最新刊期
卷 56 ， 期 10 ， 2022
- 摘要：In this paper,an efficient model for analysis of the transient contact and dynamics of gear pairs is proposed for in-depth study on the mechanism of nonlinear dynamics of gear pairs. This model couples the dynamic loaded tooth contact analysis(DLTCA)and the system dynamic analysis by considering the coupling effects between gear contact characteristics and system vibration,to form a closed-loop dynamic analysis process of ‘excitation-response-feedback'. According to the research findings,the reaction of dynamic displacement changes the contact state of tooth surface and affects the vibrational excitation such as dynamic mesh stiffness and composite mesh error; the increase of dynamic displacement near the resonance region may lead to total contact loss of tooth surface, resulting in nonlinear dynamics such as response amplitude jump. However,increasing meshing damping and helix angle weakens or eliminates the nonlinear dynamics. Factors such as tooth surface error,modification and clearance were included in the coupling model and experiments were conducted to verify effectiveness of this model. The results show that the proposed model can simulate the dynamic meshing process of gear pairs more accurately,and can be a good supplement to the current model of clearance-type nonlinear dynamics.关键词：dynamic loaded tooth contact analysis;gear dynamics;dynamic mesh stiffness;nonlinear vibration252|23|0更新时间：2025-07-09
- 摘要：A numerical model of planetary roller screw is established by using the finite element method to reveal the dynamic contact load characteristics of synchromesh between the thread pair and gear pair in the planetary roller screw. According to the motion principle of planetary roller screw, the theoretical calculation formulas of the axial speed and displacement of nuts are derived, and the static load distribution model of thread tooth is provided. The numerical results are compared with the theoretical values in terms of kinematics and static loads, and the relative errors are both less than 5%, which verifies the correctness of the model. Based on the numerical model, the influence of different nut loads, screw speeds and friction coefficients on the dynamic contact load of each contact pair of planetary roller screw is analyzed. The results show that the fluctuation of contact load curves increases with the increase of screw speed, and the fluctuation of contact load curves between gear pair and roller shaft end and cage decreases periodically. The steady state contact load of the screw pair fluctuates slightly under the influence of the synchromesh of thread pair and gear pair and the meshing excitation of the gear pair. As the nut load increases, the contact load of all contact pairs(but the gear pair)increases in direct proportion. The thread pair and the cage share partial load of the gear pair, leading to the reduction of the contact load of the gear pair. As the friction coefficient increases, the contact load increases obviously, and the fluctuation of each contact load curve becomes larger.关键词：planetary roller screw;synchromesh;dynamic contact;finite element method;contact load103|23|0更新时间：2025-07-09
- 摘要：To improve the motion servo control accuracy of pneumatic cylinder, a novel high-frequency longitudinal vibration friction-reducing pneumatic cylinder based on the inverse piezoelectric effect of piezoelectric stacks and vibration friction reduction principle is designed, expecting to weaken the uncertainty and negative damping characteristic of pneumatic cylinder friction by high-frequency vibration. Considering that the valve-controlled cylinder pneumatic system is a strongly nonlinear system, the model-based nonlinear controller is preferred for a high-precision motion trajectory tracking control. As a relatively common nonlinear control algorithm, the sliding mode control is highly robust to modeling errors, unmodeled dynamics and external disturbances. To this end, a model-based integral sliding mode controller is constructed for performing trajectory tracking tests. The test results show that the high-frequency longitudinal vibration can not only reduce the pneumatic cylinder friction, but also effectively improve its motion trajectory tracking accuracy. The designed model-based nonlinear sliding mode controller is effective, and the maximum tracking error is reduced by 19.61% and 20.55% when tracking sinusoidal reference trajectories with frequencies of 0.25 Hz and 0.125 Hz respectively. The approach of reducing friction using high-frequency vibration can improve the motion control accuracy of the pneumatic cylinder. It can be also used in the occasions where a high-precision control of the pneumatic cylinder is required.关键词：pneumatic cylinder;high-frequency vibration;reducing friction;integral sliding mode controller;motion trajectory tracking107|5|0更新时间：2025-07-09
- 摘要：The traditional grey wolf algorithm achieves low convergence efficiency and tends to get struck in local extremum in solving path planning problems for mobile robots. As a result, this paper proposes an improved grey wolf algorithm(Tent-initialized grey wolf optimization, TGWO)based on the population initialization of Tent chaotic mapping, Firstly, the population initialization method based on Tent chaotic mapping is adopted to enrich the diversity of the population, which can improve the convergence speed. Secondly, the improvement strategy based on exponential convergence factor is proposed to better fit the search process of the grey wolf, and the global exploration and local exploitation capabilities of the algorithm are balanced by improving the control parameter H. Finally, the dynamic weight factor and the fitness scale coefficient are integrated to update the individual positions of the grey wolves, so as to improve the independent searching ability of the individual, and prevent the algorithm from getting trapped into local optimum. To verify the effectiveness of the proposed algorithm, experiments are carried out by comparing the TGWO, traditional GWO and three improved typical algorithms for global path planning simulation using eight standard test functions and three sets of grid environments with different complexities. The results are as follows: 1)For both unimodal and multi-modal functions, the convergence performance and optimization accuracy of TGWO algorithm are better than others; 2)Under the simulation scenes, compared with the traditional GWO, each improved strategy proposed for TGWO algorithm effectively improves the performance of path optimization; 3)TGWO are superior to other algorithms in terms of the 4 indicators including the average path length, standard deviation of path lengths, average number of iterations and average time for optimization. All these verify the superiority and robustness of TGWO algorithm in path optimization.关键词：mobile robot;path planning;grey wolf optimization algorithm;Tent chaotic mapping;nonlinear control parameter;inertia weight coefficient127|18|0更新时间：2025-07-09
- 摘要：This paper proposes a lightweight multi-modal pedestrian detection algorithm based on deep learning MBNet algorithm to address the problem of 24/7 multi-modal pedestrian detection algorithm having a large size, high computation load and insufficient efficiency. First, the CSP-ResNet18 lightweight feature extraction network is built using the ResNet18 algorithm combined with the idea of cross-stage linking to ensure accuracy of the detection algorithm; then, the lightweight efficient channel attention module is introduced to enhance the feature extraction network's ability to focus on important features, which can improve the detection accuracy of the algorithm by introducing very few parameters; finally, the feature extraction network of MBNet algorithm is reconstructed by introducing a lightweight Ghost convolution module, which can further reduce the parameters required and the size of the algorithm and improve its detection efficiency while ensuring the feature extraction performance. The proposed G-MBNet algorithm is tested on the KAIST pedestrian dataset, and the experimental results show that the size of G-MBNet algorithm is 32.33% that of the original algorithm; the number of parameters is 37.81% that of the original algorithm; the detection speed is 1.53 times that of the original algorithm. The experiments verify that G-MBNet algorithm can effectively improve the detection speed while ensuring the pedestrian recognition accuracy.关键词：pedestrian detection;multi-modal fusion;lightweight network;Ghost convolution;attention mechanism161|5|0更新时间：2025-07-09
- 摘要：In this paper, a 3-D distributed parameter model of cross-flow plate fin heat exchanger(PFHE)is constructed using MATLAB program by considering the longitudinal and transverse heat conduction to study the flow and heat transfer of the multi-stream cross-flow PFHE. The simulation results coincide with the thermodynamic experimental results of the three-stream plate fin heat exchanger. An analysis is conducted on the effects of configuration and operation parameters of the cross-flow plate fin exchanger on heat transfer amount and the pump power. According to the results, the three-stream cross flow PFHE studied has an extreme value of pump power that shows the following changes: it first increases with the mass flowrate of fluid A, and when the mass flowrate reaches 1 300 kg/h, it decreases with the mass flowrate. Another analysis is carried out by setting four different xy projected areas of PFHE. The results are as follows: The amount of heat transfer basically remains the same when the xy projected area remains unchanged and the length of one side of the PFHE is changed; However, the amount of heat transfer per unit pump power is the greatest and the pump power consumption the lowest when the length of the PFHE along y direction is 0.15—0.20 m. The research findings provide theoretical guidance for the selection of optimized operation parameters, efficient and compact design of the cross-flow PFHE.关键词：plate fin heat exchanger;cross flow;distributed parameter model;heat transfer amount;pump power82|20|0更新时间：2025-07-09
- 摘要：An encoder-decoder-based super resolution network for license plate images was proposed for the lack of key information on license plate images caused by blur, stain, damage, distortion, and tilt in complex actual scenes and for the recognition difficulty due to low contrast between the license plate background and characters of new-energy vehicles. Firstly, a license plate reconstruction generator network based on the encoder-decoder structure is constructed. The texture and characters of the license plate image are extracted by an encoder, and the license plate features are reconstructed by a decoder. Then, a discriminator network based on semantic supervision is designed, and the adversarial loss and CTC loss are introduced into the network loss to enhance the ability of the generator network to represent the semantic features of license plate images. Finally, the features of the vertex points of the license plate are extracted based on VGG16 network, and a coordinate transformation method is utilized to correct the license plate image and further improve the reconstruction quality and recognition accuracy. Super-resolution reconstruction and recognition tests were performed on the self-built XAUAT-Parking dataset and the public CCPD dataset with the proposed network. The test results showed that the proposed network has an average peak signal to noise ratio(PSNR)of 25.5 dB and a structural similarity(SSIM)of 0.989 on the CCPD dataset. The PSNR and SSIM on the XAUAT-Parking dataset can reach 26.6 dB and 0.997 respectively. According to the research results, the proposed network has a good super-resolution reconstruction effect of license plate images and a strong robustness to the missing of key license plate information.关键词：license plate image;super resolution;image correction;vgg16 network;encoder-decoder structure;generative adversarial network69|12|0更新时间：2025-07-09
- 摘要：An experiment research is made on the surface charge distribution under different voltage parameters to explore the mechanism of action of the surface charge in the transformation of the discharge mode featuring dielectric barrier discharge(DBD). Firstly, a surface charge measurement system with a microsecond-level resolution is built according to the Pockels effect. The system is used to measure the two-dimensional distribution of the dielectric surface charge density and discharge current waveform of the flat electrode in atmospheric pressure helium environment under different voltage parameters, and the probability distribution of surface charge in each density interval is counted. The discharge modes under different voltage parameters are judged according to the current waveform, two-dimensional distribution and probability distribution of surface charge density. Finally, the two-dimensional distribution of charge density and probability distribution in different discharge modes are analyzed, and the mechanism of action of the dielectric surface charge on the transformation of discharge mode with the change of the applied voltage parameters is obtained. Before the next discharge, the charges accumulated on the dielectric surface and the remaining charged particles in the air gap will generate a reverse electric field, making the discharge easier occur in this area, thus promoting the evolution of the discharge mode from uniform discharge to filamentous discharge. The experimental results show that with the increase of voltage, the surface charge distribution gradually changes from a single charge spot to multiple charge spots, and the discharge mode shows different forms of filament discharge. With the increase of frequency, the surface charge distribution changes from a uniform distribution to a charge spot distribution. The diameter of the charge spot increases continuously, and the total charge increases from 0.21 nC to 0.41 nC. The results can provide a reference for the mechanism of the influence of surface charges on the evolution of discharge modes in DBD under an atmospheric pressure.关键词：dielectric barrier discharge;surface charge distribution;discharge characteristics;atmospheric pressure helium;Pockels effect50|13|0更新时间：2025-07-09
- 摘要：This paper proposes a specific emitter identification model suitable for one-dimensional signals under open set scenes based on prototype network. The model is used to solve the problems of weak robustness and low recognition of existing algorithms for specific emitter identification under open set scenes. Firstly, the I/Q signals collected are preprocessed by power normalization, slicing and noise addition. Then, a one-dimensional convolutional neural network for recognition of I/Q signals is designed, and a squeeze-and-excitation block with attentional mechanism is added to the network to improve the weights of feature channels with high efficiency. Finally, the preprocessed data set is used to train and test the network based on the idea of prototype learning. During the training process, the distance cross entropy loss function is used for prototype learning for each category, taking the distance between the signal features and the prototype as the classification basis. At the same time, the prototype loss function is used to increase the inter-class distance by compacting the intra-class signals, which further enhances the classification ability. During the testing process, the network can learn an adaptive distance threshold for each category by using the adaptive distance classification rule. The distance threshold is used for the classification of known classes and the detection of unknown ones. Experiments are carried out on the signals collected from five ZigBee devices. Simulation results show that the recognition rate of proposed model is about 8% higher than the common models based on extreme value theory between a signal-to-noise ratio from -10 dB to 10 dB.关键词：specific emitter identification;open set scenes;prototype network;convolutional neural network42|51|0更新时间：2025-07-09
- 摘要：An economical, convenient and undisturbed drone detection method using sound and multiscale group convolution network with attention mechanism in mixed domain of channel space(ECSANet)is proposed in the context of susceptibility to electronic interference in identification of drones by radar and radio, and the interference of light and obstruction in identification of drones by images in public environments such as urban parks, squares and large amusement parks. Firstly, nine kinds of sound dataset of civil drones are established, and their logarithmic Mel spectra and dynamic characteristics are extracted. Secondly, based on packet convolution, channel shuffling and residual structure, a multi-scale group convolution network with channel shuffle(MSSGNet)is designed to reduce the network parameters and avoid over fitting. Then, the efficient channel and spatial attention(ECSA)is designed to extract more and more effective features of drone sounds. Finally, the ECSA is inserted into the MSSGNet to form an improved multiscale group convolution network with attention mechanism in mixed domain of channel space(ECSANet), offering a new method for sound recognition of drones. The designed ECSANet is used to identify the self-built civil drone sound dataset and environmental sound dataset urbansound8k. The results reveal that when compared with benchmark networks such as ResNet18, ResNet34, ResNeXt18, and MobileNetV2, the MSSGNet has fewer network parameters but a higher identification accuracy(up to 95.1%). The ECSA can be inserted into a variety of networks to improve identification accuracy of network models without introducing too many parameters, and it works well for sound classification tasks like drones. As compared with the MSSGNet, the improved ECSANet has an identification accuracy of 95.9%, an increase of 0.8 percent, demonstrating the superiority and feasibility in identifying a small sample of drones.关键词：drone;voice recognition;log Mel-spectrogram;neural network;mixed domain attention mechanism37|5|0更新时间：2025-07-09
- 摘要：The computational models of single-channel wall jet cooling with film suction are established at the leading edge of turbine blades in this paper to reveal the interference effect of film suction on the flow and heat transfer of wall jet and obtain the flow and heat transfer characteristics in the wall jet cooling channel. The RANS method with SST k-ω turbulence model is adopted to research the effects of film suction, jet Reynolds number, film hole position, number and other factors on the internal cooling characteristics of wall jet. The results show that film suction can significantly improve the stability of flow structures. The heat transfer coefficient near the inlet of film hole can be raised notably by the separation vortex. The decreased mass flow rate of the wall jet brought from the film suction is not conductive to the cooling of the downstream target. However, the decreasing level of flow loss at the stagnation area and channel is larger than the mixing loss in film hole, thereby reducing the overall flow loss coefficient by 4.5%. With the increase of the Reynolds number, the heat transfer intensity will improve, which, however, has little effect on the flow structure. Among the structures with a single film hole, the opening at the position of the leading edge stagnation line can provide the highest film flow ratio and has a good cooling effect on the target surface inside the leading edge. Among the structures with multiple holes, the structure with double film holes has the largest flow loss, and the structure with three film holes has the most balanced flow loss and heat transfer intensity. The research results provide a basis for the arrangement of film holes for the wall jet cooling structure, and provide a reference for further improvement of the cooling effect.关键词：turbine blade;film suction;wall jet cooling;numerical simulation43|12|0更新时间：2025-07-09
- 摘要：Currently, the last stator of the multi-stage axial flow compressor is faced with such remarkable problems as large blade turning angle, severe corner separation and significant flow loss. Against this background, we propose a three-dimensional geometrical parameterization method for tandem blades using the last stator of an industrial 6.5-stage axial flow compressor as example. This method enables a flexible control of spanwise distribution of tandem parameters as well as lean and bow of blades, thus supporting the redesign of single blades into tandem blades. Using the numerical methods, we also investigate the impact of tandem blades on the aerodynamic performance and internal flow field of the whole compressor. The following results are obtained: 1)The adiabatic efficiency of the 6.5-stage axial flow compressor increased by 0.965% under the design conditions after the single-blade configuration of the last stator is redesigned into a tandem-blade one, and the operating range was also widened; 2)The local jet-like acceleration in the slit region of the tandem blade is observed to be responsible for the suppression of circumferential and radial development of the corner separation; 3)The tandem parameters at the hub have a greater impact on the aerodynamic performance of the compressor than at the tip, and the percent pitch than the axial overlap. The three-dimensional parametric modeling method for tandem blades proposed in this work and the findings of flow improvement mechanism of three-dimensional tandem blades have reference value for the design optimization of three-dimensional tandem blades.关键词：3D tandem blade;last stator;axial overlap;percent pitch;multi-stage axial flow compressor51|28|0更新时间：2025-07-09
- 摘要：This research was conducted to explore the influence of a non-uniform change of blade tip clearance along the circumferential direction on the performance of a large low-pressure axial flow fan. In this research, a large civil low-pressure axial flow fan was taken as the research object, with two key parameters(namely, the average clearance and the non-uniformity)representing the circumferential non-uniform clearance of the axial flow fan selected as the influencing factors. Steady and unsteady numerical simulations were conducted to research the influence of circumferential non-uniform blade tip clearance on the external characteristics of the fan, and on the blade tip clearance flow and flow filed change. The results show that both the increase in the average clearance and non-uniformity of the axial flow fan led to the decrease of the fan's efficiency and static pressure, and the influence caused by the change of the average clearance is significantly greater than that by non-uniformity. When the clearance is large, blade tip leakage flows include not only the main leakage flow with a vortex core, but also an additional leakage flow without a vortex core. The non-uniform blade tip clearance will change the starting position and development direction of blade tip leakage flow. In addition, the blade tip leakage flow will be subject to a periodic change due to the entrainment of the leakage vortex from its leading blade. This research is helpful in the design and efficient operation of low-pressure axial flow fans.关键词：axial-flow fan;non-uniform clearance;non-uniformity;leakage vortex;numerical simulation58|5|0更新时间：2025-07-09
- 摘要：An isothermal heat treatment method is proposed to refine Mg2Si size, so as to solve the problem of poor mechanical properties caused by coarse size of primary Mg2Si phase in Mg matrix composites reinforced with high volume fraction Mg2Si. In this paper, the effects of semi-solid isothermal heat treatment on the morphology of Mg2Si, matrix microstructure and hardness of Mg2Si/AZ91 composites with 10% volume fraction are studied, and its evolution mechanism is revealed. The results show that the primary Mg2Si phase with low curvature dissolves preferentially during the isothermal heat treatment process, resulting in the fusing and forming independent particles at the dendrite wall, and then transforms into spherules with the lowest surface energy. With the extension of holding time, the primary Mg2Si phase grows by merging. After isothermal treatment with different parameters, the primary Mg2Si phase has the best refinement effect with a particle size of 30.6 μm after being kept at 510 ℃ for 60 min, reduced by 58.6%. During the heat treatment, α-Mg dendrite homogenizes with Mg17Al12 phase distributed along grain boundary, and α-Mg grains are spheroidizing and the grains size decreases. At the same time, it is found that the hardness of the composite decreases obviously after the isothermal heat treatment, but increases with the refinement of the primary Mg2Si and the α-Mg grains. The hardness change is ascribed to the interaction of solution strengthening, hard phase disappearing and grain refinement strengthening. This paper provides experimental and theoretical basis for improving the morphology and properties of Mg2Si/AZ91 composites.关键词：Mg2Si/AZ91 composites;semi-solid isothermal heat treatment;microstructure evolution;hardness54|7|0更新时间：2025-07-09
- 摘要：A fast in-situ passive vision system is established to identify the defect types in the context of the potential morphology defects of the arc welding assisted aluminum alloy droplet deposition additive manufacturing and the lag of the entire monitoring system caused by the image processing time. Firstly, the binary string descriptors of the key points of the deposition layer morphology are automatically extracted based on ORB algorithm; then the BOW model is used to obtain the image feature description vectors with the same dimension; finally, the SVM classifier is trained with the extracted feature vectors, and the performance is verified in terms of classification accuracy and processing time. The results show that the ORB-SVM model has an accuracy of 0.96 for recognizing the deposition layer morphology, and the total time for feature extraction, encoding and recognition of a single image is about 9 milliseconds. In addition, it provides a feasible solution to ensure the deposition layer accuracy of arc welding assisted droplet deposition additive manufacturing under complex manufacturing conditions and has a great potential in real-time monitoring.关键词：arc welding assisted droplet deposition;deposition layer morphology;defect identification41|7|0更新时间：2025-07-09
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0