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This thesis is concerned with the development of a computer algorithm for determining the principal dimensions of a container ship at the preliminary design stage. The algorithm was devised to aid a Naval Architect to design the most economical ship, given the ship owner's requirements. The emphasis has been on developing an algorithm which acts as an aid in the design process. There are basically four models of the computer aided ship design which can be used in stages. The first model or algorithm is based on a deterministic approach with parametric variation of principal dimensions to locate the optimum design with minimum required freight rate. The second model incorporates optimisation techniques to arrive at the optimum ship. Though the optimisation technique is very powerful in the search of an optimum both in computer time and computing cost, the parametric method is preferred where a designer has little faith in the optimisation process or as an aid to check the answer arrived at in the optimisation process. The third model of the computer aided design can be used once the optimum has been found. A new approach to carry out sensitivity analysis is introduced. This approach overcomes the deficiencies of the past approach, in the sense that sensitivity analysis is carried out for achievable variation in variables rather than an arbitrary variation. The third model of computer aided design may be used once the designer has identified the variables, the variation of which, influences the required freight rate most. The use of the third model of the ship design may be adequate in identifying the total risk of the project. Together with sensitivity analysis, the designer can evaluate the total risk involved in an investment since the third model also incorporates a simple approach to risk analysis. However three estimates are required in the third model compared to single estimates of variables in the first and the second model. The fourth model incorporates the risk analysis by Monte Carlo method of simulation. In this model the designer can assess the xvii total risk of the project by generating the risk profile of the Required Freight Rate. The designer must either subjectively or objectively input the probability distribution of each of the influencing variables before using the fourth model. The four computer aided design models form a complete suite of computer programs, which can either be used in a deterministic mode, (first and second model), or in a probabilistic mode, (third and fourth model). Compared to previous ship design algorithms developed solely to deal with deterministic phase, this thesis incorporates ideas on how to incorporate uncertainty and assess risk in capital investment in a shipping venture. The designer can either use these computer models in stages, from deterministic phase to probabilistic phase or the models can be used on their own.

This thesis presents a study on SWATH type vessels which is directed towards the collection and use for structural design of experimental data related to motions and primary dynamic loads of such vessels. This data will be of use in the validation of a mathematical model for motion and wave load predictions recently developed at the Department. Further, experimental data on slamming will also be acquired to lay a foundation for the future development of a reliable analytical model. Design loads pertinent to SWATHs comprising the extreme primary loads, lifetime cyclic loads and local panel pressures are then built upon the former findings to be of use in structural designs, especially in the determination of initial scantlings and fatigue characterisation. Examples are given throughout on the evaluation of hypothetical SWATHs operating in the North Atlantic. The underlying theoretical formulation of SWATH ship motions is presented together with a description of a newly developed motion prediction theory. This is followed by a clarification of the procedures for conducting seakeeping tests on SWATH models. Validation of the analytical motion model by the measured data of single and tandem strut SWATH models is then presented. Subsequently, practical applications of implementing motion predictions to the assessment of SWATH operatiblity in real seaways are described. Theoretical background of SWATH primary wave loads is briefly outlined. The enhancement of the motion program MARCHS to tackle the primary load on SWATHs is described. The development of experimental data on SWATH loadings by way of seakeeping techniques is presented. Correlation of this experimental data and the theoretical assessment is made to demonstrate the validity of the mathematical model so developed. Lifetime cyclic and extreme loads required in the fatigue and ultimate strength designs, respectively, are developed by applying long- and short-term wave statistics.

Prediction of the hydrodynamic forces on planing craft by strip method requires the force acting on two-dimensional sections in vertical motion on the free surface to be known. The motion of a transverse section of a prismatic hull in steady planing corresponds to a constant velocity water entry of a wedge shaped section. The force acting on the wedge section before the chines get wetted is found from a consideration of the rate of change of the section added mass. The current added mass impact theory does not give a satisfying definition of the change in added mass after chines wetting, and hence predictions of non-constant velocity water entry can not be made accurately. As a consequence, the theory is not applicable for use in prediction of the lifting force on hulls in unsteady planing or on hulls in steady planing with non-straight keel line, i.e. phenomena corresponding to non-constant water entry. Also, in unsteady planing, sections experience exit motion due to the pitch and heave response of the craft. If applying the added mass theory in exit predictions, the resulting force acts in the direction of motion, something in contradiction with intuition and common sense. The work described in this thesis has resulted in a new added mass theory for water entry and exit of transverse sections of typical planing craft. A program of numerical simulations and experiments with wedge shaped sections has been carried out, providing force data for water entry and exit of such bodies to and from the water. Analysis of these data have led to separation of the added mass and damping forces and to the development of quasi-empirical expressions applicable for both constant and non-constant velocity force predictions. Thus the new theory provides a basis for strip method for prediction of the unsteady motion forces of planing craft. Further, the new added mass theory for water entry has been applied to predict the steady planing lift force on slender body hulls, and consistency with published planing data has been found. Also, an empirical aspect ratio correction has been derived, allowing application to large aspect ratio (non-slender) planing hulls.

Today we are sitting on a huge wealth of structural reliability theory but its application in ship design and construction is far behind. Researchers and practitioners face a daunting task of dove-tailing the theoretical achievements into the established processes in the industry. The research is aimed to create a computational framework to facilitate fatigue reliability of ship structures. Modeling, transformation and optimization, the three key elements underlying the success of computational mechanics are adopted as the basic methodology through the research. The whole work is presented in a way that is most suitable for software development. The foundation of the framework is constituted of reliability methods at component level. Looking at the second-moment reliability theory from a minimum distance point of view the author derives a generic set of formulations that incorporate all major first and second order reliability methods (FORM, SORM). Practical ways to treat correlation and non- Gaussian variables are discussed in detail. Monte Carlo simulation (MCS) also accounts for significant part of the research with emphasis on variance reduction techniques in a proposed Markov chain kernel method. Existing response surface methods (RSM) are reviewed and improved with much weight given to sampling techniques and determination of the quadratic form. Time-variant problem is touched upon and methods to convert it to nested reliability problems are discussed. In the upper layer of the framework common fatigue damage models are compared. Random process simulation and rain-flow counting are used to study effect of wide-banded non-Gaussian process. At the center of this layer is spectral fatigue analysis based on SN curve and first-principle stress and hydrodynamic analysis. Pseudo-excitation is introduced to get linear equivalent stress RAO in the non-linear ship-wave system. Finally response surface method is applied to this model to calculate probability of failure and design sensitivity in the case studies of a double hull oil tanker and a bulk carrier.

No description available.

No description available.