最新刊期
卷 51 ， 期 12 ， 2017
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Modeling and Experimental Analysis for Worktable Dynamic Characteristics of CNC Gear Hobbing Machine
摘要：To reveal the dynamic characteristics of worktable axle of CNC gear hobbing machine due to interrupted cutting, the servo control system of the worktable is analyzed. According to electromechanical principle and mechanical dynamic principle, every component model of the servo control system is constructed to derive an overall servo control system model of the rotary table. Considering the nonlinear Stribeck friction factor, a simulation model of the worktable servo system is established by Simulink. The effects of different position and speed command frequency variation on the dynamic response of the workpiece axis servo system are discussed and the servo dynamic characteristics reflecting the location and speed of the worktable axle are obtained. When the servo system of the rotary table runs at low speed, the “flat top” exists in the position tracking, and the “dead zone” exists in the speed tracking. The position and speed following rate of the servo system of the rotary worktable decrease with the increasing given command frequency, especially when the instruction frequency increases to 31 Hz, the following rate is less than 10%. The model accuracy is verified by online test of the worktable, the experimental response curves coincide with the simulated ones well at the same command frequency.关键词：CNC gear hobbing machine;dynamic characteristics;servo model;permanent magnet synchronous motor654|6|0更新时间：2025-07-09 - 摘要：A method of human motion posture analysis using synchrosqueezed wavelet transform with adjustable parameters(SSTAP)is proposed to focus on the problems of complicated radar echoes of human motion, small frequency difference of micro-Doppler(MD)to the human motion postures(HMP), and difficulties to distinguish the detailed frequencysignatures of different body movements by conventional methods. An HMP model and a radar echoes model of human micro-motions are established from measured data based on motion capture technology. Then, the SSTAP method is used to decompose the radar echoes signals and the time-frequency characteristics of the main parts of bodies are obtained. The time-frequency characteristics of the body's overall echo signal with the best resolution are obtained through adjusting two parameters of the SSTAP. The information of HMP is finally obtained by comparing the time-frequency characteristics of whole human body with those of each part of the body. Experiment results and comparisons with the generalized S transform(GST)and wavelet transform(WT)show that, the human MD signatures from the SSTAP are more clear and easily recognized, and the SSTAP is better in describing the signatures of HMP and increases the recognizable rate by 17% and 14%, respectively.关键词：synchrosqueezed wavelet;radar echo;human motion posture;micro-Doppler frequency654|5|1更新时间：2025-07-09
- 摘要：An orthogonal demodulator with auto gain control(AGC)function for wideband(0.8-2.7 GHz)receivers is proposed to realize the compatibility of receivers to multi-mode wireless communication standards and the AGC in the signal path. The demodulator adopts a wideband RF variable gain amplifier and an IF variable gain amplifier in the main signal path, while the frequency translation is performed by using a variable gain Gilbert cell. A root-mean-square(RMS)power detector is designed in the feedback path to detect the amplitude of output signal and then transfer it to a dc voltage. An AGC close loop system is formed through controlling the gain of blocks in the main path by the output voltage of the power detector. The demodulator just adopts analog circuits to realize AGC function, and avoids the drawbacks of traditional digital-assisted AGC mechanism, such as much more pins, complex algorithms and limited resolution resulted from a finite step length. The demodulator is implemented with 0.18 μm BiCMOS technology. Measurement results show that when the operation frequency is within 0.8 GHz to 2.7 GHz, the tunable conversion gain range of the demodulator is from -36 dB to 36 dB, and the demodulation bandwidth is 100 MHz; When the gain is in maximum, the noise figure is 9 dB, the error of the orthogonal phase is 1.6 degree and the error of the amplitude is 0.9 dB.关键词：quadrature demodulator;wireless receiver;wide band;auto gain control;Gilbert cell486|5|0更新时间：2025-07-09
- 摘要：A fast method for blind identification of(2, 1, m)convolutional codes in the case of high error bit ratios is proposed to solve the problems that the existing methods for blind identification of convolutional codes have low robustness and need to know encoder parameters a priori and large computation. First, a set of parity check equations is established and its solution is the parity check vector of a(2, 1, m)convolutional code. Then, based on the structural properties of coefficients of the parity check equations, unknown elements of the parity check vector are recursively estimated from values of the elements having been estimated. When there are errors in the received bits, the estimation of an unknown element is jointly determined by several parity check equations in each recursion. Finally, the correctness of estimations of the parity check vector is tested based on the property of free distance of convolutional codes and constant false-alarm criterion, and the generator matrix of the(2, 1, m)convolutional code is identified accordingly. When the encoder parameters are unknown, these parameters can be quickly identified from the testing results of the parity check vector estimations. Simulation results show that the proposed method has good tolerance to error bits and low computational complexity, and does not need to know the encoder parameters a priori. When the error bit ratio is 0.08, the correct identification ratio of the method reaches 80%, while the method based on matrix analysis cannot achieve a correct identification.关键词：convolutional code;blind identification;parity check equation;high robustness489|5|1更新时间：2025-07-09
- 摘要：A modified facet model is presented to solve the problem that the classical facet model in the synthetic aperture radar has large error of backscattered field from facets and results in blurring imaging in complex ocean surface. Firstly, an accurate model is built to calculate the permittivity of sea water with foams. Then, a concrete ocean surface is built based on the spectral model of Elfouhaily, and is divided into many little facets. The scattered field for each facet is calculated, and the result of electromagnetic scattering from ocean surface is obtained by superposing these scattered fields. A comparison with the measured data shows that when incidence angles are large, simulation results of the classical facet model appear an attenuation, while the modified facet model with foams reduces the attenuation about 10 dB and enhances the coincidence degree with the measured data. Experiment results by using the modified facet model to analyze the ocean surface electromagnetic scattering properties and Brewster effect show that the wind speeds influence the Brewster effect obviously. When the wind speeds at P-band increase from 4 m/s to 10 m/s, the Brewster effect is weakened about 85%.关键词：modified facet model;ocean surface electromagnetic scattering;Brewster effect633|5|1更新时间：2025-07-09
- 摘要：A transmission scheme based on hybrid carrier logistic phase scrambling(HC-Logistic)is proposed for the problem that signals are easily intercepted during satellite communication transmission. Firstly, signal sources are mapped on the baseband using QPSK mapping, and the resulting signals are then processed by the weighted fractional Fourier transform. Then, the signals are further combined with the chaotic phase scrambling codes generated by the Logistic map to obtain final baseband encryption signals. Finally, the resulting signals are processed by a digital-analog conversion and an up-conversion and then sent into the satellite channel. Simulation results show that the signals' characteristics of the constellation are difficult to be identified after encrypting by the HC-Logistic scheme. Moreover, since Logistic map is sensitive to the initial, the computational cost of intercepting HC-Logistic scheme is 1020 times of that of the traditional weighted fractional Fourier transform scheme.关键词：satellite communication;secure transmission;Logistic mapping;constellation543|5|4更新时间：2025-07-09
- 摘要：Aiming at the problems caused by the nonlinear relations between the attributes of high dimensional data in cluster analysis, such as uneven distribution of data, invalidation of traditional similarity measures and difficulty of accurate representation of the result class, a clustering algorithm for high dimensional nonlinear feature data is proposed based on kernel principal component analysis(KPCA)and density clustering(DBSCAN). To extract the nonlinear characteristics of high dimensional data, the KPCA theory is adopted to map the original to a higher dimensional data space, thus a set of directions in principal component space-PCS for extracting the nonlinear characteristics of data and reduced dimensions can be obtained. The similarity distance of data in PCS is defined to improve the traditional DBSCAN clustering algorithm and 3δ statistical theory is used to characterize the clustering results. A case of hypertension group clustering is provided to illustrate the feasibility of the proposed method, and the results show that the proposed method can effectively obtain the nonlinear characteristics of the high dimensional data and realize cluster analysis and cluster center knowledge expression to solve the difficulties in the traditional DBSCAN clustering method for cluster analysis of high dimensional data.关键词：nonlinear feature;high dimensional data;kernel principal component analysis;density clustering609|5|2更新时间：2025-07-09
- 摘要：A novel wafer segmentation method based on the closest affine iterative point(ICP)is proposed to address the problems inherent in wafer segmentation relying on the hardware instruments, such as high production cost, complicated process and unstable segmentation effects. The method is independent on hardware facilities, and establishes the feature point sets of the wafer template image and the target image by utilizing the Canny operator to extract edges of the images and obtains the rough wafer rectangle information through Hough's straight line detection. The affine ICP algorithm is then used to perform precise registration with the initial value that is the coordinates of the upper left corner of the rectangle. The model image is matched with the reference image which results in a rapid and accurate wafer segmentation. Theoretical analysis and experimental results show that the computational complexity of the method is low and a single sample segmentation takes no more than 0.9 seconds, while the sample segmentation accuracy is significantly higher than those of other algorithms. Therefore, the proposed method satisfies the real-time detection requirements of automatic production lines.关键词：wafer segmentation;line detection;shape registration;affine iterative closest point477|5|1更新时间：2025-07-09
- 摘要：A novel segmentation algorithm for road scenes based on hierarchical graph-based inference(HGI)is proposed to solve the problem that object boundaries extracted by existing graph-based segmentation algorithms are not fine enough and it is hard to adapt to complex road scene layouts. The algorithm first over-segments an image into small homogeneous regions called superpixels, and then the random forest model is used to train a multi-class regressor and a consistency regressor of superpixels. Regression results are then used to calculate the energy terms in a Markov random field(MRF)energy function. An initial segmentation of the image is obtained by using the superpixel MRF inference. A pixel-level labeling based on fully connected conditional random fields is constructed to avoid the label confusion caused by the superpixels and to get a fine segmentation finally. Experimental results show that the proposed algorithm solves the label confusion in the superpixel inference and gets fine segmentation boundaries for both the images in manually labeled datasets and the real road scenes. A comparison with the traditional MRF graph-based inference methods shows that the HGI algorithm provides improvements of 2% and 3% on the overall precision and per-class average metrics, respectively.关键词：road scene segmentation;multi-class image labeling;random forest;markov random field410|5|2更新时间：2025-07-09
- 摘要：To further improve 3D reconstruction accuracy of tool wear area, a transform-domain fusion method is proposed. Nonsubsampled contourlet transform(NSCT)and wavelet transform(WT)are combined in the transform domain. The low-frequency coefficients obtained by NSCT are fused with WT method, and the corresponding high-frequency coefficients are fused based on the regional variance criteria, so that the clearly-focused tool image is obtained to highlight the overall gray level information and edge detail information of tool wear image, so as to obtain clearer two-dimensional tool image and more accurate wear pattern. The 3D morphology and wear volume obtained by the three methods are compared with the results from microscope, it is found that this 3D morphology with the proposed method best coincides with the microscope result, and the average relative error of the wear volume is less than 10%. Compared with the traditional WT and NSCT methods, it is found that the proposed method has certain advantages in terms of the image clarity and accuracy of the wear volume and the reconstruction results are superior to ones obtained by using of non-subsampled contourlet transform or wavelet transform method alone for 3D reconstruction of the tool wear area.关键词：tool wear;transform-domain fusion;three-dimensional reconstruction449|5|2更新时间：2025-07-09
- 摘要：To improve the performance of bolt connection, bolted joint surface is taken as the object, and optimization design for the joint surface shape is completed according to the distribution of contact pressure and the size of effective contact area. Finite element method is used to discretize the elastic contact interface, the elastic contact model is established from the contact interface node. The relationship between contact gap and contact pressure at nodes is transformed into a mathematical programming problem. Regarding the contact performance as the objective, an optimization design method for bolted connection is proposed to homogenize the contact pressure and expand the effective contact area by changing the shape of the joint surface. The design scheme is processed by ANSYS parametric design language and the analysis cases include single bolt connection and flange connection. It indicates that the proposed scheme can reduce the peak and dispersion of the contact pressure and increase the effective contact area. Compared with the method by increasing the thickness of the connecting member, the proposed scheme also ensures that the natural frequency of the connecting structure does not lower. The feasibility and effectiveness of the proposed optimization design are verified by these cases.关键词：bolted connection;contact surface;elastic contact;optimization design470|5|7更新时间：2025-07-09
- 摘要：In order to suppress unbalance response of rotor-bearing system caused by synchronous revolution of residual unbalance, a method, which is based on a hybrid flexure pivot-tilting pads bearing and considering increase the eccentricity to increase the oil film stiffness so that suppress unbalance response, is proposed. First, the oil film pressure distribution model is obtained by combining flow balance principle with Reynolds equation, and the torque equilibrium equation of pads and rotor movement function are built. Then, the standard transfer function of the simplified rotor-bearing system is deduced according to its differential equation of motion. Finally, the positioning strategy of desired position of rotor center is studied in order to determine the eccentricity control scheme, and the position-control force equation is fitted by the method of least squares. Results show that the proposed positioning method can achieve high positioning accuracy. Oil film stiffness can be improved by increasing the eccentricity and the unbalance response of the rotor-bearing system can be effectively restrained. The vibration amplitude of x and y direction are both reduced to about 10% of the original.关键词：transfer function;rotor-bearing system;eccentricity;unbalance response;positioning strategy of rotor center409|6|1更新时间：2025-07-09
- 摘要：The film cooling performance in a gas turbine trailing edge cut-back region is numerically investigated by using the unsteady Detached-Eddy-Simulation(DES)method. The laterally-averaged cooling effectiveness on the adiabatic wall at the downstream of ribs is predicted at three blowing ratios(M=0.5,0.8,1.1)and three rib-array configurations(double in-line rib array G1, pin-fin array G2a and pin-fin array G2b), and numerical results are compared with measurement data. Results and a comparison with the steady RANS(Reynolds-averaged Navier-Stokes equations)show that, the unsteady DES method has a superior accuracy in predicting the film cooling effectiveness distributions on the adiabatic wall at the downstream of ribs. The laterally-averaged cooling effectiveness on the wall at the downstream of ribs goes up along the streamwise direction and then goes down sharply after reaching the maximum value at three blowing ratios. When M=0.8, the coolant coverage on the adiabatic wall along the axial direction reaches the farthest among three blowing ratio cases, and is occurred just at the downstream middle region of ribs. However, the area with better film cooling effectiveness(temperature below 310 K)is the smallest among the three blowing ratio cases. The film cooling effectiveness significantly decreases on the rear part of the adiabatic wall for three rib-array configurations, and the periodical vortex shedding is appeared at the downstream of the blunt lip. It indicates that the vortex shedding structures are closely related to geometrical configuration of the rib-array. The temperature distributions on the adiabatic wall downstream of ribs are much uniform for the pin-fin ribs(G2a and G2b). Among three rib-array configurations, G2b performs better than the other two designs in both the film cooling thickness and the stability in the trailing edge cut-back region.关键词：trailing edge cut-back;film cooling effectiveness;blowing ratio;rib437|5|4更新时间：2025-07-09
- 摘要：Particulate matter emissions of polyoxymethylene dimethyl ethers(PODE)/diesel mixture with different PODE blending ratios(10%, 20% and 30%)are conducted on a turbocharged intercooled high-pressure common-rail diesel engine. Effects of PODE blending ratio on the diesel NOx, smoke and particle size distribution are analyzed. The oxidation features and activation energy of pyrolysis of particles are studied by using the thermogravimetric analysis method and the pyrolysis kinetics method. Results show that the addition of PODE in diesel fuel reduces smoke emission and the decrement becomes more pronounced with the increase of PODE blending ratio. However, the NOx emissions increase slightly at medium and high loads. When PODE blending ratio increases, the total particle concentration decreases, the distribution curve of particle sizes shifts to the smaller particle size, the proportion of nucleation-mode particles increases and the proportion of accumulation-mode particles decreases. In addition, the peak values of particle number concentration, surface area concentration and volume concentration decrease. With the addition of PODE in diesel fuel, the content of soluble organic fraction(SOF)in particulate matters increases, the peak value of the mass loss rate of soot particles increases and its peak temperature decreases. Meantime, the activation energy of pyrolysis reaction of particles reduces, which indicates that the particles are more easily oxidized.关键词：common-rail diesel engine;polyoxymethylene dimethyl ethers;particulate matter;particle size;thermogravimetric analysis528|5|6更新时间：2025-07-09
- 摘要：A model of the single-machine infinite-bus system containing STATCOM on the electromechanical time scale is deduced to understand the mechanism of STATCOM affecting the grid power oscillation. The dynamic physical mechanism of STATCOM affecting the transient performance of synchronous generator in the power oscillation mitigation mode is discussed by adopting the method of electrical torque analysis. The results show that when the power angle is used as feedback signal, P and D controllers affect the synchronizing and the damping characteristics of the synchronous generator, respectively; and when the rotor speed is utilized as the feedback signal, P, I and D controllers affect the damping, synchronizing and inertia characteristics, respectively. In addition, the principles of different control strategies that influence the equivalent inertia, the synchronizing and the damping coefficients of the power grid are explained. Moreover, the important factors that influence the performance of power oscillation mitigation are analyzed, providing a theoretical foundation for the design of STATCOM control strategies. Simulation results show the correctness of the conclusions derived in this paper.关键词：static synchronous compensator;power oscillation;virtual inertia;equivalent damping coefficient;equivalent synchronous coefficient470|5|9更新时间：2025-07-09
- 摘要：To reveal the equivalence between oscillating impulse voltage and standard impulse voltage(SIV)and the breakdown characteristics of transformer oil in a highly non-uniform electric field under oscillating lightning impulse, three positive oscillating lightning impulse(OLI)waveforms with oscillating frequency of 100, 300 and 400 kHz are adopted as the test waveforms to compare with the standard lightning impulse(SLI)and a 5 mm-distance point-ball structure serves as the electrode. Waveforms of these three kinds of OLI and SLI are recorded and the V-t characteristics, minimum breakdown voltage and breakdown maximum time lag in different lightning impulse are counted and analyzed. The results show that for a large oscillation of the breakdown waveforms under OIV, it is necessary to connect a resistance in series to restrain; the breakdown points distribute near the peak of wave under SLI while they distribute near the peaks in every period of oscillation under OLI; the minimum breakdown voltage under OIV increases with the increasing frequency but the maximum breakdown time lag decreases with the increasing frequency and lasts longer than SLI.关键词：breakdown characteristics;oscillating impulse voltage(OIV);transformer oil;highly non-uniform electric field558|6|1更新时间：2025-07-09
- 摘要：Two types of volute tongue are designed for a multi-blade centrifugal fan used in range hoods. One is an inner concave arc volute tongue and the other is an inner concave grooved volute tongue. The effects of the inner concave volute tongues on both the aerodynamic performance and the noise of the multi-blade centrifugal fan are studied by using the measurement and numerical simulation methods. Compared with the traditional tongue, the impact of the air flow discharged by the impeller on the surface of the volute tongue is weakened and the inverse pressure gradient of the flow field near the volute tongue is reduced when the inner concave arc and the inner concave grooved volute tongues are used. Under the condition that the total pressure and operating efficiency of the multi-blade centrifugal fan keep constant, the aerodynamic noise is reduced. Experimental results show that the sound pressure level of the multi-blade centrifugal fans with the inner concave arc volute tongue and the inner concave grooved volute tongue goes down by 1.4 dB and 1.7 dB, respectively. At the same time, the effective flow area at the fan outlet increases because the flow separation occurred near the volute tongue is suppressed. The vortex intensity and the corresponding influence area are reduced. These results show that the flow rate of the multi-blade centrifugal fan with the concave volute tongues effectively increases.关键词：multi-blade centrifugal fan;volute tongue;aerodynamic performance;noise;numerical simulation683|5|5更新时间：2025-07-09
- 摘要：In order to improve the resolution of flowing structures simulated with the weighted essentially non-oscillatory(WENO)scheme, an improved WENO scheme(WENO-EX)is constructed. By considering the interaction among the smoothness indicators of sub-stencils and whole stencil, which is based on the classic WENO scheme(WENO-JS)proposed by Jiang and Shu, a term characterizing the smoothness of the whole stencil is introduced to constitute the new smoothness indicator which changes the assignment of the nonlinear weights. The theoretical analysis shows that the improved WENO scheme can keep the original design accuracy, and obtain smaller dissipation and higher resolution with larger nonlinear weight assignment to the discontinuous stencil. Subsequently, numerical simulations for the linear transport equation with different initial conditions and typical shock problems such as the double Mach reflection and shock-vortex interaction governed by the Euler equations are conducted with different WENO schemes, and the WENO-EX scheme achieves better numerical results. The results show that WENO-EX scheme has smaller error with the same grid in smooth regions, and higher resolution of flowing structures in dealing with problems containing discontinuities.关键词：weighted essentially non-oscillatory scheme;smoothness indicator;high accuracy;high resolution411|5|0更新时间：2025-07-09
- 摘要：A new strategy is adopted to construct the hydrogel microchannel with the enzymatically-crosslinked gelatin by evaluating the different concentration gelatin hydrogel, which aims to solve the difficulty of fabricating circular microchannel by soft hydrogel. The relationship of the gelatin properties(mechanical, forming and biological)with its concentration is revealed and discussed, and the molding process of gelatin hydrogel microchannel is proposed. The structural, mechanical and endothelialization properties of gelatin hydrogel microchannel are also studied. The experimental results indicate that with the increasing gelatin concentration, the mechanical property and microstructure replication property of the composite hydrogels are gradually improved, however, superior concentration causes lower biological performance. Hence, the hydrogel with 0. 1 g/mL gelatin is chosen as the optimal composition to build circular microchannel. The approach for fabricating microchannel retains the original mechanical properties of the hydrogel, although certain error exists in the forming process from characterizing morphology and the dimension of the microchannel. Besides, the microchannel gelatin facilitates attaching and spreading of human umbilical endothelial cells(HUVECs)to form a uniform endothelialized layer around the channel surface. Following the evaluation of different concentrations of enzymatically crosslinked gelatin hydrogel, the biomimetic microchannel can be expected to apply to reconstruction of substantive functional organs.关键词：substantive functional organs;gelatin;mTG;hydrogel;microchannel744|5|2更新时间：2025-07-09
- 摘要：Aiming at poor mechanical property and shaping ability of natural hydrogel fiber, combining micro-fluidics with photo-crosslinking, an alginate/GelMA hybrid hydrogel with enhanced mechanical properties in high-throughput manner is fabricated. The impacts of the micro-fluidic nozzle size and the hydrogel monomer concentration on the shaping capability, mechanical property and structural feature of hydrogel are investigated. The fabricated hydrogel fiber is smooth with uniform distribution in diameter(390±50 μm)to show the controllability in hydrogel fabrication. SEM results indicate that the hydrogel is endowed with denser lamella microstructure along with increasing concentrations of alginate and GelMA monomer, and the elastic modulus of hydrogel rises accordingly. The biocompatibility of hydrogel fiber is validated by the cell experiments, and the cell viability maintains 80% after 5 days culture. In the animal experiment, ambient subcutaneous tissue remains normal after one week hydrogel implanting, and the surrounding inflammation relieves and hydrogel degrades to some extent in the third week after implanting. This research result of alginate/GelMa hydrogel fiber with enhanced mechanical property is expected to realize high-throughput establishment of three-dimensional muscle micro-tissue model.关键词：hydrogel fiber with enhanced mechanical property;high throughput fabrication;alginate;GelMA;photo-crosslinking;micro-fluidics595|5|0更新时间：2025-07-09
- 摘要：The mesh-less moving particle semi-implicit method is employed within the Lagrangian framework to investigate the special geometry of the single film bubble with gas being shrouded by a layer of liquid film, and its special dynamic characteristic that surface tension acts both on the inside and outside interfaces. A surface tension model of the single-film-double-interfaces is established based on the surface tension model of surface free energies, and the complex interface movement in the oscillation process of the single-film bubble is calculated and captured. Moreover, the coalescence and connection process of two single-film bubbles are simulated and analyzed, and the typical flow phenomena and deformation characteristics of the liquid film are obtained. Results show that the leading role of the surface tension in the bubble deforming process reduces when either the surface tension coefficient decreases or the fluid viscosity increases. Furthermore, a concave tangent method is proposed to calculate the angle of the liquid film of the connected bubbles, which helps to describe the shape of connected bubble, quantitatively. These results provide some theoretical supports to the industrial froth breaking.关键词：moving particles semi-implicit method;surface tension;sing-film bubble;bubble coalescence;bubble connection511|5|0更新时间：2025-07-09
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