A digital method of modeling two-input quadratic systems with general random inputs

A digital method of estimating linear and quadratic transfer functions of a two-input/multiple-output quadratically nonlinear system with general (i.e., non-Gaussian as well as Gaussian) random inputs is described. The approach is based on a frequency domain second-order Volterra functional series representation for a two-input/multiple-output system. Practical applications where it is important to have the capability to model dual-input nonlinear systems include: ground vibration tests of aircraft where two random exciting forces are applied in order to inject sufficient energy into all modes of the system; and experimental studies of transition to turbulence in fluids and plasmas, where the two inputs consist of two different velocity components, and plasma density and potential fluctuations, respectively. The approach described is being utilized to investigate such applications