Measurement of Structure-Borne Sound Energy Flow Along Pipes. Part 3: Analysis of Systematic and Random Errors

摘要

Errors in methods based on finite difference approximations and using cross spectral densities of accelerations at closely spaced pipe cross sections for measuring structure-borne energy flow in thin walled circular cylindrical pipes (by separating the contributions of longitudinal torsional and bending waves) are analyzed. A quantity called direct field ratio, that defines the ratio between the measured energy flow and the energy flow that would be measured in a free propagating wave under noise-free conditions is introduced. It indicates conditions where the estimates of the cross spectral density are sensitive to several error sources.