Identification of Light Damping in Structures

Different 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 damping. Method 1 is identification by ARMA models assuming a white noise input. Method 2 is identification by simulation 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 experimental cases has been considered. The first case was a naturally damped monopile which was considered to be linear viscous damped. The second case was nonlinear viscous damping of the monopile due to a mounted damper on the monopile. The two cases illustrate identification of lightly damping in the linear and the nonlinear case.