Browsing by Author "Pearce, H T"
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- ItemOpen AccessFinite element analyses of a wave loaded pile : deterministic and probabilistic(1991) Grant, C L; Pearce, H TThe problem of pile stick-up, where the pile has been stabbed into the pile guide of the platform to be fixed to the sea-bed and is loaded by the current and waves of the ocean, was recently of concern when the fixation of the first local offshore production platform took place. A previous investigation considered the resonant behaviour of the undriven pile subjected to various predicted sea states and various methods were examined to limit the large displacements anticipated. In the present work, a refined model of the problem is developed using the ABAQUS finite element program. Of particular interest is the applicability of the , probabilistic finite element method (PFEM). It is important to appreciate that a mere deterministic dynamic analysis - however accurate analytically - may be of limited value when applied to structures in the ocean. The response achieved thus will either be unelegantly conservative or very unreliable due to the many uncertain parameters that pervade the field of structural dynamics in the ocean. Traditionally, statistical methods are reverted to with uncertainty analyses, but they seldom have much appeal because of the computational effort involved. The PFEM was found quite attractive with a formulation where the uncertainty of the drag coefficient and the inertia coefficient were investigated. It was concluded that the uncertainty in these coefficients should be limited to a coefficient of variation of approximately 20% and that the simplified model on which the formulation was based should be refined if acceptable results for the purposes of design were required.
- ItemOpen AccessThe finite element analysis of convection heat transfer(1988) Burness, Bruce Peter; Pearce, H TThis thesis reviews the development and current methods of numerical convection heat transfer from available literature, encompassing an analysis of the various finite element formulations available for investigating convection. It further describes the finite element formulation for the primitive variable convection heat transfer equations via a Galerkin weighted residual scheme and using mixed interpolation, and it demonstrates the capability of this method by means of five practical examples, namely natural convection in a thermally driven square cavity, a thermally driven vertical slot, a thermally driven triangular cavity, and a liquid convective diode, and forced convection in a cooling pond. This study also provides the background and framework for the problem of transient convection heat transfer, and for further steady-state studies using parameters outside those considered herein.
- ItemOpen AccessNumerical analysis of cables in the offshore environment(1988) Davies, Graham John; Pearce, H TThe extraction of mineral resources from deep ocean waters has been made possible by the development of large compliant offshore structures. Mooring cables are crucial components in these offshore facilities and form the basis of this study. The aims of this thesis are: to provide a comprehensive review on all aspects of cables, to determine criteria for numerical modelling, and to ascertain the capabilities of the finite element method for cable analyses using the F.E. package ABAQUS. Difficulties associated with large sag cables arise as a result of their inherent flexibility which causes ill-conditioning of the stiffness matrices. Furthermore, the cable winding configuration causes a nonlinear stress-strain relationship, it's sagged geometry results in nonlinear strain-displacement relations, and the immersion in water leads to nonlinear fluid loadings arising from Morison's Equation as well as uncertainties in the fluid parameters. Various models, starting with the developed. Convergence difficulties basic catenary, have been at start-up, caused by a lack of stiffness in the transverse direction, are avoided by supporting the cable when applying loads. It is further established that numerical analyses of flexible structures are most stable in dynamic analyses and when under tension. In general both displacement based isoparametric and hybrid beam elements were found to be more reliable and applicable than truss elements. Cable whip, ocean floor contact and harmonic motions of cables were analysed. Finally a cable/tower interaction was modelled and subjected to a Stokes's wave. Conclusions and guidelines are presented based on the numerical experiments carried out in this study.