Advanced Search

2011 Vol. 37, No. 2

  Previous Issue | Next Issue 
Display Method:
Prototype SMA actuated locking device for small space magnetic bearing flywheels
Yan Xiaojun, Zhang Xiaoyong, Nie Jingxu, Zhang Shaowei
2011, 37(2): 127-131.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1220
Abstract:
Based on magnetic levitation principle, the magnetic bearing flywheel is a new type of inertial actuator used in satellite attitude control. A locking device was used to eliminate the gap between the rotor and stator of magnetic bearing flywheel so as to protect it from shock and vibration damage during launch phase. The present pyrotechnical or motor actuated locking devices have the disadvantages of high shock, large size and un-resetable. A prototype shape memory alloys (SMA)actuated locking device for small space magnetic bearing flywheel was developed in this investigation. A method and procedures to design the actuator element based on Liang-s constitutive model was presented. Then the SMA locking device was assembled and the function, environment and vibration tests were carried out. Test results show that the device can complete lock function within 6 s and release function within 1 s under satellite power supply of 28 V. It can also undergo the environment and vibration tests which simulate the launch phase. It is concluded that the new SMA locking device owning advantages of great locking force, small size, low shock and easy to reset has a potential use in space engineering.
Direct reaching sliding mode control
Jiang Yuxian, Zhou Yinqiang, Zhao Xia
2011, 37(2): 132-135.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1079
Abstract:
Sliding mode control(SMC) system synthesized by traditional reaching condition can not grantee all phase trajectories from the neighborhood of the sliding mode to direct reach the nearby sliding mode branch. It will cause the state transition to be slow and overshooting which are not allowed in some engineering. In order to make the dynamic procedure of a SMC system unidirectional convergent, the direct-reaching SMC(DRSMC) was presented. By analyzing the shortcomings in the expression of traditional reaching condition, the definition of direct-reaching function and the establishment of direct-reaching condition were introduced. Direct-reaching condition(DRC) is the basis of using DRSMC to synthesize a SMC system. A DRSMC system is composed of a command mode model and an on-off type DRSMC model. Different from the traditional reaching condition, the control which satisfies the DRC can guarantee all phase trajectories from the neighborhood of sliding mode to direct reach the nearby branch of the sliding mode and then go to zero state. Therefore the state transition process will be fast and monotonous. The DRSMC was applied to an example system and was simulated. The simulation result accords with the performance expectation of DRSMC.
In-orbit spacecraft-s earth and atmosphere radiation environment analysis
Yuan Yukai, Chen Hongyu, Wu Huiying
2011, 37(2): 136-139.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1363
Abstract:
To provide quantitative reference for related space mission analysis, the remote sensing the earth and atmosphere radiation (EAR) simplified model was proposed. A universal irradiation model that suited for most kinds of spacecraft orbit was introduced, which reduced different orbit scenarios to different angles between the orbit plane and the dawn-dusk plane of the earth. Then the spacecraft position on each orbit, or the phase, was taken into account. The spacecraft remote sensing mode determined the main axis and field of view(FOV).Irradiance propagation process was described with common hypothesis. Then the result display in two ways: distribution map and quantitative graph, which the former shows the relative position where the EAR is in the spacecraft-s 2π hemisphere FOV, then the latter shows the magnitude distribution based on the average albedo. The following magnitude integral according to different off-axis angle could transform the faint target detecting requirement of space mission into the payload’s stray light/radiation blocking requirement. A low earth orbit(LEO) observation example has been demonstrated at visible band.
Application of H∞ theory in electro-hydraulic loading system of helicopter pitch adjusting booster
Liu Guojian, Li Yunhua, Zheng Qi, Guo Zhongwei
2011, 37(2): 140-143.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1024
Abstract:
A dynamic model of electric-hydraulic loading system was established based on the principle analysis of electro-hydraulic load simulator, which was applied to the earth-experiment of hydraulic assistor for the helicopter pitch adjusting. Controllers designed by conventional control theory were not effectual because of the uncertain factors such as difficulties in access to precise structure parameters of electric-hydraulic loading system and nonlinearity of loading flux in servo valve. Therefore the robust control strategy of electric-hydraulic loading system based on H∞ theory was investigated in this work. Through choosing suitable weight functions and using the designing method of mixed sensitivity, the robust controller was solved by the linear matrix inequality (LMI) algorithm. The experiment results prove the high efficiency and superiority of the robust force controller which is presented by this work.
Identification method of tool wear based on empirical mode decomposition and least squares support vector machine
Guan Shan, Wang Longshan, Nie Peng
2011, 37(2): 144-148.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 815
Abstract:
In view of the non-stationary characteristics of acoustic emission signal of tool wear, and the slow convergence rate of learning algorithm and easily dropping into the local minimum value for back propagation neural networks, a novel method of tool wear state identification based on empirical mode decomposition and least squares support vector machine was proposed. Firstly, the empirical mode decomposition method was used to decompose the collected acoustic emission signals into a number of stationary intrinsic mode function, and then autoregressive model of each intrinsic mode function was established respectively. Finally, auto regression model coefficients were selected to constitute the feature vector. The feature was divided into two groups, one group was used to train the least squares support vector machine and the other was used to identify the tool wear state. The identification result proves that this method is superior to neural network, and it has a higher identification rate. It is proved that this method is efficient and feasible.
Software reliability growth model with S-shaped testing effort function
Li Qiuying, Li Haifeng, Lu Minyan, Wang Xuecheng
2011, 37(2): 149-154,160.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1146
Abstract:
The shape of the observed reliability growth curve depends strongly on the time distribution of the testing effort. Thus, the reliability estimation power of software reliability growth model (SRGM) can be improved by considering the testing effort function (TEF). Due to the integrated effects of software structure and learning factor on testing process, testing effort increasing rate may exhibit an S-shaped varying trend first increasing and then decreasing. To accurately describe this S-shaped varying trend, two S-shaped testing effort functions were proposed first, i.e. delayed S-shaped TEF and inflected S-shaped TEF, which were simple and flexible. Then two new SRGMs were put forward by combining two S-shaped TEFs into SRGM, i.e. DSTEF-SRGM and ISTEF-SRGM. Finally, for two real failure data-sets, the case study was done by comparing these two S-shaped TEF-SRGMs with several classical SRGMs and other representative SRGMs considering TEF in the form of estimation power. The result shows that compared with these comparison models, the proposed ISTEF-SRGM has the best fitting results on each data-set. In other words, the proposed ISTEF-SRGM provides novel applicability and a significantly better power of reliability estimation.
Multi-dimensional state space model to aircraft-deck landing safety
Tian Jin, Zhao Tingdi
2011, 37(2): 155-160.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1142
Abstract:
There are lots of factors from human, machine and environment involved in aircraft-deck landing process, and the factors show multivariable nonlinearity and strong coupling, which brings some difficulty to real-time and effective safety monitoring, identification and decision-making to aircraft-deck landing process. To solve the problem, the principle of multi-dimensional state space to safety was expressed, and multivariable statistics analysis (MSA) was introduced to put forward a method with which the model of multi-dimensional state space to safety could be established and applied on systems analysis, so that the safety characteristics embedded in system state information could be discovered. The deck landing process of a type of USA aircraft was illustrated, characteristic variables that influence aircraft-deck landing safety were extracted based on statistical data, its multi-dimensional state space model describing aircraft-deck landing safety was established, and dimension of the space and the corresponding state variables were identified. The method supported aircraft-deck landing safety analysis, monitoring and decision-making with a reasonable and simplified data processing, and the case analysis result accorded approximately with reality, which demonstrated practicability and credibility of the method.
Design optimization and simulation of mechanical anti-load simulator
Wang Wei, Li Xiongfeng, Zhang Xinhua, Yu Wenpeng
2011, 37(2): 161-166.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1033
Abstract:
The dynamics and extraneous torques models of an anti-load simulator were built according to the complex vector and virtual displacement principles respectively. To avoid the problem that the solution is not consistent when the traditional genetic algorithm (GA) is used in the parameters optimization, the hierarchical optimization of GA based on the parametric sensitivity was applied to optimize the design parameters of the mechanism of the anti-load simulator. Then a virtual prototype was designed according to the optimizing results, and testified by the simulation in ADAMS with various loads applied. The results show that the prototype is able to withstand the complex environment conditions and loads in simulating tests. Finally, the real anti-load simulator was established with functions working in environment tests and under various loads.
Design of sliding model and dynamic inverse control law for a missile based on RBF neural-networks
Yang Zhifeng, Lei Humin, Li Qingliang, Li Jiong
2011, 37(2): 167-170.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1084
Abstract:
A radial basic function (RBF) neural networks based sliding model control and dynamic inverse control approach to a missile was presented. The basic control law was designed by dynamic inversion, and neural networks based sliding model and dynamic inverse controller was designed for the slow loop to compensate the uncertainty of the whole control system. The RBF neural networks were used to approximate the uncertainty of slow states model of missile and the approximation errors of the neural networks were introduced to the design of adaptive adjust law to improve the quality of the systems. Sliding model controller was used to attenuate the uncertainty of model and the approximation errors of the neural networks. The controller could guarantee stability of overall system and attenuate effect of uncertainty of model and approximation errors of neural networks to a prescribed level. Finally, simulation results show the effectiveness of the control method.
Net barrier strength and performance evaluation of AAS by FE method
Deng Ying, Yan Xiaojun, Zhang Hui
2011, 37(2): 171-174.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1011
Abstract:
The performance of aircraft arresting system (AAS) and strength of net barrier was evaluated by means of nonlinear finite element (FE), considering contact, net mass and material properties. Key problems, such as FE model, boundary condition and numerical convergence caused by complex nonlinear system, were solved. The simulation results provide stress distribution of AAS to evaluate strength margin of the net barrier. It is worth well of pointing out that the method can also be used to check effectiveness of controller-s method. The results also show that this method could describe arresting processes closely to actual state. Consequently, the procedures can be effective in an AAS design.
Analysis for whole airspace flight key factors of unmanned aerial vehicles
Cai Zhihao, Yang Liman, Wang Yingxun, Li Xinjun
2011, 37(2): 175-179,184.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1918
Abstract:
Aiming at the problem of unmanned aerial Vehicles(UAVs) entering non-segregated airspace, UAVs-safety and the key factors of improving their airspace flight capacity were analyzed, according to the characteristics of large scale, medium scale, small scale and low speed, medium speed, high speed UAVs coexisting. The approaches include category management, autonomous navigation and control, dynamic mission planning, coordination mechanisms, sense and avoid, etc. Based on improving the UAVs-reliability, they would have the ability of air traffic management in whole airspace. Modeling and simulation are effective method to validate these approaches. The final target is reducing the cost of UAVs, improving the ability to share more airspace and achieving the goal of manned and unmanned air vehicles flying together.
Internal charging protection technology of typical space polymer dielectric material
Wang Jinfeng, Zheng Xiaoquan, Li Shengtao, Bai Jingjing
2011, 37(2): 180-184.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 888
Abstract:
Besides efficient shield,the best method for eliminating the pulsed discharge induced by the deep charge of spacecraft dielectric was to use dielectric materials or insulation structural components that never produce any pulsed discharges. By non-linearity modification experiment research on several typical polymer dielectrics like Polyimide,Epoxide resin and Teflon, it was found that through the addition of the inorganic powder that possess a conductivity much higher than that of the polymer, the composite dielectric material would produce a remarkable non-linearity conductance character. By this way,the excessive charges would be discharged as a method of non-pulsed conducting current before the deep dielectric charging reaches the discharge threshold. It was proved that, even the normal resistance could be increased by this method. Finally, the mechanism on the non-linearity conductance of the composite material was investigated.
Text and position coding of human-machine display interface
Zhang Lei, Zhuang Damin
2011, 37(2): 185-188.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 945
Abstract:
In process of operating aircraft, pilots need to use large amounts of information. So reasonable coding of information can improve driving safety. According to research requirements, a task model was developed for the ergonomics experiment. After subjects complete the tasks, their correct rate and reaction time were measured. Combined the measured results with eye movement data, the impact of text and position coding on information identification was analyzed to provide a scientific basis for the ergonomics design of information interface. Experimental results show that subject-s identification of the text information is affected by the position coding. And position coding relates to vision scope and attention allocation strategy.Identification efficiency of the center is better than the periphery, and the left position is better than the right position. Identification efficiency of Chinese information is better than English, the impact of mother tongue should be considered in the practical application.
Optical-flow based circle biased proportional navigation
Qin Tian, Chen Wanchun, Xing Xiaolan
2011, 37(2): 189-192.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 955
Abstract:
For the passive homing missiles, a developed guidance law based on optical flow was proposed to impact a moving target with an impact angle constraint. In contrast to optical-flow based circle navigation guidance, it is more practical and precise. Meanwhile the improved one does not require the range information, which avoids the problem that the range information can not be measured directly by a passive homing seeker. Based on a measurement model using an optical sensor and optical flow calculation and inspired by the insect navigation, the optical flow was used in guidance and control for a passive homing missile. Employing the structure of biased proportional navigation, the bias term was redesigned to ensure the impact angle. The simulation results show that, a small miss distance and a desired impact angle are obtained when the new guidance law is used to impact a moving ground target, also this guidance law is much robust to measurement noise.
Influence of gap parameters on aerodynamics of multi-element airfoil
Qin Xuguo, Liu Peiqing, Qu Qiulin, Peng Guohui
2011, 37(2): 193-196.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1417
Abstract:
The effect of flap and slat riggings on the multi-element airfoil was investigated numerically. The compressible Navier-Stokes equations were solved by the finite-volume method. Spalart-Allmaras (S-A) turbulence model was used. The effects of flap and slat riggings on lift coefficients and pressure coefficients were provided. The validation of computation agreed well with the experimental results. The computations on the effect of flap and slat riggings shows that lift coefficient has an optimum with every design parameter. With proper flap and slat riggings, the adverse pressure gradient and the separation on the backward wing section could be suppressed, and the wake from forward wing section does not mix with the boundary layer of backward wing section. So the performance of the airfoil can be improved.
Modeling of complex reflection coefficient for time-evolving sea surfaces
Li Xiaofei, Xu Xiaojian
2011, 37(2): 197-201.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1291
Abstract:
Based on the two-dimensional time-varying sea surface model and first-order small slope approximation method, the time-varying and statistical characteristics of complex reflection coefficients from sea surfaces were investigated. In terms of electromagnetic scattering amplitudes, the reflection coefficients and their coherent and incoherent components were derived. The theoretical formula of coherent part is coincident with the empirical model. Simulation results demonstrate that the coherent amplitudes accord with the empirical counterparts, while the phases have unavoidable disturbances, which can not be predicted by empirical formula. Middleton phase difference statistical model was introduced to model the time-varying property of reflection coefficients. The simulated statistics are shown to be in good agreement with the theoretical model, and the contour plots of probability density function can predict the correlation between the complex reflection coefficients adequately. Such agreement suggests that the complex reflection coefficients have a Gaussian distribution on short time scales, but are modulated in amplitude and frequency by the long surface waves.
Evaluation of engineering turbulence models for complex supersonic flows
Zhao Rui, Yan Chao
2011, 37(2): 202-205,215.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1248
Abstract:
Supersonic flows past a series of two-dimensional compression ramps were simulated by employing three popular engineering turbulence models, namely Spalart-Allmaras(SA), k-ω, shear stress transport(SST). The performance of the three engineering turbulence models was evaluated and summarized. All three turbulence models are reasonably accurate to predict the surface pressure, skin friction and heat transfer distribution for "weak" shock/boundary-layer interactions, but show significant discrepancies with experimental data for "strong" interactions. Each turbulence model shows much different simulation capability with the separation lengths increased, and the numerical method has much effect too.
Binocular vision-based short-range navigation method for autonomous aerial refueling
Xie Hongwen, Wang Honglun
2011, 37(2): 206-209.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1454
Abstract:
To solve the short-range precise navigation problem in the probe-and-drogue autonomous aerial refueling, a binocular vision-based short-range navigation method was presented. This method used two cameras installed on the receiver to capture the images of the optical markers mounted on the end surface of the drogue, then detected the light spot regions in the images by contour tracking algorithm and calculated their gray scale centers as the image points of the optical markers. These image points were matched according to epipolar geometry constraints, and the position and attitude of the drogue were calculated using space circle fitting arithmetic. A three-dimensional virtual scene of probe-and-drogue aerial refueling was established to simulate this navigation method. Simulation results show that this method has a high position and attitude measurement accuracy during the short-range docking maneuver, fulfilling the demand of autonomous aerial refueling.
Formation cooperative planning method based on multi-agent with resource constraints
Yang Fei, Wang Qing, Wu Zhendong
2011, 37(2): 210-215.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1059
Abstract:
After analysis on the anti-ship combat process of ship formation, theory of multi-agent system (MAS) was introduced into the decision-making process, and then the formation cooperative anti-ship combat agent model was established. Aiming at the key problem that the resource constraints among formation agents induced resource occupied conflict in the formation agent cooperation process, a principal and subordinate structure multi-agent planning pattern was proposed accomplished with proposing a MAS planning method combining centralization with distribution. The simulation result showed that the method could effectively realize the cooperation among combat formation agents, and ensured the formation agents achieving anticipated tactical goal under the condition of resource constraints.
Pre-whitening filter of fractal noise in fiber optic gyroscope
Hua Chunhong, Ren Zhang, Zhang Minhu
2011, 37(2): 216-219.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 889
Abstract:
Fractal noise in fiber optic gyroscope (FOG) usually is long-term dependent, which causes FOG a rather slow drift. In order to filter this noise, a pre-whitening filter based on fractional difference (FD) was proposed. By this filter, fractal noise could be transformed into Gaussian white noise (GWN). And through wavelet analysis, the pre-whitening noise could be eliminated by Bayes soft-threshold denoising in wavelet domain. On the two aforementioned steps, it came into a pre-whitening filter method of fractal noise. After the test data processing of FOG-VG949p, the results show that its fractal noise was removed efficiently, so the slow drift is restrained. The high frequency noise terms of FOG also greatly decrease.
Online calibration based on in-flight alignment and optimal design
Zhang Xiaoyue, Yang Gongliu, Zhang Chunxi
2011, 37(2): 220-222.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1046
Abstract:
The navigation system precision was influenced by the output error of fiber optic gyro(FOG) inertial measurement unit(IMU). In order to complement ground calibration, FOG strapdown inertial navigation system(SINS) online calibration was carried out in airborne guidance weapon in-flight alignment process. In-flight alignment/online calibration model of FOG-SINS was introduced, based on which the Kalman filter was designed. Simulation analysis of error excitation and influence on navigation precision were carried out, and filter optimal design was completed. At last, the simulation results with or without optimal design were obtained which indicated that: FOG-SINS free inertial navigation precision was improved after optimal design.
Computerized tomography image registration based on sinogram
Sun Jingjing, Yang Min, Liu Jinghua, Wu Wenjin
2011, 37(2): 223-226.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 2982
Abstract:
In order to resolve the image registration problem in X-ray nondestructive testing, a new computerized tomography image registration algorithm based the mathematical relationship between the parts displacement and the change of the projection data was proposed. The algorithm preprocesses the projection data considering the practical computed tomography system, and utilizes the correlation between the projection data to search for the parts displacement. The algorithm can deal with registration problem of the two dimensional rigid transformation in the parallel and fan beam geometry. Because the proposed algorithm is done in the projection field before image reconstruction, it is more adaptive comparing with the conventional registration algorithms in the image field. Especially when the projection quality is low, there is missing projection and high level noise and there are severe artifacts in the reconstructed images, the proposed algorithm is more effective and reliable. The registration results of a sealed apparatus verify the performance of the algorithm.
Internal performance of counterflow thrust vectoring nozzle under different flight conditions
Zou Xinhua, Wang Qiang
2011, 37(2): 227-230,236.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1087
Abstract:
An analysis of the impact of internal performance on the counterflow thrust vectoring nozzle under different flight conditions was presented by numerical simulation. The results show in static conditions counterflow phenomena occurs on two nozzles of different slot hights when the secondary pressure is at 60 795-87 139.5 Pa and 50 662.5-91 192.5 Pa without jet attachment. And with the secondary pressure increasing ,the pitch-thrust-vector angles decrease and thrust ratios increase. When the Ma number is 0.6 and 1.2, jet attachment occurs on the nozzle with smaller slot hight and can not apply to actual fluidic control. But to the nozzle with larger slot hight, when the Ma number is 0.6,counterflow phenomena occurs at secondary pressure 40 530-87 139.5 Pa without jet attachment. When the Ma number is 1.2,there is no counterflow phenomena at considered secondary pressure.
Research and application of virtual maintenance technology
Zhou Dong, Huo Lin, Wang Meihui, Mao Deyao
2011, 37(2): 231-236.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1443
Abstract:
The theory of virtual maintenance is not fully studied and researches are deficiency in the field of virtual maintenance modeling and simulation. The methodology architecture of virtual maintenance were discussed and built, and virtual maintenance model and simulation control method were studied. The model of virtual maintenance called maintenance task net (MTN) was presented, and MTN based on Petri net can describe maintenance process and the factors including state, action and condition. In addition,the fire rules and the control mechanism of virtual maintenance simulation which is driven by MTN were presented.A case study of the line replaceable unit(LRU) repair of an aircraft was conducted, and the result confirms the validation and feasibility of all the studies, which can become a new technique means for maintainability engineering.
Structural optimization of spacecraft based on two-level multi-point approximate method
Chen Shenyan, Huang Hai
2011, 37(2): 237-240.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 867
Abstract:
At the primal design stage of a new satellite, finite element model of the initial structure was established. Taking thicknesses of pipe beams and rectangle thin-wall beams as design variables, and considering constraints of natural frequency and strength, a structural optimization model was developed to approach minimum mass. Two-level multi-point approximation method was applied in structural optimization. In each calculation cycle, the original optimization problem was transformed to a first level multi-point approximate problem, and it was also approached by a second approximate problem which can be quickly solved by dual method. Three stages were implemented in the whole optimization process: initial optimum searching tests, design revision and re-optimization. Among the first stages, five runs were set with different constraints, design variables bounds and structural centroid heights, through which the design direction and interval of various structural parameters were obtained. Then the original structure was revised according to the results of the first stage. A new optimization model with fewer design variables and more reasonable variables bounds is established in the third stage and a feasible design is achieved, which provide references to detail design of the satellite structure. It indicates that the applied design procedure and optimization method are effective in engineering structural optimization problem.
Simulation for throttling effect of small aperture multistage orifice units
Liu Wanlong, Liang Guozhu, Xu Ming, Zhang Huazhao
2011, 37(2): 241-244.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1124
Abstract:
Throttling effect of small aperture multistage orifice units was studied through simulation method. It was found that strict initial flow field was needed in this kind of simulation, and the simulation would be dummy-balanced with irrational initial flow field. This problem was solved by iterative finding proper initial flow field. The multistage orifice units with 0.1 mm aperture and 0.025 aperture ratio were simulated. The simulation result shows that the number of the orifices is the major factor which influences the flow coefficients of the multistage orifice units. Fitted formulae for the flow coefficients were given depending on the simulation results. The fitted formulae can be applied to actual engineering design calculation.
Novel tracking loop of BOC signal based on subcarrier tracking
Yang Zaixiu, Huang Zhigang, Geng Shengqun
2011, 37(2): 245-248.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1225
Abstract:
In order to eliminate the tracking ambiguity of binary offset carrier (BOC) signal, a novel tracking loop based on subcarrier tracking was proposed. Compared with traditional tracking loop, the proposed architecture provides a subcarrier locked loop to track subcarrier. The innovative tracking loop architecture resolves the tracking ambiguity problem by tracking the subcarrier and spread spectrum code respectively. The subcarrier was synchronized with the local sinusoidal signal using phase lock loop (PLL), which exploits the periodic feature of the subcarrier of BOC signal. Figures of merit, such as code tracking error, tracking threshold and mean time to lose lock (MTLL) have been analyzed and evaluated through software simulations. Simulation results show that the novel tracking loop can improve the tracking performance of weak signal and enhance the tracking loop stability with little degradation in tracking accuracy.
Decoupling analysis between yaw and collective pitch controls of coaxial helicopter using free wake arithmetic
Xu Guanfeng, Chen Ming
2011, 37(2): 249-252.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1063
Abstract:
The yaw control of coaxial helicopters is gained from the differential control of collective pitches of up and down rotors. Hence, a coupling phenomenon can be found. Employing the free wake arithmetic, the aerodynamic analysis for the small coaxial helicopter was made, mainly focusing on the coupling between yaw and collective pitch controls in hover flight. The computation showed the relationship between collective pitches of two rotors when the yaw control or collective pitch control was given. From those results, the characteristics of decoupling control could be identified. And those data was transformed into several simple functions using the curve fitting method. These results will be significant for designing the flight control system.

Copyright © Journal of Beijing University of Aeronautics and Astronautics

Address: Editorial Department of Journal of Beijing University of Aeronautics and Astronautics, 37 Xueyuan Road, Haidian District, Beijing Post Code: 100191 Email: jbuaa@buaa.edu.cn

Supported by: Beijing Renhe Information Technology Co., Ltd.