Sensor arrangement scheme design is the most basic and key link in structural health monitoring, a good sensor arrangement scheme not only meets the requirements of structural health monitoring, but also needs to reduce the cost as much as possible to get the true response of the structure by minimizing the influence of errors such as noise, etc. as well as the requirements of the field environment.
In order to solve this problem, this paper proposes a method of optimal sensor placement based on modal confidence matrix. According to the modal matrix of the structure, the modal confidence matrix of the structure is calculated. Based on the principle of modal observability, the maximum value of the non diagonal element in the modal confidence matrix is selected as the evaluation standard, and the sensor layout scheme is optimized by iterative method. The specific operation steps are as follows:1)Determine the number of modes needed to be identified and the number of sensors needed for structural health monitoring, and determine the positions of all available measuring points according to the site environment; 2)Select a group of initial sensor measuring point layout. The initial measurement point scheme can be determined according to experience, which is less than the number of modes to be identified. The modal confidence matrix corresponding to the group of measuring points is calculated and the corresponding value of the largest non diagonal element is recorded; 3)Select one of the remaining optional measurement points to add to the current measurement point layout scheme, calculate the modal confidence matrix corresponding to the new measurement point scheme, and record the largest non diagonal element in the modal confidence matrix; 4)Replace the selected measuring points, repeat the calculation steps of the modal confidence matrix and record the maximum non diagonal elements. Repeat this step until all the points to be selected have been calculated. Compared with the maximum value of the non large diagonal elements of the modal confidence matrix corresponding to all the alternative test points, the smallest maximum non diagonal elements of the modal confidence matrix corresponding to the test points are selected to add to the current test point layout scheme; 5)Repeat steps 3) and 4) until the sensor measurement points and the maximum non diagonal element of the modal confidence matrix meet the requirements. For some complex structures, the maximum non diagonal element of the modal confidence matrix is less than 0.25.
According to the above methods, this paper takes the beam string structure as an example to establish the numerical model, and simulates the actual engineering environment, and carries out the trial calculation of the optimal arrangement of sensors. After trial calculation, the convergence of this method is good and the feasibility of calculation is high; it can effectively reduce the economic cost of sensor arrangement, reduce the influence of error factors, and improve the effectiveness and accuracy of modal identification. And according to the trial calculation of the example, this paper proposes:the iterative process of the step-by-step accumulation method can be divided into three stages:fast descent stage, stable stage and iterative end stage. The actual sensor arrangement scheme should be selected in the stable stage process to avoid using the results of iterative end stage as much as possible.