Active damping of space structures by contact pressure control in joints

Lightweight flexible structures; e.g., for large deployable space systems, often consist of truss structures. Microslip and macroslip in the joint contact surfaces are the dominating dissipation mechanisms, when compared to material damping and environmental damping, if no additional damping measures are applied. So far only control of operational modes by actuators in the truss element is realized. This paper aims to control the nonlinear transfer behavior of joints by adapting the contact pressure. This is achieved by piezoelectric elements in bolted connections. Active joint description by ordinary differential equations (ODE) with internal variables, based on experimental data, is implemented in the hybrid multibody system (MBS) of the assembled truss structure. The structural response is decomposed into large rigid body motion and superimposed small elastic deformations. The equations of motion are linearized by a perturbation technique based on the splitting of low frequency and high frequency modal contents. The flexibility of the MBS is treated by superposition of structural modes calculated by the finite element method (FEM), in the sense of a Ritz approximation. Simulation of free, as well as forced, vibrations of the structure with active joints in a closed control loop underline the gain of damping performance compared to the associated passive system.