Optimisation of pneumatic circuit aimed at improving the vibro-isolation properties of seat suspension

The object of a numerical simulation and optimisation is the seat with a visco-elastic passive suspension, with improved vibro-isolation properties by means the multi-criteria optimisation. Basing on the verified passive seat suspension model, a modification of the pneumatic circuit in order to help the working machines operators against vibration is considered. The root mean square (RMS) acceleration measured at the seat and the maximum relative displacement of the seat suspension are minimised as the chosen vibro-isolation criteria. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The application of robust control for vibration damping of working machines seat suspensions

The object of simulation is the seat with a visco–elastic active suspension, with improved vibro–isolation properties using the robust control. Based on the verified passive seat suspension model, the robust control possibilities in order to help the working machines operators against vibration is considered. As the viobro–isolation criteria, the seat effective amplitude transmissibility factor (SEAT) and maximum relative displacement between the working machine's cabin floor and the seat is chosen and evaluated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vibration reduction of a three DOF non-linear spring pendulum

The dynamic response of mechanical and civil structures subject to high-amplitude vibration is often dangerous and undesirable. Vibrations and dynamic chaos should be controlled or eliminated in both structures and machines. This can be employed via passive and active control methods. In this paper, a tuned absorber, in the transversally direction, is connected to an externally excited spring–pendulum system (three degree of freedom), subjected to harmonic excitation. The tuned absorber is usually designed to control one frequency at primary resonance where system damage is probable. Active control is also applied to the considered system via negative displacement feedback to change the linear frequency of the system and to shift it away from the resonating one. Also active control is applied to improve the behavior of the spring–pendulum at the primary resonance via negative velocity feedback or its square or cubic value. The multiple time scale perturbation technique is applied throughout. The stability of the system is investigated applying both frequency response function and phase-plane method. The effects of the absorber and different parameters on system behavior are studied numerically. Optimum working conditions of the system are extracted applying both passive and active control methods, to be used in the design of such systems.     

Modeling of a vehicle seat suspension system with pneumatic spring and viscous dampers

The paper contains physical and mathematical model of the passive system of seat suspension, used in trucks and buses. Spring force in this system is performed by air spring, whereas damping force is generated by two viscous dampers. Based on the experimental research of characteristic parts of the suspension system, the parameters of mathematical model are determined. Both results of computer simulations and experiments are presented as power spectral density of acceleration courses, measured on seat, in comparison with courses measured on excitation platform in laboratory. Transmissibility of real system and its model are also presented in the paper. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Parametric study of nonlinear adaptive control algorithm with magneto-rheological suspension systems

This paper describes the details of the simulation analysis of a nonlinear model-based adaptive suspension control system [Song X, Ahmadian M, Southward SC, Miller LR. An adaptive semiactive control algorithm for magneto-rheological suspension systems. ASME J Vibr Acoust, in press; Song X. Design of adaptive vibration control systems with application of magneto-rheological dampers. Dissertation, Virginia Tech, December, 1999]. The numerical aspect of the simulation study of a seat suspension with application of magneto-rheological dampers will be presented. Magneto-rheological (MR) dampers have strong nonlinearities such as bi-linearity, hysteresis, and saturation related to magnetism, which can be represented by appropriate mathematic functions, respectively. Thus the model-based adaptive algorithm becomes complicated because of involvement of MR damper models. One objective of this study is to investigate the effect of MR damper model simplifications on the adaptive suspension performance. Furthermore, simulation is also applied to do parametric study of adaptive algorithm parameters such as filtering and step size. The numerical results compare the proposed adaptive controller with passive dampers to validate not only its effectiveness but also obtain some guidance information for its experimental implementation.     

Vibration reduction in ultrasonic machine to external and tuned excitation forces

The dynamic response of mechanical and civil structures subject to high-amplitude vibration is often dangerous and undesirable. Sometimes controlled vibration is desirable as in ultrasonic machining (USM). Ultrasonic machining (USM) is the removal of material by the abrading action of grit-loaded liquid slurry circulating between the workpiece and a tool vibrating perpendicular to the workface at a frequency above the audible range. A high-frequency power source activates a stack of magnetostrictive material, which produces a low-amplitude vibration of the toolholder. This motion is transmitted under light pressure to the slurry, which abrades the workpiece into a conjugate image of the tool form. This can be achieved via passive and active control methods. In this paper, multi-tool techniques are used in the ultrasonic machining via reducing the vibration in the tool holder and providing reasonable amplitudes for the tools represented by the absorbers. The coupling of the tool holder and absorbers simulating ultrasonic cutting process are investigated. This leads to a multi-degree-of-freedom system subject to external and tuned excitation forces. Multiple scale perturbation method is applied to obtain the solution up to the second order approximation. Different resonance cases are reported and studied numerically. The stability of the system is investigated applying both phase-plane and frequency response techniques. The effects of the different parameters of the absorbers on the system behavior are studied numerically. Comparison with the available published work is reported.     

Modelling of working machines seat suspension with an air-spring and hydraulic shock-absorber

For the purpose of this paper, an exemplary seat suspension system is modelled and simulated numerically. The system consists of a shear guidance mechanism of a suspended seat, an air-spring, a hydraulic shock-absorber and end-stop buffers. As results of computer simulations, the power spectral densities of acceleration and the transmissibility functions of seat suspension are evaluated with respect to results measured experimentally. The verification of simulation model is performed in the basis of Seat Effective Amplitude Transmissibility factor (SEAT) and the maximum relative displacement of suspension system. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bi-harmonically excited pendulum: shifted resonances and quenching the low frequency excitation

The effect of the harmonic high-frequency vibration of the suspension point on a mathematical pendulum is well known [1]. It can be described as stiffening/softening or stabilization/destabilization of the up-pointing and down-pointing equilibriums for pure vertical or pure horizontal excitation. If the excitation is tilted the effect of biasing appears in addition [2]. The effects of bi-harmonic excitation are more complex. Two of them are discussed in the recent paper. The first one occurs if one of the excitation frequencies is high and another one is low. Then the so called shifted or conjugated resonances can be observed [3]. The second one takes place if the two excitation frequencies are high but their difference is small (slowly modulated high-frequency excitation according to [4]). It is shown that in that case it is possible to choose the bi-harmonic excitation in order to quench the resonance of the pendulum without changing its basic frequency. The analysis is fulfilled both for the external and parametric excitations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ultra-low frequency passive vertical vibration isolation system

An ultra-low frequency passive vertical vibration isolator is constructed by mounting a couple of additional masses on the crank-arms of the torsion spring. The theoretical analysis and experimental results show that the system with additional masses can achieve better vertical vibration isolation and longer resonant period. Measured displacement response of the test mass under seismic excitation reaches 3 x 10^{-12 m/√ Hz} around 10 Hz, and the isolation ratio comes to about 60 dB attenuation at 6 Hz, which is about 30 dB lower than that of the system without additional masses.     

Ultra-low frequency passive vertical vibration isolation system

An ultra-low frequency passive vertical vibration isolator is constructed by mounting a couple of additional masses on the crank-arms of the torsion spring. The theoretical analysis and experimental results show that the system with additional masses can achieve better vertical vibration isolation and longer resonant period. Measured displacement response of the test mass under seismic excitation reaches 3 x 10^{-12 m/√ Hz} around 10 Hz, and the isolation ratio comes to about 60 dB attenuation at 6 Hz, which is about 30 dB lower than that of the system without additional masses. Project supported by the National Natural Science Foundation of China (Grant Nos. 19425008, 49674246 and 59678032).     

Stability study of the human body-seat system into an autovehicle

The paper presents the study of the human body, as a mechanical system, seated inside an autovehicle and exposed under the vertical harmonic vibration action during the auto vehicle motion time. The human body may be roughly approximated by a linear lumped parameter at low frequencies and low vibration levels. Therefore, the model has 5 DOFs in translation, where 4 DOFs represents the human body and 1 DOF is for the seat cushion The mechanical model of the human body, in sitting position on the seat cushion of a vehicle seat, consists of four parts: pelvis, upper torso, viscera and head.. The eigenvalues for the human body – seat system and the damping ratio for the system was been calculate. The system stability analysis is given by the existence of a Lyapunov function for the system. The stability of a system can also be characterized by the eigenvalues of the system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elimination of tall building vibration resulting from ground motions

In this paper, the vibration problems of tall buildings are considered. The focus is on vibration caused by earthquakes, semi–seismic phenomena and ground vibrations of other origins. The construction consists of the main system and a vibration eliminator (passive tuned mass damper – pendulum type) which is attuned to the first eigenfrequency of the main structure. The analysis focuses on elimination of structure vibration caused by horizontal components of ground motions, while the functioning of the eliminator is simultaneously influenced by the vertical component (parametric effect – the possibility of improper functioning of the device). The vertical periodic movement of the support point can cause changes of the vibration eliminator's stiffness. In such a case parametric excitation occurs in the system, which signifies that parametric resonance may appear. The numerical analysis of the problem was performed with the Newmark method in conjunction with FEM. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

势阱深度对双稳态电磁发电系统发电性能的影响研究

电磁式振动能量捕获技术从单稳态系统发展到多稳态系统,拓宽了响应频带,增大了输出电压,能够获得较好的发电性能.以附加线性振子的双稳态电磁式振动能量捕获器为研究对象,主要研究了势阱深度对双稳态系统发电性能的影响,并基于最优发电性能下的势阱深度,研究了双稳态系统结构参数中质量比与调频比对系统发电性能的影响.通过数值仿真结果说明,在外部激励频率为低频时:势阱深度较大时,双稳态系统的振子只能在一个阱内发生小幅振动运动;当势阱深度小到一定程度时,双稳态系统的振子跨过势垒在两个阱间内发生大幅混沌运动或周期运动,其优于小幅振动运动时的平均输出功率.通过数值模拟,得到双稳态系统具有较高的发电性能下的最优质量比、调频比以及阻尼比参数.     

1:2 and 1:3 internal resonance active absorber for non-linear vibrating system

Vibration and dynamic chaos should be controlled in either structures or machines. An active vibration absorber for suppressing the vibration of the non-linear plant when subjected to external and parametric excitations is studied in the presence of one-to-two and one-to-three internal resonance. The main attention is focused on the study of the active control and stability of two systems, which can be used to reduce vibrations due to rotor blade flapping motion. The method of multiple scale perturbation technique is applied to determine four first-order non-linear ordinary differential equations that govern the modulation of the amplitudes and phases in the presence of internal resonance of the two systems with quadratic and cubic order of control. These equations are used to determine the steady state solutions and their stability. The stability study of non-linear periodic solution for two cases (1:2 and 1:3 internal resonance) and the stability of the obtained numerical solution are investigated using frequency, force-response curves and phase-plane method. Also, effects of some parameters on the steady state solution of the vibrating system are investigated and reported in this paper. Variation of some parameters leads to the bending of the frequency, force-response curves and hence to the jump phenomenon occurrence. The reported results are compared to the available published work.     

Analysis of vibration effects on the comfort of intercity bus users by oscillatory model with ten degrees of freedom

The paper analyzes the effects of vibrations on the comfort of intercity bus IK-301 users. Evaluation of vibration effects was carried out according to the criteria set out in the 1997 ISO 2631-1 standard for comfort in public means of transport. Comfort is determined for the space of a driver, passenger in the middle part of the bus and passenger in the rear overhang. Also, the allowable exposure time to vibrations in drivers for the reduced comfort criterion was determined according to the 1978 ISO 2631-1 standard. The bus spatial oscillatory model with ten degrees of freedom was developed for the needs of the analysis. Bus excitation was generated applying the Power Spectral Density of the asphalt-concrete road roughness, as described by the H. Braun model. The allowable vibration exposure time for the driver’s body decreases as the spring stiffness of the driver’s seat suspension system increases. Simulation was performed using the MATLAB software.     

Nonlinear dynamic analysis of 2-DOF nonlinear vibration isolation floating raft systems with feedback control

In this paper, the average method is adopted to analysis dynamic characteristics of nonlinear vibration isolation floating raft system with feedback control. The analytic results show that the purposes of reducing amplitude of oscillation and complicating the motion can be achieved by adjusting properly the system parameters, exciting frequency and control gain. The conclusions can provide some available evidences for the design and improvement of both the passive and active control of the vibration isolation systems. By altering the exciting frequency and control gain, complex motion of the system can be obtained. Numerical simulations show the system exhibits period vibration, double period vibration and quasi-period motion.     

基于非线性能量阱的双频激励非线性系统减振

针对某型民用航空发动机双频带激励特点,建立了单自由度线性振子耦合非线性能量阱（nonlinear energy sink,NES）的动力学模型.根据典型双转子发动机在巡航状态下低、高特征频率比（1∶4.74）,为系统设定双频带简谐外激励.利用四阶Runge-Kutta算法,研究了耦合NES振子时系统的振动抑制特征,并从外激励频率对系统主振子动能、系统总体能量的影响等方面,与未耦合NES系统、耦合线性动力吸振器两种情况下的数值计算结果进行对比分析.研究结果表明NES对双频带外激励具有更好的振动抑制效果,用NES降低航空发动机振动有可行性.     

Preloading effects on clearance problem in rotor-coupling vibration system: experimentation and simulation

Preloading effects on the bilinear system with clearance have been demonstrated in this literature for the harmonically excited vibration. Different preloading forces can cause the different equilibrium positions of the system from where the vibration starts. This paper deals with the nonlinear responses by the changing of the equilibrium positions for a wide range of the excitation frequency. Experimentation has been considered with extensive care to understand the practical feasibility of the simulation. The clearance problem of the rotary machinery has been investigated for a wide excitation frequency zone thoroughly in the experiment to understand its contribution for introducing the chaos and the multiple periods.     

Vibration control of active vehicle suspension system using fuzzy logic algorithm

Vehicle suspension along with tires and steering linkages is designed for safe vehicle control and to be free of irritating vibrations. Therefore the suspension system designs are a compromise between ride softness and handing ability. However, this work is concerned with a theoretical investigation into the ride behavior of actively suspended vehicles. It is based on using fuzzy logic control (FLC) to implement a new sort of active suspension system. Comparisons between the behavior of active suspension system with FLC with those obtained from active systems with linear-quadratic regulator (LQR), ideal skyhook system and the conventional passive suspension systems. Results are introduced in such a way to predict the benefits that could be achieved from a fuzzy logic system over other competing systems. Furthermore, a controller is designed and made by using results of FLC system, theoretical inputs are used to examine the validity of this controller. Moreover, comparison between actual outputs from this controller with those obtained theoretically is made to judge the validity of the controller. The results indicate that the controller has a good capability in simulation of the theoretical model.