Numerical Investigation of Hydrodynamic Interaction Among Three Dimensional Box-Shaped Floating Structures

Abstract

Two or more floating bodies in waves can experience significant hydrodynamic interactions when they are in close proximity. Hydrodynamic interactions between multiple floating bodies are important for many applications in the field of marine and ocean engineering. In this thesis, simple box-shaped or, pontoon-type floating bodies are chosen for numerical investigation. A general method is proposed for the hydrodynamic analysis of multiple floating bodies in a regular wave system. The three dimensional source distribution method also known as lower order panel method has been adopted to determine the added mass coefficients, damping coefficients and first order wave exciting forces and moments by taking into account the effect of hydrodynamic interactions among the different floating bodies, and the coupled equations of motions are solved directly. To apply lower order panel method, the submerged surfaces of the floating bodies are divided into a large number of small quadrilateral plane elements and the solution for the velocity potential or source strength is approximated by a constant value on each element. Based on the formulation for 3-D source distribution method, a computer code in FORTRAN has been developed by modifying and extending a computer code that has been written previously for the frequency domain analysis of a single floating body. To justify the validity of the code, wave exciting forces and motion responses for a box-cylinder model and a twin vertical cylinder are checked with published numerical as well as experimental results. After verification of the code, detailed analysis in the frequency domain is carried out for simple box-type or, pontoon–type rigid bodies. A number of different panel or, mesh size is tested to select an acceptable panel size for the wetted surface of the floating bodies. Various multi-body models considered in this work are: a two-body model, a three-body model, a nine-body model and a long array of twenty-one-body model of identical floating boxes. Numerical investigation is also conducted for non-identical twin body models. To depict the intensity of hydrodynamic interactions for various multi-body models, numerical results for an identical isolated body case is also plotted along with the multi-body case results. The influence of gap or, separation distance, wave heading and arrangement in the array is investigated thoroughly in this thesis to have an insight for hydrodynamic interactions between box-shaped floating bodies in regular waves.