Abstract:The threat models and spoofing attack detection technology about navigation satellite timing receiver were summarized. Combined with the operating principle and characteristics of timing receiver, a general framework of timing receiver reinforcement technology was presented. On this basis, two interference detection methods of clock aided method and network aided method were proposed according to the analysis of development tendency of timing receiver reinforcement technology. The former took the advantage of multi satellite clock difference redundancy and the local clock characteristics, while the latter took the advantage of the GNSS timing receiver network with the characteristics of data communication and wide coverage. The interference detection results can be used to integrity assessment and guide the GNSS timing receiver working mode, thus improving the satellite timing reliability and integrity in complicated interference environment.

Abstract:Interference and multipath were the two dominant factors that affect the guidance and positioning performance of GNSS (Global Navigation Satellite System). According to the problem of anti-interference, a two-stage anti-jamming algorithm was proposed for GNSS antenna array. In the first stage, the PI (power inversion) algorithm was applied to suppress the interference. Then, the SNR (Signal-to-Noise-Ratio) of GNSS signal was improved by dispreading processing, and the spatial signature vector was estimated. In the second stage, the estimated spatial signature vector was used to weight and sum the output signal of the first stage. The proposed algorithm could null the interference and steer beams in the direction of GNSS signals simultaneously. Simulation results show that the performance of the proposed algorithm is better than PI algorithm, and it is similar to MVDR (Minimum Variance Distortionless Response) algorithm. The proposed algorithm requires no array calibration and aided altitude measurement unit, which has less implementation cost than MVDR algorithm.

Abstract:Array processing is widely used to achieve anti-jamming and multipath mitigation in GNSS(Global Navigation Satillite System) receivers for its ability to provide spatial resolution. According to different influences of interference and multipath signals to the signal processing in GNSS receivers, a two-stage anti-jamming and multipath mitigation structure divided by the correlation integrator was proposed. In the first stage, before despreading the space-time covariance matrix was estimated and anti-jamming was realized by using the subspace projection technique with the assumption that the interference power was bigger than the sum of GNSS signal and noise. In the second stage, spatial smoothing was used for multipath decoherence, and then a beamformer based on GSC (Generalized Sidelobe Cancellation) method with householder transform was implemented for multipath mitigation. Theoretical analysis and simulation results show that the proposed method can effectively suppress the strong interference and can significantly reduce the multipath signal effects on code measurement of GNSS receiver.

Abstract:Sample covariance matrix inversion was a basic operation unit in the realization of space-time antijamming algorithm, and its computation load grew rapidly with the increasing number of time taps, which directly restricted the application of space-time anti-jamming technique in GNSS (Global Navigation Satellite System) receiver. Aiming at this problem, a space-time anti-jamming algorithm based on block Toeplitz inversion was adopted into antijamming processing. By improving the estimation method of the covariance matrix, the algorithm got a sample covariance matrix both in the form of block Toeplitz matrix and Hermite matrix, and then the fast block Toeplitz inversion algorithm was applied to reduce the inversion complexity of covariance matrix of K taps from O［K³］to O［K²］. Theoretical analysis and simulation results show that when comparing with the traditional algorithm under the condition of 4 antenna elements and 15 taps, the anti-jamming performance cost of the proposed algorithm is less than 1dB, and its computation load reduction is about 2/3 times of the traditional algorithm.

Abstract:Numerically controlled oscillator is usually adopted in current GNSS(Global Navigation Satellite System) frequency domain anti-jamming receiver. Constrained by hardware, numerically controlled oscillator phase truncation is needed. But, whether numerically controlled oscillator phase is truncated reasonably influences anti-jamming performance greatly. Aiming at the problem, its effect on mixing and frequency domain anti-jamming was analyzed theoretically based on local oscillator spur caused by numerically controlled oscillator phase truncation. A theoretical computing module of numerically controlled oscillator look-up table width was brought forward. Thus, carrier noise loss approximated that of receiver with non-truncated phase numerically controlled oscillator. Simulations show that numerically controlled oscillator look-up table width computed by that module is no more than 10bit, when suppressing narrow band interference whose band is above 100kHz and jam-signal-ratio is below 80dBc. When adopting that width, carrier noise loss of receiver with numerically controlled oscillator phase truncation increases 0.6dB at most, compared to that of receiver with non-truncated numerically controlled oscillator phase.

Abstract:Because it is difficult to obtain the priori position for time-free positioning algorithm, the coarse-time GPS(Global Positioning System) positioning algorithm with ambiguity search was proposed. Four satellites, which are the most reasonable combinations based on minimum root mean square of residuals criterion, were selected for coarse positioning by iterating through all combinations of integer ambiguity. The full pseudoranges of all satellites were constructed based on the priori position. The position was estimated using time-free positioning algorithm. The performance of the proposed method was verified by using the observation data of 11 IGS(International GNSS Service) stations. This method can achieve coarse-time GPS positioning even if the priori position is unknown, and provides comparable positioning results as compared with the traditional precise-time positioning. 

Abstract:Multi-GNSS(Global Navigation Satellite System) united positioning was simulated based on researches of high earth orbital positioning. On the weakest signal acquisition C/N₀ threshold, 15dBHz, feasibility of satellite beam main lobe and side lobe receiving was analyzed, and the dilution of precision values with different GNSS system united cases were also analyzed. Simulation results show that when the receiving signal’s C/N₀ of both main lobe and side lobe is larger than the threshold, 3 systems united or more can satisfy positioning. When the side lobe loss isn’t compensated, C/N₀ of receiving signal is weaker than threshold so that any case of multi-system united can’t realize positioning. Analysis of dilution of precision values shows that geometrical dilution of precision of single system and double systems united changes violently. Geometrical dilution of precision of 4 systems united decreases 16.93% than that of 3 systems united. On the condition of 3 systems united, the case of American GPS(Global Position System) united with Chinese BDS(BeiDou navigation satellite System) and European Galileo system(Galileo satellite navigation system) is best since its geometrical dilution of precision is smoother than others. Theory analysis and simulation results provide beneficial suggestions for researching of lunar explorer positioning and space borne GNSS multi-system receiver.

Abstract:BeiDou navigation satellite system transmits triple-frequency signals which are benefit for the fast and accurate fixation of carrier phase integer ambiguity. Traditional TCAR(Three Carrier Ambiguity Resolution) method based on geometry-free model finds the suitable combination coefficients of carrier phase and pseudo-range observations by using traversal integer search method, which makes the higher noise level and the lower success reliability. In the analysis of the error characteristics of the pseudo-range observations, the weighted combined noise level was defined and a new procedure within its constrains to select the optimal combination coefficients was introduced. With using Hatch filter to improve the real-time estimation accuracy of ionospheric delay, the integer ambiguity of three linearly independent combination coefficients was fixed successfully, thus the basic integer ambiguities were determined. Finally, the performances of the improved TCAR are showed both in short-baseline and long-baseline condition: compared with traditional TCAR method, the total noise level has decreased by 20% for extra-wide lane and wide lane; the fixation success rate of ambiguity has improved about 10%~18%; the success reliability of basic ambiguities has achieved 90% with 30 seconds epochs smoothing.

Abstract:Code phase discriminator is the important part of the delay-locked loop, so its performance affects the pseudo-code tracking precision of receiver directly. Aim at influence of the input signal’s finite word-length effect on the discriminator’s performance, a new method based on signal statistical character was proposed and the effect of input signal’s finiteword length of unified early minus late amplitude discriminator on output performance was analyzed. Analysis and simulation show that the influence of input signal’s finite word-length effect in the case of high SNR(Signal-to-Noise Ratio) is more obvious than in the case of low SNR. The loss of pseudo-code tracking precision caused by finite word length increases as the increasing of input signal’s SNR. The deviation of the code phase discriminator with up to 4 bits almost has not influence on the pseudo-code tracking accuracy. This conclusion can be used to guide the low power and miniaturization design of receiver.

Abstract:Doppler shift and signal power attenuation in the complex environment both can make deviation bigger or even lose lock. Because the conventional Kalman filter can’t meet the dual requirements of high dynamic and high sensitivity when tracking maneuvering targets, a new carrier tracking method based on variable dimension Kalman filter was presented. By introducing motor model and non-monitor model of the carrier tracking and through putting in a maneuvering detector to monitor target movements, the real-time and effective switching of carrier tracking model was realized, so the adaptive tracking of carrier in motor and non-monitor state was achieved and the error caused by the change of maneuverability was overcome. 〖JP3〗Theoretical analysis and simulation results show that: comparing with the tracking algorithm based on standard Kalman filter, the phase tracking error of this algorithm is reduced by about 37.5% and the frequency tracking error is reduced by about 77% in weak carriertonoise ratio as low as 30dBHz environment.

Abstract:Based on the two-day profile of Chinese rendezvous and docking mission, a 5-revolution short-rendezvous phasing strategy was proposed by cutting down the flight duration for orbit determination, computation of maneuver parameters and command uploading, and non-visible course of flight. This phasing strategy was solved by using the algorithm of four-impulse modified special-point maneuver. The required precision of orbit determination to meet the control precision at the end of phasing was obtained. Then, the optimal phase range and total velocity increment were analyzed. Further results show that the optimal phase range is affected by the target spacecraft’s orbit injection accuracy, the chaser’s orbit insert precision and apogee height, the target orbital altitude and the final desired target point of rendezvous phasing. Finally, in order to obtain the starting phase angle, both the target spacecraft’s phasing strategy and the chaser’s launch chances are analyzed for the short rendezvous mission.

Abstract:Space web system is a new type of lightweight flexible space structure, which indicates great potential application value. Firstly, according to different mechanical environment in space and on the ground, the dynamic model of space web was established. Then, the reliability of the simulation model was validated by the ground test. Finally, based on performance parameters, for instance, deployment area, flight distance, etc, the dynamic characteristics were simulated and analyzed, such as the web shape, stress distribution and energy change, and the influence of the orbit height, capture direction and casting parameters on the deployment process were also analyzed.

Abstract:Based on CUDA Fortran for compressible turbulence simulations, a finite volume computational fluid dynamics solver on the GPU(Graphical Processing Unit） was developed. The solver was implemented with an AUSMPW+ scheme for the spatial dispersion, the k-ω SST model for turbulence model, and MPI communication for parallel computing. Some optimization strategies for fluxes computation and multi-GPU parallel algorithms for overlap of PCIe data transfer and MPI communication with GPU computation have been discussed for the latest generation GPU architecture. Several test cases, such as a supersonic inlet and a space shuttle were chosen to demonstrate the acceleration performance of GPU on large-scale grid size. Results show that when using a NVIDIA GTX Titan Black GPU, the computational expense can be reduced by 107～125 times than using a single core of an Intel Xeon E5-2670 CPU. Fast computing for a complex configuration with 0.134 billion grid sizes has been achieved by using 4 GPUs and the parallel efficiency is 91.6%.

Abstract:The hover duration performances of miniature VTOL(Vertical Takeoff and Landing) air vehicles depend on the performance of propulsion system. Based on the mass models of battery, motor and ESC(Electronic Speed Controller), and the relationship between provided force and required power of propeller, the duration calculation model of vertical takeoff and landing air vehicles was established by using the battery constant-current discharge model. The influence of propulsion parameters and payload on vehicle duration is analyzed, which would be used for preliminary design of VTOL air vehicles and components selection of propulsion system.

Abstract:The trajectory of intercept hypersonic vehicle in Near Space was designed with trajectory programming method. The problem of intercepting the hypersonic vehicle in near space was analyzed and defined as long-range hypersonic intercept problem in near space, and the requirements for trajectory programming were proposed. A two-stage boost engine interceptor was designed, and the interceptor mass point model of plane motion was built in considering the earth curvature and rotation. And then, according to the requirements of trajectory programming, the trajectory restraint was designed. And the trajectory problem was established with such indexes, they were maximum terminal velocity, minimum distance error to the final point and minimum whole heat quantity. Particle swarm optimization algorithm was used to solve the problem. Results show that the programmed trajectory is a lofted trajectory which can fly out of atmosphere and reenter into it. When comparing with the proportion navigation trajectory and the near optimal trajectory, the missile will fly outside of atmospheric for most time, which can reduce the aerodynamic heat effects and cut down the requirements for the material, and provide a better initial operation environment for the terminal guidance phase.

Abstract:In view of the effect of coning motion on missile stability, a nonlinear mathematical model of missile coning motion control was established. By introducing the concept of complex attack angle, the nonlinear model that was difficult to be resolved by analytical means could be transformed to a general resolvable model. According to the linear model of the missile complex attack angle motion equations, the range of stability control of the guidance and control system parameters were deduced, the influence of damping loop and control loop of control system on the stability of missile coning motion was analyzed, and the method to judge the stability of coning motion control was proposed. Simulation results validate the feasibility and correctness of this method, which provides a reference for the design of missile coning motion of guidance and control system.

Abstract:In order to meet the demand of real-time spatial data processing and improve the online processing capability of photogrammetric system, a kind of online photogrammetry method is proposed. According to the proposed method, system based on embedded architecture is then designed. Online photogrammetric data processing is realized by using FPGA(Field Programmable Gate Array), ARM+DSP(Advanced RISC Machine coupled with Digit Signal Processor) and other embedded computing technologies to build specialized hardware operating environment as well as transplanting and optimizing the existing photogrammetric algorithm to the embedded system. Aerial photogrammetric experiment shows that the method can achieve high-speed and stable online processing of photogrammetric data. And the experiment also verifies the feasibility of the proposed online photogrammetric system based on embedded architecture, which can improve the processing the efficiency of photogrammetry to a higher level and broaden the application field of photogrammetry.

Abstract:Multi-camera trajectory triangulation is proposed to determine a point target trajectory in different conditions of time information. The target trajectory is parameterized by time polynomial. The motion parameters can be determined by triangulating the series of sight rays of multi-camera and the target trajectory where the object space collinearity error is minimized. In contrast with the traditional triangulation, this method can not only get higher precision, but also adapt to the conditions of asynchrony, no time registration or even no time information among multi-camera. In contrast with the monocular system, there is no request of camera motion. Synthesized and real data experiments show the validity and high precision of the proposed method.

Abstract:The enriched finite element method is used to solve the stress intensity factors for two bonded dissimilar materials containing a crack along the bond. By appending the displacement expressions for an interface crack to the common element, the enriched and transition element displacement model are obtained; the enriched finite element equation is derived. Two enrichment schemes are introduced to establish the finite element models for square plate center interface crack and rectangular plate unilateral oblique interface crack. The stress intensity factors are calculated directly from the finite element equation. The results, which are obtained by compared with analytical results, demonstrate that the enriched finite element method is a convenient and high precision calculation method for interface crack problems.

Abstract:Experiments of steel tube confined concrete targets impacted by 12.7mm armor piercing projectile were firstly carried out, and then the depth formula of hard core projectile was established to explore the anti-projectile performance of steel tube confined concrete targets. The results show that the failure mode of steel tube confined concrete targets differs a lot from the failure mode of the unconfined concrete. The steel tube confined concrete targets develops hoop cracks on side face and works better in anti-projectile performance than the infinite concrete targets. Steel tube confined concrete targets also work well against multi-impact. 

Abstract:Based on brief introduction of the conception of underwater terrain-aided navigation, the key problems and research progress of underwater terrain-aided navigation were introduced from the view of terrainaided navigation algorithm, underwater digital map technology, and experimentation. The direction of research and development of application was pointed out as well.

Abstract:A finite time convergent zero-effort miss guidance law considering the dynamics of the missile autopilot is proposed for the problems of intercepting high speed and maneuvering targets. The three-dimensional relative geometric relation between the missile and target is decoupled. A new three-dimensional zero-effort miss guidance model incorporating the dynamics of the missile autopilot is derived. Based on the adaptive sliding mode control theory and the finite time stability theory, the zero-effort miss in pitch plane and yaw plane is chosen as the sliding mode surfaces, and then the three-dimensional adaptive sliding mode guidance with finite time convergent zero-effort miss is proposed. The guidance law’s stability and finite time convergence ability are analyzed and proved. Simulation results show that the proposed guidance law can achieve the finite time convergence of the zero-effort miss, and has better guidance precision compared with the proportional guidance law.

Abstract:Time-delay control system is very important to magnetic flux compression generator’s operation. Based on circuit delay scheme, an appropriate model was built to analyze the initiation time sequence, and its errors dispersion was analyzed. A switch driven by detonation was proposed, its voltage endurance capability and plate deformation were analyzed by simulation. On this basis, six switches were tested at high voltage. The data shows that, there is no voltage breakdown at 5kV, responsetime distributes in 66±5μs with standard deviation of 2.7μs, conducting time is equal or greater than 900μs, discharge efficient is approximately equal to 90%. A minitype magnetic flux compression generator was used to test the time-delay control system and the results show that, the time difference between magnetic flux compression generator’s operation and current peak is only 1.8μs with the error being 7.8%. 

Abstract:A continuous self-calibration and self-alignment method based on attitude angle was proposed for the calibration and initial alignment of floated inertial platform (FLIP) system. According to the working principles of floated platform, the inertial sensor error models were built and the attitude dynamic model for the FLIP was established; in order to make the platform to be rotated in the gravity plane, the torquing policy was designed; using the theory of piece wise constant system (PWCS) and output sensitivity, the observability of system was analyzed. Finally, the proposed method was verified by simulations. The simulation results show that the proposed method can synchronously calibrate and align 42 error coefficients of the FLIP with high accuracy and significantly improve the measurement precision of the system. 

Abstract:The formability of EFP(Explosively Formed Projectile) in multi-functional warhead scheme was analyzed by using AUTODYN simulation software. Compared with the traditional layout program, the changed fragment scheme changes the deformation process of shaped charge liner and leads to the shape variation of EFP, thus reducing the penetrating performance. Through analyzing the structural parameters, the optimized solution was proposed to solve the shaping problem of EFP after the adjustment of fragment scheme.

Abstract:There is no doubt that remaining useful life prediction is important to the health management of modern equipment. Particle filter method has been widely applied to the prediction of equipment remaining useful life in recent years, because it can solve the filtering problem of nonlinear and non-Gaussian systems better and it allows the uncertainty management. However, the prediction performance of a particle filter method is largely dependent on the prediction model and is very sensitive to the initial distribution of the model parameters. These flaws limit the further development of particle filter methods in the prediction to a certain extent. Aiming at the shortcomings of the basic particle filter prediction method, a kind of general prediction framework based on degradation rate tracking particle filter was presented. In the proposed method, the statistical rule of historical data was utilized to guide the degradation rate tracking of target data and simplify the prediction process. The remaining useful life prediction cases of rolling bearings and Li-ion battery verified the effectiveness of the proposed method.

Abstract:The nonideal random property of the pseudo code should be taken into account to analyze the code tracking error accurately in the present of partial-band interference. A precise power spectrum model of the code was introduced, and the tracking errors obtained by simplified spectrum and precise spectrum were compared for different interference bandwidths. The REC(Relative Error Coefficient) was defined to quantitatively describe the effect of nonideal random property on the tracking error. If the interference bandwidth is larger, the REC will be smaller, and the effect of nonideal random property on the tracking error will be smaller, then the analysis results based on simplified spectrum and precise spectrum will tend to agree. When the REC is smaller than 0.2, the minimum interference bandwidths are presented for GPS L1 C/A codes. The bandwidths are the bounds of the application scope of the analysis based on simplified spectrum. Research results indicate that: if the interference bandwidth is larger than three hundred times of the frequency of the code period, the change of the code tracking error induced by the nonideal random property can be neglected. Conversely, the analysis based on precise spectrum will be necessary in the study of code tracking precision.

Abstract:Computational experiments based on artificial society make it possible to study and quantitatively analyze the emergency management process. However, emergency management refers to multi-disciplines and multidomain, and models have the characteristics of multi-hierarchy, nonlinearity and multi-granularity, so a standard workflow is needed to guide the modeling development and management of artificial society. The model architecture of emergency management was carded, and the artificial society modeling method based on domain specific modeling was introduced to solve the multi-domain modeling problems. Moreover, the formal description methods as well as model encoding were implemented, which promoted the effective management of models. The development methods and management problems were discussed in details in the case study of H1N1 models, which provided the integrative model services for computational experiments oriented to emergency management. 

Abstract:Complexity of NAMD(Networked Air and Missile Defense) systems which is evolved in networked centric warfare makes researches on its modeling and simulation still stay in the initial exploring phase. Many novel characters of systems operation for this domain were introduced, and several models for it were developed from target，weapon and C2 (command and control) perspective respectively, eventually a typical simulation case of relay guidance was designed for models validation. Results analysis not only demonstrates the process of NAMD, but also push forward the effectiveness simulation of NAMD. 

Abstract:Based on the concepts of hypergraphs and operation cooperation, the abstract operation cooperative relation with formalization method was described, the incidence matrix was created, the hypergraphs model was built, and the vertex’s degree and correlation coefficient of this model were defined innovatively. The model can represent the character of operation cooperative relation and support relation analysis. A hypergraphs model about attack cooperative relation was established through an experiment, and the value of degree and coefficient was analyzed. Experiment result proves that the model is feasible.