Dynamics of suspended cables under turbulence loading: reduced models of wind field and mechanical system.

In cables, turbulent wind may cause large amplitude oscillations. The prediction of cable response under wind action requires the use of high-dimensional numerical models either to describe the spatial wind field or to model the expected large cable oscillations. The paper discusses the ability of reduction techniques, for loading and cable descriptions, in reproducing accurately the dynamic response of a suspended cable excited by an artificially generated 3D turbulent wind field. The cable response to turbulent wind has been analyzed by means of a large dimensional model making use of the FE method and compared to the response predicted using reduced models for wind and mechanical system. Both the mechanical system and the spatially varying wind velocities are projected on the basis of cable eigenfunctions, retaining in the reduced models few degrees-of-freedom associated with the low-frequency modes. The numerical investigation performed by the refined finite element model provides novel findings on the cable response to wind and permits to demonstrate the effectiveness of the reduced models in the description of cable dynamics. In particular, the refined FE model enlightens how in the static configuration under wind loading the effects of the fluid-structure interaction is such that the linear aerodynamic damping, even for radially symmetric sections, couples the in-plane and out-plane cable oscillations, dominating the response also with respect to the involved geometric and aerodynamic nonlinearities. The analysis of the FEM response to complete and reduced wind models shows that most of the responses are given by the low modes and it is possible to strongly reduce the problem dimensionality. Use of an analytical model based on few low-frequency modes shows that the prediction of the cable response is well described by using reduced models for both wind and cable. Finally, the weak nonlinear modal coupling found in the dynamic responses is mainly due to the high level of aerodynamic damping introduced by the fluid-structure interaction.