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Computer graphics applications in offshore hydrodynamics Hodgkinson, Derek Anthony Martin

Abstract

The results of hydrodynamic analyses of two problems involving offshore structures are displayed graphically. This form of presentation of the results and the liberal use of colour have been found to significantly help the ease in which the results are interpreted. For the transformation of waves around an artificial island, a time history of the evolution of the regular, unidirectional wave field around an artificial island is obtained. Through the use of colour, regions in which wave breaking occurs have been clearly defined. The numerical technique used is based on the finite element method using eight noded isoparametric elements. The determination of the transformed wave field takes wave breaking, wave refraction, diffraction, reflection and shoaling into account. The graphical display is achieved by using a plotting program developed for the output of finite element analyses. The motions of a semi-submersible rig are computed from the RAO curves of the rig, used to obtain its' small response in a random sea. The numerical technique used in the analysis assumes that the vertical members are slender and may be analysed using the Morison equation whereas the hulls are treated as large members which are discretised and analysed using diffraction theory. The discretisation of the cylinders and hulls together with the time history of the rig's motions are displayed graphically. Once again, the graphical display is plotted using a program developed for the output of finite element analyses for four noded elements. In this case, a finite element technique has not been employed but the results were ordered to act as though this is the case. The slender members (cylinders) and large members (hulls) are clearly distinguishable by using different colours. The elements used in the analysis are also clearly shown. The VAX 11/730 system was used to obtain the results shown. A video tape, using the results of a time stepping procedure, was made by successively recording the hardcopies produced by the VAX printer. The time stepping could also be seen, in real time, on the IRIS.

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