最新刊期
卷 56 ， 期 11 ， 2022
- 摘要：This paper proposes an adaptive-neural-network-based terminal sliding mode control algorithm based on partitional approximation of dynamic models of robot manipulators to realize tracking of the desired trajectory of each joint generated by trajectory planning of six-axis robot manipulators when models are unknown and there is external disturbance. In addition, a non-singular terminal sliding mode manifold is proposed to accelerate the convergence of the tracking error and avoid the singular problem in the control with the conventional terminal sliding mode. Since the system model is unknown, multi-group RBF neural networks are utilized to approximate the dynamic model parameters, and the model is reconstructed by an adaptive weight update law. The model reconstruction errors are compensated by the designed robust terms. Simulation analysis is carried out in Simulink. According to the analysis results, compared with the RBF neural network global approximation algorithm, the proposed control method can reduce the maximum steady-state error of the manipulator joints by 83.7%. When the time-varying load is added to the end effector, the maximum steady-state error of the joints is reduced by 85.6%. Therefore, the proposed control is an effective and feasible trajectory tracking method for the six-axis robot manipulator under the condition of load variation.关键词：six-axis manipulator;non-singular terminal sliding mode;dynamic model;RBF neural network;trajectory tracking60|12|0更新时间：2025-07-09
- 摘要：This paper proposes the design of hybrid transmission error(HTE)of spiral bevel gears to reduce the noise caused by high order frequency of loaded transmission errors. The local synthetic parameters with minimum fluctuation of loaded transmission error(LTE)and symmetry of geometric transmission error under working load were determined through optimization to obtain the machine-tool setting for spiral bevel gears. The pinion rotation angle and transmission error amplitude of symmetric parabola transmission error(PTE)at five key points were calculated through tooth contact analysis(TCA)to determine the harmonic function expression within a meshing period; the higher order parabolic coefficients of transmission error curves on both sides of the harmonic function were calculated according to the condition of continuous tangent at the meshing transfer point; the basic roll ratio and high order modified coefficient of pinion, corresponding to three-segment transmission error, were obtained by using reverse tooth contact analysis method. The numerical results show that stable meshing among tooth pairs can be realized and the meshing impact can be reduced under an intersection angle of 180° at transfer points under light loads; the high-frequency amplitude of the loaded transmission error can be reduced by the composite transmission error design under the working load. The gear grinding of compound transmission error can be realized by setting the high order modified roll coefficient of three-segment transmission error.关键词：spiral bevel gears;transmission error;high-order modified roll method;spectrogram;meshing stability52|5|0更新时间：2025-07-09
- 摘要：This paper investigates the applicable pH value ranges for TiO2to remove F- from water. First, TiO2-Ca and TiO2-Mg nanoparticles modified by Ca2+ and Mg2+ are successfully gained by in-situ hydrolysis and doping. Then field emission scanning electron microscopy(FESEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), N2 adsorption-desorption analysis and Zeta potential analysis are carried out for characterization. The results show that the modified anatase phase TiO2 was successfully synthesized, and that the isoelectric points of TiO2-Ca and TiO2-Mg were increased to 4.51 and 5.08 respectively. The modified TiO2 samples were applied to remove the low-concentration fluoride ions from water. The results show that the adsorption of fluoride ions by TiO2-Ca and TiO2-Mg can reach equilibrium within 20 min, with the adsorption capacity reaching 22.51 mg·g-1 and 20.87 mg·g-1 respectively. Compared with the raw TiO2, the applicable pH value ranges of TiO2-Ca and TiO2-Mg are expanded to 5 and 6 respectively, and their sedimentation performance is greatly improved. Among the common coexisting ions, only high-concentrations PO3-4 and CO2-3 can significantly affect their adsorption performance. After the desorption and regeneration cycle was repeated 20 times, the adsorption of F- in water by TiO2-Ca and TiO2-Mg did not decrease significantly. This shows that modification by Ca2+ and Mg2+ has obvious effects on the physicochemical properties and fluorine ion adsorption of TiO2 samples. In addition, the adsorption is a spontaneous exothermic process and the removal of F- by TiO2-Ca and TiO2-Mg mainly involves ion exchange. The research results will provide theoretical and technical support for the application of the environmental-friendly TiO2 in the removal of low-concentration fluoride ions from water.关键词：titanium dioxide(TiO2);modification;fluorine ion;adsorption;ion exchange52|9|0更新时间：2025-07-09
- 摘要：This paper studies the effects of honeycomb cell diameter, radial clearance and operating conditions on the leakage flow characteristics of labyrinth honeycomb seal. The leakage flow rate of the labyrinth honeycomb seal is measured at seven different pressure ratios and five different radial gaps using the stationary experimental test rig. Furthermore, the leakage flow characteristics of the experimental labyrinth honeycomb seal are numerically investigated using three-dimensional Reynolds-averaged Navier-Stokes(RANS)and standard k-ε turbulence model. The effects of the pressure ratios(1.05-1.6), radial clearances(0.4-1.2 mm), rotational speeds(0-8 000 r/min)and honeycomb cell diameters(0-3.2 mm)on leakage flow characteristics of the labyrinth honeycomb seal are analyzed and compared with those of the smooth labyrinth seal. According to the results, the leakage flow rate of labyrinth honeycomb seal increases almost linearly with the increase of pressure ratios; the leakage flow coefficient of labyrinth honeycomb seal decreases slightly with the increase of the radial clearance by up to 10%. The rotational speed has little effect on the leakage flow rate when it is lower than 3 000 r/min. When the rotational speed is higher than 3 000 r/min, the leakage flow coefficient of labyrinth honeycomb seal decreases significantly as the honeycomb cell structure can suppress the circumferential flow and thus improve the sealing performance of the labyrinth honeycomb seal. The leakage flow coefficient of labyrinth honeycomb seal at 8 000 r/min is reduced up to 51% compared with that when the rotational speed is 0. The leakage flow coefficient of the labyrinth honeycomb seal first decreases and then increases with the increase of honeycomb cell diameter. The smallest leakage flow coefficient of the labyrinth honeycomb seal is obtained when the honeycomb cell diameter is 0.6 mm, same as the tooth width. In addition, the leakage flow coefficient of the labyrinth honeycomb seal is 3.0%-5.5% lower than that of the smooth labyrinth seal. When the honeycomb cell diameter is less than 1.6 mm, the sealing performance of the labyrinth honeycomb seal is better than that of the smooth labyrinth seal. The research results in this paper can provide reference for the performance analysis and structure design of the labyrinth honeycomb seal.关键词：labyrinth honeycomb seal;leakage characteristic;seal performance;honeycomb cell diameter;radial clearance48|7|0更新时间：2025-07-09
- 摘要：This paper studies the impact of electron irradiation on the dynamic characteristics of 1 200 V SiC MOSFETs and the corresponding mechanism in an attempt to tackle the aging of SiC power field-effect transistors used in high-energy particle irradiation applications such as the space and nuclear industry. First, the SiC MOSFET is irradiated with a dose of 200 kGy under 10 MeV electron beam. Then the SiC MOSFET is tested for switching in a double-pulse test circuit, and parameters such as switching speed and switching transient energy loss are recorded. After that, the static characteristics of the device are tested to obtain the threshold voltage, gate resistance, parasitic capacitance and other parameters. Finally, the impact of electron irradiation on the dynamic characteristics of SiC MOSFETs is analyzed by comparing the dynamic and static characteristic parameters of irradiated and non-irradiated devices. The results show that the turn-on delay time of the irradiated device is reduced by 11.6 ns, the turn-on transient energy loss is reduced by 0.18 μJ, the turn-off delay time increases by 48.4 ns, and the turn-off transient energy loss increases by 0.11 μJ under a drain voltage of 800 V, a drain current of 15 A, and an external gate resistance of 200 Ω. It is found that the positive fixed charge in the oxide layer increases by 7.14×1011 cm-2 after irradiation, and the threshold voltage of the device decreases by 1.5 V; ionizing electron irradiation in the oxide layer creates electron hole pairs and the oxide layer traps the holes and form positive fixed charges, which reduces the threshold voltage of the device. This is the main reason for faster turn-on and slower turn-off of the device after electron irradiation. The research results can provide some reference for the application of SiC power devices in the irradiation environment and for manufacturers to improve the reliability of SiC MOSFETs in the irradiation environment.关键词：SiC power device;field effect transistor;electron irradiation;dynamic characteristics60|31|0更新时间：2025-07-09
- 摘要：This paper explores the effects of residual stresses on the pitting corrosion of 304 stainless steel pipes. The open circuit potential(OCP), polarization test, electrochemical impedance spectroscopy(EIS), Mott-Schottky and other methods are used to study the effects of stresses and Cl- concentration on the corrosion of cold-bent 304 stainless steel elbows. The pitting corrosion and passive film characteristics of different parts of the elbow in 100 and 1 000 mg/L Cl- solution were tested. How the stresses and Cl- concentration affect the pitting corrosion of stainless steel and the corresponding corrosion mechanism were analyzed. The results show that the residual stresses on the U-bend tensile surface and compression surface of 304 stainless steel after cold machining are tensile and compressive stresses respectively, and that there is almost no stress on the undeformed straight pipe. The corrosion test shows that when the Cl- concentration is 100 mg/L, the residual stress will enhance the ability of stainless steel to resist Cl- pitting corrosion and reduce the carrier concentration of the passivation film. The effects of tensile stress are stronger than those of compressive stress and the maximum pit depth is 80.426 μm). When the Cl- concentration is 1 000 mg/L, both tensile and compressive stresses reduce the ability of stainless steel to resist Cl- pitting corrosion, and the pit size at the tensile stress is the greatest under the same concentration condition(117.956 μm).关键词：stainless steel;residual stress;chloride ions;pitting corrosion;corrosion mechanism39|7|0更新时间：2025-07-09
- 摘要：The venting holes of the conventional passive pressure control system of near space vehicles may cause the high temperature gas outside to flow back into the cabin, thus disabling the instruments inside the cabin. To solve this problem, a pressure control device filled with phase change materials is proposed in this paper. This device can balance the pressure difference inside and outside the cabin, and ensure vehicle safety by cooling the high-temperature backflow. The device performance is analyzed and structure optimized through numerical simulation. The optimized device is then used during rapid ascent, maneuvering flight and rapid descent of a near space vehicle. Numerical simulation results show that the mass of the phase change material and the volume of the optimized device are reduced by about 45% and 10% respectively. Moreover, the pressure difference inside and outside the cabin is maintained below 50 Pa and the backflow temperature is reduced to 340 K after the optimized pressure control device is used on the near space vehicle. Therefore, the proposed pressure control device can both control the pressure and lower the temperature, promising good application prospects in the field of aerospace.关键词：near space vehicle;passive pressure control system;phase change pressure control device30|11|0更新时间：2025-07-09
- 摘要：This paper proposes a multi-objective optimization design method based on multi-level reliability analysis to ensure higher reliability and safety of all-electric aircraft power system. With this method, the complex all-electric aircraft power system design process is decoupled into two levels, and a nonlinear optimization model is established for each level by considering such indexes as cost and reliability. Then hierarchic analysis is carried out to determine the weight coefficients and simplify the multi-objective optimization problem into a single-objective optimization problem by using such weight coefficients. Meanwhile, a nonlinear model is linearized into a 01 programming model and the optimal power system topology and rated power of each power device under different weight coefficients are obtained by solving this model. According to the analysis results of design under different weight coefficients, the following conclusions are made: Under a low weight coefficient of reliability, the all-electric aircraft power system has a simple topology with low costs; Under a high weight coefficient of reliability, the all-electric aircraft power system has a complex topology with high costs. Simulation results show that this method can optimize the design in cost, reliability and other indexes. This reflects that this method is of good guiding significance in the initial design of all-electric aircraft power system.关键词：all-electric aircraft;power system design;01 programming;multi-level design40|10|0更新时间：2025-07-09
- 摘要：This paper analyzes the main sources of exergy destruction during the non-equilibrium combustion of the hydrogen-natural gas engine. The performance of five representative CH4/H2 kinetic models in the literature is re-evaluated and a method for calculating exergy destruction of elementary reactions is preliminarily established based on non-equilibrium thermodynamics. Combined with the selected kinetic model, the exergy destruction behaviors during the auto-ignition of CH4/H2 mixtures under different initial conditions(temperatures, equivalence ratios, hydrogen ratios)are numerically analyzed. According to the results, with the initial temperature increases, exergy destruction caused by chemical reaction decreases, while exergy destruction from incomplete combustion increases. Moreover, H2 addition shows little effect on the total exergy destruction, but effectively extends the low exergy destruction zone of CH4 combustion. The time histories of exergy destruction at different temperatures and varied H2 additions are compared; the rates of production(ROP)of H(·overO)2 and(·overO)H radicals, as well as the contribution of the elementary reactions that dominate their generation and consumption to the exergy destruction, are analyzed, to reveal the effects of initial temperature and H2 addition on exergy destruction of CH4 combustion. Furthermore, the discrepancy in exergy destruction between CH4 high-/low-temperature oxidation pathways is thermodynamically clarified by comparing the Gibbs free energy of key species during fuel oxidation. The research results reveal the effects of H2 addition on exergy destruction during CH4 combustion at molecular reaction level, and is expected to provide theoretical guidance for further reducing exergy destruction of hydrogen-natural gas engine combustion.关键词：auto-ignition;H2 addition;non-equilibrium thermodynamic;exergy destruction;elementary reaction41|5|0更新时间：2025-07-09
- 摘要：This paper proposes an adjustable focusing method for adaptive beamforming to address the problems of large relative bandwidth of speech signals, errors in microphones and insufficient broadband interference suppression with existing adaptive beamforming methods. Firstly, the Capon spectrum is processed as the probability density function of the received signals, and the focusing matrix based on the array observation data is designed for different frequency bands, so as to automatically adjust the frequency focusing degree according to the interference power; then, the focused sample covariance matrix(SCM)and the interference-plus-noise covariance matrix(INCM)in each frequency band are obtained, and the INCM of the broadband data is reconstructed by using the focusing matrix; finally, the desired signal covariance matrix(DSCM)at the reference frequency is reconstructed, the steering vector(SV)is corrected and the weighting vector of the proposed beamformer is obtained. According to the results of several numerical simulations, the proposed method allow the desired signals to be effectively received and the wideband interference sufficiently suppressed; the focusing error of the proposed method under strong interference is only about 1% that of the existing methods; when all signals have an incident angle error of 3° and the signal-to-noise ratio(SNR)is 15 dB, the output signal-to-interference-and-noise-ratio(SINR)of the proposed method is about 12 dB higher than the existing methods.关键词：speech enhancement;focusing matrix;adaptive beamforming;wideband interference;steering vector59|5|0更新时间：2025-07-09
- 摘要：In this paper, a narrowband active noise control(ANC)system is established to deal with engine order noise pollution in the hydraulic excavator cabin. The system incorporates a delay notch algorithm proposed based on the conventional narrowband ANC algorithm, which established a secondary path model with delay points. The system replaces the convolution calculation with the operation of indexing delay points in the process of filtering reference signals, which improves the computational efficiency. For the passband interference of irrelevant frequency components in the cabin, a two-stage adaptive notch filter was introduced to enhance the stability of the system. Numerical simulation analysis and bench experiments verified the noise reduction performance of the system under interference. The secondary sound source placement strategy analysis was also carried out together with the real machine experiment with ANC bench. The results show that noise of the second, fourth and sixth orders of the engine is lowered by 14.83 dB(A), 20.82 dB(A)and 19.43 dB(A)respectively under steady state condition. The indicates that the system has certain practicability in the real-world complex environment. The system was also further compared with active noise reduction headphones and passive noise control technology. It is found that the active noise control system proposed in this paper has good practical significance and development prospects in engineering applications.关键词：excavator cabin;active noise control;passband interference cancellation;secondary sound source placement33|6|0更新时间：2025-07-09
- 摘要：The massive high-dimensional SMART data attributes tend to cause a low precision in the detection of solid-state drive(SSD)faults. For this reason, this paper proposes an SSD fault detection method-GAL based on dimensionality reduction with GRU sparse auto-encoder based on an improved structure of the auto-encoder with gated recurrent unit(GRU)according to temporal characteristics of SSD SMART data. First, the GRUAE model is trained with SSD SMART data. Then the encoder of GRUAE model is used as the dimensionality reduction tool to reduce the original high-dimensional SSD SMART data. This is to reduce the influence of noise features in original SSD SAMRT data and highlight the features more relevant to data characteristics to improve the precision of fault detection. Finally, long short-term memory is used for fault detection with low-dimensional SSD SMART data. The precision, recall and F0.5 score of various algorithms are compared based on the dataset from Alibaba. The experimental results show that GAL improves the fault detection precision, recall and F0.5-score of the two types of flash SSDs by 4%, 5%, 4% and 4%, 8% and 5%, respectively, reaching 97%, 95%, 97% and 97%, 96%, 97%, respectively, compared with the condition with no dimensionality reduction. In addition, the precision, recall and F0.5 score of GAL are respectively 53%, 25% and 43% higher than those of the method compared关键词：fault detection;dimensionality reduction;sparse auto-encoder;solid state drive;gated recurrent unit37|54|0更新时间：2025-07-09
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