最新刊期
卷 54 ， 期 11 ， 2020
- 摘要：In order to reveal the influences of the aromatics with different structures on the physicochemical properties of diesel burning PM this paper studies the effects of aromatics addition on the physicochemical properties of diesel burning PM. Experiments were conducted in a high pressure common-rail diesel engine, and three fuels including pure diesel, diesel/benzene(30% benzene+70% diesel, by vol.)and diesel/tetralin(30% tetralin+70% diesel, by vol.)were used. Burning PM were analyzed by transmission electron microscope(TEM), Raman spectroscopy(RS), X-ray photoelectron spectroscopy(XPS)and thermogravimetric analysis(TGA). The experimental results showed that the diesel soot has a highest oxidation temperature of 594.5 ℃, followed by the diesel/tetralin soot with 589.8 ℃, while the diesel/benzene soot has a lowest oxidation temperature of 575.8 ℃. Besides, TEM, RS and XPS results revealed that compared with pure diesel soot, benzene/diesel soot and tetralin/diesel soot have larger mean primary particle diameters which increased 0.411 nm and 2.169 nm respectively, also with higher AD1/AG and ID1/IG, and greater sp3/sp2 ratio. These results indicate that burning particle samples from diesel/aromatics mixtures have lower degree of graphitization and more disordered nanostructure.关键词：diesel burning particulate matter;aromatics;morphology;surface chemistry294|4|2更新时间：2025-07-09
- 摘要：By solving the RANS equations coupled with plasma actuation forces, the influence of single dielectric barrier discharge(SDBD)plasma actuation on film cooling effect at plain surface was numerically investigated. With the experiment data, the reliabilities of linearized plasma force model and numerical methods were validated. Under six different dimensionless actuation strengths, five different dimensionless actuation frequencies and three blowing ratios, the film cooling effects on plain wall surface were predicted. The computed film cooling effectiveness distributions and flow structures near the film cooled surface with SDBD plasma actuation were compared with the cases without plasma actuation. The numerical results show that compared with the case without SDBD actuator, the film cooling effect on plain wall surface is significantly enhanced. With SDBD plasma actuation, the development of counter-rotating kidney vortex pair downstream the cooling hole is suppressed, resulting in a larger near-wall streamwise velocity gradient, higher peak value of near-wall streamwise velocity, and wider coolant coverage along both spanwise and streamwise directions, than the case without plasma actuation. As the dimensionless actuation strength increases from 40 to 140, the film cooling effect on plain wall surface is improved significantly. As the dimensionless actuation strength is equal to 100, the maximum centerline and laterally averaged film cooling effectiveness are increased by 105% and 200% respectively, compared with the case without plasma actuation. As the dimensionless actuation frequency increases from 1.25 to 6.25, the film cooling effectiveness on plain wall surface is kept increasing. When the dimensionless actuation frequency is equal to 3.75, the maximum centerline and laterally averaged film cooling effectiveness on plain wall surface are higher than the case without plasma actuation by 75% and 100% respectively. As the blowing ratio increases, the film cooling effect on plain wall surface is decreased correspondingly. As blowing ratio increases from 0.5 to 1.0, the maximum centerline and laterally averaged film cooling effectiveness on plain wall surface are decreased by 23.9% and 49.2%, respectively.关键词：film cooling;plasma;single dielectric barrier discharge;actuation strength;actuation frequency;blowing ratio281|4|2更新时间：2025-07-09
- 摘要：The spiral groove dry gas seal is designed according to the sealing requirements of the shaft end in 450 MWe supercritical CO2(SCO2)compressor. The influences of spiral angle and groove depth on the sealing performance of the designed dry gas seal are numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes(RANS)equations and SST turbulence model. The accuracy of the numerical method is validated by comparison of the experimental data for dry gas seal with air working fluid. The leakage flow rate, opening force and opening force leakage ratio of the spiral groove dry gas seal at five different spiral groove depths and four different spiral angles are numerically analyzed. The results show that the increase in the spiral groove depth leads to an intense increase in the maximum pressure and the high pressure area in the groove root region of the dry gas seal, which results in a higher opening force and bigger leakage rate. When the groove thickness increases from 3 μm to 7 μm, the maximum increase of opening force is 9.07% when the spiral angle is 20°; the maximum increase of leakage rate is 18.67% when the spiral angle is 25°. The maximum opening force leakage ratio is reached when the spiral groove angle is 15°, which means the dry gas seal with this groove angle has the best comprehensive sealing performance. The performance analysis of the spiral groove dry gas seal at the shaft end of the compressor in this study provides a reference for the SCO2 power cycle seal design.关键词：SCO2 compressor;spiral groove dry gas seal;leakage flow;opening force-to-leakage ratio;numerical simulation306|4|8更新时间：2025-07-09
- 摘要：To accurately calculate the amount of the tooth surface modification to reduce the amplitude of load transmission error(ALTE), considering the load-bearing deformation of the teeth between different meshing areas in the process of gear meshing, a design method of compensation modification for multi-pair contact of high contact ratio helical gears is proposed. The transmission error of modified tooth surface is predesigned based on the magnitude and direction of ALTE of the standard tooth surface under the design load, and the precise compensation modification in different meshing areas of the tooth is realized by optimizing the TE to control the value of the tooth surface modification. The model of a further longitudinal modified tooth surface is established, and the additional angle of rack cutters and the parameters of the longitudinal correction are taken as the optimization variables. The optimal tooth surface modification values are determined by the fast elitist non-dominated sorting genetic algorithm(NSGA-II)based on the minimum ALTE. The results show that the change of load-bearing deformation caused by the change of meshing pairs is the main cause for the fluctuation of the ALTE. After the tooth surface compensation modification, the ALTE decreases greatly, and under the designed load, the ALTE drops to almost zero. The further longitudinal correction can also effectively compensate the difference of tooth deformation between different meshing areas of the teeth, avoiding the edge contact, and reducing the vibration and noise of gears.关键词：high contact ratio;helical gears;amplitude of load transmission error;transmission error;compensation modification design294|4|2更新时间：2025-07-09
- 摘要：Aiming at the limitation of theoretical formula design and the low efficiency of finite element method for multi-variable and multi-constraint optimization in spring optimization design, a two-step strategy for spring optimization considering section shape and geometry size is proposed. In the first step, geometry sizes of the spring is optimized with the helical spring theoretical formulae combined with the multi-start search algorithm. In the second step, a spring model considering cross-section shape is established by the finite element method. The optimal solution of geometry sizes is taken as the initial value, and the cross-section shape as well as geometry sizes are optimized by the zero-order method to acquire the optimal solution. Simulation results show that the two-step strategy can optimize the spring design by considering section shape and geometry size, expanding the design range of the spring. Compared with the results optimized directly based on FEM, the calculation time of the two-step optimization strategy is reduced by 55.86%, which shows that the two-step strategy is efficient to reduce the iterative number of FEM optimization. Optimization objective is increased by 14.31%, and the local optimal solution is improved.关键词：spring;optimal design;finite element method;section shape;geometry size140|4|0更新时间：2025-07-09
- 摘要：In order to reduce the aerodynamic noise of the traditional blade-type axial fan and inspired by the owl wing profile and non-smooth edge structure, the thickness distribution at the 40% span of the long-eared owl with silent flight characteristics was extracted based on the medial camber line distribution of the prototype axial fan as a benchmark. Combined with the non-smooth structural features of the long-eared owl wing edges and coupled with a sinusoidal sawtooth structure at the trailing edge of the imitated owl blade, bionic reconstruction of the axial fan blade was performed and used in the modified blade design to reduce the noise of axial fans. Based on the numerical calculation results of the internal flow field of axial fan, the large eddy simulation(LES)combined with the FW-H sound analogy method developed by Ffowcs Williams and Hawkings was used to numerically simulate the sound field characteristics of the axial fan. The research results show that the overall noise reduction of the bionic coupled blade fan is 2 dB and the air volume is increased by 4.69% compared with the prototype fan. The internal flow field and sound field of the fan show that the bionic coupled blade makes the air flow transition from the suction surface to the pressure surface more smoothly, which not only improves the local impact of the air flow on the leading edge of the blade, but also reduces the leakage vortex strength at the tip clearance. In addition, the turbulence boundary layer generated by the bionic coupled blades and the degree of airflow pulsation and airflow unevenness caused by the wake vortex shedding are weakened, and both broadband noise and discrete noise are reduced in the low-mid frequency range. Therefore, the bionic coupled blade not only improves the local pressure pulsation at the leading edge of the blade, but also reduces the intensity of the sound source at the trailing edge serration and improves the trailing vortex distribution at the trailing edge of the blade.关键词：long-eared owl wing;non-smooth structure;aerodynamic noise;axial fan;numerical simulation302|4|8更新时间：2025-07-09
- 摘要：In this paper, theoretical investigation of the new type of ring resonance radial elastic metamaterial plate structure is conducted, which aims at the problem that the radial elastic metamaterial structure with low-frequency vibration damping band gap is not easy to process and cannot meet industrial needs. In contrast to the traditional structure, the proposed new structure is created by an external octagon and an internal structure connected by connecting blocks. Finite element calculation results show that the two complete band gaps in the dispersion relations coincide with the band gap in the transmission spectra of the finite period structure, in which the first band gap is 2 171.9 - 2 716.9 Hz and the second band gap is 4 747.5 - 9 067.5 Hz. By analyzing the intrinsic displacement field of special points at the band gap boundary the formation mechanism of first and second band gap is attributed to the internal structure and local resonance of octagonal matrix. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the internal structure radius and connection block width geometrical parameters will affect the quality of the internal structure and the equivalent rigidity of the connection block, and thus affect all changes in the band gap, while the width of the octagonal matrix only has a large effect on the high frequency band gap. These characteristics of band gap in the proposed radial elastic metamateria can potentially be applied to industrial equipment.关键词：radial elastic metamaterial;local resonance;band gap173|4|2更新时间：2025-07-09
- 摘要：Aiming at large time delay, strong coupling and external disturbance in compression refrigeration system, a predictive auto disturbance rejection control strategy with finite time extended state observer is proposed. Via model identification of compression refrigeration system, the transfer function matrix of double input and double output is obtained. The Smith predictor is used to predict the actual output of the refrigeration system, so as to reduce the influence of time delay in the operation process. Then the refrigeration system is decoupled into two single input and single output systems by series of decoupling controller. To improve the disturbance rejection ability and response rate of this system, a finite time convergent extended state observer is introduced, and its finite time convergence is proved by the constructing Lyapunov function. The state estimation and disturbance compensation of the decoupled system are carried out by the finite time convergent extended state observer and control law, and the proportional controller is used to control the system, thus the independent control of superheat and evaporator temperature is realized. Compared with the predictive auto disturbance rejection control based on the linear extended state observer, the simulation results show that this strategy can reduce the regulation time by about 50%, the dynamic landing by about 30%, and has good robustness when the parameters are perturbed; the experimental results show that this strategy can reduce the regulation time by about 30%, and the dynamic landing by about 12%. The dynamic performance and disturbance rejection performance of refrigeration system are significantly improved.关键词：compression chiller system;active disturbance rejection control;Smith predictor;extended state observer277|4|0更新时间：2025-07-09
- 摘要：Aiming at the abruptness posed by public opinion emergencies, limited labeled data and management resources, we proposed an unsupervised algorithm for evaluating the importance of public opinion changing trend and controlling the important public opinion events within limited time and reducing their harmful influence to the society. Firstly, the importance of changing trend evaluation problem is transformed into a multi-index ranking based on the management experience. Secondly, to solve the problems posed by limited labeled data, we use the principal curve algorithm to formulate the problem of changing trend evaluation, and use the third-order Bessel curve to obtain the final ranking results. The designed model can fully capture the structural and value characteristics of the original data. Finally, we employ the typical public data set and the self-built public opinion event data set to verify the proposed method. The experimental results verify that the developed method has high efficiency in public opinion event changing trend ranking without prior knowledge, and provides a decision support for public opinion event management with limited resources.关键词：public opinion management;limited resources;unsupervised learning;Bessel curve311|4|2更新时间：2025-07-09
- 摘要：To solve the problems of coarse-grained network traffic fingerprints and large memory consumption in the matching phase, we proposed a fine-grained network traffic classification architecture to achieve automated signature generation and optimize memory. As some portion of the data payload in a function is invariant and the signature reflecting the application function is atypical in internet traffic, the signature generation is mapped into the problem of obtaining the frequently occurring substrings and their corresponding occurrence frequency. In the case of online matching, according to the idea of k-means classification, the distance is redefined and the rules are reorganized using the heuristic heterogeneous bit-split deterministic finite automaton method to achieve the purpose of optimizing memory usage. The experimental results show that without knowing the format of the network traffic protocol, the method can automatically generate fine-grained traffic fingerprints with an average recognition accuracy of 93.65%, and is not sensitive to noise. In addition, if all fingerprint character fragments are re-optimized during matching, when the number of fingerprint rules is above 4 000, it can save nearly 50% of memory requirements compared with the previous bit-split string matching methods.关键词：fine-grained traffic;automated signature generation;bit-split deterministic finite automata;heuristic algorithm;string matching280|4|0更新时间：2025-07-09
- 摘要：To obtain the long-distance dependence between different feature points in the feature map of the convolutional neural network, so that the convolutional neural network can better distinguish the foreground target and background information, a spatial attention mechanism with global features is proposed. Combining the multi-channel original feature map into a single-channel feature fusion map through the channel fusion layer, the influence of the information distribution between channels on obtaining spatial attention weights is eliminated; the feature fusion map through global feature acquisition processing to obtain the global feature map, which represents the correlation between a feature point and all points in the feature fusion map; the global feature map is multiplied by the learnable variable with an initial value of 0, and copies itself to the size of the original feature map in channel domain. The expanded global feature map is added to the original feature map to obtain a feature map with attention mechanism. After adding the spatial attention mechanism with global features to different convolutional neural networks, the experimental results show that in the brain wave two-classification task, the algorithm classification accuracy is heightenedby the maximum of 0.839%; in the CIFAR-10 data set multi-classification task, the classification accuracy of the algorithm is improvedby the maximum of 0.484%; in the single-category detection of night vehicles, the algorithm is heightenedby the maximum of 3.860% with the evaluation standard of the average accuracy value of Intersection over union(IoU)greater than 0.5, and the algorithm is improvedby the maximum of 11.726% with the evaluation standard of the average accuracy value of IoU greater than 0.75; in the multi-category detection of the voc2007 data set, the algorithm has improved by the maximum of 0.778% with the evaluation criterion of the average precision value of IoU greater than 0.5, and the algorithm has improvedby the maximum of 1.232% with the evaluation criterion of the average precision value of IoU greater than 0.75.关键词：convolutional neural networks;spatial attention mechanism;global features;feature fusion;target classification;target detection250|4|3更新时间：2025-07-09
- 摘要：The traditional label distribution learning algorithms utilize the label correlation in a global way but ignore the local correlation. An algorithm called label distribution learning via sample sparse representation(LDL-SR)is proposed. Particularly, to capture the sample local correlation, LDL-SR uses the self-expressiveness property of samples to establish a sparse representation optimization model. Then, by the well-designed objective function, the obtained sparse coefficient is introduced into the label space to predict the correlation of the labels to help the training of the label distribution model. The sparse representation optimization model can be solved with alternating direction multiplier method(ADMM), and limited memory quasi-Newton method(L-BFGS)is chosen to optimize the target function of the label distribution model. Finally, LDL-SR calculates the predicted label distribution via the maximum entropy model. Compared with 7 existing label distribution learning algorithms, the experimental results on 11 real-world datasets show that this algorithm achieves an average ranking of 1.52 in 55 comparative experiments under different evaluation measures. Compared with the PT-SVM, AA-kNN, and the LDLLC algorithms on facial expression dataset SBU-3DFE, the accuracy of expression discrimination is enhanced by 3.10%, 2.53% and 2.48% respectively. It is found that LDL-SR can achieve good prediction accuracy and stable performance on different real-world datasets.关键词：label distribution learning;sparse representation;maximum entropy model247|4|0更新时间：2025-07-09
- 摘要：In view of the problems existing in the TBM(tunnel boring machine)cutterhead muck transfer simulation research that the grading and shape parameters of rock chips are not considered comprehensively, and the influence of the scraper bucket structure is not clearly revealed, a numerical model of the mucking process including chip falling, shoveling and sliding was built considering the grading and shape of rock chips by using the clump strategy of a particle-based discrete element method, and the numerical model was verified by scaled mucking tests. Numerical simulations were carried out to study the influence of disc cutters, bucket structure, bucket height and bucket width on the cutterhead’s mucking performance considering the average mucking speed and passing rate. The simulation results show that the influence of the disc cutters on the mucking process can be ignored. The triangle section type is a more reasonable bucket structure. The recommended value of bucket height is approximately 30-50 mm smaller than the disc cutter height. The recommended value of bucket width is 50% of the width of the chip discharging chute. The numerical model built in this paper provides an effective approach for the study of mucking process of TBM cutterhead, and the conclusions can be used as theoretical basis for the design of scraper buckets.关键词：tunnel boring machine;muck transfer;scraper bucket;particle-based discrete element method98|4|3更新时间：2025-07-09
- 摘要：The fixed threshold equalization strategy and the traditional fuzzy equalization strategy usually result in overvoltage or undervoltage protection to malfunction at the end of the battery pack charge and discharge, and it is difficult to be fully balanced, because a large difference between the batteries makes the balance insufficient. A variable universe double fuzzy controller(VDF)equalization strategy is thus proposed. The lithium battery simulation model is established according to the experimental data of charged and discharged NCR18650B ternary lithium battery. The state of charge(SOC)of the single lithium battery is used as the input of the first-level fuzzy controller, and its output multiplied by the lithium battery working current value is used to adjust the output domain of the second-level fuzzy controller; the difference between the SOC of a single lithium battery and the average SOC of the battery pack and its rate of change are used as the input of the second-level fuzzy controller, and its output is used as the equalizing current; the extreme difference of SOC between the single cells in the battery pack represents the inconsistency, and the equilibrium time is determined by the first convergence of the extreme difference to 0.05. The simulation results from Simulink show that the VDF equalization strategy effectively reduces the voltage protection malfunction. With constant charge and discharge current and in custom dynamic stress test(DST), VDF equalization strategy is compared with the traditional fuzzy equalization strategy, and the results show that the equalization rate increases by above 30%, and as a large difference exists between the batteries, the consistency increases by above 20% after the end of the equalization.关键词：variable universe double fuzzy controller;lithium battery;state of charge;malfunction;the extreme difference266|4|3更新时间：2025-07-09
- 摘要：To reveal the bubble detachment behaviors during subcooled boiling process, a data driven statistical analysis method according to the finite mixing model(FMM)and the standard variance decomposition(Sobol model)is employed to investigate the influence factors of bubble departure diameter on superheated wall surface in vertical flow boiling. The data driven database is constructed and modified based on the experimental data and empirical correlations collected from literature. The dimensionless parameters describing flow boiling are chosen as the input variables of this model, and bubble departure diameter as the output variable. Kullback-Leibler divergence and χ2 distance are adopted for determining the importance degree order of input variables. The preliminary results of sensitivity analysis show that the effects of Reynolds number and vapour-liquid density ratio on bubble departure diameter are the most significant among these inputs. The results coincide well with those obtained by the traditional methods, which indicates the feasibility of the data-driven method in analyzing engineering problems. In addition, FMM is more general than Sobol model based on the present database, and can be applied directly based on these data.关键词：flow boiling;bubble departure diameter;data driven analysis;finite mixture model278|4|2更新时间：2025-07-09
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