Abstract:For the purpose of raising observation effectiveness and improving observation capability, the problem of observation task dispatch of vehicular optical observation equipment was addressed. The problem was modeled as one that aims to find the optimal observation plan. The mathematical description of observation plan was presented, the constraints which a plan must satisfy were summarized and the metrics which testify the plan quality were proposed. The multiple-attributes-decision-making method was employed to calculate the overall efficacy of plans and the optimal plan was obtained by sorting. Sample simulation showed the effectiveness of the proposed approach. The model and method fulfilled in this paper were novel and extendible, which is valuable for the application of vehicular optical observation equipment.

Abstract:To study the effect of Bang-Bang controlled canard on aerodynamic characteristics of the rotating projectile, the nested grid in CFD software was used to simulate the spinning of missile and the deflection of canard. By this method, aerodynamic characteristics of the Bang-Bang controlled rotating missile at different angles, Mach numbers and rotation speeds were numerically simulated, and the aerodynamic law of the rotating missile was obtained. The research shows that the immediate change of lateral forces will take place in projectile body and tail fin, due to the variation in canard washing current direction which coupled the missile spin. Compared with those without canard control, the periodic average lateral force coefficient under control decreases, while the normal force coefficient increases. Due to lateral force, the net force in a period deviates from the vertical direction, and the deviation angle of which decreases with the increase of Mach number, spin rate and attack angle.

Abstract:In order to improve the forecasting accuracy and generalization ability, a target maneuver trajectory forecasting approach based on ensemble learning theory and KELM (kernel extreme learning machine) optimized by the modified bat-inspired algorithm was proposed. A KELM model optimized by improved bat-inspired algorithm was constructed. Combined with the ensemble learning theory, the improved KELM neural network was regarded as weak predictor to generate strong predictor, the structure and parameters of the strong predictor were continuously optimized through training, and a target maneuver trajectory prediction model based on the ensemble learning theory was obtained. Based on samples of different sizes, the prediction performance of the model proposed in this paper was compared with BP (back propagation) neural network, support vector machine and extreme learning machine. The simulation results show that the generalization ability and prediction accuracy of the prediction model proposed is good.

Abstract:In order to investigate the acoustic oscillation characteristics of gas-liquid pintle rocket engine and provide a reference for later optimization designs, a LOX/GCH₄ pintle engine with rectangular combustor was manufactured. The Euler-Lagrange method was used to simulate the acoustic response produced by transverse velocity disturbance, and the effect of acoustic excitation frequency on the transient spray combustion process was studied before fire tests. Numerical results show that the adopted transverse velocity disturbance can produce the first-order transverse acoustic oscillation response with the same oscillation frequency in the combustion chamber. The response of spray combustion to acoustic excitation can be greatly affected by the relative size of the disturbance frequency and the combustor natural frequency of first-order transverse oscillation mode. When the disturbance frequency and the natural frequency are equal, the pressure and heat of reaction oscillate in phase with the velocity disturbance in the first half of combustor, and the significant increase of pressure oscillation amplitude also causes spray flame to swing synchronously. Meanwhile, there is a tendency to shift from diffusion combustion to premixed combustion in the combustor. Methane burns completely in the shorter distance and the combustor temperature tends to be uniform.

Abstract:The three-dimensional coupled heat transfer between high-temperature gas, regenerative cooling panels with parallel cooling channels were numerically investigated, in which kerosene of supercritical pressure was used as the coolant. Combined with theoretical analysis, the influence of panel configuration was studied and discussed. Results indicate that the temperature of the gas heated surface rise with the thickness of gas side wall, the width and height of the cooling channels, while heat flux of the gas heated surface decreases with the increase of these parameters. It was found that the percentage of the heat absorbed by kerosene from the bottom walls, side walls and top walls of the cooling channels hardly changes with the thickness of gas side wall, while it changes with the variation of width and height of the cooling channels.

Abstract:Based on an open water tunnel, an experimental system for the coupling of ventilated cavity and supersonic jets was constructed. Four variable length experimental models were designed, focusing on the influence of the relative position of the jet and the ventilated cavity on the interaction mechanism. For different experimental models, the ventilation flow and jet flow were changed to obtain the dynamic process of the evolution of the cavity interface under different working conditions. Experiment observed three distinct mechanisms, which were divided into the following types:the jet fully inflated the cavity and the jet partially deflated the cavity; the jet fully deflated the cavity. By combining the experimental results and Paryshev′s theory, the calculation model of the cavity size and critical transition conditions for different mechanism were further constructed. When Ｊ≤0.1, the cavitation length can be described by the classic cavity empirical formula; When 0.1<Ｊ<1.5, the cavitation length is divided into two parts:the model length and the tail cavity length, and the length of the closed cavity from the nozzle outlet is only related to the parameter Ｊ; When Ｊ≥1.5, the ventilated cavity closes at the tail of the nozzle, the cavity length is approximately equal to the model length.

Abstract:Composite solid propellant is a kind of composite material with high packing fraction. It has the characteristic of heterogeneity in meso-scale because of the random distribution of oxidizer and metal particles in the matrix. Effects of particle gradation, spatial distribution and content must be taken into consideration while studying the combustion characteristics and mechanical property of the solid propellant in meso-scale. A random sphere packing model of nitrate ester plasticized polyether propellant based on molecular dynamics method was built. Monte-Carlo simulation was used to calculate the two-point correlation function of the random sphere pack. The effects of packing fraction, particle gradation and particle size on the two-point correlation function were studied. From the statistical significance, to obtain the minimum size of representative volume element with the characteristics of ergodicity, statistical homogeneity and isotropy can effectively reduce the calculation cost of subsequent research. The meso-scale propellant model established in this research is important and basic for the study on the complex nonlinear processes of the composite solid propellant such as combustion, decomposition, agglomeration.

Abstract:A group delay model based on trigonometric function series was proposed. And it was theoretically proved that only a finite order of trigonometric function group delay can characterize the influence of arbitrary group delay on signal correlation peaks. On this basis, the trigonometric decomposition series of the group delay were obtained by measuring the correlation peaks and matching the correlation peaks under different combinations of trigonometric function group delays. As a result, the equivalent group delay with similar effects on the correlation peaks was obtained. Simulation results show that the correlation peak of the signal is approximately the same as that of the ideal correlation peak, and the delay estimation error is less than 0.1 ns at different delay time intervals after calibration of the channel by using the group delay estimated by this method.

Abstract:In order to reduce the false alarm rate and improve the detection efficiency for video smoke detection, the Y^dU^aV^a color model was proposed, which can characterize the spatial distribution and temporal variation of smoke. By using this color model to quickly screen the suspected smoke image blocks, the false alarm rate was reduced and the computing efficiency was improved. An improved MobileNetV3 network structure was proposed, which is aimed to extract deep features of images and to classify the suspected smoke image blocks so as to detect whether there is smoke in a video. The simulation results of video smoke detection show that this method has high accuracy, high detection frame rate, and low false alarm rate.

Abstract:In order to avoid introducing periodic fluctuations in the clock offset of onboard atomic clock into the system time, it is necessary to eliminate the periodic fluctuations when establishing the autonomous time benchmark of satellite navigation system constellation. Based on the clock offset of BeiDou atomic clock provided by IGS, a method of periodic fluctuation correction for onboard atomic clock based on spectrum analysis was proposed. By comparing the performance of frequency stability of onboard atomic clock offset before and after correction, it is proved that this method can successfully eliminate the periodic fluctuation of satellite clock offset caused by environmental factors. Performances of different types of onboard atomic clock of BeiDou are improved after correction. Through this method, performances of onboard atomic clocks with different orbital types in the system have been improved remarkably. Among them, the frequency stability in 10 000 seconds of GEO(geostationary satellite) satellite-borne atomic clocks has been improved about 50%, MEO(medium orbit earth satellite) about 23%, and IGSO(inclined geosynchronous orbit satellite) about 15%. Through this correction method, the frequency stability of cesium clocks in ground stations has been achieved in both BDS-2 and BDS-3 satellite-borne atomic clocks, which lays foundation to the star autonomous timekeeping based entirely on satellite-borne atomic clocks.

Abstract:In order to verify the accuracy of different occultation data inversion of the wet temperature profile, it is necessary to quantify the error characteristics. The piecewise linear interpolation method, with time window 1 h and horizontal distance 100 km as the matching criterion was adopted. The average deviation and standard deviation of each interpolated height layer temperature of 0.2~30 km were statistically analyzed to explore the deviation characteristics of different occultation data. By using the complete IGRA (integrated global radiosonde archive) sounding data during 2018-2019, the deviation of different occultation data in China was evaluated. The results show that, for the above kind of occultation data, the temperature deviation is negative, and the overall average deviation is from -0.5 to 0.5 K. The absolute value of occultation data is less than 0.4 K compared with the IGRA data, and the accuracy of occultation data is equivalent to IGRA sounding station data. Through the significant detection analysis, it was found that the relative deviation of refractivity is small, combined with the statistical F=0.985 7>0.05, which shows that the detection accuracy of different masking plans has no obvious difference.

Abstract:In order to reduce the impact of the “similarity drift” problem, a matching strategy based on “neighborhood propagation” was proposed, which maps the intra-modal neighbours of the query items onto the target space, and takes their nearest neighbours in the target space as cross-modal neighbours of the query term. Experiments on real data sets prove that the similarity drifting problem exists widely, and the proposed matching strategy can effectively reduce its impact and improve the accuracy of matching.

Abstract:In order to evaluate the lethality and injury radius of the stun grenade fragments, and to reduce its average specific kinetic energy, the calculation model of the average specific kinetic energy of fragments was established, based on the Monte Carlo subdivision projection simulation method. With co-simulation method of LS-DYNA and self-programming, the calculation models of average specific kinetic energy of natural fragments and semi-prefabricated fragments of stun grenade were simulated and compared separately. The mass distribution, initial velocity, vertical target distribution, average specific kinetic energy threshold and safety radius of the whole fragments in the whole-time domain were obtained. The results show that the mass distribution and initial velocity threshold of semi-prefabricated fragments are lower and more concentrated than that of the natural fragments under the same charge parameters; within the range of less than 2.5 m, the average specific kinetic energy threshold of semi-prefabricated fragments is lower than that of the natural fragments; within the range of more than 2.5 m, the average specific kinetic energy threshold of semi-prefabricated fragments is higher than that of the natural fragments. Compared with the natural fragments, the semi-prefabricated fragments can significantly reduce the lethality radius, but cannot significantly improve the safety radius.

Abstract:In order to achieve efficient data transmission of SpaceFibre node, a system design scheme of SpaceFibre node based on FPGA (field programmable gate array) was proposed aiming at the key problems and technologies in network protocols. The polling and arbitration algorithm was adopted to solve the flow control token words application conflict of multiple virtual channels. An efficient processing state machine based on QoS (quality of service) mechanism was designed, which can realize QoS scheduling for multiple virtual channels. A parallel partitioned storage architecture and a resend control algorithm were proposed, which can realize efficient error recovery based on FDIR (fault detection isolation and recovery) mechanism. Different parallel processing schemes were designed for cyclic redundancy check of various data formats and calculation of pseudo-random sequence. A simulation platform was built by ModelSim to test the function simulation of the node system, and the system verification was completed on Virtex-6 FPGA. The results show that the function of SpaceFibre bus node can be realized, and the serial transmission speeds up to 3.125 Gbit/s, which can meet the demand of high-speed data transmission.

Abstract:Aiming at the difficulties in the choosing and planning in multi-period weapon systems development problems, an optimization simulation approach combining multi-objective optimization algorithm and reinforcement learning technique was proposed. A multi-objective optimization model was built to maximize the capability and minimize the cost of weapon portfolios in each period. Moreover, a solving algorithm based on the non-dominated sorting genetic algorithm-Ⅲ was presented to obtain the Pareto set in each period, based on which an optimization model for multi-period problem was built. The Q-Learning method, one of the reinforcement learning algorithms, searches within the Pareto set using two different ways for the selection of weapon portfolios in each period, whose outcome is used for the selection in the next period and the optimization of the portfolios over the entire planning horizon. An illustrative example was studied to demonstrate the effectiveness of the proposed model and hybrid algorithm, which can support the decision making on the weapons development and planning.

Abstract:In order to solve the problem of bearing-only target location for single unmanned aerial vehicle in the dynamic battlefield environment, a new trajectory optimization algorithm based on dynamic window approach was proposed. The maximizing determinant of the Fisher information matrix was set as the trajectory criterion. In the dynamic battlefield, which consisted of dynamic detection radar and fixed/moving obstacles the criterion, based on the idea of dynamic window approach, was extended from the traditional single-step optimal principle to the evaluation of multi-step predicted trajectory. At the same time, the effects of the detection radar and fixed/moving obstacles on the predicted trajectory were also considered. The optimal heading of unmanned aerial vehicle was chosen by the moving horizon method. And the numerical simulations show that the algorithm enables the unmanned aerial vehicle to ensure the high-precision bearing-only target localization under the condition of effectively avoiding the radar threat and fixed/moving obstacles, which provides new ideas for solving the problem of single unmanned aerial vehicle bearing-only target localization in a dynamic battlefield environment.

Abstract:In order to study the characteristics of liquid spurt caused by the hydrodynamic ram and its influencing factors, experiments in which high-velocity fragment impacts the liquid-filled container have been conducted. The characteristics of cavity oscillation in the container, the pressure distribution and the liquid spurt outside the container were tested. Experimental results show that there are two different phases of the liquid spurt. The first phase occurs within 400～700 μs after the cavity grows to its maximum volume and the liquid spurt has an arrow-shaped head. In the second phase, a number of similar pulsating spurt occurs, and each single pulsating occurs after each time of the cavity collapse. The liquid spurt has an umbrella-shaped head with a linear-shape tail. The pressure in the liquid and the shape of penetration orifice affects the velocity of the liquid spurt. The relative velocity of liquid spurt decreases in inverse proportion with the increase of the fragment impact velocity. The velocity of the liquid spurt fluctuates in the motivation. The velocity of the liquid spurt decreases and the location of the inflection point of the velocity can be closer to the penetration orifice with the increase of the number of spurts.

Abstract:In order to acquire the permeability of quartz hybrid phenolic materials at different temperatures, the experimental device which was used for measurement in gas permeation process in quartz hybrid phenolic materials was developed, and a method based on Darcy′s law for measuring permeability of quartz hybrid phenolic materials was presented. Quartz hybrid phenolic materials at different pyrolysis temperatures were chosen as the research object, and the gas pressure between down and upper materials and the gas flow rate through the materials were obtained. The permeability of the materials was obtained according to Darcy′s law. The results show that the permeability of complex pore composites can be measured by this experimental device. As the results show, the permeability of the quartz hybrid phenolic material is positively correlated with the pyrolysis temperature. The higher the pyrolysis temperature is, the greater the permeability be. The permeability level is in 10-13 m² at 673 K pyrolysis temperature and in 10-12 m² at 873 K and 1 073 K pyrolysis temperature. Furthermore, permeability of quartz hybrid phenolic materials and pyrolysis temperature meet the formula K=9.5×10-15T-6.32×10-12. The experimental results have enriched the basic physical data of this kind of resin-based composite materials, and provided a basis for the analysis of material permeability and thermal mass diffusion characteristics.

Abstract:In order to study the effect of elastic stress and elastoplastic strain on the corrosion behavior of 921A steel in simulated seawater, the electrochemical properties of 921A steel under the synergistic action of load and corrosion, such as open circuit potential, potentiodynamic polarization curves and EIS(electrochemical impedance spectroscopy), were tested by a homemade load-electrochemical experimental device. The corrosion rate correction factor under stress was defined by the charge transfer resistance obtained by EIS, and the experimental corrosion rate correction factor was compared with the theoretical value. Results show that the effects of elastic tensile stress and the elastic compressive stress on the mechanochemical effect are symmetrical. The mechanochemical effect increases with the increase of the elastic stress, and increases first and then decreases with the increase of the elastoplastic strain. The effect of the elastoplastic strain on mechanochemical effect is far greater than that of the elastic stress. In the scope of this study, the maximum negative shift of corrosion potential caused by the elastoplastic strain is 62.6 mV, and the corresponding corrosion rate correction factor is 4.113, while those caused by the elastic stress are 24.5 mV and 1.746, respectively. Therefore, the effect of stress and strain on the corrosion behavior of 921A steel in seawater cannot be ignored.

Abstract:It is difficult to simulate the long-distance transport of charged particle clusters above kilometer level by using particle simulation methods directly. To solve this problem, based on the electrostatic model, the moving window technology was introduced to make the 100-meter particle transmission moving window advance with the movement of the cluster, and a long-distance transmission model of the charged particle cluster was established. Compared with the radial expansion characteristics of the charged particle cluster obtained by the simulation with the calculation results of the envelope equation, the two are in good agreement, which proves the feasibility of combining the moving window technology in the simulation study of the long-distance transport of the charged particle cluster and the rationality of the transmission model. This model was further used to analyze the long-range transmission process of the 100 MeV relativistic electron beam cluster and the changes of its internal parameters and self-generated field. It was found that the self-generated electric field and magnetic field of the beam are in a highly symmetrical distribution in the radial direction, and in a slightly forward distribution in the axial direction. At the same time, the axial velocity distribution of the particle inside the beam also changes.