (SMs) assembled using periodically arranged cross-like and square steel sections in a soil medium to assess the feasibility of their use for seismic wave attenuation. Four types of SMs with different steel sections were considered. The finite element method was used to carry out numerical simulations to investigate the band gap characteristics, vibration modes, and the effects of various parameters of the SMs. The results show that SMs with three complete band gaps (CBGs) below 20 Hz are of particular interest for low-frequency vibration control. The SMs composed of square steel sections exhibit a more favorable performance as compared to the SMs composed of cross-like steel sections in terms of the formation of wider CBGs. The volume fraction of steel is beneficial for enlarging the CBGs by planarizing the upper and lower edges of a single CBG. Moreover, geometric and material parameters play important roles in the band gap distributions. A vibration simulation analysis was carried out to simulate the seismic wave propagation through the SMs to the buildings, and the results indicate that Bragg scattering is the formation mechanism for the first CBG of the four SMs. This study provides a new way to build SMs by designing the volume fraction and steel section shapes to provide ultra-low and broad-band frequency vibration isolation capabilities that will allow the shielding of seismic waves in specific frequency ranges.

An Adjustable Low-Frequency Vibration Isolation Stewart Platform Based On Electromagnetic Negative Stiffness

With the continuously increasing requirements for vibration isolation in multiple degrees-of-freedom(DOFs), the negative stiffness(NS) passive Stewart platform with simple, reliable structure and good vibration isolation capability have become a concern. However, it has the disadvantage of unadjustable stiffness, which limits its application prospects. An adjustable electromagnetic negative stiffness (AENS) Stewart platform is proposed in this paper. It can realize good stiffness match conveniently and has high vibration isolation performance in all 6 DOFs. Firstly, this paper introduces the structural composition of the system. Then, the kinematics model is constructed by the vector method, the dynamic model is constructed by the second Lagrange equation, and the multi-DOFs transmissibility rate matrix is given. Finally, the performance of AENS Stewart platform are verified through experiments. The experimental results show that it can reduce the natural frequency from 3.94 Hz to 2.69 Hz, 7.69 Hz to 5.17 Hz, 9.5 Hz to 6.35 Hz, and 9.5 Hz to 6.35 Hz in the X(Y), Z, α(β), and γ DOFs, respectively. Convenient stiffness matching and good low-frequency vibration isolation in multi-DOFs make AENS platform have great application potential.

Performance Improvement of Active MacPherson Suspension Using a Pneumatic Muscle and an Intelligent Vibration Compensator

This paper presents an intelligent control strategy for an active MacPherson suspension driven by a pneumatic muscle (PM) actuated system and evaluates its improved control performance on a self-developed test-rig. To fulfill the fully-functional test and analysis of active suspension systems, this test-rig comprises three units: 1. an active MacPherson suspension unit, which consists of a PM mechanism and two MacPherson struts, is built to isolate vibration from road disturbances; 2. a road profile generator (RPG) unit, which can produce a vertical force to lift the car-body according to various road profiles; 3. a PC-based control (PBC) unit, which computes, sends and receives signals for both of the active MacPherson suspension and the PC-based control unit. The objective of this study is to improve the MacPherson suspension in terms of the capability of road vibration isolation by using the PM actuation that can actively provide extra compensatory force for MacPherson struts. Then, for motion control of the PM, this study employs an interval type-2 adaptive fuzzy controller to approximate the optimal control law and adopts a self-tuning and fuzzy sliding mode compensator to compensate unmodeled dynamics for the active MacPherson suspension system. Three experiments are conducted to compare the active MacPherson suspension system with the original MacPherson struts through various road profiles on the test-rig. The results show the significant improvement for the proposed active MacPherson suspension system in suppressing the displacement and acceleration of the car-body.

Influence characteristics of electrical parameters and vibration isolation properties of the stretcher system based on parallel mechanism and self-powered magneto-rheological damper

For reducing multidimensional vibrations endured by supine patients on ambulances, a new ambulance stretcher composed of parallel mechanism and self-powered magneto-rheological damper is introduced. The main thrust of this work is to investigate the vibration isolation capability and energy conversion efficiency of the proposed stretcher with changes in electrical parameters. First, the kinematic and dynamic equations are deduced by geometry and Lagrange approach, respectively. Subsequently, the circuit model of self-powered magneto-rheological damper is created. The frequency response function is derived by Kirchhoff’s law, which indicates the electrical power utilization rate. Then, the vibration isolation capability of the self-powered stretcher system is analyzed with changes in electrical parameters. Compared with passive control, the vibration isolation capability of the self-powered stretcher is improved significantly in horizontal, longitudinal, vertical, and pitch directions. The first two resonance peaks of displacement response are insensitive to changes in electrical parameters in all directions. Last, the energy conversion efficiency of the self-powered stretcher is discussed. Decreasing resistance and inductance could improve energy conversion efficiency significantly.

A novel bio-inspired multi-joint anti-vibration structure and its nonlinear HSLDS properties

A unique bio-inspired multi-joint leg-like or limb-like vibration isolation structure is studied by mimicking the skeleton and joint structures of animal legs, and its advantage in passive vibration isolation is systematically investigated. This bio-inspired structure uses several small quadrilateral structures composed by short adjustable rods and a transverse spring to simulate the multi-articulation of animal legs and adopts long rods to simulate the skeleton. The equivalent static stiffness property, loading capacity and dynamic vibration isolation performance of the structure are systematically studied. It is shown that the nonlinear stiffness characteristics of the structure can lead to very excellent vibration isolation capability in the low-frequency band. Different from many existing quasi-zero-stiffness (QZS) isolators in the literature, this novel anti-vibration structure can demonstrate superior high static but low dynamic stiffness (HSLDS) property and thus excellent vibration isolation performance, subject to large vibration amplitude. Through adjusting proper structural parameters including the rod-length, assembly angle, spring stiffness and layer number according to the influence of the structural parameters on the nonlinear stiffness property, the new structure can have the optimal vibration isolation performance without sacrificing its loading capacity to meet actual requirements. Especially, the length of long rods which is used to simulate the skeleton can be adjusted to obtain better vibration isolation performance than adjusting other parameters, followed by the adjustment of the parameters of small quadrilateral structures. The analysis of the influence of structural parameters on the vibration isolation performance shows that the symmetry between different layers has an important role in maintaining the characteristic of the HSLDS. The comparison with other existing vibration isolation structures of the QZS property also indicates that, the new vibration isolation structure can have a better vibration isolation performance with relatively a smaller size of the overall structure. Experiments are successfully conducted and validated the beneficial nonlinear properties of the structure. This novelbio-inspired anti-vibration structure would have great advantages in practical engineering applications.

Influential characteristics of electromagnetic parameters on self-powered MR damper and its application in vehicle suspension system

In order to reuse the energy dissipated by magneto-rheological (MR) damper, a self-powered MR damper is designed and analyzed theoretically. The main thrust of this work is establishing the mechanical-electromagnetic coupling model of quarter vehicle suspension based on self-powered MR damper, whilst the energy conversion efficiency of self-powered MR damper with electromagnetic parameters changing is investigated. The magnetic circuit model is formulated firstly. The influence of electromagnetic parameters on current in MR damper is analyzed systemically in frequency domain. A multi-objective optimization method is performed to determine the electromagnetic parameters. Subsequently a quarter vehicle suspension system with self-powered MR damper is introduced. The mechanical-electromagnetic coupling model is established. The frequency response function is derived under random road excitation. The vibration isolation capability of the proposed quarter vehicle suspension system is addressed in time and frequency domain respectively. Compared to passive control, the amplitude of sprung mass velocity, acceleration and transmissibility are reduced by 51%, 78% and about 10 dB in time and frequency domain respectively. Finally the energy conversion efficiency of self-powered MR damper with magnetic parameters changing under random road excitation is discussed. The vibration isolation performance of self-powered MR damper is more effective than passive control, especially in resonance range of the suspension system.

Design and experimental investigation of a novel compliant positioning stage with low-frequency vibration isolation capability

Nowadays, those compliant positioning stages with the advantages of compact structure, micro-displacement output precision and negligible friction have been widely used in ultra-precision engineering. As a novel scheme, a z-directional positioning stage is proposed and discussed detailedly in this article. First, the conceptual scheme is clarified and structure optimization is conducted for obtaining a better performance. Attributed to the combination of the lever-principle amplifier and bridge-principle amplifier, a large amplification ratio could be ensured. Following that, the ideal displacement amplification ratio model is constructed based on the kinematics method for rapid evaluation of the displacement output performance. Meanwhile, the dynamic model is established through Lagrange’s equation on the basis of Pseudo Rigid Body Model (PRBM) method. The corresponding numerical simulations prove the effectiveness of the built theoretical model. Finally, an engineering prototype is processed and experimental tests are carried out to validate the capability of the positioning stage. The test results demonstrate that the designed stage could achieve the required performance and possess a high positioning accuracy, which meanwhile shows a special capability of low-frequency vibration isolation.

Experimental study of vibration isolation in thin-walled structural assemblies with embedded total-internal-reflection metasurfaces

The concept of total-internal-reflection elastic metasurface (TIR-MS) was recently proposed [1] and employed within flexible planar waveguides in order to create highly subwavelength sound-hard barriers impenetrable to low frequency elastic waves. The underlying physical mechanism relies on the design of engineered interfaces exhibiting extreme phase gradients such that any incoming wave at, approximately, any incidence will experience total-internal-reflection conditions. At the design frequency, the metasurface exhibits a large phase gradient such that, in accordance with the generalized Snell's law, the first critical angle is virtually always exceeded. It is worth noting that in practical realizations, the actual total reflection performance might vary depending on the angle of incidence. This dependence is due to the discrete implementation of the metasurface which results in diffraction effects. This paper presents the results of an experimental study that explores the vibration isolation performance of TIR-MS when applied to structures made of complex combinations of different elastic waveguides (e.g. bolted assemblies of beams, plates, and shells). Such system can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. Experimental results confirm that, when the TIR-MS is embedded in the host waveguide, significant vibration isolation capabilities are achieved under quasi-omnidirectional incidence and highly subwavelength excitation conditions (i.e. the ratio of the operating wavelength to the width of the TIR-MS is approximately 5.25). These experimental results suggest new interesting directions to achieve vibration isolation and mechanical energy filtering for practical engineering systems.

Analysis and optimization of coupled vibration between substructures of a multi-axle vehicle

The vibration from transport vehicles may negatively affect the ride comfort in the cab and the product safety in the carriage. A 15 degrees of freedom vehicle model consisted of a cab, a carriage, a chassis, and mounts and suspensions between them are introduced to present the vibration behavior of a three-axle vehicle. Two indices, the coupling factor and the vibration attenuation factor, are employed to quantify the correlation between structures and the vibration isolation capability of subsystems. A sensitivity analysis is carried out with a 43-factor optimal Latin hypercube design, concerning the effect of mass properties, geometries, stiffness, and damping on the vibration coupling effect and the vibration attenuation of subsystems. Results show obvious trade-offs between the vibration coupling effect and the vibration attenuation among different subsystems. Based on the significant factor identified, multi-objective optimizations are conducted to improve the vibration performance of both the cab and the carriage and simultaneously reduce the correlations between structures using different algorithms. Comparison between different optimal results indicates that a compromise can be achieved between the ride comfort and the cargo safety based on a lightweight constraint.

Dynamic modeling and decoupled control of a flexible Stewart platform for vibration isolation

The vibration isolation system is crucial to high-precision space systems. This paper studies dynamics and control of a six-axis vibration isolator via a flexible Stewart platform. The parasitic stiffness induced by flexible joints is considered in dynamics modeling and compensated in control for the first time. The explicit dynamic equations are established based on the pseudo-rigid-body model and the principle of virtual power. After validation by ADAMS/Flex and the finite element method, the dynamic equations are used for designing a decoupled controller. The control force is synthesized based on the leg’s force and position feedback. The impact of bending and torsional stiffness of flexible joints is compensated and the MIMO system is consequently decoupled in modal space, making parameter design and performance implementation more convenient and effective. The identical sub-controller for every SISO system makes the six-DOF isolator achieve the capability of vibration isolation simultaneously for the six modes. With a proportional plus integral compensator as the sub-controller, the vibration isolation bandwidth and active damping can be regulated separately.

Dynamics and performance evaluation of an asymmetric nonlinear vibration isolation mechanism

In this work, the dynamics and performance of a harmonically excited asymmetric nonlinear vibration isolation mechanism is investigated using the multi harmonic balance method (MHBM). Asymmetry in the system is introduced in the form of a constant load along with the harmonic excitation. Instead of a truncated cubic nonlinear system considered in the previous works, the fully nonlinear system without any approximation is considered in this study. The MHBM framework considered in this paper is a systematic and computationally efficient method to generate periodic solutions of any order, continue their branches, identify stable, and unstable branches along with the types of bifurcations. Dynamics of the system is investigated with forcing frequency and forcing amplitude as the parameters. With an increase in the value of the constant load, the response diagram shows double folding with softening and hardening behavior and multiple jumps, disappearance of certain types of bifurcations, loss of stability of the periodic solutions, existence of higher order periodic solutions, and chaotic solutions. The transmissibility plots in the presence of the constant load show substantial deterioration in the vibration isolation capability of the isolation system. A comparison of the fully nonlinear system and the truncated cubic system is performed at the end to show that the solutions are qualitatively same but quantitatively different which is an important aspect in practical applications of isolation systems.

A new hybrid observer based rotor imbalance vibration control via passive autobalancer and active bearing actuation

Many researchers have explored the use of active bearings, such as non-contact Active Magnetic Bearings (AMB), to control imbalance vibration in rotor systems. Meanwhile, the advantages of a passive Auto-balancer device (ABD) eliminating the imbalance effect of rotor without using other active means have been recently studied. This paper develops a new hybrid imbalance vibration control approach for an ABD-rotor system supported by a normal passive bearing in augmented with an AMB to enhance the balancing and vibration isolation capabilities. Essentially, an ABD consists of several freely moving eccentric balancing masses mounted on the rotor, which, at supercritical operating speeds, act to cancel the rotor's imbalance at steady-state. However, due to the inherent nonlinearity of the ABD, the potential for other, non-synchronous limit-cycle behavior exists resulting in increased rotor vibration. To address this, the algorithm of proposed hybrid control is designed to guarantee globally asymptotic stability of the synchronous balanced condition. This algorithm also incorporates with a “Luenberger-like” observer that continuously estimates the states of a balancer ball circulating around within ABD. In particular, it is shown that the balanced equilibrium can be made globally attractive under the hybrid control strategy, and that the control power levels of AMB are significantly reduced via the addition of the ABD because the control is designed such that it is only switched on for the abnormal operation of ABD and will be disengaged otherwise. Moreover, unlike other imbalance vibration control applications based upon ABD such as rotor speed regulator [21,22], this approach enables the controller to achieve the desirable performance without altering rotor speed once the rotor initially reaches the target speed. These applications are relevant to limited power applications such as in satellite reaction wheels, flywheel energy storage batteries or CD-ROM application.