JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Three-dimension micro magnetic detector based on GMI effect

WEI Shuang-cheng, DENG Jia-hao, HAN Chao, Yang Yu-ying

2014, 23(2): 143-146.

[Abstract](351) [PDF 390KB](83)

Abstract:
The giant magneto-impedance (GMI) effect of amorphous wire was analyzed theoretically. The amorphous wire had strong GMI effect in the stimulation of sharp pulse of 680.kHz and 18.mV. A pulse generator was designed to provide high frequency pulse to a magnetic impedance (MI) element. The induced voltage on the pickup coil wound on the amorphous wire was sampled and held with a detect circuit using analog switch. A stable magnetic sensor was constructed. A three-dimension micro magnetic field detector was designed with a central controller MSP430F449. High stability and sensitivity were obtained in the MI sensor with the detect circuit. Experiment results showed that the resolution of the detector was 1nT in the full scale of ±2 Oe and the detector worked stably from the room temperature to about 80 ℃. A small ferromagnetic target was detected by the three-dimension detector in laboratory environment without magnetic shielding. The target moving direction was ascertained with the wave shape of axis parallel in that direction.

Experimental study on vapor explosion caused by interaction between high temperature molten aluminum and water

LIU Yu, LÜ Zhong-jie, HUANG Feng-lei, GUO Xue-yong, SHEN Zheng-xiang

2014, 23(2): 147-151.

[Abstract](365) [PDF 1264KB](83)

Abstract:
In order to study the mechanism of steam explosion caused by the interactionbetween coolant and melted metal drops with high temperature, the process of explosion generated by water following interaction with molten metal drops is carried out. In the experiment,liquid aluminum and water with different ratios and different temperatures were evaluated, and the influence of different water temperatures on the steam explosion was studied. The corresponding rules of steam explosion at the different experimental conditions were derived. The difference between experiment resultants was analyzed. The experimental results show that when the ratios of liquid aluminum to water are within a certain range, explosions maybe happen, and the higher the temperature of water is, the less likely explosions will occur while other conditions remain the same. The research results would provide an insight into controlling steam explosion.

One-piece coal mine mobile refuge chamber with safety structure and less sealing risk based on FEA

ZHAO Huan-juan, QIAN Xin-ming, HUANG Ping, WANG Chen

2014, 23(2): 152-157.

[Abstract](574) [PDF 1129KB](100)

Abstract:
In order to reduce the risk of sealing and improve the structural strength for a coal mine mobile refuge chamber, a new type of one-piece model was designed. Mechanical and mathematical calculation performed an important role. Calculated according to statics and relevant contents, the structure had the same total volume as the traditional segmented structure, but had shorter length, wider width and greater height. Those prevented the structure from stress or deformation failure. Some reinforcing ribs with enough moments of inertia were welded in the external shell. Because of the one-piece structure, this refuge chamber reduced the risk of sealing which was a serious problem of segmented structure. Impact load with 300 ms duration and 0.6 MPa over-pressure was settled. Explicit nonlinear dynamic analysis program was used to simulate the response of the refuge chamber. The maximum stress and the maximum displacement were obtained. The refuge chamber including blast airtight doors could meet the rigidity requirement. Weak parts of the chamber were the front and back end shell where bigger displacement values occurred than others. Thus, the calculation indicated that the refuge chamber could meet structural safety requirements. Based on the numerical analysis, suggestions were put forward for further resistance ability improvement. Only large inclined shaft with larger wellhead was suitable for this one-piece coal mine mobile refuge chamber.

Modified attitude pursuit guidance law for low-cost missiles using strap-down seekers

SONG Tao, LIN De-fu, LI Chuan

2014, 23(2): 158-164.

[Abstract](417) [PDF 379KB](175)

Abstract:
Attitude pursuit guidance law is suitable for low cost missiles. A strap-down seeker is used to achieve this guidance law. The additional angles of attack or sideslip caused by wind and by control system are considered as two disturbing factors which make attitude pursuit law impossible. Therefore, general attitude pursuit guidance law did not account for this two disturbing factors, because with those disturbing factors, it is difficult to apply. To solve the problem, the principle of strap-down seeker detecting target is investigated, the mathematical control model is established, then a modified attitude pursuit guidance law which employs the angular correction for those two disturbing factors is presented. It is proved that the modified attitude pursuit guidance law is appropriated to both in the presence of the additional angle of attack or sideslip via the simulations with the mathematical control model and Monte-Carlo method.

Numerical film torque modeling of friction pair in hydro-viscous clutchs

YAO Shou-wen, CUI Hong-wei, WANG Xiu-peng, FENG Shan-shan

2014, 23(2): 165-171.

[Abstract](586) [PDF 2449KB](96)

Abstract:
A numerical model to predict film torque of hydro-viscous clutch was developed. The model was established with computational fluid dynamics (CFD). The pressure distribution, velocity of flow and film torque were obtained based on vertical-horizontal grooved plate and radial grooved plate separately. The boundary conditions, such as the relative rotation, the fluid temperature and the oil feeding pressure, were also discussed. The results showed that the film torque of two kinds of grooved plate increased with increasing relative rotation. However, the film torque decreased with increasing fluid temperature and feeding pressure. Meanwhile, the film torque of radial grooved plate was less than vertical-horizontal grooved plate at the same condition. Our study showed that the model can efficiently calculate the film torque with complex geometry parameters and boundary conditions.

Simulation of VGT control based on charge oxygen concentration

AN Xiao-hui, ZHANG Fu-jun, LIU Bo-lan, CUI Tao

2014, 23(2): 172-177.

[Abstract](447) [PDF 386KB](85)

Abstract:
A turbocharged diesel engine model was built with the GT-Power software, and experimentally verified. Then two different control variables for the control of the variable geometry turbocharger (VGT) were described, and their distinct effects on engine performance, i.e. NO_xand soot emissions and fuel consumption, were simulated and compared on the basis of this model. The results showed that NO_xemissions decreased obviously with the increase of exhaust gas recirculation (EGR) rate at constant boost pressure condition, but soot emissions and fuel consumption considerably increased. It was a good way to reduce NO_xemissions without increasing fuel consumption and soot emissions when VGT was controlled to maintain the excess oxygen ratio unchanged as EGR rate increases.

Simulation of a vehicle hydraulic propulsion system

JIANG Zhong-lin, WU Wei, YUAN Shi-hua, HU Ji-bin

2014, 23(2): 178-183.

[Abstract](461) [PDF 356KB](109)

Abstract:
The characteristics of a hybrid hydraulic vehicle driven by the hydraulic common rail propulsion system with a hydraulic free-piston engine and a hydraulic transformer were studied. A mathematical model of the propulsion system was established and a control method of the propulsion system was proposed. Extensive simulation results of hybrid hydraulic vehicles with the hydraulic common rail propulsion system were presented. The hydraulic common rail propulsion system achieved the switch power control and the constant power propulsion. The control method based on the propulsion, break and speed limit requirement was verified. Our results showed that the hydraulic common rail propulsion system gained an ideal acceleration process.

Influence of the cylinder head structure of a diesel engine on fatigue strength

GAI Hong-wu, CHENG Ying, YAO Xiu-gong

2014, 23(2): 184-189.

[Abstract](320) [PDF 1800KB](95)

Abstract:
Using finite element method, influence of diesel cylinder head structure on fatigue strength is investigated. A simplified head model with function characteristics is built for thermal-mechanical simulation. From the simulation results, the influence of valve bridge structure and roof transition fillet dimension on fatigue strength are obtained. And a new valve bridge structure which can effectively improve the fatigue life is proposed.

Investigating fatigue behavior of gear components with the acoustic emission technique

SHI Peng-fei, HUANG Jie

2014, 23(2): 190-195.

[Abstract](409) [PDF 354KB](109)

Abstract:
A novel method is presented to evaluate the complicated fatigue behavior of gears made of 20Cr2Ni4A. Fatigue tests are conducted in a high-frequency push-pull fatigue tester, and acoustic emission (AE) technique is used to acquire metal fatigue signals. After analyzing large number of AE frequency spectrum, we find that: the crack extension can be expressed as the energy of specific frequency band, which is abbreviated as F-energy. To further validate the fatigue behavior, some correlation analysis is applied between F-energy and some AE parameters. Experimental results show that there is significant correlation among the F-energy, root mean square (RMS), relative energy, and hits. The findings can be used to validate the effectiveness of the F-energy in predicting fatigue crack propagation and remaining life for parts in-service. F-energy, as a new AE parameter, is first put forward in the area of fatigue crack growth.

Electroencephalogram characters of parallax stereo watching asthenopia

LIU Shuang, WU Ping-dong, HUANG Jie, ZHANG Gui-xin, YANG Qiu-ling

2014, 23(2): 196-202.

[Abstract](593) [PDF 537KB](78)

Abstract:
The electroencephalogram (EEG) characters value of observers can be deduced by collecting brain electrical information when the observers are watching parallax stereo video. The characters value will change clearly when watching asthenopia appear. To investigate the characters of parallax stereo watching asthenopia, the EEG of observers were recorded through the whole watching process of parallax stereo films until watching asthenopia appeared. The recorded EEG data of observers belongs to time-domain information. Fourier transform can process these data to frequency spectrum information. Theαandβwaves average power can be got by Newton-Cotes equation from the information. The ratio ofβpower to the sum ofαandβpower,C_V, can be defined as EEG characters value of parallax stereo watching asthenopia and used to estimate the asthenopia degree of observers. Our experiments show that the smaller theC_Vis, the more serious the asthenopia is.

Analysis of thermal-mechanical coupled characteristics of vehicle twin-tube shock absorber

YAO Ming-tao, LONG Kai, HE Li-ping

2014, 23(2): 203-209.

[Abstract](820) [PDF 383KB](83)

Abstract:
A comprehensive model that included mechanical dynamics of the shock absorber coupled with its thermal properties was proposed innovatively. Moreover a thermal-mechanical coupled model which reflected the closed-loop positive feedback system was established by using MATLAB/SIMULINK, and some curves of shock absorber temperature rising characteristic were obtained by simulation & computation under several operating modes and different parameters conditions. Research results show that: shock absorber design parameters, external excitations, and thermo-physical properties parameter, such as oil density have effect on the shock absorber temperature rising characteristic. However other thermo-physical properties parameters, such as oil specific heat, cylinder density, cylinder specific heat, and cylinder thermal conductivity, have no effect on it. The results may be used for studying reliability design of the shock absorber.

Consensus problem of multi-agent systems under arbitrary topology

DONG Li-jing, CHAI Sen-chun, ZHANG Bai-hai

2014, 23(2): 210-217.

[Abstract](446) [PDF 381KB](106)

Abstract:
Consensus problem of second-order leader-following multi-agent systems under arbitrary topology is investigated in this paper. Arbitrary topology means the variable topology shifts continuously rather than switches among several different structures. For ensuring the consensus of leader-following multi-agent systems, some sufficient conditions and controller design principles are deduced both for a double-integrator case and a nonlinear case. Certainly, numerical simulations are carried out to prove the feasibility and effectiveness of theory derivation, which vividly illustrates that the following agents can successfully track the leader agent.

Contour tracking using weighted structure tensor based variational level set

HU Hong-wei, MA Bo, CAO Shu-juan

2014, 23(2): 218-225.

[Abstract](363) [PDF 4426KB](70)

Abstract:
A novel contour tracking method using weighted structure tensor based variational level set is proposed in this paper. The image is first converted to weighted structure tensor field by extracting a positive definite symmetric covariance matrix for each pixel. Then, a level set method is employed to represent object contour implicitly which separates the image domain into two areas each modeled by tensor field based Gaussian mixture model separately. By solving a gradient flow equation of energy functional with respect to the level set, the object contour will converge to its real profile in the newly arrived frame. Experimental results on several video sequences demonstrate the better performance of our method than the other two contour tracking algorithms.

Earth-observation satellite attitude control using passive and active hybrid magnetically suspended flywheels

YANG Zhao-hua, YANG Ning-ning, YU Yuan-jin

2014, 23(2): 226-234.

[Abstract](476) [PDF 593KB](82)

Abstract:
The control strategy is presented using passive and active hybrid magnetically suspended flywheels (P&A MSFWs), which can help meet the requirements of high precision and high stability for earth-observation satellites. Compared with the conventional flywheel, P&A MSFW has more rotation degrees of freedom (DOFs) since the rotor is suspended by magnetic bearings, and thus requires more efficient controllers. A modified sliding mode control law (SMC) to our novel nonlinear and coupled system is presented, which is interrupted by inertia matrix uncertainties and external disturbances. SMC law via Lyapunov method is improved, and a fuzzy control scheme is used to attenuate the chatting and control attitude accuracy and maintain the robustness of SMC. Simulation results are provided to illustrate the efficiency of our model by using our control law.

On measured-error pretreatment of bionic polarization navigation

GUAN Gui-xia, HAN Yu-zhang, WU Min-hua, LI Lei-lei

2014, 23(2): 235-239.

[Abstract](531) [PDF 419KB](130)

Abstract:
A signal pre-treatment algorithm based on combination of 3-dimension system identification and Kalman filtering estimation (3DSKE) is proposed. The aim of designing the 3DSKE algorithm is to reduce errors caused by random noise, but leave the systematical errors caused by signal source remained to be solved by a special method. The 3DSKE algorithm is especially suitable for time series of pure measured data without dynamic equation and on-line real-time execution. The simulated result shows that the 3DSKE algorithm can help the basic theoretic calculation to realize feasible, stable, fast, high accurate and auto-executing computing process for the navigation applications.

Expert ranking method based on ListNet with multiple features

CHEN Fang-qiong, YU Zheng-tao, WU Ze-jian, MAO Cun-li, ZHANG You-ming

2014, 23(2): 240-247.

[Abstract](412) [PDF 373KB](98)

Abstract:
The quality of expert ranking directly affects the expert retrieval precision. According to the characteristics of the expert entity, an expert ranking model based on the list with multiple features was proposed. Firstly, multiple features was selected through the analysis of expert pages; secondly, in order to learn parameters through gradient descent and construct expert ranking model, all features were integrated into ListNet ranking model; finally, expert ranking contrast experiment will be performed using the trained model.The experimental results show that the proposed method has a good effect, and the value of NDCG@1 increased 14.2% comparing with the pairwise method with expert ranking.

Practical calibration method for instantaneous polarization radar systems utilizing a metal sphere

YANG Ning, ZHAO Guo-qiang, SUN Hou-jun, LÜ Xin

2014, 23(2): 248-253.

[Abstract](387) [PDF 772KB](115)

Abstract:
A practical calibration method is proposed for instantaneous polarization radar systems. The method only needs one measurement by using a metal sphere. The distortions of system and the actual polarization scattering matrix (PSM) of target can be obtained. First, an instantaneous polarization radar system is presented. The system can obtain PSM by a single pulse echo. The dual-polarization antenna can transmit and receive two orthogonal polarization waves. The multilayer micro-strip patch antenna is adopted for this kind of radar system. Second, based on the multi-port network theory, the operation and system errors of instantaneous polarization radar system are analyzed. By making assumption on the cross-talk factors of antenna, distortion matrices ofRandTare derived. Finally, the calibration method based on instantaneous polarization measurement is introduced. Simulation results show the performance of this calibration method. The values of calibrated PSM are in agreement with the actual ones after calibration.

Employment of predictive search algorithm in digital image correlation

MA Zhi-feng, WANG Hao, HAN Fu-hai

2014, 23(2): 254-259.

[Abstract](338) [PDF 1186KB](104)

Abstract:
A predictive search algorithm to estimate the size and direction of displacement vectors was presented. The algorithm decreased the time of calculating the displacement of each pixel. In addition, the updating reference image scheme was used to update the reference image and to decrease the computation time when the displacement was larger than a certain number. In this way, the search range and computational complexity were cut down, and less EMS memory was occupied. The capability of proposed search algorithm was then verified by the results of both computer simulation and experiments. The results showed that the algorithm could improve the efficiency of correlation method and satisfy the accuracy requirement for practical displacement measuring.

Study of word length selection for DDCs used in ultra-low symbol rate receivers

ZHU Ya-ping, CUI Song-qi

2014, 23(2): 260-264.

[Abstract](213) [PDF 308KB](88)

Abstract:
The relationship between the hardware requirement of digital down converters (DDCs) in ultra-low symbol rate receivers and the word length is studied. Through analyzing the impact of word length selection to the system performance, a modified scheme is presented to decline the resource consumption without too much degradation on the signal to noise ratio (SNR). Theoretical analysis and numerical results demonstrate that compared to the traditional design, the proposed scheme could save dozens of memory resources. The scheme also includes some selectable parameters to achieve desired performance in various circumstances. Different from previous work in DDCs that concentrates mostly on the structure design, this paper considers special applications such as ultra-low symbol rate receivers.

Synthesis and crystal structure of bis(1,3-diisopropyl-4,5-dimethylimidazolium) hexatungstate

MA Xiao-li, SUN Shuai

2014, 23(2): 265-269.

[Abstract](276) [PDF 1113KB](111)

Abstract:
The title compound bis (1,3-diisopropyl-4,5-dimethylimidazolium) hexatungstate, [C₁₁H₂₁N₂]₂[W₆O₁₉], was synthesized and characterized by single-crystal X-ray diffraction, IR and elemental analysis. It crystallizes in the monoclinic system, space groupP2₁/nwith a=1.112.84(14),b=1.283.84(17),c=1.293.28(17) nm,β=96.410(2)°,V=1.836.2(4) nm³, C₂₂H₄₂N₄O₁₉W₆,M_r=1.769.70,D_c=3.201 g/cm³,F(000)=1.596,Z=2,μ(MoKα)=18.797 mm^-1, the finalR=0.031.3,_wR=0.059.8 for observed reflections (I>2σ(I)).

Effect of pad geometry on current density and temperature distributions in solder bump joints

LI Yi, ZHAO Xiu-chen, LIU Ying, LI Hong-yang

2014, 23(2): 270-278.

[Abstract](403) [PDF 4823KB](88)

Abstract:
Three-dimensional thermo-electrical finite element analyses were conducted to simulate the current density and temperature distributions in solder bump joints with different pad geometries. The effects of pad thickness, diameter and shape on current density and temperate distributions were investigated respectively. It was found that pads with larger thickness or/and diameter could reduce current density and temperature in solder bump significantly. Pad shapes affected the current density and temperature distributions in solder bumps. The relatively low current density and temperature didn't occur in the bump joint with traditional rounded pad but occurred in bump joints with octagonal and nonagonal pads respectively. Therefore, optimized pad geometry may be designed to alleviate the current crowding effect and reduce the bump temperature, and therefore delay electromigration failure and increase the mean-time-to-failure.

Synthesis and characterization of N,N-(pyromellitoyl)-bis-L-phenylalanine diacid ester butynediol

TANG Qi-heng, AI Qing-song, HE Ji-yu, LI Xiao-dong, YANG Rong-jie

2014, 23(2): 279-284.

[Abstract](357) [PDF 341KB](91)

Abstract:
N,N-(pyromellitoyl)-bis-L-phenylalanine diacid ester butynediol (PBDCB) from pyromellitic dianhydride (PMDA), butynediol (2-butyne-1,4-diol) and DL-phenylalanine (DLP) was synthesized. The PBDCB can be used as chain extender for thermoplastic polyurethane. The starting material of N,N-(pyromellitoyl)-bis-L-phenylalanine diacid (PBD) was synthesized through addition reaction between PMDA and DLP. Then, PBD was esterified using triethylamine as catalyst and attached antacids as well as dimethylacetamide (DMAc) as solvent. The obtained PBDCB was characterized using Fourier transformed infrared spectroscopy (FTIR), nuclear magnetic resonance (¹H NMR) spectroscopy, mass spectrometry (MS), thermal gravimetric (TG), and differential scanning calorimetry (DSC). The results showed that the PBDCB was highly thermal stable.

2014 Vol. 23, No. 2