JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Acoustic Emission and Damage Characteristics of Alumina

2009, 18(2): 127-130.

[Abstract](197)

Abstract:
Advanced multi-channels acoustic emission (AE) system is used to study the fracture process of alumina material subjected by three-point-bending loading. Using AE counts and AE hits, the location of damage and damage characteristics are discussed. AE energy, AE counts, AE amplitude changing with loading time are analyzed for the notched alumina specimen. It is indicated that AE characteristic parameters reflect the damage process and fracture of material.

Numerical Simulation of the Shaped Charge Jet Velocity Effected by Warhead Shell

HAN Feng, HU Yang, ZHANG Han

2009, 18(2): 131-135.

[Abstract](190)

Abstract:
The numerical simulation for the process of shaped charge jet produced with the shell of explosives is performed by means of the ANSYS/LS-DYNA 3D software. The effect of warhead shell on shaped charge jet velocity has been analyzed qualitatively in this paper. The numerical simulation results are creditable and in agreement well with that of the corresponding experiment. The research results show that the jet velocity of explosive with metal shell is higher than that without shell; when the shell thickness increases, jet's head speed also increases; when the shell thickness increased to certain value, the jet velocity will not change any longer; with the same shell thickness, the bigger material density the higher jet's head velocity.

Explosive Field Visualization Based on Image Fusion

ZHANG Wen-yao, JIANG Ling-shuang

2009, 18(2): 136-140.

[Abstract](182)

Abstract:
The advantages and disadvantages of two existing methods for explosive field visualization are analyzed in this paper. And a new method based on image fusion is proposed to integrate their complementary advantages. With the method, two source images built by equal mapping and modulus mapping are individually decomposed into two Gauss-Laplacian pyramid sequences. Then, the two individual sequences are used to make a composite one according to the process of fusion. Finally, a new image is reconstructed from the composite sequence. Experimental results show that the new images integrate the advantages of sources, effectively improve the visualization, and disclose more information about explosive field.

Two-Dimensional Euler Adaptive Mesh Method on Detonation

HAO Peng-cheng, FENG Qi-jing, YAO Wen

2009, 18(2): 141-145.

[Abstract](194)

Abstract:
The adaptive mesh refinement (AMR) method is applied in the 2-D Euler multi-component elastic-plastic hydrodynamics code (MEPH2Y). It is applied on detonation. Firstly, the AMR method is described, including a conservative spatial interpolation, the time integration methodology with the adapitve time increment and an adaptive computational region method. The advantage of AMR technique is exhibited by numerical examples, including the 1-D C-J detonation and the 2-D implosion ignited from a single point. Results show that AMR can promote the computational efficiency, keeping the accuracy in interesting regions.

Cook-off Test and Numerical Simulation for Explosive Heated by Fire

WANG Pei, CHEN Lang, WANG Xiao-feng, NAN Hai, FENG Chang-gen

2009, 18(2): 146-151.

[Abstract](163)

Abstract:
In order to investigate thermal response of explosive at fast cook-off environment, the fast cook-off tests for GHL explosive, subjected to external fire scenario, were carried out. The ignition time was measured. A thermal reaction model of GHL explosive was established. The external flame flow and decomposing heat of explosive were considered. The numerical simulation of cook-off test was conducted by computational fluid dynamics(CFD) software, FLUENT. Comparing the calculated results with the measured, external heat flow and kinetic parameters of GHL explosive were achieved. Ignition temperature, ignition position and temperature distribution in explosive were analyzed. The optimization of fuel pool size was also discussed by calculations. The measured results show that only burning reactions occurred during the tests. The ignition time and ignition temperature were 43?s and 583?K respectively. The ignition position lied in the underside of both ends of cylindrical explosive, which was placed horizontally. The modeled results indicate that the optimum fuel pool is 1?000?mm wide, which can ensure complete engulfment of explosive cylinder by external fire and save fuel oil.

Research on Bond-Slip Constitutive Relation for Steel Reinforced Concrete Members

LIANG Bin, MENG Fan-shen, LIU Jun-ling

2009, 18(2): 152-156.

[Abstract](129)

Abstract:
The constitutive relation of bond-slip on steel and concrete interface is proposed for short steel reinforced concrete (SRC) column. Based on the experimental research on bond-slip performance, a mechanical model of short SRC column in pulling or pushing test is established. By means of the elasto-plasticity theory the explicit formulation of bond-slip constitutive relationτ-sin different anchor-hold place of push and pull member is investigated under the conditions of balance and boundary. The study shows that the constitutive relation is relevant to the embedment length and the thickness of concrete cover. The results are continuous descriptions of bond-slip constitutive relation and can be used to analyze the non-linear performance of SRC members. Results indicate that the principle of the method is correct and it performs well for short SRC column.

Numerical Simulation Research of Liquid-Solid Two-Phase Flow in Abrasive Water Jet Nozzle

NIE Bai-sheng, MENG Jun-qing, JI Zong-feng

2009, 18(2): 157-161.

[Abstract](183)

Abstract:
According to the Lagrange discrete phase model of multiphase flow, mathematical model of the abrasive water-jet (AWJ) nozzle based on the multi-phase movement was introduced, then the boundary conditions was determined and the liquid-solid turbulence which is isothermal, can not be compressed and steady-state in the cone-cylinder nozzles of the export of the pre-mixed AWJ was simulated applying the software FLUENT. The results showed that: the axial velocity and dynamic pressure of the continuous phase in the nozzle were axial symmetry notable, and at the axis had a extreme point; abrasive accelerated at two points, in front contractive segment, the rate increased rapidly, and in the back straight one, the speed accelerated slowly. The length of the cylinder is 100 mm, the diameter of the nozzle is 8?mm, and the angle of the cone is 15°. There is a extreme point of the rate at the point 10?mm in the established model. The results of simulation laid the foundation for optimizing the nozzle structure, improving efficiency and developing the nozzle.

Dynamic Parallel Method for Eulerian Method of Elastoplastic Hydrodynamics in Three Dimension

LI Zheng, LIANG Xian-hong, HE Chang-jiang, WANG Shuang-hu

2009, 18(2): 162-165.

[Abstract](206)

Abstract:
Eulerian method is a main numerical simulation method in elastoplastic hydrodynamics, which is suitable for the problems with multi-component and large deformation. As the feature of the problems to be simulated, such as detonation and penetration, the dynamic parallel method (DPM) is designed to adjust the computational domain dynamically to get better load balance. Dynamic parallel method can be separated into two parts: one is division of initial computational domain and location of the data, the other is expansion of the computational domain and adjustment of the data location. DPM program can greatly shorten computational time and be preferable in simulating actual problems. The speedup of the DPM program is linear in parallel test. DPM can be popularized to parallel program of other multi-component high dimension Eulerian methods naturally.

Numerical Simulation of Orepass Choking-up Treatment Adopting Blasting Method

YANG Ren-shu, JIANG Lin-lin, GUO Dong-ming, YUE Zhong-wen

2009, 18(2): 166-170.

[Abstract](169)

Abstract:
Numerical simulation studies on blasting in ore-pass with charge both 250?kg and 500?kg are carried out. Adopting fluid-solid coupling method, the whole process from detonating to shockwave transference in the ore-pass reappears. The air shockwave's attenuation, chocking-up surface pressure and ore-wall press are analyzed. The results show that the biggest pressure of ore-wall happened at 0.43?m height, and the peak pressure are 167.0?MPa (250?kg) and 341.1?MPa (500?kg) individually. The choking-up zone's stress state from center to edge represents transition from press to strain, and the strain/press stress peak values are 9.2/4.8?MPa (250?kg) and 17.2/12.5?MPa (500?kg). The shockwave's attenuation values got from both experiential formula and simulation are compared, the experiential formula values are 2.54-3.49 times of the simulation results.

New Method of Manufacturing Micro Parts UsingThiobacillus Ferrooxidans

LIU Yu-de, WANG Xi-bin, YANG Yue, L U Liang, LONG Zhen-hai, ZHAO Fu

2009, 18(2): 171-175.

[Abstract](180)

Abstract:
A new method of processing and manufacturing certain parts of instruments through biological approach is studied. Knowledge of feasibility of micro-manufacturing is obtained by comparing experimental results of etching surfaces of copper, aluminium alloy, brass, steel and stainless steel using strain ofThiobacillus ferrooxidans(T.f.). Our experimental results show that certain metals can be etched usingT.f., the most feasible material is copper, followed by brass, etc., with stainless steel the least. The surface of the stainless steel material is nearly unchanged during surface-etching. Micro parts made of copper or brass can be satisfactorily processed withT.f. and the rate of processing on copper is about 14?μm/h. Furthermore, surface roughness and processing speed are controlled by pH value and temperature of etching liquid, in addition to swing rate of the the swing bed.

Ocean Wave Simulation near the Seashore

ZHAO Xin, LI Feng-xia, CHEN Hong-min, ZHAN Shou-yi

2009, 18(2): 181-185.

[Abstract](209)

Abstract:
In order to realize real-time simulation of ocean surface near the seashore, a new modeling method for shallow ocean wave and a level of detail (LOD) scheme are proposed in this paper. This modeling method describes ocean wave by modifying the sine wave, and gets wave direction at any ocean floor position by using wave number decomposition. The LOD scheme is proposed to realize real-time rendering of large-scale ocean surface by simplifying the ocean surface regular mesh based on real-time optimally adapting meshes (ROAM). Experimental results show that this method can get fast rendering speed and realistic effect.

Optimized Modeling Method for Unbalanced Data in High-Level Visual Semantic Concept Classification

TAN Li, CAO Yuan-da, YANG Ming-hua, HE Qiao-yan

2009, 18(2): 186-191.

[Abstract](157)

Abstract:
To solve the unbalanced data problems of learning models for semantic concepts, an optimized modeling method based on the posterior probability support vector machine (PPSVM) is presented. A neighbor-based posterior probability estimator for visual concepts is provided. The proposed method has been applied in a high-level visual semantic concept classification system and the experiment results show that it results in enhanced performance over the baseline SVM models, as well as in improved robustness with respect to high-level visual semantic concept classification.

Rapid State Augmentation for Compressed EKF-Based Simultaneous Localization and Mapping

DOU Li-hua, ZHANG Hai-qiang, CHEN Jie, FANG Hao

2009, 18(2): 192-197.

[Abstract](213)

Abstract:
A new method for speeding up the state augment operations involved in the compressed extended Kalman filter-based simultaneous localization and mapping (CEKF-SLAM) algorithm was proposed. State augment usually requires a fully-updated state covariance so as to append the information of newly observed landmarks, thus computational volume increases quadratically with the number of landmarks in the whole map. It was proved that state augment can also be achieved by augmenting just one auxiliary coefficient matrix. This method can yield identical estimation results as those using EKF-SLAM algorithm, and computational amount grows only linearly with number of increased landmarks in the local map. The efficiency of this quick state augment for CEKF-SLAM algorithm has been validated by a sophisticated simulation project.

Research on Search Laws of Image Guided Missile

WANG Xiao-fang, LIN Hai

2009, 18(2): 198-202.

[Abstract](157)

Abstract:
When image guided missile adopts guided search and common search law to search ground targets, under some conditions the movement of image on the monitor screen will be dissymmetrical, which is harmful for shooter to acquire and capture targets. To remove the dissymmetry of the image movement, such common search laws as parallel search law, "X" style search law, search law of one-dimension visual effect and cone search law are improved and designed again. Simulation results show that the dissymmetry can be removed by adopting all the above four improved search laws, but the search track of improved cone search law has serious transmutation compared with the original search track. The other three improved search laws have little transmutation of the search track, and they all can keep the main characters of the original search law. Study results are helpful for image guided missile in adopting guided search to choose appropriate search law.

ICI Cancellation Algorithm for OFDM Based Aeronautical Communication Systems and Its Performance Analysis

AN Jian-ping, ZHANG De-sheng, WU Yan-bo

2009, 18(2): 203-208.

[Abstract](92)

Abstract:
The aeronautical en-route communication channel is modeled as a two-ray double-selective channel. Based on the channel model, a low-complexity iteration self-cancellation algorithm is proposed to cancel the inter-carrier interference (ICI) of orthogonal frequency division multiplexing (OFDM) system in aeronautical communications. ICI can be completely suppressed by the proposed algorithm if channel parameters are estimated ideally. We analyzed the SNR loss with variant iteration times theoretically, and pointed out how to choose the optimum iteration times. The algorithm is especially useful to the situation with high aviation velocity, as less iteration is sufficient to separate the interference with larger Doppler shift, and less noise will be introduced. We carried out Monte Carlo simulation with typical aeronautical en-route channel, and the simulation results are in agreement with the deduced theoretical performance expressions and validate the effect of our cancellation algorithm.

Fast Approaches for Sub-pixel Precision Variable Block Size Motion Estimation

ZHANG Ying, SIU Wan-chi, SHEN Ting-zhi

2009, 18(2): 209-214.

[Abstract](210)

Abstract:
The new features of H.264 video coding standard make the motion estimation module much more time consuming than before. Especially, the motion search is required for each of the 4 modes for inter prediction. In order to reduce the computational complexity, we analyze the statistics of results of motion estimation, such as the continuity of best modes of blocks in successive frames and the chance to give up a sub-partition mode (smaller than 16×16) after integer-pixel motion estimation, from which we suggest to make mode prediction based on the motion information of the previous frame and skip sub-pixel motion estimation in sub-partition mode selectively. According to the experimental result, the proposed algorithm can save 75% of the computational time with a slight degradation (0.03?dB) on PSNR compared with the pseudocode of fast search motion estimation in JM12.2.

Research and Application of Broad-Storage Architecture in Digital Television System

XING Ling, MA Jian-guo, LI You-ping, LIU Zhi-wen

2009, 18(2): 215-219.

[Abstract](119)

Abstract:
A new dual-mode transmission networks (DMTN) based on broad-storage architecture for digital television (DTV) is proposed, in which the primary TV network is superimposed by a complementary framework based on broad-storage TV (BSTV). The necessity of congregating hot TV resources is discussed via analyzing the scale-free properties in DMTN. The self-organized parallel broadcasting technology (SPBT) and the uniform content locator (UCL) are studied to utilize availably transmission channels and to help consumers to communicate with each other expediently. Experimental results show that DMTN can provide not only traditional TV services on schedule, but also digital interactive TV services on demand by using a single channel.

Design of Multi-band Small Antenna Based on Single Split-Ring Resonator

YANG Xi, YU Zhi-yuan, SHI Qing-fan

2009, 18(2): 220-223.

[Abstract](152)

Abstract:
To use the single split-ring resonator (SRR) as a basic unit cell for small antenna with multi-band frequency response is proposed. The structure of antenna is consisted of a single spilt-ring resonator and a coupled microstrip line. The designed antenna is numerically optimized with CST Microwave Studio. The radiation properties of the antenna show that there are three frequency bands among which two bands are 1.3?GHz and 2.1?GHz ultra-wideband (UWB), respectively, whereS₁₁is less than -10?dB. The gain at every frequency for the multi-band antenna is above 2.6?dBi, and it increases monotonously with the frequency in the two UWB.

Selectivity of New β-Cyclodextrin Derivatives as CGC Stationary Phases and Application for the Analysis of Volatile Compounds in Traditional Chinese Medicines

QI Mei-ling, GUO Yan-ni, FANG Liang-hua, ZHANG Cong

2009, 18(2): 224-228.

[Abstract](98)

Abstract:
New cyclodextrin derivatives (CDs), heptakis(2,6-di-O-methyl-3-O-methoxymethyl)-β-CD (Ⅰ) and heptakis(2,3,6-tri-O-methoxymethyl)-β-CD (Ⅱ), were investigated for their chromatographic performance as stationary phases for capillary gas chromatography (CGC). Both of the CDs exhibited good selectivity and satisfactory separation for test mixtures and aromatic positional isomers, and volatile compounds fromLigusticum chuanxiongHort. Additionally, the selectivity and elution orders of major compounds were compared with a well-recognized commercial column on the basis of the results by gas chromatography-mass spectrometry (GC-MS). The present work demonstrates the good selectivity of the two new CDs and can be used as GC stationary phases for the separation of positional isomers and analytes in complex samples.

Polyoxometalates Pillared Hydrotalcite: Synthesis and Catalysis in Transesterification of Dimethyl Carbonate and Phenol

LUO Sheng-jun, CHI Ying-nan, HU Chang-wen

2009, 18(2): 229-232.

[Abstract](225)

Abstract:
The salts of para-tungstic and para-molybdic were heterogenized for their effective use as solid catalysts in the transesterification reaction of dimethyl carbonate and phenol by inserting them between the layers of Mg₂Al-hydrotalcite. These catalysts were characterized by FT-IR spectra and X-ray powder diffraction. Polyoxometalates (POMs) clusters were intercalated into the interlayer of layered double hydroxide (LDH) via anion exchange with organic acid precursor in Mg₂Al-LDH, and the integrity of the clusters^6-and^6-was maintained. The intercalated para-molybdic cluster showed high catalytic activity and reusability in the transesterification under mild reaction conditions. When the reaction was carried out at 180?℃, with a molar ratio of phenol to DMC of 1∶1, a reaction time 10?h, and a catalyst amount 1%(wt), the conversion of phenol was 10.0%, the selectivities of diphenyl carbonate and methyl phenyl carbonate were 10.7% and 86.1%, respectively.

Supramolecular Sheet Co(Ⅱ) Complex Assembled by Hydrogen Bond

LIU Gui-lei, LI Hui, SONG Fang, QIN Yong-jie

2009, 18(2): 233-237.

[Abstract](95)

Abstract:
The title complex, ]_<em>n( 1 ) was synthesized by liquid/liquid diffusion method at room temperature. The complex crystallizes in monoclinic, space group P2(1)/C, witha0.877?5(6)nm,b1.171?5(8)nm,c0.751?8(5)nm,V0.739?3(9)nm³, C₁₀H₁₄CoN4O₈,M_r377.18,D_c1.694?g/cm³,μ1.210?mm^-1,F(000)386,Z2, the finalR0.022?9 andwR0.066?1 for 3?137 observed reflections (I>2σ(I)). In the structure of 1 , the center atom of cobalt revealed a centrosymmetric, six-coordinate structure, with two Py ligands, two monodentate nitrate groups and two water molecules. It is notable that a series of hydrogen bonds (O—H…O) formed two kinds of rings exist in the structure, which linked neighboring six-coordinate polymer into a two-dimensional H-bonding network, and then assembled into a three-dimensional supramolecular architecture through electrostatic and hydrophobic interaction. In the structure, supramolecular sheet was observed, which contains alternative organic and inorganic layers.

Study of Crystal Defects and Spectroscopy Characteristics of Ammonium Polyphosphate

YI De-qi, YANG Rong-jie

2009, 18(2): 238-242.

[Abstract](253)

Abstract:
Two kinds of commercial ammonium polyphosphate (APP) and three kinds of APP which were prepared in the laboratory were studied by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In identification of the form Ⅱ crystal APP by XRD and FTIR, some discrepancies were discussed. It is pointed out that the absorbance of the FTIR spectra at 682?cm^-1can exist not only in the form Ⅰ APP, but also in the form Ⅱ APP with the crystal lattice defects. The SEM images indicate that the form Ⅱ APP is of multilayer crystal structure. XRD and TEM can reveal the crystal lattice defects.

Information Geometry of GARCH Model

CAO Li-mei, SUN Hua-fei, WANG Xiao-jie

2009, 18(2): 243-246.

[Abstract](186)

Abstract:
A statistical manifold of non-exponential type coming from a model for economics describing stock return process is constructed, with its geometric structure investigated and both Gaussian curvatures and mean curvatures of its curved exponential submanifolds deducted. A few graphs describing relevant scalar curvature, mean curvature and Gaussian curvature are also introduced.

Eigenvector Method for Ranking Alternatives with Vague Value Measurements

HOU Fu-jun, WU Qi-zong

2009, 18(2): 247-252.

[Abstract](104)

Abstract:
An eigenvector method for ranking alternatives whose measurements are given as vague values is provided. Firstly, a positive matrix is constructed which is defined as evaluation information matrix (EIM). Based on four assumptions for evaluating alternatives, a ranking eigenvector is defined. And then it is proved, based on positive matrix theory, that the EIM’s eigenvector corresponding to the maximal eigenvalue is the ranking vector. For alternatives whose characteristics are presented by vague sets, the proposed techniques can evaluate the degree of suitability to which an alternative satisfies the decision-maker’s requirement efficiently.

2009 Vol. 18, No. 2