The nonlinear hydroelastic behaviour of flexible walls

A computational model is developed to study the hydroelastic response of simple panels and compliant walls to a uniform flow. Numerical experiments are presented which simulate the history of hydroelastically unstable disturbances as they evolve from amplitudes that may be treated by linear theory to amplitudes for which non-linearity in both the wall and flow cannot be neglected. The method is first applied to simple unsupported flexible panels. Unstable deformations of these panels are seen to be dominated by the fundamental mode. When some panel damping is incorporated, the panel ultimately settles into a static buckled state; however, this long-time response may be preceded by sustained nonlinear oscillations. The amplitudes and frequencies of these oscillations are characterized as a function of wail and flow properties. The method is then used to study a compliant wall comprising a spring-backed flexible plate. For low levels of wall damping, linearly unstable waves evolve into a complex limit-cycle Butter-type response. For high levels of damping small-amplitude unstable disturbances evolve into saturated nonlinear divergence waves that have sharp peaks and shallow troughs. These have much slower downstream wave travel than small-amplitude growing divergence waves. Features of the simulated waves and their dependence on the freestream how show good qualitative agreement with experimentally measured nonlinear divergence waves. The characteristic waveform of the nonlinear divergence waves is shown to be attributable to the hydrodynamic stiffness pressure field generated by large-amplitude disturbances. (C) 1997 Academic Press Limited.