論地聲能量在壩體中的傳遞

Abstract

土石流作為一種較為常見的自然災害，每次發生都會對工程和人們生活造成影響。為防止土石流造成的災害，人們在土石流的高發地修建堤壩，並建立觀測站對土石流進行監測預警。 地聲探測器（Geophone）是常用的土石流監測儀器之一，人們通過它的幫助在監測和預警土石流的方面已有了大量的成果。但地聲探測器（Geophone）通常埋設在堤壩內部，而聲波傳入堤壩後，會在堤壩內部的邊界上不斷反射，這使得地聲探測器（Geophone）所檢測到的振動信號是多個反射波疊加後的結果。而堤壩內多個反射波疊加產生的能量與土石流本身的聯繫，至今少有結論。本文嘗試從理論模型出發，探討地聲從土石流進入大壩過程中的特性，最終通過實驗進行驗證。 通過對以往文獻的回顧，確定了在實際應用當中，地聲探測器（Geophone）所採集的數據常選用振幅作為研究對象，在此基礎上更延伸出了時域分析、頻域分析和時頻域分析，同時得到了土石流產生信號所在的頻段。 為了得到理論模型中的振幅參數，本文在假設土石流介質是一種連續且各項同性的介質後，引入基礎的應力應變理論，從運動方程著手，推導出土石流介質中的波動方程。為了解算波動方程，本文分析了土石流介質上層和底層，以及大壩左右兩邊的邊界條件。以大壩的左右兩邊的邊界將介質劃為三個區域，通過分離變量和三角函數的正交推導出了三個區域之間波的振幅比。 為了驗證推導求得的振幅比，本研究通過實驗室水槽，模擬了土石流翻越大壩的情形，並用地聲實際測量了大壩前和大壩內部的振動信號。採集到的振動信號，以頻域和時頻域分析為主，與理論相結合，得到大壩前和大壩內的能量比值。並通過討論大壩的介質和寬度，得到了大壩介質遠大於土石流介質時，沒有信號能夠進入到大壩中，以及隨著大壩的寬度變寬，共振頻率將會向低頻移動的結論。

As a common natural disaster, debris flow will affect the engineering and people's life every time. In order to prevent the disasters, people build dams in the place of high incidence areas ,and set up observation stations to observe and warn debris flow. Geophone is one of the common instruments for observe debris flow.For it’s help,people has achieved a lot in observing and warning.However,Geophone is usually embedded in the dam, and the sound wave will reflect continuously on the boundary of the dam after it is transmitted into the dam.It causes that the vibration signal detected by the geophone is the reflected waves after superposition. However, there are few conclusions about the relationship between the reflected waves after superposition and debris flow. Based on the theoretical model,this paper wants to discuss features about sound wave entering from debris flow to dam.And finally it will be proved by experiment. After reviewing the previous literature, in actual event,the amplitude is often selected as the research object in the data collected by the geophone. On this basis,people find the time-domain analysis, frequency-domain analysis and time-frequency-domain analysis. At the same time,we get the frequency range of debres flow. In order to fine the amplitude in the theoretical model, this paper assumes that the debris flow is continuous and isotropic.And than,it derives the wave equation in debris flow from stress-strain theory and the motion equation.This wave equation will be solved by two kinds of boundary conditions.One kind is upper and lower layers of the debris flow,the other kind is left and right sides of the dam.The whole medium is divided into three areas by the boundary of the left and right sides of the dam and these three have different amplitude ratio.We need use separation of variables and orthogonality of trigonometric functions to solve it. The method of prove amplitude ratio we calculate,this paper also analysis the data from laboratory.Geophones are used in model of dam and riverbed to get data.And the signals are mainly analyzed in frequency domain and time-frequency domain.By calculating energy ratio,we contrast it with amplitude ratio from the wave equation. By discussing the medium and width of the dam, it is concluded that when the dam medium is much larger than the earth rock flow medium, no signal can enter the dam.And the resonance frequency will move to low frequency as the dam width becomes wider.