[in Japanese]

View full abstract

This paper describes the results of on-site experiments and numerical analyses for investigation of water surface oscillation in an open channel of a hydraulic power plant. Firstly, experiments were carried out and characteristics of the oscillation were clarified. Secondly, numerical analyses with use of long-wave equation and finite difference method were performed on the same condition with experiments, and the emergence of the water surface oscillation was confirmed. On both investigations, strong interactions between water surface and Karman vortices behind columnar structures in the channel were observed. Computations with structures having reshaped streamline body section were also done and distinct deduction of oscillation amplitudes were found. Thus, it was concluded that the interaction between free surface waves and Karman vortices is the cause of the oscillation.

View full abstract

As the numerical simulation of complex topography blocks (Sept., 1993) used in previous research involves scattered vortices in the flow field and complicated configurations, we decided to solve by a fundamental mean flow equation that included effects of turbulence. In "Numerical prediction of short range diffusion processes of air pollutants in urban areas", we therefore employed the frequently applied k-ε type two-equation turbulence model that is comparatively simple but is also flawed. This model contains domains where the wall function is hard to deal with, so we then took up the problem of how to improve on this, and were able to obtain suitable using the standard type of the k-ε two-equation turbulence model. The above-mentioned three-dimensional analysis however consumes a great deal of computing time even for a supercomputer, and it is difficult to expand the analytic scope with this model. We therefore altered our course and significantly expanded the scope of analysis by adopting a method (referred to as the "wind system estimation model" which is based on calculus of variational principle, and is the WINDO4 method that uses the EXPRESS code developed by Ishikawa and Chino) that determines total wind velocities by weighted interpolation of outside wind velocity data taken from several observatory sites to points in a three-dimensional mesh system which can even be computed by a smaller computer so that we could simulate everything from an entire municipal area to a wide-range area. This model does not strictly achieve numerical simulation of air flow, but it determines the flow field in order to satisfy the continuous condition of incompressible viscous flows (in other words, it satisfies the law of conservation of mass), so it is therefore called the "mass consistent model". We first determined the three-dimensional wind field of the entire Yokkaichi area from observatory site wind velocity data obtained by the wind system estimation model. The method of determining diffusion analysis and concentration distribution from three-dimensional wind field is still being studied. We therefore decided to make do for the time being by creating a program based on this which computes the diffusion process of air pollutants in the Yokkaichi area. As a method of computation, the wind field for the entire Yokkaichi area can be obtained by the wind system estimation model through interpolation of observatory sites using points in the three-dimensional finite-difference mesh system. Using this method, we can trace the advection current diffusion process of diffused substances in the form of time development by the box model of finite-difference calculus. For test computation, we performed the simulation to trace hypothetical pollutants released from near Yokkaichi Station (Kintetsu) using time development form in the previous paper. Now, in this paper, the results of the real situation for sulfer dioxide diffusion processes of Yokkaichi area in the past are shown. Computational results trend to agree well with the results of the other plume model and real observed data in 1973 qualitatively.

View full abstract