利用能量積分變化法分析土石流運動之特性

Abstract

本文利用能量積分值方法，來分析土石流運動及特性。並將土石流流動的特徵頻率分為四部份，第一、二部份為土石流本身運動的特徵頻率，包含河水泥水流動及土石滑動摩擦的頻率：0~40Hz，以及土石相互撞擊的頻率：40~80Hz；第三、四部分是土石流通過產生的聲音頻率：120~160Hz及160~200Hz。 本文首先經由鐵球撞擊砂面的實驗，觀察能量積分值隨地聲探測器與撞擊點的距離改變的趨勢，並利用高速攝影機拍攝撞擊過程，與地聲探測器量測到的時域訊號及FFT轉換後的頻域訊號做比較。再利用相同的分析方法針對南投縣神木村愛玉子溪上的地聲探測器在七二水災土石流發生時所接收到的地聲訊號進行分析。首先分析單場土石流事件中，土石流特徵頻率範圍能量積分值的變化，確認利用能量積分值的變化的確可以反應土石流的流況及特性。接著再更進一步分析2004年7月2日整天的地聲資料，發現在已知的土石流事件中，能量積分值產生明顯的突然躍起現象，並由此推論未經紀錄的土石流事件，驗證了能量積分值方法是可行的物理方法。

By using Fast Fourier Transform, we transformed the data from time domain to frequency domain and integrate a range of frequency domain in order to obtain the accumulative energy curve and to analyze the debris flow event. First of all, we consider four ranges of characteristic frequency of debris flow which ranges from 0-40Hz, 40-80Hz, 120-160Hz and 160-200Hz. Secondly, we do the experiment by using an iron ball to hit gravels and use a high speed CCD to catch images. Then we compare the images with time domain signals and frequency domain signals. Finally, we analyze the geophone data from debris flow event occurred in Aiyuzi River, Nantou County on July 2, 2004 by using energy integral method. We integrate the energy between the specific ranges for a one minute and every 0.001 minute record. Then calculate the time increment. In this way, we obtain the variation of the energy integral of the characteristic frequency of debris flow per minute and every 0.001 minute. We use the variation to compare with the time domain signals and the CCD image. It is found that the result can pinpoint the properties of debris flow. We prove that the energy integral method is a practicable method and it may be used for debris flow warning in the future.