Research on optimized layout of bridge sensors based on MAC stepwise addition and subtraction algorithm

The difference in the location and number of sensors induces the acquisition effect of structural state information in the bridge health monitoring system to a certain extent, which is also one of the most difficult problems restricting the development of bridge health monitoring technology. Based on the Modal Assurance Criterion, this paper took a cantilever simply supported beam as an example and adopted the Effective Independence method, Kinetic Energy method and QR decomposition method to optimize a sensor layout. Taking the number of sensors as 5, the layout and MAC matrix factors were analyzed by comparing the MAC matrix and its distribution diagrams obtained by different methods. The results showed that the stepwise subtraction method based on QR decomposition was the best. And by changing the number of sensor, it was found that the optimal number of sensor was 9. It was also found that the existing methods had the shortcomings of over-reliance on the selection of initial measuring points. In order to improve this defect, cyclic iteration of stepwise addition and subtraction was introduced, and an optimal layout method based on the stepwise addition and subtraction of the number of sensors was proposed. Through screening and optimization of this method, the average off-diagonal element in the calculation example was reduced from 0.118 to 0.006 to achieve the satisfactory optimization effect. At the same time, this method was employed to optimize the layout of a concrete continuous rigid-frame bridge with 9 and 19 sensors, and the results showed that the sensor layout was more uniform. Therefore, the proposed method provides the opportunity to obtain fair optimization results and to have a considerable engineering application value

Effects of mechanical vibration on bone – a critical review

The benefits of reduced treatment time and comfort for patients undergoing corrective dental treatment with devices gave rise to the creation and modification of long-standing treatment protocols. One of the protocols used for these purposes is mechanical vibration. Objective: This review aimed to study the effects of mechanical vibration on bone. Methods: Portal Capes (periodicos.capes.gov.br) database was searched using the keywords “vibration” and “bone” with no date limit. Based on the title and abstract, the first 50 relevant studies were retrieved. The measured frequencies were between 4 and 150 Hz. Regarding exposure time and the number of applications, the variation is so wide that the average or median would not represent a realistic sample pattern. Results: In the retrieved studies, 41 reported improvements in bone conditions. Research studies show that a reproducible protocol is being applied in most studies on the effects of mechanical vibration on bone tissue. Conclusion: There is stimulation of bone biology, regardless of species, in the sense of osteogenesis in individuals exposed to high frequency mechanical vibration. To improve research protocols on the effects of vibrations on the body, more studies are needed

Impact of shafting angle of F5 cold rolling mill on the dynamics of main drive system

In view of the torsional vibration problem of the main drive system of the F5 rolling mill in a steel plant, two sets of torque monitoring sensors were installed on the cross universal joint shaft on site. Through online monitoring, it is found that the torsional vibration frequency of the cross universal joint shaft is twice the rotational frequency of the drive system, and the vibration amplitude of the upper shaft is greater than that of the lower shaft. Considering the influence of the inclination angle of the cross universal joint shaft, the transmission system can be simplified as a multi-body dynamic model of a five-inertia spring-mass system. Combined with the effect of the rolling torque of the strip and the electromagnetic torque of the main motor on the main drive system, a simulation model considering multi-physics coupled torsional vibration was established MATLAB/Simulink. The simulation shows that the torsional vibration frequency changes linearly with the rolling speed, which is always twice the rotational frequency of the transmission system, and the vibration amplitude also changes with the rolling speed, consistent with the field test results. As the diameter of the work roll increases, the angle of inclination of the universal joint shaft decreases, and the value of the torsional amplitude of the system also decreases. When the inclination angle is not considered at all, the torsional vibration of the system disappears, it shows that the inclination angle of the cross universal joint shaft is the root cause of the double rotational frequency torsional vibration of the main drive system. Since the inclination of the cross universal joint cannot be eliminated, the simulation results show that the torsional vibration of the transmission system can be effectively reduced by using large-diameter work rolls and reducing the stiffness of the upper cross universal joint while increasing the stiffness of the lower universal joint. When the lower shaft stiffness increases to 1.3 times, the upper shaft stiffness decreases to 0.8 times, and the work roll diameter is 425 mm, the torsional vibration amplitude of the upper connecting shaft decreases by 22.3 % at the rolling speed of 1200 m/min

Application of clustering algorithms to detect abnormal state of pumping equipment

The article is devoted to detection of an abnormal and pre-emergency state of pumping equipment using clustering and anomaly search algorithms. A background for research is the need to search for and apply methods for assessing the technical condition and identifying emerging defects in an automated mode for a wide range of equipment that give results at an earlier stage than existing ones. To achieve this goal, we consider the use of machine learning methods to analyze the parameters of equipment operation over a certain time period in order to create an algorithm for detecting anomalies in data, which in this case will be signs of abnormal operation. This article discusses the application of clustering based on the k-means method. So, in this research three normal operating modes of pumping equipment were recognized in the synthesized data. Based on the analysis of the distribution of each measurement to the corresponding nearest cluster centroid, the maximum distance from each measurement point to it was determined, which further served as a criterion for classifying a certain measurement as data outliers. As a result of the analysis, five measurements were identified that correspond to the abnormal operation of oil pumping equipment. Also, the ranges of normal operation of the equipment were compiled for each of the measured parameters of its operation, which forms the threshold values for classifying the state of the equipment as an abnormal or emergency state. The proposed approach has such advantages as the possibility of full automation, adaptation to various operating modes of the equipment, no need to share data outside the pumping station, early detection of emerging defects and the onset of an emergency

Application of distance field-based algorithm to adjacent spline surfaces for composite structures boundary modeling

The complex boundary modeling required for simulating composite materials was applied to a broad range of problems, including surface overlap and gap. A novel method for the simultaneous fitting of adjacent spline surfaces based on a distance field has been devised. The fitting method for spline surfaces was constructed using offline spline surface, facet simplification, and residual solid reconstruction. The distance field-based approach of simultaneous fitting of neighboring spline surfaces included producing a distance field for a spline surface and then applying that distance field to nearby spline surfaces. There would be junction and separation issues if neighboring spline surfaces were fitted individually. By simultaneously fitting the nearby spline surfaces with the aid of the equivalence surface of the distance field, it was feasible to avoid overlap and gap

Application of A* algorithm in intelligent vehicle path planning

Path planning is one of the important directions in the field of intelligent vehicles research. Traditional path planning algorithms generally use Dijkstra algorithm, Breadth-First-Search (BFS) algorithm and A* algorithm. Dijkstra algorithm is a search-based algorithm, which can search to an optimal path, but the disadvantage is too many expansion nodes, which leads to insufficient search efficiency. BFS algorithm is a heuristic search algorithm, which reduces the disadvantage of too many expansion nodes and improves the search efficiency by heuristic function. A* algorithm is a heuristic search algorithm that combines Dijkstra’s algorithm and BFS algorithm, which has higher search efficiency and can search to an optimal path at the same time, but it is still lacking in the search mode and smoothness of the planned route. This paper first introduces the general path planning algorithm, then introduces and analyzes the A* algorithm, and proposes improvement measures for its shortcomings; finally, the executability and effectiveness of the improved algorithm are tested using simulation, and compared with the traditional A* algorithm, and the results show that the improved A* algorithm has good effect on path planning of intelligent vehicles

Multi-axis vibration test technology of satellite based on vector-fixture’s design and applications

Aiming at the problems that the three-direction uniaxial sequential vibration test cannot effectively simulate the real launch environment of the satellite, and the high cost of the multi-axis shaker and the limitation of engineering application, the multi-axis vibration test scheme based on vector-fixture is proposed. Taking the vibration magnitude of uniaxial vibration test on the satellite mounting surface as equivalent reference, the appropriate vector direction is determined to carry out vector-fixture design. By analyzing the multi-axial vibration test data of the real structure of a satellite, it can be seen that: The “satellite-fixture” mounting surface can reach the set vibration magnitude at low frequencies, and undertest occurs at high frequency due to structural resonance and other factors; By optimizing the control strategy, the degree of over-test and under-test in the three directions can be balanced. According to the mission characteristics and development cycle of micro-nano satellites, this paper provides an efficient vibration test scheme

Repetitive impacts recovering using variational mode extraction with constructed reference enhanced by improved blind deconvolution

The impulse and modulation characteristic of rolling bearing’ faulty signal is often very weak when early fault arises in rolling bearing or gears, and the main reasons are due to the signal attenuation caused by too long signal acquisition path and the interference of other multi-source vibration. In order to extract the weak feature accurately, a method named as variational mode extraction (VME) based on constructed reference enhanced by improved minimum entropy de-convolution (IMED) is proposed, which combines both the advantages of IMED in solving the influence of the long signal acquisition path and VME based on constructed reference in extracting the impulse and modulation characteristic of vibration signal. Firstly, IMED is used as signal preprocessing method to analyze the vibration signal of rotating machinery to eliminate the influence of long signal acquisition path and enhance the repetitive impulse characteristics. Then, reference signal is constructed according to the prior knowledge of the rotating machinery and input it with the output signal of IMED into the VME model together, and the output result of VME not only could further enhance the impulse characteristic of vibration signal, but also obtain the modulation characteristic simultaneously. Finally, envelope spectral or enhanced envelope spectral is performed on the output signal of VME and satisfactory fault features are extracted. In order to solve the shortcomings of traditional MED, an IMED based on D-norm is proposed which has higher computational efficiency and could extract multi-harmonic impulse features. In addition, VME based on constructed reference is proposed to improve the accuracy of VME in extracting the target signal. Feasibility and superiority of the proposed method are verified by one experimental case and one engineering case