The paper aims to investigate the relationship between cerebrovascular geometry and hemodynamics in order to predict rupture and creation of cerebral aneurysms. The authors have been developing a numerical simulation system, which consists of medical image-based geometric modeling, grid generation, finite element fluid simulation, and scientific visualization. A database system is designed so as to organize and analyze medical imaging, physiological, and numerical data. The multivariate analyses are performed to estimate a maximum wall shear stress using 19 cases of the middle cerebral artery (MCA) calculations from the database system. The results are compared and show good agreement with those of numerical analysis. It is found that diameter of the MCA, ratio of diameter of branching to that of the MCA, and bifurcation angle between the MCA and brunching arteries are important geometric factors in determining the maximum wall shear stresses.

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The process of breakup of a single bubble passing through an orifice and the mechanism of sound generation during the process are described in this paper. A micro jet grows in the downstream direction in a bubble after the bubble passes through the orifice. The bubble then breaks into small bubbles because the micro jet hits the opposite side of the bubble. The sound was found to be generated when the bubble broke. The relationships of breakup position with diameter of a bubble, free stream velocity, pressure difference and a growth rate of the micro jet in a bubble are discussed.

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A laminar to turbulent transition process of a three-dimensional boundary layer in a rotating-disk flow initiated by a localized strong disturbance was experimentally investigated by a single hot-wire probe in a laboratory frame. The hot-wire analyses showed that the point disturbance develops into an isolated turbulent patch accompanied by different types of traveling waves. The configuration in the plane view of the turbulent patch is a crescent different from an arrowhead-shaped turbulent spot in a Blasius boundary layer. Comparison with the prediction by Itoh's linear stability theory enabled us the identification of the traveling waves around the patch; the streamline-curvature (S-C) unstable waves propagating outward grow around outer edge of the patch while the cross-flow (C-F) unstable waves developing in the upstream region of the trailing edge travel in the inward direction. The characteristic features of these waves are in good agreement with the theoretical results. Since the turbulence is produced in the center region of the wave packet, which mode mainly contributes to the breakdown into turbulence still remains unclear.

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