Abstract:Arming at the formation reconfiguration problem for the elliptic reference orbit under J₂perturbation, a multiple impulsive trajectory optimization strategy was developed on the basis of the Gauss variation equation and with the objective function of minimal fuel consumption. A relative dynamics equation using the orbital element difference was derived, in which the J₂ perturbation and the coupling effects between in-plane and out-of-plane relative movements were considered. The hybrid approach of the genetic algorithm and the sequence quadratic programming was proposed to optimize the total velocity increment. The simulation results show that the hybrid approach is effective, and can obtain the feasible solution efficiently. Since the J₂ perturbation and elliptic reference orbit are considered in the study, the approach has some reference significance for the trajectory optimization of space mission.

Abstract:A fluid-thermal-structural integrated method was presented based on finite volume method for hypersonic aeroheating-structural-thermal interaction. A system of unified integral equations was developed as the control equations for physical process of aero-heating and structural heat transfer. The whole physical field was discretized by using an up-wind finite volume method, which avoids the fussy data exchange and computational complexity in coupling method. To demonstrate its capability, applications for fluid-thermal-structural analysis of hypersonic ow over 2D stainless steel cylinder in steady and unsteady states, were performed and discussed. The numerical results show that the maximum temperature of about 648 K occurs at the stagnation point of stainless steel cylinder in a steady state and the objective physical processes in a good agreement with measured values in unsteady state. Compared with the coupling method, the integrated algorithm has shown a better stability with lesser griddependence，which provides theoretical and technical support for the thermal protection system of hypersonic vehicles.

Abstract:In order to investigate the differences of the transition mechanisms between four roughness shapes, a fifth-order WCNS scheme was used to simulate the supersonic flat-plate boundary layer transition induced by the square, cylinder, diamond and hemisphere roughness elements at Mach 4.20. Results show that the square roughness element has the longest separated region where the absolute instability is formed, thus resulting in the earliest transition. The diamond roughness element has the widest separated region and leads to the widest turbulent wake region. The cylinder and hemisphere roughness elements are less effective in inducing transition compared with the square and diamond roughness elements.

Abstract:Aimed at the problem that the current elasticity-based mesh deformation method always cannot control some poor elements suffering “negative volume” and extreme distortion, the volume and the extruding constraints on modulus of elasticity were introduced to solve above shortages and a modified elasticity-based method based on these geometry constraints was presented. Combined with Patrick mesh quality measure, the differences between the modified method and the classical method were fully analyzed by testing a 3D cubic model with three types of motion or deformation in wide-range, such as rotation, translation, and stretch. The modified method was applied to simulate the plunging motion of NACA0012 airfoil and stretching deformation of wing. Results show this modified method can improve the robustness of elasticity-based method by constraining poor elements in wide-range of motion or deformation, thus providing a better support for solving the unsteady flow problems.

Abstract:Based on NACA2412 airfoil, the improved stress expression model established by considering the influence of distribution mass can achieve the allowable range of inflation pressure of the flexible film wings. The results show that smaller the size of the flexible wing inflatable units are, the greater the allowable range of the inflation pressure can be. ABAQUS/CAE software was used for simulating the stress and deformation of flexible aerated wing under different inflation pressure conditions. The unique way of warping of asymmetric airfoil after inflating was found. The risk points of flexible skin were determined. The typical lines were used to analyze the local mechanical properties of the inflatable wing. The improved inflatable wing with surface coating obtained a good effect of improving the structure mechanical properties.

Abstract:An advanced criterion of optimal sensor placement was proposed for aeroservoelastic analysis of high-aspect-ratio flexible aircraft based on classical sensor placement index. The trace of observability Gramian matrix was proved to be the vibration energy, and the dimension of the ellipsoid was introduced as the geometric mean of eigenvalues, a high efficient simplified method was given as a computational approach. Different modes and sensors placement influences on the system were evaluated though the properties of H₂ norm in connection with system impulse response, a balance between the low and the high frequency modes was achieved to guarantee the dominant of low order vibration and avoid overflow. Considering the bending moment of the body, the bend and torsion of the wings, the different sensor placement indexes were evaluated. Results shows that the sensor placement can be set accurately and effectively, while different modes can also be fully weighted and reflected by the proposed criterion. This method can be used as an optimal tool to set the sensor placement through the whole flight track and it has a great value in engineering application.

Abstract:The reasonability of the structure design of aircraft engine and after-body directly affects the components matching and performance of the engine. The numerical analysis for the internal and external field characteristics of the conformal asymmetric nozzle of flying-wing unmanned aerial vehicle in the typical flight condition was carried out by adopting the 3D Reynolds-averaged N-S equation and k-ωSST turbulence model. The thrust performance of afterbody nozzle and also the variation trend of the 3D flow characteristics against the blow-down ratio of secondary flow were obtained. The results show that under a fixed blow-down ratio of the engine nozzle, the main flow field characteristics of the after-body nozzle can be effectively improved by reasonably optimizing the secondary flow channel and increasing the blow-down ratio of secondary flow；when the flow rate of secondary flow and main flow is within the range of 0.2% to 1.86%, the changing range of nozzle axial thrust coefficient is about 3%. Overexpansion of the engine′s main flow is weakened to a certain extent and thrust loss of the engine is decreased. Therefore, the blow-down ratio of secondary flow has great influence on the performance of the after-body nozzle of unmanned aerial vehicle.

Abstract:In order to analyze the influence of gas liquid ratio on the combustion of liquid centered swirl coaxial injector, hot tests were conducted with a combustion gas generator under different gas liquid ratio. This combustion gas generator was equipped with liquid centered swirl coaxial injector. The results show that there exist three combustion conditions: stable combustion, transition from stable combustion to low frequency combustion instability and low frequency combustion instability. The low frequency combustion instability is not related to the oscillation of the supply system. It occurs because the triple flame moves away from the injection panel, when the triple flame arrives at the point of the impinging sprays, the stability of the triple flames decrease rapidly, making the flame front oscillating in the recirculation zone.

Abstract:The accurate estimation of the initial error and the guidance instrumentation error plays a key role in the precision assessment of the maneuvering launched vehicle, so a new estimation method based on nonlinear model was proposed. The platform initial angle error was transformed into the orientation error. The true apparent acceleration was accurately calculated by using the fixed point iteration method. Then, the trajectory parameters of the truth launch coordinate were represented by a nonlinear function with the initial error and the guidance instrumentation error. A nonlinear model was constructed by using the exterior trajectory measurements. This model can simultaneously estimate the initial error, the guidance instrumentation error, the measurement systematic error, and the time-zero deviation between telemetry data and exterior data, and it can avoid the linear approximation of the initial error. The Bayes MAP (maximum a posterior) estimation is given to obtain the optimal estimation of these errors by using the nonlinear model and the prior information, and it is proved to be convergent. Experimental results show that the proposed method improves the estimation accuracy of the initial error and the guidance instrumentation error when compared with the linear method and other nonlinear method. Furthermore, the proposed method can also achieve the selfcalibration between different measurements.

Abstract:The internet principle of “end-end” cannot distinguish host-network interface, so the intent of the user cannot be aware by the network, which decreases the efficiency of the transmission. The novel edge computing-based active network especially for user intent, i-ECAN, was proposed, and the concept of the user forwarding intent was designed, which was utilized to inform the network the intent directly by the end system and was executed on the basis of the resource of edge computing. The i-ECAN can embody the user′s intention in the forwarding decision of network nodes and be used in mobile communication, video broadcast, and data fusion in internet of things. In the wireless network based on CORE simulator, the switching time of normal wireless network and wireless network based on i-ECAN was compared, which proves the rationality and the feasibility of i-ECAN. The i-ECAN extends the interface between the end system and the network, which enforces the collaboration between machines and networks.

Abstract:A novel algorithm which is based on both the flows′ size and transmission rate was proposed for elephant flow detection. In order to meet the performance requirement of high speed networks, the data structure of elephant flow detection was indexed by Hash table, which combines the Hash conflict resolution with the eviction of cached flow entry to identify the elephant flow efficiently. A theoretical analysis was conducted to demonstrate the accuracy, performance and memory overhead of the detection algorithm. Experimental results on real data sets show that the proposed algorithm outperforms least recently used detection algorithm, its derivations and compact space saving detection algorithm in terms of accuracy and performance with similar memory overhead.

Abstract:According to the problem of switch allocation, a network latency equalization-oriented switch allocation strategy was proposed to improve system performance by designing a more fairness switch allocation strategy and improving the degree of network latency equalization. The evaluation of the design with SPEC CPU2006 benchmarks was performed in a full-system simulator. Compared with the canonical separable switch allocator and the TS-Router (recently proposed switch allocator), the experiments show that the approach decreases LSD (latency standard deviation) by 13.8% and 3.9% respectively, as well as ML (maximum latency) by 45.6% and 15.1% respectively. The approach improves system throughput by 0.8% over that of TS-Router. Finally, the design is implemented based on the separable switch allocator, and it can perform the evaluation in speed, area and power.

Abstract:In the hybrid center control networks, the flows of isomerization networks have its own regularity and characteristic. While ignoring the regularity of the flows in isomerization networks, the original single and stateless network resource scheduling algorithms which discretely maximize value can cause the problems such as the low utilization, easier to concuss, some delayed network traffic. The topological architecture of the hybrid network which combines normal network with centered intelligent controllable network was analyzed, specially aimed to the common problems such as the flow burst，unpredictable flow，path jam/connection shocking scene. Then the resource scheduling algorithm named POS and POS-FME based on expectation and status were proposed. The algorithms consider the running status of hybrid network, evaluate the available resources of the system, and match available resources for various flows in the system, and have a certain prediction effect. The algorithms avoid the scenes of low running efficiency in the hybrid network, improve the utilization rate by about 10%~30% im comparison with the traditional algorithm, and also reduce the concussion and average delay through experiments.

Abstract:Taking advantage of parallelism and flexibility of field-programmable gate array, a novel Boolean satisfiability solver based on an improved local search algorithm on the reconfigurable hardware platform was proposed to solve largescale Boolean satisfiability problems. In comparison with the past solver, the preprocessing technology can strongly improve the efficiency of solver; the strategy of strengthening the variable selection can avoid the same variable flipped continuously and repeatedly. It can reduce the possibility of search falling into local optimum. The experimental results indicate that the solver can solve problems of up to 32k variables/128k clauses, and has better performance than previous works.

Abstract:The S-Tag (Shadow Tag) mechanism of SRAM(static random access memory) data consistency maintaining for DMA(direct memory access) accessing was proposed for the independent design of MDSP(multi-core digital signal processor). The pipelining implementation can efficiently support DMA nonblocking data transfer, and release the CPU. Experimental results and tests in real chips show that the proposed mechanism outperforms the state-of-art ones with respect to bandwidth and bandwidth utilization while keeping relatively lower hardware cost.

Abstract:To improve the feature selection stability of evolutionary algorithms, a new method for stable feature selection based on multiobjective ant colony optimization was developed. Feature selection results of three feature ranking methods by resampling policy were combined to provide stable features′ information for multiobjective ant colony optimization; the feature′s Fisher discriminant value and maximal information coefficient value were integrated as heuristic information; the classification correctness rate and value of extensions of Kuncheva similarity measure were taken as two optimization objectives to balance algorithm′s classification performance and its stability. Some comparisons and experiments were carried out on four benchmark data sets, and results show that the proposed method has a better tradeoff between classification performance and feature selection stability.

Abstract:In order to meet the complexity and uncertainty of virus diffusion in cyberspace operation, escape status and quarantined status were introduced into the virus diffusion model based on a traditional diffusion model, and its stability was discussed. The escape and quarantined mechanism of cyberspace operation was introduced. Via Routh stability criterion, the local stability of system equilibrium point was demonstrated as well as the basic reproductive number R0. Simulations were given to illustrate the influence of node connectivity, node distribution density, and node contact ratio on information diffusion. The results show that the information diffusion can be effectively controlled by changing the parameter regulations on node connectivity, node distribution density, and node contact ratio.

Abstract:In order to improve the security of covert information transmission in network steganography, a decoy method of multi-level steganography based on vertical multiprotocol collaboration was proposed. The proposed method consisted of 2 levels. The upper level was used to carry the decoy message to deceive the detector. The lower level used the vertical relationship of multiprotocol to encode steganogram. Experimental results show that the proposed method is more undetectable than others due to the usage of decoy message and multilevel steganography.

Abstract:In order to track the ship with static electric field, aiming at the problem of traditional Kalman filters, a new nonlinear filter was designed. Ship state space model was established, and the problem of traditional Kalman filtering algorithm in ship tracking was analyzed; according to the relationship of noise covariance between the continuous white noise and discrete white noise sequence, a new progressive update extended Kalman filter was proposed on progressive Bayes theory. Simulation results show that the new method can effectively reduce the filtering performance degradation and filtering divergence caused by large initial error, thus can effectively be used to track the ship, and has high practical value.

Abstract:Aimed at the problems which are serious couple interference and measure high angular velocity and angular acceleration when the aerocraft is circumrotating highly about itself, a new ASUKF (adaptive simple uncertain Kalman filter) algorithm was put forward. The ASUKF algorithm used hyper-spherical distribution and linear displace to accomplish simple sampling calculation and weight value calculation, and improved the algorithm′s efficiency. Characteristics of noise and linear equation were employed to finish selfadapting control. The ASUKF algorithm used sub-optimal estimation to compute procedural noise, and was judged that it is positive to prevent the algorithm invalidation. The simulation result shows that the ASUKF algorithm can reduce roll angle′s error and couple interference and improve aero-craft′s landing precision.

Abstract:In order to solve the contradiction between the tracking speed and the peaking phenomenon of the linear motor, a PD controller was proposed via nonlinear extended state observer. The unmodeled dynamics and disturbance were defined as overall disturbance and viewed as a new system state. A NLESO (nonlinear extended state observer) was designed to estimate the velocity of the mover and the overall disturbance. With the linearization via dynamic compensation, a PD controller with compensation was designed by using the outputs from the NLESO and TD, and the stability proof of closed-loop control system was given. The effectiveness of the proposed controller was verified when compared with other two PD controllers based on LESO in the experimental platform made by Googol company. Experimental results demonstrate that the linear motor servo system with the proposed PD controller via NLESO has the advantages of high tracking speed, high tracking precision, small peaking phenomenon and strong robustness.

Abstract:In order to study the electrostatic field in the flowing medium, the model of metal plate in the laminar flow was built on the basis of the related knowledge of electrochemistry and fluid mechanics, and the analytic expression of corrosion potential based on point charge source in the three-layered media model was deduced by using the expansion of Bessel function and its inverse operation, then the expression of electric field was obtained in the meantime. The corrosion potential of metal plate varying from different flow rates at arbitrary seawater depth was calculated by the listed expression. The simulation result was tested and verified through experiment. The result shows that the model in current density generated in the electrochemical reaction under laminar flow conditions is in better agreement with the experimental data, and the electric field distribution changes with the flow velocity and the length of the laminar flow direction.

Abstract:For demanding of high performance analog-to-digital converter for aerospace electronic systems, a 12 bit pipelined analog-to-digital converter with speed of 50 MS/s which can work well in harsh temperature and radiation environment, was presented and implemented with 0.13 μm standard complementary metal Oxide semiconductor process. By employing the circuit without sample-and-hold amplifier, the radiation hardened circuit, and the layout technology, the impact of total ionizing dose effect was significantly alleviated while reducing the power consumption. Test results show that the design achieves a 64 dB signaltonoise ratio, a 73.5 dB spurious-free dynamic range, maximum 0.22 dB differential nonlinearity within wide temperature range of -55~125 ℃ and survive a total dose of 150 krad(Si).

Abstract:A theoretical and simulated calculation of the processes proceeding in a gain generator of a combustiondriven cw DF chemical laser with preheated primary dilution He was reported. Investigation results demonstrate that for DF lasers with fuel systems of (H₂+NF₃+He)+D₂ and (C₂H₄+NF₃+He)+D₂, when the primary dilution He is preheated to (1100 K,1300 K), the available specific output power is improved by (21%, 24%) and (46%, 56%) respectively; and at the same time, the fuel consumption in the combustor is reduced by (255%, 29%) and (32%, 36%) respectively. In practical application, the primary dilution He can be heated to 800℃(1100 K) successfully. Therefore, preheating the primary dilution He is a feasible and effective method to improve the laser output characteristics, which can facilitate the development of more compact chemical lasers with higher efficiency.

Abstract:A new model, a model of random nonprobabilistic reliability, to evaluate the structure reliability was established based on the theory of random probability and interval non-probabilistic reliability for the randomness of material properties and loads of vessels in-service, and for region character of hull resistance testing result under the inspection of corrosion damage. Furthermore, the method to calculate the reliability index of the new model was investigated in the view of random variables and interval variables mutual transformation. Based on this new model, the reliability of vessel hull structure yield strength was analyzed. The result shows that the model can well reflect the objective uncertainty of structure variables as well as abate the conservatism of evaluation results, and has a strong applicability in reliability evaluation of ships in-service which contain the random variables and the interval variables simultaneously.

Abstract:In order to obtain the magnetic gradient tensor of magnetic target, the method of rotating-calculating magnetic gradient tensor was proposed. The enough magnetic gradient data can be measured by rotating the magnetic gradiometer about the vertical axis, and it is used to calculate the magnetic gradient tensor. The difference of the magnetic gradient tensor between theoretical value and measurement value was used as the reference, and the rotation angle, inclination angle and baseline length of calculation model were optimized. The influence of three-axis pointing error of magnetometer on the calculation result of magnetic tensor was analyzed. The simulation results show that the proposed method is effective in calculating the magnetic gradient tensor. There is little difference between the calculated value and the theoretical value.

Abstract:In order to enhance the stability of the explosive null gate and reduce the requirements of the groove filling process in the applications, the method which used the detonating cord to replace the partial groove charge structure was proposed by taking the gap null gate as the research object. The combination experiments of detonating cord with different size parameters, groove charge and null gate gap were carried out, and the optimal filling material combination which has simple filling process and more stable control ability of the signal channel was expected to be obtained. Results indicate that the stability and reliability of the explosive null gate device can be guaranteed, and the parameters of the explosive null gate consisting of detonating cord be properly configured.