2020 volumne 41卷 Issue 02
ZHANG Jiankang, ZHAO Youyou, SHANG Yingbo, MU Xiaomin
Abstract: The existing channel estimation algorithms have witnessed the disadvantages of high estimation error due to the fast time-varying channel and large propagation delay in the aeronautical communication system. This paper proposed an feedback iterative channel estimation algorithm based on the two-path Rice channel model for the en-route scenario. The proposed algorithm only used a small pilot overhead for rough least square (LS) channel estimation and signal detection, after being modulated and encoded, the obtained signals were fed back to the channel estimator used as pilot symbols again. Finally, the proposed scheme was capable of converging to a stable performance with two iterations. The simulation results demonstrate that the proposed channel estimation scheme was capable of achieving about 2 dB mean square error when the signal-to-noise ratio (SNR) was less than 20 dB, which verified that this algorithm could improve the accuracy of the aeronautical channel estimation.
Wei Hongbin,Zhang Duanjin,Du Guangming,Xiao Wenfu
Abstract: The queuing and weighing problem was common in bulk vegetable area of supermarket. If weighingequipment could automatically recognize vegetable, it would effectively improve the operational efficiency ofsupermarket. Therefore, a vegetable recognition method based on improved YOLOv3 was proposed. Firstly ,vegetable pictures were collected by using high-definition camera and web crawler technology. Secondly, 15groups of anchors suitable for vegetable datasets were obtained by K -means clustering analysis. Thirdly, a newbounding box regression loss function DIoU was proposed to improve the precision of detection task. Finally, asthere were many large objects in vegetable datasets, 5 groups of feature pyramids with different scales were ob-tained by enhancing feature extraction network to realize vegetable detection task. The mAP of the improvedYOLOv3 algorithm on the test dataset was 93. 2%, and the recognition rate was 35 fps. This method improvedthe recognition of mAP while guaranteeing real-time object detection.
Wang Zhu,Liu Chunlong,Luo Qinghua
Abstract: The accuracy of flow measurement could be affected by the consistency of the pair of ultrasonic sen-sors. In view of the problem of poor consistency of different ultrasonic sensors, this paper aimed to analyze theinfluence of several closely related parameters , and provide theoretical basis for the selection of the pair of sen-sors used in the same flowmeter. At the same time , the transmission line method , alternative method and vari-able frequency excitation signal were used to realize the test of ultrasonic sensors, and the specific circuit de-sign method to realize the test was given. The experimental results showed that the proposed method was stableand reliable, and a pair of ultrasonic sensors with good test performance consistency could ensure the flowmeasurement accuracy.
Liu Huajun 1,Zhang Ruijue 2,Liu Jianfeng 2,Wang Sheng 2,Xiaqiao Bridge 1
Abstract: Most defogging systems mainly focused on single image , lacking in stability and real-time perform-ance. Besides, the traditional image haze removal algorithm had high complexity and the histogram of brightarea was overexposed, it was difficult to be applied to real-time video image restoration. Facing this problems ,a 1080P full-hd video image real-time enhanced defogging system based on FPGA was designed and constructed. At first , the histogram statistics was conducted in RGB color space by using blocks and dividing the chan-nels. And then, the combined histogram of multi-channel was clips at a predetermined value, thereby limitingthe contrast amplification. Finally, the bilinear interpolation is performed between the new histogram. We sim-ulated the improved CLAHE algorithm, and tested the system for foggy video, image and outdoor scenes. Ex-perimental results showed that the system can real-time process 30 frames per second 1 920x 1080 resolutionimages, compared with the mainstream methods, the defogging effect was better and more stable. The systempower was less than 5 watts, so it could be applied to low power consumption.
Bai Guochang,Yao Jiliang
Abstract: When the traditional sliding mode observer was used to observe the line back electromotive force( line back-EMF) of brushless dc motor ( BLDCM), a low-pass filter was required because of the excessivechattering of the system. However, the phase delay caused by the filter could not be accurately compensated ,resulting in inaccurate commutation. This paper proposed to apply the sigmoid function to the sliding modeobserver, and used its smooth and continuous characteristics to reduce chattering. At the same time, a variablesliding mode gain was deduced to further weaken the chattering of the system based on the Lyapunov theorem.Through these measures, the line back-EMF observations observed could directly determine the commutationsignal. The simulation and experimental results showed that the improved sliding mode observer reduced thepeak value of line back-EMF observation errors at 400 r/ min and 3 000 r/min by 70% and 54. 8% respective-ly, obtained more accurate commutation signals, and improved the brushless de motor positionless control sys-tem performance.
Gao Xianglin,Wang Jianming,Wang Yan,Li Bozhi
Abstract: Aiming at the prediction of weld fatigue life of moving components of scissors lifting platform, asimulation method of weld fatigue life of moving components based on BS7608 standard was proposed. Firstly ,the time-varying load at the hinge of the moving component is obtained by multi-body dynamics simulation a-nalysis. And the load was mapped to the local coordinate system of the component to be analyzed by coordinatetransformation. Then, the FEM model of the fatigue life prediction was established in the local coordinate sys-tem of the component to be analyzed. The modeling process involved the key problems such as reasonable se-lection of hinges to define the static constraints of displacement, and the application of time-varying loads onthe hinges in the local coordinate system. According to the S-N curve provided by BS standard, the fatigue lifedistribution of base metal and weld was predicted. The correctness and validity of this method were verified bythe fatigue test results. It shed new lights on the fatigue life prediction of weld of components with wide range ofrigid body motion.
Wang Gang1,2,Song Jian 1,2,Zhang Jianwei 3,Wang Bingbing 3
Abstract: Grain geometry models with inhomogeneity of microstructures and crystal plastic finite elementmethods ( FEMs) have attracted more attention over recent years. To obtain constitutive parameters , anisotropyelastic and plastic constants of 18CrNiMo7-6 alloy steel were studied by using a crystal plastic FEM with soft-ware ABAQUS. Further, based on a polycrystalline FEM, sensitivity analysis of plastic parameters was carriedout with a crystal ratio-dependent hardening model. In line with numerical calculations and tensile tests, a costfunction was proposed and applied to determine a set of optimal plastic parameters. The results provided neces-sary material parameters for analysis of uneven stress concentration induced by microstructures.
Liu Zhihua,Zhang Tianzeng,Yang Mengjian,Dai Qilong,Zhang Yinxia
Abstract: The performance and processing technology of surface modification layer of 18CrNiMo7-6 gear steelafter ultrasonic rolling were studied. The measurement instructions, such as 3D surface topography measure-ment system , microhardness instrument , super depth of field 3D microscopy system and high power X-ray dif-fractometer were used respectively, to observe the variation of surface modification layer of the sample. Theeffects of ultrasonic rolling process parameters on surface modification layer were studied by single factor test.The results showed that after ultrasonic rolling, the surface roughness of the specimen is decreased from theuntreated 3. 003um to 0. 468um. Significant work hardening formed on the surface of the material after ultra-sonic rolling. Surface microhardness increased by 22. T% from 360. 9 HV to442. 9 HV , and the high hardness layer reached 300 um. Flat surface appeared after ultrasonic rolling. The maximum residual compressive stressoccured at a distance of 40 um from the surface, which was about -790. 97 MPa. Ultrasonic rolling technology significantly improveed the properties of the modification layer.
ZHANG Zhigang, ZHOU Xiang, FANG Zhanpeng, XIAO Yanqiu
Abstract: The modeling method for the compliant rod with large deformation was studied by using absolute nodal coordinate method, and the rigid-flexible coupling dynamic equations of the compliant mechanism were established.Considering the deformation characteristics of the compliant rod at the external connection, the new ANCF beam element with end deformation constraints was proposed.Based on the locking alleviation technique, the effect of the locking phenomenon of the absolute nodal coordinate beam element on the dynamic simulation of compliant mechanism was investigated.Finally, numerical examples were given to verify the accuracy and effectiveness of the absolute nodal coordinate method for the dynamic problems of compliant mechanisms.
Qin Shengwei,Zhang Yufang,Zhang stick
Abstract: Based on DEFORM-HT software, the gas carburizing process of 18CrNiMo7-6 steel was numerically simulated: the influence of two different diffusion coefficient models on the carburizing process of alloy steel was studied, that is, the model D(T, C) and the model D(T, M, C) considering temperature, alloy elements, and carbon atoms; and numerical simulation and experimental verification of three carburizing processes with different carburizing layer depths. The distribution of carbon content along the depth of the three carburizing processes was measured by the mechanical stripping method, and compared with the simulation results, it was found that the simulation accuracy of the D(T,M,C) model was higher; but when the carburizing layer depth reached When the thickness is 4 mm, the test results of the surface carbon content are quite different from the simulation, which is because elements such as Cr and Mo combine with carbon atoms to form a large number of carbides during the long-term carburizing process, which reduces the diffusion coefficient of carbon atoms. At the same time, the surface carbon content of the sample reached 1.0%, which was higher than the ambient carbon potential of 0.8% in the last stage of the carburizing process.
Zhang Jian 1,Zhang Yuxiao 1,Strong Bear 2,Zhu Yongsheng 3,Xie Jiaxin 1
Abstract: Aiming at the influence of the high penetration rate of distributed power generation on the stable operation of distribution network, a method of analyzing the coordination and optimization of voltage and reactive power on the demand side by adding demand response is proposed. Based on the models of interruptible and transferable loads, a distribution network voltage and reactive power coordination optimization model considering demand response is established; and the original mixed integer nonlinear model is linearized by the second-order cone method, and a mixed integer second-order cone programming model is established ; Analyze the effects of demand response on voltage reactive power and grid stability before and after. The results show that the established model can effectively accommodate distributed energy, improve energy utilization, reduce system operating costs and significantly improve voltage.
Jia Rubin,Gao Jinfeng
Abstract: The dissolved gas content in transformer oil is an important index to measure the operation status of transformers. The differential autoregressive moving average model (ARIMA) is used to predict the gas content in transformer oil. This method uses the time corresponding to the gas content value as an index to input the prediction model through python programming. The original non-stationary time series is converted into a stationary time series by means of difference processing, and then several sets of models are obtained by using the autocorrelation function and partial autocorrelation function parameter selection principles, and are used in the process of optimizing several sets of models. A set of optimal models were obtained by Chichi information, Bayesian information, and Hannan-Quine criteria. Finally, the residuals of the optimal models were tested by correlation testing methods, and the gas content was predicted using the models that met the residual requirements. Experiments show that the proposed prediction method has high prediction accuracy, which can provide a valuable reference for rationally arranging the condition-based maintenance of transformers.
Zhang Qinglin,Xin Xiaonan,Cheng Zhiping
Abstract: Aiming at the problem of continuous power supply to loads and stable operation of the system when the main grid has an unplanned failure and the microgrid is connected to the island, in order to coordinate and control the equipment in the power network from a global perspective, a microgrid reconfiguration model is established. A reconstruction method combining depth-first search and gray wolf optimization algorithm is proposed. In this method, the switch state and the power of the adjustable equipment are used as optimization variables. Aiming at the non-radial grid structure problem in the process of reconstruction optimization, the depth-first search is used to identify, analyze and process the grid structure. The network power flow distribution is calculated by the method, and the reconstruction scheme is obtained by using the gray wolf optimization algorithm as the framework. The simulation results show that the proposed hybrid reconstruction method has stronger global search ability, and its reconstruction results are feasible and better, and the reconstruction strategy takes the combination of switch state and power as the optimization variable, which is better than only the switch state or only Variables with power are more advantageous for system optimization and adjustment.
Song Linjian,Zhao Jun
Abstract: Under the action of vertical load, the reinforced concrete shear wall may buckling failure caused by insufficient stability, so that the shear wall cannot effectively exert its excellent bearing capacity and seismic performance. According to the mechanical characteristics of reinforced concrete shear walls in actual engineering structures, the boundary conditions were analyzed and simplified reasonably, and the theoretical analysis model of orthotropic plates with simply supported opposite sides and free opposite sides was established. Based on the value principle, the critical stress expression corresponding to the out-of-plane instability failure of the shear wall under vertical load is deduced. According to the calculation formula of the critical stress obtained, the influence of factors such as the height and thickness of the shear wall, the diameter and spacing of the longitudinal reinforcement on the critical stress of the reinforced concrete shear wall are studied, and the improvement of the reinforced concrete shear wall under the vertical load is further discussed. effective method for stability.
Zhe Zhang 1,History 1Li Guoqiang 2,Soup 3,Li Feiran 3,Wang Yan 3,Sun Dongsheng 3,Dunn Peak 1
Abstract: On the basis of embedded connectors, a kind of embedded connectors with flanges is proposed. According to the actual engineering, push-out tests of 8 specimens are carried out, and the relationship between load-slip curves at different stages is analyzed, and the shear resistance is studied. Influencing factors and failure modes of bearing capacity. The results show that: when the width-thickness ratio of the steel flange plate meets certain conditions, the cracks at the thick part of the concrete slab are straight lines, and the cracks at the width of the slab are corrugated lines; , the concrete cracks were not fully developed, and the loading could not continue due to the instability of the flange plate, so the test ended early. The shear bearing capacity of the unbending specimen of the flange plate is about 1.5 times of the theoretical calculation value of the bearing capacity of the existing embedded connector, which proves that the flange plate significantly improves the resistance of the new connector compared with the embedded connector. shear capacity.
Winson,Jia Shuyao,Gao Xingpu
Abstract: In order to study the effects of lateral pressure coefficient λ, elastic modulus E of backfill material, and soft filling length Lr on the jamming control of double-shield TBM in deep squeeze formation, the interaction model between TBM and surrounding rock was established by using 3DEC. In the numerical calculation, the improved Burgers (CVISC) viscoelastic-plastic creep constitutive was used to simulate the dynamic step-by-step excavation of the TBM. The results showed that: (1) The larger the λ, the more unfavorable the TBM jamming control: when λ≤1 When λ≥1.2, the degree of influence is small; when 1<λ≤1.2, the degree of influence gradually increases; when λ≥1.2, the total resistance of the TBM rises sharply, which is extremely unfavorable to the control of the jamming machine; (2) The larger the backfill material E, the smaller the total contact pressure and total resistance of the TBM, which is more beneficial to the control of TBM jamming; (3) The larger L r is , the greater the total resistance of the TBM is, and the greater the probability of TBM jamming is; , in order to reduce the probability of jamming, the length of the soft filling stage should be shortened as much as possible.
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