Direct Differentiation of the Particle Finite-Element Method for Fluid-Structure Interaction

Sensitivity analysis of fluid-structure interaction (FSI) provides an important tool for assessing the reliability and performance of coastal infrastructure subjected to storm and tsunami hazards. As a preliminary step for gradient-based applications in reliability, optimization, system identification, and performance-based engineering of coastal infrastructure, the direct differentiation method (DDM) is applied to FSI simulations using the particle finite-element method (PFEM). The DDM computes derivatives of FSI response with respect to uncertain design and modeling parameters of the structural and fluid domains that are solved in a monolithic system via the PFEM. Geometric nonlinearity of the free surface fluid flow is considered in the governing equations of the DDM along with sensitivity of material and geometric nonlinear response in the structural domain. The analytical derivatives of elemental matrices and vectors with respect to element properties are evaluated and implemented in an open source finite element software framework. Examples involving both hydrostatic and hydrodynamic loading show that the sensitivity of nodal displacements, pressures, and forces computed by the finite-difference method (FDM) converge to the DDM for simple beam models as well as for a reinforced-concrete frame structure. (C) 2015 American Society of Civil Engineers.