Theoretical and experimental investigations of large amplitude ship motions and loads in regular head seas
The aim of this research is to develop computational tools to predict the large amplitude motions and loads on ships travelling with forward speed in waves. An experimental research programme was completed to validate the non-linear prediction method. In this thesis, the results of theoretical and experimental investigations to predict the non-linear ship motions, slamming pressures and bending moments in regular head seas are presented. The ship hull is considered to be a Timoshenko beam, where the vibratory elastic response of the ship is calculated by the modal superposition method with the solution represented in terms of a series of normal modes. It is assumed that the mode shapes and natural frequencies can be determined by a separate structural analysis where this modal information is appropriate to the vessel in the equilibrium reference condition when floating in calm water. The global dynamic shear force and bending moment values are predicted using two different methods:The first method developed is based on the elastic vibratory response due to the total hydrodynamic force; The other is based on the rigid body response due to the linear force superimposed with the elastic response due to the impact forces. The results by the elastic vibratory response due to the total hydrodynamic force (method 1) have a good agreement with the experimental results and these are much better than the results by the rigid body response superimposed with the elastic response (method 2). The non-linear effects due to the change of the hydrodynamic coefficients and the non-linear restoring force should be considered in the ship motion and load predictions. The nonlinearity of ship motions as well as a significant nonlinearity between the hogging and sagging wave and global bending moments are shown in the results obtained from the non-linear theoretical predictions and the experimental data. The non-linear ship motions and sea loads, predicted by the practical computational tools, newly developed in this thesis, can be used to further ship structural strength analysis and guide ship hull design.