Numerical and Experimental Simulations of Effect of

Purification Apparatus Set in Gokasho-Bay


Toru Sato, Kenzo Tonoki, Kentaro Ebara, Shigeru Tabeta


University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656

Tel: 03-5841-6523, Fax: 03-5802-3374



The authors took part in a project for developing a new computational ocean model called the MEC model, the specialty of which is that the model comprises hydrostatic and full-3D (non-hydrostatic) models for analysing physical phenomena with two different spatial scales, i.e. the sea size (1km-100km) and the artefact size (1m-100m). We applied the numerical model to the simulation of purification effects of the Density Current Generator set in Hazama-Inlet, Gokasyo-Bay in Mie, Japan, where red tide had often devastated fishery since 1970s and are seldom observed after the installation of the apparatus.

At the same time, we carried out hydraulic model experiments by using a distorted model installed in a basin with the diameter of 3m, in order to obtain a knowledge on diffusion by tide and density current in the topography of real sea. In this model basin, tide can be generated by the reciprocal movement of a float-type tide generator. Two stratified water-layers were set in advance and density current between them was produced by putting dyed water with intermediate density. We propose a new similarity law for density current in distorted-model experiments. The luminance method was used to measure the areal concentration of the dye.

Simulation results obtained both by the numerical and hydraulic models suggested that the apparatus puts the water including nutrients sucked from the bottom onto the thermocline and such water never mixes in the vertical direction near the apparatus due to the strong stratification in summer, and that the water of nutrients on the thermocline spread to the whole bay within a week mainly by tidal motion.


                         Computed Temperature Distribution                         Computed Salinity Distribution


                         Distortion Model Experiment                       Measure Dye Distribution by Luminance Method