Thesis (Ph. D.)--University of Texas at Austin, 2004. / Vita. Includes bibliographical references (leaves 275-293). Also available in an electronic version.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: John L. Tassoulas. Vita. Includes bibliographical references. Also available from UMI.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 199-210). Available also in a digital version from Dissertation Abstracts.

No description available.

The effects of wave directionality on the loads and motions of long structures is investigated in this thesis. A numerical method based on Green's theorem is developed to compute the exciting forces and hydrodynamic coefficients due to the interaction of a regular oblique wave train with an infinitely long, semi-immersed floating cylinder of arbitrary shape. Comparisons are made with previous results obtained using other solution techniques. The results obtained from the solution of the oblique wave diffraction problem are used to determine the transfer functions and response amplitude operators for a structure of finite length and hence the loads and amplitudes of motion of the structure in short-crested seas. The wave loads and body motions in short-crested seas are compared to corresponding results for long-crested seas. This is expressed as a directionally averaged, frequency dependent reduction factor for the wave loads and a response ratio for the body motions. Numerical results are presented for the force reduction factor and response ratio of a long floating box subject to a directional wave spectrum with a cosine power type energy spreading function. Applications of the results of the present procedure include such long structures as floating bridges and breakwaters. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A numerical method is described to study directional wave effects on large offshore structures of arbitrary shape, based on an extension of linear diffraction wave theory for regular waves. A computer program has been developed to compute loading transfer functions and response amplitude operators and hence the loading and response spectra for both long- and short-crested random waves. Cosine powered directional spreading functions which are independent of frequency have been used to account for the shortcrestedness of waves. Comparisions of the results for long- and short-crested seas show that there is a significant reduction in the loading, and hence in the response, due to shortcrestedness of waves. The probabilistic properties of the components of the loading and response are described. Since the sea surface is assumed to follow a Gaussian distribution, these are also random Gaussian variables. In short-crested waves, the loading and response components occur both in-line and transverse to the principal wave direction. Thus the maximum horizontal loading and response may occur in an arbitrary horizontal direction. An analytical method is developed to describe also the probabilistic properties of the maxima of the components and the maxima of their horizontal resultants. In the present study, results are described for a freely floating box. Comparisons are made with published results and are found to be quite favourable. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The present investigation considers the hydrodynamic forces acting on a slender structure subjected to a combined wave and current flow regime. The experimental aspect of the study measured the in-line peak-to-peak forces on a vertical cylinder mounted in a wave-current flume. Although there were some inconsistencies in the data, the general trend indicated a substantial increase in the force with a positive underlying current and a less pronounced increase for a negative current. A numerical analysis of the problem evaluated Morison's equation using the current-invariant force transfer coefficients and flow kinematics obtained through Stokes Fifth Order Wave Theory. The results of this analysis revealed a trend qualitatively similar to that found experimentally. The important distinction between the results obtained through the experimental investigation and those obtained numerically was the consistent over-prediction observed in the numerical analysis. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

No description available.

Polymer composite materials, particularly glass reinforced plastics (GRP), are increasingly being used in the offshore industry and their behaviour in fire is studied using mathematical and numerical modelling. A generalised finite element method is developed to analyse the thermally induced response of a widely used GRP, consisting of polyester resin and glass fibre reinforcement. GRP panels, pipes and joins subject to hydrocarbon fires (i.e. high temperatures) are studied. One- and two-dimensional mathematical models are developed to study the fire performance of: (i) single-skinned GRP panels, (ii) twin-skinned GRP-Vermiculux sandwich panels, and (iii) thin and thick GRP joins (step panels). The models involve thermochemical decomposition of the material (pyrolysis) and include: (i) transient heat conduction, (ii) gas mass movement and internal heat convection of pyrolysis gases, (iii) mass loss and Arrhenius rate decomposition of the resin material into gases and char, and (iv) endothermicity of pyrolysis. The effect of imperfect bonding on heat transfer in sandwich panels and the accumulation of pyrolysis gases and internal pressurisation in thick step panels are also included. The models may be used with any combination of steady or time-dependent boundary conditions including temperature, radiation, chemical reactions, mass diffusion and free and forced convections. Various positions of panels, i.e. vertical, horizontal and inclined are studied. The material is assumed homogeneous and orthotropic with respect to thermal and transport properties which may vary with temperature, pore pressure and moisture. The finite element models use weighted residual approach with linear elements for one- dimensional and quadrilateral elements for two-dimensional. Non-linear terms and coefficients are evaluated explicitly using an iterative-updating method and nodal temperatures and pore pressures implicitly using Crank-Nicolson solution. The classical finite difference time stepping algorithm is used where an efficient solution is achieved using variable time step. Numerical results are presented in the form of temperature versus time, temperature versus distance, pore pressure versus distance, mass loss versus distance and moisture versus distance and compared with experimental data where available. It is shown that the decomposition of the material, endothermicity of pyrolysis and the movement of pyrolysis gases make substantial contributions towards the cooling behaviour and delaying the bum-through. The effect of gas mass movement and surface chemical reactions across the boundary layer adjacent to the fire-exposed surface is very important in introducing a theoretical boundary condition. An investigation into the effect of inclusion the variable thermal properties reveals considerable improvement in thermal predictions. Sandwich panels consisting of GRP/Vermiculux/GRP offer good thermal insulation. Thermal contact resistance at an imperfect bonding is important where an average difference of 12% can be found between the thermal responses of sandwich panels with perfect and imperfect bonding. For thin GRP step panels, a one-dimensional solution is found adequate to predict the fire resistance behaviour of the material. For thick GRP step panels, the effect of internal pressurisation coupled with temperature on the thermal response is considerable.