Advanced Search

2015 Vol. 41, No. 4

  Previous Issue | Next Issue 
Display Method:
Volume 41 Issue42015
2015 Year 41 Volume 4 Issue E-journal
Cover Catalogue Main indicators of periodicals
iconDownload (35487) 809 iconPreview
Design and optimization of improving stability of curvilinear blade-stiffened panels
XU Yuanming, WANG Dong
2015, 41(4): 567-573. doi: 10.13700/j.bh.1001-5965.2014.0257
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 661
Abstract:
Stiffened panels are widely used in the aerospace field as a typical structure. To further expand the design space of straight stiffened panels, an optimization framework for curvilinear blade-stiffened panels was developed based on ModelCenter optimization environment, Catia and Abaqus. Stiffeners were generated by equally-splitm cubic B-spline interpolation function, which had no limit to the number of parameters, thus providing a sufficiently large optimization space for curvilinear stiffened panels. On the other hand, two methods were taken to load on stiffeners including collecting loaded edges of stiffeners and making stiffeners perpendicular to panel edges and some new configurations of stiffened panels were proposed. Optimization results show that for single-axle load, curvilinear stiffened panels in comparison with straight stiffened panels make very small stability improvement. But for multi-axial load, curvilinear stiffened panels have better stability than straight stiffened panels.
Interference characteristics analysis of optical fiber Fabry-Perot cavity with graphene diaphragm
LI Cheng, GUO Tingting, XIAO Jun, FAN Shangchun, JIN Wei
2015, 41(4): 574-579. doi: 10.13700/j.bh.1001-5965.2014.0279
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 689
Abstract:
With regard to the design of optical fiber Fabry-Perot cavity using graphene as sensitive diaphragm, the deflection change under uniformly distributed loads in graphene film was analyzed by finite element method based on the large deflection elastic theory of circular film. The pressure-sensing mathematical model of optical fiber Fabry-Perot cavity with graphene diaphragm was established based on the working principle of Fabry-Perot interferometer. The effects of graphene film layer and incident light angle on the film reflectivity were obtained according to the refractive index characteristics of the film. Then the interference spectra change, caused by both the cavity length losses and the film deflection deformations under the pressure loads, were analyzed. The simulation results show that adding the film layer can increase the film reflectivity and further improve the optical interference performance; however, a decreasing effect on the deflection deformation is caused by the film layer with the increase of pressure load. Thus, an 8 layer graphene film can achieve a reflectivity of 0.715% and an approximate theoretical sensitivity of 10nm/kPa for a 40μm Fabry-Perot cavity length with a membrane diameter of 25μm. It provides a theoretical basis for the design and fabrication of high-sensitivity fiber-tip pressure sensor with multiple-layer graphene diaphragm.
Sub-pixel X-corner detection and location with directional characteristics
MENG Cai, XUE Jiao
2015, 41(4): 580-588. doi: 10.13700/j.bh.1001-5965.2014.0293
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 694
Abstract:
X-corner points are widely used in camera calibration and visible-spectrum visual tracking system as they can provide not only location information, but also direction information. To accurately detect the location and direction of X-corner points, a new algorithm based on the symmetry calculation of X-corner points was proposed. The algorithm mainly consists of two parts. First, the pixel position of the X-corner is determined by using the value of symmetry calculation. Then the sub-pixel location for the X-corner was obtained based on the quadratic curve fitting and inter-section of lines. Through a series of experiments and a comparison with Harris algorithm and Micron Tracker system, the impacts of Gauss noise and distortion on the positioning accuracy and robustness were analyzed. Experiments show that the method can effectively detect X-corners and exclude other types of corner points and disturbance, and thus has higher localization accuracy and robustness.
Metal molten behavior with ultra high frequency pulsed arc welding
YANG Mingxuan, YANG Zhou, CONG Baoqiang, WANG Qiang, QI Bojin
2015, 41(4): 589-593. doi: 10.13700/j.bh.1001-5965.2014.0246
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 531
Abstract:
Molten liquid metal is the key factor of the fundamental research during welding process, as it is the transfer element between arc behavior and solidification. Researches of the characteristics of molten pool were carried out by ultra high frequency pulsed arc welding (UHFP-AW), especially with the focus on the effect of arc force. The methods combining experiments and theoretical study were produced for the analyses of important factors, such as fluid status, velocity and temperature distribution of molten pool. And the fluid in molten surface was monitored as the supplement for further study. The results indicate the significant effect of the arc plasma on heat and force of molten pool with UHFP-AW. The monitor data demonstrate that the velocity of surface fluid is more than 30cm/s, and the double-circulation exists with surface depression caused by larger velocity during UHFP-AW. As a result, the temperature diffusion of molten pool would reduce, which can limit the impact of arc heat on base metal effectively. It is the key for controlling the grain size of titanium alloys with arc welding process.
Grid generation criterions in hypersonic aeroheating computations
ZHANG Zhichao, GAO Zhenxun, JIANG Chongwen, LEE Chunhian
2015, 41(4): 594-600. doi: 10.13700/j.bh.1001-5965.2014.0288
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 935
Abstract:
Three wall normal grid generation criterions in hypersonic aeroheating computations are analyzed, including mean free path (MFP), and cell Reynolds number based on freestream parameters and wall parameters respectively. A wall parameter prediction method is proposed to avoid trial computations when MFP and cell Reynolds number based on wall parameters criterions are used. The proposed method is utilized and combined with different grid generation criterions to generate several grids. A comparison with the experimental data is conducted to test if the wall normal mesh size determined by the grid criterions can satisfy the precision requirement of thermal environment simulation, and also to verify the wall parameter prediction method proposed. Numerical simulations of two-dimensional cylinder with perfect and real gas effects, and three-dimensional blunt bicone are carried out. It can be concluded that the wall parameter prediction method is reliable, the criterion of the cell Reynolds number based on freestream parameters would amplify the wall grid scale with the increase of the freestream temperature, both MFP and cell Reynolds number based on wall parameters are influenced by wall temperature rather than by freestream temperature, and the grid scale determined by these two criterions are consistent and can satisfy the precision requirements of hypersonic aeroheating computations.
Demonstration platform for collaborative design of space science missions
DENG Li, HAN Chao, CAO Jinbin, SONG You
2015, 41(4): 601-608. doi: 10.13700/j.bh.1001-5965.2014.0284
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 768
Abstract:
There are several problems during the demonstration process of collaborative design of space science missions, such as strong coupling between sub-system solutions, poor data consistency, difficulty in data modification, and associated relationship between data and demonstration process. In order to solve these problems, a multi-layer digital model for typical space missions was proposed. The demonstration process was graphically modeled, and the mapping between the process and data was established. The shared data pool was provided as the data collaboration mechanism for all users and all sub-system solutions. The message bus was adopted as the timely reminder to notify the changes of data. The design solution coupling matrix was used to describe the coupling relationship between sub-system solutions and to gain the system solution for the missions by the automatically merged method. The demonstration platform, as a distributed platform for the collaborative design of space science missions, uses the technology architecture of Eclipse RCP and Spring and integrates the middlewares of Hibernate and Activiti5. The platform can provide a unified portal and support multi-user, multi-mission, multi-solution and multi-version data management, and also support process monitor and data interactive collaboration. A space mission was used as an example to verify the efficacy of the platform.
SEL rate prediction for SRAM using pulsed laser sensitivity mapping
YU Yongtao, HAN Jianwei, FENG Guoqiang, CAI Minghui
2015, 41(4): 609-615. doi: 10.13700/j.bh.1001-5965.2014.0301
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 790
Abstract:
The classical approaches for single event latchup (SEL) rate prediction are based on the rectangular parallelepiped (RPP) model of only one sensitive volume. However, the experiment results of SEL sensitivity mapping of static random access memory (SRAM) show that the device has not only one sensitive volume (SV). The in-flight SEL rate of the device was corrected using the experiment results of pulsed laser SEL sensitivity mapping of SRAM K6R4016V1D.The SEL sensitivity maps of the SRAM by pulsed laser were first obtained and then the SV number of the device was calculated. The SEL rates of the device were predicted and discussed for different space orbits, radiation particles, SV thicknesses and SV number in particular. The results show that SEL rate caused by heavy ion decreases with SV number. The correction of the SV number is essential for SEL rate due to proton direct ionization; otherwise, the contribution of direct ionization of protons to SEL rate would be greatly overestimated.
Analysis of stratospheric lighter-than-air vehicle's aerodynamic characteristics based on large eddy simulation
WANG Yufu, TAO Guoquan, LIU Dongxu, WU Zhe
2015, 41(4): 616-623. doi: 10.13700/j.bh.1001-5965.2014.0535
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 604
Abstract:
Flowing over stratospheric lighter-than-air vehicle (SLV) with spherical capsule shape at supercritical Reynolds number were simulated by using large eddy simulation (LES) method. Meanwhile, the results at different sphere spacing were analyzed and compared so that the influence of different sphere spacing on stratospheric lighter-than-air vehicle's aerodynamic characteristics was obtained. Compared with the results of the experiments, the calculations of time-average drag coefficients agreed well with Achenbach's experimental results in the single sphere. The method was verified accurate on the analysis of flow over spheres at supercritical Reynolds number. The drag coefficients of the two spheres at different sphere spacing and frequency spectrum were studied. With the increase of the upstream and downstream spheres' spacing, the whole drags increased first, then decreased, and the the dominant frequencies of G=1.5D and G=2D. With the increasing of G, the interaction between the two spheres and the influence of upstream sphere's trailing vortex to downstream sphere's trailing vortex waned.
Two-stage acquisition algorithm for DSSS signal based on compressive sensing
CHENG Yanhe, YANG Wenge
2015, 41(4): 624-631. doi: 10.13700/j.bh.1001-5965.2014.0666
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 597
Abstract:
According to the restriction between the acquisition performance and the hardware consumption, a two-stage compressive acquisition method was proposed based on compressive sensing, specifically some coarse acquisition values can be got by the first stage, following by accurately detecting the signal in the values by the second stage. Firstly, the sparsity of DSSS signal in the correlation domain was explored, so as to build the sparsity transformation matrix. Secondly, the measurement matrixes and detection algorithms in both stages were produced according to the deterministic Walsh-Hadamard matrix. Finally, the acquisition performance of the provided method was analyzed theoretically in terms of the detection probability and the mean acquisition time, which was also verified by Monte Carle method. The theoretical analysis and the simulation results show that the novel method can use much less correlations to achieve the same performance as conventional parallel correlation-based methods.
Calculation method of fracture toughness of materials at transition state
GAO Chao, HE Yuting, CUI Ronghong, WU Liming
2015, 41(4): 632-640. doi: 10.13700/j.bh.1001-5965.2014.0255
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 784
Abstract:
The fracture toughness of materials is very important for damage tolerance design and assessment technology, while the test method to obtain the fracture toughness in the transition state is costly and time-consuming. In order to overcome these disadvantages, a determination method of fracture toughness based on calculation in the transition state was presented. The triaxial stress constraint parameter for the three-dimensional crack tip was analyzed, the relation between fracture toughness and material tensile properties was researched with the energy criterion for material fracture, meanwhile the relation expression in the three-dimensional stress state for I type crack fracture and the determination method of fracture toughness of materials based on calculation in the transition state were obtained. The fracture toughness in the transition state for 2219-T87 aluminum alloy was calculated with the determination method and empirical formula most of the theoretical calculation values were safer compared with test results and smaller than the values calculated by the empirical formula.
Online programming technique for flexible assembly of fuselage
WU Fengfeng, LI Dongsheng, WANG Liang
2015, 41(4): 641-648. doi: 10.13700/j.bh.1001-5965.2014.0256
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 563
Abstract:
In order to meet the deep flexible demands of “one fixture with more models” and “one fixture with more states” for digital assembly of fuselage, enable the “bridge-frame” flexible tooling to have better capacity for independent adaptability, its kinematic model must be set up and its movement controls strategy must be planned properly by online programming technique. For the locating styles of fuselage and the characteristics of flexible tooling, the kinematic model of flexible tooling was set up, then simulation model-based online programming disciplines, the way of building reference points for assembly and the technology of movement controls strategy planning were studied. The way of building a process-driven simulation environment based on structure function was proposed. In order to generate the codes quickly to control motion, the online programming system for flexible assembly of fuselage was developed. With the assembly of rear fuselage, for example , the accuracy, high efficiency and strong independent adaptability of this system were verified.
Depth information extraction of on-board monocular vision based on a single vertical target image
HUANG Xiaoyun, GAO Feng, XU Guoyan, DING Nenggen, XING Longlong
2015, 41(4): 649-655. doi: 10.13700/j.bh.1001-5965.2014.0272
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 809
Abstract:
Calculating obstacle distance for on-board monocular vision system on intelligent vehicle was investigated when the obstacle has been detected. An extraction method of depth information only using a single target image without any internal camera parameters was developed. The mapping relation between image row pixel values and the actual imaging angles was established with the image of vertical target, which was placed in the front of a camera. The obstacle depth information was extracted in real time by combining the projection geometry model. Given the characteristic of vertical target image, an algorithm of sub-pixel corner detection and location was designed, which includes region of interest setting, template matching, candidate points clustering and screening and precise location, etc. Experimental results show that the method has high precision and real-time performance. Compared with the method of putting reference on the road, it does not need large calibration site and could avoid the data fitting error. And the method also has a simple calibration procedure with a single image, which is suitable for practical application.
Hydrodynamic features of underwater vehicles based on flow control
ZHANG Xiaoshi, WANG Cong, CAO Wei, ZHAO Chenggong
2015, 41(4): 656-662. doi: 10.13700/j.bh.1001-5965.2014.0299
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 686
Abstract:
The hydrodynamic characteristics of underwater vehicles were numerical modelling studied by CFX. Shear stress transport turbulence model control equation of mixed media, Reynolds-averaged Navier-Stokes equation and mass transport equation between each phase were solved, and three dimensional numerical simulation methods were adopted to contrast and analyze the variation characteristics of cavity shape, surface pressure distribution and drag coefficient of underwater vehicles with different flow controlschemes. The effects of different parameters on drag reduction effect were also discussed. The result shows that, for the vertical underwater launching vehicles under cross-flow effect, multiphase flow control can not only lower the asymmetry of ventilated cavity and drag force of vehicles, but also balance the pressure on the positive side and back surfaces to realize the control of cavity shape and surface pressure characteristics etc. of vehicle multiphase flow. Furthermore, the location of ventilation hole has a significant influence on drag reduction effect.
Tool path generation for Loop subdivision surface based finish machining
CHEN Tiantian, ZHAO Gang
2015, 41(4): 663-668. doi: 10.13700/j.bh.1001-5965.2014.0308
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 773
Abstract:
Both smooth design model and discrete machining model can be represented by the subdivision surface, which avoids the complex progress of model transformation. Subdivision surface can be used to generate a smooth limit surface on an arbitrary topology mesh, and thus has great advantage in modeling complex parts. In addition, it has great potential for applications in NC machining. The algorithm for tool path generation of finish machining based on Loop subdivision surface was investigated. The method of adaptive interpolation Loop subdivision surfaces was proposed to control the chord error between limit mesh and limit surface. The finish machining model was then decomposed into different regions by iso-slope curve tracing method, and different tool path patterns were calculated to obtain an even cusp height. Therefore, it is simple to generate the even cusp height tool path of the entire finish machining model, and the conflict between large-scale subdivision data and required high surface quality and precision is also solved. Milling test is implemented to verify the algorithm proposed.
Edge-preserving filtering based on saliency map
FENG Ce, DAI Shuling, ZHAO Shuaihe
2015, 41(4): 669-674. doi: 10.13700/j.bh.1001-5965.2014.0309
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 725
Abstract:
A new edge-preserving filtering algorithm based on the saliency map was proposed to avoid the halo effect along salient edges in traditional edge-preserving filtering. The saliency map was characterized by the salient edges in the image and insensibility to noise. The key idea of our filtering algorithm was to simplify the decision of gray standard deviation in bilateral filtering by using the characteristics. We first obtained a saliency map of the original image, and then blurred the image adaptively according to the local saliency value. If the local saliency value is high, the standard deviation would become small to retain the region. If the local saliency value is low, the standard deviation would become large to smooth the region. Therefore, the filtering proposed could avoid unwanted smoothing near salient edges. Experiments show that the proposed filtering performs better in comparison with guided filtering and bilateral filtering. A variety of applications including high dynamic range (HDR) Tone mapping and stylization by our filtering algorithm are also demonstrated.
Prediction of forming limit diagram of AA7075-O aluminum alloy sheet based on modified M-K model
YANG Xiying, LANG Lihui, LIU Kangning, CAI Gaocan, GUO Chan
2015, 41(4): 675-679. doi: 10.13700/j.bh.1001-5965.2014.0310
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 973
Abstract:
To accurately predict the forming limit diagram of AA7075-O aluminum alloy sheet, a modified M-K model was put forward based on the ductile fracture criterion and the traditional M-K model. By using the method which combined the uniaxial tension simulation with experiment, the history of stress-strain of the dangerous element was substituted into the C-L ductile fracture criterion which was implemented into Abaqus/Explicit to get the material constant. Based on the forming limit data obtained by the uniaxial tensile, the initial thickness imperfection in the modified M-K model was obtained by the method which was programed in MATLAB. At room temperature, the experimental forming limit data of AA7075-O aluminum alloy sheet were tested through the uniaxial tensile, wide plate bending and hydraulic bulging experiments. Meanwhile, the theoretical forming limit curves obtained by the modified M-K model and the traditional M-K model were computed respectively. By comparison, the modified M-K model is proved to be feasible and more accurate.
Energy-saving resource scheduling algorithm based on workload characteristic clustering
XIA Qingxin, LAN Yuqing, TANG Tian, XIAO Limin
2015, 41(4): 680-685. doi: 10.13700/j.bh.1001-5965.2014.0407
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 649
Abstract:
When infrastructure as a service (IaaS) providers offer high performance services for users, they must think about how to reduce the energy cost of the cloud platform without violating the service level agreement (SLA). A resource scheduling algorithm to ensure SLA was proposed based on clustering analysis of the load characteristic. Ultimately, the targets of reducing SLA violation rate and saving energy were realized. The resource scheduling algorithm was analyzed based on improved K-means clustering analysis and extraction of workload characteristic according to energy consumption. Physical resources were effectively allocated to ensure the requirement of energy saving of IaaS platform. Based on the extension of the CloudSim simulation platform, the algorithm proposed was compared with the optimized best fit decreasing (BFD ) to show lower SLA violation rate and energy consumption.
Tube free bulging experiment with force-end and material properties testing
CHENG Pengzhi, LANG Lihui, GE Yulong, RUAN Shangwen, WANG Tao, WU Hai
2015, 41(4): 686-692. doi: 10.13700/j.bh.1001-5965.2014.0603
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 996
Abstract:
Compared with uniaxial tension, the material property parameters obtained by tube bulging test (TBT) can accurately reflect the plastic forming properties of materials under high-pressure fluid condition. Different end-conditions will seriously affect the experiment results of TBT. According to the defects of existed experimental method and equipment internationally, a special TBT system, with accurate boundary conditions and loading units, was successfully designed and developed. The axial force, axial displacement, and the internal pressure are the key points of the system which could be accurately controlled in real-time bycontrol strategy of displacement under dynamic active loading state and proportional servo valves. The free sliding of fixed tube ends was implemented by a special designed fixture. During the experimental process, the real-time thickness and bulging height in the pole, and the real-time internal pressure were monitored by the ultrasonic thickness gauge, the magnetostrictive displacement sensor and the ultra-high pressure sensor. The stress-strain curve and material properties were derived by the Swift material constitutive model and the monitor data. The experimental data demonstrate that the two load balance conditions, which are the balance of two axial forces with internal pressure and the balance of two axial contractive displacements, are always satisfied during all the test process. The test data processing results show that the monitor data have good repeatability and can be used to get the material properties.
Experiment of chloride effect on strength of alkali-activated slag paste
CHENG Yin, HUANG Xin
2015, 41(4): 693-700. doi: 10.13700/j.bh.1001-5965.2015.0072
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 727
Abstract:
Based on the results of unconfined compression tests of alkali-activated slag (KC) paste mixed with sodium chloride (NaCl) and calcium chloride (CaCl2), the influence law of the KC paste strength changing with chloride was studied. X-ray diffraction (XRD), thermal gravity-differential thermal gravity analysis (TG-DTG), the test of ionic concentrations in the pore solution and the test of degree of hydration were used to analyze the mechanism of effect of two kinds of chlorideon KC paste strength. The research results show that the KC paste compressive strength increased with the increase in the concentration of NaCl; and KC paste compressive strength basically unchanged with the increase in the concentration of CaCl2. The Friedel's salt (Fs) was generated in KC paste mixed with NaCl and CaCl2, but it has no effect on the paste strength. The generation of sodium hydroxide (NaOH) in the KC paste mixed with NaCl was the main reason for its strength enhancement. NaOH existed in the KC paste improved the liquid alkalinity of paste, promoted hydration of slag and generated more calcium silicate hydrate (CSH) to improve the paste strength.
Generation of unsteady inflow conditions for compressible LES with a modified vortex method
XIE Baolin, SHAO Liang
2015, 41(4): 701-706. doi: 10.13700/j.bh.1001-5965.2014.0281
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 704
Abstract:
This article is to explore and modify vortex method to generate large eddy simulation (LES) inlet condition. In the modification, a density distribution of vortex which can avoid unreasonable vortex quantity in local place was used. The movement of vortex was controlled by Langevin equation, which mimics the active grid turbulence so as to generate an unsteady flow field which is more like the real turbulence. Knowing the results of Reynolds-averaged Navier-Stokes equations (RANS) and reconstructing the turbulence by vortex method (VM), the method was tested in the experimental channel. The statistical results of both inlet and outlet of the channel were given, which include the mean velocity, the vorticity and the Reynolds stress. By analyzing the generated field with the reference of direct numerical simulation (DNS) results and comparing with the results of original method, during the development of turbulence in the channel, it shows that the modified vortex method is viable and cost-effective for generating unsteady inflow condition for LES.
Relationship between bias spring parameters and output performances of SMA actuators
YANG Baofeng, ZHANG Xiaoyong, YAN Xiaojun
2015, 41(4): 707-712. doi: 10.13700/j.bh.1001-5965.2014.0297
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 601
Abstract:
The parameters of the bias spring have great impacts on the output performances of the shape memory alloy (SMA) actuator. To investigate the rules of influences, the output stroke and response rate of a SMA actuator with different bias spring stiffness and precompression load were studied. The output degradation due to cyclic actuation was also investigated. Experimental results show that the strokes and response rates decrease with the increase of preloads or stiffness. The performance of the actuator degrades significantly in the first few cycles and stabilizes eventually with the increase of the number of cycles. The test results also indicate that less cycling is needed to stabilize the actuator when the preload is increased, and the stiffness seems to affect the cyclic performance of the actuator slightly.
Object tracking in surveillance videos using spatial-temporal correlation graph model
ZHANG Cheng, MA Huadong, FU Huiyuan
2015, 41(4): 713-720. doi: 10.13700/j.bh.1001-5965.2014.0472
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 837
Abstract:
Object tracking in non-overlapping multi-camera surveillance is a challenging problem since the transition time between cameras varies greatly from individual to individual with uncertainty. The key problem of object tracking in wide areas is data association and how to find correspondences between objects via camera topology. A novel graph model was proposed to capture the spatial-temporal correlation among objects, which are moving in the camera network. Source/sink regions are graph nodes, and the graph edges are constructed by the spatial and temporal constrains. Specifically, a tracking method combining appearance model and graph model was proposed to solve the problem of object re-identification and data association via bipartite matching in multi-camera object tracking. In addition, region covariance descriptor was utilized to fuse the appearance feature. Experiments with real videos validate the proposed approach.
Signature scheme for network coding against inter-generation pollution attacks
PENG Tianli, SHANG Tao, LIU Jianwei
2015, 41(4): 721-726. doi: 10.13700/j.bh.1001-5965.2014.0478
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 664
Abstract:
The concept of generation is introduced into network coding so as to adapt to the needs of real-time application. Considering that network coding is vulnerable to inter-generation pollution attacks and causes message crosstalk, a generation-identifier based signature scheme for network coding was proposed. Firstly, the two-level private keys, including the generation private key and the message private key, both derived by the generation identifier were set. This procedure enabled nodes to judge the generation attribute of messages and decided whether to continue coding. Secondly, a signature algorithm was constructed with homomorphic property by using the bilinear pairing. Meanwhile the two-level private keys were separated to verify signatures by batch, which made nodes verify all the massages of the same generation simultaneously. Finally, through the analysis of random oracle model, the scheme was proved secure against adaptively chosen message attack. The result indicates that the scheme can reduce computation cost and improve performance of the system.
Explicit moment integration algorithm and its application
FU Zihao, GONG Guanghong
2015, 41(4): 727-731. doi: 10.13700/j.bh.1001-5965.2014.0266
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 733
Abstract:
The calculation of moment is often used in finite element method, volume calculation, moment of inertia calculation, etc. A discrete method of the computational domain in three-dimensional space was proposed firstly based on the superposition of moment. An explicit formula was derived in three-dimensional space and then extended to n-dimensional space, which can be easily implemented on the computer. Secondly, a parallel algorithm of moment calculation was designed and implemented with mixed Fortran and Python. Thirdly, a zero-order and second-order moment was calculated in a multi-fidelity example. The efficiency of the algorithm was compared with a serial algorithm and a successive dimensionality reduction algorithm. Meanwhile, efficiency analysis and error analysis were presented. The result shows that the explicit moment integration algorithm can be easily implemented with programs and runs faster than the serial algorithm. It is highly parallel and can also be easily extended to a higher dimensional space. The algorithm is highly parallel, whose error mainly comes from the discrete process of the computational domain.
3D face recognition based on local radial binary pattern
LIU Qing, SUN Junhua
2015, 41(4): 732-736. doi: 10.13700/j.bh.1001-5965.2014.0289
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 629
Abstract:
An operator named local radial binary pattern (LRBP) was proposed for extracting local features in face recognition. The binary sequence encoding scheme of the LRBP is different from that of the local binary pattern. Firstly, the proposed LRBP operator was used in 3D face recognition. 3D face depth images were preprocessed and divided into subregions. Then the signature sequences of the subregions were extracted by the LRBP operator. The feature vectors of a 3D face depth image were obtained by connecting the signature sequences of all the subregions of the image. Finally, the 3D face feature vectors were trained and recognized using the Fisherface method. Experiments were conducted using the 3D face database of Institute of Automation, Chinese Academy of Sciences. The results show that the proposed method can effectively promote the efficiency of 3D face recognition without reducing the recognition rates.
Dynamics modeling and motion programming for electromagnetic formation flight
SHAO Longfei, SHI Peng, ZHAO Yushan
2015, 41(4): 737-743. doi: 10.13700/j.bh.1001-5965.2014.0305
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 650
Abstract:
Based on the mechanism of electromagnetic spacecraft, the relative translational “tethered” dynamics model for two-craft electromagnetic formation flight (EMFF) in low earth orbit was developed by using Lagrange theory. The linearized equations for motion and stability analysis of two-craft radial and along-track formation were investigated. To stabilize the formation structure, the feedback control law was studied. The motion programming of electromagnetic formation could be transformed into a standard optimal problem, which could be perfectly solved by the Gauss pseudospectral method. In order to deal with the reconfiguration maneuver of multi-craft electromagnetic formation, the sequence control strategy was proposed. Then the multi-craft problem was transformed into a multi-phase motion planning problem. Thus, the problem of multi-phase optimal control could be solved by Gauss pseudospectral optimization software (GPOPS). The simulation result shows that the methods of dynamics modeling and motion planning proposed in this paper are valid.
Storage life evaluation method based on segmented nonlinear Arrhenius model
ZHOU Jie, YAO Jun, SONG Yan
2015, 41(4): 744-750. doi: 10.13700/j.bh.1001-5965.2014.0319
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 715
Abstract:
Considering that logarithm linear Arrhenius model is only suitable for a small temperature range, a correction method for the Arrhenius model was given. As the step-down-stress accelerated life testing has the advantages of higher failure rate, less sample size, and simpler testing equipment, an evaluation method used in engineering practice for step-down-stress accelerated storage life testing was provided based on the segmented nonlinear Arrhenius model. A mathematical model for failure data conversion under step down stress based on the segmented nonlinear Arrhenius model was first established. The maximum likelihood function of the whole samples was given. The segmented nonlinear Arrhenius model parameter estimation could then be obtained by employing the genetic algorithm to solve nonlinear equations. Taking the step-down-stress accelerated storage life testing of radar altimeter as an example for analysis, the results of average life expectancy, the failure rate and reliability function based on logarithm linear Arrhenius model accelerated storage life evaluation method, the results based on segmented nonlinear Arrhenius model accelerated storage life evaluation method, and the results from field data were compared. The relative error of the results based on the segmented nonlinear Arrhenius model accelerated storage life evaluation method is within 5%. The efficiency and accuracy of the step-down-stress accelerated storage life evaluation method based on the segmented nonlinear Arrhenius model is verified.
Recognition of Chinese characters based on multi-scale gradient and deep neural network
PAN Weishen, JIN Lianwen, FENG Ziyong
2015, 41(4): 751-756. doi: 10.13700/j.bh.1001-5965.2014.0499
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 806
Abstract:
The method to extract the gradient histogram feature of the Chinese characters with a multi-scale sliding window and to recognize the printed Chinese characters with deep neural network was presented. In order to acquire the spatial information of the gradient histogram, a retractable sliding window technique was proposed for segmenting the images and getting the gradient feature information from different scales which can effectively combine all the global features and local block features of Chinese characters. The experiment was carried out by using a 5-layer deep neural network to classify 3755 categories of printed Chinese characters.A Dropout technique was applied so as to prevent over-fitting training and to improve the generalization ability of the neural network. The accuracy of the experiment reaches 98.292%, which has better recognition performance and demonstrates that the method of applying a multi-scale gradient feature and deep neural network model on the recognition of Chinese characters is effective.

Copyright © Journal of Beijing University of Aeronautics and Astronautics

Address: Editorial Department of Journal of Beijing University of Aeronautics and Astronautics, 37 Xueyuan Road, Haidian District, Beijing Post Code: 100191 Email: jbuaa@buaa.edu.cn

Supported by: Beijing Renhe Information Technology Co., Ltd.