A LAGRANGIAN-LAGRANGIAN FRAMEWORK FOR THE SIMULATION OF FLUID-SOLID INTERACTION PROBLEMS WITH RIGID AND FLEXIBLE COMPONENTS By

This work is concerned with formulating and validating a Lagrangian-Lagrangian (LL) approach for the simulation of fully resolved Fluid Solid/Structure Interaction (FSI) problems. In the proposed approach, the method of Smoothed Particle Hydrodynamics (SPH) is used to simulate the fluid dynamics in a Lagrangian framework. The solid phase is a general multibody dynamics system composed of a collection of interacting rigid and deformable objects. While the motion of arbitrarily shaped rigid objects is approached in a classical 3D rigid body dynamics framework, the Absolute Nodal Coordinate Formulation (ANCF) is used to model the deformable components, thus enabling the investigation of compliant elements that experience large deformations with entangling and self-contact. The dynamics of the two phases, fluid and solid, are coupled with the help of Lagrangian markers, referred to as Boundary Condition Enforcing (BCE) markers used to impose no-slip and impenetrability conditions. The BCE markers, which are associated both with the solid suspended bodies and with any confining boundary walls, are distributed in a narrow layer on and below the surface of solid objects. The solid-solid interaction is known to have a crucial effect on the small-scale behavior of fluid-solid mixtures. The dry encounter of solid surfaces is resolved herein through a penalty based approach. However, using this model for the short range interaction of solid surfaces in fluid media does not follow the real physics of wet interaction. To accommodate this, a lubrication force model consistent with SPH is adopted herein to capture the short range interaction of arbitrary shapes in fluid. The ensuing fluid-solid interaction forces are mapped into generalized forces on the rigid and flexible bodies and subsequently used to update the dynamics of the solid objects according to the rigid or flexible body motion. The software implementation of the proposed LL approach is used to investigate the twoand three-dimensional (2D, 3D) pipe flow of dilute suspensions of macroscopic neutrally buoyant rigid