A New Iwan/Palmov Implementation for Fast Simulation and System Identification
While Iwan elements have been shown to be an effective model for the stiffness and energy dissipation in bolted joints, they are presently somewhat expensive to integrate. Currently, the Newmark-beta algorithm is used to integrate the equations of motion when a structure contains Iwan elements, and a small time step is needed to maintain accuracy. This paper presents a new way of simulating Iwan elements that speeds up the simulations dramatically by using closed form expressions for the micro-slip regime and using an averaging method for regions of time in which no external force is applied. With this method the response can be computed in about a hundredth of the time. The proposed algorithm is demonstrated on a single degree-of-freedom (SDOF) system to understand the range over which it retains accuracy. Although current implementation is applicable to SDOF systems, it can simulate the response of each mode in a structure that is modeled using the modal Iwan approach (i.e. assuming uncoupled, weakly-nonlinear modes).
KeywordsNon-linear damping Iwan model method of averaging Newmark-beta integration Runge-Kutta
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