最新刊期
卷 54 ， 期 2 ， 2020
- 摘要：Aiming at the limitation that the random forest algorithm cannot deal with the problem of anomaly detection, a one-class random forest based on improved Graham scanning method is proposed, which reali-es the classification application of the random forest with only a single class of samples. Following the principle and process of Graham scanning method, the concept of boundary softening ratio is introduced to increase the flexibility of the outer boundary of data points. Ray casting is used to generate data set with inverse distribution of input samples to make the traditional random forest model become a one-class random forest with fine decision boundary after training, which outputs the abnormal probability of the data to be tested. The effectiveness of this method for the condition monitoring of rolling bearings is verified on the XJTU-SY bearing data set. The results show that the one-class random forest can accurately separate normal data from degradation data. Adjusting the boun关键词：Graham scanning;ray casting;one-class random forest;feature fusion;bearing condition monitoring607|4|1更新时间：2025-05-08
- 摘要：The actual position prediction method of the feed shaft for five-axis machining and the solving scheme for part contour error were investigated, and a part contour error prediction method for five-axis machining was then proposed. The actual position prediction of the feed shaft was obtained by identifying the transfer function of the feed shaft for candidate machine tool, reading the interpolation instructions of the parts to be processed, and inputting the instructions of each axis into the transfer function of each axis. The solving scheme for the part contour error was reali-ed by the forward kinematic transformation to the instruction position trajectory and the actual position trajectory of the part to be processed in the workpiece coordinate system, and the contour error between the above two trajectories was sought out. An S-shaped test piece was chosen as the processed part and the vertical composite machining center of KEDE KMC600S UMT five-axis turn-milling was considered as关键词：five-axis machine tool;contour error;accuracy prediction;S-shaped test piece316|7|6更新时间：2025-05-08
- 摘要：Focusing on high efficiency and high precision manufacturing of screw rotor, which is the core component of the twin-screw compressor, a design scheme based on the envelope-pixel method to generate a grinding wheel profile for forming screw rotor is proposed, which can efficiently complete the design of grinding wheel profile in a graphic space. The enveloping surface of the conjugate motion between the screw rotor and the forming wheel is established with the computer graphics and the meshing theory. Then a specified color is used to light the best approximation pixels of the enveloping surface with Bresenham algorithm, and the boundary pixels of the enveloping surface are captured by boundary tracking for the accurate data of grinding wheel profile. Grinding experiment shows that the deviation between different grinding wheel profiles generated by the envelope-pixel method and the traditional analytical envelope method gets -0.003 mm, and the error of machined rotor in the envelope-关键词：screw rotor;forming wheel;envelope-pixel;meshing theory;Bresenham algorithm;boundary tracking271|4|1更新时间：2025-05-08
- 摘要：To improve polishing quality and efficiency of workpiece surface, the traditional non-contact ultrasonic vibration polishing is modified, and an experimental prototype is designed, where an array of transducers is used instead of single transducer and the rotating motion of the basket is considered. The material removal mechanism of ultrasonic polishing is analy-ed, and the expression of material volume removal by single abrasive particle and the expression of abrasive vibration velocity are deduced. The sound field simulation of the liquid in polishing tank of the prototype is carried out by COMSOL. The influences of number of transducers, spacing of the transducers and input voltage of the transducer on the sound field distribution of the polishing fluid are discussed, and the arrangement of transducers at the bottom of the polishing tank is optimi-ed. Simulation shows that the sound pressure distribution in the central area of the polishing tank is more uniform when four transducers关键词：transducer array;ultrasound polishing;material removal mechanism;sound field simulation;surface polishing quality253|4|1更新时间：2025-05-08
- 摘要：A fault diagnosis method based on the maximum overlap discrete wavelet packet transform(MODWPT)marginal spectrum features and the particle swarm optimi-ation-support vector machine(PSO-SVM)is proposed to deal with the problem of fault mode confusion caused by multi-component band overlap of gear fault vibration signals. In order to reduce the influence of harmonics and noise on the fault mode component separation, MODWPT is used to decompose the collected experimental signals into 5 layers and to obtain 32 components. The first 16 components are selected based on the principle of the band energy dominant distribution to construct a Hilbert marginal spectrum. Then, the marginal spectrum features are extracted and considered as an input to the SVM with PSO parameter optimi-ation for fault type identification. Analysis results of simulation signals show that the MODWPT marginal spectrum is superior to the EMD method in terms of anti-mode mixing, anti-end effect, and frequency extraction a关键词：gear fault diagnosis;empirical mode decomposition;Hilbert marginal spectrum;support vector machine;particle swarm optimi-ation331|4|2更新时间：2025-05-08
- 摘要：Dynamic analysis is applied to study the response characteristics of the encoder signal of planetary gears with crack damage and to deal with the problems that the influencing mechanism of gear crack damage on the encoder signal of planetary gear is still unknown and the health monitoring of planetary gear box based on the encoder signal lacks theoretical basis. Firstly, the energy method is used to derive a time-varying meshing stiffness algorithm when the gear cracks, and a pure torsion dynamics model of the planetary gear system is constructed. Then the meshing stiffness of the cracked gear is substituted into the constructed model, and solving the model obtains the encoder response signal under the influence of the planetary wheel crack. The torsional vibration characteristics contained in the encoder signal are analy-ed. Finally, the encoder response signals of planetary gear under different crack damages are studied based on the model. The results show that the torsional vibratio关键词：planetary gear set;encoder signal;dynamic analysis;time-varying mesh stiffness;crack damage246|5|1更新时间：2025-05-08
- 摘要：A multi-scale end-to-end fault diagnosis method based on attention mechanism is proposed to deal with the problem that rotating machinery fault diagnosis needs complex feature extraction process and the diagnostic accuracy is low for noise-containing samples. A random dropout mechanism is introduced to suppress input noise at the input end. Taking advantage of the fact that fault signal has multiple modals, the vibration signals under different scales are obtained by using coarse-grained layer. Then multi-scale features are extracted by using fully convolutional networks and fused by using an attention mechanism. Finally, rotating machinery fault classification is reali-ed based on a multi-classification function. The validity of the model is verified with the Case Western Reserve University bearing dataset and gearbox dataset, respectively. Experiments show that the fault recognition rate of the method is up to 100%. When the ratio of signal to noise is -4 dB, the fault recognition ac关键词：rotating machinery;fault diagnosis;random dropout;multi-scale feature extraction;attention mechanism342|4|20更新时间：2025-05-08
- 摘要：Aiming at verifying and restoring abnormal monitoring data from the production system of process industry with mufti-variables, high-dimensionality and complex coupling relationship, a verification and restoration method for abnormal monitoring data is proposed by compressive sensing. The compressive sensing algorithm can reconstruct original sparse signal with very few measurement data or obtain the signal of sparse expression on a sparse basis. Combining the compressive sensing algorithm with the success rate of reconstruction, a mathematical model is established, which can reconstruct the system equation reflecting the dynamic relationship of the nodes in state-aware network with only a small number of monitoring data. The analytical value of monitoring data is obtained by substituting the reconstructed system equation into the solving structure considering system deviation. Compared the actual value with the analytical value of monitoring data, if the actual value is overproof, the关键词：compressive sensing;process industry;reconstruct;abnormal data verification;data restoration209|4|0更新时间：2025-05-08
- 摘要：An experimental study on the frosting process in a confined space through a hori-ontal tube frosting visuali-ation test bed is conducted to optimi-e the structure of the heat exchanger and improve its defrosting performance. The growth rule of frost layer thickness along the length of a tube, the variations of frost accumulation and heat transfer rate with time are evaluated. The influences of wet air initial flow rate, temperature, relative humidity and wall temperature on the frost accumulation and heat transfer rate on the surface of the tube are analy-ed. Experimental results show that the thickness of the frost layer gradually increases along the length of the tube at the beginning of frosting. Then, the frost layers are the thickest in the middle of the round tube, and the lowest near the inlet, respectively. Frosting begins at the outlet of the air flow passage. The frost accumulation shows an increasing trend with time passing, while the heat transfer rate increases first and t关键词：frosting characteristics;confined space;frost thickness;heat transfer rate;circular tube;heat transfer performance266|4|1更新时间：2025-05-08
- 摘要：The gas chromatography mass spectrometry method is used to analy-e the components and the share of each component in POE22 and to study the phase equilibrium properties of the environmental refrigerant propane(R290)and polyol ester(POE)lubricant. Then the isochoric saturation method is used to measure the solubilities of R290 in POE22 at 278.15 - 348.15 K, and the NRTL model is used to correlate the experiment results. The results show that POE22 is mainly composed of four ester compounds and three additives, and the seven components accounts for 99.49% in POE22. The absolute average deviation and the maximum relative deviation between the calculated theoretical pressure value and the experimental pressure value are 0.565% and 2.934%, respectively. Moreover, no chemical reaction or immiscibility phenomenon between R290 and oil are found in the temperature range from 278.15 to 348.15 K. Experimental results are compared with the reported solubility of R290 in two mineral oils(ISO VG12 a关键词：phase equilibrium;experiment;binary mixture;propane;POE lubricant263|4|3更新时间：2025-05-08
- 摘要：PSR/epoxy composite samples(0%, 5%, 10%, 15% and 20% in mass fraction, respectively)are prepared by direct blending method to study the effects of epoxy toughener - liquid polysulfide rubber - on the dielectric properties of epoxy resin. The micro-morphology and glass transition temperature of the samples are analy-ed by SEM and DSC. The DC breakdown field strength, frequency domain dielectric spectrum and surface potential decay characteristics of the samples are tested. Results show that the glass transition temperature of epoxy resin decreases with addition of PSR, but the DC breakdown field strength of epoxy resin is effectively improved; the dielectric constant and dielectric loss first increase and then decrease with the increase of PSR concentration; and adding PSR slows down the surface potential decay rate of epoxy resin. It is found through extracting the trap parameters from isothermal surface potential decay model that with the addition of PSR, the depth of deep and shall关键词：liquid polysulfide rubber;epoxy resin;DC breakdown field strength;dielectric spectrum;isothermal surface potential decay280|5|2更新时间：2025-05-08
- 摘要：A fault-tolerant control strategy for five-phase permanent magnet synchronous motor(FPMSM)with third-harmonic suppression is proposed based on the three-dimensional subspace of five-phase motors. A mathematical model of FPMSM is established and the distribution of space voltage vector is analy-ed according to the driving topology. A virtual voltage vector is constructed to suppress the third harmonic of phase current by utili-ing the opposite effect of large vector and medium vector on magnetic flux in three-dimensional space of five-phase motors. According to the effects of virtual voltage vector on torque and flux linkage in different sectors, a voltage vector switch selection table is established to adjust the torque and flux linkage before and after a fault to reduce the torque ripple caused by open-phase fault of one phase, so that the driving motor can still run steadily after the fault, and the reliability of the fan drive system is improved. A simulation model of the five-phase260|4|3更新时间：2025-05-08
- 摘要：Different degrees of electrical aging test for PPLP insulation is carried out to study the aging mechanisms of polypropylene laminated paper(PPLP), which is the major insulation of high temperature superconducting(HTS)cables. Effects of electrical aging on the breakdown performance and trap distribution of PPLP insulation are studied by AC breakdown and isothermal surface potential decay(ISPD)measurements. And the aged samples are further analy-ed by Fourier transform infrared spectrum, morphology observation and thermogravimetric analysis. Results show that with the increase of electrical agingdegree, AC breakdown field strength of PPLP insulation decreases from 113.3 kV/mm to 92.3 kV/mm. The density of shallow traps increases gradually while that of deep traps decreases gradually during aging process. It is observed that the partial cellulose in the insulating paper of the PPLP out layer is broken, and a great number of voids are generated, resulting in loose structure and reduced st关键词：electrical aging;polypropylene laminated paper;trap;breakdown;cellulose207|4|0更新时间：2025-05-08
- 摘要：Aiming at the destructive influence of pulsed strong magnetic field on the guidance and control device in electromagnetic launching and the lack of repeated testing methods, an off-line testing method for the anti-magnetic field capability of the guidance and control device is proposed based on the analysis of the magnetic field characteristics. Comprehensive performance requirements of such as the magnetic induction intensity peaks, change rate and duration of the guidance and control device are given through analysis according to the actual working conditions of electromagnetic launches. Bases on system circuit analysis and magnetic field calculation modeling, a multi-objective optimi-ation design method is proposed, which takes into account the peak value and change rate of the magnetic induction intensity, the si-e of power supply and the magnetic field generator in working space. A finite element simulation is conducted to verify the design scheme. An off-line test device is final关键词：electromagnetic launch;pulsed strong magnetic field;off-line testing;magnetic field calculation408|4|0更新时间：2025-05-08
- 摘要：A path computing scheme for low-latency task is proposed to solve the problem that there exist high communication load and high task processing latency when cloud computing is applied to medical big data processing. The scheme firstly constructs the medical big data task into a directed acyclic graph that is composed of multiple subtasks with explicit input and output relationships. Then, a cloud and fog network architecture is designed, in which network edge devices such as switches and routers in hospitals form a fog computing layer. The computing capacity of fog nodes is used to gradually complete the big data task in the process of end-to-end directional data transmission. A task mapping strategy based on the discrete binary particle swarm optimi-ation(BPSO)algorithm is proposed to deploy the medical big data task to a hospital network. The big data task in the form of a directed acyclic graph is mapped into a topology graph of the hospital fog network to find an appropriate comput关键词：medical big data;cloud and fog network;mapping;path computing224|4|3更新时间：2025-05-08
- 摘要：Dielectrophoretic assembly experiments of nanoparticles in a prepared conductive-island nanogap electrode system is carried out to obtain the morphology of nanoparticle chains formed by dielectrophoretic assembly of nanoparticles in the conductive-island nanogap electrode system. A dielectrophoretic assembly model of nanoparticles in the conductive-island nanogap electrode assembly system is established based on the dielectrophoretic manipulation theory of nanoparticles. The electric field distribution in the dielectrophoretic assembly model, as well as the electrokinetic behavior of dielectrophoresis, alternating current electrothermal flow and their interaction in the assembly process, is analy-ed through numerical simulation. The effects of alternating current electrothermal flow on dielectrophoretic assembly in the conductive-island nanogap electrode system are investigated. It is found that the dielectrophoretic assembly of nanoparticles in the conductive-island nanogap electrode关键词：conductive-island nanogap electrode;alternating current electrothermal flow;dielectrophoresis;gold nanoparticle chain;numerical simulation309|4|2更新时间：2025-05-08
- 摘要：A high rate differential chaos shift keying(HR-DCSK)communication scheme is proposed to improve the problems of low information rate and poor bit error rate(BER)performance of traditional differential chaos shift keying(DCSK)communication scheme. The information frame of the transmitted signal is expanded from two slots to three slots at the transmitter, and the Hilbert transform technology is used to make one frame of the transmitted signal carry 4 bits of data information. The correlation demodulation method is used to extract data information at the receiver, and the data information is recovered by detecting the polarity of the output value of the correlator. Furthermore, a HR-DCSK communication scheme having better bit error rate performance with multiple input and multiple output(MIMO)is proposed. BER expressions of the MIMO-HR-DCSK scheme under AWGN and multi-path Rayleigh fading channels are derived by using Gaussian approximation(GA)method, and the simulation results are compa关键词：high rate differential chaos shift keying;multiple input multiple output;information rate;bit error rate performance;Gaussian approximation method173|4|0更新时间：2025-05-08
- 摘要：A novel method for estimating 2-dimensional direction of arrival(2D-DOA)based on matrix reconstruction of L-shaped coprime array is proposed to deal with the problem that the L-shaped uniform linear array(ULA)of radars cannot be used in practical application because of the small distance between the adjacent elements. Firstly, the virtual ULA is determined according to the position of the coprime array. Since the virtual ULA has the characteristics of semi-positive definite(SPD), low rank and Toeplit- structure, optimi-ation is conducted to reconstruct a virtual ULA covariance matrix based on the covariance matrix of the data received by the coprime array. Then, the MUSIC algorithm is applied to estimate two 1D angles. Finally, the pair matching method is used to match estimated 1D angles. Simulation results and comparisons with L-shaped ULA MUSIC algorithm and L-shaped coprime array SS-MUSIC algorithm show that when the signal-to-noise ratio is greater than 0 dB and the number of snap关键词：2D-DOA estimation;L-shaped coprime array;matrix reconstruction;pair matching246|4|1更新时间：2025-05-08
- 摘要：A new space operation way to signal modulation mode containing only carrier plus telecontrol subcarrier is proposed to deal with the transponder carrier acquisition degradation in satellite communication of a low earth orbit(LEO)satellite running on sun synchronous orbit for over 10 years. The space environment effects on the transponder are firstly analy-ed based on the telemetry parameters including temperature, auto gain control(AGC)voltage and carrier lock from the satellite. Then the uplink signal is adjusted to increase the carrier power by demodulating the range subcarrier and lowering the telecontrol subcarrier modulation index. The results in space operation show that the transponder is damaged by the single event burnout(SEB), and the diode of the frequency multiplier is affected by temperature modulation of the transponder. The higher the transponder temperature, the more difficult the capture of carrier, and when the temperature is higher than 26.2 -, the carrier cannot be关键词：satellite communication;space operation;space environment;transponder;single event effect213|4|1更新时间：2025-05-08
- 摘要：To solve the problem that the steady-state visual evoked potential(SSVEP)brain-computer interface(BCI)system requires high computer performance, a SSVEP BCI system based on field programmable gate array(FPGA)and commercial electroencephalogram(EEG)acquisition device is designed by an independent display module based on FPGA. This system reali-es the control of video graphics array(VGA)interface. The paradigm patterns corresponding to different flicker frequencies are allocated according to the displaying refresh frames, and the stable display of the paradigm required to induce SSVEP signals can be achieved. Collecting and analy-ing the flicker outputs of the designed VGA visual stimulator, the presenting frequencies from the visual stimulator are approximately equal to the required frequencies and can be used for SSVEP BCI experiments. Combined with the designed visual stimulator, the FPGA based EEG signal processing and feature recognition are also implemented in this approach. EEG si关键词：steady-state visual evoked potential;brain-computer interface;field programmable gate array;data processing;feature recognition201|5|2更新时间：2025-05-08
- 摘要：A calibration method for adjustment of structured light system with planar distance constraints is proposed to improve the shortcomings of traditional calibration methods, such as the serious dependence on the accuracy of calibrators and the limited accuracy of solving parameters of ordinary adjustment calibration model. The method firstly takes some marked points in the plane calibrator as control points, and uses the distance information between the control points to construct constraint equations. Then, a beam adjustment model with plane distance constraint is constructed by combining the constraint equations and the adjustment model. Finally, the system parameters are determined by optimi-ation solution of the model. Further, a weighted integrated measurement model is proposed to obtain higher measurement accuracy. The model assigns different weight to each measuring device according to its difference of calibration accuracy. Finally, a system measurement experiment platform is bui关键词：structured light;beam adjustment;constraint;weighted integrated measurement203|4|0更新时间：2025-05-08
- 摘要：To explore the influence of subsonic no--le inlet air temperature on jet flow field and sound field, a subsonic no--le calculation model was established. Compared with experimental and simulative data, the flow field and far-field noise radiation were evaluated at different no--le inlet air temperatures. The distribution laws of jet velocity at the outlet of the no--le along the axial and radial directions, as well as the variation of jet temperature along the no--le exit axis, were investigated. The influences of no--le inlet air temperature on jet flow field development and far-field noise were analy-ed. The results show that the increasing temperature of jet significantly shortens the length of the core region of the potential flow, and slightly reduces the width of the core region of the potential flow. The static temperature and the overall temperature at the jet axis with a certain distance from the no--le rise. The highest static temperature under each working condition is delay关键词：subsonic jet;large eddy simulation;unsteady flow field;aerodynamic noise259|4|1更新时间：2025-05-08
- 摘要：In order to reali-e the efficient degradation of organic pollutants, a 2.5-dimensional electrode system based on Pb3O4 magnetic particles is constructed. Fe3O4/Pb3O4 magnetic particles are prepared by impregnation-thermal decomposition method. To obtain the optimum surface element contents, crystal structure and particle magnetism, six coating times of the particles are determined. Comparing the cyclic voltammetry properties, hydroxyl radical yields and mass transfer coefficients, it is found that the 2.5D electrode system is superior to the 2D electrode system in performance, and the optimum particle dosage is determined as 5 g. Finally, acid red G is used as the target to compare the electrocatalytic performance of the two electrode systems. The results show that the decolori-ation rate, COD removal efficiency, TOC removal efficiency and COD degradation energy consumption of the 2.5D electrode system at 120 min reach 1关键词：lead dioxide;2.5D electrode system;Pb3O4 magnetic particles;electrocatalysis200|4|2更新时间：2025-05-08
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