最新刊期
卷 55 ， 期 1 ， 2021
- 摘要：Three types of asymmetric acoustic metamaterials, i.e., with material asymmetry, geometrical asymmetry, and resonant asymmetry, are designed to achieve abnormal acoustic characteristics, and the formation mechanisms for anisotropic reflection characteristics and equivalent parameters are systematically studied. Acoustic properties of the three types of asymmetric acoustic metamaterials are studied by simulation and experiment, and The experimental results show that anisotropic reflection phase can be realized when material asymmetry and geometrical asymmetry form asymmetric resonance characteristics, and anisotropic reflection amplitude can be further realized by considering material loss. Asymmetric resonance characteristics also produce anisotropic equivalent parameters, and a modified direct method is proposed to obtain unified equivalent parameters for asymmetric acoustic metamaterials. The calculated unified equivalent parameters have a corresponding relationship with amplitude of transmission and meet the requirements of passive materials, which validates the correctness of the method. The present work can provide some references for the realization of acoustic devices with zero reflection.关键词：acoustic metamaterials;asymmetric resonance;anisotropy;reflection characteristic;equivalent parameters403|4|0更新时间：2025-07-09
- 摘要：To improve the hydrogenation/dehydrogenation kinetics ofNaAlH4, an amorphousTiB2@C catalyst was prepared by a two-step process, and the effect of this catalyst on the synthesis and reversible hydrogen storage performance ofNaAlH4 was systematically studied. Results show thatTiB2@C can catalyze the synthesis ofNaAlH4 by usingNaH and Al as raw materials through a ball milling procedure at room temperature under 5 MPa hydrogen pressure. Compared with as-milled pureNaAlH4, the desorption temperature and apparent activation energy of the as-preparedNaAlH4-6%TiB2@C are dramatically reduced. Moreover, this composite shows obviously increased hydrogen absorption/desorption kinetics and excellent cycling stability during 10 hydrogen absorption/desorption cycles. The improvements of the synthesis and reversible hydrogen storage performances ofNaAlH4 are mainly due to the synergistic catalytic effect ofTiB2 and C inTiB2@C catalyst.关键词：hydrogen storage;NaAlH4;catalyst;ball milling131|5|0更新时间：2025-07-09
- 摘要：To enhance the rapidity, sensitivity, reliability and selectivity of differential protection for hybrid three-terminal HVDC lines and buses, a new differential protection scheme based on Hausdorff distance algorithm is proposed. When a fault occurs in ±800 kV mixed three-terminal DC line, the fault component values of line-mode current on both sides in T-zone are used as the fault direction discrimination basis of this scheme, and the scheme quantifies the difference of short-window data between the current waveforms of the first and last sides of the line, and uses the difference of current similarity between the first and last ends of the line to determine the internal faults and external faults, as well as the faults of unipolar and bipolar. The Hausdorff distance between T-zone sender(LCC side)’s current and two T-zone receiver(MMC side)’s total current is taken as the criterion of T-zone bus fault identification and protection. Then the hybrid three-terminal DC transmission system model is established by PSCAD and the protection method is verified by MATLAB. The simulation results show that the proposed scheme has strong ability to tolerate the transition resistance(500 Ω), and has the advantages of high reliability and speediness to ensure quick and reliable action within 3 ms. The communication time accuracy requirement on both sides of the line is low, and the scheme has a certain ability to resist noise and abnormal data. Under different working conditions, the fault area and the faults inside or outside the area can be quickly identified, and fault pole selection can be achieved.关键词：hybrid three-terminal DC system;differential protection;Hausdorff distance algorithm;T-zone;line-mode current fault component115|4|4更新时间：2025-07-09
- 摘要：To reduce the size of traditional waveguide flange in satellite systems, a novel solution to flangeless waveguide connection is proposed using gap waveguide technology. Bed of nails is arranged surrounding the outer surface of a waveguide, called part A. Part B is another waveguide with stepped transition to an enlarged end acting as the shielding cavity. Part A is inserted into part B, and a pluggable waveguide connection is constructed in the form of clearance fit. A contactless EBG structure is formed in the pluggable part under proper size conditions, and the EM wave leakage from the tiny air gap between contact surfaces is suppressed by EBG’s stop band, achieving a good EM transmission performance between two waveguides. Two kinds of Ku band prototype of the flangeless waveguide are designed and measured. Over the frequency range from 9.84 GHz to 15 GHz, the measured insertion loss of the two prototypes is less than 0.06 dB, and the return loss is better than 30 dB and 20 dB respectively. Compared with traditional WR75 waveguide flanges, the sectional size of the two prototypes decreases by more than 60% and 70%, respectively. The proposed flangeless waveguide has compact size and good error tolerance performance in manufacturing and assembling, and is easy to use, which is conductive to making fast and flexible waveguide connection without connecting screws and can be widely used in various kinds of microwave components and systems.关键词：flangeless;waveguide;gap waveguide;electromagnetic band gap86|4|1更新时间：2025-07-09
- 摘要：To alleviate the performance bottleneck of SHA-1 fingerprint computing of data de-duplication in high-performance solid-state storage system, we propose an improvement strategy for fingerprint calculation of data de-duplication, R-dedup, which uses Rabin hash instead of original data to reduce SHA-1 fingerprint calculation. Based on content defined chunking algorithm, R-dedup further divides each data chunk formed after segmentation into smaller 48-byte length data slices. Owing to the shorter length of Rabin hash than the original data slice, the collision probability of multiple Rabin hashes is very low, and the Rabin hash of data slice can be obtained from the intermediate calculation results of sliding window of content defined chunking algorithm. The Rabin hash of data slice is used to replace the original data as the SHA-1 fingerprint input value of the data chunk, so as to reduce the data calculation amount of SHA-1 function and improve the performance. Five representative datasets, including Linux kernel and imagenet, are selected to compare the data chunking performance, SHA-1 computing performance, index table retrieval performance and I/O performance between R-dedup and standard content defined chunking of data de-duplication. The results show that R-dedup has only about 4% error fluctuation compared with the standard content defined chunking method in terms of data chunking performance, I/O performance and index retrieval performance. Compared with the standard content defined chunking strategy, R-dedup can improve the performance of SHA-1 fingerprint computing by 165% - 422% and the overall system throughput by 6% - 54%.关键词：storage system;data de-duplication;solid-state drive;Rabin hash;performance improvement103|4|0更新时间：2025-07-09
- 摘要：A pruning method based on separable convolution is proposed to reduce parameters and calculation amount in the tracking network. Separable convolution decomposes the traditional convolutional layer into two parts, i.e. pointwise convolution and depthwise convolution in the tracking network. In pointwise convolution, the importance of the input feature map channel in the linear combination is evaluated by the weights in pointwise convolutions, so that the smaller weights and their associated feature channel ought to be pruned. In depthwise convolutions, the K-L divergence is adopted to measure the similarity of filters, and the similar filters are then pruned to reduce redundancy. With the improvements above, iterative pruning is performed. The parameters in the tracker are reduced by 22.54%, and the computation is reduced by 17.8%. On the NVIDIA TX2, the tracking rate increases by 14.95% for CPU and 13.07% for GPU without significant degradation of tracking performance in VOT benchmark.关键词：object tracking;convolutional neural networks;separable convolution;filter pruning122|4|1更新时间：2025-07-09
- 摘要：Aiming at the characteristics of non-linearity, pure lag and strong interference in the main steam pressure control of gas-fired power boilers, a first-order time-delay model of the main steam pressure sliding mode predictive optimization control strategy is proposed. The generalized predictive control is used to make real-time predictions of the gain and main steam pressure of the sliding mode controller. According to the prediction deviation of the main steam pressure, feedback correction and rolling optimization are exerted on the sliding mode gain to reduce the chattering of the sliding mode control system. By providing a nonlinear compensation to the flow characteristics of the gas control valve, the best control law in discrete form is obtained via optimizing the objective function. Compared with conventional PID control, sliding mode control and dynamic matrix control, the simulations show that the proposed control strategy during model adaptation reduces the adjustment time by up to 19.1 s and the overshoot by up to 16.4%; the sliding mode function chattering is small, and the system has good anti-interference, following and robust performances. The engineering application indicates that once adopting the proposed strategy, the system chattering is reduced by 60% compared with single sliding mode control, the main steam pressure control deviation is less than ±0.05 MPa, and the system stability and anti-interference ability are significantly improved.关键词：gas-fired power boiler;main steam pressure;generalized predictive control;sliding mode control;rolling optimization182|4|1更新时间：2025-07-09
- 摘要：To solve the risk of large forecast errors of a single model and the inability to make full use of historical data in the traditional regional power grid load forecasting, this paper proposes a linear combination model of regional power grid load forecasting, i.e. combination model of grey Verhulst and system dynamics. Taking the historical data of social electricity consumption as the original data, the grey differential equation and the whitening differential equation are successively established and solved to obtain the load forecast time series based on the grey Verhulst model, which is adopted to predict the load growth in accordance with the S-shaped curve or the load growth in saturation stage. Comprehensively considering the impacts of economy, population, energy substitution and re-electrification on social electricity consumption, the economic subsystem, population subsystem, energy substitution and re-electrification subsystem and power consumption subsystem of load forecasting are established, then a load forecasting model based on system dynamics is obtained, which is suitable for load forecasting with complex structure, rich original information and close connection among the subsystems. Without increasing complexity, single model is linearly combined following the minimum variance criterion to establish a combined model for regional power grid load forecasting. All areas in Zaozhuang city are employed to analyze the calculation examples. The results show that after making full use of the historical load data, the prediction accuracy of 71% of the areas is higher than that of a single model; after considering the minimum variance criterion to linearly combine the single model, 29% of the areas encounter lower risk of large prediction errors than a single model.关键词：regional power grid load forecasting;grey Verhulst model;system dynamics model;minimum variance criterion;linear combination model84|4|3更新时间：2025-07-09
- 摘要：To improve the mode switching quality of dual-mode hydro-mechanical transmission(DHMT), orthogonal test and range analysis methods were used to optimize the switching timing sequence of multiple clutches during the switching process. Based on the analysis of DHMT transmission principle and mode switching process, the models of mode switching process and switching quality evaluation index were established. A timing optimization method of DHMT clutch switching based on orthogonal test and range analysis was presented. The orthogonal test table was designed with the switching time sequence of multiple clutches participating in the mode switching process as the influence factor, and orthogonal test simulation was carried out. The range analysis of the simulation results was carried out to get the influence degree of each clutch’s switching time sequence on each evaluation index. After comprehensive balance of all indexes, the optimization scheme combination of DHMT clutch switching timing sequence was obtained. The simulation results show that the impact degree of the mode switching process based on the optimization scheme is 6.15 m/s3, lower than the domestic standard of 17.64 m/s3, and the sliding power is 2.80 kJ and the switching time was 1.05 s, both within the reasonable range. The test results are close to the simulation results and the variation trend is consistent, which verifies the correctness of the model built in the paper, and further indicates that the DHMT mode switching quality can be effectively improved by optimizing the timing sequence of clutch switching. This research can provide a theoretical reference for the formulation of control strategy of mode switching process of dual-mode hydro-mechanical transmission device.关键词：dual-mode hydro-mechanical transmission;clutch;switching time sequence;optimization81|4|7更新时间：2025-07-09
- 摘要：To solve the dynamic modeling problem of water-lubricated rubber journal bearing with journal misalignment, a 32-coefficient dynamic model is proposed, and the related elastohydrodynamic lubrication model is established. Then the dynamic characteristics of the bearings in 8-coefficient model and 32 coefficient model are solved by difference methods. The influences of eccentricity and journal misalignment angle on the bearing dynamic characteristic coefficient are analyzed. The results show that the stiffness and damping coefficient increase with the eccentricity in the 8-coefficient model, and increase exponentially at large eccentricity; the angular stiffness and angular damping coefficient also increase with the eccentricity in the 32-coefficient model of bearing. With the increase of journal misalignment angle, the displacement stiffness coefficient, displacement damping coefficient, angular stiffness coefficient, angular damping coefficient, angular-force cross stiffness coefficient, angular-force cross stiffness damping coefficient, displacement-torque cross stiffness coefficient and displacement-torque cross damping coefficient in the 32-coefficient model of bearing increase successively. This research may provide a reference for the optimal design of water-lubricated rubber journal bearings.关键词：rubber journal bearing;journal misalignment;dynamic characteristics;water lubrication82|4|3更新时间：2025-07-09
- 摘要：To solve the difficulties in the design of the double-circular-arc harmonic hob with positive rake angle(DFHP)and in the control of tooth profile error, considering actual machining, the precise conjugate tooth profile of the cutting edge on rake face and a mathematical simulation model for the hobbing of flexspline are established. For studying the influences of DFHP’s rake angle and top edge clearance angle on the machining error of DFHP, a mathematical simulation of hob machining is carried out. In order to reduce the machining error of DFHP, the normal tooth profile of the traditional positive rake hob is regarded as the equivalent tooth profile of DFHP without theoretical error, and the DFHP three-dimensional solid model is redesigned. The results show that the tooth profile errors of the equivalent tooth profile of DFHP and the machined flexspline increase with the positive rake angle and the top edge clearance angle of the hob. The DFHP design method without theoretical error reduces the tooth profile error of the flexspline from 6.2 microns to 0.14 microns. So reducing the rake angle and top edge clearance angle of DFHP can reduce the machining error of DFHP, and the new DFHP design method can not only construct an accurate DFHP three-dimensional solid model, but also effectively reduce the machining error of DFHP.关键词：double-circular-arc harmonic drive;flexspline;flexspline hob;tooth profile error90|4|2更新时间：2025-07-09
- 摘要：To further improve the blade tip film cooling effectiveness and reduce the tip leakage flow, the flow and heat transfer characteristics of blade squealer tip with the application of oval-hole and radial inclination angle were numerically investigated using the three-dimensional RANS equation and standard k-ω turbulence model based on CFX software. Taking the first stage of GEE3 turbine rotor as the research object, the tangent direction of camber line is designed as the long axis direction of the oval-hole. The inclination angle includes the positive inclination which leans to the pressure side and the negative deflection which leans to the suction side. Numerical simulation results of eight structures were obtained at three blowing ratios. The results show that the average film cooling effectiveness of oval-hole is more than twice that of traditional circular hole at low blowing ratios, but it is limited by the contraction of oval-hole outflow region at high blowing ratios. The cooling effectiveness of the oval-hole with positive inclination angle is better than that of round hole without deflection angle at all blowing ratios. The positive inclination structure has better local cooling effect, but most of the cooling area is on the pressure surface side; however, the negative deflection structure effectively expands the film cooling range at medium and high blowing ratios, but its cooling effect is poor at low blowing ratios. The positive inclination structure leads the film cooling flow towards the leakage flow inlet, which can enhance the blocking effect and reduce the leakage flow, and the maximum relative reduction rate of leakage flow is 11.4%. The negative inclination structure leads to the generation of vortexes in squealer tips due to the large flow deflection, which drains a part of the main flow, and the leakage flow is increased by 16.6% under the large inclination angle structure.关键词：squealer tip;film cooling;oval-hole;leakage flow94|5|3更新时间：2025-07-09
- 摘要：To eliminate the wrong data and reduce error, the particle image velocimetry(PIV)flow field data are decomposed into several intrinsic mode functions by empirical mode decomposition. The flow field data can be reconstructed and wrong data can be eliminated effectively by smoothing the intrinsic mode functions with abnormal waveform and superposing the processed intrinsic mode functions and other intrinsic mode functions with normal waveform. Through calculating the correlation coefficient between each intrinsic mode function and original flow field data, the above process can be simplified as deleting the intrinsic mode functions uncorrelated to original flow field data and superposing other intrinsic mode functions to eliminate the wrong data directly when the decomposed intrinsic mode functions are numerous and the wrong data are concentrated in a certain intrinsic mode function. Two simulated standard flow fields with artificially added errors of 1.7% and 3.3% are processed by the above-mentioned method, and the errors of the two processed flow field data are 0.002% and 0.18%, respectively. The original experimental flow field data are processed by this method. The results show that the wrong data can be effectively eliminated, and the flow field characteristics are more clear and accurate. These research results can be used to reduce error in the tempolabile flow field data.关键词：particle image velocimetry;empirical mode decomposition;intrinsic mode function;correlation coefficient86|4|0更新时间：2025-07-09
- 摘要：To study the reaction path and reaction sensitivity of 2,5-dimethyl-tetrahydrofuran(DMTHF)combustion, the thermodynamic and reaction kinetic properties of reactants, products and transition products of DMTHF oxidation are calculated by combining the high-precision electronic structure theory and the elementary reaction statistical mechanics. On this basis, the general high-temperature oxidation mechanism of tetrahydrofuran family fuels is established and verified by the results of the DMTHF laminar flame experiments at different temperatures, pressures, and equivalence ratios. It is shown that in the H-abstraction reactions of DMTHF, the H-abstraction reaction dominates at position 2; the reaction to generate P1 dominates in the oxidation reaction path of DMTHF-MJ in pyrolysis reactions. The path analysis of DMTHF shows that more methyl groups on the ring structure for DMTHF may result in much more complicated reactions; large amount of consumption of H and OH radicals in the conversion reactions between C3H6 and AC3H5 radicals has a strong impact on the DMTHF oxidation reactions.关键词：2,5-dimethyl-tetrahydrofuran;reaction kinetics;reaction path analysis;sensitivity analysis102|4|0更新时间：2025-07-09
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