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The velocity potential theory has been adopted to investigate the two-dimensional vortex shedding problems in marine hydrodynamics. The theory can find its applications to the lifting body problems such as a hydrofoil advancing near the free surface, the flow passing through an orifice of a damaged compartment, the vortex shedding at sharp edges of a marine structure. Since the viscosity of the fluid is assumed to be confined within a thin boundary layer along the surface of the structure, the fluid flow can be described by velocity potential theory. Literature review on vortex shedding has been presented. The development of relevant theories and their applications have been discussed. The challenges and suitable methodologies are investigated. When the steady motion and small amplitude unsteady motion of a hydrofoil advancing near free surface is considered, a flat vortex sheet is introduced and imposed behind the trailing edge; linear free surface conditions are imposed to study the free surface effects. Free surface Green functions, which satisfy free surface boundary conditions, are adopted to account for the free surface effects which are found to be highly significant. To study the non-linear effects of body surface boundary condition and vortex wake when the attack angle or the motion amplitude becomes moderately large, we introduce a time stepping scheme. The vortices shed from the trailing edge are approximated by introducing point vortex. The non-linear effects of body surface condition and vortex wake are investigated. Further studies on the submerged foil and surface piercing structures with vortex shedding are presented; efforts are made to investigate the non-linear wave-body interaction problems with vortex shedding. The non-linear free surface and non-linear vortex wake are found to have significant effects on the fluid flow and the hydrodynamic force.

An animal model with an exteriorised but intact enterohepatic circulation was developed in the dog to produce graduated biliary obstruction and to facilitate the collection of bile samples. Seven dogs were studied with chronic biliary obstruction which consisted of various degrees of partial and complete biliary obstructions and another three, for simple complete biliary obstruction. Alterations of bile composition during chronic biliary obstruction are reported for the first time. The concentration of bile acid, phospholipids and cholesterol in bile was significantly decreased during chronic biliary obstruction. The proportion, i.e. molar ratio, of cholesterol in the biliary lipids was usually decreased. After release of biliary obstruction, recovery of both concentration and molar ratio of cholesterol in bile, which were lower than the control, took much longer than that of bile acid and phospholipids. The cholesterol supersaturation of bile occurred after 48 br complete obstruction during the chronic experiment, while the cholesterol concentration was extremely low and the molar ratio of cholesterol did not significantly increase. This supers a turation did not exist 6 hours after release of the complete obstruction and the molar ratio of cholesterol in bile soon became lower than the control level. That the role of this kind of supers a turation is not significant in the formation of cholesterol gallstones has been discussed. The alterations of bile composition in simple complete biliary obstruction was similar to that in the chronic experiment, but the cholesterol saturation in bile did not increase but rather, decreased. The ratio between bile acids, phospholipids and cholesterol in the bile secreted during the control were changed during and after various kinds of biliary obstruction. The significance of this in studying the mechanism of biliary lipid secretion has been discussed.