JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Protection and reinforcement technology of smart penetration fuze

2012, 21(3): 285-290.

[Abstract](1016) [PDF 543KB](272)

Abstract:
The urgent needs of using earth penetrating weapons (EPW) and the latest development of the penetration fuze bring many new challenges and problems during the process of application of penetration fuze. In this paper, various failure modes of penetration fuze happened during the EPW penetrated into hard and deeply buried targets (HDBT) are introduced and the corresponding protection and reinforcement system of penetration fuze is established. At the meanwhile, two kinds of protection measures are proposed, one is making four kinds of buffer materials surrounded the fuze shell; another one is changing the energy absorption structures of these buffer materials. To verify the effects of these protection measures, simulation technology with the finite element method is adopted, and the results show that two protection measures are available. That is to say the impact from the targets on the fuze body is reduced apparently. All these researches lay a certain theoretical foundation to the protection technology about penetration fuze.

Performance analysis of fast GPS signal acquisition based on PMF and Window FFT

LI Chuan-jun, YANG Shu-xing, JI Zhen

2012, 21(3): 291-297.

[Abstract](1135) [PDF 313KB](164)

Abstract:
Combining the advantages of partial matched filter (PMF) and fast Fourier transform (FFT), an improved fast acquisition method for GPS C/A code is proposed. According to PMF-FFT acquisition architecture, the greater the number of PMF will bring out the more slowly amplitude decreasing of the amplitude-frequency response, the smaller scale of the corresponding PMF, and the larger computation of the FFT. In order to compensate the frequency spectrum attenuation caused by spectrum leakage and fence effect, adding window function to PMF-FFT is presented. Through comparing the influences to the acquisition performance based on rectangular, Hamming, Blackman and Rife-Vincent (Ⅲ) window functions, an improved Rife-Vincent Ⅲ windowing algorithm is recommended for the fast acquisition based on PMF-FFT.

Elasto-plastic analysis of crack in metallic foams

XIE Ling-yun, SUN Jun-jun, SUN Zhu-feng, FAN Tian-you

2012, 21(3): 298-301.

[Abstract](761) [PDF 161KB](149)

Abstract:
To determine the solutions of the well-known problem of a finite width strip with single edge crack, some results on elasto-plastic fracture analysis for metallic foams are reported. Meanwhile, in order to discuss and put an insight into the nonlinear fracture analysis, the Dugdale model for plastic deformation of this configuration for metallic foams is recommended and solved. Combining the asymptotic solution with the Dugdale model and elastic solution, the stress field in the plastic zone and the size of the plastic zone are expressed as analytical forms. Based on Williams expansion method, the estimate of the scale factor is also completed and analyzed. In view of these analytical solutions, the results show the scale factor is a useful parameter for the fracture theory of metallic foams.

Orientation density and workspace analysis of a parallel stabilized platform testing system

JIANG Fang, DING Hong-sheng, FU Tie, DONG Zhong-hui

2012, 21(3): 302-308.

[Abstract](1508) [PDF 992KB](150)

Abstract:
An optimized workspace calculation method is proposed for parallel stabilized platform testing systems. This method refines the searched space progressively in order to approach the boundary of the workspace from both the inside and the outside of it. The orientation density is defined and used as an evaluation index to calculate the orientation workspace. The algorithm of the orientation density is embedded into the computer program of the workspace calculation. Then the workspaces of the testing system are solved. In the solution, the orientation density is regarded as a discrete function of the reachable workspace. As a result, the reachable workspace and the orientation workspace are represented in the same multidimensional graphs. Finally the useful workspace of the testing system is determined based on these results. This case study indicates that the calculation efficiency is enhanced by adopting the optimized method and the practicability of workspace study is improved by proposing the orientation density.

Numerical simulation of the flow field of a flat torque converter

YAN Qing-dong, LIU Cheng, WEI Wei

2012, 21(3): 309-314.

[Abstract](870) [PDF 1184KB](144)

Abstract:
A flexible flat torque converter was proposed to fulfill the requirement of miniaturization and power density maximization for automobiles. Constructed by two arcs joined by lines, the torus was designed directly from design path. The influence of flatness on the performance of the torque converter was evaluated. The software CFX and standardk-εmodel were adopted to simulate the internal flow fields of the torque converter under different flatness ratios. The results indicated that the performance of the torque converter got worse as the flatness declined, but the capacity of pump increased. The efficiency and the torque ratio dropped slightly as the flatness ratio decreased. So the torque converter could be squashed appropriately to get high power density without too much efficiency sacrifice. But when the flatness ratio was below 0.2, there was a significant drop in the efficiency.

Control of magnetic levitation positioning stage with an eddy current damper

WANG Wei-ming, SHAN Ming-cai, MA Shu-yuan, TANG Shui-yuan

2012, 21(3): 315-320.

[Abstract](903) [PDF 326KB](127)

Abstract:
To enhance the system damping, a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table, four Halbach permanent magnetic arrays, four stators and displacement sensors. The dynamics model of this stage was a complex nonlinear, strong coupling system which made the control strategy to be a focus research. The nonlinear controller of the system was proposed based on the theory of differential geometry. Both simulation and experimental results show that either the decoupling control of the movement can be realized in horizontal and vertical directions, and the control performance was improved by the damper, verifying the validity and efficiency of this method.

Steady air injection flow control for increasing the surge margin of radial flow compressor

ISLEM Benhegouga, YANG Ce, LI Du, CHEN Shan

2012, 21(3): 321-327.

[Abstract](786) [PDF 671KB](113)

Abstract:
Steady air injection upstream of the leading edge was used to increase the surge margin of a centrifugal compressor. To reveal the mechanism, steady numerical simulations were performed on a high pressure ratio centrifugal compressor rotor operated with a rotor tip speed of 586 m/s. Eight different injection yaw angle with four different injection mass flow was performed to determine the configuration that provide the best results for the compression system studied in this work. The injection angle,α, was fifteen degree and the injectors were placed at short distance (ten percent of the inlet tip radius upstream of the compressor face) to achieve maximum control over the leading edge flow by varying individual injection parameters. The results show that at design speed (n50.000 r/min) with injection flow rate more than 2% of the main flow rate and yaw angle between 20° and 30°, the mass flow rate at stall decreases for approximately 8%. But with higher injection rate, other compressor parameters were affected such as compressor efficiency and compressor total pressure ratio.

Variable dimensional state space based global path planning for mobile robot

ZHANG Hao-jie, CHEN Hui-yan, JIANG Yan, GONG Jian-wei, XIONG Guang-ming

2012, 21(3): 328-335.

[Abstract](1066) [PDF 1014KB](123)

Abstract:
A variable dimensional state space (VDSS) has been proposed to improve the re-planning time when the robotic systems operate in large unknown environments. VDSS is constructed by uniforming lattice state space and grid state space. In VDSS, the lattice state space is only used to construct search space in the local area which is a small circle area near the robot, and grid state space elsewhere. We have tested VDSS with up to 80 indoor and outdoor maps in simulation and on segbot robot platform. Through the simulation and segbot robot experiments, it shows that exploring on VDSS is significantly faster than exploring on lattice state space by Anytime Dynamic A^*(AD^*) planner and VDSS is feasible to be used on robotic systems.

Real-time performance of periodic data transmission in EPA industrial Ethernet

LIU Ning, ZHONG Chong-quan, MO Ya-lin

2012, 21(3): 336-342.

[Abstract](922) [PDF 312KB](128)

Abstract:
To evaluate and improve the real-time performance of Ethernet for plant automation (EPA) industrial Ethernet, the real-time performance of EPA periodic data transmission was theoretically and experimentally studied. By analyzing information transmission regularity and EPA deterministic scheduling mechanism, periodic messages were categorized as different modes according to their entering-queue time. The scheduling characteristics and delivery time of each mode and their interacting relations were studied, during which the models of real-time performance of periodic information transmission in EPA system were established. On this basis, an experimental platform is developed to test the delivery time of periodic messages transmission in EPA system. According to the analysis and the experiment, the main factors that limit the real-time performance of EPA periodic data transmission and the improvement methods were proposed.

Analysis of metropolis parking problems and solutions based on GIS

LIU Yue-jun, WANG Wu-hong, GUO Hong-wei, LIU Hao

2012, 21(3): 343-348.

[Abstract](794) [PDF 303KB](132)

Abstract:
The rapid development of the social economy strongly promotes the urbanization and motorization. Meanwhile, parking problems become serious due to the long-term imbalance between parking demands and facility constructions. Thus there is an increasing urgency in finding solutions for parking problems. Based on the methodology framework of geographic information system (GIS), the metropolis parking problems are discussed in this paper. The characteristics of parking demand and the reasons for parking problems are investigated in detail. Then, the basic parking principle and strategies for solving parking problems are suggested with the example of Beijing. The results are hoped to improve the parking environment in metropolis.

Transmission resonance and color generation of metal- dielectric subwavelength gratings in visible regions

CHEN Yong-li, YU Hong-mei, LIU Wen-xia

2012, 21(3): 349-353.

[Abstract](737) [PDF 776KB](128)

Abstract:
Metal-dielectric subwavelength gratings unders-polarized andp-polarized visible radiation are studied for discovering their intriguing behaviors of spectral resonance and color property. The dependence of their resonance and color on grating parameters as well as angle of incidence and position of plane of incidence is also analyzed. Fors-polarized light, the behavior of spectral resonance with single peak and higher peak efficiency is found. While transmission spectra forp-polarized light are not able to achieve a behavior like that ofs-polarization, creating a perceived color is feasible. Moreover, a security grating with distinctive color shifts has been designed and its resonant properties as well as related color variation have also been provided.

Hybrid dynamic model of polymer electrolyte membrane fuel cell stack using variable neural network

LI Peng, CHEN Jie, CAI Tao, WANG Guang-hui

2012, 21(3): 354-361.

[Abstract](911) [PDF 301KB](127)

Abstract:
The polymer electrolyte membrane (PEM) fuel cell has been regarded as a potential alternative power source, and a model is necessary for its design, control and power management. A hybrid dynamic model of PEM fuel cell, which combines the advantages of mechanism model and black-box model, is proposed in this paper. To improve the performance, the static neural network and variable neural network are used to build the black-box model. The static neural network can significantly improve the static performance of the hybrid model, and the variable neural network makes the hybrid dynamic model predict the real PEM fuel cell behavior with required accuracy. Finally, the hybrid dynamic model is validated with a 500 W PEM fuel cell. The static and transient experiment results show that the hybrid dynamic model can predict the behavior of the fuel cell stack accurately and therefore can be effectively utilized in practical application.

New design of high-precision oven controlled crystal oscillator

DONG Shao-feng, DU Bao-qiang, ZHOU Wei

2012, 21(3): 362-369.

[Abstract](972) [PDF 285KB](134)

Abstract:
Combining oven controlled technique, digital compensation, high-resolution frequency difference measurement and self-calibration technique, a new design method of precise oven controlled crystal oscillator (OCXO) is proposed. Fine compensation is made in the vicinity of the crystal temperature inflection point by using the non-real-time temperature compensation strategy, and self-calibration system is integrated in the crystal. The method improves the digital compensated phase noise, simplifies the traditional OCXO development system, reduces the cost and shortens the developing cycle. Experiment results show that with a standard reference signal and self-calibration updated data, the oscillator can work stable and achieve its best performence. The performance index of crystal oscillator had an improvement with one to two orders of magnitude on the basis of original technical index. The method is widely used in the improvement of high-end crystal oscillator and atomic clock.

Decoder-based transient signal post-processing for ITU-T G 719 at low bit rate

WANG Jing, JI Xuan, HE Hai-long, KUANG Jing-ming

2012, 21(3): 370-375.

[Abstract](1025) [PDF 217KB](113)

Abstract:
Associated with ITU-T G 719, a post-processing method in frequency domain for enhancing the perceptual quality of the decoded transient audio is proposed only to the audio decoder with no side information from the encoder. The proposed post-filter is used to filter the frequency coefficients of the decoded transient frame and consists of a short-term post-filter and a spectral tilt compensation filter which are derived from linear predictive coding (LPC) predictor based on the discrete cosine transform (DCT) coefficients of the decoded transient frame. As a result, the post-filter in frequency domain shapes the temporal noise in time domain and controls the pre-echo noise effectively while enhancing the transient perception. Listening test results show that the preferring ratio of the post-processed transient signal is higher than that of the original decoded signal at a low bit rate of 32 kbit/s in G 719 and the post-processing module brings a complexity of 12.399 WMOPS to the decoder.

Hardware-in-the-loop simulation of communication networks

YANG Jie, LI Yin

2012, 21(3): 376-381.

[Abstract](994) [PDF 431KB](136)

Abstract:
To enhance the fidelity and accuracy of the simulation of communication networks, hardware-in-the-loop (HITL) simulation was employed. HITL simulation methods was classified into three categories, of which the merits and shortages were compared. Combing system-in-the-loop (SITL) simulation principle with high level architecture (HLA), an HITL simulation model of asynchronous transfer mode (ATM) network was constructed. The throughput and end-to-end delay of all-digital simulation and HITL simulation was analyzed, which showed that HITL simulation was more reliable and effectively improved the simulation credibility of communication network. Meanwhile, HLA-SITL method was fast and easy to achieve and low-cost during design lifecycle. Thus, it was a feasible way to research and analyze the large-scale network.

Global stability of interval recurrent neural networks

YUAN Zhu-gang, LIU Zhi-yuan, PEI Run, SHEN Tao

2012, 21(3): 382-386.

[Abstract](729) [PDF 177KB](133)

Abstract:
The robust global exponential stability of a class of interval recurrent neural networks (RNNs) is studied, and a new robust stability criterion is obtained in the form of linear matrix inequality. The problem of robust stability of interval RNNs is transformed into a problem of solving a class of linear matrix inequalities. Thus, the robust stability of interval RNNs can be analyzed by directly using the linear matrix inequalities (LMI) toolbox of MATLAB. Numerical example is given to show the effectiveness of the obtained results.

Stability analysis and controller design of T-S fuzzy systems with time-delay under imperfect premise matching

ZHANG Ze-jian, HUANG Xian-lin, BAN Xiao-jun, GAO Xiao-zhi

2012, 21(3): 387-393.

[Abstract](985) [PDF 210KB](123)

Abstract:
The issue of the stability and controller design of Takagi-Sugeno (T-S) fuzzy control systems with time-delay is investigated under imperfect premise matching when the T-S fuzzy time-delay model and fuzzy controller do not share the same membership functions. A new stability criterion which contains the information of membership functions is derived. The new stability criterion is less conservative, and enhances the design flexibility. Two numerical examples are presented to illustrate the conservativeness and effectiveness of the proposed method.

Fast speedometer identification in dynamic scene based on phase correlation

WANG Yu-tang, FU Meng-yin, YANG Yi

2012, 21(3): 394-399.

[Abstract](797) [PDF 728KB](120)

Abstract:
Speedometer identification has been researched for many years. The common approaches to that problem are usually based on image subtraction, which does not adapt to image offsets caused by camera vibration. To cope with the rapidity, robust and accurate requirements of this kind of work in dynamic scene, a fast speedometer identification algorithm is proposed, it utilizes phase correlation method based on regional entire template translation to estimate the offset between images. In order to effectively reduce unnecessary computation and false detection rate, an improved linear Hough transform method with two optimization strategies is presented for pointer line detection. Based on VC++ 6.0 software platform with OpenCV library, the algorithm performance under experiments has shown that it celerity and precision.

Method to generate training samples for neural network used in target recognition

HE Hao, LUO Qing-sheng, LUO Xiao, XU Ru-qiang, LI Gang

2012, 21(3): 400-407.

[Abstract](766) [PDF 531KB](129)

Abstract:
Training neural network to recognize targets needs a lot of samples. People usually get these samples in a non-systematic way, which can miss or overemphasize some target information. To improve this situation, a new method based on virtual model and invariant moments was proposed to generate training samples. The method was composed of the following steps: use computer and simulation software to build target object’s virtual model and then simulate the environment, light condition, camera parameter, etc.; rotate the model by spin and nutation of inclination to get the image sequence by virtual camera; preprocess each image and transfer them into binary image; calculate the invariant moments for each image and get a vectors’ sequence. The vectors’ sequence which was proved to be complete became the training samples together with the target outputs. The simulated results showed that the proposed method could be used to recognize the real targets and improve the accuracy of target recognition effectively when the sampling interval was short enough and the circumstance simulation was close enough.

Service-oriented air combat simulation architecture

ZHAO Zhi-gao, ZHANG Shu-guang, SUN Jin-biao, YAN Bin

2012, 21(3): 408-414.

[Abstract](701) [PDF 404KB](119)

Abstract:
Service-oriented air combat simulation architecture is proposed. The core design goal is high agility which represents the ability to accommodate the simulation requirements change. Its main idea is to design model units as services that can communicate and interoperate with any other services at runtime. A service is autonomous and is fully defined by a description contract which contains some combination of syntactic, semantic, and behavioral information. Based on the architecture, air combat simulation system can be described as an abstract composition of description contracts. It becomes concrete at run time as services that implement the constituent description contracts are discovered and bind. The whole process is a continuous run-time activity that responds to simulation needs and the availability of services. This provides benefits of implementation transparency and minimal dependency between models. Thus, simulation system can minimize the impact of change on it and increase the overall efficiency to respond to requirements change.

Fusion of multispectral image and panchromatic image based on NSCT and NMF

WU Yi-quan, WU Chao, WU Shi-hua

2012, 21(3): 415-420.

[Abstract](757) [PDF 615KB](115)

Abstract:
A novel fusion method of multispectral image and panchromatic image based on nonsubsampled contourlet transform (NSCT) and non-negative matrix factorization (NMF) is presented, the aim of which is to preserve both spectral and spatial information simultaneously in fused image. NMF is a matrix factorization method, which can extract the local feature by choosing suitable dimension of the feature subspace. Firstly the multispectral image was represented in intensity hue saturation (IHS) system. Then the I component and panchromatic image were decomposed by NSCT. Next we used NMF to learn the feature of both multispectral and panchromatic images’ low-frequency subbands, and the selection principle of the other coefficients was absolute maximum criterion. Finally the new coefficients were reconstructed to get the fused image. Experiments are carried out and the results are compared with some other methods, which show that the new method performs better in improving the spatial resolution and preserving the feature information than the other existing relative methods.

Synthesis and crystal structure of a nitrogen-rich compound: 3,5-diazido-1,2,4-triazole

LI Ya-yu, PANG Si-ping, SUN Cheng-hui, LI Sheng-hua

2012, 21(3): 421-426.

[Abstract](1872) [PDF 238KB](160)

Abstract:
The compound of 3,5-diazido-1,2,4-triazole was synthesized by the reaction of 2,5,2',5'-tetrachloro-1,1'-azo-1,3,4-triazole with sodium azide at 50℃. Its crystal structure was determined by single-crystal X-ray diffraction. It crystallizes in monoclinic, space group Cc witha=1.212 4(2) nm,b=2.342 4(5) nm,c=0.804 74(16) nm,β=125.56(3)°,V=1.859 3(6) nm³,Z=4, C₂HN₉,Mr=151.04,D_c=1.62 g/cm³,F=(000)912 andμ(MoKa)=0.129 mm^-1, the finalR=0.039 7 andwR=0.087 4. X-ray analysis indicates a stronger intermolecular hydrogen bonding, leading to the formation of a trimmer, containing a nine-membered cyclic ring with graph-set R₃³(9) in the compound.

2012 Vol. 21, No. 3