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2015 Vol. 41, No. 1

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2015 Year 41 Volume 1 Issue E-journal
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Parameter optimization of pulse compression method in air-coupled ultrasonic testing
ZHOU Zhenggan, MA Baoquan, SUN Zhiming, ZHOU Hui, HUANG Ziyu, LIU Jingjing
2015, 41(1): 1-7. doi: 10.13700/j.bh.1001-5965.2014.0037
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A variety of pulse compression methods are viewed as viable solutions to improve the signal to noise ratio (SNR) of received signal in air-coupled ultrasonic testing. However, the use of corresponding method to realistic inspection is faced with problem of optimal parameter selection to get better compression effect. Based on the basic principle of pulse compression method and its implementation in ultrasonic testing, an air-coupled ultrasonic testing system with function of real-time pulse compression processing of ultrasonic signal was established. The impact of key parameters of linear frequency modulation, nonlinear frequency modulation and phase coded pulse compression method on compression effect in narrow-band air-coupled ultrasonic transducer was analyzed, respectively, and then the optimal parameter selection criteria was acquired. Finally, the corresponding pulse compression method of optimized parameters was verified in air-coupled ultrasonic inspection of a honeycomb sandwich composite sample with simulated defects.
Design of high-gain unknown input observer based on Riccati equation
ZHU Fanglai, ZHANG Yongjun
2015, 41(1): 8-13. doi: 10.13700/j.bh.1001-5965.2014.0041
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For a class of Lipschitz nonlinear system, the reconstruction problems of state estimation, unknown input and measurement noise were studied. Regarding the measurement noise as an extended state, the original system can be transformed into a descriptor system. For the descriptor system, first, a high-gain observer which can estimate the states and the measurement noise of original system simultaneously was developed based on the solution of a Riccati equation. Second, a second-order high gain sliding mode observer was used to exactly estimate the derivatives of the system outputs in a finite time. Third, by using the estimates of the states and the output derivatives, an algebraic unknown input reconstruction method was proposed. It was pointed out that both the unknown input and measurement noise reconstruction methods are suitable for stronger time-varying signals. Finally, a numerical simulation of a practical model was given to illustrate the effectiveness of the proposed methods.
Method for airborne video capture and preprocessing based on FPGA
JIANG Hongxu, LI Huiyong, LIU Tingshan, DUAN Miyi, ZHANG Ping
2015, 41(1): 14-22. doi: 10.13700/j.bh.1001-5965.2014.0467
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Video capture, color space conversion and video data transmission were researched in order to improve video capture and pre-processing performance of airborne multi-mode video coding system. Taking into account the requirements of real-time multi-mode video capture, a robust video capture strategy based on field-programmable gate array (FPGA) was designed. It monitors the correctness of video capture on-time to avoid accumulation of errors by adopting self-checking mechanism. To solve the problem of wastes of computing resources and increasement of power consumption in floating-point multiplication, a truncated look-up table multiplier based on the separation of high and low bits was designed to save memory and computation bandwidth. It achieves an efficient color space conversion combining pipeline technique, with power consumption decreasing 27% at most without loss of computing precision and processing performance. Considering the frequent transmission of mass data between FPGA and digital signal processor (DSP), a data interaction mechanism taking FPGA as the control core was proposed, adopting the transmission mode of serial rapid I/O (SRIO). The burden of DSP was alleviated due to concentrating on video coding, and thus the application performance was improved.
Wind turbine airfoil design method with low noise and experimental analysis
WANG Quan, CHEN Jin, CHENG Jiangtao, WANG Jun, SUN Jinfeng, YOU Ying
2015, 41(1): 23-28. doi: 10.13700/j.bh.1001-5965.2014.0072
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In order to study the noise characteristic of wind turbine airfoils, the airfoil optimal design mathematic model was built based on airfoil functional integrated theory and noise calculated model. The new optimized objective function of maximizing lift/drag to noise was developed on the design angle of attack. Then, the comparison of sound pressure level between CQU-DTU-B18 and NACA-64-618 airfoil was analyzed under the same condition of wind tunnel experiment and wind speed. It is indicated that the changed trend of the predicted noise results are in agreement with that of the tested data, though there is a certain difference between the theory results and experiment data. Compared with NACA-64-618 airfoil, the CQU-DTU-B18 airfoil exhibits lower noise, which validates the feasibility of this design method. It is a guide to design wind turbine airfoil with lower noise and to reduce airfoil noise.
Storage life assessment for solid propellant based on generalized linear model
HONG Dongpao, WANG Yinghua, GUAN Fei, MA Xiaobing
2015, 41(1): 29-32. doi: 10.13700/j.bh.1001-5965.2014.0030
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To describe the influence of performance degradation on storage life and reliability for solid propellant, a method of storage life and reliability assessment based on generalized linear model was proposed. According to the characteristic of solid propellant degradation data, the local scale model was introduced to relate the solid propellant tensile strength to storage time, and the storage life and reliability model for solid propellant was established. The maximum likelihood estimations of the model coefficients were obtained with the generalized linear model for Poisson distribution. Furthermore, the approximated confidence interval for the reliability function was obtained with Fisher information matrix according to the normal law. The instance analysis shows that the performance data under varied storage time was used synthetically to enlarge the sample size and increase the information for storage reliability assessment. Thus, the storage life and reliability assessment precision was improved
Evaluation method for distortion of arbitrary waveform
SUN Jingyu, WANG Zhongyu, LIANG Zhiguo
2015, 41(1): 33-37. doi: 10.13700/j.bh.1001-5965.2014.0079
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The index of distortion to evaluate the total quality of waveforms has special advantages and has been accepted widely by most people. Based on the analyses of the distortion definition of arbitrary waveform, a method using nonlinear-curve-fitting to evaluate the distortion of arbitrary waveform was discussed. Firstly, by moving the model in time domain, the“similar-fitting” model to the arbitrary waveform to be evaluated can be obtained. Then, using the least-square fitting method, the fitting curve on amplitude domain can be gotten, and this is just the best fitting curve to the arbitrary waveform to be evaluated. Thus, the distortion of the arbitrary waveform can be calculated. The results of the experiment show that this method has obviously practicability and flexibility, and can resolve the problem of evaluation for the distortion of arbitrary waveform. And then, it can resolve the problem of calibration for arbitrary waveform and arbitrary waveform generator (AWG).
Experimental investigation on operational performance of loop heat pipe subjected to acceleration force
XIE Yongqi, YU Yin, XIE Liyao, GAO Hongxia, YU Jianzu
2015, 41(1): 38-44. doi: 10.13700/j.bh.1001-5965.2014.0049
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To solve the problem of temperature oscillation, even operation failure when loop heat pipe with single compensation chamber was subjected to acceleration force, the experimental setup was built for testing the performance of dual compensation champers loop heat pipe (DCCLHP) based on the centrifugal machine system with constant acceleration. The operational characteristics of DCCLHP were researched when it was subjected to acceleration force after reaching the steady state at gravity field. The influence of different heat load, acceleration value and direction on the performance was analyzed. The results show that the operation of DCCLHP can get to the steady state at 7 g acceleration field. The steady operation temperature at elevated acceleration field is lower than that at gravity field and the heat load and acceleration force have an impact on the decrease. It takes less time along the acceleration direction from compensation chamber 2 to compensation chamber 1 than in the opposite direction when it gets to the steady operation. Moreover, the temperature oscillations at the outlet condenser and liquid line occur as a result of the acceleration effect.
V-estimator with corrective term for K-distribution shape parameter
LI Dapeng
2015, 41(1): 45-49. doi: 10.13700/j.bh.1001-5965.2014.0054
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The V-estimator (VE) for K-distribution shape parameter proposed by Oliver in 1993, bears the characteristics of without solving non-linear equations so it has a high estimating efficiency, but the estimating accuracy of it is lower than that of many other moment estimators, sometimes the VE even results in odd value. In order to make the best use of the advantages and bypass the disadvantages, on the basis of derivation and analysis of the VE bias, by means of a set of Monte-Carlo experiments, the V-estimator with corrective term (VCE) was discussed, which overcomes the shortcomings above of the VE. Simulation results show that not only the estimating accuracy of the VCE is significantly superior to the VE, but also, on both of estimating accuracy and efficiency, to the U-estimator considered as the moment estimator with the highest accuracy usually. Especially, experiment results demonstrate that the VCE is better suited to performing in the case of small samples, this feature makes it possible that the VCE is more applicable to the practice.
Nonlinear dynamic behaviors of electro-hydraulic servo system under friction
ZHU Yong, JIANG Wanlu, ZHENG Zhi
2015, 41(1): 50-57. doi: 10.13700/j.bh.1001-5965.2013.0685
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With electro-hydraulic servo system as the research object, the influence laws of nonlinear friction on system dynamic characteristics were explored. Based on the principle of the nonlinear dynamics, the nonlinear dynamical model of system was established. Then, a conclusion was put forward that the effect of nonlinear friction could be described by Van Der Pol equation. The bifurcation phenomenon and typical nonlinear dynamical behaviors which implied within the system were revealed through numerical experimental analysis. Moreover, with the nonlinear dynamics methods, the measured dynamic data were thoroughly analyzed. And the “limit cycle oscillation” phenomenon caused by friction was revealed. The results indicate that the nonlinear effect of friction can cause nonlinear vibration occurred in system working process. The influence of friction on system dynamic characteristics cannot be ignored. The nonlinear effect of friction should be taken into account in system modeling and dynamic characteristics research.
Dynamic modeling for a morphing aircraft and dynamic characteristics analysis
ZHANG Jie, WU Sentang
2015, 41(1): 58-64. doi: 10.13700/j.bh.1001-5965.2014.0048
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The physical model of a variable-span variable-sweep morphing aircraft was simplified. Based on Kane's method, the morphing movements were assumed to be controllable known input, and the wings' movements were expressed by constraint equations. The six components of the translational velocity and the angular velocity of the morphing aircraft's body in the body coordinate frame were selected as the generalized speeds. Six degree-of-freedom dynamic model was built. Additional forces and additional moments were defined to describe the dynamic influence imposed on the morphing aircraft by the morphing movement. The simulation results show that, in the condition of steady-state flight, the additional forces and moments cased by the wings' morphing are small compared to the variations of aerodynamic forces. The aircraft's longitudinal dynamic responses during the morphing process are simulated and analyzed at different morphing speeds. Results show that the aircraft's height, velocity and pitch angle will change considerably during morphing process.
Fast Bayesian DOA estimator using continuous ant colony optimization
JIAO Yameng, HUANG Jianguo, HAN Jing
2015, 41(1): 65-70. doi: 10.13700/j.bh.1001-5965.2014.0051
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For the effectiveness of the ant colony optimization algorithm for solving high-dimensional nonlinear search problem, a Bayesian maximum posteriori direction of arrival (DOA) estimation fast algorithm based on the ant colony optimization algorithm (ACO-Bayesian) was proposed. This algorithm adopts Bayesian maximum posteriori probability function as the objective function of the ant colony algorithm, exploits a weighted sum of several one-dimensional Gaussian functions in the sampling process. The global maximum of Bayesian spatial spectrum function can be reached after reasonable iterations. Simulation results show that the proposed algorithm provides similar performance to that achieved by Bayesian estimator, but its computational complexity cost is only 1/14 of original method. The water tank experiment results verified the correctness and validity of the proposed ACO-Bayesian method, which promote them to promising in engineering applications.
Method to estimate the Doppler parameters of moon-borne SAR using JPL ephemeris
DING Yixing, GUO Huadong, LIU Guang
2015, 41(1): 71-76. doi: 10.13700/j.bh.1001-5965.2014.0053
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Compared with the low earth orbit synthetic aperture radar (SAR) system, the moon-borne SAR is distinct from its unique imaging geometry, so the Doppler parameters estimation method is different from conventional pickaback and satellite-borne SAR. Precise jet propulsion laboratory (JPL) ephemeris was used to interpolate the position, velocity and acceleration of lunar barycenter as well as the libration in geocentric inertial coordinate system. Then the position, velocity and acceleration of an object at any selenographic coordinates were able to be acquired via the coordinate transformation. Based on this, two quadratic equation sets were put forward to calculate the beam direction at any off-nadir angle and squint angle, and to solve the modulus value of line of sight, then coordinating the footprint center. Simulation results show that the beam angle needs a continuous adjustment along the orbit to point the earth disk in moon-borne SAR case, and the antenna position displacement leads to a significant shift on the Doppler parameters.
Maneuvering target tracking with modified unbiased FIR filter
FU Jinbin, SUN Jinping, LU Songtao, ZHANG Yaotian
2015, 41(1): 77-82. doi: 10.13700/j.bh.1001-5965.2014.0068
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In the field of maneuvering target tracking, the performance of Kalman filter(KF)and its variants is dependeds on the accuracy of the assumed process noise statistics. If the assumed process noise is not accurate, the performance of the KF and its improved algorithms will be degraded significantly. In some cases, the filters might even cannot be converged. Unbiased finite impulse response (UFIR) filter does not need the prior knowledge of the process noise statistics during filtering. Hence, it can be utilized to overcome the problem of the inaccurate assumed process noise statistics to realize the maneuvering target tracking. Since the generalized noise power gain (GNPG) of the existing UFIR filter cannot be adapted to the measurements innovation, an improved UFIR filter was proposed. The proposed UFIR dynamically adjusts GNPG according to the ratio of measurements innovations between the adjacent time such that it can improve the detecting ability of the UFIR filter for target maneuver. The simulation results illustrate that if assumed process noise is accurate, the performance of the existing UFIR filter and the proposed FIR filter is similar to KF; but if assumed process noise is not accurate, the performance of the proposed UFIR shows better than the other ones.
Hybrid iteration sliding mode control for ultra-low altitude airdrop level off
LIU Ri, SUN Xiuxia, DONG Wenhan
2015, 41(1): 83-89. doi: 10.13700/j.bh.1001-5965.2014.0020
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For the ultra-low altitude airdrop level off stage, many uncertain factors such as ground effect, sensor measurement errors and low altitude airflow interfere the precision of trajectory tracking, which exert serious threats on the aircraft safety and mission performance, a hybrid iteration sliding mode flight controller was designed. In the first order sliding mode, a global dynamic switching function was adopted, which eliminated the reaching stage of sliding mode and ensured the whole response robustness. In the second order sliding mode, a nonlinear integral switching function was adopted and the overshoot caused by the integral term was brought to the first order sliding mode, so not only the tracking accuracy was guaranteed but also the dynamic performance was improved. Lyapunov stability theory and Barbalat lemma analysis show that the flight control law can completely reject constant model perturbation and disturbances, and can control the upper bounds of the steady errors with dynamic model perturbation and disturbances. Simulation results confirm the robustness and ascendant tracking performance of the proposed approach.
Method of testability evaluation using hierarchical testability model
YIN Yuanwei, SHANG Chaoxuan, MA Yanheng, LI Gang
2015, 41(1): 90-95. doi: 10.13700/j.bh.1001-5965.2014.0029
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The layered and modularized design is always used in complex electronic equipment, where the maintenance level and test requirement are both characterized by hierarchy configuration. Therefore, a novel evaluation approach was presented based on hierarchical testability model. The multi-signal flow graph model has ability to present multi-fault factors, according to the hierarchical classification based on maintenance level and physical structure of equipment, the multi-signal flow graph model could be established for each level respectively. For any part which can't be tested or maintained, the multi-signal flow graph model would be established on lower level; thereby the hierarchical testability model was built up. The hierarchical dependence matrix was obtained based on above model, and then the testing level of equipment on each maintenance level was obtained by using the mathematical model of testability evaluation. The analysis results of example prove that this method could effectively evaluate the testability levels of equipments in different situations, at the same time this method could provide available guidance and assistance for the design of testability and maintenance.
Intelligent decision-making algorithm based on bounded FART-Q
ZHOU Yanan, GONG Guanghong
2015, 41(1): 96-101. doi: 10.13700/j.bh.1001-5965.2014.0076
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Fuzzy adaptive resonance theory (ART) with bounded side length was proposed to address the problem emerged while applying fuzzy ART to intelligent decision-making. Integrating the modified fuzzy ART and Q learning algorithm, bounded fuzzy ART-Q learning (FART-Q) intelligent decision-making network was built. The original fuzzy ART might make unreasonable classifications only according to the fuzzy similarity between input vector and weight vector, without considering the physical meaning of the state variables. To solve this problem, a modified algorithm was proposed, strengthening the resonance condition of fuzzy ART with bounded side length. The improvement made it possible both to limit the side length according to the physical meaning of the state variables and to reduce the number of categories. The minefield navigation simulation was conducted to verify the availability and effectiveness of bounded FART-Q. Compared with the original fuzzy ART, the modified algorithm is able to make classifications more reasonably with higher success rate and less operation time.
Modeling and reinforcement decision analysis in air force combat based on data link
NIU Dezhi, CHEN Changxing, XU Haoxiang, LI Yongbin, WANG Zhuo, CHEN Qiang
2015, 41(1): 102-109. doi: 10.13700/j.bh.1001-5965.2014.0130
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Force change problem during air combat course was studied. First of all, operation ability index of aircraft was converted to average combat level. Furthermore, in view of data link's influence on air combat and reinforcement force's joining to original force, differential equation model of every force changing which was represented by variety of aircraft number was set up based on Lanchester equation. Then numerical computation method of the model was given, and what time step should meet in discrete computation was pointed out. According to different reinforcement mode, the model was extended to different representation forms. Simulation experiment shows there is effective reinforcement time range if reinforcement force was joined in air combat, reinforcement only in one time and reinforcement with constant deceleration have merits on time. High reinforcement efficiency of the two reinforcement mode was illustrated by constructing the judgment function, which provides one new thought for air combat application and decision making.
Offline signature verification based on ASIFT
TANG Youbao, BU Wei, ZHANG Enze, WU Xiangqian
2015, 41(1): 110-116. doi: 10.13700/j.bh.1001-5965.2014.0453
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A novel offline signature verification method based on the affine and scale invariant feature transform (ASIFT) was proposed by analyzing the existing local invariant features and the property of the disguised signature. The method consists of the following steps, the preprocessing including image graying and resizing was performed on the signature images; the key points were detected and the corresponding descriptors were extracted from the processed images; the descriptors extracted from the query and reference images were matched and the random sample consensus (RANSAC) algorithm was used to refine the matched result. Then the average distance was computed according to the distances between the descriptors of the correct matched points. The verification decision was given by comparing the average distance and the number of the correct matched points with the thresholds. The proposed method was evaluated on a public signature dataset including the disguised signatures and the experimental results show that the proposed method outperforms the state-of-the-art algorithms with reducing the equal error rate (EER) by 5%.
Video encryption algorithm of content associated key
WANG Wei, HUANG Hao, XIE Changsheng, HAN Lin
2015, 41(1): 117-123. doi: 10.13700/j.bh.1001-5965.2014.0459
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With the development of computer technology and video, display technology, there are new requirements of video encryption algorithm. A video content associated key concept was proposed and used in the encryption of video after the research of current video encryption algorithm's defects in video copyright protection technologies. The extraction algorithm which used the motion vector prediction residual as sensitive data extracted the sensitive data from the plaintext video. The extraction algorithm effectively destroyed the video quality within 10% sensitive data extraction ratio. In order to prove the effect of extraction algorithm, the video quality measurement algorithm of peak signal to noise ratio (PSNR) and structural similarity index measurement (SSIM) was used to assess encrypted videos with different video contents and parameters, and proved the performance by performance analysis and comparison with other algorithm. The experiment results show the validity and consistency of video encryption algorithm based on the content associated key.
Synchronizing compensation control of electro-hydraulic load simulator using command signal of actuator
HAN Songshan, JIAO Zongxia, SHANG Yaoxing, WANG Chengwen
2015, 41(1): 124-132. doi: 10.13700/j.bh.1001-5965.2014.0052
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Electro-hydraulic load simulator is a typical case of the force (torque) servo system which is strongly coupled with a hydraulic position system. How to eliminate the extraneous torque from motion disturbances is the key difficulty in electro-hydraulic load simulators. Based on theoretical analysis of traditional synchronizing compensation controllers, the improved synchronizing compensation algorithm was put forward. This algorithm can make full use of actuator's velocity command signal and load simulator's torque feedback signal, which does not need actuator's velocity signal, acceleration signal and servo-valve current signal. Due to utilizing load simulator's torque feedback signal, it can effectively eliminate the extraneous torque and achieve a more accurate synchronizing compensation than traditional velocity synchronizing controller in big gradient loading conditions. The comparison results based on simulations and experiments show that this algorithm is more effective to eliminate extraneous torque from motion disturbances and improve the dynamic torque tracking accuracy in various typical operating conditions.
Dynamic flight stability of a model dronefly in hovering and forward flight
XU Na, SUN Mao
2015, 41(1): 133-140. doi: 10.13700/j.bh.1001-5965.2014.0069
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Insects usually keep hovering or forward flight. Thus the dynamic stability of the two types of flight is significant to study the insect flight. The dynamic flight stability of a model dronefly in hovering and forward flight was studied. On the basis of an averaged model and the small disturbance theory, the linearized equations of longitudinal and lateral motion were given. The method of computational fluid dynamics was used to compute the aerodynamic derivatives and the eigenvalue and eigenvector analysis was applied to solve the equations of motion. The experiment results reveal that at hovering, the longitudinal and lateral disturbed motion both includes the unstable mode, therefore hovering is unstable. At forward flight, for the longitudinal motion, the time for initial disturbances to double for the unstable mode is decreasing, and the instability of the longitudinal motion is increasing; the instability of the lateral motion decreases to a weakly or neutrally stable mode. The forward flight of dronefly is unstable.
Flow rate of nitrogen-rich air and influence factors for onboard air separation unit
SHAO Lei, LIU Weihua, FENG Shiyu, GU Yuankang, LIU Weipan
2015, 41(1): 141-146. doi: 10.13700/j.bh.1001-5965.2014.0080
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The flow rate of a certain type onboard air separation unit to produce the nitrogen-rich air related with the flight height, inlet pressure, temperature and the nitrogen concentration was experimentally studied on a test apparatus. An empirical correlation to predict the flow rate of the nitrogen-rich air was obtained and verified via the polynomial fitting method and experimental data. In addition, the influence factors affecting the flow rate were investigated and the variation of the flow rate along the entire flight profile was calculated. Results indicate that, the obtained empirical correlation has high prediction accuracy; the flow rate of the nitrogen-rich air along the flight profile could be calculated based on the present mathematical model; under a constant pressure, temperature, flow rate of the nitrogen-rich air is reversely proportional to the nitrogen concentration, so when nitrogen concentration increases, the flow rate decreases; especially, the effect will be larger under the higher inlet temperature and pressure; the flight height, pressure, temperature are proportional to the flow rate, and the lower nitrogen concentration, higher flight height, temperature and pressure will bring larger impact on the flow rate. The research results could be beneficial to the design of fuel tank inert system.
Aeroelasticity quick analysis method of very propeller/flexible wing system
XIE Changchuan, ZHANG Lijuan, LIU Yi, YANG Chao
2015, 41(1): 147-153. doi: 10.13700/j.bh.1001-5965.2014.0025
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The propeller's revolving slipstream passing wing changes the drag/lift property of the wing. For the hyper long endurance unmanned flight vehicles design, the slipstream effect should be analyzed for the aeroelasticity of the very flexible wing. The Prandtl revised blade element-momentum theory was applied to calculate the aerodynamic parameters and in-plane loads (1P loads) of the slipstream. Then a Rankine vortex core was placed along the propeller's installation axis to simulate slipstream's induced effect on the wing. Further, the 3-D lifting-line method was utilized to calculate the steady aerodynamic loads of the curved bending wing. And the generalized surface splines and large deflection interpolation method were adopted to solve the geometrical characters of structure/aerodynamic coupling problem. Coupling with the nonlinear finite element method of the structure, the iterative approach was constructed for the solving of propeller's slipstream, 1P loads and the static aeroelasticity of very flexible wing. Finally, a validation study of a very flexible rectangular wing with one propeller was carried out using the method constructed. The numerical results show that the revolving slipstream changed the local incidence angle of a wing, thus changing the aerodynamic forces and deformation distribution. And in the small advance ratios situation, it has greater influences. The results demonstrate the applicability of this method in early stages of aircraft design.
Estimation of target's acceleration based on empirical wavelet transform
CHEN Hao, GUO Junhai
2015, 41(1): 154-159. doi: 10.13700/j.bh.1001-5965.2014.0036
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Target's accelerations lead to spectrum shift and broadening of target's echo signal, resulting in the inaccuracy estimation of target's Doppler frequency with traditional pulse radar velocity measurement method. To overcome the effect of acceleration on pulse radar velocity measurement, an empirical wavelet transform (EWT) based radial acceleration estimation method was proposed. The instantaneous frequency of the echo signal can be extracted through EWT and energy-oriented principal frequency components extraction method. The high order coefficients of the phase were obtained through robust least square fitting on the instantaneous frequency, which correspond to the radial velocity and radial acceleration respectively. After compensating the echo signal with estimated accelerations, the Doppler frequency of echo signal can be accurately estimated. Simulations show that the EWT method is a fast algorithm with high estimation accuracy, and the estimation error is close to Cramer-Rao lower bound. Applying EWT method on measured pulse radar data of high speed vehicle, the estimated acceleration error is smaller than 0.4 m/s2. EWT method is applicable in real time pulse radar acceleration estimation.
Trajectory optimization of two aircrafts in collaborative passive target tracking
RAN Huaming, ZHOU Rui, WU Jiang, DONG Zhuoning
2015, 41(1): 160-166. doi: 10.13700/j.bh.1001-5965.2014.0039
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To solve high accuracy requirement in collaborative passive tracking of two aircrafts, according to the geometric situation of the two aircrafts to the target, the effect of the geometric situation to the passive detection accuracy was analyzed, the formula of position dilution of precision (PDOP) was presented, the optimal geometric configuration of two aircrafts was obtained. A control structure of two aircrafts' collaborative passive target tracking system was presented, extended information filter (EIF) was used to estimate target state, maximizing the information entropy was used as the optimal performance index for trajectory optimization, receding horizon optimization (RHO) was used to control aircrafts' motion in real-time. The simulation results demonstrate that this trajectory optimization algorithm can make aircrafts fly with the trajectory which meet the optimal geometric configuration, illustrate the validity of the optimal geometric configuration based on PDOP, reduce location estimation error of target, and improve the collaborative passive tracking precision of two aircrafts.
Decomposition and coverage of multi-UAV cooperative search area
YU Sinan, ZHOU Rui, XIA Jie, CHE Jun
2015, 41(1): 167-173. doi: 10.13700/j.bh.1001-5965.2014.0056
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Coverage search of multi aircraft is a major task for unmanned aerial vehicle (UAV). After dividing the searching area, the problem turns into single UAV coverage search problem in each sub-area. This method will make the whole search problem simpler. The parallel searching strategy was analyzed in detail. Using the parallel searching strategy, the bases of determining the beginning point, turning key points and the ending point was given. This strategy enabled 100% coverage in the search area. The minimal turning radius impacts search path and different situations were discussed. The convex polygon search area was decomposed using a method based on the initial position and the percent of search area of each UAV. Based on the characteristic of UAV searching, the decomposition result was mainly assessed by the quantity of turning. The path from initial position to the search beginning point was discussed. Finally, the simulation result proves this method is feasible.
Analysis method of iGPS measurement uncertainty spatial distribution
SUN Fulong, ZHAO Gang, WANG Wei, CHEN Lei
2015, 41(1): 174-180. doi: 10.13700/j.bh.1001-5965.2014.0044
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The spatial distribution of iGPS measurement uncertainty was studied to help rapid assessment and layout optimization of iGPS measurement. According to the measurement model of iGPS, a typical two-station model of measurement uncertainty was established. Furthermore, a universal analysis method of iGPS measurement uncertainty distribution was proposed and modified in accordance with transmitter coverage. This method is applicable to diverse iGPS measurement environment with an arbitrary number of the transmitters in different layouts, and can be used to calculate the measurement uncertainty at any spatial point. Real measurement environment with two stations and four stations were established respectively. The distribution of actual measured deviations corresponded to the numerical simulation results. This analysis method was proved effective to describe the measurement uncertainty distribution pattern of iGPS.
Simulation on stealth characteristics of X-tail near space airship
XIAO Houdi, LIU Longbin, LÜ Mingyun
2015, 41(1): 181-186. doi: 10.13700/j.bh.1001-5965.2014.0047
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Abstract:
In order to reduce the radar cross section (RCS) of near space airship, the effect on the RCS of near space airship was studied, when its X-tail has different deformation angles. The RCS character effect of head, side and tail in the near space airship was simulated, when X-tail has different deformation angles based on physical optics method. Physical optics and multilevel fast multipole method (MLFMM) were applied to simulate the RCS of contrast ball, and the results show that the physical optics method is accurate and appropriate. The simulation results show that the X-tail angle on different deformation has less influence on head RCS of airship, but has great influence on side RCS of airship. The side RCS reduced to 13.7% when deformation angle changed from 0 ° to 20 °. The deformation of X-tail can significantly improve the performance of near space airship lateral stealth, while increasing the other direction RCS.

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