Abstract:Trajectory optimum design for flight vehicles using pseudo-spectral methods has been a hot research direction in recent years, but studies about the overview of this field are very few. Based on the systematic research of domestic and overseas related literatures, the basic principles of several pseudo-spectral methods which have a wide range of applications in aerospace field were expounded; the thoughts and formulas for transforming continuous optimal control problems into nonlinear programming problems were concluded; the applications of pseudo-spectral method in the trajectory optimum design for flight vehicles were summarized; the development directions of pseudo-spectral method and its application in trajectory optimization design for flight vehicles were discussed.

Abstract:Aiming at the near space airship, the natural convection characteristics of the helium inside an airship were simulated numerically. On the basis of the computational fluid dynamics method and user-defined function, external temperature boundary condition was imported into the wall grids. Under conditions of different steady states, the motion characteristics and influence regulations of gas natural convection inside the airship were analyzed by researching the characteristic parameters of flow field, such as distribution of pressure, temperature, speed. Besides, the unstable change process of natural convection was also studied preliminarily. The simulation results show that natural convection of helium inside a near space airship has some active influence on heat exchange of inside helium, but the influence is very weak on stressed skin and structural safety.

Abstract:The stratospheric airships generally act with the redundant control effectors, thus a control allocation approach based on generalized inverse was applied to the airship attitude control system and the weighted pseudo-inverse control allocation method was adopted on the basis of characteristics of airship control effectors. The simulation results of a stratospheric airship attitude control show that: the designed control allocation approach can realize the coordinated operation of redundant control effectors effectively and its control effect on attitude angle is good, which avoids the premature saturation of control surface when using single effector; the reasonable adjustment of control allocation weights can reduce energy consumption, enhance instantaneity and provide convenience in engineering.

Abstract:The high-aspect-ratio low-speed near-space aircrafts may undergo very large deformation during flight, so a high demand of moving mesh is required for the analysis method based on computational fluid dynamics. To this end, a moving mesh strategy for large deformation of the boundary was presented. The strategy which is based on the mapping interpolation method reflects the displacement of boundary mesh to flow field mesh using a certain kind of weight and then updates the position of mesh nodes. Inverse distance’s nth-power was chosen as the weighting factor and the influence of different weight index n on the mesh deformation was studied, then the analysis of some two-dimensional and threedimensional moving mesh cases was carried out. The results suggest that this method is capable of handling the large deformation and ensuring the quality of deformed mesh.

Abstract:Taking inflatable structures of stratospheric airships as the main study object, the minimum differential pressure and the stress of inflatable structures were computed according to its design theory and a finite element model of inflatable structure for stratospheric airship was established. On the basis of the model verification, nonlinear finite element method was applied to simulate inflatable structural performance so as to obtain the distribution and change laws of the deformations and stresses of inflatable structure with the variations of pressure load and gondola load. The effects of structural reinforcement devices on the stress and deformation of inflatable structure also were evaluated. The simulation results can serve as reference for the structural design of the stratospheric airship.

Abstract:Taking a ducted fan rotor as the study object, the reasons why open rotor and ducted rotor produce different lift were researched through the momentum theory. At the same time, the three-dimensional Navier-Stokes equations and SST k-ω turbulence model were used to simulate the complex flow around the open and ducted rotor, which was based on the sliding mesh method. It also analyzed their differences in lift coefficient, power coefficient and efficiency at different rotating speed. The duct restrains tip vortexes and reduces energy wastage markedly, which make the lift coefficient increase 23% and the radio of lift and power coefficient augment 40%. Efficiency is obviously improved and the required power coefficient is slightly increased to 0.05. The results coincide with the theoretical analysis.

Abstract:The inflatable wing is a good innovational conception for the near space solar-powered aircraft. The problems of configuration characteristics and aerodynamic analysis of inflatable wings were taken as the aim of the current study. First, configuration characteristics were analyzed and designed. Then the model of 3d network inflatable wing was developed. With computational fluid dynamics method, aerodynamic performances of 2d inflatable wing profile and 3d network inflatable wing were studied. Numerical simulation result shows that the aerodynamic performances of 2d inflatable wing profile and 3d network inflatable wing have reduced slightly at the design Reynolds number. Meanwhile, with the structure of flow field and mechanism analysis, the reason for the total drag coefficients of inflatable wings increasing significantly lies in that, in those bumpy areas of the inflatable wing, vortexes which cause the friction drag has a reduction in some extent, but the pressure drag has a significant increase, so the total aerodynamic performance decreases.

Abstract:In order to simplify the description of the problems and to be convenient for mathematical manipulation, a series of hypotheses about the dynamic glide problem of unpowered aircraft were made. Under these hypotheses, a dynamics model of dynamic soaring, which is a 3-dimentional ordinary differential equations in the velocity space with a single input, was built. The largest growing area of mechanical energy in this velocity space, which is called energy-gained spindle, was obtained theoretically and the maximum rate of energy increasing was also deduced. The conclusion that the larger wind gradient, the smaller drag and the smaller area-mass ratio are more in favor of gaining energy for the engines aircraft gives a deeper understanding of the dynamic soaring energy and it can help the practice. 

Abstract:Minimizing the total weight of a stratospheric airship reflects the design object of lowest total cost to a certain extent. To meet the power requirement of payload is the springboard and goal for the conceptual design of the airship. The model of paving solar cells on curved surface and the model of energy-closed loop during day and night were introduced in the parametric modeling of the airship. The particle swarm optimization algorithm was used to optimize the parameters of the outside size. The design object is to find a feasible airship which has minimum total mass and satisfies the constraints with three balances: the diurnal balance between the energy supply and the energy requirement, the balance between mass and buoyancy, and the balance between drag and thrust. The sensitivity of the optimization results with different requirement of payload power and payload specific power was analyzed. The analysis results show that: the total airship weight increases linearly with the payload power; the total airship weight decreases steeply with the payload power density, but the change rate of the total weight also decreases and the total weight tends to be stable. The results of energy system simulation indicate the validity of the conceptual design method, as well as the critical characteristics of the design results.

Abstract:The aerodynamic shape, overall design and operation principle of stratospheric airships are different from the conventional aircrafts such as airplane and missile, and the flight mechanism. The dynamics characteristics of the stratospheric airship are different from the conventional aircrafts. Therefore, the inherent mechanism and characteristics of the stratospheric airship need to be further investigated. The linearization equations of motion for stratospheric airship were derived by using the “small disturbance” theory, which could be divided into longitudinal motion and lateral-directional motion. The fight modes and mode parameters were defined, and an analytical method was proposed to analyze the flight dynamics. Flight modes of the stratospheric airship were investigated based on eigenvalue and eigenvector of the state equations. Results show that the longitudinal motion includes three modes: heave mode, surge mode and pendulum mode, whereas the lateral motion includes another three modes: yaw mode, sideslip mode and roll oscillation mode.

Abstract:Fast independent component analysis dimensionality reduction for hyperspectral image needs a large amount of matrix and iterative computation. By analyzing hotspots of the fast independent component analysis algorithm, such as covariance matrix calculation, white processing, ICA iteration and IC transformation, a GPU-oriented mapping scheme and the optimization strategy based on GPU-oriented algorithm on memory accessing and computationcommunication overlapping were proposed. The performance impact of thread-block size was also investigated. Experimental results show that better performance was obtained when dealing with the hyperspectral image dimensionality reduction problem: the GPU-oriented fast independent component analysis algorithm can reach a speedup of 72 times than the sequential code on CPU, and it runs 4～6.5 times faster than the case when using a 16-core CPU. 

Abstract:For the main computation of smoothed particle hydrodynamics was finite nearest particle search, a novel scheme to parallelize the smoothed particle hydrodynamics method based on the concept of particle decomposition was proposed. Any serial smoothed particle hydrodynamics code could be easily parallelized by using the proposed scheme. The amount of information, which was transformed in each time step, depended only on the total number of particles, but not on the spatial distribution of particles. Therefore, the proposed scheme was particularly useful for the parallel simulation of cases involved violent free surface movements. From the simulation results of a 3D dam break case with a total number of 0.4 million, the proposed scheme can achieve a speedup ratio about 16, which proves that the proposed scheme maybe is better than the domain decomposition scheme(without considering dynamic load balance).

Abstract:Without knowing the approximate position of the receiver, the millisecond recovery algorithm of traditional global navigation satellite system signal-radiation existed problem of increasing computation, but unable to be applied. A fast positioning method for BDS receiver was proposed according to the high navigation data rate of GEO(Geosynchronous Earth Orbit) satellites in BeiDou Navigation Satellite System. Firstly, an approximate position was got by coarse positioning using GEO constellation. Then the signal transmission time recovery of MEO/IGSO satellite was made according to the approximate position. Finally, all the visible satellites were used for precise positioning. Using iGMAS stations observation pseudorange to verify the proposed algorithm. The stations in China can 100% got full-pseudorange and obtained fast positioning. By using BDS broadcast ephemeris data, a simulation environment was built. The white noise with 6 meters standard deviation is added to satellites pseudorang. And the cut-off angle of elevation is 0°. The success rate of the quick location method is bigger than 98.68%. And about 80% of Chinese surrounding area can 100% guarantee a complete satellite signal emission time restoration and obtain an accurate position.

Abstract:CNR（Carrier-to-Noise Ratio）, an important indicator to evaluate the navigation signal quality, which directly affected the global navigation satellite system receiver performances of signal acquisition, carrier tracking, and data demodulation. Based on the distortion model of ICAO 2OS(International Civil Aviation Organization 2nd Order Step), the analytical expressions between CNR estimation and the distortion parameters of ICAO 2OS threat model were induced by using both coherent early-late processing and non-coherent early-late processing. And the influence of distortion parameters on CNR estimation error was analyzed. Theoretical analysis and simulation results show that carrier-to-noise ratio only changes in the 10^-2 order of magnitude when the TMA(Threat Model A) parameter changes within the set range, and can reach about 0.1dBHz caused by the TMB(Threat Model B) parameters. When increasing the TMB oscillation frequency and decreasing the attenuation factor can increase the estimated CNR. Consequently the distortion parameters of ICAO 2OS threat model have a small influence on the CNR estimation loss. Therefore, using the output CNR of the global navigation satellite system receiver to monitor the navigation signal abnormality is not reliable.

Abstract:According to the traditional adaptive polarization filter algorithms had problems of low convergence speed and the iterative factor being hard to choose, a fast adaptive polarization filter was designed by utilizing the estimation theory of polarizing cluster center. The interference signal in polarimetric radar reception could be cancelled accurately and adaptively pulse-by-pulse. The range-gated technique in-pulse was adopted to obtain the interference signal samples. The current polarization state of the interference signal was estimated rapidly by computing the polarizing cluster center directly. Based on the principal of minimum interference output power, the fast filter process could be carried out. Compared to the traditional polarization filter, it is faster in convergence and more stable to the performance of interference suppression. Rapidity and efficiency of the filter algorithm are validated by simulation results.

Abstract:The compressed sensing theory was applied to curvilinear aperture optimizing and 3-dimentional target feature extraction of curvilinear synthetic aperture radar. First, the echo signal target sparse representation model was built. Based on the incoherence principle between sparse matrix and sampling matrix of the compressed sensing theory, a guideline of evaluation to curvilinear aperture optimizing was found. Moreover, the 3-dimentional target feature extraction was realized by employing the basis pursuit method. Simulation results prove the correctness of the aperture optimization strategies with the incoherence principle as well as the efficiency of the basis pursuit method in target feature extraction.

Abstract:Based on the interferometric phase filtering problem of synthetic aperture radar, a modified patch-based locally optimal wiener algorithm was proposed. The proposed algorithm was the linear minimum mean square error estimator under the Gaussian additive noise condition and jointly estimated the first moment and second moment of the image, namely, mean and covariance using nonlocal means which was the state-of-art technique. When applied to interferometric phase filtering, two modifications were proposed according to the spatial variation of the noise. First, mean value, instead of median value, was used in the estimation of the noise standard deviation. Second, the number of clusters was determined adaptively according to the ratio of the maximum value to the mean value of the noise standard deviation. Experimental results on both simulation and real data show that the modified patch-based locally optimal wiener is effective and is superior to the other three algorithms.

Abstract:A pulse shaping filter at the transmitter was set up to reduce the modulation bandwidth and inhibit the out-of-band spurious, and made use of a matched filter at the receiver to obtain the maximum signal noise ratio. A cascaded multistage half-band shaping filter was designed and the minimum phase and maximum phase decomposition method was used, which facilitated the filter available in the practical communication system. Simulation result indicates that distinguished from the raised cosine finite impulse response filter, the designed filter has many advantages: the pass-band with lower ups and downs, less cost on the hardware resource, and extra power gain at low SNR for different modulation.

Abstract:Considering that the receiver was not only affected by the non-Gaussian noise but also affected by its internal and external environment of Gaussian noise, a mixed model composed by non-Gaussian distribution plus Gaussian distribution was proposed. A blind detection algorithm based on Markov Chain Monte Carlo method was designed according to the properties of the mixed model. The blind detection algorithm could estimate the channel fading coefficient, parameters of noise model and could detect signal element. Detect signals based on Bayesian hierarchical model was using Gibbs sample and M-H sample for parameter updating. The algorithm has a high iterative efficiency and precision. Results show that the proposed blind detection algorithm performs as well as the optimal detection algorithm and has important realistic significance in super low-freguency signal reception.

Abstract:With the increase of domestic and foreign launching tasks, it is becoming a serious challenge that plenty of failure or invalid spacecrafts in the process of space resources recycling. The active debris removal can be regarded as an effective and fundamental means that can realize the reuse of space resources and safe disposal. The concept of active debris removal is clarified and its development process also is analyzed. Some key techniques, such as relative navigation, coordinated control, capture method and device for non-cooperative target, are proposed. It will provide some fruitful reference for our country′s active debris removal in future.

Abstract:Experiments on continuous rotating detonation wave of H₂/air were performed with constant air mass flow rate and varied H₂/air equivalence ratio(ER). Three different propagation modes of the continuous rotating detonation wave were found as the decreasing of ER, namely, one direction mode at high ER from 0.90 to 1.86, two-wave collision propagation mode at low ER of about 0.75, hybrid mode of one direction mode and two-wave collision propagation mode at middle ER. The propagation characteristics of the high-frequency pressures were analyzed and the mode transition mechanism of continuous rotating detonation wave was preliminarily studied. With a higher ER, the strength of the detonation wave is increased and the loss and velocity deficit during the propagation are relatively small, and the continuous rotating detonation wave can be sustained in the one direction mode; while with a lower ER, the strength of the continuous rotating detonation wave is reduced and the influence of the loss and velocity deficit during the propagation is relatively enlarged, only in the two-wave collision propagation mode can the continuous rotating detonation wave be sustained. This can be attributed to the collision of the two counter-propagating shock waves in the two-wave collision propagation mode, which will promote the heat release, will enable the continuous rotating detonation wave to propagate steadily at a low ER, and will make the two-wave collision propagation mode possibly be the ultimate propagation mode of continuous rotating detonation wave. 

Abstract:Bending experiments were carried out to investigate mechanical properties and failure processes of composite T-joints with two defects. The defects of interfacial debonding and fillet-filling ratio were introduced to induce different failure modes of the T-joints. Results suggest that a great diversity exists among the T-joints under various failure modes. The maximum bending load of the intact T-joint is 288.5N, while interfacial debonding will reduce its carrying capacity by 30%. The reduction of the fillet-filling ratio leads to the initiation and propagation of the cracks in the fillet, which greatly decreases bending mechanical properties of the composite T-joints.

Abstract:On the basis of relative motion theory, a midcourse guidance method of exoatmospheric interception was developed. The mechanism of this method is that treating the initial and modified trajectories as chief and deputy space objects respectively, modeling the dynamics of the deputy relative to the chief by the relative motion theory and solving the initial corrections through the final relative states. The universal relative motion model was provided and then the state transition matrix of relative motion under the influence of J₂ disturbance was derived by employing the geometry and the variation method. Lastly the midcourse guidance method using state transition matrix was proposed on this basis. Simulation example shows that the proposed method serves as an efficient support for midcourse guidance of interceptors in practice.

Abstract:The construction mode of manned lunar spacecraft was designed by using the classic staging combination design method of lunar spacecraft. A preliminary estimation of the rocket carrying capacity was made according to the analysis of the different staging methods, and the exploration schemes of human-machine synergy are obtained as well. The staging method can provide a new solution to orbit transfer vehicle and landing craft design. The mass estimation of lunar craft based on the analysis of different staging options was given, and the corresponding rocket carrying capacity of different flight modes was compared. The study can provide reference to the scheme of our country’s first manned lunar mission.

Abstract:In order to evaluate the M219 cavity noise at 0.6, 0.85 and 1.35 Mach number, nonlinear acoustic solver is combined with Reynolds-averaged Navier-Stokes equations. The flow field of a cavity is calculated by means of Reynolds-averaged Navier-Stokes equations, which contains basic characteristics of average flow field and turbulence statistical average solution of statistics description of turbulence fluctuation. Noise source is refactored by the nonlinear acoustic solver. Spread of pressure fluctuation is simulated precisely. A comparison shows that the simulation results of nonlinear acoustic solver agree well with the experiment results. Compared with detached eddy simulation，nonlinear acoustic solver can greatly reduce the amount of mesh. In addition, the method can provide some reference for internal weapons bay design. 

Abstract:Due to the limited transmission range of airborne nodes, aeronautical ad hoc network suffers from frequent network partitioning in the highly-dynamic environment, which may affect the operation of network applications. In order to guarantee end-to-end connectivity, aeronautical ad hoc network should have the ability of fault-tolerance against link or node failures. Therefore, one or more relay nodes are required for constructing such a fault-tolerant network. As airborne nodes move, relay nodes need to move as well in order to re-establish the topology as quickly as possible. An online algorithm is proposed for relay nodes’ speed control to realize the network fault-tolerant during running time. Based on the network’s actual state, the online algorithm calculates relay nodes’ velocities such that the network can keep fault-tolerance and relay nodes, can travel a short total distance during the running time. Simulations demonstrate that the proposed algorithm is of great potential to be applied to aeronautical ad hoc networks.

Abstract:A general mathematics model for cooperative task allocation of multi-UAVs with time windows constrains was proposed which incorporating task gains and execution time directly, and simplifing the model formulation and algorithm designing. By defining a suitable particle structure, an algorithm based on the principles of discrete particle swarm optimization and Guo Tao algorithm was designed. The Inver-over Operator was directed by the swarm, the local and global optimal. Variable learning selection probability is introduced into the algorithm to select the learning particles, and the Inver-Over operator was modified. Simulation verifies the proposed task planning methodology for complex missions.

Abstract:Based on linear mixture assumption or training the classifiers by large amount of data, many methods used to recognize and estimate gas mixtures were adopted the nonorthogonal decomposition of steady response signal. Considering orthogonal decomposition approaches were mainly applied to analyze transient response signals, a gas mixture estimation model based on response equivalent and orthogonal decomposition of transient response signals was put forward. A novel nonlinear gas-mixing model was built after the analysis of MOS(Metal Oxide Semiconductor) gas sensor response characteristics based on the component equivalent expression for different gas responses. A new orthogonal basis function, the EQL (Extended Quasi-Legendre) basis, was proposed and applied to the decomposition of a transient response signal from the gas sensor. After the exponential relationship between the coefficients and the gas concentration was verified via regression analysis, the components in the gas mixture were separated, and their concentrations were estimated simultaneously. Experimental result shows that even though only the prior knowledge of single gas responses was applied to build the model, the concentration determined from the transient response of the gas mixture can reach an error within 15%.

Abstract:The whole antimissile process can be viewed as an iteratively process based on impact points forecasting which showes that impact points was mainly focused on by present research in the following way. The time-space requirements for impact points forecasting were analyzed, and 3 forecasting criterions were proposed. The antimissile single impact points forecasting model at 3 criterions was established, and the unknown variables of the model were changed into values which radar can measure. For shoot-look-shoot scenario and shoot-shoot scenario, antimissile multiple impact points forecasting and optimization model was gave at 3 criterions, and the calculating method of latest launch time was discussed. The impact of different look occasion was analyzed and modeled during impact points forecasting process. Partial theories and methods was exploratory research, related conclusions made may be benefits for antimissile sustained shooting decision making.

Abstract:Since the traditional capture probability model can not solve the problem of long-range anti-ship missile’s target capture calculation, a model was put forward to work out its maneuver acquisition probability by using search theory. The target distribution probability density function was established according to the target maneuvering rules. According to "inverted four times square law" of the terminal guidance radar target detection probability and missile target relative motion trajectory, the anti-ship missile’s detection function was constructed. The target acquisition probability could be calculated by the integral operation of their multiplication. The calculation results show that, if long-range anti-ship missiles do not take maneuver search strategy, acquisition probability decreases by 0.47 when target indication error increases 1km, acquisition probability decreases by 0.3 when target velocity increases 10 knot, and acquisition probability decreases by 0.3 when terminal guidance radar search radius reduced by 50%. If the antiship missile takes parallel search strategy, the impact of above factors on its acquisition probability has fallen dramatically. This method takes the following factors into account, such as target maneuver rules, sensor detection rules and missile acquisition strategy, and the maneuver acquisition probability of long-range anti-ship missile can be figured out accordingly.