Applied Mechanics and Materials Vols. 578-579

Abstract: Wavelet basis selection is an important part in the wavelet denoising of structural vibration signal. However, some defects are present in the existing methods, such as large computation and a single optimal index. In order to solve these problems, a new selection method based on multiple index is proposed in this paper. Firstly, the wavelet basis category which suits for the vibration signal denoising is determined by analyzing the characteristics of wavelet basis and vibration signal. Then, a multiple index evaluation function is constructed by mean square error indicator (MSE), signal-to-noise ratio indicator (SNR) and correlation coefficient indicator (ρ), the weights of index are received by analytic hierarchy process (AHP), the wavelet basis with biggest evaluation function value is considered as optimal wavelet basis. At the end of the paper, a experiment is provided to verify the effectiveness of the new method, the results show that the new method is better than the other four methods in MSE, SNR and ρ index.

Abstract: There is little research on health monitoring technology of coastal ports at present. Based on the characteristics of high-piled wharf in coastal ports and staying in particular environment, the mechanical properties of coastal high-piled wharf is analyzed, and the health monitoring parameters are proposed. Finally, the health monitoring system of coastal high-piled wharf is constructed. And the appropriate structural health monitoring system is designed for standardized front segment of a high-piled wharf in the Tianjin port. The monitoring parameters are proposed, and the sensors and specification parameters are provided to reach the point. The data acquisition and transmission subsystem implementation technology and related indicators are given. This can provide a reference for the long-term health monitoring system construction in coastal high-piled wharf structure.

Abstract: In this study, the Tabu search (TS) algorithm is introduced into the optimal sensor placement (OSP) problem in the field of the structural health monitoring and moving force identification. A TS-based OSP procedure is proposed and further evaluated by some numerical simulations on a 2D planar truss model. The mean values of off-diagonal elements in a modal assurance criterion (MAC) matrix are used as the optimization objective function. Based on the criteria of MAC, determinant of fisher matrix, matrix condition number, and the least mean square error, the TS-based OSP procedure is evaluated through comparing with ones due to both of the energy coefficient-effective independence (ECEFI) and the effective independence (EFI) algorithms. The results show that the proposed TS-based OSP procedure is feasible with a higher accuracy.

Abstract: This paper has been prototyped fine 1:20 scale model of the finite element numerical simulation analysis of each parameter sensitivity test conditions, based on similar principles of dynamics, through the production of about 1/20 the proportion of prototype scale model of the bridge, dynamic characteristics of research conducted scale model of finite element analysis, and study whether there are cracks in the presence of dynamic response mode model, summarized the structure of the bridge structure in a given period reflect the physical characteristics of the local sound voiceprint and bridges under the geometric structure of the physical parameters of a period of time to maintain the basic stability conditions, the "voiceprint" has a high probability of stability.

Abstract: This article took gravity wharf engineering as the object of study to explore its deformation law by using GPS positioning technology. First, we will introduce the layout of a GPS control network at the wharf and then monitor the displacement of the gravity wharf through GPS-RTK、DBS-RTK and GPS static positioning technologies separately. Comparing three groups of monitoring data, we came to the conclusion that this gravity wharf is very stable, which has also proved the feasibility to apply GPS positioning technology to the displacement monitoring of the gravity wharf.

Abstract: According to the regular pattern of the grid structure truss, learning from the methods applied to composite damage detection, for grid structure, the paper proposed the concept of the amplitude matrix which comes from cross-correlation function of response signals. A corresponding amplitude distribution map can be obtained. The injuries in different position bring different amplitude distribution maps. The damage area would be determined by comparing these maps with the map derived from intact structure.

Abstract: In order to meet the demand of video detection and fast repair of cracks on large submerged structure in different depths, this paper designed an ultrasonic cleaning device with adjustable power. A hydraulic pressure sensor collects the pressure signal in the place to be detected in real time and then sends it to the MCU to deal with. This device will adjust the duty ratio of ultrasonic signal synchronously according to different signal of depth, while making the ultrasonic cleaning head work under the rated output power, so as to avoid the surface damage of building material and achieve the balanced cleaning effect. By testing in different water depths from 0 to 4 m, this device can well meet the submerged cleaning demands. It provides a good reference to design ultrasonic cleaning devices for greater depth range underwater.

Abstract: In this study, a two step damage prognosis method is proposed for beam-like truss structures via combining modal curvature change (MCC) with modal strain energy change ratio (MSECR). Changes in the modal curvature and the elemental strain energy are selected as the indicator of damage prognosis. Different damage elements with different damage degrees are simulated. In the first step, the finite element method is used to model a beam-like truss structure and the displacement modes are got. The damage region is estimated by the MCC of top and bottom chords of a beam-like truss structure. In the second step, the elemental MSECR in the damage region is calculated and the maximum MSECR element is deemed as the damage element. The simulation results show that this method can accurately locate the damage in the beam-like truss structure.

Abstract: A new damage identification method for arch bridge structures under a moving load based on the difference of deflection is presented. The function of the deflection at the mid span of the arch with the changing positions of the moving load is derived using the Moore integral method. It can be concluded from the results that when the moving load is in the area without damage, this target indicates to be linear functions with the cosine of an angle (θ) between moving load and horizontal. Nevertheless, this target is multinomial with the change of cosθ in the damage area. In order to validate the proposed damage detection algorithm, a steel arch modal is simulated, which is proved to be practicable in projects. The results indicate that the location and degree of single damage can be identified accurately.

Abstract: Both Stepwise Regression (SR) and Partial Least Squares Regression (PLSR) can be applied in data analysis of dam security monitoring, and achieve in fitting and forecasting. However, SR and PLSR models still can be optimized. A variety of programs are studied and compared based on actual dam security monitoring data. The results show that the optimized-model is better in fitting and forecasting the monitoring data.