VARIATIONAL METHODS AND APPLICATIONS FOR TURBULENT SINGLE AND TWO-PHASE FLUID-STRUCTURE INTERACTION

Abstract

The present thesis deals with the development of a novel three-dimensional multifield and flexible multibody computational framework based on the continuum mechanics laws to model single and two-phase fluid-structure interactions. Starting with the canonical convection-diffusion-reaction (CDR) equation, a novel positivity preserving variational (PPV) method is proposed to get stable and accurate numerical solution. The PPV method is then extended to phase-field Allen-Cahn equation and coupled with Navier-Stokes equations to model the two-phase flow. Turbulent flow is handled by a hybrid RANS/LES model through the application of the PPV method on the turbulence transport equation. The two-phase turbulent flow system is then coupled with structure in a partitioned manner via nonlinear iterative force correction scheme. This coupled framework is stable and advantageous in high fluid density ratio and low structure-to-fluid mass ratio regimes. The ultimate problem of the offshore vessel-riser system is demonstrated by the integrated and robust solver.