JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Bi-objective path optimization of flapping airfoils based on a surrogate model

ZHAO Liang-yu, XU Yong, XU Lai-bin, YANG Shu-xing

2011, 20(2): 143-151.

[Abstract](1010) [PDF 455KB](312)

Abstract:
A bi-objective optimization problem for flapping airfoils is solved to maximize the time-averaged thrust coefficient and the propulsive efficiency. Design variables include the plunging amplitude, the pitching amplitude and the phase shift angle. A well defined Kriging model is used to substitute the time-consuming high fidelity model, and a multi-objective genetic algorithm is employed as the search algorithm. The optimization results show that the propulsive efficiency can be improved by reducing the plunging amplitude and the phase shift angle in a proper way. The results of global sensitivity analysis using the Sobol's method show that both of the time-averaged thrust coefficient and the propulsive efficiency are most sensitive to the plunging amplitude, and second most sensitive to the pitching amplitude. It is also observed that the phase shift angle has an un-negligible influence on the propulsive efficiency, and has little effect on the time-averaged thrust coefficient.

Effect of direction error on the miss distance of rolling missiles with x-rudder

SHI Jiao, TANG Sheng-jing, GAO Feng

2011, 20(2): 152-157.

[Abstract](1056) [PDF 320KB](315)

Abstract:
Based on the analysis of periodic equivalent control force of rolling missiles with x-rudder, the guidance loop model with direction error is established and the relationship between direction error and miss distance is analyzed. Results show that the miss distance is zero or a constant or infinite, and it is always zero when the real parts of system matrix eigenvalues decided by direction error are both positive values in an ideal system, in which all the lags are neglected. However, the miss distance gradually increases with the increase of the direction error and its variation is small when direction error is not more than 5° in the system, in which seeker lag and missile body lag are considered.

Robustness assessment for flight control system of an oceanographic unmanned aerial vehicle

LI Meng, LIU Li, VERES S. M.

2011, 20(2): 158-167.

[Abstract](1129) [PDF 566KB](237)

Abstract:
A post-design robustness assessment for the longitudinal flight control system of an oceanographic unmanned aerial vehicle (UAV) is presented in this paper. Two novel systematic approaches of generating the linear fractional transformation (LFT) model directly from nonlinear equations are proposed for this particular robustness analysis problem. The closed-loop system combined with each controller is used to determine combinations of aerodynamic parameters that result in worst-case performance. Classical simultaneous gain and phase margin stability metrics currently used in the aerospace industry are introduced for the certification of robustness of this uncertain multivariable system. The results show that the control system remains stable and achieves desired performance for all possible parameter variations over a specified range in both frequency domain and time domain.

Study on fragmentation of PELE against thin targets

JIANG Jian-wei, ZHANG Mou, MEN Jian-bing, WANG Shu-you

2011, 20(2): 168-172.

[Abstract](827) [PDF 539KB](234)

Abstract:
The fragments mass and size from penetrator with enhanced lateral effect (PELE) perforating thin rolled homogenous armor (RHA) target was characterized through theoretical and numerical methods. An analytical model based on energy-limited spall (ELS) was proposed to predict fragments mass distribution of PELE with different cores and impact velocities. For different cores the expansion can be represented by a scaling factorlin the analytical calculation. The explicit finite-element (FE)-analysis of PELE fragmentation was implemented with stochastic failure criterion in AUTODYN-3D code. By statistical distribution of "weak points" in numerical model of PELE, the dynamic fragmentation was delineated to simulate Flaw-limited spall as in real material. To verify the accuracy of theoretical calculation and validate numerical results, experiments of PELE perforating thin RHA target was setup, fragments were collected by using recovery cabin filled with foam and soft sands. Both energy limited spall theory and Flaw limited approach showed accurate results compared with experimental data.

Numerical simulation of shock initiation of the coated-type projectile penetrating target

YU Qing-bo, WANG Hai-fu, JIN Xue-ke

2011, 20(2): 173-178.

[Abstract](878) [PDF 484KB](262)

Abstract:
The behavior of the charge initiation of the coated-type projectile penetrating target is researched by means of numerical simulation. The influences on charge initiation of the projectile shape, shell thickness, charge diameter, and projectile velocity are analyzed. Results show that projectile shape takes an obvious impact on critical detonation velocity, that for the projectile with the same quality, it is more vulnerable for the cylindrical projectile with the one length-diameter ratio to occurring shock initiation than the spherical projectile, the charge diameter is an important factor that affecting critical detonation velocity, which significantly decreases as the charge diameter increases.

Experimental research on electric insulator damaged by chemical pollutant

WEI Ji-feng, WANG Shu-shan, ZHANG Zhi-wei

2011, 20(2): 179-182.

[Abstract](836) [PDF 349KB](267)

Abstract:
As a main insulating device of power system, insulator can be damaged by chemical pollutant, which does threaten the electric system. An artificial pollution test system is utilized to study the damage mode for a suspension insulator, and the effects of concentration and existing state on damage efficiency of chemical pollutant are studied. Testing results show that the damage mode is flashover damage, whose efficiency increases with the decrease of creepage distance. The concentration of conductive particle of chemical pollution can effectively elevate damage efficiency, though it has a critical value. Unlike natural pollution, chemical pollutant can make insulator flashover damage whether in wet or dry condition. The damage process and relative results reveal the damage rule of insulator by chemical pollutant. Those studies put forward a new means to damage electric insulated device, and provide important reference to the protection design of electric insulator.

Ballistic limit and residual velocity of PELE penetrating against metal target

JI Peng-yuan, WANG Hai-fu

2011, 20(2): 183-186.

[Abstract](954) [PDF 318KB](230)

Abstract:
Based on analyzing the conservation of energy of penetrator with enhanced lateral efficiency (PELE) the penetrating against metal target, a theoretical expression predicting the residual velocity of PELE perforating the target is obtained. By modifying De Marre semi-experience formula,the ballistic limit velocities of PELE penetrating into 2024 aluminum alloy and 45^#steel targets are also given. The theoretical predictions fit well with experimental or simulative results.

Influence of structure parameters on terminal effect of small caliber PELE impacting metal target

JI Peng-yuan, WANG Hai-fu, ZHENG Yuan-feng, YU Qing-bo

2011, 20(2): 187-191.

[Abstract](843) [PDF 571KB](233)

Abstract:
By changing the length-diameter ratios and inner-to-outer diameter ratios, some numerical simulations were made on PELE normal penetrating metal target using AUTODYN-3D code. The influence rules of length-diameter ratio and inner-to-outer diameter ratio to the terminal effect of PELE are obtained. When the length-diameter ratio is in the range of 4-7, inner-to-outer diameter ratio is in the range of 0.54-0.72, the PELE can perform satisfactory double terminal effects embodied in armor-piercing and fragment killing. Based on simulation results, a test projectile is designed and an impact experiment of PELE is carried out, which demonstrate the efficiency of the simulation method.

Different human-simulated characteristics of the driver models in the forward simulation of hybrid electric vehicles

WANG Wei-da, XIANG Chang-le, LIU Hui, HAN Li-jin

2011, 20(2): 192-198.

[Abstract](887) [PDF 348KB](238)

Abstract:
Based on the control theories of PID, fuzzy logic and expert PID, the driver models are built and applied in the forward simulation for hybrid electric vehicles (HEV). The impact to the vehicle speed tracking and the fuel economy is compared among the different driver models. The different human-simulated characteristics of the driver models are emphatically analyzed. The analysis results indicate that the driver models based on PID, simple fuzzy logic and expert PID are corresponding to the handling characteristics of different drives. The driver models of different human-simulated characteristics bring the handling divergence of drivers with different driving level and habit to the HEV forward simulation, and that is significant to the all-around verification and validation of the control strategy for HEV. System simulation results of different driver models validate the impact of driver models to the dynamic and fuel economy performance of HEV.

Fault diagnosis of power-shift steering transmission based on multiple outputs least squares support vector regression

ZHANG Ying-feng, MA Biao, FANG Jing, ZHANG Hai-ling, FAN Yu-heng

2011, 20(2): 199-204.

[Abstract](840) [PDF 443KB](262)

Abstract:
A method of multiple outputs least squares support vector regression (LS-SVR) was developed and described in detail, with the radial basis function (RBF) as the kernel function. The method was applied to predict the future state of the power-shift steering transmission (PSST). A prediction model of PSST was gotten with multiple outputs LS-SVR. The model performance was greatly influenced by the penalty parameter γ and kernel parameter σ²which were optimized using cross validation method. The training and prediction of the model were done with spectrometric oil analysis data. The predictive and actual values were compared and a fault in the second PSST was found. The research proved that this method had good accuracy in PSST fault prediction, and any possible problem in PSST could be found through a comparative analysis.

Combustion condition of diesel engine by cylinder pressure oriented to control

WANG Jun, ZHANG You-tong, HAN Shu, LI Jiong

2011, 20(2): 205-210.

[Abstract](980) [PDF 349KB](216)

Abstract:
According to demand of electronic control and combustion process measurement in diesel engine, cylinder pressure difference method was introduced to study combustion condition. Combustion parameters such as intensity, phase and heat-releasing rate were used to describe combustion condition. Combustion commencement angle, maximal burst pressure and its angle, and bar-center point in pressure difference curve were selected as character parameters to demonstrate overall combustion charater. The 4100 diesel engine was simulated with GT-POWER software, relation of pressure character index with injection timing and injection quantity was resolved by simulation and measurement of pressure data, and varying trend of each pressure character index with diesel engine emission NO_xbased on experimental data was analyzed. The results indicated that pressure character index had direct relationship with injection fuel timing and engine output parameter, and pressure character index could be used as combustion condition flag.

Field measurement method for ultrasonic transducer based on inverse Abel transform

KONG Tao, XU Chun-guang, XIAO Ding-guo

2011, 20(2): 211-215.

[Abstract](882) [PDF 464KB](253)

Abstract:
A new reflection approach for field distribution measurement of ultrasonic transducers was investigated. Instead of a point-like reflection target (rigid sphere) or thin wires (line-like targets), a line response function of experimental knife-edge distribution combined with the inverse Abel transforms was used to estimate the lateral beam distributions of ultrasonic transducers. The measurement steps were as follows: ① A knife-edge was scanned perpendicularly to acoustic beam axis of the transducer using an ultrasonic C-scan system to obtain its ultrasonic image line response function, ② the transverse beam distribution was solved by the inverse Abel transforms, and ③ experiments were performed to obtain the lateral beam profiles of two transducers, with and without focus, and the results were compared with those from a hydrophone. The results showed that this method was effective for ultrasonic field measurement and could be as a substitute for hydrophone in most cases.

Online tool-wear measurement of small-diameter end mills based on machine vision

YUAN Wei, ZHANG Zhi-jing, JIN Xin, LIU Bing-bing

2011, 20(2): 216-220.

[Abstract](1213) [PDF 440KB](228)

Abstract:
The objective of this study was to develop an online tool-wear-measurement scheme for small diameter end-mills based on machine vision to increase tool life and the production efficiency. The geometrical features of wear zone of each end mill were analyzed, and three tool wear criterions of small-diameter end mills were defined. With the uEye camera, macro lens and 3-axis micro milling machine, it was proved the feasibility of measuring flank wear with the milling tests on a 45# steel workpiece. The design of experiment (DOE) showed thatV_cwas the most remarkable effect factor for the flank wear of small-diameter end mill. The wear curve of the experiments of milling was very similar to the Taylor curve.

Strain transfer mechanism of passive wireless surface acoustic wave torque sensors using shear lag theory

ZHANG Yun-tao, XU Chun-guang, PAN Qin-xue, LIU Jing, LI Xi-peng

2011, 20(2): 221-226.

[Abstract](1114) [PDF 405KB](233)

Abstract:
A shear-lag theory was developed to investigate the strain transfer from the metal substrate to the surface acoustic wave (SAW) resonator through a bonding layer. A three-layer model of host structure-adhesive layer-resonator layer was established. The strain transfer was theoretically analyzed, and the main factors impacting the SAW sensor measurement were studied. The relationship between the sensor response and the individual effect of all these factors under static loads was discussed. Results showed that better accuracy could be achieved with increase in the adhesive stiffness or resonator length, or decrease in the adhesive thickness. The values of the strain transfer rate calculated from the analytical model agreed well with that from the available experiment data.

Petri net model for diagnosis of permanent faults of a hydraulic system

ZHANG Bo, DOU Li-hua, MA Tao, LI Peng

2011, 20(2): 227-232.

[Abstract](828) [PDF 300KB](257)

Abstract:
Petri net model is applied to diagnose the permanent fault of hydraulic system within the framework of interpreted Petri net. The permanent fault is described as redundant structure of the model. A definition and a theorem are proposed to determine the diagnosability of the hydraulic system. The relations bwtween the diagnosability and other structure properties are also discussed. An example of actual hydraulic system is presented and its permanent fault can be diagnosed by the proposed method efficiently.

Adaptive hierarchical block tracking method in case of partial occlusions

LUO Tao, WANG Jian-zhong, LU Pei-yuan

2011, 20(2): 233-237.

[Abstract](876) [PDF 606KB](286)

Abstract:
In order to solve the tracking problem occurred during occlusions, an adaptive hierarchical block tracking method is proposed after analyzing the changes of the target characteristics under partial occlusions. Firstly, color histogram features are selected to describe the target. The similarity between the target model and the candidates is measured by the Bhattacharyya coefficient, which can also be used to evaluate the degree of occlusions. The object is divided into four blocks when it is occluded, and the mean shift procedure is used to track each block separately. Then, according to the value of the Bhattacharyya coefficient, the partially occluded block is found and divided into four sub-blocks, which are tracked by block matching algorithm separately. Finally, the information of all the blocks is used to determine the displacement vector of the target. Experimental results show that compared to the traditional mean shift tracking method, this method can make full use of the features of the unoccluded sub-blocks, improve the tracking accuracy and solve the target tracking problem in case of partial occlusions.

Electronic stabilization of catadioptric panoramic image

MA Zi-ling, WANG Jian-zhong

2011, 20(2): 238-243.

[Abstract](894) [PDF 447KB](233)

Abstract:
An effective algorithm of electronic image stabilization (EIS) of catadioptric panoramic imaging system for track robots is presented. The key techniques of this algorithm are as follows: ① A model of electronic image stabilization is built by analyzing the imaging theory and the principle of EIS, and the image shift function of unwrapped panoramic image is deduced; ② The relationship equation between motion estimation parameters of annular panoramic image and motion estimation parameters of unwrapped panoramic image is developed according to the constrained aspect ratio of real objects, motion parameters of annular panoramic image are firstly estimated, and then motion parameters among the image shift function are carried out according to the relationship equation; ③ An excessive stabilization threshold is presented to prevent the phenomena of excessive stabilization, and the Kalman filtering is adopted to smooth the image sequences. Numerical experimental results show that this algorithm can effectively smooth out the unwanted motion and follow the intentional camera movement under certain resolutions.

Ontology-based question expansion for question similarity calculation

LIU Li, FAN Xiao-zhong, QI Quan, LIU Xiao-ming

2011, 20(2): 244-248.

[Abstract](913) [PDF 294KB](219)

Abstract:
A new ontology-based question expansion (OBQE) method is proposed for question similarity calculation in a frequently asked question (FAQ) answering system. Traditional question similarity calculation methods use "word" to compose question vector, that the semantic relations between words are ignored. OBQE takes the relation as an important part. The process of the new system is: ① to build two-layered domain ontology referring to WordNet and domain corpse; ② to expand question trunks into domain cases; ③ to use domain case composed vector to calculate question similarity. The experimental result shows that the performance of question similarity calculation with OBQE is being improved.

Mathematical simulations of the galvanic coupling intra-body communication by using the transfer function method

SONG Yong, ZHANG Kai, HAO Qun, WANG Ming, CHU Yi-fang, KANG Bang-zhi

2011, 20(2): 249-255.

[Abstract](1161) [PDF 448KB](228)

Abstract:
The galvanic coupling intra-body communication (IBC) was mathematically simulated based on the proposed transfer function. Firstly, a galvanic coupling IBC circuit model was developed and the corresponding parameters were discussed. Secondly, the transfer function of the galvanic coupling IBC was derived and proposed. Finally, the signal attenuation characteristics of the galvanic coupling IBC were measured along different signal transmission paths of actual human bodies, while the corresponding mathematical simulations based on the proposed transfer function were carried out. Our investigation showed that the mathematical simulation results coincided with the measured results over the frequency range of 100.kHz to 5.MHz, which indicated that the proposed transfer function could be useful for theoretical analysis and application of the galvanic coupling IBC.

Experimental investigation of nonlinear process based on cSHG/DFG in PPLN waveguide

SHEN Shi-kui, NING Chun-mei, YANG Ai-ying, SUN Yu-nan

2011, 20(2): 256-260.

[Abstract](925) [PDF 344KB](224)

Abstract:
Effects of second harmonic generation (SHG) and cascaded second harmonic generation/difference frequency generation(cSHG/DFG) based on the quasi-phase-matching (QPM) condition in periodically poled lithium niobate (PPLN) waveguide were investigated experimentally. SHG conversion efficiency of -13.6.dB and QPM bandwidth of 0.45.nm were achieved using a 16.1.dBm power of fundamental wave at 1.550.4.nm. Using pulsed all-fiber passive mode locked laser and tunable continuous wave laser, cSHG/DFG effect utilized for optical sampling was observed. Conversion efficiencies were calculated, and 11.88.nm-wide QPM bandwidth was achieved through changing the wavelength of input signal. Conversion efficiency of cSHG/DFG effect increased linearly with the total injected power.

Novel image restoration model coupling gradient fidelity term based on adaptive total variation

SHI Ming-zhu, XU Ting-fa, LIANG Jiong, FENG Liang, ZHANG Kun, ZHOU Li-wei

2011, 20(2): 261-266.

[Abstract](1106) [PDF 790KB](241)

Abstract:
A novel image restoration model coupling with a gradient fidelity term based on adaptive total variation is proposed in this paper. In order to choose proper parameters, the selection criteria were analyzed theoretically, and a simple scheme to demonstrate its validity was adopted experimentally. To make fair comparisons of performances of three models, the same numerical algorithm was used to solve partial differential equations. Both the international standard test image on Lena and HR image of CBERS-02B of Dalian city were used to verify the performance of the model. Experimental results illustrate that the new model not only preserved the edge and important details but also alleviated the staircase effect effectively.

Densities of methanol+trimethyl phosphate binary mixtures from (293.15 to 333.15) K and viscosities of trimethyl phosphate from (283.15 to 373.15) K

WANG Li-sheng, TIAN Na-na, FAN Chuan-lei

2011, 20(2): 267-271.

[Abstract](882) [PDF 314KB](267)

Abstract:
Densities of methanol+trimethyl phosphate binary mixtures were measured over a temperature range of (293.15 to 333.15).K at atmospheric pressure. From these data, excess molar volume(V^E) was calculated. Viscosities of trimethyl phosphate were also measured over a temperature range of (283.15 to 373.15).K and the data were fitted to the Andrade equation. The density data were fitted to a second-order polynomial. The excess molar volumes were fitted to the Redlich-Kister equation using a nonlinear regression method. Results show that the density and viscosity gradually decreases with the increase of temperature.

Failure mode prediction of sandwich plate under bending loads

SUN Ling-yu, CHEN Wei-wei, FENG Jiang-bo

2011, 20(2): 272-279.

[Abstract](907) [PDF 539KB](219)

Abstract:
To understand the relationship between the collapse mechanisms and geometry parameters of sandwich plate with two aluminum alloy faces and one polyurethane foam core, samples subjected to three-point bending loads were studied through simulation, test and analytic methods. Based on published papers, the dimensionless values of limit loads for different failure modes were modified according to real test condition. The load-deformation relation from the analytical formulae was compared with that from experimental and numerical results. A mechanism map was provided to reveal the dependence of the dominant collapse mechanism upon the geometry parameters of the face and the core. The results show that the prediction accuracy was high only if the face thickness was much smaller than the core thickness.

Synthesis and performance of miktoarm star copolymers of styrene and butadiene

ZHANG Hai-yan, KE Yong, YAO Ming, ZHAO Su-he, ZHANG Xing-ying

2011, 20(2): 280-284.

[Abstract](777) [PDF 269KB](223)

Abstract:
A novel multifunctional macromolecular organolithium initiator (PD-Sn-(RLi)₃) was prepared via living anionic polymerization and used for the synthesis of miktoarm star copolymers in cyclohexane. The average molecular weight, polydispersity index, microstructure and unit composition of the miktoarm star copolymers were characterized with GPC and¹H-NMR. Performances of the miktoarm star styrene-butadiene rubbers were investigated in comparison with those of the blend rubbers such as the tin-coupled star-shaped random copolymers of styrene-butadiene rubber(S-SBR)/natural rubber (NR) blend rubber and S-SBR/Cis-1, 4-polybutadiene rubber (Cis-BR) blend rubber.

2011 Vol. 20, No. 2