Identification of nonlinear viscous damping and Coulomb friction from the free response data

In this paper, a single degree of freedom system with nonlinear viscous damping and Coulomb friction is considered. A procedure for simultaneous identification of the nonlinear damping and Coulomb friction from the free response signals of the system is described. The procedure is based on the moving rectangle window method. The free vibration differential equation of the single degree of freedom system is established, and from its free response curve, the nonlinear damping characteristics and the Coulomb friction can be obtained by moving the rectangle window with fixed length along the time axis. In simulations, different kinds of the nonlinear damping models contained in the single degree of freedom system are respectively investigated, and the Coulomb friction value keeps constant. The validity and accuracy of the proposed method are illustrated by the good simulation results. In addition, the computing accuracy of the nonlinear viscous damping is higher than that of the Coulomb friction.