Abstract:The passive safety features for spacecraft in close relative hovering with respect to circular reference orbit were analyzed by solving the minimum relative distance during the free motion with zero initial velocity. The passive safety features of spacecraft relative hovering can be described as the state of empty intersection between the relative motion trajectory and the target′s no-fly zone after the disappearance of the control force. This problem can be by transformed into the problem of minimum relative distance with zero initial velocity. The minimum relative distance varies with the initial position, and may be located in the integer period minimum value or the non-integer period minimum value point. The existence conditions of two kinds of minimum value points were analyzed. Then the calculation method of critical passive safe hovering area was obtained by solving the boundary condition in two cases. For the typical relative hovering scenario, the critical safe hovering area under the constraint of plane circle and three-dimensional spherical no-fly zone was simulated and analyzed. The effects of model error and J₂ perturbation on hovering passive safety features were evaluated. This analysis method can provide consultation for hovering mission design with passive safety features.

Abstract:To increase its authority in rarefied air and improve its environmental suitability in near space flow control, the characteristics of plasma synthetic jet actuator with cavity pressurization were investigated. A simplified model was proposed to analyze the cavity pressurization performance. The calculation showed that the chamber pressure is effectively improved by the high pressure air supply. Besides, the chamber pressure shows good following characteristics, which provide a novel method to control plasma synthetic jet intensity. The experimental system of plasma synthetic jet actuator with cavity pressurization was built. The measured chamber pressure was in good agreement with the calculated result, with a maximum error of 2.6 %. The high-speed schlieren visualization showed that the jet front velocity is significantly improved with cavity pressurization. The peak velocity increases from 256 m/s to 507 m/s.

Abstract:Aiming at the low search efficiency of the traditional backtracking algorithm when planning the function sequence of the payload system based on the knowledge model, an improved algorithm named as WIM-CGA for CGA (co-evolutionary genetic algorithm) was proposed, which was based on the WIM (worst individual mutation) strategy. The algorithm adopted a dual-route evolution scheme in the genetic process, which was “the better individuals perform standard genetic processes, and the worse individuals perform mutation operation”, to improve the solution accuracy and search efficiency. Simulation results show that under the same test conditions, when the function scale is 50 and the constraint density is 1.0, the average accuracy of the optimal solution of WIM-CGA within the limited time is 54.15% higher than that of GAC-BS (BS based on generalized arc consistency) and 6.18% higher than CGA, and when optimal solution accuracy reaches 90%, the iteration times of WIM-CGA is 65.79% lower than that of CGA, and the time consumed is reduced by 48.97%. The efficiency of functional sequence planning is improved significantly.

Abstract:In using the combination system with visual and IMU (inertial measurement unit) to estimate the relative pose of non-cooperative target in space, the external parameters of the system have a great influence on the estimation accuracy. Considering the complex and time-consuming calibration of the external parameters, a method to estimate the relative pose and calibrate the external parameters simultaneously by using visual and IMU combination system was presented. This method takes the external parameters as the state variables and forms the system state equation together with the relative orbital kinematics equation, the relative attitude equation and the IMU model. Then, the relative pose, IMU biases and external parameters of the visual and IMU were estimated by using the extended Kalman filter designed with the state equation and the observation of the monocular vision. The validity of the method was verified by mathematical simulation. The simulation results show that this method can estimate the relative pose and IMU biases effectively and calibrate the external parameters, when the deviation of external parameters existed.

Abstract:In order to quantify the influence of uncertainties in the terminal guidance initial parameters for unpowered gliding vehicle, an uncertainty-based design optimization method of terminal guidance initial parameters was developed to improve the accuracy of impact point. The sliding-mode variable structure control was used to predict trajectory of vehicle in real time to meet the requirements of high dynamic strike in the terminal stage of flight vehicle. In consideration of the uncertainties in the terminal guidance initial parameters, the optimization model of uncertainty-based terminal guidance initial parameters and guidance law parameters was built. The circular error probability and the probability of impact points in the effective damage radius were considered into the multiple-objective function. Effective global optimization and Monte Carlos method were used to obtain the optimum of initial parameters and guidance law parameters efficiently. It was shown that the accuracy of impact point is improved significantly, which can further provide decision support for the connection point of terminal guidance in the stage of vehicle conceptual design.

Abstract:A method of trajectory design and optimization for fast reentry arrival was proposed for the applications of large reentry velocity and strictly constrained flight time. The proposed method quickly decreased trajectory inclination and flattened trajectory on the initial reentry stage using large attack-angle, and the attack-angle and bank-angle variation rules on the later reentry stage and glide stage were jointly designed and optimized to significantly decrease terminal velocity and satisfy the constraints of terminal height, terminal heading and maximal dynamic pressure, maximal heat, etc. The proposed method can increase the ability of fast arrival for traditional lifting body vehicle and expand its application. Simulation results demonstrate that the terminal velocity is less than 7Ma and the lateral maneuver capacity is greater than 800 kilometers in the 12 minutes of flight time under the condition of typical vehicle parameter and large reentry velocity.

Abstract:To improve the safety of the webbing subsystem of the survival parachute, the dynamic model of parachute-webbing-dummy system was developed, and the load of the center of mass of dummy was analyzed for the varied parameters of webbing and detachment lock. For the airdrop test of dummy in the high speed, the fifteen degree of freedom dynamic model for the parachute, detachment lock and dummy was developed by using the multi-body dynamic method. The webbing was modeled by semi-mass-damping model to join the parachute, detachment lock and dummy. The parachute opening force was calculated by using the load of test. The dynamic process of dummy and the webbing for the typical condition was simulated by using the proposed model, and the reasonableness of the model was verified. The effect of the load of the dummy mass center was analyzed for the position of detachment lock, the length of webbing, and the property of the webbing material. The results of the analysis can be used for the design of the webbing and the determination of the position of the detachment lock.

Abstract:Based on the bolted flange connection structure between stages of rocket(missile), multiple experimental specimens were designed and manufactured, and four impact failure experiments of drop hammer were designed and carried out, which refers to the finite element model established by using the ABAQUS software. These experiments include axial and transverse two working conditions, and some structural characteristics of the specimen were different, such as the uniform and non-uniform distribution condition of the bolt group, the diameter of bolt and the gap between the bolt and bolt hole. In the process of experiments, the time history response data of bolts force, the time history response data of strain at key point of column section, impact force and impact velocity were collected. According to the experimental results and the measured data, the failure mechanism of the connection structure under impact load was analyzed, and it was verified that the numerical simulation results were in good agreement with the experimental results. The results in this research can be used as a reference for the load bearing capacity design of connection structure between stages of rocket(missile) under impact load.

Abstract:The main errors of tri-axial magnetometer include scale deviation error, sensitivity error and tri-axial non-orthogonal error. The non-orthogonal error of the sensor was analyzed under tri-axial orthogonal coordinate system. The sensor error model was established, and the influence of error on the shaking of the sensor was analyzed. Shake 1° to produce the error up to 109.5 nT, the error increases with the increase of the shaking angle. To control the shaking error, the calibration model was established, and through the nonlinear curve fitting to estimate the model parameters of the calibration model accurately. After compensation, the sensor output error was greatly reduced, and the shaking error can be controlled below 0.03 nT, which shows that this method can effectively reduce the influence of shaking on sensor output.

Abstract:As the applications and the demands of in-pipe robot are increasing, the problems in robot such as the coupling of output functions, the low positioning accuracy and the low reliability in complex environment, are becoming more and more serious. The axiomatic design theory was applied to the design of in-pipe robot, and a purely hydraulic drive in-pipe robot based on the flexible support structure was presented, which can meet the special needs in the horizontal well. The principle and process of axiomatic design were summarized, and the robot concept design was carried out to complete the design coupling analysis. The concrete composition of mechanical system and hydraulic system of robot were designed and its working mechanism was analyzed. Based on AMESim, the motion principle of the robot was simulated and analyzed, and the results show that the robot can achieve automatic reciprocating motion, the traction force can reach 30 kN, and the motion speed can reach 0.12 m/s. Moreover, the traction capacity and the motion speed of the robot can be adjusted separately, which means the decoupling design is realized.

Abstract:A multi-objective coordinated attitude control method was studied, which is aimed at the high precision attitude control of the dual layer air spring vibration isolation mounting. After establishing the dynamics model of dual layer air spring vibration isolation mounting and the equivalent model of charge and discharge control, the control response characteristic model was established. Then the multi-objective coordinated attitude control model was brought out based on the multi-objective satisfactory optimization method. This control method can adapt to the attitude control coupling of the superstratum and the substratum air spring vibration isolation mounting. And it can also restrain the elasticity distortion influence on the attitude equilibrium control. This control method was verified on a dual layer air spring vibration isolation mounting experimental system. It can be used in a dual air spring vibration isolation mounting for some large ship generator set and can realize the high vibration isolation efficiency.

Abstract:The existed drum-like silencer usually consists of expansion chamber with RBC (rigid back cavity) and tensioned membrane. With the effect of vibration radiation of the membrane, the transmitted acoustic energy can be reduced. In order to enable the silencer with ability of vibration isolation, a new type of silencer with FBC (flexible back cavity) was presented. The acoustic theoretical model was established using Fourier-Galerkin method. Then, the TL (transmission loss) characteristic was compared with the RBC model. Further, the silencing mechanism of the FBC silencer was studied, and the influence of the FBC parameters on the performance was also analyzed. Results indicate that the proposed FBC silencer has a better performance in low frequency. Compared with the RBC silencer having the same structural size, it can greatly improve the acoustic absorption band can be improved.

Abstract:The existing testability allocation methods exist some unreasonable problems, such as the allocation index is too low or too high. The reason is that those methods apply linear allocation function which is not consistent with testability index. Therefore, a novel allocation function based on inverse tangent function was constructed, and the allocation algorithm of fault detection rate and fault isolation rate was presented. The comparative analysis among the proposed method and the classic fault rate allocation and comprehensive weighted allocation methods shows the superiority of the method proposed. With the increase of the allocation weight (fault rate), the amplification of allocation index gradually decreases, and there will be no unreasonable allocation index which is either too low or higher than 1.

Abstract:For the noise control of the ships, due to the rigid limit of the general conditions and the acoustical abnormity, the traditional acoustical design method of the new ships cannot be used directly. For the noise control of the in-service ships, the optimized integrating method of the techniques was proposed. Based on the tactical requirement, the top noise-control targets were designed, and the targets with four criteria were validated. Combining the noise data of the refit test and the existing techniques, the primary composition project of the noise-control techniques was established. With the acoustical evaluation and optimizing, the optimized distributive system of the targets and the final composition project of the noise-control techniques were obtained. The method was validated with a model experiment. The results showed that the method can achieve an optimized composition of the noise-control techniques in the refit of the in-service ships.

Abstract:Pumps-motor aggregate is the power unit of the ship ruder system, which requires high reliability and quietness. Misalignment of the pumps-motor aggregate induces abrasion of bearing and impact between stator and rotor, result in instability and characteristic line spectrum. Plum-shaped flexible couplings possess many advantages such as simple in structure, high compensatory ability and good damping capacity, which have been widely used in ship ruder system. Establishing parallel misalignment model and angular deviation misalignment model of plum-shaped flexible coupling, and analyzing vibrating characteristic of pumps-motor aggregate provide theoretical analysis and test data on misalignment status diagnose of pumps-motor aggregate.

Abstract:In order to make the naval gun satisfy the terminal angular constraint while striking near shore maneuver target in terminal guidance section, a space terminal guidance law based on the adaptive RBF(radial basis function) approximation network and dynamic surface was proposed, which takes the dynamic characteristics of autopilot in consideration. The space relative motion model was constructed, and the extended state observer with modified tracking differentiator was used to estimate the acceleration of target. Aiming at zeroing the tracking error about line of sight angle and angular velocity, the nonsingular terminal sliding mode was designed with adopting adaptive exponential reaching law. The adaptive RBF approximation network was applied to weaken control instruction chattering. The tracking error about line of sight angle and angular velocity in system is uniformly bounded, which was proved by Lyapunov second method. Simulation experiment shows this terminal guidance law makes the guided projectile possess well terminal guidance performance while striking targets with different maneuver forms in space.

Abstract:In order to reduce the vessel′s shaft-related electric field, the equivalent circuit of shaft-related electric field was established on the basis of the analysis of the ship aft end structure, and it proved that the fluctuating resistance between the carbon brush and slip ring is the main factor that produces shaft-related electric field. The principle of the ASG (active shaft grounding) system was studied, and the prototype ASG system was developed and tested by shrinkage ratio ship model and real vessel experiments. The results showed that the shaft-rate electric field can be reduced effectively by 90% when the ASG system is employed. In addition, the ASG system will make static electric field increase when the resistance between the carbon brush and slip ring counts much in the equivalent circuit. After analyzing the factors that affect the output current of ASG system, it was found that the maximal output current is firmly related with the cathodic protection state, but not the sailing speed.

Abstract:Based on the equivalent dipole method, the analytical formula of compensation dipole field was given from the length, the angle and the size of compensated dipole. The electric field model of “corrosion dipole + compensation dipole” was established by using the principle of charge vector superposition. The simulation was taken to verify the validity of the “corrosion dipole + compensation dipole” electric field model, then to verify the influence of the compensate dipole on the ship′s electric field, finally the optimal solution was obtained. The test results show that compensation effect is the best when the compensation anode is farthest away from the terminal of compensation system, and the compensation system is parallel to the horizontal plane; as well as the original ship corrosion electric field can be offset theoretically under the compensation optimal condition.

Abstract:Due to its periodic structure, the regular planar array has problems, such as wide beamwidth, high global side lobe in beam synthesis. So, an array optimization method based on the improved genetic algorithm was proposed. A planar grid microphone array was designed to satisfy the requirement of element spacing. An objective function with the main lobe width as the constraint and the global side lobe level as the fitness was constructed. The strategy of free intersection among individuals and random element number forced mutation was adopted to increase the searching range of the population on the basis of conventional genetic algorithms. A number of optimized arrays were obtained through simulation. Compared with several regular planar arrays, the random arrays optimized by the improved genetic algorithm have better performance under different signal-to-noise ratio inputs; compared with several conventional optimization algorithms, the improved genetic algorithm has stronger search ability, the number of random arrays is more, and the performance is better, which proves the feasibility of the proposed method.

Abstract:The design of the antenna beam angle and the installation layout of sun-synchronous orbit satellites with the three-axis stabilized sun oriented attitude were put forward. And the antenna beam design and its layout scheme for obtaining the maximum data transmission time to the ground station were proposed. According to the orbit design scheme of the scientific observation satellite, a data transmission antenna pointing to specified ground station antenna beam-pointing simulation model was established. By using the satellite toolkit STK simulation software, the effect of various antenna beam angle schemes and the antenna installation orientation on the data transmission time were simulated and analyzed, the different regularities about the time of data transmission for the satellites of pointing to solar and earth station were discovered. According to the relationship between the satellite-borne data transmission capability and the different antenna beam width, the optimal antenna beam width for data transmission was obtained, which provides a design basis for the beam design and installation of this kind of satellite.

Abstract:In order to enhance the anti-jamming capability of aeronautic swarm tactical network in complicated electromagnetic environment, the simultaneous transmitting and receiving based cognitive anti-jamming radio was employed in aeronautic swarm network, and the improved energy detection method was proposed to jamming sensing. In the case of single and multi-jammer, the closed expression of false alarm probability was derived, the false detection probability and the optimal decision threshold of jamming sensing. Simulation results show that jamming sensing performance can be improved by adjusting the parameter p of the improved energy detector.

Abstract:For channel′s time variability and severe rain attenuation at Ka band when near-earth satellites transmit data, using ACM (adaptive coding and modulation) technology can make full use of link resources, and further improve data throughput relative to traditional constant coding and modulation. The design method of the near-earth satellite data transmission link with ACM mode was proposed. The data transmission link model was established under the rainfall environment, then the ACM selection mode was determined depending on the channel condition. The maximum likelihood signal to noise estimation algorithm based on pilot symbols and the moving average smoothing method were adopted at channel estimation to reduce the fluctuation of the estimated value effectively. Simulation results show that no matter on clear or rainy days, the proposed satellite data transmission link ACM mode design method can obtain high data throughput while ensuring system reliability.

Abstract:Based on over-damped RLC nonsynchronous discharge circuits, a novel high voltage rectangular waveform forming method was proposed. The theoretical analysis showed that the double exponential waveform approaches the rising edge and the flattop of rectangular waveform in a particular situation. Meanwhile the numerical simulation showed the tail of double exponential waveform can be cut off by the artificial current zero. A prototype was designed and tested. The results showed that the prototype can output an adjustable unipolar rectangular pulse with 17 kV amplitude, 330 ns ~ 5.8 μs flattop duration and 110 ~ 350 ns rising time on insulation specimen. The rising time, the positive flattop duration and the negative one of rectangular pulse are adjustable independently. The waveform is not sensitive to specimen variety.

Abstract:In order to study the influence of uncertain component failure rates to systematic reliability, a new systematic reliability life-based moment-independent importance measure was presented to analyze the components average impact of component failure rate under uncertainty to systematic reliability life. Inspired by the idea of the Borgonovo moment-independent sensitivity analysis, the proposed method fully takes the complete uncertainty information of systematic reliability life into consideration. Since the moment-independent importance measure was hardly solved accurately due to the implicit format of the inverse function of systematic reliability life function to systematic reliability function, therefore, a new method for Kriging adaptive surrogate model solving was proposed to improve the model prediction precision by adopting the response variation coefficient as the adaptive learning function and automatically increasing new samples. The two test cases of the valve control system and the civil aircraft electro-hydraulic actuator system results show that in the premise of computation accuracy, the Kriging model of systematic reliability life function can be fully approximated by adding small number of systematic reliability life test samples to the variation coefficient adaptive learning function. Hence, the new Kriging model successfully solves the importance measure problem, and the rationality of the proposed method and the high efficiency of the new algorithm are therefore verified.

Abstract:In order to improve the near-source region accuracy of the FFP (fast field program) of ocean acoustics, the factors affected the accuracy of the classical FFP were analyzed, which includes the approximation of Bessel function, the neglection of incoming wave term and the low sampling frequency at the farthest horizontal distance region. These factors can lead to large near-source region errors and incorrect results at the farthest horizontal distance region (after the calculation, the acoustic field in the region should be removed). Based on the classical FFP model, improving near-source region accuracy algorithms were presented, which includes the approximate Bessel function with incoming wave term and the solutions in the up-down two triangular domains by covering the source point and symmetric axis with the wavenumber integration solutions (using exact Bessel function). The test cases show that, compared with the classical FFP model, the proposed model can significantly improve the near-field calculation accuracy and the comprehensive performance under the condition of less absolute time increased; compared with the direct wavenumber integration method, the integration time of the improved model is significantly reduced and the practical application value is higher under the condition of the same error order of magnitude.

Abstract:The calculation model for bottom reverberation was improved with the closed-form formulas based on Lambert′s law and the numerical computation method of curve fitting, in order to solve the problem of traditional bistatic bottom reverberation. Different forms of non-flat bottom were designed and their bistatic reverberation were researched. The influence of fitting steps on the computational accuracy of signal-to-reverberation-ratio was also discussed in the situation of periodic or aperiodic non-flat bottom. The simulation showed that the proposed method can quickly get the signal-to-reverberation-ratio of complex bottom terrain when the fitting step is appropriate. Compared with the classical elemental scattering model, the developed model can improve the computational efficiency greatly, while simultaneously keeping the accuracy.

Abstract:The surface deformation of airborne radome fabricated by PMI foam sandwich structure will happen when environment temperature was changed and the deformation will influence the performance of the radome. However, it is difficult to detect and analyze the thermal deformation of the radome in real time. The radome was calculated and analyzed by the model, which was established by using indirect thermal-structural coupling method in ANSYS. The traditional thermal expansion flake model used to analyze the calculation result in theory. Based on the analysis, the temperature shock test was designed and carried out. Result shows that the thermal-structural coupling deformation of the radome fabricated by PMI foam sandwich structure as the comprehensive strain trend that the expansion degree is the largest at the edge and the expansion degree gradually decreases from the edge to the center of the transparent surface. The average difference between the strain value of indirect thermal-structural coupling calculation and the measured strain value is 35.08%. The value proves the certain degree of credibility of the analysis method and the thermal-structure coupling model.