JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Research on dynamic stability rotational speed range of rolling projectiles with different characteristics

WANG Ya-fei, YU Jian-qiao, SU Xiao-long, WANG Lin-lin

2014, 23(3): 285-291.

[Abstract](1390) [PDF 356KB](684)

Abstract:
Traditional dynamic stability analyses of the rolling projectiles are mainly based on solving the systems’ transfer functions or angular motion's homogeneous equations to obtain their characteristic roots. The solving processes of these methods are complex and lacking further analysis of the results. To solve this problem, Routh stability criterion is introduced to determine the stability of rolling missiles based on the transfer function model, and an important advantage of this method is that it is unnecessary to solve the system's characteristic equation. Rotational speed ranges satisfying the dynamic stability of rolling projectiles with four different characteristics are acquired, and the correctness of analysis results is verified by computing the system's root locus. The analysis results show that the relation between stability and rotational speed for static stable missiles is opposite to that for spin-stabilized projectiles, and the relative size of gyroscopic effect and Magnus effect has an extremely important influence on the trend of the stability of the system with increasing rotational speed.

Stability analysis of tactical missile autopilots based on vector margin

WANG Jiang, LIN De-fu, Li Quan-yun

2014, 23(3): 292-298.

[Abstract](2027) [PDF 351KB](793)

Abstract:
A novel stability computation approach for tactical missile autopilots is detailed. The limitations of traditional stability margins are exhibited. Then the vector margin is introduced and compared with sensitivity function to show their essential relationship. The longitudinal three-loop autopilot for tactical missiles is presented and used as the baseline for all the available linear autopilots. Ten linear autopilot topologies using all the measurable feedback components are given with the identical closed-loop characteristic equation and time-domain step response. However, the stability of the ten autopilots differs when considering the actuator dynamics, which limits their application. Then vector margin method is adopted to compute and evaluate the stability of all available autopilots. The analysis and computation results show that the vector margin method could better evaluate autopilot stability.

Motion planning of UAV group using modified gyroscopic force for guidance and avoidance

YANG Sheng-qing, YU Jian-qiao

2014, 23(3): 299-305.

[Abstract](1156) [PDF 386KB](534)

Abstract:
It is comment that unmanned aerial vehicles (UAVs) have limitation on information capturing in reality applications. Therefore, online method of motion planning is necessary for such UAVs. Gyroscopic force (GF) is used for obstacle avoidance as an online method. However, classical GF has shortcoming in generating orbit for UAV with high velocity because the GF results in a time-varying turning radius. Modified gyroscopic force (MGF) given by function of velocity can overcome this shortcoming and help get a more practical control law for avoidance. MGF can also be used to implement the guidance of UAV by designing particular active conditions. Interactions in forms of stress function and damping force are introduced so that an UAV group can have coordinated motion. By combining controls of MGF and interactions, motion planning of UAV group in obstacle environment can be implemented.

Research of the ATR system based on the 3-D models and L-M BP neural network

MU Cheng-po, YUAN Zhi-jie, WANG Ji-yuan, CHEN Yuan-qian, DONG Qing-xian

2014, 23(3): 306-310.

[Abstract](1001) [PDF 690KB](464)

Abstract:
Automatic target recognition (ATR) is an important issue for military applications, the topic of the ATR system belongs to the field of pattern recognition and classification. In the paper, we present an approach for building an ATR system with improved artificial neural network to recognize and classify the typical targets in the battle field. The invariant features of Hu invariant moments and roundness were selected to be the inputs of the neural network because they have the invariances of rotation, translation and scaling. The pictures of the targets are generated by the 3-D models to improve the recognition rate because it is necessary to provide enough pictures for training the artificial neural network. The simulations prove that the approach can be implement ed in the ATR system and it has a high recognition rate and can be applied in real time.

Dynamic environment prediction of spacecraft using dynamic substructuring

YANG Wu, LIU Li, DONG Wei-li

2014, 23(3): 311-317.

[Abstract](942) [PDF 423KB](497)

Abstract:
A low frequency dynamic environment prediction of spacecraft using dynamic substructuring is presented. The dynamic environment could be used to describe the level of the excitation on the spacecraft itself and auxiliary equipment. In addition, the dynamic environment is a criterion for the structural dynamic design as well as the ground verification test. The proposed prediction method could solve two major problems. The first is the time consumption of analyzing the whole spacecraft model due to the huge amount of degrees of freedom, and the second is multi-source for component structural dynamic models from distributive departments. To demonstrate the feasibility and efficiency, the proposed prediction method is applied to resolve a launching satellite case, and the results were compared with those obtained by the traditional prediction technology using the finite element method.

Anovel profile error model to calculate contact error

LIU Qin, WU Wei-ren, ZHANG Zhi-jing, JIN Xin

2014, 23(3): 318-324.

[Abstract](1084) [PDF 557KB](484)

Abstract:
A new profile model based on multi-scale asperities is developed and contact error is calculated.After stratified sampling, the model can get the distribution law of entity points on each cross section.Asperity radius of curvature is estimated by the relationship between circle radius and the section interval. Contact error is related to surface form error. A model equation of contact error plane is calculated through a method based on static equilibrium theory. Three contact asperities which determine the contact error plane on the rough surface are studied. The simulation results show that contact error can be accurately calculated according to the profile error model.

Variation analysis of precision mechanical assembly considering form errors and local deformation

ZHANG Ting-yu, JIN Xin, ZHANG Zhi-jing, YE Xin

2014, 23(3): 325-331.

[Abstract](1040) [PDF 490KB](524)

Abstract:
A method to analyze the effect of form errors and local deformation on the assembly accuracy and its stability in a non-rigid assembly system is proposed. The contact finite element method was used to obtain local deformation of mating surfaces, which was superposed onto form errors to obtain real mating surface data of assemblies. Then mating variation was obtained by establishing virtual contact planes. Finally, an experiment of the assembly of two cylindrical components was carried out to verify the validity of the proposed method. By comparing the calculation accuracies of 3D assembly with and without taking into account local deformation, the results showed that the effects of local deformation of mating surfaces on calculation accuracy of mating variation was not neglectable compared with form errors.

Thermal efficiency characteristics of hydrogen internal combustion engine

SUN Bai-gang, XIANG Qing-hua, LIU Fu-shui

2014, 23(3): 332-338.

[Abstract](1375) [PDF 383KB](530)

Abstract:
To study the economic advantages of hydrogen internal combustion engine, an experimental study was carried out using a 2.0.L port fuel-injected (PFI) hydrogen internal combustion engine. Influences of fuel-air equivalence ratioΦ, speed, and ignition advance angle on heat efficiency were determined. Test results showed that indicated thermal efficiency (ITE) firstly increased with fuel-air equivalence ratio, achieved the maximum value of 40.4% (Φ=0.3), and then decreased whenΦwas more than 0.3. ITE increased as speed rises. Mechanical efficiency increased as fuel-air equivalence ratio increased, whereas mechanical efficiency decreased as speed increased, with maximum mechanical efficiency reaching 90%. Brake thermal efficiency (BTE) was influenced by ITE and mechanical efficiency, at the maximum value of 35% (Φ=0.5, 2.000.r/min). The optimal ignition advance angle of each condition resulting in the maximum BTE was also studied. With increasing fuel-air equivalence ratio, the optimal ignition angle became closer to the top dead center (TDC). The test results and the conclusions exhibited a guiding role on hydrogen internal combustion engine optimization.

NO_xemission characteristics of hydrogen internal combustion engine

SUN Bai-gang, DUAN Jun-fa, LIU Fu-shui

2014, 23(3): 339-344.

[Abstract](857) [PDF 363KB](475)

Abstract:
In order to investigate the NO_xemission of hydrogen internal combustion engines. A test system for four-cylinder intake port-fuel-injection hydrogen internal combustion engine(H₂ICE) is established to study the effect of fuel-air equivalence ratio, ignition advance angle,engine speed and exhaust gas recirculation on NO_xemission. Experimental results show that the fuel-air equivalence ratio is the key factor to NO_xemission,NO_xemission concentration is always higher than 8.000×10^-6when the fuel-air equivalence ratio is larger than 0.8 and lower than 500×10^-6when the fuel-air equivalence ratio is smaller than 0.5. The ignition advance angle and engine speed also play important roles on NO_xemission formation.EGR is an useful method to reduce NO_xemission concentration at large fuel-air equivalence ratio especially when engine speed is low and EGR ratio is high.

Robust lane recognition for structured road based on monocular vision

WANG Bao-feng, QI Zhi-quan, MA Guo-cheng

2014, 23(3): 345-351.

[Abstract](1269) [PDF 2385KB](449)

Abstract:
A robust lane detection and tracking system based on monocular vision is presented in this paper. First, the lane detection algorithm can transform raw images into top view images by inverse perspective mapping (IPM), and detect both inner sides of the lane accurately from the top view images. Then the system will turn to lane tracking procedures to extract the lane according to the information of last frame. If it fails to track the lane, lane detection will be triggered again until the true lane is found. In this system,θ-oriented Hough transform is applied to extract candidate lane markers, and a geometrical analysis of the lane candidates is proposed to remove the outliers. Additionally, vanishing point and region of interest(ROI) dynamically planning are used to enhance the accuracy and efficiency. The system was tested under various road conditions, and the result turned out to be robust and reliable.

Case-based retrieval approach for machining fixture design utilizing ontology

GAO Bo, YAN Yan, DING Hong-sheng, ZHANG Fa-ping, WANG Guo-xin

2014, 23(3): 352-357.

[Abstract](1000) [PDF 1199KB](488)

Abstract:
In order to develop an intelligent case-based reasoning (CBR) system to reuse fixture design knowledge, ontology technology was integrated in CBR system by semantic annotation of fixture design case. Domain ontology of fixture design was constructed; concepts and relations were defined and represented. The 2-level similarity evaluation approach of domain ontology was presented. The concept similarity of cases was calculated as the first grade case retrieval. Numerical measurement was the second grade case retrieval, which adopted various methods to calculate different types of attribute values. The problem of similarity measurement of fixture design case was resolved. Prototype system based on the proposed method was illustrated and the retrieval approach was proved to be efficient.

Adaptive robust control for electrical cylinder with friction compensation using modified LuGre model

HAO Ren-jian, WANG Jun-zheng, ZHAO Jiang-bo, WANG Shou-kun

2014, 23(3): 358-367.

[Abstract](1061) [PDF 488KB](444)

Abstract:
The position tracking control problem of an electrical cylinder in the presence of dynamic friction nonlinearities in its transmission process is addressed in this paper. First, a torque decoupling approach is proposed to formulate the dynamic model. Secondly, to compensate the friction in the case of servo motion, a modified LuGre model is designed to make a continuous transition between a static model at a high speed and a LuGre model at a low speed to avoid instability due to discretization with a finite sampling rate. To accelerate the speed of estimating time-varying parameters, a fast adaption law is proposed by designing an attraction domain around a rough value related to the load force. Finally, a discontinuous projection based adaptive robust controller is synthesized to effectively handle parametric uncertainties for ensuring a guaranteed robust performance. A Lyapunov stability analysis demonstrates that all signals including tracking errors have the guaranteed convergent and bounded performance. Extensive comparative simulations with sinusoidal and point-point tracks are obtained respectively in low and high speeds. The results show the effectiveness and the achievable control performance of the proposed control strategy.

Mobile business process modeling using high level Petri nets

CHE Hai-ying, GAO Hui-ying, JU Yan-bing

2014, 23(3): 368-374.

[Abstract](988) [PDF 382KB](547)

Abstract:
This paper aims at providing an effective modeling methods for more and more mobile business applications. First a high level Petri nets method-Xml nets is introduced, which combines the advantage of Petri nets and XML. Petri nets have strict mathematics and intuitionistic diagram expression way, rich system describing means and system behavior analytical technology, and the related powerful supporting tools. XML, as an extensible markup language, is already a information description de facto standard. XML nets could be utilized to model both the controlling flow and the data flow of mobile business process effectively, which consequently enables the analysis and optimization of the mobile business processes and could be utilized to simulate the execution of the mobile business process with the Petri nets tools to improve the system execution efficiency. In this paper, to demonstrate the modeling of the controlling flow and data flow of mobile business process, an instrument repair business case is modeled with XML nets.

TV/L2-based image denoising algorithm with automatic parameter selection

WANG Bao-xian, TANG Lin-bo, ZHAO Bao-jun, DENG Chen-wei, YANG Jing-lin

2014, 23(3): 375-382.

[Abstract](1217) [PDF 2926KB](428)

Abstract:
In order to improve the adaptiveness of TV/L2-based image denoising algorithm in different signal-to-noise ratio (SNR) environments, an iterative denoising method with automatic parameter selection is proposed. Based upon the close connection between optimization function of denoising problem and regularization parameter, an updating model is built to select the regularized parameter. Both the parameter and the objective function are dynamically updated in alternating minimization iterations, consequently, it can make the algorithm work in different SNR environments. Meanwhile, a strategy for choosing the initial regularization parameter is presented. Considering Morozov discrepancy principle, a convex function with respect to the regularization parameter is modeled. Via the optimization method, it is easy and fast to find the convergence value of parameter, which is suitable for the iterative image denoising algorithm. Comparing with several state-of-the-art algorithms, many experiments confirm that the denoising algorithm with the proposed parameter selection is highly effective to evaluate peak signal-to-noise ratio (PSNR) and structural similarity (SSIM), especially in low SNR environment.

High-performance wall-climbing robot for inspection and maintenance

SHAO Jie, GAO Xue-shan, DAI Fu-quan, ZONG Cheng-guo, BAI Yang, GUO Wen-zeng, LI Jun

2014, 23(3): 383-389.

[Abstract](1702) [PDF 2097KB](452)

Abstract:
A wall-climbing robot that can continuously work on many types of wall surfaces has been developed. This robot based on low-vacuum adsorption principle consists of a locomotion mechanism, a sealing device, a fluid machine and a detecting system. The adsorption force is analyzed in details and its influencing factors are given. The robot prototype, which has the features of high adhesion efficiency, light body in weight, small size in structure and good capability in payload, is tested in outdoor and indoor environments. Through the experiments, the influences of the impeller slit and the seal clearance are discussed. In addition, the robot functions such as adsorption performance, locomotion performance and wall adaptability are tested by experiments. The experiments have verified that the robot not only can climb on many types of wall surfaces, but also has outstanding locomotion ability and payload capacity.

Determining relative position and attitude of a close non-cooperative target based on the SIFT algorithm

HAO Wei-wei, ZHANG Xiao-fang, HUANG Yu, YANG Feng, GUO Bai-wei

2014, 23(3): 390-394.

[Abstract](964) [PDF 1204KB](494)

Abstract:
A binocular stereo vision positioning method based on the scale-invariant feature transform (SIFT) algorithm is proposed. The SIFT algorithm is for extracting distinctive invariant features from images. First, image median filtering is used to eliminate image noise. Then,according to the characteristics of the target satellite, image map is used to extract the middle part of the target satellite. At last, the feature match point under the SIFT algorithm is extracted, and the three-dimensional position and orientation are calculated. The features are invariant to image scale and rotation, and are shown to provide robust matching across a substantial range of affine distortion, change in 3D viewpoint, addition of noise, and change in illumination. The experimental result shows that the algorithm works well and the maximum relative error is within 0.02.m and 2.5 °.

Design and implementation of scenic-spot introduction-task-oriented 3D virtual human spoken dialogue system

WU Wang-hui, XIE Xiang, JIAO Yi-shan, ZHANG Zheng, GAO Gao

2014, 23(3): 395-400.

[Abstract](1226) [PDF 1055KB](552)

Abstract:
A scenic-spot introduction-task-oriented 3D virtual human spoken dialogue system—EasyGuide is introduced. The system includes five modules: natural language processing, task domain knowledge database, dialogue management, voice processing and 3D virtual human text-to-visual speech synthesis. In the first module, dictionary construction along with sentence analysis and semantic representation are illustrated specifically. A tree-structured knowledge database is designed for the task domain. A novel framework based on the keyword analysis and context constraints is proposed as the dialogue management. As for voice processing module, a software development kit which performs speech recognition and synthesis is introduced briefly. In the last module, 3D viseme synthesis is explained with examples and a text-driven facial animation system is presented. Evaluation results show that the system can achieve satisfactory performance.

Theoretical investigation on the dendritic cells algorithm

FANG Xian-jin, WANG Li

2014, 23(3): 401-406.

[Abstract](962) [PDF 327KB](462)

Abstract:
The aims of this paper are to helpunderstand the dendritic cells algorithm (DCA) and reduce the potential incorrect applications and implementations, to clearly present the formal description of the dendritic cells algorithm, and to theoretically deduce the algorithm's runtime complexity and detection performance. The entire dendritic cells population of the algorithm is specified using quantitative measures at the functional level.Basic set theory and computational functions, such as addition, multiplication and recursion, are used for clarity and definition, and theoretical analysis is implemented via introduction of three runtime variables in terms of three phases of the algorithm. Consequently, the data structures, procedural operations and pseudocode description of the dendritic cells algorithm are given. The standard DCA achieves a lower bound ofΩ(n) runtime complexity and an upper bound ofO(n²) runtime complexity under the worst case. In addition, the algorithm's runtime complexity can be improved toO(max(nN, nδ)) by utilizing segmentation approach, wherenis the number of input instances,Nis the population size andδis the size of each segment.

Efficient Luby transform encoding algorithm based on short cycle elimination

CAO Cong-zhe, FEI Ze-song, KUANG Jing-ming

2014, 23(3): 407-412.

[Abstract](1219) [PDF 351KB](511)

Abstract:
An effective Luby transform (LT) encoding algorithm based on short cycle elimination is proposed to improve decoding probabilities of short length LT codes. By searching the generator matrix, some special encoded symbols are generated by the encoder to effectively break the short cycles that have negative effect on the performance of LT codes. Analysis and numerical results show that by employing the proposed algorithm, the encoding complexity decreases and the decoding probabilities improve both in binary erasure channels (BECs) and additive white gauss noise (AWGN) channels.

Degradation of effective carrier-power-to-noise density ratio based on code tracking spectral sensitivity coefficient for GNSS radio frequency compatibility in C band

LIU Mei-hong, ZHAN Xing-qun, NIU Man-cang

2014, 23(3): 413-419.

[Abstract](1234) [PDF 1410KB](480)

Abstract:
The frequency band between 5.010.MHz and 5.030.MHz allocated as C band has been used as a candidate in the global navigation satellite systems (GNSS) along with more and more navigation services in L band. The potential benefits and technical requirements of C band for satellite navigation have been analyzed before. However the degradation of effective carrier-power-to-noise density ratio(Δ (C/N₀)_eff) based on code tracking spectral sensitivity coefficient(CT_SSC) as a compatibility assessment methodology for potential GNSS radio frequency compatibility in C-Band has not been discussed clearly. So the compatibility of the signals in the C band between BeiDou (BD) B1C and GPS L1C, L1C/A, Galileo E1Os as the interoperability or classical signals in L band is analyzed. Simulation results reveal the interference degree between BD III B1C and GPS L1C/A, L1C, Galileo E1OS. The results can also reveal that the multiplexed binary offset carrier (MBOC) and binary phase shift keying (BPSK) modulation is not appropriate for C band.

Synergistic effect of salts on inducing obvious viscoelastic behavior of cationic trimeric surfactant solutions

MU Rui-hua, WU Wen-hui

2014, 23(3): 420-426.

[Abstract](1039) [PDF 405KB](475)

Abstract:
A viscoelastic system formed by the solutions of di(2-hydroxyl-dimethylene ether)-α,ω,γ-triple (dimethyloctadecylammonium chlorine) (18-4(OH)-18-4(OH)-18) is proposed to solve the problems of poor temperature and shear resistances of clean fracturing fluid. The apparent viscosity of 18-4(OH)-18-4(OH)-18 solution affected by inorganic salt, hydrotropic salt and their mixtures is investigated using steady state measurements. Meanwhile, the temperature and shear resistances of systems of 18-4(OH)-18-4(OH)-18 and several common single-chain surfactants are compared. The rheological experiments show that, the coexistence of NaSal and NaCl makes it easier for the system to promote micellar growth yielding wormlike micelles than single NaSal or NaCl. The apparent viscosity of 18-4(OH)-18-4(OH)-18 solution maintains over 87.5.mPa·s above 100.℃. The results indicate that there exists a synergistic effect in solutions of 18-4(OH)-18-4(OH)-18 trimeric surfactant with NaSal and NaCl.

2014 Vol. 23, No. 3