Hideo Ohtani

THE CHARACTERISTIC OF LOCAL SCOUR AROUND THE CLOSUER WORKS AND THE APPLICATION TO THE BOTTOM CHANGE SIMULATION

River works are ordinary executed during dry season. But recently, there are not less works that the large double sheet piles closure work is set in the river all the year around. In this case, the closure works must be solid against the flow in the rainy season, and the protection works have to be designed considering not only the local sour depth but also the area of the degradation.In this study, the sour characteristic around the closure works is investigated by hydraulic experiments. The sour depth is affected by the dimensionless sheer stress and the ratio of the closure width and water depth. As for the closures shape of the angle to the flow direction, the scour depth is deeper in case of the 90 degrees, on the contrary the area of the degradation along the wall is larger in case of 45 degrees. It also develops that the vortex at the corner causes the local scour. So we suggest the new simulation method for the local scour, to which the vortex shear stress model is introduced. As a result, the good results are obtained, which represent the local sour as well as the river bed configuration.

VISUALIZATION OF FLOW PATTERN OF TSUNAMI IN A HARBOR

Tsunami causes extreme erosion and accretion in the bottom of a harbor.The collision force of the floating objects is also one of the problems in tsunamis disaster.To understand them, hydraulic model experiments are carried out.Flow pattern in a harbor by tsunami are measured by PTV (Particle Tracking Velocimetry), one of the flow visualization methods.Tsunami intrudes in the harbor along the breakwater, and generates a circulation inside.In case of tsunami that has a large wave gradient, the super-critical flow and hydraulic jumps can be seen in the mouth of a harbor.Accuracy of PTV was also verified in the experiment.The velocity by PTV is compared with that by an electromagnetic current meter.Those have quite good agreements except the space where the hydraulic jump exists.

CHARACTERISICS OF SURGING DISCHARGE CHANNEL WITH BASIN AND A NUMERICAL SIMULATION METHOD

In an intake and discharge channel of an electric power plant or a LNG plant, surging phenomena of water may cause a siphon break or an overflow at pits, and then may give a damage to the facility. A new numerical simulation method to predict surging was developed. In the method, the “slot model” was applied to the pressurized flow, and the MacCormacks scheme is used to simulate the mixed flow condition of sub-critical and supercritical flow. The water level in a discharge basin which is usually set at the end of the discharge channel can be calculated simultaneously. The laboratory tests were carried out to verify the simulation model for three types of channels. Three types of channels were a pressurized channel, an open channel and a channel which had a vertical bend at the end. All the channels have a discharge basin at the end. It is shown that the model can simulate an unsteady surging phenomenon for almost all types of channels.

A CONTROL METHOD OF SURGING IN DISCHARGE CHANNEL WITH VERTICAL SHAFTS

A discharge channel of a power station is composed of open channel, tunnel and vertical shafts. Surging phenomenon occurs in the discharge channel when pumps stop all at once. The surging propagates with highly pressurized flow forward the lower narrow channel to make the water spouting from the vertical shafts.We simulated physically the phenomena in the discharge channel through the laboratory tests and simulated mathmatically the water motion by means of the slot model. The laboratory tests, the calculation and the field investigation showed that the phenomenon of surging and spouting water could be depressed by a sophisticated stopping-operation of the pumps.