Diagnostic Inferring on the Bases of Nonlinear Models

Physical phenomena accompanying destruction processes of technical systems are nonlinear and "low-energetic" by nature, while during wearing out mainly a nonlinear disturbance changes. Out of many inference techniques - on the observation basis of the state of the system - the best one is undoubtedly the well-defined mathematical model, allowing inferring `backwards' and `forward', which means finding the genesis and prognosis of the phenomenon. However, such model should be nonlinear. Problems related to the identification of nonlinear dynamic models in a frequency domain and a proposition of solving this problem for the needs of technical diagnostics, i.e. in situations when the observed wear out effects are significantly smaller than the dynamic effects - are discussed in the hereby paper. The bases of the proposed method constitute the discussion of possible solutions of a certain class of nonlinear differential equations and resulting from that statements on the possibility of nonlinear disturbance approximations by a series of the selected harmonic frequencies.