最新刊期
卷 54 ， 期 12 ， 2020
- 摘要：An adaptive speed control method with sliding mode variable structure is proposed to improve the control performance of permanent magnet synchronous motor(PMSM)speed servo system and to enhance its anti-inertia disturbance capability. A speed control method of sliding mode control(SMC)is adopted in the PMSM double closed-loop control system, and an integral sliding mode surface is introduced into SMC to avoid the requirement of acceleration signal in the control and to reduce the steady state error of the system. In addition, the sigmoid function is used to replace the traditional sign function in the reaching law to further improve the dynamic quality of the system. In order to solve the problem of rotational inertia variation caused by load change in PMSM control system, the rotational inertia is estimated in real time based on the theory of discrete model reference adaptive system(MRAS), and the inertia identification value is updated to the SMC to realize adaptive SMC speed control. Experimental results show that the proposed adaptive SMC control method has a faster speed response, and the speed response time is reduced from 85 ms to 54 ms compared with the conventional SMC control. Moreover, it has stronger robustness to inertia disturbances. This method is suitable for servo control of some special time-varying inertia occasions, such as printing machinery, textile machinery, and cable equipment.关键词：permanent magnet synchronous motor;inertia identification;adaptive;sliding mode control438|4|3更新时间：2025-07-09
- 摘要：In view of the research status that most of the current studies in the field of soft robots only focus on the actuating function of soft active materials but ignore the sensing function, an actuating/sensing integrated flexible gripper robot is developed. Exploring the structural design and fabrication process of polyvinyl chloride gel actuator, a manufacturing process of CNT/PDMS flexible sensing structure is then investigated. An actuating/sensing integrated functional structure is designed and manufactured, where the PVC gel actuators are taken as the actuating units and the CNT/PDMS 3D structures as the sensing units. The results show that the bending angle of single finger can reach 32.5 degrees under 800 V DC voltage. Driven by 400 V DC voltage, the gripper consisting of two flexible fingers can grasp deformable silicone rubber cylinders with a diameter of 15 mm and shore hardness of 10 - 20, 30 - 50 respectively. As grasping the cylinders with different hardness, the resistance change rates of CNT/PDMS demonstrate differently, indicating that the CNT/PDMS flexible sensing structure can sense the softness and hardness of the grasped object, thus verifying the feasibility of the design of actuating/sensing integrated structure proposed in this approach. The results may offer reference for following design and fabrication of the soft robots.关键词：soft active materials;polyvinyl chloride gel;flexible sensing materials;actuating/sensing integration;soft robots280|4|1更新时间：2025-07-09
- 摘要：A new image description generation model with deep compositional captioner based attention mechanism(named Att-DCC model)based on the encoder-decoder framework is proposed to better understand the “novel concepts” that do not appear in the training set for the task of image description generation. A convolutional neural network with spatial attention mechanism is introduced into the model, and global visual features, semantic labels and visual information after spatial attention are well integrated. In addition, a multi-modal layer with an adaptive attention mechanism is introduced to transfer the learning results to novel concepts, which reduces the complexity of training process and improves learning performance. This work extends the existing multi-modal fusion and introduces multiple attention mechanisms to enhance the performance of novel concept learning. Att-DCC model is used to test and analyze 14 novel concepts in two batches on MSCOCO2014 data set. The experimental results show that the proposed model achieves average results of 42.56% and 42.14% for two batches of novel concepts(8 and 6, respectively)in terms of the F1 score, and in general, the prediction results are more accurate than those of the representative NOC model and DCC model.关键词：image captioning;attention mechanism;convolutional neural network;novel concept264|4|0更新时间：2025-07-09
- 摘要：A distributed Alamouti-based protocol for virtual full-duplex(VFD)relaying networks(DA-VFD)is proposed to solve the problem that single-input single-output(SISO)system cannot achieve the transmit diversity, and self-interference(SI)in full-duplex(FD)system degrades the system performance. In order to obtain the second-order transmit diversity against the channel fading, which leads to drawbacks of the BER performance, DA-VFD combines three time slots as a group for transmission: The source transmit symbols and the complex conjugate of the symbols are transmitted to the relay node and the destination node within the first and the second time slots, and the receiving symbols from the first two slots are demodulated together in the third time slot. Since the formula used for joint demodulation has the form Alamouti, the destination can obtain the second-order transmission diversity, which can resist the adverse effect of channel fading on system error performance. At the same time, because the two half duplex nodes are isolated geographically, the signals sent by one node will not be received by the other node, which avoids the system performance degradation brought by SI in full-duplex communication and the hardware requirements by SI elimination. Finally, the spectral efficiency of full duplex communication is achieved through the coordination between two half duplex relays. Simulation results show that the BER performance of DA-VFD is not affected by RSI and outperforms the existing Alamouti FD. When the spectral efficiency is 1.33 b/(s·Hz)and the quality of SI cancellation is 0.5, DA-VFD obtains about 2 dB more BER gains than Alamouti FD; when the spectral efficiency is 2.67 b/(s·Hz)and the quality of SI cancellation is 0.5, DA-VFD obtains about 6 dB more BER gains than Alamouti FD.关键词：cooperative network;distributed Alamouti coding;virtual full-duplex transmission;transmit diversity190|4|1更新时间：2025-07-09
- 摘要：A single carrier iterative equalizer receiver with feedback filter bank is proposed to solve the multipath effect in broadband wireless communication. Firstly, a feedback filter bank and a feedforward filter are designed by exploiting signal diversity brought by multipath delay. The main function of the feedback filter bank in the equalizer is to eliminate intersymbol interference between different delay signals as much as possible, and the main function of the feedforward filter is to combine the multipath components after the interference elimination. Then, by exploiting the minimum mean square error criterion, the feedforward coefficient and the feedback filter bank coefficient are optimized jointly to obtain the optimal solutions of the coefficients, and the optimal separation and diversity combination of multipath components are realized. Finally, the correlation coefficients in the filter coefficients are estimated, and the maximum ratio combination is carried out for the cyclic prefix part of the balanced signal to increase the signal to noise ratio. Simulation results and a comparison with the existing single carrier iterative equalizer receivers show that in the case that the length of the multipath channel does not exceed the length of the cyclic prefix, when the bit error rate is 10-5, the performance of the receiver improves by 0.5 dB after the first iteration, and approximates the matched filter boundary faster with the increase of iteration times; In the case that the length of the multipath channel exceeds the length of the cyclic prefix, the “platform effect” of bit error rate and frame error rate are eliminated effectively, and when the bit error rate is 10-5, the performance is improved by 4 dB after two iterations to approximate the matched filter boundary.关键词：multipath effect;single carrier;iterative equalization;feedback filter bank;signal diversity179|4|2更新时间：2025-07-09
- 摘要：A point cloud classification network with multi-level and multi-scale(MLMS-Net)is proposed to improve the problem that the traditional point cloud classification network extracts single-level features and teh classification accuracy is low. First, a preprocessing algorithm is used to segment the original point cloud into small samples to obtain mini-batch and so as to improve training efficiency; Then the K-nearest neighbor algorithm and an edge feature vector are used to extract the low-level structure features and edge features of the point cloud, and the context information is effectively obtained through setting different neighborhood values. Local fine-grained descriptions are obtained through multi-level expression within and between points. Then convolutional neural networks are constructed for two low-level features separately. With the deepening of the network level, the degree of feature abstraction level is higher and higher, and the degree of distinction increases, so as to effectively improve the accuracy; Finally, the post-processing module is used to fuse the deep features, and the point cloud classification task is completed. The Vaihingen data set is used to test the MLMS-Net network, its classification accuracy is improved by 0.6% to 15.9% compared with that of the single-level network.关键词：point cloud classification;convolutional neural network;edge features;local fine-grained193|4|0更新时间：2025-07-09
- 摘要：An algorithm for suppressing jamming in the fractional Fourier transform(FRFT)domain is proposed to solve the problem of self-screening dense false target jamming in linear frequency modulation(LFM)coherent radar. Firstly, when LFM radar is jammed, slope varying LFM(SV-LFM)waveform is transmitted to obtain a coherent processing interval echo. Then, the maximum high-order moment criterion is used to estimate the jamming slope in each pulse repetition period and determine the optimal order of FRFT. The optimal order FRFT of the echo is calculated, and the FRFT peak value covers and filters out part of the jamming. Finally, pulse compression and coherent integration are carried out for the filtered echo to realize the final suppression of jamming. For the radar of SV-LFM waveform, the processing of pulse compression and coherent integration have certain suppression effects on dense false targets, and better suppression effect can be achieved by combining with jamming filtering. Experimental results show that SV-LFM with variable bandwidth has higher compatibility with radar moving target detection, and the critical signal to noise ratio of real target detection is less than 1 dB, compared to ideal non-agility case. After jamming suppression, the critical jamming to signal ratio increases by about 20 dB, and the number of false targets reduces by about 40%.关键词：dense false target jamming;radar;linear frequency modulation;slope varying;fractional Fourier transform;jamming suppression189|4|6更新时间：2025-07-09
-
Numerical Investigation to Effect of Spacer Grid on the Subcooled Flow Boiling in Single Rod Channel
摘要：To investigate the influence of spacer grid on the thermal-hydraulic characteristics of coolant in fuel rod bundle channel, a single fuel rod and a spacer grid in the center of 5×5 bundle channel are selected for the numerical analysis. Following Eulerian theory, a mathematical model of multiphase flow for the subcooled boiling of coolant in a vertical single rod channel is established. The accuracy of the model is verified by a comparison of numerical simulation results with experiment data. The spatial distribution characteristics of the relevant thermal parameters in the single rod channel with or without spacer grid are obtained, and the influence of spacer grid on the flow and heat transfer characteristics of subcooled boiling is revealed. The results show that compared with the rod channel without spacer grid, the flow field and temperature field rotate anticlockwise in a certain degree after passing through the spacer grid and the mixing wings. The maximum value of the average secondary flow can reach 13.5% of the inlet velocity, and the local secondary flow can reach 60%. The pressure drop of the whole device with spacer grid is only 5% higher than that without spacer grid. The spacer grid can significantly make liquid phase convection heat flux increase, and the maximum increase can reach 44.3%. As a result, the liquid subcooling, wall superheat and vapor volume fraction are further reduced, thus enhancing the safety of nuclear reactor.关键词：subcooled boiling;computational fluid dynamics;spacer grid;thermal-hydraulic123|4|0更新时间：2025-07-09 - 摘要：The extreme seeking control(ESC)algorithm is utilized to realize the real-time minimization of the power consumption of the sub-cooler vapor injection transcritical CO2 heat pump water heater system. The ESC takes the power consumption as the feedback, and the manipulated inputs are the discharge pressure and the medium pressure. A dynamic simulation model based on Dymold(Modelica 3.2.3)and ThermSystems(TLK-thermo, GmbH)is developed for a sub-cooler vapor injection transcritical CO2 heat pumps to evaluate the proposed multi-variable ESC method under the design condition. Given the initial state of the system with discharge pressure and medium pressure at 12 and 7 MPa, environmental temperature at -12 ℃, inlet and outlet water temperature at 45 and 65 ℃, both the discharge pressure and the medium pressure converge to the optimal operation parameters under the manipulation of the ESC controller. This study also simulates the operation results of the ESC at four different initial states(discharge pressure and medium pressure at 10 and 6 MPa, 10 and 8 MPa, 14 and 6 MPa and 14 and 8 MPa, respectively). The system can reach and converge to the lowest power consumption point of the system, and the reliability of the method is verified.关键词：vapor injection;CO2;extreme seeking control122|4|0更新时间：2025-07-09
- 摘要：A comprehensive optimization study is carried out by an intelligent algorithm to uniformize the electric and stress field distributions of three-phase spacer in 252 kV compact gas insulated metal enclosed transmission line. 3-D finite element simulation models of the three-phase spacer are established. Distributions of electric and stress fields for three structures are compared and the influences of structural parameters on electric and stress fields are studied. Then, a Bernstein equation is established to describe the profile of insulator surface, and the corresponding constraints and simplification methods are also discussed. The intelligent optimization of the three-phase spacer is realized by combining COMSOL and MATLAB and using a particle swarm algorithm. Results and a comparison with the original structure show that the maximum values of total field, tangential field and stress of the optimized spacer decrease by 13.5%, 16.0% and 8.5%, respectively, and all of them meet control values. The proposed optimization method for complex profile efficiently improves the distributions of the electric and stress fields. The results provides guidance and reference for the structural design of 252 kV compact gas insulated metal enclosed transmission line.关键词：gas insulated metal enclosed transmission line;three-phase spacer;Bernstein equation;intelligent algorithm162|4|3更新时间：2025-07-09
- 摘要：The IDEAL algorithm is implanted into the two-phase flow solver interFoam in the most popular open-source computational fluid dynamics software OpenFOAM to solve the problem that the existing applications of the IDEAL algorithm in the numerical simulation of two-phase flows are mainly based on the structured grids or two-dimensional unstructured grids, and its further application in complex problems is limited. Then, its performance advantages over the PIMPLE algorithm are verified using four numerical examples, i.e., two-dimensional dam break, two-dimensional single-bubble rising, three-dimensional non-coaxial double-bubble rising, and gas-liquid two-phase flow in an undulating pipeline. The research results indicate that the computational time of the IDEAL algorithm is reduced by 17.6% - +∞ compared with the PIMPLE algorithm. Moreover, the PIMPLE algorithm is difficult to converge in some cases, whereas the IDEAL algorithm can still obtain the convergent solution quickly. This study lays a foundation for extending the IDEAL algorithm to complex two-phase flow problems.关键词：two-phase flow;computational fluid dynamics;IDEAL algorithm;OpenFOAM;computational performance178|4|1更新时间：2025-07-09
- 摘要：To research the cooling and lubricating effects on the grinding interface under minimum quantity lubrication, a molecular dynamics simulation of grinding interface under minimum quantity lubrication with ionic liquid is performed. The heat partition relationship on the grinding interface is analyzed, and the generation and transfer mechanisms of grinding heat on the grinding interface are revealed. The variations of grinding force, grinding force ratio, and the liquid film between abrasive grain and workpiece are investigated. The results show that the cooling effect of the ionic liquid droplet is outstanding. The heat partition ratio of the workpiece reaches 74.1% in dry grinding, and under minimum quantity lubrication, the heat partition ratio of the workpiece is reduced to 68% - 69%. Grinding heat is mainly generated from the lattice deformation of the workpiece material in the shear zone, and the secondary heat source is friction between the abrasive grain and the workpiece. The generated heat is firstly transferred into the workpiece substrate, the abrasive grain, and the grinding chip directly, afterwards, a portion of heat in the grinding chip is transferred into the ionic liquid droplet, then a portion of the heat in the ionic liquid droplet is transferred into the abrasive grain. The grinding force linearly increases with the increasing undeformed chip thickness. As the abrasive grain cutting into the workpiece, highly compressive stress appears on the grain-workpiece and grain-chip interfaces, which leads to difficulty in forming a boundary lubricating film.关键词：minimum quantity lubrication;grinding;cooling and lubricating;molecular dynamics;ionic liquid190|4|4更新时间：2025-07-09
- 摘要：To evaluate the change of single point incremental forming force under the multiple assistive technologies, two technologies of static pressure support and ultrasonic vibration simultaneously assisted single point incremental forming are taken as an example to simulate the forming force. The truncated cone is used as the target part, and ABAQUS is used to perform modeling assembly, material definition, meshing and boundary constraints for the sheet metal, fixture and tool head. Under the assumption of uniform load and periodic amplitude setting, the static pressure support load and ultrasonic vibration track are introduced to establish a finite element simulation model of the single point incremental forming process considering hydrostatic support and ultrasonic vibration. The following laws are found in simulating the forming force: The vertical force FZ obeys a stepwise increase change law as a whole, and FX and FY obey a sinusoidal staggered periodic fluctuation law as a whole; The vertical force FZ is much larger than the horizontal forces FX and FY, indicating that FZ is the main forming force; The vertical force FZ increases with the increasing static pressure, and the vertical force FZ first decreases and then increases with the increasing amplitude and frequency. To verify the simulative results, a corresponding experimental program is designed, and the obtained results coincide well with the trend of the simulative ones.关键词：multi-technical assistance;forming force;simulation173|4|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