Roger Stanway

Identification of structural vibration parameters by using a frequency domain filter

In this paper a sequential, least squares, frequency domain filter is presented for the identification of structural vibration parameters from measured responses and known excitations. The validity of the approach is demonstrated by using simulated data for two multi-degree of freedom systems. Parameter estimates are given as they converge, together with computation times measured in CPU seconds on an IBM 3083 computer.

Identification of the Damping Law of an Electro-Rheological Fluid: A Sequential Filtering Approach

In this paper an approach is described to identifying the damping law of an electro-rheological (ER) fluid in vibration. The damping law is obtained by employing a nonlinear, sequential filter to estimate the parameters associated with an nth-power velocity model of the damping mechanism. To establish experimental requirements the application of the technique is first examined under controlled conditions in a numerical study. The feasibility of the approach is then demonstrated in an experimental study to identify the damping law of a prototype ER damper.

Identification of nth-power velocity damping

This paper demonstrates how the two damping parameters associated with the non-linear nth-power velocity model can be identified from the time series records of the displacement and velocity responses to sinusoidal excitation. No restriction is imposed on the level of damping present and estimates are acquired by minimizing the square of the error between observed responses and those predicted by a linearized model. The problems of noise contamination and uncertain initial conditions are treated by using simulated data and converged estimates are presented with computation times measured in CPU seconds on a VAX 11780 computer.

Design and application of a finite element package for modelling turbomachinery vibrations

Abstract The purpose of this paper is to review the modelling of lateral vibrations in turbomachinery and to justify and describe the systematic development of a software package based upon finite element techniques. The package is capable of providing stability analysis, steady state and transient responses which were required in connection with a study to compare vibration control techniques. Emphasis is placed on user-friendliness and careful validation by comparison with available results from rotor-bearing systems of gradually increasing complexity. A series of examples is included to illustrate the application of the package and compare its performance with other well known methods. Computational requirements (for an IBM 3083 machine) are discussed in some detail.

Active vibration control of turbomachinery: A numerical investigation of modal controllers

Abstract In this paper the authors report on the results of a numerical study which examines the application of modal techniques for controlling lateral vibrations in rotating machinery. The basis of the investigation is a finite-element model of a multiple-disc rotor running in flexibly-supported fluid-film bearings. The influence of modal control using full state-variable feedback is first demonstrated. It is then shown how an estimation algorithm is applied to reconstruct the state vector from the minimum number of measurements. Finally the implications of deliberately reducing the order the modal controller/estimator on the stability of the closed-loop system are examined and the effect of measurement noise is considered. It is emphasised that the eventual implementation of the proposed approach to controlling multiple modes of vibration depends upon the availability of accurate mathematical models of the dynamics of the physical system.

An Experiment to Identify the Structural Dynamics of a Portal Frame

This paper describes the application of sequential frequency domain techniques to the estimation of mass, stiffness, and damping parameters using measured frequency response functions from a portal frame rig. The theory of the method has been described in the authors’ previous publications. A portal frame is representative of many engineering structures. It is lightly damped and may be thought of as an element of several larger structures such as bridges, transmission towers, and the steel foundations of modern power generating plant. The results offered in this paper are thus of interest to a broad range of engineering problems where it is required to obtain mathematical models in terms of physical parameters.

Identification of combined viscous and Coulomb friction - a numerical comparison of least-squares algorithms

In this paper the authors present a numerical comparison of three least-squares techniques - Gauss-Newton, quasi-linearisation and non-linear filtering - for identifying viscous and Coulomb friction parameters in a single-degree-of-freedom vibrating system.

Nonlinear Identification of a Squeeze-Film Damper

Described is an experimental study to identify the damping laws associated with a squeeze-film vibration damper. This is achieved by using a non-linear filtering algorithm to process displacement responses of the damper ring to synchronous excitation and thus to estimate the parameters in an nth-power velocity model. The experimental facility is described in detail and a representative selection of results is included. The identified models are validated through the prediction of damper-ring orbits and comparison with observed responses.

Estimation of the Linearized Damping Coefficients of a Squeeze-Film Vibration Isolator

In this paper the authors present experimental confirmation of the feasibility of a new approach to the estimation of the four damping coefficients associated with a squeeze-film vibration isolator. The design and construction of the experimental facility is described in detail. A time-domain filtering algorithm is applied to process the displacement responses to single-frequency excitation and thus extract information on the linearized dynamics of the squeeze-film. The estimated coefficients are validated by comparing performance predictions with those obtained from spectrum analysis and from short-bearing theory. The significance of the results is discussed and suggestions are made for further work in this area.

Estimation of mass, damping and stiffness parameters in mechanical vibrating structures

In this paper, the authors describe the development of a technique for estimating numerical values for the mass, damping and stiffness parameters in linearised models of mechanical vibrating structures. It is shown how an existing non-linear filtering algorithm has been transformed to the frequency domain and subsequently reformulated as a linear filter. Experimental case studies involving a portal-frame rig and a squeeze-film damper illustrate the application of the technique.