In this work, a new active mount featuring piezostack actuators and a rubber element is proposed and applied to a vibration control system. After describing the configuration and operating principle of the proposed mount, an appropriate rubber element and appropriate piezostacks are designed and manufactured. Subsequently, the dynamic characteristics of the piezostacks and the rubber element are experimentally identified. A vibration control system with a supported mass of 50 kg is then constructed, and its governing equations of motion are derived. In order to actively attenuate the vibration transmitted from the base excitation, a robust sliding mode controller is formulated with consideration of parameter uncertainties. The controller is then experimentally realized and vibration control performances (acceleration and transmitted force) of the proposed mount are evaluated in both time and frequency domains.

The issue which is always debated in the magnetorheological (MR) fluid is the dynamic and static yield stress values obtained from a flow curve. To evaluate these, a suitable constitutive equations are required. The aim of this article is to provide suitable rheological models for the prediction of static and dynamic yield stress from a single flow curve under wide shear rate and magnetic field ranges. The proposed model is well suited for isotropic and anisotropic particle-based MR fluids. The parameters, like yield stress, critical shear rate and viscosity at high shear rate obtained from the fit show systematic variation with applied magnetic field strength. These variations in the parameters can be related to the mesostructure formation and its influence on the MR suspension rheological properties. To further confirm the value of the static yield stress derived from the proposed model, the small-strain oscillatory shear flow experiment is carried out and the static yield stress values are obtained. These values agree well with that obtained from the proposed model. Similarly, to evaluate the dynamic yield stress from the flow curve, modified three parameter model applied to soft glassy materials is used. Here, the critical shear rate parameter obtained from the proposed model is used to deduce dynamic yield stress. It is identified that the values obtained are lower than the static yield stress. Furthermore, at low magnetic field, the static and dynamic yield stress follows the relationship defined by the square dependence of the magnetic field strength. The difference between the static and dynamic yield stress values at high field is greater for anisotropic particle based MR fluid than isotropic particle based MR fluid. This reflects the contribution of particle-particle and particle-carrier interaction in the value of the yield stress in anisotropic particle based MR fluid. Thus, the present model provides a clear idea of the dissipation process that occurs in a shear MR fluid.

A hybrid mount for shipboard machinery installed on naval ships was developed. The mount is combined with a rubber mount and a piezostack actuator. The rubber mount is one of the most popular and effective passive mounts to have been applied to various vibration systems to date. The piezostack actuator is featured by a fast response time, small displacement and low power consumption. Through a series of experimental tests conducted in accordance with MIL-M- 17185A(SHIPS), MIL-M-17508F(SH), and MIL-S-901D which are US military specifications relatedto the performance requirements of the mount, it has been confirmed that the hybrid mount shows more effective performance for use in naval ships.

Abstract:In this study, a semi-active magneto-rheological (MR) mount is designed and manufactured to minimize unwanted vibrations for the cabin of heavy vehicles. Normally, working conditions in heavy vehicles are extremely rugged. Usually, the heavy vehicles use passive rubber mounts for the reduction of vibrations from road. However, the passive mount has definite performance limitations because the passive mount has a fixed resonance frequency when the design is finished. An MR application is one of the solutions because the viscosity of MR fluid can be controlled. As a first step, an experimental apparatus was established for performance evaluation of the mounts. The apparatus has hydraulic excitatory, force, and displacement sensors. Performance of two different passive mounts used in industrial fields were evaluated. The passive mount data of force-displacement, force-velocity, and displacement transmissibility were collected and tested. After that, an MR mount was designed and manufactured that provides better performance using the passive mount data. The MR mount uses two different flow paths, annular duct and radial channels, for generating the required damping force. The field-dependent damping forces were then evaluated with respect to the moving stroke and input current. In this work, in order to control the damping force, an on-off controller associated with the fast Fourier transform (FFT) was used. The control results of the MR mount were compared with the results of passive rubber mounts. It was shown that the semi-active MR mount can attenuate vibrations more effectively at all frequency ranges compared with the passive rubber mount.

Passive-type control devices such as resilient mounts and wire rope isolators are generally used for protecting the shipboard equipment from shock loading and for suppressing the mechanical vibration of the equipment in naval ships. To improve the performance of the control device, a new hybrid mount is under development in this study.This mount consists of a passive-type rubber element and an active-type piezo-stack element. It can be expected that the mount has enhanced performance of about 20 dB or more with respect to transmissibility through a series of performance tests of prototype mount.