Nonlinear water-wave structure interaction

Abstract

A numerical model of the interaction of highly deformable fluid-filled membranes and ocean waves has been developed and verified. The fluid domain is modeled using a boundary element model and the membrane is modeled using a finite element model. The finite element model was developed previously, and required little modification. However, the hydrodynamics in the finite element model was simplistic and the boundary element model of the fluid domain was developed to provide a better representation of the potentially nonconservative hydrodynamic loadings on the membrane. The finite element model predicts the nonlinear dynamic behavior of cable and membrane structures where the nonlinearities arise from large displacements, surface rotations, nonlinear stress-strain relationships and nonconservative loadings. The total Langrangian description and the principle of virtual work are used to formulate the equilibrium equations. Explicit stress-strain relationships are neither assumed nor required. The hydrodynamic loadings induced by water waves on structures are computed using a boundary element model. Large body hydrodynamics and ideal fluid flow are assumed and the diffraction/radiation problem solved. Either linear waves or finite amplitude waves are assumed in the model; thus the nonlinear kinematic and dynamic free surface boundary conditions are treated iteratively. To implicitly include time in the governing field equations Volterra's method was used. The models were coupled in an iterative procedure to model the wave structure interaction. Numerical results were compared to results of large scale test conducted on a 3-ft diameter membrane cylinder.