Abstract:In view of the effects of the vertical deflection on trajectory impact accuracy, the influence mechanisms of the vertical deflection on the launching coordinate system, the initial parameter, the force during the flight, the control criteria of the program angle, and the trajectory parameter under the geocentric coordinate system were analyzed respectively by combining with the particle dynamics model of the ballistic vehicle. Then, the mathematical models of the effects of the vertical deflection were established. Furthermore, based on the given computing method of trajectory impact deflection and taking a flight trajectory as example, the impact errors under different geodetic latitude of launch point and different launch azimuth angle were presented quantitatively. The research is of great reference value in the aspect of the improvement of the impact accuracy for the ballistic vehicle.

Abstract:The dual quaternion was used to investigate the 6-DOF (six degree-of-freedom) relative motion of spacecraft, and an integrated controller of attitude and orbit with input saturation constraint was designed. Firstly, the dual number and dual quaternion followed by the derivation of 6-DOF relative motion of attitude and orbit coupled model were introduced. Then, an explicitly bounded controller was proposed by using the property that the absolute value of hyperbolic tangent function was less than 1. Two coupled adaptive regulators were respectively designed to adjust the outputs of the controller dynamically. Thirdly, it is proved by a rigorous theoretical analysis that the closedloop system is globally and asymptotically stable. Finally, numerical simulation experiment is implemented to demonstrate the validity and effectiveness of the proposed controller. Experimental results show that both the obtained control torque and control force satisfy the given constraints, the 6-DOF relative motion of spacecraft can be controlled accurately and the method is robust to parameter uncertainties and external disturbance. Compared with other methods, the proposed method has the following advantages: the convergence rate is faster, the max magnitude of output control torque and control force are both smaller, and the consumed energy is less.

Abstract:To clarify the physical essential, a perspective of force balance to dynamic soaring was put forward. Equilibrium equations were derived according to physical laws. The solution of the equations solved mathematically formed a curve. Simulations of the curve were made in the cases of an albatross and an unmanned air vehicle in different wind gradients for instances. The results of analysis and simulation indicate that the curve is the velocity set that satisfies the equilibrium equations; the curve consists of a climbing branch and a diving one; the climbing branch exists only if the gradient is sufficiently large, and it is critical to dynamic soaring.

Abstract:In some fields of computational fluid dynamics, the nearest distance from a certain point in the flow field to the wall surface is usually required. In order to improve the precision as well as the efficiency of the computation result, the KD tree method was applied to the wall distance computation of unstructured mesh, and then the wall distances of several three dimensional configurations were computed. Results show that the method computing wall distances based on KD tree can achieve the capability of great robustness, high efficiency and precision, and is suitable for complex configuration. Besides, the method has good universality so that it can be applied to many other types of mesh.

Abstract:Mathematical models of lunar and Earth shadow were established for lunar orbits. Also, the criterion was proposed to decide whether the satellite was in the shadow area. Golden section search optimization was used to search out the boundary values of the shadow area. In combination with specific cases, the optimal targeting lunar orbit was given by the genetic algorithm which was embedded in tabu search. The mathematical models of lunar orbit shadow given out in this article are simple enough to be used in onboard computer. Meanwhile, they can meet the engineering accuracy requirements. The embedded genetic algorithm has advantage of fast convergence without trapping in local optimum.

Abstract:A closed-loop linear covariance analysis method was proposed for orbital rendezvous using AON (angles-only navigation). The SRUKF (square root unscented Kalman filter) based on AON algorithm was constructed and the observation sensitivity matrix was further calculated. The multi-impulsive Hill guidance law was employed to derive the closed-loop linear covariance analysis model. The results of the numerical simulation indicate that the closedloop linear covariance analysis result fits the 1000 times Monte Carlo shooting well. The covariance analysis method is applicable to the traditional EKF (extended Kalman filter) based on the AON method, but has an estimation bias along downrange, which is equivalent to the variance of trajectory dispersion. The major axis and minor axis of error ellipse achieved with EKF based on covariance respectively are about 24.68% and 20.56% longer than the results from SRUKF based error ellipse. Besides, SRUKF and EKF have the same order computational burden for the state estimation, but the SRUKF is about 10% faster than the EKF due to using two powerful linear algebra techniques, QR decomposition and Cholesky factor updating.

Abstract:A near space atmospheric density detection method based on hypersonic reentry sphere was proposed with the aim of overcoming the shortages of current detection methods, such as the low accuracy, the high cost and the weak time-space conformity. The measurement error was analyzed according to the kinematic equation of reentry sphere. The results show that the atmospheric density below the height of 90 km can be detected with the accuracy level below 6%. The antenna placement scheme was determined by analyzing the 6-DOF (degree of freedom) motion model of the sphere with eccentric balancing weight and combining with the numerical simulation of aerodynamic heat. Numerical calculation of heat conduction along ballistic trajectory for the eccentric sphere with double radome was achieved and the thermal protection scheme was performed eventually to demonstrate the feasibility of this detection scheme. The proposed detection method of atmospheric density can provide a meaningful reference to the construction of highaccuracy nearspace atmospheric density.

Abstract:Due to the guidance law with terminal intercept angle and payload constraints which can cause big engorge loss, a guidance law considering maneuvering efficiency constraint was proposed. A closed-loop sub-optimum guidance law with time-varying control weight coefficient considering first-order missile dynamic characteristics was elicited according to the optimal quadratic theory; The drag coefficient was introduced into the time-varying control weight coefficient, and the constraint boundary of maneuvering efficiency through iterations was obtained; the time-varying weight coefficient was changed into function of time-to-go and delay time, and the trajectories with guidance law considering maneuvering efficiency was emulated. Results indicate that, for constant velocity and maneuvering target, the new guidance law and the guidance law with payload constraint can meet the requirement of trajectory shaping when compared with the guidance law with intercept angle, and the acceleration command of guidance law with constraint considering maneuvering is more reasonable. And the new guidance law can reduce the velocity loss and avoid the payload saturation at the same time, and enhance the guidance accuracy and damage effect. Moreover, it is not necessary to balance solutions of time-varying weight coefficient, so the iteration speed will be improved when accuracy is guaranteed.

Abstract:Considering the urgent need of rapid trajectory generation of boost-glide missile in mobile condition, seven key parameters of control variables were selected as the firing data, and the corresponding iterative calculation algorithms were proposed. The full-range trajectory was divided into the boost phase, initial phase, glide phase and dive attack phase, all these flight phases were described in a unified dynamics model. Firing data in different phases were calculated rapidly one by one, and multiple constraints were satisfied strictly, with the help of the parameterized iterative algorithm. Furthermore, a partly recalculation mode which uses the firing data of the center trajectory in the boost phase and recalculates the others was proposed on the basis of the full mode. The simulation results indicate that this method can achieve a great performance in the quick attack to a ground stationary target in mobile condition.

Abstract:Aerodynamic configurations in the conceptual design of a near-space HSUAV (high supersonic unmanned aerial vehicle) were investigated. To accelerate the aerodynamic configuration design process, a set of tools for the aerodynamic configuration design and analysis, including the parametric geometry modeling code, the grid generation script, the flow field analysis software and the aerodynamic result analysis code, were developed. Following the request for proposal of the HSUAV, an aerodynamic configuration for the HSUAV, in which the wing was integrated into fuselage, was proposed. The wing used a double-wedge airfoil, and the empennage was in V tail. In order to meet the requirement of the air mass flow captured by the inlet, the straight leading edge of the HSUAV was modified into the arched leading edge. Numerical simulation method was employed to evaluate the aerodynamic characteristics of the HSUAV configurations with different wing aspect ratios and dihedrals. Based on the evaluations, the most suitable wing aspect ratio and dihedral were selected, and the final aerodynamic configuration for the HSUAV was obtained. The viability of the final aerodynamic configuration of the HSUAV was verified by the detailed flow field analysis.

Abstract:Considering the suppression of transmitting deceptive jamming in radar countermeasure, a discrimination method based on frequency diversity array was proposed. In FDA(frequency diversity array) radar, the phase difference between different element of echo was dependent on both range and angle，which implies that the false targets could be suppressed due to the mismatch in either range or angle. The phase difference formula of echo, jamming and mixed signal were derived, the influence on the phase difference of matched filtering, frequency shift and signal mixing was analyzed in detailed, and the entire identifiable process was introduced . The effectiveness of our proposed scheme in suppressing jamming was demonstrated via theoretical analysis and computer simulations. Results show that the proposed method can discriminate false targets successfully in different scenarios and has a better environmental adaptation.

Abstract:A self-optimizing iterative classification method based on image segments which classifies high-resolution remote sensing images by acquiring training samples through semi-supervised fuzzy Cmeans and designing the self-optimizing iterative classifier based on support vector machine was proposed. Image segments could be obtained by fractal net evolution approach and a few labeled samples were selected; based on labeled samples, image segments were clustered by semi-supervised fuzzy C-means clustering method and then training samples could be obtained by intensity filtration from clustering results; the self-optimizing iterative support vector machine was designed to carry on classification iteratively until the classification requirements were met and during the classification process, training samples were updated and optimized to improve the performance of the classifier by statistical analyses of the two adjacent classifications. QuickBird and WorldView images of Wuhan City were classified by the method proposed by this paper and the overall accuracy achieved 94.67% and 92%. In comparison with the overall accuracy of the classification with training samples selected by manual work, the regular support vector machine classification method and the least squares support vector machine classification method, the accuracy of the suggested method is obviously higher and the classification effect is better.

Abstract:Regarding the problem of systematic pseudorange bias in BeiDou navigation system application, the pseudorange observations quality of Beidou triple frequency was analyzed from the multipath angle. The analysis results verified that the bias was related to the type of satellite orbit, satellite elevation angle and the signal frequency. In order to eliminate the effects of this systematic bias, a correction model for triple-frequency pseudorange bias was established with the continuous piecewise linear function. Compared with the traditional correction model, the proposed model used the Beidou measured data from a longer range and considered the accuracy of information of corrections. The correctness and superiority of the proposed model were verified by the experimental results on the basis of the dynamic precise point positioning.

Abstract:Effective C/N₀(carrier-to-noise ratio) is an important index of GNSS (global navigation satellite system) receiver data demodulation and tracking performance. During past years, analysis of interferences effects on effective C/N₀ have been put forward. However, effective C/N₀ limits analysis hasn’t been presented. Thus, effective C/N₀ limits were analyzed. The theory model of effective C/N₀ and BER (bit error ratio) were derived in the presence of CWI(continuous wave interference), and results show that effective C/N₀ fails to evaluate data demodulation performance under specific condition. Then, the mechanism of effective C//N₀ malfunction was elaborated and the application condition of effective C//N₀ was presented. Finally, theory analysis is verified by simulations.

Abstract:For the rendezvous problem of the Lagrange vehicles with quantized data exchange and communication delay, a model-dependent and discontinuous right-hand side control algorithm was proposed, and a uniform quantizer was designed. The stability of controller was considered by using the graph, matrix theory, and the practical stability theory. It was shown that the rendezvous with error bound is rigorously proven in an undirected topology via quantized data exchange and communication delay. The numerical example based on MATLAB software also verifies the effectiveness of the algorithms.

Abstract:Aided by elevation information provided by height sensor, SAR (synthetic aperture radar) platform geo-location was realized by combining the high-precision image matching technology and the INS (inertial navigation system) drift correction method. According to the fact that the platform is on the centerline of SAR image at the middle imaging time, some points on the centerline of a single image were equably selected to conduct the high precision matching with the optical reference image. The projection position of SAR platform on the horizontal plane was calculated and the spatial position was positioned by making use of the elevation information. By use of the position results of sequence images, the drifting parameters of INS were estimated and then the outputting position data were corrected to achieve the high-accuracy platform geo-location. The impacts of different errors on location precision were analyzed and the precision estimation formulas were derived. Both simulation and real data test results show high precision and practical value for engineering of the proposed method.

Abstract:The length of physical slot is stationary in the time division duplex mode of the Massive MIMO system. Consequently, the length of the allocated physical slots cannot be adjusted according to different lengths of coherence intervals. The mismatch between slot and coherence leads to a waste of the time-frequency resource. Therefore, the whole network capacity of the system is not optimal. A variable-length slot allocation scheme based on hierarchical users was proposed to make the allocated physical slots match their corresponding coherence intervals well. In the proposed scheme, terminals were divided into different categories according to their mobility, and variable length slots were assigned to terminals in different categories flexibly. So the waste of time-frequency resource waste and the excessive channel estimation can be alleviated. The resource efficiency and the sum rate of the system are verified to be optimized and the simulation validates the proposed scheme. 

Abstract:Avoiding or tracking aerial targets for UAVs (unmanned aerial vehicles) can be regarded as a nonlinear motion guidance and control problem. In such kind of tasks, both of UAVs and targets have high maneuverability and time sensitivity. According to these characteristics, a motion guidance method in fine time based on Lyapunov stability theory was proposed. A framework for solving the two problems was constructed, then collision avoidance and maneuvering target tracking problem were transformed into reaching virtual target and rendezvous problem respectively. The problem of collision avoidance of UAVs was converted into the control problem of realizing parallel navigation, and then the guidance law was designed using the Lyapunov stability theory. For the problem of tracking maneuvering target, the guidance law was designed according the requirement of rendezvous based on former guidance law. The simulated experiments in a Gazebo platform were conducted, and results showed that the proposed method can effectively avoid larger maneuver overload for UAVs, thus having better adaptability for time-varying and parameters.

Abstract:A coupling control strategy was proposed for the BTT (banktoturn) flight phase of hypersonic vehicle, according to the strong coupling among the channels of pitch, yaw, and rolling. Based on the nonlinear generable predictive control method, a hierarchy-structured predictive controller was designed and analyzed for rotation motion dynamics of a generic hypersonic vehicle, which has the characteristics of fast variability, high nonlinearity, and uncertain parameters. After analyzing the main influence factors and their effect laws during the BTT flight phase, a coupling control strategy called “decrease angle of attack—rolling fast—increase the angle of attack again” was proposed. Simulation studies were conducted to investigate the feasibility of the proposed control strategy for the hypersonic vehicle. The simulation results demonstrate that the proposed control strategy lowers the control requirement of yaw channel, lowers the probability of being out of control in the BTT flight phase, and increases the reliability of the control system.

Abstract:A novel terminal guidance law based on stochastic fast smooth second-order sliding modes control theory was proposed to handle the track imprecision mainly caused by stochastic maneuvering of the target, inertial lag, and model uncertainties. It is assumed that the target acceleration term was a zero mean Gaussian white noise and the missile-interceptor guidance system became a stochastic uncertain nonlinear system driven by additive noise, which did not have any equilibrium. So a concept of finite-time second-order mean-square practical convergence was presented and the finite-time convergence property of proposed control was proved. Then the direct hit sliding mode manifold was chosen and the guidance law was designed. The applicability of the new guidance law was illustrated through simulations of a guided missile intercepting a stochastic maneuvering target in tail chase and headon intercepts case, respectively. Results show the validity and effectiveness of the proposed method, while a comparison is made with the augmented proportional navigation guidance law, the traditional sliding mode guidance law and smooth second order sliding mode guidance law.

Abstract:Due to the strong-nonlinearity and non-Gaussianity of the UAV (unmanned aerial vehicle) relative navigation system, the accuracy of the traditional relative navigation filter, which is designed based on the Kalman filtering algorithm, decreases or even diverge. In view of the advantages of HCKF (high degree cubature Kalman filter) and MCKF (maximum correntropy Kalman filter) in coping with nonlinear problems and non-Gaussian problems, respectively, the measurement update equation was modified by the measurement update method of MCKF, and the traditional measurement update problem was recast as a linear regression problem. In addition, the Gaussian assumption of the measurement noise was avoided, the system nonlinearity and measurement noise non-Gaussianity were solved at the same time. The simulation was conducted, and the simulation results indicated that RHCF is superior to HCKF and MCKF. Hence, the effectiveness of the proposed algorithm is verified.

Abstract:In order to determine the FCS (flight control system) performances which the WTBVFT (wind tunnel based virtual flight testing) can evaluate, and lay the foundations for designing the WTBVFT evaluation methods, the flight performance indexes and flight quality indexes of FCSs which WTBVFT can perform the work of evaluation were proposed according to the features of WTBVFT; the evaluation capability differences among the WTBVFT, the HILS (hardware-in-the-loop simulation) and the flight tests were compared; the differences of evaluation results between WTBVFT and free flight caused by the features of WTBVFT were analyzed; from the aspects of testing, data processing, and the performance determination, the specific requirements of the WTBVFT evaluation methods for evaluating the above indexes were proposed and the evaluation requirement differences among the WTBVFT, HILS, and flight tests were compared.

Abstract:Low-speed maglev train is suspended above the guideway by the electromagnetic force. Compared with the wheel train, the maglev train has the advantage of low noise, small turning radius and advanced climbing capacity. The system stability problem in the condition of output saturation was studied to avoid instability phenomenon caused by network voltage constraints so as to improve the reliability of the system. A single-point levitation system model of the maglev train was established and a stable levitation control algorithm was designed. Based on the analysis of the output saturation element of the levitation controller, a maximal ellipsoid searching optimization method was presented for controller parameters design. Parameter optimization is achieved without changing the design of the control algorithm. Simulation and experimental results show that the optimized controller can get better control results, which can be used for the guidance of practical system operation.

Abstract:Aiming at solving the existing drawbacks of indices of the Mahalanobis distance, an importance measure based on the Moore-Penrose Mahalanobis distance weighted by spectral decomposition was proposed. Through building the generalized matrix inversion of covariance matrix of multi-output and the spectral decomposition, the problems that the covariance matrix was be inversed and misidentification for lacking the adequate consideration about the relation among the multiple outputs were solved. Thus, the limitations of indices of Mahalanobis distance were overcome. The results of numerical examples and engineer instance show that the proposed importance measurement can accurately get the effects of input variables on the integrated performance of multi-output structure system, thus providing effective information for reliability design.

Abstract:A SWATH (small waterplane area twin hull) in head regular waves was investigated by experimental method. The influences of speed and vertical position of towing point on the seakeeping performance of SWATH were analyzed. The experimental results illustrate that: the transfer functions of both heave and pitch modes depict two peak values with the increase of wave length under different speeds; with the increase of advancing speed, the peak value of transfer functions of heave mode remains almost constant, while the peak value of pitch mode changes moderately; the motion responses with the towing point at center of gravity are slightly smaller than those with the towing point at the thrust axis during all wave lengths except the resonant zone at short waves.

Abstract:The harmonic balance method is one of the computational methods in frequency domain with a high computational efficiency, which has won special attention in present numerical studies of unsteady flow, and it has an obvious advantage especially for periodic unsteady flow problems. A harmonic balance method was used to simulate the forced pitching oscillation of the HBS(hyper ballistic shape) in different conditions, and then the coefficient of force and moment versus angle of attack were rebuilt. A comparison was made with the time domain method to investigate the performance of the harmonic balance method. Results show that the harmonic balance method is applicable to simulate middle and small amplitude pitching, and the computing time won’t be effected by the frequency. Therefore, the harmonic balance method has obvious advantage for problems with a long period.

Abstract:Coolant flow rate of fuel for scramjet exceeds stoichiometric flow rate in the high flight Mach number. In order to lower the coolant flow rate of fuel and implement the matching between coolant flow rate and stoichiometric flow rate, the potential working for the cooling fuel was analyzed by exergy method. The properties of the cooling of fuel at supercritical pressures determines the quantity of exergy. The exergy was calculated according to the distribution of scramjet wall’s temperature, scramjet wall’s heat flux, and the exergy equilibrium equation was given. It is concluded that the heat of scramjet wall is 562.4 kW and the exergy is 541.3 kW when the maximum temperature of scramjet wall is 1200 K. It is also concluded that the potential working is lowered while the coolant flow rate of fuel is increased and the output temperature of fuel is increased, and the potential working is not changed when the output pressure of fuel is increased.

Abstract:The material removal rate of HEP (hydrodynamic effect polishing) was mainly affected by the distribution of hydrodynamic pressure and shear stress on the workpiece surface, and the key process parameters were sought out accordingly. Based on the fluid dynamic simulation and experiment exploration, it investigated in detail how the material removal rate was affected by the wheel immersed depth, the wheel rotated speed and the polishing clearance. The analysis results show that the wheel immersed depth has little effect on the removal rate while the removal rate decreases along with the reduction of the speed and the increase of the polishing clearance. Considering the practical process condition, the optimal wheel immersed depth, speed and polishing clearance are （2/3）R, 300 r/min and 25 μm respectively. Meanwhile, the temperature stability of the polishing head was monitored, and it reached thermal equilibrium within 4 hours at start of the device. Therefore the stability of polishing clearance affected by the temperature can be guaranteed by idling with preheating section.

Abstract:Present work is focused on the investigation of the propagation characteristics of making wave on the free surface in finite depth water. On the basis of linear hydrodynamic theory, phase function was extracted from the integral representation of 3-D Kelvin source Green function in finite depth water. By adopting the stationary phase analysis method, the constant phase curves and propagation wave patterns were investigated at subcritical and supercritical speed zones respectively. Results indicate that the far field wave systems are composed of transverse and divergent wave patterns if depth Froude number F_h<1. If F_h>1, only divergent wave patterns are found in the far field. The influence scope of propagating waves above can be determined by the Kelvin angle whose degree changes with depth Froude number and increases to 90 degrees near the critical depth Froude number F_h=1. Based on the geometrical parameters, such as ship model particulars, relative position of two ships and tank breadth, a discriminant method is proposed for two ship models advancing parallel in calm water of finite depth, which is taken the side wall effects into account in towing tank. In this discrimination method, the interferences of the reflected steady waves from the tank walls, which may act on both ships, are also considered. Under the experimental conditions, the side wall effects are examined in a two-model test.

Abstract:The BG(band gap) theory of PCs(phononic crystals ) is introduced into the structure design for equipment shell, and the cylindrical shell section of equipment was designed to be periodically composite material structure. Utilizing the model synthetic technology, the transmission characteristics of flexural vibration in the periodic and the non-periodic cylindrical shells are calculated and compared. Results show that, in the periodic shell structure, there exist several flexural vibration BGs; whereas in the non-periodic shell, these BGs will disappear. Further, a periodic cylindrical shell made of composite laminated material is constructed and its vibration properties of are investigated. As expected, the existence of BGs in such a periodic structure is guaranteed and flexural vibration transmitting in this system will be attenuated apparently. Finally, as for practical engineering application, vibration properties of a complex equipment shell of which has periodic section in it are studied. Calculation results reveal that the introduction of BG theory into the vibration control for engineered equipment shell is quite feasible, since the complex equipment shell with locally periodic structure always maintain the BG characteristics.