Abstract:

ESDU 93016 introduces a computer program that implements the method of ESDU 90006 but modified to take into account the residual gain and phase variation effects of modes whose resonant frequencies lie outside the range of analysis. The system is modelled as a set of lightly-damped coupled second-order differential equations with constant coefficients; the response determined from those equations is equivalent to the sum of the responses of a related set of single degree-of-freedom systems. The program requires initial estimates of the resonant frequency of each response mode together with an associated frequency range and they are obtained from a visual inspection of the Nyquist or Bode diagram of the measurement data. From those initial values the program determines the damping ratio of the modes. These values provide a starting point for a non-linear parameter estimation procedure using a Newton-Gauss algorithm from which the mode characteristics that satisfy the complete measurement data are found. The program will handle up to 3000 measurement points and nine separate response modes. Examples illustrate the use of the program for systems with two and four degrees-of-freedom, and show clearly the input format required and the output provided. The program is available as ESDUpac A9316.