JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Dynamic characteristics of the coupled system of footbridge and human

NIU Shao-hua, GAO Shi-qiao, WANG Dong, KASPERSKI M, AGU E

2013, 22(3): 285-290.

[Abstract](867) [PDF 1034KB](1122)

Abstract:
The influence of human body on dynamic characteristics of footbridge was analyzed. A realistic footbridge was measured during a mass event. A simulation experiment system including a simple beam as object and a shaker as back ground excitation was built. The acceleration responses of beam were measured when person in static and active stated stood on the beam. The dynamic parameters of the structure were identified by the time-domain approach and verified by theoretical and laboratory tests. The results showed that for the human-structure coupled system, nature frequency of the structure decreased and damping increased. Moreover, the increase of damping with passive person was bigger than that with active person.

Gao’s interacting shear flows (ISF) theory and its inferences and their applications

YU Yong, ZHANG Hai-rong

2013, 22(3): 291-300.

[Abstract](645) [PDF 440KB](1050)

Abstract:
Gao's viscous/in-viscid interacting shear flows (ISF) theory, proposed by professor Gao Zhi in Institute of Mechanics, China Academy of Science, and its inferences and their applications in computational fluid dynamics (CFD) are reviewed and some subjects worthy to be studied are proposed in this paper. The flow-field and motion law of ISF, mathematics definition of strong viscous shear layer flow in ISF, ISF equations, wall-surface compatibility criteria (Gao's criteria), space scale variety law of strong viscous shear layer reveals flow mechanism and local space small scale triggered by strong interaction that cause some abnormal severe local pneumatic heating phenomenon in hypersonic flow. Gao's ISF theory was used in near wall flow, free ISF flow simulation and design of computing grids, Gao's wall-surface criteria were used to verify calculation reliability and accuracy of near wall flows, ISF theory approximate analytical result of shock waves-boundary layer interaction and ISF equations were used to obtain the numerical exact solution of local area flow (such as stationary point flow). Some new subjects, such as, improving near-wall turbulent models according to the turbulent flow simulation satisfying the wall-criteria and illustrating relation between grid-convergence based on the wall criteria and other convergence tactics, are suggested. The necessity of applying Gao's ISF theory and wall criteria is revealed. Difficulties and importance of hypersonic viscous/in-viscid interaction phenomenon were also emphasized.

Mechanics analysis of a wheelchair robot with wheel-track coupling mechanism

LI Jing-yi, BAI Yang, JIN Fei, WANG Dong-xiao, GAO Xue-shan

2013, 22(3): 301-307.

[Abstract](1551) [PDF 627KB](1518)

Abstract:
A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presented in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities whether on flat ground or stairs and obstacles in the city. The wheel-track coupling mechanism is designed and the stability of the bodywork of the wheelchair robot on the stairs is analyzed. In order to obtain the stability of wheelchair robot when it climbs obstacles, centroid projection method is applied to analyze the static stability, stability margin is proposed to provide the stability under some dynamic forces, and the push rod rotation angle in terms of the guaranteed stability margin is given. Finally, the dynamic model of the wheelchair robot based on Lagrange equation is established, which can be a theoretical foundation for the wheelchair control system design.

Path planning method for controlling multi-UAVs to reach multi-waypoints simultaneously under the view of visual navigation

YANG Dong-xiao, LI Jie, LI Da-lin, GUAN Zhen-yu

2013, 22(3): 308-312.

[Abstract](974) [PDF 295KB](871)

Abstract:
There is a high demand for unmanned aerial vehicle (UAV) flight stability when using vision as a detection method for navigation control. To meet such demand, a new path planning method for controlling multi-UAVs is studied to reach multi-waypoints simultaneously under the view of visual navigation technology. A model based on the stable-shortest pythagorean-hodograph(PH) curve is established, which could not only satisfy the demands of visual navigation and control law, but also be easy to compute. Based on the model, a planning algorithm to guide multi-UAVs to reach multi-waypoints at the same time without collisions is developed. The simulation results show that the paths have shorter distance and smaller curvature than traditional methods, which could help to avoid collisions.

Weighted sum based method on the optimal weights for weapon evaluation

XIE Zhi-jian, BO Yu-cheng

2013, 22(3): 313-318.

[Abstract](575) [PDF 323KB](1207)

Abstract:
In order to solve instability problem of calculation precision resulting from the selection of each target weight in evaluating weapon systems,a weighted sum based method is proposed. Specifically, the subjective weights depending on experts' experience are substituted by the optimal weights. The optimal weights are acquired through constructing a mathematical programming model based on subjective weights and objective weights. The method of solving subjective weights is the same as before, and the objective weights were solved by means of grey theory. The case analysis shows that the method of improved weighted sum can improve the evaluation precision up to more than 5%, and minimize the instability of calculation precision resulting from only using subjective weights. The method that the optimal weights substituted the subjective weights is brought forward in improving evaluation precision for the first time. The ideas of the optimal weights and the proposed method are described and analyzed.

Orderly delay control technique for a new type of arthropod robot

CHANG Qing, HAN Bao-ling, LUO Qing-sheng

2013, 22(3): 319-323.

[Abstract](649) [PDF 2260KB](1039)

Abstract:
The orderly delay control technique for a new type of arthropod robot is studied in this paper. The orderly delay controller is composed of three parts. The first part is a central pattern generator (CPG) with periodical output. The second part is a neural pathway (NP) that generates the time delay characteristic of various gait patterns. The last part is a locomotion nerve center (LNC) that decides the frequency of the CPG output and generates orderly phase delay by changing the parameters of NP. And then signals that fit for different gaits can be obtained through the regulation of LNC. Experiments are implemented with a robot following mathematical simulation of the controller. The experimental results show that various gait patterns can be realized successfully with the method proposed in this paper.

Method with repeated extraction-insertion cycles to improve the needle insertion accuracy

ZHANG Shao-hua, JIN Xin, ZHANG Zhi-jing, YE Xin, LIU Bing-bing

2013, 22(3): 324-329.

[Abstract](621) [PDF 1226KB](764)

Abstract:
In order to improve the effectiveness of percutaneous diagnosis and therapies, the needle insertion into the deforming soft and inhomogenous tissue should be accurate. In this study a needle with 6 degrees of freedom force/torque sensor is used to find the relationship between the pathway's length and the force. Our experiments show that the method with repeated extraction-insertion cycles can make the needle approach the target as much as possible. Meanwhile a method to obtain the appropriaterepeated extraction-insertion cycles is given to drive the needle to execute the repeated cycles efficiently. Experiments and discussions were conducted to preliminarily validate the method.

Self-excited vibration of driveline for vehicle launch

WU Guang-qiang, LUAN Wen-bo

2013, 22(3): 330-336.

[Abstract](691) [PDF 523KB](1238)

Abstract:
The launch shudder phenomenon induced by self-excited vibration of driveline was studied with a compact car equipped with AMT as research object. The research showed that self-excited vibration was closely related with damping of driveline, the variation of friction coefficient, equivalent radius of friction plate and applied force of pressure plate. Six DOFs torsional vibration model of vehicle driveline was established according to the parameters of the certain compact car. The simulation was carried out and the result was compared with test data. It was found that the negative slope of friction coefficient with relative slip speed does not necessarily lead to self-excited vibration and the frequency of self-excited vibration on 1st gear is near to the 1st order of torsional natural frequency. The influence of each viscous damping in driveline on self-excited vibration was analyzed by simulation and the results showed that increasing the torsional dampings of half-axles and tires properly was effective to improve launch shudder phenomenon.

Vibration energy regeneration of electric vehicle shock absorber

ZHANG Jun, LIANG Xin-cheng, TANG Jian-hua

2013, 22(3): 337-341.

[Abstract](568) [PDF 388KB](1032)

Abstract:
The twin-tube shock absorber was studied and the relevant factors of thermal equilibrium were simulated. The dynamic model of the shock absorber was constructed and simulation curves of force-displacement and force-velocity were output. The experiment of the twin-tube shock absorber was carried out, and the results were compared with the modeling resultss. Further, the vibration energy regeneration model was established, and the bench simulation study was carried out. The results showed that the energy regeneration model not only absorbed shock energy but also converted vibration energy into electricity energy.

Threshold values of traffic flow for the provision of exclusive bus lanes

SUN Feng, WANG Dian-hai, MA Dong-fang, JIN Sheng

2013, 22(3): 342-349.

[Abstract](644) [PDF 365KB](827)

Abstract:
A simulation network model was established using VISSIM software and verified by the T-test. The model took into consideration the road conditions, pedestrian crossing, traffic composition, bus stops and traffic signal. The operating characteristics of buses and cars under different flow conditions were studied using the simulation model, and the speed-flow models of buses and cars were established based on the simulation results. Finally, the threshold values of traffic flow for the provision of exclusive bus lanes was determined with the target of optimal travel benefits (per capita), which would provide a basis for the planning and design of exclusive bus lanes on urban roads.

Micro-Doppler effect testing technique for attitude of projectile in space flight

ZHANG Wan-jun, WU Xiao-ying, ZHANG Xiao-wei, NIU Min-jie, LENG Xue-bing

2013, 22(3): 350-353.

[Abstract](631) [PDF 286KB](942)

Abstract:
To measure projectile attitude in space flight, based on continuous wave (CW) radar, a new micro-Doppler effect testing technique is developed in this paper.It also establishes radar testing model for attitude of flying projectile and resolve micro-Doppler effect of projectile motion attitude. By distinguishing and geting attitude parameters such as micro-motion period, this technique can intuitively estimate the flight stability of projectile, and the validity of this technique is proved according to flight tests.

Cruise missile multiple routes planning based on hybrid particle swarm optimization

LI Fan, HAO Bo, ZHAO Jian-hui, XUE Lei

2013, 22(3): 354-360.

[Abstract](647) [PDF 399KB](1031)

Abstract:
In order to solve cruise missile route planning problem for low-altitude penetration, a hybrid particle swarm optimization (HPSO) algorithm is proposed. Firstly, K-means clustering algorithm is applied to divide the particle swarm into multiple isolated sub-populations, then niche algorithm is adopted to make all particles independently search for optimal values in their own sub-populations. Finally simulated annealing (SA) algorithm is introduced to avoid the weakness of PSO algorithm,which can easily be trapped into the local optimum in the search process. The optimal value obtained by every sub-population search corresponds to an optimal route, multiple different optimal routes are provided for cruise missile. Simulation results show that the HPSO algorithm has a fast convergence rate, and the planned routes have flat ballisticpaths and short ranges which meet the low-altitude penetration requirements.

User growth and penetration modeling for converged heterogeneous network

SADIA Murawwat, ZHAO San-yuan, YUE Lei, ZHANG Chao, XUE Cheng-bo, MUHAMMAD Imran Malik, SHEN Ting-zhi

2013, 22(3): 361-366.

[Abstract](720) [PDF 435KB](873)

Abstract:
To evaluate the trail potential of converged heterogeneous network (CHN) market, the logistic method for adoption modeling of CHN is used. User growth & penetration have been taken as two variants to find saturation condition in market. Model is continuous in time but modifications are done for discrete recurrence equation, commonly known as logistic map. Dynamic and static phases are taken into consideration while penetration decay is not covered in this model.

Performance of Luby transform coded frequency hopping systems in partial-band jamming

BU Xiang-yuan, QIU Yuan, YANG Hang, ZHOU Rong-hua, MA Yuan-yuan

2013, 22(3): 367-373.

[Abstract](594) [PDF 361KB](814)

Abstract:
Luby transform (LT) codes are proposed to suppress the effect of partial band noise jamming in frequency hopping (FH) communication systems. A decoding scheme for joint erasures of severely jammed symbols and error correction is proposed. If an uncorrectable error is detected, the receiver erases the jammed symbols and uses incremental redundancy to increase the error-correcting capability. The performance of LT codes, under power-oppressive partial band noise jamming (PBNJ) with the additive white Gaussian noise (AWGN), is evaluated via simulation. Even if the jammer spreads its high power over half of the hopping bandwidth, LT codes are shown to achieve a target bit error probability of 10^-5, demonstrating their effectiveness as high-performance codes to improve the ability of FH systems to combat varying partial band noise jamming.

Novel channel estimation model for OFDM in time-varying channel

GAO Fei, JI Peng-fei, XUE Yan-ming, LI Yun-long

2013, 22(3): 374-379.

[Abstract](659) [PDF 356KB](889)

Abstract:
A new channel estimation method for orthogonal frequency division multiplexing (OFDM) system with large subcarriers and serious intercarrier interference (ICI) is proposed. The channel frequency-domain (CFD) matrix of each delay path is factorized to the product of a diagonal delay matrix and a circular ICI matrix in this model. To reduce the coefficient number, the circular ICI matrix is squeezed by using Hamming-window as the reshaping pulse in the transmitter. Meanwhile, the elements of the diagonal delay matrix are approximated with a discrete prolate spheroidal basis expansion model (DPS-BEM). A least-square (LS) estimator is used to estimate the reduced channel coefficients. The proposed method is theoretically derived and simulated. The simulation results indicate that the model has good performance and is appropriate for various channel environments. The method also has low complexity and good spectral efficiency.

Barometric altimeter in wireless communication network indoor positioning system

HU Zheng-qun, ZHANG Li-rong

2013, 22(3): 380-386.

[Abstract](691) [PDF 512KB](1084)

Abstract:
A differential barometric altimetry technology based on the digital pressure sensors is put forward by using the existing mobile phone base station as reference. The height of known base station is precise. The pressure and temperature of the known base station is measured by sensors and transmitted to users. The absolute height value of user will be calculated by combining the barometric pressure values and temperature values from the base station with the locally measured values. In order to decrease system errors caused by inconsistency between the measured pressure value at base station and the locally measured pressure value, weights correction is applied based on multiple reference stations. The calculated height value is accurate due to eliminating the measured errors caused by irregular changes of atmospheric pressure, with the error less than 1.m. Resolution of elevation positioning depends upon the resolution of the pressure sensor, the relationship between which is approximately linear. When the resolution of sensor is 0.01.hPa, the resolution of elevation positioning is about 0.1.m. In addition, the data frame format at base station is designed in this article. Experimental results show that the method is accurate, reliable, stable and has the ability to distinguish floors and stair steps.

Multi-agent consensus algorithm for second-order systems with a time-varying reference state

SONG Li, WU Qing-he

2013, 22(3): 387-393.

[Abstract](1195) [PDF 393KB](778)

Abstract:
Two second-order consensus algorithms with a time-vary reference state without relative velocity measurements are proposed in a directed topology. Necessary and sufficient conditions are presented to ensure second-order consensus. It is shown that all the coupling strengths and the eigenvalues of the Laplacian matrix play important roles in reaching consensus. Specially when all nonzero eigenvalues of the Laplacian matrix are real, consensus can be achieved if and only if the coupling strengths are positive and the directed topology has a spanning tree for the first algorithm, and for the second one, consensus can be achieved if and only if the coupling strengths are positive. Finally, simulation examples are presented to verify the theoretical analysis.

Image super-resolution reconstruction based on sparse representation and residual compensation

SHI Jun, WANG Xiao-hua

2013, 22(3): 394-399.

[Abstract](655) [PDF 2673KB](616)

Abstract:
A super-resolution reconstruction algorithm is proposed. The algorithm is based on the idea of the sparse representation of signals, by using the fact that the sparsest representation of a signal is unique as the constraint of the patched-based reconstruction, and compensating residual errors of the reconstruction results both locally and globally to solve the distortion problem in patch-based reconstruction algorithms. Three reconstruction algorithms are compared. The results show that the images reconstructed with the new algorithm have the best quality.

Centrality measure of complex networks based on resource flow

CHEN Guo-qiang, Wang Yu-ping, LIU Sheng-hua

2013, 22(3): 400-409.

[Abstract](869) [PDF 450KB](9)

Abstract:
A new centrality measure for complex networks, called resource flow centrality, is proposed in this paper. This centrality measure is based on the concept of the resource flow in networks. It not only can be applied to the connected networks, but also the disconnected networks. Moreover, it overcomes some disadvantages of several common centrality measures. The performance of the proposed measure is compared with some standard centrality measures using a classic dataset and the results indicate the proposed measure performs more reasonably. The statistical distribution of the proposed centrality is investigated by experiments on large scale computer generated graphs and two networks from the real world.

Comprehensive evaluation of communication network based on network carrying and associating relation

ZHOU Wan-yin, LI Ming-hui, XIA Jing-bo

2013, 22(3): 410-416.

[Abstract](811) [PDF 404KB](1005)

Abstract:
In order to solve the problem of integrated management in different types of networks, a comprehensive evaluation method for a communication network is presented via network carrying and associating relation. Based on the abstract and analysis of network relation, the principle and procedure of the evaluation method are discussed. The method considers the effect of individual diversity of network running indicator, and reflects the contribution and associating degree of network carrying relation. Experiment results verify that the proposed method is correct and efficient. The research provides a new idea for the future network management.

Diversity of supramolecular architecture of H₂salpn coordination compounds based on its flexibility

TANG Bei-bei, HE Fei-yue, LI Hui

2013, 22(3): 417-422.

[Abstract](898) [PDF 1593KB](924)

Abstract:
Two complexes, [Cu(saipn)]·NH(CH₃)₂(1) and [Ni(saipn)·H₂O] (2) (H₂salpn=N, N-bis(salicylidene)-propane-1,3-diamine) were characterized by IR, element analysis and single crystal X-ray diffraction analysis. Crystal data for complex 1: monoclinic,P2₁/C,a=1.097.4×10^-7cm,b=1.480.6×10^-7cm,c=1.031.5×10^-7cm,β=94.43(3))°. The Cu (Ⅱ) ion in complex 1 is four coordinated with distorted square planar coordination geometry. The crystal structure of complex 1 consists of coordination complex and a guest molecule NH(CH₃)₂that can act as both H-bonding donor and acceptor and plays an important role in constructing supramolecular architecture. Crystal structure data for complex 2: orthorhombic,Pnma,a=8.676.3×10^-8cm,b=2.414.5×10^-7cm,c=7.538.8×10^-8cm. The Ni(Ⅱ) ion in complex 2 is five-coordinated with a butterfly coordination geometry. The coordinated water molecule plays a key role in hydrogen-bonded networks.

Numerical study of the effect of flow rate and temperature on parison swell and sag in extrusion

PENG Jiong, LI Jing, CHEN Jin-nan, LIU Sha-li

2013, 22(3): 423-426.

[Abstract](684) [PDF 733KB](1041)

Abstract:
Swell and sag drawdown significantly influence the high density polyethylene parison. Numerical simulations of the flow field of a HDPE melt were performed using the finite element method for the die of plastic pipe extrusion and parison formation. The constitutive equation of Carreau law was used to describe the polymer melt in the flow domain. The distributions of the velocity, shear rate, viscosity, pressure, thickness and radius are presented with Polyflow. The effect of flow rate and temperature on extrusion swell and parison sag was investigated. The results show that the thickness of the parison increases with increasing flow rate. The thickness and radius of the parison are more sensitive to changes in flow rates than to changes in temperatures.

2013 Vol. 22, No. 3