Akinori Nakata

SCALE MODEL EXPERIMENT ON INTERNAL FLOW OF SELECTIVE WITHDRAWAL EQUIPMENT WITH ELEVATING RUBBER SHEETS

This paper presents results of a scale model experiment on internal flow field of newly developed selective withdrawal equipment with elevating rubber sheets. In order to clarify the flow pattern, a visualization-measurement was conducted using a 2-D PIV system. Horizontal and vertical cross sections of the flow field were measured under different conditions of the flow rate and the depth of the intake. The obtained data were described in the form of the vector map, and a generation limit of the airentraining vortex was also shown. These results will be utilized for validation of prediction models using CFD.

Gradient-based PIV using Neural Networks

Conventional PIVs are not always capable of measuring the entire field of two-dimensional flow in rivers and oceans as they often contain an insufficient amount of tracers. However, Gradient-Based PIV using Neural Networks is potentially able to perform these field measurements. In a previous study, we evaluated its usefulness using artificially generated images. Here we apply this method to surface velocity measurements of experimental open channel flow. The open channel was filled with water and its flow was 100mm wide and 40mm depth. The flow rate was kept at a constant value of 60cm3/s. Floating tracers were used to measure the surface velocity. Several images were taken with the tracer population ranging from 18% to 81% of the water surface. The obtained velocity data were compared with those produced by conventional PIVs. As a result, it was found that Gradient-Based PIV using Neural Networks is capable of observing two-dimensional flow even when the tracer population is 18% of the water surface.

Effects of Weir Plate Inclination Angle on Flow-Induced Vibration of Long-Span, Shell-Type Gates.

Here we present detailed experimental results concerning flow-induced vibrations of long-span, shell-type gates in which the upstream gate face consists of vertical and inclined skin plates (also referred to as weir plates). Such shell-type gates possess two degrees-of-freedom, one each in the streamwise (horizontal) and vertical directions, due to bending flexibility in those two directions.The streamwise and vertical vibrations can become closely coupled with each other through the hydrodynamic forces acting on the weir plates, resulting in severe self excited vibrations. A two-dimensional laboratory model of a long-span, shell-type gate was operated with underflow only (i.e., no overflow) at small gate openings with several different inclined weir plate geometries, ranging from a 17.5°to a 65°inclination angle (relative to the horizontal) for the inclined weir plate. By measuring the gates vertical and horizontal displacements, it was possible to determine the vibration frequency, the excitation ratio (negative damping ratio) and the trajectories of gate motion. These results show that inclination angle of the inclined weir plate angle plays a significant role in determining the gates susceptibility to this type of dynamic instability. Long-span, shell-type gates with an inclined weir plate angle of about 60°relative to the horizontal were found to be the most unstable.