最新刊期
卷 55 ， 期 5 ， 2021
- 摘要：In order to study the effect of iodine value on the emission characteristics of biodiesel combustion particulate matter, the engine exhaust particle sizer and carbon analyzer were used to analyze the particle size distribution and carbon component of particulate matter from different biodiesels. The results show that the maximum explosion pressure, combustion temperature and combustion duration of three biodiesels are higher than that of diesel at the maximum engine torque speed 2 400 r/min and 100% load. The greater the iodine value is, the shorter the combustion duration becomes. The use of biodiesel can effectively reduce the amount of particulate matter emissions, with a maximum reduction of 85%, and the particle size of biodiesel particles is decreased. The higher the iodine value is, the more the particulate matter is produced. The emission concentration of soybean oil methyl ester particles with larger iodine value is 5.3 times that of waste oil methyl ester particles with lower iodine value. The main components of organic carbon(OC)in the carbonaceous component of particulate matter are OC1 and OC4, which account for more than 60% of the total carbon(TC). The main component of elemental carbon(EC)is EC2, which accounts for more than 50% of the total EC. The ratio of diesel particulate organic carbon(OC)to elemental carbon(EC)in the carbonaceous component of particulate matter is 7.4, and the biodiesel OC/EC value is 18.2-24.5. The higher the iodine value of biodiesel, the higher the OC/EC value of particulate matter carbon component. Using biodiesel with lower iodine value can reduce particulate matter emission more effectively.关键词：biodiesel;particulate matter;iodine value;particle size distribution;carbon component85|4|3更新时间：2025-07-09
- 摘要：To select the best leakage model and investigate the effects of the operational conditions on the rotordynamic characteristics of the straight-through labyrinth seal, the rotordynamic characteristics prediction method and program of labyrinth seals are developed based on the one-control-volume Bulk-Flow model considering the isentropic process. Through the applicability analysis of 72 leakage models, it is found that the best leakage model is the one that uses Neumann's leakage equation, Chaplygin's discharge coefficient, Swamee & Jain's friction factor and Kurohashi's kinetic energy carryover coefficient(for positive preswirl conditions)or Neumann's kinetic energy carryover coefficient(for negative preswirl conditions). The developed method combined with the best leakage model has an average prediction error of about 10% for the cross-coupled stiffness and direct damping of labyrinth seals. The developed prediction program is used to investigate the effects of pressure ratios(0.3, 0.5, 0.7)and preswirl ratios(-0.8, -0.4, 0, 0.4, 0.8)on the rotordynamic characteristics of labyrinth seals. The results show that the cross-coupled stiffness and direct damping of labyrinth seals are sensitive to the inlet pressure, but are insensitive to the outlet pressure. The crossover frequency is hardly affected by the inlet and outlet pressures. Increasing preswirl ratio results in a decrease in the effective damping of labyrinth seals. For positive preswirl conditions, negative effective damping exists and the crossover frequency significantly increases with the preswirl ratio, which is a destabilizing factor for rotor system. The influence of inlet preswirl velocity is more significant at the upstream cavities of the seal. Therefore, anti-swirl devices should be installed at the seal entrance to suppress the circumferential flow of the leakage flow. The presented prediction method and program can provide technical approaches for rapid evaluation of the rotordynamic coefficients of labyrinth seals.关键词：labyrinth seal;Bulk-Flow model;leakage model;rotordynamic characteristics61|4|5更新时间：2025-07-09
- 摘要：Series axis of multi-axis CNC machine tool introduces low-order modes to result in a difficultly controlled tracking error. A comprehensive control strategy of modal filter and notch filter is proposed. Establishing a dynamic model of the ball-screw servo feed system with a series of shafts, the mechanical modes introduced by the series of shafts are analyzed. A combination scheme of notch filter controller with modal filter controller is designed to suppress the high-order modes of the ball-screw feed system and the low-order modes introduced by the series axis. The influence of each combination scheme on servo bandwidth and tracking error is discussed. It is concluded that for a ball-screw servo feed system with a series axis, the low-order modes caused by the series axis are the key modes that limit the increase in the bandwidth of the position loop; the notch filter commonly used in engineering suppresses high-order modes, such as the first-order and second-order torsional vibration of the screw, which cannot increase the bandwidth of the position loop of the ball-screw servo feed system with serial axis, and cannot effectively control the tracking error. For the ball-screw servo feed system with serial axis, the tracking error control strategy ought to choose as speed feedforward controller+low-order modal filter+high-order modal notch filter.关键词：series axis;modal filter;notch filter;tracking error;CNC machine tool61|4|2更新时间：2025-07-09
- 摘要：To avoid the use of support structures in the additive manufacturing process of components, this paper proposes an additive manufacturing oriented topology optimization method for self-supporting structures based on element filtering. By using 4-node rectangular element to discretize the design domain, a finite element model of overhang is established. A filtering rule of the self-supporting element based on Heaviside function is constructed by simulating the layer-by-layer forming process of additive manufacturing. The self-supporting elements are retained, and the non-self-supporting elements are deleted by this rule layer-by-layer. Based on the solid isotropic material with penalization(SIMP)model, the additive manufacturing oriented self-supporting structure topology optimization model is formulated, and the method of moving asymptotes is used to solve this optimization problem. The topology optimization method of self-supporting structures is applied to the topology optimization for the Messerschmidt-Bölkow-Blohm(MBB)beam. The results of case studies show that compared with the traditional topology optimization method, this method can achieve optimal design of self-supporting structure for the MBB beams along four printing directions, and moreover, the material and printing time can be saved up to 20.6% and 16.6% at most, respectively. It can solve the problem that traditional topology optimization structures need supports in additive manufacturing process.关键词：additive manufacturing;self-supporting element filtering;topology optimization;density-based method;self-supporting structure66|6|3更新时间：2025-07-09
- 摘要：To dynamically express the uncertain loads of hydraulic components of construction machinery under different working conditions in system dynamics simulation, a lumped parameters dynamic response model of hydraulic component load is proposed. For the non-stationary random cyclic load of hydraulic components, the wavelet transform method is used to decompose it into a trend term and a random term. The non-stationary trend term is expressed by a lumped parameter model calibrated by data from field tests, and the stable random term is expressed by a random harmonic function based on the principle of energy equivalence, and the load model is synthesized by the above two terms. Then, taking rotary load of a certain type of hydraulic excavator as an example, the load model of the rotary motor is established and the response of the load model is compared with the field test data under a certain working condition to prove the feasibility and effectiveness of the load model construction method. The research results show that the lumped parameter dynamic response model can realize the dynamic expression of the hydraulic component loads under different working conditions, which helps improve the adaptability of the hydraulic system dynamic simulation of construction machinery to complex and variable working conditions.关键词：construction machinery;load;system dynamics simulation;wavelet decomposition;lumped parameter95|4|1更新时间：2025-07-09
- 摘要：To solve the problem of pads floating state prediction of the fluid pivot tilting pad journal bearing, a lubrication analysis model considering the coupling effects of inner hydrodynamic film and outer hydrostatic film was proposed. The lubrication characteristics of traditional fixed pad bearing, mechanical pivot tilting pad bearing and fluid pivot tilting pad bearing under different working conditions were compared. The results show that static characteristics of the fluid pivot tilting pad bearing, such as the film thickness, film pressure and film temperature, are better than that of the traditional fixed pad and tilting pad bearings. Moreover, the direct stiffness and damping are about an order of magnitude higher than the traditional bearings. Therefore, fluid pivot tilting pad bearing can significantly improve the bearing safety and the stability of rotor system. However, pads may suffer two equilibrium states under certain working conditions, which will result in unstable working state and sudden change of bearing performance. This work may provide reference for designing the fluid pivot tilting pad journal bearings.关键词：fluid pivot tilting-pad bearing;lubrication theory;pressure coupling;floating state92|4|1更新时间：2025-07-09
- 摘要：Aiming at the problems of manual identification, subjectivity, low efficiency, and lack of integrated analysis from waveform features and image features in using the time-of-flight, diffraction(TOFD)data for weld defect recognition, a deep learning fusion model(DLFM)and a weld defect recognition method are proposed. Based on the analyses of TOFD detection principle and weld defect detection data characteristics, a defect feature representation method considering waveform data and image data is set up, and the defect standard data set is established. Combining waveform sequence data analysis module based on time convolution network(TCN), image data analysis module based on convolutional neural network(CNN)and feature adaptive fusion classification module, the DLFM with pattern classification is constructed. A case study of TOFD weld defect recognition is conducted to illustrate the work. The results show that the proposed DLFM has higher defect recognition rate than the method based on CNN, TCN or CNN-TCN. The proposed method improves the traditional deep learning models, and can be applied to the other pattern recognition fields with stronger universality.关键词：time-of-flight diffraction;weld defect recognition;feature adaptive fusion;deep learning138|4|1更新时间：2025-07-09
- 摘要：To optimize the transmission performance of virtual data space network, an intelligent TCP congestion control algorithm based on proximal policy optimization is proposed(TCP-PPO2). The TCP congestion control process is abstracted as a Markov decision process, which can be partially observed. In this process, an agent is constructed to interact with the network environment. The agent adjusts the size of congestion window by observing the characteristics of network state. The network environment feeds back a reward value to the agent, and the agent tries to maximize the expected reward value in an episode. The state space including throughput, network delay and other network characteristics is designed, so that agents can observe enough information to make decisions and reduce performance overhead. The weighted reward function is designed to balance the throughput and delay. The parameters of the agent model are updated by the proximal policy optimization algorithm, and excessive parameter updates are truncated. The parameter update is limited to a certain range, which reduces the oscillation problem in the process of gradient descent, and realizes quick convergence of the training process. The TCP congestion control algorithm based on proximal policy optimization is implemented on NS3 simulator, and compared with the mainstream congestion control algorithms such as cubic, HighSpeed and NewReno. The results show that the throughput performance of TCP-PPO2 can reach more than 2-3 times of the comparison method, while the delay value of 80% of the sampling points only increases 4% compared with the minimum link delay.关键词：virtual data space;proximal policy optimization;congestion control;TCP72|5|0更新时间：2025-07-09
- 摘要：Aiming at the problem that the existing anti-spoofing detection algorithms difficultly detect unknown domain attacks, this paper proposes a face anti-spoofing detection algorithm using generative adversarial networks with hypercomplex wavelet transform to improve the ability of face recognition system to determine the face anti-spoofing. Four different types of datasets are adopted, in which three datasets are randomly selected as the training ones, and the remainder as the test dataset to serve for unknown face anti-spoofing detection during training. The training datasets are regarded as three source domain datasets, which are input into the generation network to make a feature generator against three discriminators. When this feature generator successfully deceives the three discriminators, a feature space sharing three source domains and being different from these domains is formed to detect the characteristics of the unknown domain data. The triple constraint functions inter-class and intra-class are set up to improve the performance of the discriminator, and the detailed subbands of the hypercomplex wavelet transform and the convolution network are combined to learn the detailed features in multiple directions of images. Then the depth map and remote photo plethysmography signal are embedded in the feature space to enhance the generalization performance of the generated feature space for the living face features. The test dataset for discriminative classification in the feature space is used to obtain live/fake results. The results show that on the CASIA-FASD, Replay-Attack and NUAA datasets, the proposed algorithm gets the AUC of 84.65%, 86.06% and 91.21%, the HTER of 24.05%, 21.05% and 15.01%, which are higher than those of the comparative algorithms.关键词：face anti-spoofing detection;hypercomplex wavelet;generative adversarial networks77|5|4更新时间：2025-07-09
- 摘要：Activity wireless sensing is an important technology to implement health monitoring. Although the research on activity perception based on Wi-Fi has made good progress, there are still some problems, such as the difficulty of feature extraction in the traditional machine learning and the single feature extraction method in deep learning, which leads to insufficient feature extraction and low recognition accuracy. Here AHNNet, a hybrid neural network of human activity recognition integrating attention mechanism is proposed. Analyzing the influence factors of channel state information, the amplitude data of channel state information are used as the basic data for activity recognition, and the time sliding window is used to divide the long time human activity sequence into short time series to construct the sample data, which solves the difficulties of non-real-time and non-fixed length global human activity data. AHNNet parallelizes the bidirectional gated recurrent network and the temporal convolutional network to extract the features of the input data, so as to fully reveal the relationship between potential features of data. To further improve the performance of model recognition, AHNNet is combined with attention mechanism to strengthen the main features of data in bidirectional gated recurrent network. Then, the features extracted from the bidirectional gated recurrent network and the temporal convolutional network are fused to increase the diversity of the features, and the fused features are input into the Softmax classifier for classification to obtain the activity corresponding to human activity data. Experimental results demonstrate that AHNNet has stronger classification ability than the other models, and the average accuracy rate achieves 97.15%, and AHNNet has fewer parameters while maintaining high accuracy. The competing model demonstrates that the accuracy rate is 95.7% in the bedroom environment, 1.45% lower than that in the standard data acquisition room. AHNNet has good recognition effect and robustness, especially in complex home environment.关键词：human activity recognition;channel state information;bidirectional gated recurrent network;temporal convolutional network;attention mechanism69|4|1更新时间：2025-07-09
- 摘要：In view of the requirements of temperature control accuracy and response rate of electromagnetic stir-frying machine for producing the Chinese drug beads, an improved particle swarm optimization(PSO)radial basis function neural network(RBFNN)PID control method is proposed based on interference observer. According to the structure of the electromagnetic stir-frying machine of Asini Coii Colla beads, the mathematical model of temperature control system of the special electromagnetic stir-frying machine is established. Analyzing the structure of the control system, the RBF neural network structure is constructed. Adopting the self-learning ability of the RBF neural network, the gradient descent method is chosen to adjust its own parameters adequately to realize the dynamic adjustment of PID parameters, thus the system inertia and time lag are suppressed efficiently. Analyzing and constructing a disturbance observer model, the interference is real-time observed and effectively compensated to reduce the influence of external interference. To obtain the best control performance, the RBF neural network model parameters are optimized by the improved particle swarm optimization algorithm with the system error instantaneous values for the fitness function to make up for the RBF neural network model parameters' accuracy. Simulation results show that the regulating time of this control method is reduced by 35 s and 19 s, and the overshoot is reduced by 19.2% and 13.1%, respectively, compared with the traditional PID control method and RBFNN-PID control method. The external interference suppression ability is increased by 50% on average compared with the case without interference observer.关键词：electromagnetic stir-frying machine;temperature control;disturbance observer;improved particle swarm optimization;radial basis function neural network60|4|4更新时间：2025-07-09
- 摘要：A pilot protection for high voltage direct current(HVDC)transmission line based on polarity characteristics of control signal deviation is proposed to solve the problem of insufficient performance of traditional HVDC transmission line backup protection. Analyzing the fault characteristics of the converter control signals from the fault transient stage to the fault steady stage, it is concluded that when the fault occurs in DC system, the deviations of constant current control signals at rectifier and inverter are positive and the deviation of constant extinction angle control signal at inverter is negative, while these polarity characteristics are obviously different when the fault occurs in AC system. By observing the polarity differences of control signal after the fault occurs on the AC/DC side, a start criterion based on the change rate of control signal amplitude and a protection main criterion based on the polarity characteristics of control signal deviation are established. Combining the blocking signal of DC bus protection, a novel DC transmission line pilot protection principle is proposed to identify the fault that occurs on it. The simulation results show that the proposed backup protection can identify the DC line fault within 25-100 ms, and it can also effectively identify the 500 Ω high resistance fault. The protection principle only needs the transmission of single-way logic information and lower communication requirement, and works longer during the fault transient stage to the fault steady stage, and its overall performance is better than the traditional current differential protection.关键词：high voltage direct current;transmission line;converter;control signal;polarity characteristics;pilot protection42|4|2更新时间：2025-07-09
- 摘要：In order to resolve the problem that the dynamic range of the readout circuit for femto-level capacitive sensors is severely decreased by the relatively large parasitic capacitance caused by chip fabrication process and application environment, this paper proposes a fully differential readout circuit for capacitive sensors with automatic gain control. A switched capacitor sensing circuit is employed to realize capacitance-voltage conversion and a fully differential amplifier with 3-bit automatic gain control is then adopted to amplify the sensor signal while adaptively suppressing the voltage generated by the large parasitic capacitance. The differential output voltage of the amplifier is converted into digital output by a 12-bit successive approximation AD converter. This circuit is designed by 0.18 μm CMOS technology with 3.3 V power supply. Simulation results show that the proposed readout circuit achieves detection range larger than 1 pF, detection accuracy less than 1 fF, parasitic capacitance tolerance range of 2-10 pF, and measurement time of 1.2 ms. The circuit has 1.8 mW power consumption and 1.2 mm×0.89 mm silicon area, and can be applied in applications such as capacitive touch screens and mini-accelerators to improve the measurement accuracy.关键词：capacitive sensor;parasitic capacitance;readout circuit;automatic gain control;successive approximation AD converter;capacitance-voltage conversion409|4|2更新时间：2025-07-09
- 摘要：The flow field of a Y-type active micromixer with an impeller and two inlets is numerically simulated using moving the particle semi-implicit method, in which the fully developed velocity inlet model and the moving boundary model are combined. A high efficiency inclined continuous inlet model based on position judgment is proposed. A local mixing rate calculation method, which can describe ideal ordered mixing, is defined, and the key parameters of this method are determined through numerical experiments. Simulation of the flow field shows that for the continuous mixing of two immiscible liquids, the mixing mainly happens in the counter current region of the chamber. The mixing index at the outlet channel fluctuates periodically due to the multiple effects of continuous inflow, rotation of blade, and geometry of this mixer. This paper reveals the mixing mechanism and the transportation process in a steady-state period, and studies the influences of inlet velocity and rotating speed on mixing index. It is found that the mixing index can be improved by properly reducing the inlet flow rate or increasing the rotating speed, but the mixing degree will decrease if the inlet flow rate is too small.关键词：micromixer;moving particle semi-implicit method;flow mechanism;mixing index38|4|3更新时间：2025-07-09
- 摘要：To study the compensation networks in wireless charging systems and the safety of electromagnetic exposure in wireless charging with charging coil for electric vehicles, the transmission characteristics of four basic resonance compensation networks are analyzed. Then, a double-sided LCC resonant topology is proposed and analyzed based on the circuit model theoretically. The four basic resonance compensation networks and the double-sided LCC resonant topology are compared with respect to the transmission power and the transmission efficiency using the Matlab/Simulink software. The coupling coefficient and magnetic flux density are studied at different air-gaps and misalignments between the primary coil and the secondary coil. A human body model is modeled to study the magnetic flux density at different measuring points using the finite element method software COMSOL. The results show that the double-sided LCC resonant topology has a high anti-offset capability, which is suitable for dynamic high-power wireless charging for electric vehicles. Moreover, the maximum magnetic induction intensity at the ankle point is 2.043 μT, accounting for 7.57% of the threshold. The magnetic induction density at other points in a human body model is below the safety limits of GB/T 38775.4—2020 guidelines. It indicates that the high frequency electromagnetic exposure produced by coils will not affect human electromagnetic safety when the electric vehicles are wireless charged. The assessment in this paper is conducive to the development of wireless charging for electric vehicles.关键词：electric vehicle;wireless charging;magnetic coupling resonance;double-sided LCC resonant topology;electromagnetic safety56|4|5更新时间：2025-07-09
- 摘要：Combining the non-embedded polynomial chaotic expansion method, sparse grid, Sobol Indic technology and Reynolds-averaged Navier-Stokes(RANS)equation solving method, an uncertainty quantitative analysis method for the aerodynamic and heat transfer performance of the turbine blade squealer tip was proposed. Numerical simulations were consistent with experimental data, which verified the effectiveness of the numerical method for predicting the aerodynamic and heat transfer performance of the squealer tip. The aerodynamic and heat transfer performance of the GE-E3 rotor blade tip was quantified on the basis of the uncertainties of the tip clearance, the total temperature of the mainstream inlet and the blowing ratio. The influences of the uncertain inputs on the average film cooling effectiveness, gap leakage and downstream total pressure loss coefficient were analyzed in detail. The Sobol Indic method was used to quantify the contribution of each uncertain variable to the uncertainty of the tip aerothermal characteristics. The results of the uncertainty analysis show that the leakage in the leading edge area of the blade tip is not sensitive to the uncertain input, but the uncertain deviation of the leakage in the trailing edge area can reach 25%. The downstream total pressure loss coefficient is generally less affected by uncertain fluctuations. Under the influence of the uncertainty of geometry and working conditions, the statistical mean value of the blade tip film cooling effectiveness is reduced by 29.52% compared with the design value, and the probability of 10% deviation from the design value is as high as 91.83%. The sensitivity analysis results show that the tip clearance deviation is the dominant variable in the uncertainty of the tip aerodynamic performance. The variances of the tip clearance deviation to the leakage and the total downstream pressure loss coefficient account for 88.02% and 85.31%, respectively. Among the three variables studied in this paper, tip clearance has the greatest comprehensive influence on the aerodynamic performance and film cooling effectiveness of the blade squealer tip, so the machining accuracy of tip clearance should be strictly guaranteed in the process of blade machining and assembly.关键词：blade squealer tip;aerodynamic performance;film cooling effectiveness;polynomial chaos;uncertainty quantification81|5|3更新时间：2025-07-09
- 摘要：To improve the aerodynamic performance of high-load axial compressor, an active flow control method with synthetic jet applied on the endwall was proposed. A transonic axial flow compressor NASA Rotor35 was taken as the research object. On the basis of fixed endwall excitation at the core of blade tip blockage, the influences of three excitation frequencies and three jet peak velocities on the aerodynamic performance of the compressor were numerically simulated, and the influencing rules of the endwall synthetic jet excitation parameters were obtained. The results show that the excitation frequency has little influence on the near stall flow of the compressor, but has great influence on the total pressure ratio and isentropic efficiency. It is also found that there is a threshold of excitation frequency, and only when the excitation frequency is greater than the threshold, can the total pressure ratio and isentropic efficiency be higher than those of the prototype compressor. The effect of jet peak velocity on the performance of compressor is inferior to the excitation frequency. Under the action of the endwall synthetic jet exceeding the excitation frequency threshold, the compressor can obtain higher flow margin, total pressure ratio and isentropic efficiency than the prototype compressor even if the peak velocity of the jet is small, and the performance of the compressor can be further improved with the increase of the jet peak velocity.关键词：transonic axial compressor;endwall synthetic jet;active flow control;numerical simulation53|4|4更新时间：2025-07-09
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