Non-Linear Time Domain Simulation of Moored Floating Systems

This thesis describes the environmental loading and motion response prediction methods of mooring systems. The first chapter presents existing Single Point Mooring Terminals and gives a summary of previous studies carried out on this subject The main objectives of the study are also explained. Finally the structure of the thesis is given. The second chapter is concerned with the motion response prediction of moored buoys. Wave forces acting on the buoy are calculated using Morison's Equation. Catenary equations are utilized to derive cable forces. Two different buoy geometries, cylindrical and conical, are considered in the study. Experimental measurements are compared with time and frequency domain modellings. In the third chapter, diffraction theory used to derive the wave forces is explained. The tanker is modelled as a vertical elliptical cylinder with a finite draught. Calculated wave forces are compared with Oortmerssen's experiments and with the results of a 3-D program developed by Chan. The water depth effect on wave forces is investigated. Program results for various angles of incidence and for different elliptic cylinders are presented. The second order mean force is calculated using the far-field approach, introduced by Maruo. Also the radiation problem of the tanker which is modelled as an elliptical cylinder is solved. Program results are compared with Oortmerssen's experiments and with Chan's 3-D program results. Program results for different cylinders and for different water depth/draught ratios are presented. Chapter 4 describes a time domain model used to predict the motion responses of a tanker-buoy system under wave, wind and current loading. Motion equations of the tanker-buoy system are derived by using Cummins' method. Frequency-independent hydrodynamic coefficients and time histories of wave forces in irregular seas are calculated. Experimental measurements are compared with the time domain simulation results. Chapter 5 presents the results of a series of parametric studies. A computer program developed to predict the motion responses of the coupled tanker-buoy system is run for different parameters, such as; wave, wind and current angle of attacks, wind and current speed, elasticity of the mooring lines and the hawser line, buoy and tanker geometry, water depth, draught of the ship. Numerical aspects of the program, such as the solution of the differential equations and the evaluation of the convolution integral are discussed. In chapter 6 a description of model tests performed in regular waves is presented. Two sets of experiments are conducted. The first set of experiments aims to predict the motion responses of conical and cylindrical buoys, the second to predict the motion responses of the tanker-buoy system and the hawser line forces. In the final chapter general conclusions are drawn and some recommendations for future work are made