Damping Analysis Research Articles

Development of a variable stiffness magnetorheological damper with self-powered generation capability

This article reports a compact stiffness controllable magnetorheological damper with a self-powered capacity. First, the structure, working mechanism, and analysis of the damper are presented. After the prototype of the magnetorheological damper, experimental tests were conducted to evaluate its variable stiffness feature and self-powered generation capability using a hydraulic Instron test system. The testing results demonstrate that its stiffness variation range can reach 70.4% when the applied current increases from 0 to 2 A. The energy generating capability of the magnetorheological damper was also evaluated using the Instron testing system under a harmonic excitation with 0.15 Hz frequency and 30 mm displacement. The testing results illustrate that the self-powered generation component can generate 2.595 W effective power, which is enough to control the magnetorheological component of the damper. The successful development, theoretical analysis, and experimental testing of this new variable stiffness self-powered magnetorheological damper make the concept of energy-free variable stiffness magnetorheological damper feasible.

Complete Squeeze-Film Damper Analysis Based on the “Bulk Flow” Equations

The article presents the numerical adaptation of the “bulk flow” model for the analysis of squeeze-film dampers of industrial design. These components are characterized by high squeeze Reynolds numbers and by complex feeding and sealing systems. The “bulk flow” system of the equation is an efficient model for dealing with high Reynolds number regimes but its numerical treatment needs to be adapted for taking into account the feeding orifices and the circumferential groove as well as the openings of the piston ring seals. These adaptations are performed in the frame of the SIMPLE numerical algorithm used for dealing with the pressure-velocity coupling. The conservative character of the finite volume discretization is preserved without any penalty for the overall efficiency of the numerical procedure. The results depict how film discontinuities and local sources or sinks are embedded into the pressure field. Finally the complete numerical algorithm is validated against experimental data and its advantages are underlined by comparisons with a Reynolds based approach of squeeze-film dampers.

Application of CFD Analysis for Rotating Machinery—Part I: Hydrodynamic, Hydrostatic Bearings and Squeeze Film Damper

The traditional method for bearing and damper analysis usually involves a development of rather complicated numerical calculation programs that may just focus on a simplified and specific physical model. The application of the general CFD codes may make this analysis available and effective where complex flow geometries are involved or when more detailed solutions are needed. In this study, CFX-TASCflow is employed to simulate various fixed geometry fluid-film bearing and damper designs. Some of the capabilities in CFX-TASCflow are applied to simulate the pressure field and calculate the static and dynamic characteristics of hydrodynamic, hydrostatic, and hybrid bearings as well as squeeze film dampers. The comparison between the CFD analysis and current computer programs used in industry has been made. The results show reasonable agreement in general. Some of the possible reasons for the differences are discussed. It leaves room for further investigation and improvement on the methods of computation.

A Finite Element Analysis of the Harmonic Response of Damped Five-Layer Plates

Solutions have been obtained for the harmonic vibrations of five-layer plates by means of a finite element method. This method is an extension of a previously developed analysis for three-layer plates. The five-layer plates contain two constrained viscoelastic layers which provide the damping. The degenerate case when the thickness of the middle elastic layer becomes zero and the plate is reduced to a four-layer one has also been included in the solution procedure. Moreover, the method allows for the study of both torsional and transverse vibrations of five (or four)-layer beams treated as vibrating plates with a large aspect ratio. As in the case of three-layer plates, triangular finite elements are used to allow for a greater variety of shapes. In the analysis damping is introduced by replacing the real moduli of the viscoelastic material by complex equivalent moduli which account for the phase difference between strain and stress. The present method allows for the non-linear stress-strain behaviour of the viscoelastic layers, the effects of the rotatory inertia and the extension within the viscoelastic layers. The finite element computations have been verified by comparison with experimental results for four-layer and five-layer beams in transverse and torsional vibrations and a five-layer square plate in transverse vibration.

Experimental investigation of energy absorption in vertical vibrations of foundations

1. The most accurate damping characteristic is the coefficient of relative damping in analyses using the first and second soil base models. 2. The damping coefficient for steady vibrations depends for all practical purposes on the soil base type and the backfill height, the actual energy absorption being smaller than the value recommended in SNiP II-19-79.

Frequency response analysis of the stabilizing effect of a synchronous machine damper

The paper describes the application of frequency-response concepts to the analysis of a synchronous machine damper in so far as it affects the stability of the machine. The analysis of damper effects is based on Park's equations. Small-displacement theory is introduced toorganize the equations into the correct form for frequency-response computation. Nyquist diagrams are used to show the stabilizing effect of a damper and to illustrate the method of optimizing damper parameters.