THE NONLINEAR HYDROELASTIC BEHAVIOR OF FLEXIBLE WALLS

A computational model is developed to study the hydroelastic response of simple panels and compliant walls to a uniform flow. Numerical expe riments are presented which simulate the history of hydroelastically u nstable disturbances as they evolve from amplitudes that may be treate d by linear theory to amplitudes for which non-linearity in both the w all and flow cannot be neglected. The method is first applied to simpl e unsupported flexible panels. Unstable deformations of these panels a re seen to be dominated by the fundamental mode. When some panel dampi ng 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 oscill ations are characterized as a function of wail and flow properties. Th e method is then used to study a compliant wall comprising a spring-ba cked flexible plate. For low levels of wall damping, linearly unstable waves evolve into a complex limit-cycle Butter-type response. For hig h 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-amp litude growing divergence waves. Features of the simulated waves and t heir dependence on the freestream how show good qualitative agreement with experimentally measured nonlinear divergence waves. The character istic waveform of the nonlinear divergence waves is shown to be attrib utable to the hydrodynamic stiffness pressure field generated by large -amplitude disturbances. (C) 1997 Academic Press Limited.