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2021 Vol. 41, No. 9

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2021, 41(9): .
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Mechanical Engineering
Quantitative Study on Influence of Pulse Shaper on Split Hopkinson Pressure Bar (SHPB) Incident Waveform
REN Wenke, LI Wenfeng, WANG Jiangbo, XU Lizhi, GAO Guangfa
2021, 41(9): 901-910. doi:10.15918/j.tbit1001-0645.2021.010
Abstract(663) PDF(274)
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The pulse shaper is one of the most important means to achieve constant strain rate loading in split Hopkinson pressure bar (SHPB) test. In order to study the influence of pulse shaper on incident waveform, this paper took copper, brass, aluminum alloy as research objects. The experimental study on the influence of the diameter and thickness of the pulse shaper, the speed and length of the impact rod on the incident waveform was carried out on the 37 mm SHPB equipment. Moreover, combined with numerical simulation and dimensional analysis, the quantitative expressions of dimensional stress and dimensional time atT1andT2inflection points of incident wave are given. The dimensional stress atT1inflection point has linear relationship with dimensional parametersY/σ*, (d/Db)2and respectively; the dimensional time atT2has linear relationship with dimensional parametersh/LbandY/σ*.
Simulation-Based Optimization for Structural Deformation Compensation of Selective Laser Melting Process
LIU Jianhua, REN Ce, XIA Huanxiong, AO Xiaohui, LIN Shengxiang
2021, 41(9): 911-917. doi:10.15918/j.tbit1001-0645.2020.182
Abstract(520) PDF(220)
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Aiming at the deformation problem due to residual stress in the selective laser melting process, an optimization method for structural deformation compensation was introduced based on a finite-element simulation.Taking the forming of a propeller structure as a case study, a thermal-mechanical coupling macro-scale simulation model of the component based on the finite element method was first established, and the distribution characteristics of residual stress and deformation were analyzed lately.To obtain a finished part with a small enough shape error related to the desired geometry, an iterative method using the deformation field to adjust the initial design structure was proposed.Numerical experiment results show that, the maximum shape error between the finished propeller structure and the desired one cab be reduced by 94% after 4 iterations by the deformation-field feedback adjustment, in which it is also found that the residual stress and the real deformation of the finished part are essentially unchanged during the iterations.
Research on Real-time Emulator Based on Finite Element Analysis for Permanent Magnet Synchronous Motor
WANG Zhifu, SUN Qingle, LI Haolong, WANG Jun, SHEN Hongji
2021, 41(9): 918-926. doi:10.15918/j.tbit1001-0645.2020.094
Abstract(578) PDF(232)
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For three-phase permanent magnet synchronous motors, a power hardware-in-the-loop based real-time motor emulator was proposed.Firstly, a current-flux finite element back-lookup table model of permanent magnet synchronous motor based on three-phase stator coordinate system was proposed, and a mathematical model of the interface circuit was established.Based on this, the interface feedback control algorithm of voltage feedforward current was proposed, and a Fuzzy PI control algorithm was proposed for the current feedback link.Finally, a co-simulation experiment test method of Matlab/Simulink and JMAG-RT was used to simulate, analyze and verify the effectiveness of the proposed interface control algorithm and motor emulator.The simulation results show that, under rated conditions, the tracking error of the proposed interface control algorithm for the desired phase current can be less than 2%, and the emulation error of the proposed motor emulator for the motor phase current and speed characteristics can be less than 3%, verifying their effectiveness.
Research on General Characteristics of Hydraulic Torque Converter and Its Matching Method
MA Huichen, LIU Cheng, LI Juan, LI Jin
2021, 41(9): 927-934. doi:10.15918/j.tbit1001-0645.2020.156
Abstract(442) PDF(153)
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Based on the test data of a series of pump speeds and working conditions, a matching method based on the general characteristics of the hydraulic torque converter was proposed.This method was used to match engine with hydraulic torque converter.Firstly, error sources of the traditional matching method were analyzed.Secondly, this paper used the back propagation (BP) neural network, which is good at fitting and generalization, to establish a general characteristics prediction model of torque converter.The number of hidden layer nodes of neural network structure is determined.The comparison between the BP model and the traditional modification model indicated pronounced improvement with regard to performance prediction.Combined with the engine performance and the general characteristics matching model, it was found that the matching approach proposed in this paper was able to reflect the influence of pump speed on the matching conditions and improve the matching accuracy.
Aerodynamic Excitation and Vibration Analysis of Centrifugal Compressor Impeller under Dynamic and Static Interference
MA Chaochen, HONG Zhouzhensen, ZHANG Hong, WU Xintao
2021, 41(9): 935-942. doi:10.15918/j.tbit1001-0645.2020.109
Abstract(497) PDF(201)
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In order to study the aerodynamic excitation characteristics and vibration characteristics of the centrifugal compressor impeller, a unidirectional transient fluid-structure coupling model was established for calculation and analysis.The modal analysis was used to determine the resonant working condition of the impeller.Under this working condition, the unidirectional transient fluid-structure coupling calculation was performed.The time and frequency domain characteristics of the unsteady aerodynamic excitation on the impeller surface were discussed, when the impeller interacts with the intake elbow and the outlet volute.The time and frequency domain features of the impeller vibration under this aerodynamic excitation were further discussed.The results show that the main vibration components of the impeller during resonance are the vibration components at the fundamental frequency and the resonance frequency, the smaller aerodynamic excitation at the resonance frequency can cause a larger vibration amplitude;The dynamic stress and centrifugal stress at the leading edge of the long blade suction surface are relatively larger, therefore it is a dangerous point of fatigue failure, and the impeller is prone to generate fatigue cracks and occur fatigue fractures from here.
Informatics and Control
Photogrammetry and Application for Athlete Posture Measurement in Outdoor Competition
MA Shaopeng, HAO Xiaoran, WANG Shouxu, MA Qinwei, YE Xuezhou, YANG Xia, CHEN Xue, JIANG Liang, HUO Bo
2021, 41(9): 943-951. doi:10.15918/j.tbit1001-0645.2020.104
Abstract(467) PDF(213)
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To meet the needs of three-dimensional posture measurement under complex environments, using the non-contact camera measurement method and the specially designed observation equipment for winter sports, the data of 8 ski jumpers during the training process were collected. Firstly, the joint points of the athletes were identified and tracked based on a deep learning improved method. And then, the studies on athletes' attitude measurement and movement analysis were performed. Finally, the influence of the take-off speed of the athletes on the flight distance and the law of change of the main joint angle were analyzed. The results show that the take-off speed is an important factor affecting the flight distance. At the same time, the law of limb angle changes from takeoff to the initial flight stage has been obtained. The method and equipment can provide a new way for the measurement of athletes' posture and equipment motion parameters of various sports, and the observation results can provide the coaches with refined data to guide the athletes' technical movement.
Reliability Analysis on MEMS S&A Device Based on Bayesian Network
LOU Wenzhong, ZHAO Yuecen, FENG Hengzhen, SUN Yi
2021, 41(9): 952-960. doi:10.15918/j.tbit1001-0645.2020.065
Abstract(467) PDF(199)
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With the continuous development of MEMS technology, higher requirements are put forward for the reliability of the MEMS safety system in the fuze. In order to solve the problem of incomplete reliability data of various institutions and depending mainly on a large number of experiments or expert experience in the current MEMS safety and reliability analysis, in this paper, analyzing the failure status of the MEMS safety system, a fault tree of the MEMS safety system was constructed and the reliability function of each key organization was calculated. Based on this, a reliability analysis method was proposed, transforming fault tree and Bayesian network. At the same time, the probability importance and structural importance were calculated for each failure mechanism, and the key optimization mechanism in the design of MEMS safety system was proposed from the perspective of reliability importance, and some calculation example analyses were carried out. Based on the MEMS processing technology, a MEMS safety system was produced, and the reliability experiment was carried out, proving the rapidity and accuracy of the calculation of this method.
Short-Term Power Load Forecasting Method Based on FI under the Impact of Epidemic
CHENG Zhiyou, ZHANG Yangfan
2021, 41(9): 961-969. doi:10.15918/j.tbit1001-0645.2020.200
Abstract(462) PDF(171)
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The sudden COVID-19 epidemic has caused a serious impact on power load. In order to effectively deal with the impact of the epidemic and improve the accuracy of short-term load prediction under the impact of the epidemic, a short-term power load forecasting method based on fear index (FI) under the impact of epidemic was proposed. Firstly, epidemic data was used to construct the FI, together with the time information, historical load and meteorological conditions as the input variables of generalized regression neural network (GRNN) model. And then a fruit fly optimization algorithm (FOA) was used to optimize the GRNN smoothing factor to improve the accuracy and stability of the predicted results. Finally, the model was used to make the prediction. The simulation results show that this method can effectively improve the accuracy of short-term load forecasting under the impact of epidemic and provide reference for short-term load forecasting under the impact of major disasters.
A Lightweight-Network-Based Segmentation Method for Eye Features
ZHENG Shuhua, NAN Ruoyu, LI Shouxiang, WANG Xiangzhou, CHEN Mengxin
2021, 41(9): 970-976. doi:10.15918/j.tbit1001-0645.2020.119
Abstract(532) PDF(251)
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To deal with the problem of accurate and fast recognition and detection of pupil and iris features with high-resolution eye images, a lightweight semantic segmentation network DIA-UNet (dual input attention UNet) was proposed based on the UNet framework. It was arranged that, a symmetric dual coding structure was adopted to obtain the features of the eye grayscale image and its contour image synchronously, the dual attention mechanism was used to carry out the feature filtering on the decoding end, and taking the deep fusion features as a semantic segmentation output. The test results from the CASIA-Iris-Interval and high-resolution pupil datasets show that, compared with other lightweight semantic segmentation networks, the proposed DIA-UNet can guarantee the accuracy of iris and pupil segmentation, while the number of network parameters is only 0.076 Million and the processing speed is up to 123.5 FPS.
High-Performance Hardware Implementation of Elliptic CurveCryptography Point Multiplication over GF (p)
GAO Wei, LUO Yixuan, LI Jiakun, WU Haixia
2021, 41(9): 977-984. doi:10.15918/j.tbit1001-0645.2020.216
Abstract(473) PDF(189)
Abstract:
Elliptic curve cryptography (ECC) over GF (p) has been widely used in IoT security devices. Due to the limited hardware resources and the requirements of high computing speed of the security devices, a high-performance hardware structure for ECC point multiplication over GF (p) based on an improved Left-to-Right point multiplication algorithm was proposed. The structure was arranged to use module multiplexing and instruction ROM to reduce hardware resource consumption and to use high-width arithmetic and logic unit to improve the speed of point multiplication. The resource usage implemented on Virtex-5 FPGA is 2684 LUT, 16 DSP, 4 BRAM. The clock frequency reaches 150.2 MHz and it takes 4.24 ms to complete a point multiplication. The comprehensive performance is better than that of other existing high-performance ECC point multiplication hardware designs over GF (p).
Endoscopic Image Enhancement Based on Retinex Theory
CHEN Yueyang, HE Xingkuan, LI Chenyao
2021, 41(9): 985-989. doi:10.15918/j.tbit1001-0645.2020.160
Abstract(423) PDF(211)
Abstract:
In order to solve the practical problems of low brightness, nonuniform illumination and low contrast of electronic endoscopy images, an enhanced algorithm based on Retinex theory was proposed. Considering the characteristics ofL1andL2norm of image difference and the actual demand of texture suppression for illumination, the optimization expression of Retinex theory was established. Based on variational method, the illumination component and reflection component of image were obtained and the illumination correction and detail stretching were carried out respectively. To improve the contrast of vascular images, the proportion of image color channels was adjusted with an improved logarithmic histogram. Matlab test results show that the algorithm can enhance the image of electronic endoscopy preferably. Compared with the same type of algorithm, the evaluation parameters can be improved with different degrees, showing a certain practical application value.
A Radar Jamming Recognition Algorithm Based on Convolutional Neural Network
LIU Guoman, NIE Xuna
2021, 41(9): 990-998. doi:10.15918/j.tbit1001-0645.2020.220
Abstract(763) PDF(273)
Abstract:
Jamming recognition is the premise of radar anti-jamming, but the recognition method based on characteristic parameters is greatly affected by noise. In addition, the feature extraction of parameters only can take place in a certain pulse repetition time, so it is difficult to identify some jamming signals with temporal relationship. However, the idea of using features to identify interference is feasible. On this basis, a jamming identification method was proposed, taking a cascade form to join two convolutional neural networks. Based on the Pseudo Wigner-Ville distribution of the signal, this method was arranged to use the single-period time-frequency image to complete jamming pre-classification and the multi-period composite time-frequency image to complete jamming fine classification, and to recognize eight typical jamming types, especially suitable for the pulling off jamming recognition. The experiment results show that the average recognition accuracy of eight kinds of jamming can reach up to 98% on the data sets generated in this paper.
Sentiment Analysis of Online Healthcare Reviews Based on Feature Weighted Word Vector
GAO Huiying, GONG Mengqiu, LIU Jiawei
2021, 41(9): 999-1005. doi:10.15918/j.tbit1001-0645.2021.001
Abstract(441) PDF(170)
Abstract:
A sentiment analysis method of online healthcare reviews based on feature weighted word vector was proposed in view of the professional, diverse and less normative features of online healthcare reviews. The Word2vec method was used to construct the word vector model, and the sentiment word set was extracted to improve the sentiment lexicon in the field of healthcare service. The dependency between subject words and sentiment words was identified according to the syntactic relations. The expected cross entropy factor was introduced to establish a feature weighted word vector model to analyze the sentiment tendency of online healthcare reviews. The experimental results show that the accuracy, recall rate andF1value of the expanded healthcare service sentiment lexicon are higher than those of the basic sentiment lexicon. After the introduction of the expected cross entropy factor, the sentiment analysis method based on the feature weighted word vector shows better effect in the SVM classification, which reflects its good utility in the online healthcare reviews mining.
Optics and Electronics
Ship Detection in SAR Images Based on Deep Feature Enhancement Network
HAN Zishuo, WANG Chunping, FU Qiang
2021, 41(9): 1006-1014. doi:10.15918/j.tbit1001-0645.2021.004
Abstract(483) PDF(196)
Abstract:
Aiming at the difficulty of ship target detection in synthetic aperture radar images, a multi-scale target detection framework based on deep feature enhancement network was proposed. Darknet53 was used to extract features from original images, and build a four-scale feature pyramid from top to bottom. A feature fusion structure based on attention mechanism was specially designed to connect adjacent feature layers from bottom to top, and rebuild enhanced feature pyramid. Then, the proposed method utilized the candidate region and its surrounding context information to provide a higher quality judgment basis for the detector to calculate the classification confidence and target score.The average detection precision of the proposed method on SSDD public data set and SAR-Ship self-built data set were 94.43% and 91.92% respectively. The experimental results show that the proposed network framework is reasonable and has superior detection performance.
Chemical Engineering and Materials Science
Preparation of Fluorinated Polyurethane and Property Analysis
ZHAO Yun, JIAO Xiaoguang, GUO Bingzhi, FENG Caihong, LÜ Yuzhen, JIAO Qingze
2021, 41(9): 1015-1022. doi:10.15918/j.tbit1001-0645.2020.108
Abstract(517) PDF(239)
Abstract:
Fluorinated polyurethane (FPU) was synthesized taking xylene as solvent, perfluoropolyether diol and isophorone diisocyanate (IPDI) as starting materials, and 1, 4-butanediol (BDO) as a chain extender.The fluorine content in the FPU was controlled by changing the content of the soft segment of perfluoropolyether diol.Polypropylene glycol (PPG) and isophorone diisocyanate (IPDI) were used as raw materials, 1, 4-butanediol was used as a chain extender to synthesize PU as a comparison.Characterizing the structures of PU and FPU, the influence of fluorine content on the thermal stability, mechanical properties, and hydrophobic and oleophobic properties of FPU was investigated.The results show that as-obtained FPU has higher tensile strength, and better hydrophobicity while maintaining the oleophobicity of the polyurethane.

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