Abstract:Along with the maturity of high-nonlinearity optical fiber manufacturing technology and the improvement of the performance of fiber lasers, the supercontinuum sources have entered a period of rapid development. Supercontinuum generation by using optical fibers as the non-linear media has become a research hotspot. The technical schemes and recent progress of supercontinuum generation were been reviewed from three different bands:visible, near-infrared and mid-infrared. At present, the output power of the visible and near-infrared supercontinuum sources broke through 100 W. At the same time, many new schemes such as supercontinuum generation in multi-core photonic crystal fibers, fiber amplifiers and random fiber lasers were developed. The output power of mid-infrared supercontinuum generation by using fluoride and tellurite fibers as non-linear media, also reached 10 W. The output spectrum of supercontinuum generation with chalcogenide optical fibers as non-linear medium was extended to more than 12 μm.

Abstract:As an important physical parameter, the electron number density is usually used to analyze the change process of the interaction between high power microwave and plasma. The change characteristics of electrons in plasma was studied by combining the wave equation, the electron transport equation and the heavy species transport equation by using the fluid approximate method, and the average electron number density and electron energy in the plasma region were calculated with the help of the software COMSOL. Result shows that the electron avalanche effect in the plasma appears as HPM(high power microwave) propagates inside the plasma, the electron numerical density increases rapidly, and the peak value shift towards the incident direction of HPM. In addition, it can be admitted that the electron energy increases with the HPM and decreases as the electron density increases.

Abstract:In order to investigate the influence of an opening in a metal cavity on the destruction efficiency of HEMP (high-amplitude electromagnetic pulse) and HPM (high power microwave), the model of electromagnetic pulse coupling into an open-ended metal enclosure was built with the help of CST software. Based on the model, the influences of the location, size and length-to-width ratio of the aperture on coupling effects of HEMP and HPM were researched. As for HEMP, the location, size and length-to-width ratio of the aperture can exert great influence on the coupling effect, so the destruction efficiency of HEMP can be weakened by reasonable controls of these factors. As for HPM, its coupling effect is obviously stronger than that of HEMP under the same conditions. After the aperture reaches a certain size, its size and length-to-width ratio have few influences on the coupling effect of HPM, and only the location of the aperture has a great influence. The coupling effect is the weakest when the plane of the opening is in parallel with the incident direction of HPM, but the energy coupled into the cavity can easily reach the electromagnetic damage level of many electronic components.

Abstract:A laser dazzling effect assessment of optoelectronic systems based on local features and image quality in the target region was proposed. The feature points were used to describe the local feature of the image. The structural similarity index was computed to reveal the image quality. The assessment utilized the point feature matching algorithm to locate the target region in the scene image. Then the ratio of the number of feature points and the unsaturated area and also the structure similarity index in the target region between the original image and dazzled image were computed. The final assessment index was achieved by the product of these three factors above. The implementation of the assessment to a typical dazzled image suggested that this assessment can provide a more broad range of index value and more obvious nonlinear variation than that obtained by only the structural similarity index in the target region, which indicated that this assessment method suggested in this paper has the ability to show more detail of laser dazzling process and more suitable for the assessment to lase-dazzling effect to image system.

Abstract:The Mach-Zehnder interferometer and phase-diffusion main equation were used to simulate the influence of atmospheric phase fluctuation on the quantum radar, and the evolution process under phase diffusion channel was solved. The influence of atmospheric phase fluctuation on the phase estimation resolution and optimal sensitivity of the coherent state parity probe quantum radar were thoroughly analyzed, and the Cramer-Rao limit of phase estimation sensitivity under atmospheric phase fluctuation was calculated. The study found that the effect of phase fluctuation on resolution can be eliminated by increasing the average number of photons per pulse. Moreover, in the case of strong phase fluctuation, the best sensitivity of parity detection may seriously deviate from the shot noise limit, but in the case of weak phase fluctuation, it is found that the parity detection is a quasi-optimal detection compared with the Cramer-Rao limit.

Abstract:Pulsed power supply is the most vulnerable part of the electromagnetic launch system, and the failure of the pulsed power supply will make the whole system performance decline. Thus, in view of the pulse power supply failure, a model search support vector machine fault diagnosis method based on multi-layer wavelet analysis for fault information extraction was proposed. By establishing the soft fault model of pulse power supply, the current fault data samples were obtained through simulation analysis, and the discrete wavelet decomposition of the fault samples was carried out, then the wavelet coefficients of the specified layer details were obtained as the fault feature quantities. The principal component analysis of the fault feature was carried out, and the dimension of wavelet coefficients was reduced, so that the fault diagnosis was effectively carried out. Through the experiment, the proposed fault diagnosis method was compared with the other three kinds of fault diagnosis results, and the effectiveness of the method was verified.

Abstract:The impact of temperature on laser diode degradations were studied by equivalent circuit model simulation and accelerated degradation experiment. Two degradation modes of laser diode were analyzed and concluded that the active region degradation will cause the threshold current to increase, and the cavity surface degradation will cause the slope efficiency to decrease. The thermal characteristics of laser diode were modeled and simulated, and were concluded that the threshold current increases with the temperature rise. The accelerated degradation experiments were carried out by a laser diode accelerated degradation experiment platform. The results of simulation and experiment showed that the increase of temperature will aggravate the cavity surface degradation, but has no significant effect on the active region degradation of laser diode. These conclusions will improve the laser diode temperature degradation simulation modelling. The current study is beneficial for the mechanism of temperature on laser diode degradation and protective measures.

Abstract:In order to complete the high-precision measurement of the LIPS-300 ion thruster hot gap in the vacuum, high-temperature environment, a non-contact videometrics system using a telemicroscope was designed. Based on the captured image, the interactive partitioning edge detection method was used to obtain stable and clear edges of multiple circular cooperation logos, meanwhile the magnification factor calibration, image distortion correction, horizontal plane correction and hot gap subpixel level deformation detection were performed with cooperation logos. The accuracy verification experiments show that the measurement accuracy of the system is better than 6 μm under non-heating conditions, and the measurement accuracy is better than 12 μm under heating conditions. Experimental results show that the greater the temperature difference between the screen and the accelerator grid, the larger the reduction of the grid hot gap, when the screen grid and the accelerator grid temperature difference is at most 150 ℃, and the hot gap reduction reaches a maximum of 420 μm. At the same time, due to the thermal deformation of the mounting ring, the thermal deformation of the grid decreases during thermal steady state, and the negative displacement occurs during the cooling period. The results of grid thermal deformation measurements are consistent with the trend of similar previous experiments, and the system meets the requirements of ion thruster hot gap measurement.

Abstract:In order to reduce the error of single-satellite localization from frequency measurements, an algorithm of single-satellite localization from frequency measurements, which combines the initial value calibration and the second order approximation, was proposed. The algorithm obtains distance information from the satellite to the localization target at the time point when the Doppler frequency shift of the satellite receiving signal is zero, and then corrects the geometric relationship between the orbit plane and the localization target by using the distance information, thus it provides a calibration method for the selection of the initial value. By substituting the calibrated initial value into Taylor′s expansion of the localization equation containing the second order numbers, the real position of the localization target was obtained through fewer number of iteration, thus reducing the complexity of localization algorithm and improving the localization accuracy. The simulation results indicate that compared with the Doppler single-satellite localization algorithm, the iteration times and the localization error of the proposed algorithm are reduced substantially. The algorithm is easy to implement, low in computation and small in error, and has high theoretical and practical value in the field of single-satellite localization research.

Abstract:In order to establish the accurate reentry model of hypersonic vehicle, the aerodynamic parameters of the dynamic equation were fitted according to NASA′ s research data. Based on the physical properties and the practical application of the aircraft material, the constraints of heat flow, overload, dynamic pressure and fly zone constraints were set up, and the nonlinear multi-coupling optimal control problem was formed. The hp-adaptive pseudospectral method was used to transform the model. Through the mesh refinement process, the time interval of the larger change of state was further subdivided, and the optimal trajectory of the condition was calculated by using the SNOPT solver solution. A closed loop controller was designed to track the trajectory changes of the optimal trajectory, and to test the performance of the system and to evaluate it. The simulation results showed that during the whole reentry process, the speed decline process of the aircraft is stationary, the reentry trajectory can satisfy the constraint conditions, and the maximum transverse range is obtained while avoiding the no flight area. The angular velocity of the three channels is convergent and controllable, and the tracking of the attitudes is ideal. Above all, the controller can basically adjust the posture.

Abstract:In order to solve the problem of stable trajectory control of hypersonic vehicle longitudinal motion model, a backstepping control method was designed to ensure the prescribed performance on the basis of non-affine model. For the velocity subsystem, the non-affine control law was directly designed to ensure the prescribed performance, and the altitude subsystem was transformed into a strict feedback form through reasonable transformation to facilitate the design of backstepping control steps. Based on dynamic performance and steady-state accuracy, the preset performance function was designed to limit the stability of tracking error within the preset range, and the instruction filter was introduced to effectively overcome the problem of repeated derivation of virtual signal in traditional inversion control. The design of the controller does not depend on the exact model. The radial basis function was introduced to approximate the unknown function in the process. As a result, the control law has satisfactory robustness and practicability. Based on the Lyapunov stability theory, the stability of all closed-loop systems was proved. Simulation results show that the controller can track the reference signal stably.

Abstract:A hybrid optimization method combining the evolutionary algorithm and the collocation method was presented for solving the MTOP (multiobjective trajectory optimization problem) of the hypersonic glider vehicle, in which the efficiency and accuracy were balanced. According to the flight dynamic equation of the glider vehicle and the constraint condition arising in the design of the glider vehicle trajectory, the multiobjective trajectory optimization model was developed. The MTOP was transformed into the multiobjective parameter optimization problem with constraints by using the control variables discretization method; the constraint condition was dealt with the penalty function method, and the MOEA/D (multiobjective evolutionary algorithm based on decomposition) was employed to solve the problem. In order to improve the accuracy of the result, the ellipsoid aggregation method was integrated into the collocation method, in which the Pareto solution produced by the MOEA/D was the initial solution. Simulation results for MTOP with the complicated constraints demonstrate that the proposed hybrid method can generate a set of Pareto solutions, in which the gliding trajectories satisfy all the complicated constraints.

Abstract:Aiming at the problem of trajectory following for aerial vehicles, a nonsingular fast terminal sliding mode based trajectory following guidance law was developed. A trajectory following dynamic model with line-of-sight angle constraint considering the autopilot dynamics was established based on a virtual target moving along the desired trajectory. A desired line-of-sight angle was derived for the trajectory following problem. To follow the desired trajectory in finite time without singularity, the nonsingular fast terminal sliding mode control and the dynamic surface technique were used to design the guidance law. The mathematical relationship between the error of line-of-sight angle and the trajectory-following error was presented. The Lyapunov stability theorem was proved that the trajectory-following error was uniformly ultimately bounded. The proposed guidance law was compared with the trajectory shaping path following guidance law. The simulation results showed that the proposed guidance law provides better trajectory-following performance and has a better robustness.

Abstract:The influence of low air density in the plateau environment on dynamic stability of projectiles was investigated. The force equations were presented in ballistic trajectory frame and the moment equations were presented in the non-rolling body frame, and the state space model of projectile angular motion was obtained by linearization method. Four eigenvalues of the angular motion state matrix were listed, and the equations of real parts of eigenvalues were derived by complex square root calculation method. The novel definition of stability factor for projectile dynamic stability was proposed, and it is proved that the new dynamic stability criteria is consistent with the traditional dynamic stability criteria. The influence of low air density on dynamic stability of fin-stabilized projectile and spin-stabilized projectile were discussed. Simulation results demonstrate that the projectile dynamic stability is different between plateau condition and plain condition.

Abstract:Surface catalytic mechanism is dominated by CO₂ recombination during the hypersonic Mars entries, which will highly influence the aerodynamic heating. The surface CO₂ two-step catalytic model was dealt with on the basis of the three-dimensional compressible flow solver for chemical reaction system. The rates of surface chemical reactions were controlled by surface adsorption and Eley-Rideal recombination. The hypersonic flow around the 70° sphere-cone testing model was numerically solved to predict the chemical non-equilibrium aerodynamic heating with surface catalytic effects. The influence of two-step CO₂ catalytic mechanism, including two pathways, CO+O(s) and O+CO(s), on the aerodynamic heating was numerically investigated. The recombination of O₂ and CO₂ coexists and competes with each other. The catalytic heating increases monotonically with the rise of catalytic efficiency. The numerical calculation established a quantitative correlation between the catalytic pathways and the non-equilibrium heating level, and the results show that the relationships between the weight of two CO₂ catalytic pathways and the heating capacity are non-monotonic, and the combined aerodynamic heating of two pathways of CO₂ recombination is calculated to be higher than the value from single pathway. The current study contributes in several ways to our understanding of carbon-oxygen catalytic mechanism and precise evaluation of aerodynamic heating for Mars entries.

Abstract:A new estimation method based on sparse optimization was proposed. This method alleviated the ill-posedness by decreasing the dimension of parameter space. The sparse representation of the trajectory was achieved by using the B-spline function. An optimization model for trajectory estimation was constructed according to the relationship between the measurement data and the trajectory, and was solved by using the Gauss-Newton method. In this model, the number of the parameters to be estimated was determined by the number of the spline knots. A sparse optimization model for optimal knot selection was established by using the discontinuity of high order derivative of spline at the knots. This model was solved by using a convex optimization approach, and the number of knots was minimized. Simulation results showed that the sparse optimization method can dramatically improve the estimation accuracy of trajectory during the incomplete measured interval.

Abstract:For the identification problem of nonlinear systems, the accuracy and stability of the nonlinear compression measurement identification algorithm were proved in the simulation experiment, and the complete signal was obtained accurately only by using constant multiple measurement times of the signal sparsity. Compared with the least square method, the proposed algorithm has greatly reduced the needed measurements, therefore, it is possible for the identification of high-order Volterra series. Furthermore, the influence of all factors on the accuracy of system identification was analyzed, such as signal sparsity, measurement noise, measurement matrix form, etc.

Abstract:Estimation of the secondary path model is required in the implementation of the Fx-Newton algorithm. Aiming at the problem that errors exist in the estimation of the secondary path model in the active-passive vibration isolation engineering application, providing that the input signal is a sine signal, the structure model of the Fx-Newton algorithm was established, considering the error of the estimation of the secondary path model. Stability condition of the Fx-Newton algorithm was deduced. Effects of the amplitude and phase errors on the stability and convergence of the Fx-Newton algorithm were elaborated. Finally, simulations for a two-degree-of-freedom active-passive vibration isolation model were conducted and the theoretical analysis results were verified.

Abstract:Using amplitude modulation and frequency modulation transceivers as an object of study, a precise modeling of the nonlinearity of front-end low noise amplifier of the co-site receiving station was presented, the interference suppression requirements for the amplitude modulation and frequency modulation radios were analyzed, and the analytical model was verified by numerical simulation. The results show that the proposed analytical model is more accurate than the existing ones. In addition, when the interference power, the useful signal power and the noise power are the same, the requirement of interference suppression of the amplitude modulation communication system is higher than that of the frequency modulation communication system.

Abstract:A new compressed sampling digital receiver based on polyphase MWC structure was proposed to intercept wideband IF(intermediate frequency) signal. The new receiver structure includes three modules:serial parallel conversion, parallel multiplication and polyphase filtering. With the same multiplier resources, the working rate of the new receiver structure is much lower than that of the existing MWC structure. Simulation result verifies the correctness of this new structure. The design lays a foundation for the physical realization of the MWC discrete compressed sampling digital receiver on the FPGA(field programmable gate array) and makes the whole receiver structure more practical in engineering application.

Abstract:Aiming at the degradation and failure caused by vibration, temperature cycling and etc in strain balance′s measuring circuit (Wheatstone bridges), a detection method was presented. In the method, the bridge was driven on different nodes at different periods and the responses were measured. The bridge′s parameters were calculated on the basis of the theoretical calculation, and its failure was detected on the basis of the clustering method. A principle prototype was developed and the experiment research was conducted. Experiment results show that the presented method is effective, and it can indeed detect the failure and its test accuracy of bridge resistance can reach 0.2‰. The designed prototype realizes the auto-detection of degradation and failure of strain balance measuring circuit, which costs less time consumption than traditional test method and lifts the available time of the wind tunnel test.

Abstract:To research the reason why the shaft-rate electric field cannot be completely eliminated and the wave curve produced by the electrostatic field in the actual measurement, a modeling method based on rotating point charge was proposed to study the corrosion electric field of ships. The Hankel transform was used to approximate the electric field generated by point charges in the three-layer medium, the curves of induced electric field changing with time, propeller radius and water surface distance under certain rotational speed were obtained, and the correctness of the theoretical results was verified by experiments. The results showed that the induced electric field is a part of the corrosion electric field of ship, and the frequency of induced electric field is the same as the speed of propeller at a certain speed, and the amplitude of that frequency decreases with the increase of the radius of propeller and the distance from the water surface.

Abstract:Experiments on 45 steel with high-velocity impact were carried out in order to study the target resistance. Then the influence of impact velocity and target parameters on the penetration resistance was analyzed by the calculation model. Also, the DOP (depth of penetration) of different projectiles penetrating 45 steel targets were studied based on the hydrodynamic penetration model. It was shown that the experimental results of penetration resistance based on the material dynamic hardness test method agrees well with the theoretical calculation results of hydrodynamic penetration model. Simultaneously, with the increase of impact velocity, the target resistance reduces from 5.13 GPa to 3.7 GPa. Also, the target resistance shows linear trend increase with the increase of the dynamic yield strength of targets. The DOP calculated by the hydrodynamic penetration model agrees well with the corresponding experimental data. All of these proved that the method to obtain dynamic resistance is feasible, thus can provide a reference for hypervelocity penetration dynamics research.

Abstract:The functional redundancy between multiple marine environmental monitoring systems leads to resource waste and unnecessary capital investment. Therefore, the systems should be integrated optimally into an organic whole to save resources and costs of marine environmental monitoring. In light of this, the Entropy method was introduced on the basis of linear programming and the marine environmental monitoring system was divided into different modules according to functions. Taking cost and efficiency index as the main object and through reasonable allocation, the construction cost can be reduced as far as possible while ensuring that the monitoring capability after optimization and integration is not reduced.

Abstract:The asymptotic behavior was determined in terms of the topological structure of the system, the step length and the rotation angle of the corresponding rotation matrix. Some necessary and sufficient conditions for the multi-agent systems to reach second-order consensus were found. It was shown that the asymptotic consensus appears when 0 is a simple eigenvalue of the Laplacian matrix, the step length and the rotation angle is less than the critical value which was determined by an algebraic equation. Some numerical simulations were presented to demonstrate the theoretical results. Some cases on the influence of characteristic parameters on second-order consensus were designed, which showed that the conclusion of characteristic parameters can provide important criterion and theoretical support for the control theory.

Abstract:For the pixel level marked data of image segmentation is time consuming and expensive, the image segmentation under the weak supervised model with bounding box annotations was studied. The high-resolution pixel features were extracted by a pyramid densely sampled fully convolution network, and then the weakly supervised data by the GrabCut algorithm was transformed. Finally, the image features and the labeled data were jointly trained. A model of weakly supervised image semantic segmentation based on fully convolution network was constructed and verified on public data set. Experiments show that the constructed weak supervised model has a better segmentation effect compared with DET3-Proposed model, expectation-maximization model and Bbox-Seg model.

Abstract:Self-organizing behaviors are widespread in nature. In order to simulate self-organizing behaviors of the fish school through learning, the fish school simulation environment model, the agent model and the reward mechanism were built, and a multi-agent reinforcement learning approach based on Hebbian trace and actor-critic framework was proposed as well. This approach uses Hebbian trace to enhance the swimming strategy learning with memory ability and realizes the distributed learning of multi-agent based on the homogeneous hypothesis. The simulation results show that the proposed approach can be applied to self-organizing behaviors learning of the fish school in the scenarios of leader-follower, autonomous wandering and navigation. Moreover, the characteristics of the fish school based on learning methods is similar to that based on Boids rules.