非均勻底床坡度明渠之不恆定流數值模擬

Numerical Modeling of Unsteady Flow in an Open Channel with Non-constant Bottom-slope

林孟毅(Mong-Ie Lin)

指導教授 ： 蔡丁貴

共同指導教授 ： 賴經都

國立臺灣大學/工學院/土木工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.01349

摘要

在明渠水力學中，有關底床坡度變化（bottom-slope change）的研究一直是河川水利工程師的焦點。當遇到此種底床坡度變化時，流況可包括在亞臨界流（subcritical flow）與超臨界流（supercritical flow）之間轉變，即穿臨界流（transcritical flow）。由於底床坡度變化所造成水流變化，特別是穿臨界流，成為一高度困難且具挑戰性的問題。以往僅在恆定流況（steady flow state）下且較為簡單的渠道形狀得以求解。關於不恆定流（unsteady flow）此類屬於非線性微分方程領域的複雜問題，也只有在電腦問世之後，才能以數值模擬的方式描述其流況。本文主要目的為設立一可演算不恆定流通過渠道底床坡度轉變的數值模式，並將其以四種基本的底床坡度轉變進行測試一系列之不恆定流流況之應變。之前，由本模式計算之恆定流況結果與傳統方法結果先做仔細的比較以確保模式之可靠性。由上述研討，相信本模式之模擬結果可提供一些有用且寶貴的洪波沿各種不同底床坡度向下游傳播之指南。

關鍵字

不恆定流 ； 多方式特徵線法

並列摘要

The study of open channel flow with changes in the bottom-slope has been a focal point of some river-mechanics engineers. When encountered with such bottom-slope changes, the engineers may witness the flow varying between subcritical and supercritical states, which is commonly known as the transcritical flow. The analysis of flow variation due to the bottom-slope change, with the transcritical flow in particular, poses a highly difficult and challenging problem. In the past, it permitted solutions only under relatively simple channel configurations and under the steady flow state. The analysis of unsteady flow, which is a very complex phenomenon normally described by nonlinear partial differential equations, has become numerically attainable only after the computer coming into existence. The purpose of this thesis is to prepare a numerical model which can compute unsteady flows in a channel with changes in the bottom slope, and subsequently to put the model to a series of flow tests under four basic forms of bottom-slope transition. Before this, the results from a set of steady flow cases using the present modeling method have been compared carefully with those by the traditional method in order to ascertain the model reliability. It is believed that the modeling study made in this thesis can afford useful guidelines for the flood wave moving down river channels having various bottom-slope changes.

並列關鍵字

unsteady flow ； mmoc

參考文獻

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