Hirokazu Hirano

An Optimal Control Analysis of Water Pollution Problem

This paper presents an optimal control analysis applied to water pollution control using a combination of the finite element method and optimal control theory. A numerical model of water pollution can be expressed in terms of the linear two-dimensional shallow water and convection diffusion equations. These equations can be solved by the explicit Euler scheme. The method presented by Sakawa-Shindo is effectively used to implement the control theory. Considering the closed water region such as a lake or a coastal sea, into which some river is flowing, it is shown that the pollutant level in this region can be controlled by controlling the inflow velocity of the river. This paper describes the water pollution control problem with the use of inequality constraints.

Aerodynamic Characteristics of Rectangular Cylinders

Three and two-dimensional simulations of unsteady flows around a rectangular cylinder sectioned object are carried out by means of the IBTD + FS Finite Element technique without the use of a turbulence model. The three-dimensional simulations confirmed that the aerodynamic characteristics of a rectangular object with a side ratio of breadth/ depth (B/D) of 4.0 are in good agreement with the experimental result. We have succeeded in simulating the detailed behavior of the shear layer and the vortex motions around a rectangular sectioned object. The relationship between the structure and aero dynamics of rectangular sectioned objects is also investigated.

The Numerical Simulation of Snowdrift Around a Building

In this paper, we suggest a numerical simulation method of snowdrift. Two-dimensional numerical simulation method was first examined by comparison with the wind tunnel experiments. We found that the prediction method had the sufficient accuracy. Next, the simulation method was expanded to the three-dimensional simulation method. The simulation of snowdrift for the actual building was conducted to verify the applicability of the method. It became clear that the numerical simulation method was a useful tool to predict the snowdrift around the building.

Three Dimensional Numerical Flow Simulation Around Parallel Rectangular Cylinders

Abstract Noises of flow around parallel rectangular cylinders are likely to be caused by wind flow. According to the wind tunnel experiment, it is known that there are three kinds of special noises. Two kinds of noises occur when the wind comes from a perpendicular direction to the cylinders. These noises are caused by the vortex excited oscillation. Another noise occurs when the wind comes from an inclined direction to the cylinders. This noise is very high frequency, and its mechanism is not clear. Therefore in this study, the three dimensional numerical flow simulation is performed to clarify the high frequency noise of flow around parallel rectangular cylinders.

THE DEVELOPMENT OF A METHOD TO REDUCE LOW-FREQUENCY NOISE IN STEEL GIRDERS

鋼桁の構造物振動に伴い発生する30Hzから200Hz域の比較的低い騒音を低減するために, 振動している橋体部材にゴムと鋼板とからなる複合材料を直接付加する工法を開発した. この工法を用いて試験施工する機会を得て不快な低音域騒音を低減することができた. さらに施工の簡素化による工期短縮, 工費低減をも実現したので開発経緯と施工技術の両面で報告を行う.

Numerical Fluid Flow Analysis for Aerodynamic Response Characteristics of Tandem Circular Cylinders

The aerodynamic characteristics of tandem cables of cable-stayed bridges have become an increasingly serious problem with increments in span length. In order to reduce the construction cost and maintenance of cables, tandem cables have been adopted for cable-stayed bridges. These cables, however, have aerodynamic response characteristics such as wake-galloping. Therefore, a method to suppress wake-galloping in tandem cables is required. The purpose of this study is to investigate the characteristics of the wake-galloping phenomenon of tandem cables of cable-stayed bridges using numerical fluid flow analysis. The flow around the oscillating tandem circular cylinders modeled on tandem cables is calculated. The flow field is treated as an incompressible viscous flow. The Arbitrary Lagrangian-Eulerian (ALE) method is employed to solve the flow field around the cylinders, and the three-step Taylor-Galerkin method, which is based on a fractional step finite element method, is adopted for discretization.