基于分布式应变传感的冲刷监测研究

发布时间：2018-06-30 20:23

本文选题：冲刷 + FBG　；参考：《东南大学》2015年硕士论文

【摘要】：在水利、给排水、海河岸堤坝防护、桥梁、海洋平台等工程中,水流的冲刷对结构造成破坏的现象相当普遍。结构的地基往往由于水流的冲蚀而使得其强度降低,给结构的安全带来隐患。冲刷是导致桥梁水毁的一个主要原因,世界各国每年都有许多桥梁因洪水的冲刷而毁坏,而且因为水流的冲刷都发生在水下,一般很难及时发现。冲刷深度的监测对于水下结构的安全非常重要,因此,最近几年,学者们积极致力于开发各种传感器来监测冲刷深度。在前人的研究基础上,本文基于分布式长标距光纤光栅(FBG)传感技术,开发了一种新型简单的冲刷传感器,并从应变变化和频率变化两个方面验证冲刷传感器监测河床冲刷深度的性能。主要研究内容如下：(1)简单介绍了光纤光栅传感技术的传感原理、长标距FBG传感器的制作工艺和封装方法,并对封装后的长标距FBG传感器进行了基本性能的测试。封装后的长标距FBG传感器能够适用于恶劣的工作环境且具有良好的动静态测试性能。(2)利用长标距FBG的传感原理,开发了一种新型简单的冲刷传感器。当冲刷深度监测的概念是基于量测埋入河床中纤维增强复合材料(FRP)直杆的应变变化时,FRP直杆上须粘贴一个长标距FBG传感探头阵列。水流使得弹性FRP直杆在河床与水的交界处应变变化区别较大,通过河床上方和下方传感器中FBG的波长特征可以判断河床与水的交界面的高度,从而得出冲刷的深度。当冲刷深度监测的概念是基于量测埋入河床中FRP直杆的频率变化时,FRP直杆上只须粘贴一个长标距FBG。河床经过冲刷后,弹性FRP直杆露出河床部分将增大,进而导致直杆振动特性如自振频率随之改变。通过测试传感器的时程信号计算其固有振动频率,不仅可以判断有无冲刷,还能确定冲刷深度。(3)通过演绎推导,以附加质量法为基础,得出了水下结构与水耦合振动自振频率的求解公式。利用有限元软件ANSYS对水下结构进行模态分析,得出水下结构自振频率比无水时要小,水对其影响不可忽略。但是水下直杆的自振频率与悬臂长度的关系变化趋势和无水时是一致的。(4)通过水槽试验,对新开发的冲刷传感器进行了测试。水槽中填满黄沙模拟河床,试验通过水泵使水在水槽中循环流动,模拟河床的冲刷,应用新开发的冲刷传感器对某一时刻的冲刷深度进行监测。通过试验可以证明,基于两种监测概念开发的冲刷传感器均具有对河床冲刷进行实时监测的能力。
[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.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U446;U442.32

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