IDENTIFICATION OF LIGHT DAMPING IN STRUCTURES

Diffaent methods to identification of linear and nonlinear damping in lightly damped structures are discussed in this paper. The discussion is based on experiments with a 4 meter high monopile. Two alternative methods have been used for experimental cases of linear and nonlinear damp-ing. Method I is identification by ARMA models a~ssuming a white noise input. Method 2 is identification by simula-tion of a free decay response. Experimental data on the free decay response has been obtained directly by measurement as well as by the random decrement technique. Two cx-perimental cases. has been considered. The first case was a naturally damped monopile which was considered to be liw ear viscous damped. The second case was nonlinear viscous damping uf the monopilr due to a mounted danper on the monopile. The two cases illustrate identification of lightly damping in the linear and the nonlinear case. Nomenclature: Time series of noise Impulse response function of DOF no i Elemmt in the linear viscous damping matrix Element in the coulomb damping matrix Element in the damping matrix due to nonlinear viscous damping Random decrement signature of DOF no i due to trigger condition X0 on DOF no i Eigen frequency no n Damping force Element in the stiffness matrix Element in the mass matrix Number of degrees of freedom Number of data points in time serie