查看更多>>摘要：? 2022 Elsevier LtdUltrasonic technology has been widely used in uniaxial stress measurement for key components of steel structures. However, multi-dimensional stresses are described by the combination of unidirectional stresses of multi-directions, failing to reflect the true stress field inside the material. In this study, we proposed a measurement method theoretically and experimentally for average three-dimensional stresses on the cross-section of steel plates. We used ultrasonic T-waves and P-waves for stress separation and deduced the stress-acoustic relation for each stress component. The required phase velocity information was measured by the echo phase spectrum. The acoustoelastic coefficients (AECs) of eight steel specimens were experimentally calibrated. The center frequency of the transducer was selected as the optimal frequency based on calibration experiments, and the thicker the steel plate, the higher the fitting rate. Experimental verifications proved that the proposed method has good reliability on the laboratory scale.
查看更多>>摘要：? 2021 Elsevier LtdA high-resolution dynamic response is important for characterizing a system's dynamic properties. Measurements involving a limited number of points on the structure can be expanded to unmeasured points through approximation or model-based expansion techniques that rely on the introduction of a numerical model. Recently, an expansion method called System Equivalent Model Mixing (SEMM) was proposed where a numerical DoF set is used to extend an experimental model with limited measurement points. The concept of SEMM is similar to the well-known SEREP and VIKING expansion methods, but it is defined in the frequency domain. Using the dynamic substructuring approach, the equivalent experimental and numerical models are coupled so that the hybrid model inherits the dynamic properties of both models. Although the method has been well adopted, there is still no comprehensive phenomenological analysis to determine the influence of the method's parameters on the consistency of the hybrid model and thus on the accuracy of the expansion process. This paper addresses the issue by evaluating the accuracy of the SEMM expansion process, focusing on the influence of the regularity of the so-called equivalent numerical model. The introduction of quasi-equivalent numerical models into SEMM is analysed here, which can differ not only with respect to the mass and stiffness properties but also in terms of the geometry and boundary conditions. The parametric study was carried out on a real component of a household appliance, and the most influential parameters in terms of accuracy of the SEMM expansion process were identified. The analysis showed that accurate expansion results, with a small number of experimental points, is achieved if only those points are well scattered across the analysed system.
查看更多>>摘要：? 2021Feature selection algorithm based on the locally linear embedding (LLE) cannot effectively detect the changes in the neighborhood of data and cannot take full advantage of the graph-preserving ability. To address these issues, a novel filter method integrated LLE, named LLE vote, is proposed. In the proposed algorithm, we first construct two graphs of each feature through computing the local structure and sparse structure of data in high-dimensional manifold, and then a novel metric criterion is employed to rank the features by measuring the difference between the reconstructed feature and the corresponding original input. Extensive experiments are carried out on benchmark fault data set and the other kind of data from our own laboratory, and the experimental results not only demonstrate the effectiveness of the proposed method, but also indicate that the LLE vote outperforms the existing state-of-art methods.
查看更多>>摘要：? 2021 Elsevier LtdAccording to the World Health Organization (WHO), about 85 percent of the world's population suffers from back pain, the main cause being poor posture. Persistent lower back pain is found to be persistent in both the populations. The proposed solution is composed of flexible sensors that capture all the moves made by the spine, being able to identify postural deviations and help in postural reeducation. Using the Microsoft Kinect V2 sensor and photogrammetry, the body parts are identified, and their asymmetry is calculated. In this way, we support specialists in the diagnosis and treatment of postural changes. To validate the proposed approaches, students and physiotherapists performed various tests and compared the results obtained through traditional methods, showing that both the methods are showing promising outcomes to diagnose and treat diseases due to poor posture. Twelve exams were performed, to analyze the system's repeatability and evaluate the asymmetry of the limbs selected. As a result of the nine students evaluated, all the variations were between 0 and 1 centimeter, so it turned out to be efficient in evaluating the student's posture.
查看更多>>摘要：? 2021 Elsevier LtdRetroreflective films are often used to enhance ultrasonic motion sensing with laser Doppler vibrometry by increasing surface reflectivity of metallic and polymer structures. This study reveals that such a surface modification leads to undesirable effects, which manifest themselves in notable changes of observed structural elastodynamic properties. The provided analysis shows systematic changes in dispersion curves of fundamental and high order guided waves propagating in laminates and significant amplification of their attenuation. Therefore, to avoid mistakes and additional errors when interpreting results of such measurements, e.g., in application to ultrasonic material characterization, the presence of reflective films should be considered and properly quantified.
查看更多>>摘要：? 2021The research of the safety distance among drones and cable attracted wide attention with the rising deployment of unmanned aerial vehicle (UAV) to check for high-voltage overhead power systems. To increase the inspection operation's dependability and guarantee a safe and stable functioning of the transmission grid and inspections equipment, it is essential to determine the safety distance among the UAV and the driveway. Due to UAV patrol safety distances from overhead power lines, it is difficult to offer precise surfing information because of the lack of quantitative assistance. The author of the relevant study uses multi-sensor fusion data analysis (MFDA-LPTL). There have been discussions on the properties of large data sets, smart networks, and gigantic data sets before the emergence of low-cost power transmission lines and the benefits they may give. For example, using the adaptive weighted fusional method, which combines first-level data on homogenous sensor input based on critical UAV-influencing factors such as maximum inspection speed, wind speed, positioning error, and drone size, can help achieve this goal. As a secondary benefit, the theory makes use of more robust evidence than before. However, the use of big data analytics in present smart grids must be expanded due to numerous challenges, such as the need for new technologies and increased public awareness. The experimental analysis shows that the proposed MFDA-LPTL model increases the performance ratio of 98.9%, efficiency ratio of 97.2%, reduces the detection failure analysis of 10.2%, processing time of 7.8%, positioning error rate of 12.3% compared to other existing methods.
查看更多>>摘要：? 2021 Elsevier LtdSegmentation of region of interest (ROI) is an important content in automated optic inspection (AOI). Aiming at the segmentation of ROI corresponding to various defects on the corrugated sheet of plate heat exchanger (PHE), a method based on discretization - recognition strategy is proposed. Corrugated sheet is a large complex curved surface. We find a way to regard it as a combination of several inclined planes and noncontiguous horizontal planes innovatively. Through using a typical AOI coaxial imaging system, the image marked by different gray values is obtained firstly. The inclined plane region is segmented according to the gray feature. Each horizontal plane region is discretized at the same time. Then, a method based on web crawler is proposed to recognize the specific category of each horizontal plane region. Finally, the surface of the corrugated sheet is divided into four types–inclined plane, high horizontal plane, middle horizontal plane and low horizontal plane. The experimental results demonstrate the great effect.
查看更多>>摘要：? 2022 Elsevier LtdTimely and effective identification of track surface defects is helpful to improve the safety of railway operation. However, the complex service environment leads to the diversity of defects, and it is difficult to realize automatic identification. Therefore, an improved residual network feature extraction module is proposed, and a framework of track surface defect identification is constructed. To be specific, the overall framework and the core method are described in detail at first. Then, the optimal training parameters are determined through experiments, and the performance of different feature extraction modules is further compared. Finally, the performance of the proposed framework is verified by experiments using multi-class images. The results show that the average identification accuracy is 94.45%, the average frame speed is 0.000052 s. Correspondingly, the feature identification model adopted in this paper offers Accuracy of 97.09%, Loss of 0.0773 and RMSE of 0.06. The proposed model yields strong robustness.
查看更多>>摘要：? 2021BaTiO3-MLCC has the characteristics of unstable output voltage under high impact, which may lead to signal distortion and even failure of the electronic system. In this study, we aim to explore the dynamic output voltage characteristics of board level mounted BaTiO3-MLCC under high impact. A mechanical-electric effect modeling method of BaTiO3-MLCC dynamic output voltage based on dynamic model and piezoelectric effect is proposed. The high impact experimental study has been carried out, the results show that the dynamic output voltage curve of BaTiO3-MLCC and the dynamic strain curve of PCB at the installation position accord with the sinusoidal oscillation law of exponential attenuation. The characteristic frequencies of dynamic voltage curve completely include that of dynamic strain curve, and their fundamental frequencies are the same. These laws are the same as those characterized by the mechanical-electric effect model, which proves the feasibility and correctness of the proposed mechanical-electric effect modeling method.
查看更多>>摘要：? 2021 Elsevier LtdSteam dryness monitoring is significant for high-efficiency steam turbines used in power generation and boilers. Although steam dryness is a crucial process variable, Mohr titration involves expensive and complex calorimeter equipment and considerable time and effort. This paper proposes an online fully-automatic high precision steam dryness monitoring system. The automatic determination of titration endpoint using the optical method, vital steps for this system, was discussed. The design shows high repeatability and precision (about 1% at 300 mg/L). The system also has high linearity, and the R2 is 0.9999. The limit of the detection is about 15 mg/L. The measuring time is about 2 min for one measurement, which is much faster than manual titration. Thirty-eight water samples collected were tested, showing an excellent anti-interference characteristic.
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