本文選題：沖刷 + FBG�。� 參考：《東南大學(xué)》2015年碩士論文

【摘要】：在水利、給排水、海河岸堤壩防護(hù)、橋梁、海洋平臺等工程中,水流的沖刷對結(jié)構(gòu)造成破壞的現(xiàn)象相當(dāng)普遍。結(jié)構(gòu)的地基往往由于水流的沖蝕而使得其強(qiáng)度降低,給結(jié)構(gòu)的安全帶來隱患。沖刷是導(dǎo)致橋梁水毀的一個主要原因,世界各國每年都有許多橋梁因洪水的沖刷而毀壞,而且因為水流的沖刷都發(fā)生在水下,一般很難及時發(fā)現(xiàn)。沖刷深度的監(jiān)測對于水下結(jié)構(gòu)的安全非常重要,因此,最近幾年,學(xué)者們積極致力于開發(fā)各種傳感器來監(jiān)測沖刷深度。在前人的研究基礎(chǔ)上,本文基于分布式長標(biāo)距光纖光柵(FBG)傳感技術(shù),開發(fā)了一種新型簡單的沖刷傳感器,并從應(yīng)變變化和頻率變化兩個方面驗證沖刷傳感器監(jiān)測河床沖刷深度的性能。主要研究內(nèi)容如下：(1)簡單介紹了光纖光柵傳感技術(shù)的傳感原理、長標(biāo)距FBG傳感器的制作工藝和封裝方法,并對封裝后的長標(biāo)距FBG傳感器進(jìn)行了基本性能的測試。封裝后的長標(biāo)距FBG傳感器能夠適用于惡劣的工作環(huán)境且具有良好的動靜態(tài)測試性能。(2)利用長標(biāo)距FBG的傳感原理,開發(fā)了一種新型簡單的沖刷傳感器。當(dāng)沖刷深度監(jiān)測的概念是基于量測埋入河床中纖維增強(qiáng)復(fù)合材料(FRP)直桿的應(yīng)變變化時,FRP直桿上須粘貼一個長標(biāo)距FBG傳感探頭陣列。水流使得彈性FRP直桿在河床與水的交界處應(yīng)變變化區(qū)別較大,通過河床上方和下方傳感器中FBG的波長特征可以判斷河床與水的交界面的高度,從而得出沖刷的深度。當(dāng)沖刷深度監(jiān)測的概念是基于量測埋入河床中FRP直桿的頻率變化時,FRP直桿上只須粘貼一個長標(biāo)距FBG。河床經(jīng)過沖刷后,彈性FRP直桿露出河床部分將增大,進(jìn)而導(dǎo)致直桿振動特性如自振頻率隨之改變。通過測試傳感器的時程信號計算其固有振動頻率,不僅可以判斷有無沖刷,還能確定沖刷深度。(3)通過演繹推導(dǎo),以附加質(zhì)量法為基礎(chǔ),得出了水下結(jié)構(gòu)與水耦合振動自振頻率的求解公式。利用有限元軟件ANSYS對水下結(jié)構(gòu)進(jìn)行模態(tài)分析,得出水下結(jié)構(gòu)自振頻率比無水時要小,水對其影響不可忽略。但是水下直桿的自振頻率與懸臂長度的關(guān)系變化趨勢和無水時是一致的。(4)通過水槽試驗,對新開發(fā)的沖刷傳感器進(jìn)行了測試。水槽中填滿黃沙模擬河床,試驗通過水泵使水在水槽中循環(huán)流動,模擬河床的沖刷,應(yīng)用新開發(fā)的沖刷傳感器對某一時刻的沖刷深度進(jìn)行監(jiān)測。通過試驗可以證明,基于兩種監(jiān)測概念開發(fā)的沖刷傳感器均具有對河床沖刷進(jìn)行實時監(jiān)測的能力。
[Abstract]:In water conservancy, water supply and drainage, sea bank embankment protection, bridge, offshore platform and so on, the phenomenon that the water flow scour causes damage to the structure is quite common. The strength of the structure foundation is often reduced because of the erosion of the water flow, which brings hidden trouble to the safety of the structure. Scour is one of the main causes of bridge water destruction. Many bridges are destroyed by flood every year in the world, and it is difficult to find them in time because the water scour occurs under water. The monitoring of scour depth is very important for the safety of underwater structures. Therefore, in recent years, researchers have been actively working on the development of various sensors to monitor the depth of erosion. Based on the previous research, a new and simple scour sensor is developed based on distributed long distance fiber grating (FBG) sensing technology. The performance of the scour sensor to monitor the erosion depth of the river bed is verified from the two aspects of strain variation and frequency change. The main contents are as follows: (1) the principle of fiber Bragg grating sensor, the fabrication technology and packaging method of long distance FBG sensor are briefly introduced, and the basic performance of the long distance FBG sensor after encapsulation is tested. The encapsulated long distance FBG sensor can be used in harsh working environment and has good static and static performance. (2) A new and simple scour sensor is developed based on the sensing principle of long distance FBG. When the concept of scour depth monitoring is based on the measurement of the strain change of fiber reinforced composite (FRP) rod embedded in the riverbed, a long distance FBG sensor probe array must be affixed to the FRP bar. The flow of water makes the strain variation of the elastic FRP bar at the boundary between the river bed and the water more obvious. The height of the interface between the bed and the water can be determined by the wavelength characteristics of the FBG in the sensors above and below the river bed, and the depth of the scour can be obtained. When the concept of scour depth monitoring is based on the measurement of the frequency change of the FRP bar embedded in the riverbed, only a long distance FBG should be affixed to the FRP bar. After the river bed is scoured, the elastic FRP bar will increase in the exposed part of the river bed, which will lead to the change of the vibration characteristics of the straight rod such as the natural vibration frequency. By measuring the time history signal of the sensor to calculate its natural vibration frequency, not only can it be judged whether there is scour or not, but also the scour depth can be determined. (3) based on the additional mass method, The formula of natural vibration frequency of underwater structure and water coupling vibration is obtained. The modal analysis of underwater structure with finite element software ANSYS shows that the natural vibration frequency of underwater structure is smaller than that without water and the influence of water on it can not be ignored. However, the relationship between the natural vibration frequency and the cantilever length of the underwater straight rod is consistent with that when there is no water. (4) the newly developed scour sensor is tested by the flume test. The water tank was filled with yellow sand to simulate the river bed, and the water was circulated through water pump to simulate the erosion of the river bed. The newly developed scour sensor was used to monitor the erosion depth at a certain time. The experiments show that the scour sensors based on the two monitoring concepts have the ability to monitor the river bed erosion in real time.
【學(xué)位授予單位】：東南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：U446;U442.32

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