Modal and Impact Analysis of Fluid-Structure Interaction by Finite Element Methods.

Abstract

In this work, the modal and impact interactions of fluid-filled cylindrical structures are studied. The first part of the study focuses on the parametric modal analysis of fluid-coupled thin structures. This study emphasizes describing or approximating the coupled natural frequency of a fluid filled structure as a function of respective modes of the uncoupled structures. A condition to differentiate the strong and weak coupling between fluid and structure is proposed. In the second part of the study, an optimized method to simulate the dynamic 3D event of the impact of a rod with a flat surface is presented. Unlike in the 2D FEM (Finite Element Method) based contact models, in this study, both bodies undergoing the impact are considered elastic-plastic(deformable) and simulation is the dynamic event of the impact, instead of predefined 2D symmetric contact analysis. Prominent contact models and plasticity models to define material properties in ANSYS are reviewed. The coefficient of restitution (COR) for normal and oblique impact of the rods are obtained by experimentation. Experimental results of the permanent deformation on the base for different impact velocities is derived from a prominent impact study. The simulation results are in co-relation with the experiment and both indentation and flattening models on the COR and permanent deformation of the base and rod after the impact. Thus, the presented 3D explicit dynamic simulation of impact is validated to analyze the impact behavior of the two bodies without any predefined assumptions with respect to boundary conditions or material properties. Furthermore, this validated finite element method is used to simulate the impact of fluid-filled tubes. The effect of coupling on contact parameters (deformation, COR, contact force, and plastic work) is analyzed for the normal impact. It is observed that during the impact of the inclined rods and tubes, there are multiple impacts during the event. Finally, it is shown that the natural frequency of the impacting rod has a significant effect on this behavior. For the future studies, analytical modeling of the impact should also consider the vibration and natural frequency of the system in the equation of motion.