Abstract:The adaptive filtering algorithms based on the polynomial model are widely used in the field of maneuvering target tracking, but there is no uniform evaluation criterion to measure the quality of these tracking algorithms. Due to the existence of time-varying unknown inputs, the maneuvering target state estimation is actually biased. To solve this problem, the minimum mean square error bound calculation method for polynomial model Kalman filters was derived based on the minimum mean square error criterion, and the process noise variance law minimizing the state estimation mean square error was obtained. The proposed algorithm provides a unified evaluation standard for maneuvering target tracking algorithms based on the polynomial model, and also provides the basis for the setting of the actual process noise variance in maneuvering target tracking. The effectiveness of the proposed algorithm is demonstrated by the simulation results.

Abstract:Using the same stencils, the compact schemes can get higher accuracy and resolution compared with the traditional ones. But it will bring about spurious oscillations if the compact schemes are used directly. There are several methods to settle this problem. The TVD algorithm was selected in our study. Firstly, two five-order upwind compact schemes were introduced and Fourier analysis was used to compare their dissipation and dispersion characteristics. Secondly, two different TVD methods were applied to Euler equations. The performance of the numerical algorithm was assessed by performing preliminary simulations on some problems, such as the oblique shock reflection problem. The algorithm applied here is proven to have good resolution properties and robust of capturing shock waves and contacts, but it still has the problems of accuracy degree and lack of dissipation.

Abstract:Through transforming the fault diagnosis into the pattern classification of fault characteristics, a fault diagnosis method was developed, based on the cloud sorter for liquid-propellant rocket engines. The method synthesized the study on cloud model and the cloud transform, which can deal with the uncertainty and the hard partition of domain boundary for the quantitative attributes which exist in the traditional classification methods. Caculation results with test data show that the method can recognize the fault modes in the startup process of the engine timely and precisely.

Abstract:Mesh generation is the key to the numerical simulation in CFD with complex aerodynamic shapes. The algorithm of mesh generation is required to be fast and robust. First, this framework established efficient initial tetrahedron arithmetic based on viewed-able face which is fit to the arbitrary polyhedron. Then, Delaunay generation method was improved to refine meshes and the effect of different mesh quality criterion was discussed and the divergence with Delaunay face swapping was developed to optimize the mesh generation process, Finally, a vertex spring model for mesh optimization was established. The results indicate that the method established in the research is efficient and stable.

Abstract:To solve precise guidance and maneuver penetration problems for hypersonic vehicle in dive phase, the optimal guidance method with maneuver was proposed. Considering that the traditional guidance law based on zero-LOS angle rate can debase penetrative ability, it designed reference motion for the rate in diving-plane and turning-plane. Besides, in order to enhance penetrative ability farther and realize precise guidance, it took advantage of optimal control with the optimal index of maximum terminal velocity to track the LOS angle rate, and pseudo control variable was introduced to simplify the resolution of optimal control problem. Finally, it analyzed the guidance capability and stability of this method. The results of CAV-H vehicle test show that the algorithm can realize maneuvering flight, and can satisfy terminal impact point and falling angle constraints. Therefore, the method can offer reference for high precision guidance and maneuver penetration for hypersonic vehicle in dive phase.

Abstract:Solar thermal propulsion is a high efficiency propulsion system, utilizing concentrated sunlight radiation to heat low molecular weight working fluid and providing high specific impulse. With regenerative cooling, an integration of the second concentrator and thruster can cool down the former to 1600K and preheat the propellant to 600K, thus improving the energy conversion efficiency of the propulsion system. The thermal radiation simulation shows that the flowing propellant is of little influence on the cavity temperature and the cavity can maintain high temperature between 2400K and 2600K.

Abstract:Waverider slide hypersonic vehicle will be very useful for transport and even a powerful weapon in the future. The flight environment is very complex as the hypersonic vehicle flies at high speed and covers wide range, thus the control system of the hypersonic vehicle must have good adaptability. As decoupling pseudolinear system does not have fine dynamic performance, this research established the attitude model of the hypersonic vehicle, using the discoupling method and Block Backstepping theory to design the control system. The stability of close-loop system was proved and the simulation with large flight envelope and large-scale parameters perturbation was accomplished. The results showed that the method can ensure the stability of close-loop system's Lyapunov functions. With functional agility and rapid response, the control system can solve the problem brought about by large flight envelope and large-scale parameters perturbation, and can enhance the system's robustness.

Abstract:A control algorithm of adaptive sliding mode control based on fuzzy logic is proposed for the inertial stabilization problem of the floated inertial platform (FLIP). The sliding mode control was used to solve the parameters uncertainness and unmodeled dynamics of the FLIP, which guarantees the stability and rapidity of the system. Then, by focusing on the design problem of the sliding mode control, the gain of a sliding mode control was adjusted by using the fuzzy logic with an adaptive tuning algorithm，which enhanced the adaptability for random uncertainty and improved the robust performance and the stabilization accuracy of the controller. Finally, the stability and convergence of the control system were proven by using the Lyapunov method．The simulation results demonstrate that the proposed method can eliminate the input chattering of the sliding mode control efficiently, and the inertial stabilization of the FLIP is realized with the accuracy higher than 0.1 ″.

Abstract:Multiplicative extended Kalman filter (MEKF) has been widely applied in the vast majority of spacecraft attitude determination missions. For the arbitrary reference frame, the linear quaternion kinematics equation and the dynamical model of three-component attitude errors were formulated, and gyro-aided and gyro-free attitude determination schemes were designed. The typical basic equation of the MEKF was developed, including the detailed models for vector measurements, quaternion measurements and Euler angle measurements. The research can provide theory reference and technique support for spacecraft missions.

Abstract:Wear-life forecast of self-lubricating spherical plain bearing has very great significance to the operating security of equipment. To meet the demand of wear-life calculation and forecast of self-lubricating spherical plain bearing, the wear-life models for self-lubricating thrust spherical plain bearing and self-lubricating radial spherical plain bearing were created based on the principle of joint wear calculation method and the wear mechanism of self-lubricating radial spherical plain bearing. The models proposed integrated the wear mechanism of self- lubricating radial spherical plain bearing, the friction wear laws of materials, configuration, mating characteristic of the self-lubricating spherical plain bearing, and function requirement. Especially, the configuration parameters and function requirement were more specific in the models to different types and functions of self-lubricating spherical plain bearing. Example results and analysis on the models showed that the model can calculate the wear life accurately, and it is more theoretical and has a good applicability to the special designed and applied self-lubricating spherical plain bearing compared with the experiential calculation formulas used at present.

Abstract:For the problem of the cracks which appear in batches in the fuel-oil accessories rear cover, a new evadable measure for the crack guide and devolvement is put forward, by researching the main cause of the cracks and analyzing the extent of the damage caused by the cracks in different positions in the fuel-oil accessories rear cover for the aero-engine, The method changed the pristine support construction, so the new stress concentration point was formed and the stress amplitude in the key part of the stress concentration area was reduced, which transferred the crack faults from the unrepaired key part to the repairable non-critical part. Through computer simulation, the optimal parameters for the crack guided gap were determined, and the simulation result showed that the evadable measure for crack guide and devolvement is reasonable and practicable.

Abstract:Based on online dynamic balancing, a novel parameter identification method is proposed for magnetic suspending rigid rotor system. Two unbalancing masses with given magnitude and phase were added to the rotor and used as a vibration exciter. The displacement stiffness and current stiffness were identified from the unbalancing response detected by the balancing monitor. The proposed method was experimentally validated with a magnetic suspending control moment gyroscope, and the displacement stiffness and current stiffness of its magnetic bearings were obtained within a certain rotational speed interval, which demonstrates the correctness and feasibility of the method. The experimental results show that the displacement stiffness and current stiffness decrease notably with the rotational speed increased for an outer rotor magnetic bearing.

Abstract:Amplitude/frequency/phase modulation of electromagnetic(EM) wave, as the common way of carrying information, has received intensive attention recently when the wave front acts as EM vortex for information modulation. The progress on the information modulation capability of EM vortex was systematically summarized and its potential on radar information acquisition was also introduced. Aiming at the circular phased array, the echo signal model of ideal point target was established under the illumination of EM vortex wave. Once the echo signal phase of each antenna element was shifted with the same mode as being applied for submission and integrated along the circular path, the output signal of the radar array can be obtained. The output signal can be modeled as the linear superimposition of Fourier basis with the amplitude modulated by squared Bessel function. According to the spectrum characteristic of Bessel function, the approximate dual relationship between the mode number of orbital angular momentum(OAM) and the variable of azimuthal angle was analyzed. Finally, the back projection(BP) algorithm and filtered FFT based algorithm were applied to image the target. Simulations show that electromagnetic vortex wave has the potential to acquire the cross-range profile of the radar target. The research may act as a reference for the design of new mechanism radar and the development of target recognition technology.

Abstract:In recent years, a new SAR concept based on Multi-Input Multi-Output (MIMO) configuration has drawn much attention. Firstly, a review was made about the development in the field under discussion. Then, the generalized ambiguity function of the conventional SAR into MIMO SAR case was extended. Next, a detailed analysis shows that the resolution of MIMO SAR not only depends on the parameters of the waveform and synthetic aperture length, but also depends on the array geometry of the multiple transmitters and multiple receivers. Simulations with a variety of parameter combinations demonstrate the derivation and analysis.

Abstract:The deceptive stationary scene jamming is not effective for countering synthetic apreture radar (SAR) and ground moving target indication (GMTI) radar systems. To solve this deficiency, a method which transforms the stationary scene jamming signals to uniformly-moving scene jamming signals in real time is proposed. First, the echo models of moving target and stationary target were analyzed. Then, a formula which describes the relationship between moving target echo signal and stationary target echo signal was derived. Based on this formula, a three-implementation-step of this method was presented as delay operation in range time domain, stretching transformation in azimuth time domain and phase compensation. Next, the computational complexity was analyzed. Finally, the simulation results indicate that the proposed method is effective to produce false uniformly-moving scene，through which the stationary scene and important ground moving targets can be protected against SAR-GMTI.

Abstract:Low-frequency ultra-wideband synthetic aperture radar (UWB SAR) is a promising technology for landmine detection. According to the scattering characteristics of body-of-revolution (BOR) targets along with azimuth angles and incident angles, a Hidden Markov model (HMM) discrimination algorithm is proposed, using such sequential features as double-hump distance and notch frequency. First, the algorithm estimated the target scatterings in all azimuths based on regions of interest (ROI). Second, sequential aspect features were extracted by sparse time-frequency representation. Then the HMM parameters were trained with the labeled samples and the probability of occurrence was computed to discriminate suspicions targets. The experimental results indicate that the proposed algorithm is effective in BOR target discrimination. 

Abstract:A target tracking algorithm based on two-level implicit shape model is proposed to solve the tracking problem under occlusion and improve the location accuracy. Firstly, partial key points about the target and surrounding areas were extracted to build the codebook dictionary by Fast Hessian detector, and the feature description vectors of the codebook were constructed by SURF descriptor to establish the codebook support model. Secondly, the symbiotic relationship between the codebook dictionary set and target was established through the generalized Hough transform, and the online updating was accomplished by the implicit shape model. Finally, by finding the maximum value in the voting space, the target was located. According to the occlusion states in the tracking process, different voting weights were assigned to the codebook of target itself and surrounding area respectively, in order to improve the location accuracy under different occlusions. Experiments show the algorithm can locate the target robustly even though the target is occlusive, or even not visible, or returns to the field of view after missing.

Abstract:The resolution of space object images observed by ground-based telescope is greatly limited due to the influence of atmospheric turbulence. An improved blind deconvolution method is presented to enhance the performance of turbulence degraded images restoration. Firstly, a mixed noise model based blind deconvolution cost function was deduced under Gaussian and Poisson noise contamination of measurement. Then, point spread function (PSF) was described by wavefront phase aberrations in the pupil plane according to Fourier Optics theory. In this way, the estimation of PSF was generated from the wavefront phase parameterization instead of pixel domain value. Finally, the cost function was converted from constrained optimization problem to non-constrained optimization problem by means of parameterization of object image and PSF. Experimental results show that the proposed method can recover high quality image from turbulence degraded images effectively. 

Abstract:In order to reduce the bad effect in the outdoor visibility system in foggy days and achieve the real-time dehazing effect, a fast and effective method, which is based on Bayer pattern image and dark channel prior, was developed to remove the haze from single image. The color image processing pipeline was improved through this method. Bayer pattern image is the raw data captured by digital camera and costs low memory. According to the characteristics of Bayer pattern image, the original dark channel prior algorithm was optimized and improved. The atmospheric light was estimated based on the quad-tree subdivision. In the optimization process of the transmission map, the coarser estimation was refined using the Guided Filter, which was modified with the property of Bayer pattern image. Finally, the RGB image, which is displayed by the device, was recovered from the haze removal Bayer image using the demosaic algorithm. The experimental results show our new single image haze removal method improves the image quality by reducing the haze effect, and enhances the calculation speed.

Abstract:Multi-sensor image matching is meritorious both in vision mechanism studies and vision engineering. Image segmenting is an effective method for abstracting image properties, but due to the features of images with different sources, the image segmenting method cannot guarantee agreeable image properties from different sources. With a view to this problem, a method is proposed by segmenting the multi-sensor images before the matching strategy is used. Two matching strategy, the segmentation similarity and the minimal edges, can detect the right match. Matching experiments between optic and infrared images demonstrate its effectiveness.

Abstract:A coaxial transit-time oscillator with travelling-wave output structure is proposed. The extractor of this device adopts an extended interaction cavity loaded with washer-like structure, which has the advantage of high beam-wave interaction efficiency and low space charge potential energy. The extractor operating at 3π/2 mode not π-like mode improves the group velocity of wave, which is favorable for RF extraction. The loaded quality factor of the buncher is increased by introducing a prior reflector, which can obviously reduce the starting time of microwave. The device is designed and optimized by a PIC (particle in cell) code. With the voltage 530 kV，the current 12.8 kA and the guiding magnetic field 0.7 T, the output power is 2.41GW at the main frequency 7.76GHz, and the efficiency of beam-to-microwave power conversion is about 35.5%.

Abstract:Aimed at the harmonic distortion problem in the air-modulated speaker(AMS), the AMS behavioral model was represented by a Hammerstein structure, and the research on predistortion of AMS based on this model was made. As the DC offset exists in the nonlinearity of the Hammerstein model, a predistortion algorithm considering the DC offset compensation was developed. The validity of the algorithm and the necessity of the DC offset compensation were verified by computer simulation. In the experiment, a single sinusoidal excitation signal was first used to identify the Hammerstein model. Then, using the identified system parameters, the NFxPEM algorithm was performed to obtain the parameters of Wiener predistorter and to predistort the excitation signal. From the experiment results, it is found that our approach is effective in reducing the harmonic power with a relatively small upgrade in the fundamental frequency power.

Abstract:The kidney for transplantation is in serious shortage. To alleviate this problem, more and more countries have started various kidney exchange programs. The kidney exchange problem (KE) is generally modeled as a cooperative game. Each player represents an incompatible patient-donor pair. A patient may have more than one incompatible donor in reality. In light of this, the multi-donor kidney exchange game (MDKE) was defined. The structures of MDKE's feasible solutions and stable solutions were studied. It was proved that donating multiple kidneys is useless in joining in a better stable solution. Furthermore, the TTC algorithm, the NP-hardness of a stable solution and the inapproximability of a maximum cover stable solution of KE were extended to MDKE. Experiments show the effectiveness of MDKE.

Abstract:Prediction of ribonucleic acid (RNA) secondary structure remains to be one of the most important research areas in bioinformatics. The Zuker algorithm is one of the most popular methods of free energy minimization for RNA secondary structure prediction. However, general-purpose computers including parallel computers or multi-core computers exhibit parallel efficiency of no more than 50% on Zuker. For this problem, a CPU-GPU hybrid computing system that accelerates the Zuker algorithm applications for RNA secondary structure prediction is proposed. The computing tasks were allocated between CPU and GPU for parallel cooperate execution. Performance differences between the CPU and the GPU in the task-allocation scheme were considered to obtain workload balance. To improve the hybrid system performance, the Zuker algorithm was optimally implemented with special methods for CPU and GPU architecture. A speedup of 15.93× over optimized multi-core SIMD CPU implementation and performance advantage of 16% over optimized GPU implementation were shown in the experimental results. More than 14% of the sequences were executed on CPU in the hybrid system. To the best of our knowledge, our implementation combining CPU and GPU is the only accelerator platform implementing the complete Zuker algorithm. Moreover, the hybrid computing system is proven to be promising and applicable to accelerate other bioinformatics applications.

Abstract:A mathematical model is proposed to calculate the electric fields induced by the motion of metal body across the earth's magnetic field, according to deriving the expressions of electric fields induced by the vertical and horizontal DC current under seawater using the mirror image method. The magnitude and spatial distribution characteristics of the electric fields were analyzed, the results show that in the 30m depth, the magnitude of the electric field induced by a 20m′s long metal ellipsoid sailing 10m below water surface at the velocity of 4m/s is nV/m, and apparent characteristics can be noticed in its spatial distribution.

Abstract:With the advance of technology, geographic raster data's amount increases continuouslly. Single process cannot process large raster data efficiency, so it is necessary to adopt parallel processing. Traditional development method mixes algorithm, processes scheduling, memory management and data I/O together, thus it presents higher requirements for programmers and the code quality is difficult to control. This study proposes a Huge Geographic Raster Data Parallel Processing Framework (HGRDPPF). With the use of core class's real read and virtual read method, framework can achieve a large raster data's fast loading and writing by steps or blocks, and can achieve parallel task scheduling, data transfer and specific algorithm stage into tasks; through this framework, the raster file is split into sub-tasks according to the ability of computer in the cluster, and separate the raster processing algorithm from MPI API, disk IO and logic, developers can concentrate onto the algorithm itself, and achieve higher program quality. Experiments show that this framework can significantly reduce the amount of code while improving software quality, and to achieve a better parallel performance.

Abstract:With the leader-follower formation pattern, a method for UAV formation rendezvous was developed based on the pursuit strategy. Firstly, the UAV non-decoupling 3D kinematics models were established by using the curve theory of differential geometry and the Frenet-Serret frames, where the curvature and the torsion were considered as the control effort. Secondly, the mathematical descriptions of the three-dimensional formation rendezvous were provided with the models, where the impact angular constraint in missile guidance was mapped to a flight path angle of the follower in formation rendezvous, and an additional azimuth angular constraint was introduced. Thirdly, the orientation deviation between the leader and the follower was measured by using an element of the special orthogonal group, and the element was mapped to a twist in an Lie algebra space corresponding to the Lie group by local coordinate mapping. Then, a geometric guidance law for formation rendezvous was developed by using the twist, and the corresponding curvature command and torsion command were presented. Finally, the numerical simulation for multi-UAVs formation rendezvous was carried out, under the leader flying straightly and making a turn, respectively. The simulation results show that the follower can track the orientation of the leader successfully and can converge to a specified configuration, which indicates that the proposed method is available.

Abstract:Traditional quaternion-based sliding mode observer for angular velocity estimating has to introduce the process of mandatory rescaling which affects the tracking performance of the observer algorithm. In this work, a sliding mode observer design framework is proposed, based on the Lie group method of numerical integration on manifolds for angular velocity estimation of quadrotor attitude. The algorithm constructs sliding mode feedback in the space of equivalent Lie algebra of homogeneous manifolds on the basis of equivariant mapping ideological. It avoids the complexity of constructing sliding mode feedback in homogeneous space directly, and eliminates the process of mandatory rescaling which is required by the traditional methods in each integration step. The simulation results show that the algorithm of geometric sliding mode observer is effective.

Abstract:A dynamic trajectory planning algorithm based on vehicle steady-state dynamics for driver assistance systems (ADAS) under high dynamic environment is proposed. The algorithm built a 'search space' on the basis of traffic vehicle trajectory prediction and used the vehicle steady-state kinetic model as a trajectory generator. Every trajectory produced by the generator was evaluated in the search space and the optimal trajectory under optimal conditions was selected. In order to realize the closed-loop dynamic simulation, the corresponded trajectory tracking algorithms and vehicle dynamics model were also proposed. A simulation platform under Simulink environment was built for simulation tests. The results show that in the intelligent overtaking test case, the proposed algorithm is able to overtake safely and to meet the needs of intelligent assistance systems.

Abstract:Aiming at the agents group composed of multiple leader agents and multiple follower ones, a flocking behavior method with multiple leaders in obstacle environment is proposed. As a distributed control method, it controlled the follower agents with the leader agents of the group. Simultaneously, the center and average velocity of the follower agents exponentially was converged to the weighted average position and the velocity of the leader agents respectively. And the weight was dependent on the number of follower agents which were led by the leader agents. Moreover, by introducing a class of agents which are denoted as “β-agent”at the border of the obstacles, the follower agents possessed the capacity of avoiding collision with the static and dynamic obstacles. In this way, believable flocking behavior with multiple leaders in obstacle environment was generated. Simulation results with virtual humans being the members of the group demonstrate the effectiveness of the proposed method.

Abstract:The enforceability probability of satellite observation requires timely and accurate estimation to provide the fundamental basis for satellite task planning and scheduling. An estimation model of the enforceability probability of satellite earth observation is established based on the Logistic regression method. Firstly, the influence factors of observation enforceability probability were analyzed, including the property of observation task, resources limitation, competitive relations among tasks, etc. Secondly, independent variables were extracted and their quantitative methods were given, then the Logistic regression model was established. Thirdly, experiments were implemented on the planning and scheduling system of satellite imaging observation to obtain the sample data of independent variables and planning results. Moreover, the sample data was analyzed by using the Logistic regression method, and then the variables and parameters of the model and the function forms were all determined, Lastly, the effectiveness of the model was validated.

Abstract:According to the basic principles of the finite difference time domain (FDTD) method, firstly the physical field characteristics and the numerical calculation of the plasma were analyzed; and then the reentry plasma sheath formed and plasma relative dielectric constant of the wave attenuation were introduced; lastly the propagation of electromagnetic waves in the plasma with three-dimensional FDTD method and two-dimensional FDTD method were simulated. Simulation results proved that the FDTD method is an effective method to solve the electromagnetic wave propagation in the complex medium.