Vibration Isolation Characteristics Research Articles

A Novel of Low-Frequency Vibration Isolation with High-Static Low-Dynamic Stiffness Characteristic

The efficiency of quasi-zero stiffness vibration isolator will decrease when getting overloaded and underloaded. Given the variability of load in general engineering application, this paper aims at presenting a newly designed type of vibration isolation system with positive stiffness in parallel with elements of negative stiffness, which has variable carrying capacity. The vibration isolation performance of system requires overall analysis. Firstly, static analysis is applied to obtain the optimal vibration isolation parameters of the system at the equilibrium position and to verify the high-static low-dynamic stiffness characteristic of the system. Then, the nonlinear dynamic equation of the system is established. Meanwhile, the influence of excitation amplitude on the transmissibility of the system is analyzed under three different conditions by harmonic balance method. Finally, the response curves of the system to sinusoidal excitation and multi-frequency excitation are analyzed by numerical simulation. The result of numerical simulation shows that the vibration isolation system still has good low-frequency vibration isolation characteristics when dealing with different loads. The problem of poor vibration isolation performance of general quasi-zero stiffness isolators under load changes is well solved.

Performance of a launch isolator: Theoretical and experimental study

A piecewise linear vibration isolator used to isolate the rocket launch vibration is proposed and investigated in this paper. The dynamic characteristics of the piecewise linear vibration isolator are analyzed theoretically and experimentally. Assuming base excitation from the rocket, the dynamic equation is established and the response is solved by using averaging method. The influence of the system parameters such as stiffness ratio and clearance distance on the system performance is discussed. The jumping phenomenon and frequency shift are observed. The vibration isolation performance of the isolator is tested by using vibration table to simulate the launch vibration loads according to certain criterion. The theoretical and experimental results are compared and are in good accordance. The results show that the piecewise linear vibration isolation system can lower the response for large amplitude vibration excitation at launch. The results present here can be a useful guideline when design such kind of vibration isolator.

An approximate method for solving force and displacement transmissibility of a geometrically nonlinear isolation system

This study presents a modified harmonic balance method, which is used to solve the force and displacement transmissibilities of a vibration isolator with both the quasi-zero-stiffness and geometrically nonlinear damping. The steady-state response of the nonlinear isolation system is obtained by Jacobi elliptic functions, and is used to modify the harmonic components of stiffness and damping force in the harmonic balance method, which can reduce the truncation error produced by the trigonometric Fourier series. When the modified harmonic components are combined based on the orthogonality condition, the elliptic harmonic balance method (EHBM) is obtained. The results show that the amplitude–frequency response curve, and force and displacement transmissibilities obtained by using the EHBM can be compared well with those obtained by using the fourth order Runge–Kutta method. The EHBM can be used to improve the accuracy of the results at the resonance and high frequency regimes. The EHBM is simple and straightforward for the detailed study of the vibration isolation characteristics of the geometrically nonlinear isolator.

Исследование динамических характеристик спирально-тросового виброизолятора типа СТВР-400К.

Исследование динамических характеристик спирально-тросового виброизолятора типа СТВР-400К.

1/2 sub-harmonic resonance in bistable structure and its effect on vibration isolation characteristics

<sec>In the extensive modern applications, the low-frequency and heavy-load isolators are needed to reduce the vibration transmissions. The unique properties of nonlinear systems, such as jumping, bifurcation and chaos, provide new ideas for designing the new functional structures. Bistable system is a typical non-linear system, features highly static and low dynamic stiffness, which promises to realize a low-frequency isolator with ensuring heavy load capacity. However, more studies are necessary to clarify the sub-harmonic resonance and its generation process, parameter influences, vibration isolation characteristics of the bistable structure.</sec><sec>By adopting the equivalent, analytical, numerical and experimental methods, we study the 1/2 sub-harmonic resonance, evolution process and its influence on the vibration isolation characteristics of the bistable structure in this paper. When the amplitude or nonlinear stiffness coefficient <i>k</i><sub>n</sub> increases to a certain extent, 1/2 sub-harmonic resonance appears, where the response contains high-amplitude <i>ω</i>/2 component under the excitation frequency <i>ω</i>, so the energy is transferred from high frequency to low frequency. We study the bifurcation and varying processes of the fundamental and 1/2 sub-harmonic transmission by increasing the amplitude. At critical bifurcation amplitude, the sub-harmonic transmission rapidly increases from 0 to a large peak value. And then, it decreases gradually when the damping is absent. However, the peak value of 1/2 sub-harmonic does not cause the fundamental transmission to change suddenly. When considerable damping appears with the increase of the amplitude, 1/2 sub-harmonic does not always exist, instead, it follows an interesting “generation-enhancement-degeneration-disappearance” process. This process possesses great significance in applying the 1/2 sub-harmonic to vibration manipulation or avoiding the resonant enhancement induced by it. </sec><sec>Moreover, in this process, both the peak frequency and the peak transmission of the bistable isolation system descend first. The optimal combination of the parameters can reduce the resonance frequency by 17.8% through increasing the driving amplitude. However, they jump to large values when 1/2 sub-harmonic plays a dominant role. </sec><sec>Additionally, the negative stiffness <i>k</i><sub>0</sub> has a significant effect on the primary resonance characteristics: as |<i>k</i><sub>0</sub>| increases under a specified excitation amplitude, the resonance peak shifts toward higher frequency and the transmission increases. Besides the main effect on the sub-harmonic resonance and the equilibrium point, the nonlinear coefficient <i>k</i><sub>n</sub> also affects the peak and resonance frequency of the system, but the effect is much less than the influence caused by <i>k</i><sub>0</sub>.</sec><sec>Furthermore, the sub-harmonic resonances, bifurcations and vibration isolation characteristics of the bistable bulking beam structure are demonstrated experimentally. The experimental results show that: 1) the 1/2 sub-harmonic resonance can appear in a certain bandwidth and it is not monochromic; 2) the increase of the driving amplitude can reduce the transmission of the fundamental wave; 3) the transmission of 1/2 sub-harmonic jumps from 0 upward to a large value at a critical amplitude, and then it decreases gradually. The experimental results are consistent with the analytical and numerical results. The experiment also demonstrates the law of frequency shifting and the transmission reduction of peak values. Therefore, the appropriate increase of the amplitude can improve the vibration isolation capacity. However, sub-harmonic resonance will reduce the isolation effect. In practical engineering, the strong sub-harmonic resonance should be avoided in a nonlinear vibration isolation system.</sec>

Force transmissibility characteristics of a pseudoelastic oscillator

The force transmissibility characteristics of a passive vibration isolator in the form of shape memory alloy bar are investigated. The shape memory alloy bar, together with a rigid mass, constitutes a single-degree-of-freedom system. The force isolation ability of the oscillator is evaluated for both isothermal and convective environmental conditions. The transmissibility curve of an isothermal pseudoelastic oscillator displays single and double jumps depending upon the forcing amplitude. The shape memory alloy oscillator with coupled thermomechanical behaviour depends on the cooling rate near resonant frequencies. Increased cooling rate reduces both peak amplitude and the resonant frequency of the transmissibility curve. The force isolation provided by shape memory alloy oscillator is independent of the operating conditions.

Experimental study on dynamic characteristics of wire-cable vibration isolator

This study considers the dynamic experimental characteristics of the wire-cable vibration isolator. Orthogonal design scheme is adopted to reduce the test times. A wire-cable vibration isolator will be experimentally tested in the tension-compression mode to analyze its hysteretic behavior in more detail. Experimental data of restoring force and displacement are obtained through periodic test loading. The shape of hysteresis loops of vibration isolator under different excitation amplitudes, excitation frequencies and number of wire-cable loops have been obtained; the area of each hysteresis loop will be calculated by definite integral. The hysteresis loops under different conditions are studied, the results show that the wire-cable vibration isolator has excellent shock isolation characteristics; the isolator exhibits asymmetric hysteresis loops, which possess a hardening loading overlap in the loading curves. Finally, the key influence parameters of the dynamic characteristics are obtained, which establishes the foundation for designing the high performance wire-cable vibration isolator.

Analysis and Design of Magnetic Levitation and Mechanical Spring Compound Vibration Isolation Control System

In this paper, the magnetic levitation and mechanical spring compound vibration isolation control system is designed by applying maglev active control on the basis of mechanical vibration isolator. The system can effectively solve the problems of fixed structure parameters and poor environmental adaptability of passive vibration isolators, and can be applied to the anti-vibration protection of precision instruments in complex environments. This paper analyses the mechanism and characteristics of maglev vibration isolation, deduces the dynamic model of the system, discusses the design of the active vibration isolation control strategies, and carries out several simulation experiments of vibration isolation in different environments. The results show that the design scheme of the system is reasonable and feasible.

Study on dynamic characteristics of horizontal suspension in engineering vehicle seat based on rolling vibration isolation principle

The low frequency horizontal vibration of engineering vehicles is a part of multidimensional vibration, which causes driver's occupational disease. Therefore, the design of low frequency horizontal vibration isolation is of great significance. The principle of rolling vibration isolation is applied to seat suspension for low frequency horizontal vibration isolation in this paper. The natural frequency characteristic model of horizontal suspension and the seat-human system dynamics model with horizontal suspension based on the Lagrangian equation are established. The dynamic characteristics of rolling horizontal suspension are studied on account of the established models. Results show that this horizontal suspension can achieve very low natural frequency so as to isolate the low frequency vibration in horizontal direction by the matching design of the rollers and concave dimensions. The vibration isolation characteristics of the front and back seat–human system are improved with the reduction of the rollers’ radius. The vibration isolation characteristic of the front and back seat - human system increases with the increase of the concave surfaces’ radius.

Analysis and optimal design of a vibration isolation system combined with electromagnetic energy harvester

This work investigates a vibration isolation energy harvesting system and studies its design to achieve an optimal performance. The system uses a combination of elastic and magnetic components to facilitate its dual functionality. A prototype of the vibration isolation energy harvesting device is fabricated and examined experimentally. A mathematical model is developed using first principle and analyzed using the output frequency response function method. Results from model analysis show an excellent agreement with experiment. Since any vibration isolation energy harvesting system is required to perform two functions simultaneously, optimization of the system is carried out to maximize energy conversion efficiency without jeopardizing the system’s vibration isolation performance. To the knowledge of the authors, this work is the first effort to tackle the issue of simultaneous vibration isolation energy harvesting using an analytical approach. Explicit analytical relationships describing the vibration isolation energy harvesting system transmissibility and energy conversion efficiency are developed. Results exhibit a maximum attainable energy conversion efficiency in the order of 1%. Results suggest that for low acceleration levels, lower damping values are favorable and yield higher conversion efficiencies and improved vibration isolation characteristics. At higher acceleration, there is a trade-off where lower damping values worsen vibration isolation but yield higher conversion efficiencies.

Dynamic characteristics of a quasi-zero stiffness vibration isolator with nonlinear stiffness and damping

A quasi-zero stiffness (QZS) isolator is devised to acquire the feature of high-static-low-dynamic stiffness. Cam–roller–nonlinear spring mechanisms, where two horizontal dampers are installed symmetrically, are employed as a negative stiffness provider to connect in parallel with a vertical spring. From the static analysis, the piecewise restoring force in the vertical direction of the system is inferred considering possible separation between the cam and roller. The stiffness characteristics and parameters for offering zero stiffness at the equilibrium position are then determined. The dynamic equation is established and used for the deduction of the amplitude–frequency equation by means of the Harmonic Balance Method. The definitions of force and displacement transmissibility are introduced, and their expressions are derived for subsequent investigations of the effects of horizontal spring’s nonlinearity, excitation amplitude, horizontal damping, and vertical damping on the transmissibility performance. The comparative study is implemented on the isolation performance afforded by the QZS isolator and an equivalent linear counterpart, whose static bearing stiffness is same as the QZS isolator. Results indicate that the system with softening nonlinear horizontal spring can exhibit better performance than that with opposite stiffness spring. With the increase in horizontal damping ratio, the force transmissibility is further suppressed in resonance frequency range but increased in a small segment of higher frequencies and tends to unite in high frequency range. However, the horizontal damper deteriorates the ability to isolate the displacement excitation to a certain extent. Besides, the isolation capability of the QZS system depends on the magnitude of excitation amplitude. The quasi-zero stiffness system possesses lower initial isolation frequency and better isolation ability around resonance frequency compared with the linear system. Therefore, the quasi-zero stiffness isolator has superior low-frequency ability in isolating vibration over its linear counterpart.

Matching, Stability, and Vibration Analysis of Nonlinear Suspension System for Truck Cabs

To improve comfort, a nonlinear suspension system is proposed on the basis of the nonlinear vibration isolation theory and the installation space of the cab suspension system for trucks. This system is suitable for all‐floating cabs. For easy matching and design, the static and stability characteristics of the suspension system were analyzed, respectively, and the boundary condition for the stability of the system was given. Moreover, the cab simulation model was established, and the dynamic simulation was conducted. The stability analysis shows that the smaller the vibration excitation of the cab system, the higher its stability is. The dynamic simulation results show that the acceleration of the cab with the nonlinear suspension system is effectively suppressed; the dynamic deflection of the suspension is kept within a certain range, and the design space of the suspension stroke can be effectively utilized. Compared with the traditional linear suspension system, the nonlinear suspension system has better vibration isolation characteristics and can effectively improve ride comfort.

Self-sensing characteristics of vibration isolation bearing based on modified magneto-rheological elastomer

A new self-sensing bearing based on magneto-rheological elastomers (MREs) was proposed in this paper. For the application in vibration isolation system, the effects of force input and semi-active controlled electric current (force and magnetic fields) on the self-sensing characteristics of bearing were simultaneously investigated. The modified anisotropic MRE with multi-walled carbon nanotubes (MWNTs) was studied to improve its electrical properties, and the MWNTs can reduce the initial resistivity from 325.06 to [Formula: see text]. To understand the sensing behaviors of bearing, the experimental system was built. The results confirmed that the self-sensing characteristic presents an obvious monotonous declining trend with the vibration force increases, and the mechanical properties of MRB can be regulated in real-time when they are subjected to varying currents (0–1 A). This finding is significant because it suggests that the bearings based on the modified MREs are potentially capable of being used for vibration absorbers and sensors simultaneously. Based on these results, it is expected to simplify the system structure and improve the response performance of vibration isolation.

Study on the vibration isolation characteristics of an anti‐resonant hydropneumatic suspension

A novel anti-resonant hydropneumatic suspension system was presented in this study. The mathematical model of the presented suspension system was derived and the theoretical analysis was carried out. For lower frequency vibrations, the presented suspension system can achieve better vibration isolation performance comparing with the traditional hydropneumatic suspension system. The frequency spectrum on which the presented suspension achieves better vibration isolation performances can be widened by adjusting the length of the oil tube. Therefore, it is possible for the presented suspension system to achieve better vibration isolation performance on different road conditions.

Response of rubber based engine mounts with SBR as the core rubber.

Nowadays the most important and basic requirements of automotive industry are vehicle stability, driving ability, and passenger comfort; and all of these need the control of vibrations to some extent. Engine is main source of power to a vehicle but it produces vibrations, thereby reducing the performance of a vehicle. These vibrations can be eliminated by the use of engine mounts, using which an engine is mounted on the chassis of the vehicle. Its basic function is to rightly hold the engine and transmission system on chassis of the vehicle. A good engine mount should firstly isolate the engine vibrations caused by engine disturbances and next they should isolate the transfer of vibrations from engine to chassis and reversely. In view of this an attempt is made to study the performance of two elastomeric engine mounts of two separate origin with SBR (Styrene Butadiene Rubber) as their core rubber, laying main focus on their vibration isolation characteristics. The selected engine mounts are elastomeric mounts for a heavy commercial vehicle with rubber as core to resemble a sandwiched structure. In the present work firstly the damping properties and vibration isolation characteristics of SBR are identified by using a sandwiched structure. Then the engine mount are modelled using this SBR as a Hyper-elastic rubber using the best fit Hyper-elastic material model. SBR is selected due to its wide range of applications in automobile industry. The performance of two engine mounts is studied for static, harmonic and time varying loads.

Structural Design and Isolation Characteristic Analysis of New Quasi-Zero-Stiffness

This project aimed to design a new type of vibration isolation mechanism with quasi-zero-stiffness (QZS) and analyze the QZS systems’ characteristics by computation and numerical simulation. First, the force–displacement and stiffness–displacement relational expressions of the QZS systems were established based on the study of system force and stiffness characteristics. Second, the nonlinear dynamic equations of the system under the excitation of harmonic force and harmonic displacement were established, and the effect of damping ratio, excitation amplitude, and nonlinear term under the transmissibility mechanism system was analyzed by the average method. Finally, the response time and stability of the QZS vibration isolator were analyzed under different circumstances through numerical simulation. The excitation amplitude, damping ratio, and nonlinear term have a great influence on the transmissibility of the system. In addition, under three different working conditions, the mechanism can have good vibration isolation characteristics and can meet the requirement of low-frequency vibration isolation. A novel type of the QZS systems has been investigated, and it is found that the influence of the excitation amplitude and the nonlinear term are just the same on the system transmissibility through the statics and dynamics calculations. Meanwhile, when damping ratio was increased, the transmissibility of the QZS systems could be reduced. The numerical simulations show that the system has faster response and smaller amplitude for sine wave, single shock, and multi-frequency excitations, which is more suitable for low-frequency vibration isolation.

위치 결정 시스템의 안정성 개선을 위한 와전류 감쇠기(Eddy Current Damper) 설계와 응용

Air bearing-guided linear motion modules have so little friction that they are widely used for precision positioning systems. The module exhibits disturbance vibration that is difficult to control because the air bearings have too small a damping coefficient. In this paper, an eddy-current damper (ECD) is proposed for an air bearing-guided linear motion module to improve the vibration isolation characteristics. A Halbach magnet array is devised to increase the density of the magnetic flux of the ECD because a stronger magnetic field generates a greater damping force. A theoretical magnetic model of a Halbach magnet array is presented, and its working principle is investigated. In order to investigate the performance of the module, an experimental instrument with the module, ECD, and control devices was constructed. The authors compared the experimental data of the module’s positioning performance for the cases with and without the ECD.

Stiffness and vibration isolation characteristics of a torsional isolator with negative stiffness structure

This paper proposes a novel design torsional vibration isolator with negative stiffness structures. It consists of two shafts that are linked by positive springs and negative stiffness structures. The connection position of the two shafts has been designed into disc structure, which is the installation position of the positive springs and negative stiffness structures. The task of positive springs is to transmit the designed torque. In this paper, the nonlinear stiffness characteristics of the isolator are presented. The nonlinear mathematical model is presented, and its dynamic behaviors are investigated using the averaging method, and compared with that of the corresponding linear torsion isolator without negative stiffness structures. The study shows that the torsion isolator has a wider isolation region than that of the linear isolator. Furthermore, the performance of the isolator is sensitive to the damping of the system and the amplitude of vibration excitation. Choosing a suitable damping and vibration environment will be important for the stable application of this isolator.

Simultaneous topology optimization of supporting structure and loci of isolators in an active vibration isolation system

We developed a new multi-objective and multi-level optimization method to design an active vibration isolation system. Both the layout of the continuum (i.e. the supporting structure) and the loci of the isolators are designed using topology optimization technique in a unified formulation for the first time. The static, dynamic and vibration-isolation characteristics are taken into account simultaneously in the present model. Due to their different roles in the system it may be appropriate and advantageous to treat the design of the continuum layout and isolator loci as different sub-problems with different objectives in separate stages. The multi-level optimization technique, where the optimization of the supporting structure and the isolator loci are incorporated into a closed-loop, is proposed and implemented so that the interactions between these two sub-problems can be fully taken into account. Numerical results demonstrate the validity of the proposed design cycle. Comparisons show that the overall static, dynamic and vibration-isolation performance of the optimized system outperforms the ones designed by traditional methods.

Experimental Study of Vibration Isolation Characteristics of a Geometric Anti-Spring Isolator

In order to realize low-frequency vibration isolation, a novel geometric anti-spring isolator consisting of several cantilever blade springs are developed in this paper. The optimal design parameters of the geometric anti-spring isolator for different nonlinear geometric parameters are theoretically obtained. The transmissibility characteristic of the geometric anti-spring isolator is investigated through mathematical simulation. A geometric anti-spring isolator with a nonlinear geometric parameter of 0.92 is designed and its vibration isolation performance and nonlinearity characteristic is experimentally studied. The experiment results show that the designed isolator has good low-frequency vibration isolation performance, of which the initial isolation frequency is less than 3.6 Hz when the load weight is 21 kg. The jump phenomena of the response of the isolator under linear frequency sweep excitation are observed, and this result demonstrates that the geometric anti-spring isolator has a complex nonlinearity characteristics with the increment of excitation amplitude. This research work provides a theoretical and experimental basis for the application of the nonlinear geometric anti-spring low-frequency passive vibration isolation technology in engineering practice.