An Investigation of Nonlinear Damping Effects on Modal Analysis Results

摘要

The effects of well-defined nonlinearities on modal analysis results were investigated. These effects were accomplished by numerically integrating the equation of motion for a nonlinear 1 DOF system subjected to a series of harmonic forcing functions. The specific nonlinearity investigated was due to damping forces proportional to the powers of velocity other than one. This nonlinearity often occurs in mechanical systems in which objects move through fluids at moderate velocities. The analysis results for these systems with controlled nonlinear effects are displayed in a series of three-dimensional plots using state-of-the-art interactive graphics software (PDA/PATRAN). These plots depict the system's output amplitude due to parametric variations of the 1) input frequency/resonant frequency ratio, 2) damping coefficient, and (3) input amplitude. The results of these numerical integrations are curve fit in the frequency domain using a rational fraction polynomial technique to estimate the single degree of freedom parameters and then compared to the actual values used in the numerical integrations.