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Physical phenomena governed by diffusion (for example, mass or heat transfer) are often better described by rational transfer function models G(√s) in √s than by rational forms G(s) in the Laplace variable s. A striking difference between both models is that the impulse response of G(s) decreases exponentially to zero, while that of G(√s) decreases algebraically to zero. Hence, transient effects in diffusion phenomena may last long before they can be neglected in, for example, frequency response function measurements. This paper presents an extended transfer function model and an identification algorithm that can handle the slowly decaying transients and, as a consequence, (significantly) reduce the experiment time. [ABSTRACT FROM AUTHOR]

The influence of disturbing noise and nonlinear distortions on frequency response function measurements using periodic excitations has been studied in detail in the literature. A variance analysis method has been developed that allows one to detect and quantify the nonlinear distortions and the disturbing noise. In this paper, the variance analysis is generalized to detect and quantify the following nonstationary disturbances: 1) nonsynchronous periodic signals, for example, the 50 Hz mains and its harmonics, and 2) nonstationary behavior of the device under test, for example, phase or frequency modulation. [ABSTRACT FROM AUTHOR]