Abstract:With the rapid development of the scramjet, air-breathing hypersonic vehicles(AHVs) are receiving worldwide attentions, while the control system design is of the most importance. Firstly, the developments in modeling of AHVs are briefly reviewed to illustrate the complexity of the controller design. Secondly, we concentrate to display several types of design methods for AHVs, i.e., linearized model-based controller design, back-stepping controller design, T-S fuzzy controller design, adaptive control and sliding mode control. Finally, this paper summarizes several practical problems that should be taken into account at design level, for example, actuator nonlinearity, fault-tolerance control, multi-objective control, switching control, etc., which could also be regarded as some potential research directions in the control system design for AHVs.

Abstract:For the thermal analysis of equipment installed on the international space station (the ISS equipment), this paper uses formulas of external heat flux of simplified hexahedral spacecraft in the low earth orbit to calculate the external heat flux of the ISS, and analyzes the variation characteristics of the external heat flux of the ISS with orbital parameters. Based on the AMS heat flux model, the Alpha Magnetic Spectrometer (AMS) is used as an example of the ISS equipment to analyze the impacting factors of external heat flux of the ISS equipment. The results show that the external heat flux of the AMS varies with the solar beta angle and the angular distance between the ISS and Sun-ISS junction. For different solar beta angles, the thermal effect by the fixed parts of the ISS on the AMS is stable. Operations of the ISS port solar arrays, the main starboard radiator can change the external heat flux of the AMS. The variation of external heat flux of the AMS with the ISS normal flight attitude is different from the circumstance with ISS slide flight attitude. Therefore, the major impacting factors of the external heat flux of the ISS equipment are the solar beta angle, the angular distance between the ISS and the solar-ISS junction, the ISS configurations and the ISS operations.

Abstract:To achieve the manned asteroid exploration, the design and optimization method of two-impulse round-trip transfer trajectory for manned asteroid exploration is presented in the strict time constraint. According to the characteristics of the manned asteroid exploration, the scheme of the two-impulse transfer trajectory is established. Then the two-impulse round-trip transfer trajectory is designed preliminarily on the basis of the scheme. In each stage of the transfer trajectory, the launch window and the reach window are optimized by the sequential quadratic programming algorithm. Finally, the optimum two-impulse round-trip transfer trajectory is obtained. The simulation results show that the design of the optimum two-impulse round-trip transfer trajectory given in this paper is able to control the single impulse within 5 km/s, which is enough to achieve the manned asteroid exploration missions for 300 days by little energy.

Abstract:The fault detection method of symbolic dynamics is proposed to detect the tiny faults of flywheels. Firstly, the symbolic dynamics algorithm transforms the flywheel current into a series of symbols. The signal noise reduction and data compression can be accomplished by the symbol generation. Secondly, the D-Markov machine can define the abnormal transitions of symbol sequences and produce the probability state transition matrix. Then, the number of symbols is selected from the change in entropy of symbol sequences. Moreover, the symbol probability vector can be obtained according to the eigenvector of the probability state transition matrix. The threshold of distance among the symbol probability vectors can be used to detect the faults of the flywheel. Finally, The simulation results show this method can identify varying degrees of faults in the flywheel and achieve the tiny fault detection by the distance among the vectors. Compared with the extended Kalman filter method, the proposed method can detect the faults of flywheel by using the single variable without the complicated kinetic modeling. The proposed fault detection method in this paper can be also used in the other components of satellites, which can learn the system behavior from process data and have the merit of portability.

Abstract:The fault detection problem of discrete time linear switched system is studied by using the robust fault detection filter in the framework of mixed H_{_}/H_∞. First of all, residual is obtained by constructing fault detection filter. For the purpose of improving the accuracy of fault detection, weighted H_∞ performance is used as the robustness indicator of residual to disturbance, and H_{_} performance is regarded as the sensitivity indicator of residual to fault. As a result, the problem of robust fault detection filter design is converted to a multi-objective solving problem under the mixed H_{_}/H_∞. performance index. Then, multiple Lyapunov functions and average dwell time approach are used for deriving the preliminary result of filter design. Moreover, the couple between Lyapunov matrix and system matrix is removed by introducing the slack variables, and less conservative results are obtained. All results are in the form of linear matrix inequality. Finally, a numerical example that the parameters of the fault detection filter are designed is given to show that the designed filter can realize the function of fault detection.

Abstract:This paper proposes a new method based on combined multi-feature metrics in order to meet the requirements for identification of satellite local targets. Firstly, we analyze the local physical characteristic of satellite, and construct the local component fractal clustering parameter sets of the fusion morphology multi-feature metrics. Then, a component-clustering model is formulated based on weighted combination of clustering features. Consequently, an optical identification algorithm is proposed to deal with the problems of image degradation and partial occlusion in optical imaging of space targets. Based on the recognition probability in its practical application, the efficiency and robustness of the recognition algorithm is improved by using optimal weighting coefficients in the iteration of particle swarm optimization algorithm. Finally, using four typical satellites and Galileo satellite scaled model, the performance of the identification algorithm is analyzed and verified. Experimental results show that the algorithm is able to identify the satellite component and the identification probability is no less than 0.95, in the case of low contrast, SNR being 5 and severe deformation and mutual occlusion of the components.

Abstract:In order to measure the Euler angle of the axis perpendicular to the ground level (yaw axis) of the triaxial air bearing table, a new approach for attitude estimation using an indoor star tracker is proposed. Considering the difference of the working condition between the indoor star tracker and the star tracker on orbit, this study is to improve the indoor-star tracker attitude estimation. The iterative attitude algorithm is used in the attitude estimation model of the indoor-star tracker to achieve a higher precision attitude. Because the iterative attitude algorithm requires a good guess of initial altitude matrix, an attitude optimization using the particle swarm optimization is introduced to get the initial attitude matrix. The simulation results show that the improved attitude estimation based on an indoor-star tracker can improve the attitude estimation precision of the yaw axis when measuring all three Euler angles efficiently.

Abstract:In order to analyze the impact of tether flexibility on the dynamics of CCPTS (Continuous Cislunar Payloads Transfer System) the 2D flexible dynamics of CCPTS is built by using Lagrange method and the numerical simulations are presented. Firstly, the comparison analyses between the 2D flexible model and the 2D rigid model show that the flexibility of the tether affects the orbital elements and attitude elements of CCPTS, and makes these elements of CCPTS out-of-step and increases with increasing time. The chief satellite’s radial acceleration and true anomaly angular acceleration produce some burr due to the flexibility of the tether. The gravity gradient torque caused by the tether affects the CCPTS differently. The angular velocity of tether by the gravity gradient torque regularly varies with time when external torque is zero. However, the angular velocity increases linearly with time while external torque is nonzero and the increasing speed is decided by the magnitude of the external torque. Moreover, the transverse vibration and longitudinal vibration of the tether are affected by the variations of the initial tether angular velocity and tether length.

Abstract:In this paper, a set of dimension parameters of the sub-wavelength structural anti-reflection film are designed to improve the photoelectric conversion efficiency of flexible substrate solar cell and reduce the surface reflection losses. The designed parameters are simulated in TracePro optical simulation software. The simulation results show that the flux enhancement effect is optimum when the Nano-column height is 72 nm, the duty ratio is 0.5 and the grating period at 300-440 nm for the sub-wavelength structural film. Using Nano-imprinting technology, a polyimide membrane anti-reflection is fabricated based on the template of a vesicular structural anodic aluminum oxide (AAO). The influence of the technological parameters, which is of the fabricated AAO template and its Nano-imprinting technology, on the polyimide (PI) transmittance of the films is tested by scanning electron microscope and ultraviolet-visible light detector. In experiments, we fabricate the AAO template in 0.3 mol/L oxalic acid solution consecutively reacting for 1 h in 70 V constant voltage mode. The PI film is obtained with the insulation being 10 min at 280 ℃ and 800 kg pressure. The test results show that when the transmission spectrum is from 440 nm to 1 000 nm in air mass 1.5 (AM1.5) atmosphere, the transmittance of the film is increased by 2%~5% than the primitive PI film.

Abstract:In order to investigate the influence of initial disturbances on the cavity profile, tail-slapping and ballistic characteristics, the computational fluid dynamics(CFD) model that can be used to solve the coupling equations of rigid body dynamics and unsteady reynolds averaged navier-stokes (URANS) of fluid under different initial disturbances is established based on the CFD program CFX and its expression language CEL. The cavity profile pressure distribution of the projectile tail and ballistic characteristic when the tail-slapping occurs are studied using this model. The result shows that the tail-slapping of the projectile destroys the symmetry of cavity profile; the initial disturbances have slight influences on the velocity and displacements in x-direction but have obvious influences on the vertical displacements; the amplitudes and frequencies of the pitch angle, angular velocity and angular acceleration increase with the increase of the initial disturbances.

Abstract:The finite volume method, VOF (volume of fluid) multiphase flow model, and dynamic grid technique were introduced in order to conduct the numerical simulation of vertical high-speed water entry process of axisymmetric projectiles with five different heads. The influences of the head types on the cavity shape, the projectile hodrodynamics and trajectory properties were studied. The results show that the head type has significant influences on the cavity shapes, surface closing time of cavities, resistance, depth and speed of water entry process. The radius of the cavity induced by sphere and truncated sphere projectiles is smaller than that of the projectiles with the other three head types. The surface closing time decreases in the order of flat head, sphere head, cone head and truncated cone head. The pressure on the projectiles is pretty high and the distribution of the pressure on the sphere or truncated sphere head is uneven so that high shear stress exists on these heads. The water entry velocity decreases more slowly and the depth increases more quickly as the projectile head has a better streamline. The drag coefficient decreases in the order of flat head, truncated sphere head, truncated cone head, cone head, sphere head.

Abstract:In order to solve the high order controllers caused by traditional robust design method and the robust performance issues in classical PID method design process, a new kind of fixed-structure H_∞ controller design method based on constrained particle swarm optimization algorithm is proposed and applied to the missile controller design by taking the advantages of both robust method and the PID method. A gradient-based correction algorithm is used to amend the violating constraint particles, which shows the superiority of this method by comparing performance test, test functions and other three commonly used constrained optimization algorithms. Meanwhile, for the three-channel sample missile control object model, the performance index function in time domain performance, the robustness properties and constraints are provided, and then the controller is designed by adopting the gradient-based correction particle swarm algorithm for the typical missile fixed control structure. The simulation results show that the sample missile control system meets the time domain performance index and the robust performance index.

Abstract:To verify the reasonability of calculating the flexible rocket’s aerodynamic forces based on the quasi steady theory and the linear theory when both the deformation and the attack angle are small enough, the computational fluid dynamics (CFD) method is used to calculate the rocket’s lift and drag coefficients. Using this method and the empirical formula, the rocket’s aerodynamic coefficient derivatives distributions are obtained. The transfer matrix method of the linear multibody system dynamics (MSTMM) is applied to get the rocket’s frequencies and mode shapes. Under the assumption of quasi-steady theory and linear theory, using the obtained aerodynamic coefficient derivatives distribution, the aerodynamic forces of two bended rochets’ the deformations of which are based on the first order mode shape are calculated. To judge the reasonability of the linear theory, the CFD method is also used to simulate the two models. Compared with the CFD method, the proposed method has high precision under the practical flight conditions. In addition, when the bending degree is much higher than the possible deformation, the precision of the rocket’s nose is still fine but very low in the tails position for the proposed method.

Abstract:This paper proposes a debiased converted measurement filter with Doppler measurement to deal with the problem of high nonlinearities in state space model measurement equation in direction cosines coordinates of phased array radar. Considering the relationship between the range measurement error and Doppler measurement error, a pseudo measurement is constructed by the product of range and Doppler measurements to reduce the high nonlinearities of the Doppler measurement. Then, via taking the second-order Taylor series expansion to the direction cosines variable, consistent estimations of mean and covariance of the converted measurement error are derived. Finally, the problem of pseudo measurement nonlinearities is coped with by sequentially processing the position measurement and pseudo measurement. The simulation results prove that the filtering performance is improved indeed by introducing the Doppler measurement. Moreover, compared with the common extend Kalman filter and unscented Kalman filter, the proposed debiased converted measurement filter shows better tracking performance indirection cosine coordinates.

Abstract:This paper proposes an adaptive interactive multiple models (IMM) tracking algorithm in order to improve tracking performance of strong maneuvering group targets in high measurement error. First of all, we introduce a strong tracking filtering algorithm with multiple suboptimal fading factors to improve the estimation accuracy of the group centroid in the strong maneuvering stage. Secondly, considering the influence of measurement accuracy on the extension state, the measurement error and extension state are formulated in a likelihood function, and then the error covariance of the measurement can be adaptively updated by using the innovation and the memory fading iterative process. Finally, we use the quasi-Bayesian approach to adaptively update the model transition probability. The model transition probability is modified by the measurement to suppress the non-matching model and amplify the matching model. By this way, the tracking model and targets state can be matched in real time. The simulation results show that, the proposed method is effective to improve the estimation accuracy of the centroid state and the extension state.

Abstract:The tracking problem of the nonlinear system with input saturation is investigated by using a backstepping approach based on fuzzy state observer, where the underline system contains immeasurable states and unknown control directions. Firstly, a fuzzy state observer is designed to estimate the immeasurable states. Then, the Hyperbolic tangent function with smooth property and a Nussbaum function are used to handle the input saturation. The bound of the output tracking error is set by the prescribed performance methodology. A robust controller is designed combining the backstepping approach and the dynamic surface method. The Lyapunov theory is applied to analyze the stability of the system. It is proved that all the signals of the resulting closed-loop system are semi-globally uniformly ultimately bounded(SGUUB). Finally, the longitudinal dynamics as the simulation model is given to show the effectiveness of the proposed control approach.

Abstract:To improve the measurement angular resolution of star sensors while maintaining high update rates, the detector of four million pixels, parallel output data through multi-channels is chosen. The problem of star sensor’s image processing based on this kind of detector is solved by designing a method of using marker to achieve extraction of star centroid fast and efficiently. Algorithm is divided into markers calculation of multi-channel and target processing of channel boundary：markers calculation of multi-channel is mainly to solve the problem of image processing within the channel, while among channels using parallel processing method; target processing of channel boundary is mainly to solve the target cross border splicing problem. In the high frequency clock is 100 MHz, under the condition of using the FPGA implementation algorithm based on level 4 lines parallel processing architecture, and the actual test validation. The validation results show that the algorithm can quickly and correctly extracts as target point on the surface of the detector. Accuracy of positioning extraction of single star is better than 1/172 pixel, update rates is better than 9.5 Hz, which meets the requirement of the star sensor accuracy and high update rates.

Abstract:To obtain the stalling characteristics of wedge rudders under cavitation conditions and to explore the mechanism leading to the stalling, the ventilating cavitation flow field around supercavitating vehicle which uses a 24° wedge rudder as the aft control plane was investigated by establishing the three-dimensional numerical simulation model and the water tunnel experimental system. The change law of the wedge rudder's lift, drag, and cavitation characteristics along with rudder angle were studied by the numerical simulation and water tunnel experiment, respectively. According to the research results, the proposed numerical and experimental methods are reasonable; the drag coefficient of the wedge rudder varies slightly with the rudder angle in the range of 0°-5°; the lift coefficient has good linearity in the rudder angle range of 0°-8° and 9°-12°, but the slope of the former range is considerably bigger than that of the latter range. Moreover, when the rudder angle exceeds 8°, the lift coefficient of the wedge rudder will reduce sharply, stalling will happen, and the low-pressure surface of the wedge rudder will be covered by cavity. Therefore, the cavitation occurring on the low-pressure surface of the wedge rudder may be the main reason leading to the stalling. Furthermore, it is suggested that the allowable rudder angle of the 24° wedge rudder should not exceed 8°.

Abstract:Since the implicit limit state function for thermal-structural coupling of a beam is difficult to determine,a non-probabilistic resonance reliability method for the thermal-structural coupling of a beam is presented. The method is based on the theories of resonance reliability analysis,the improved Kriging model and finite element analysis techniques. In the proposed method,the approximation model for the reliability function of the beam structure is established by Kriging method,and the improved Kriging approximate model becomes more close to the limit state function by using the active learning method to improve the selecting method of new sample points. Then considering the uncertainty of structure parameters,the parameters of beam structure are described by interval variables,so that the approximation model for the non-probabilistic resonance reliability of the beam structure including ellipsoidal convex sets can be established. Finally,the non-probabilistic resonance reliability index of the beam structure is calculated by the optimization method. The calculation results show that the proposed method is of rationality and high accuracy,and can provide a feasible way for the non-probabilistic resonance reliability analysis of thermal-structural coupling of the beam structure.

Abstract:This paper proposes a two-dimensional constrained adjustment method with fused depth difference and a three-dimensional constraint adjustment method with additional depth by using the depth information from pressure transducer,in order to solve the problem of unstable vertical solutions in traditional underwater control network solutions. The considered problem exists in a control point coordinate that is determined based on a three-dimensional space distance intersection. Applying the former method with a given depth difference,the underwater control point coordinate can be determined by transforming the three-dimensional space intersection problem into a two-dimensional plane intersection problem and then constructing an adjustment model in the two-dimensional plane. Applying the latter method,the underwater control point coordinate is determined by solving the space distance equation combined with high precision observations and constrained conditions of the depth. We carried out experiments in Songhua Lake,and the experiment results show that the calculation precision of underwater control point coordinates is improved 2~5 times by applying both two methods. It implies that introducing the depth information into the calculation process of underwater control network and then constructing adjustment model can be helpful to improve the stability and precision of the three-dimensional solutions of the control network coordinates.

Abstract:To study the dynamic fracture performance about the compact tension(CT)specimen,the split Hopkinson bar was improved,and a kind of clamping device between the loading point of incident bar and transmission bar was designed to study the dynamic fracture test on the CT specimen. In terms of tensile stress wave propagation,the finite element method based on ANSYS/LS-DYNA had been adopted to realize the dynamic fracture response and calculate the relative parameters about the dynamic fracture toughness. The result shows that,the stress distribution in the CT specimens from the asymmetric state to the symmetric distribution needs about 80 μs,and then stress distribution cloud in the specimen becomes symmetric and the stresses on two points become equal. Thus the CT specimens come to the balance state,meeting the dynamic fracture toughness test requirements. The effect of the chuck section and the pin diameter on the stress wave propagation and stress balance was studied,which will provide the basis for the further research on the Hopkinson tensile bar and the dynamic fracture test on the CT specimens.

Abstract:In order to study the influence of ship tail structure on the airwake, the simple frigate shape SFS1 has been chosen for this study and the numerical simulation of ship airwakes hasbeen performed. The ANSYS FLUENT standard turbulence model is used on the structured grids generated byANSYS ICEM. The influences of the closing/opening state of the hangar, the hangar height and the flight deck length were simulated. The ship airwakes in different conditions were compared by analysing the physical parameters such as the velocity and pressure. It is shown that: the flow field environment will become better when the hangar height becomes lower and the flight deck beomes longer; the airwake becomes worse when the door is ajar than that when the door is closed or open; while neither airwake is superior when the door of hangar is closed or open completely. The present work will provide theory and data support for the modification of ship in service and the improvement of ship in construction,which will improve the ship airwake for shipboard aircrafts, and the capability to command and control the launch and recovery of shipboard aircraft.

Abstract:In order to optimize the structure configuration of the truss type legs of the self-elevating platform,the parametric modeling method and GeniE software of SESAM were adopted to evaluate the performance and strength of different leg configurations. Towing and survival conditions were analyzed in the study process. Series of leg bay heights were chosen for strength analysis under towing condition. Different leg configurations with chord spaces and bay heights under survival condition were chosen to calculate the anti-overturning capacity,maximum reaction of support,locking force and the UC values of leg components. Considering the leg weight,the optimal decision for the leg configuration was given according to the principle satisfying the optimized strength and economy. A certain jack-up unit leg design was finished rapidly by this method. The study result indicates that the present method is effective for leg configuration selection and optimization in the preliminary design stage.

Abstract:The dynamic link budget of low earth orbit (LEO) satellite data transmission link is analyzed, and the mathematical model of link efficiency is discussed. In order to enhance the data transmission link performance for exploration satellites, Variable Coding Modulation (VCM) system is applied to reduce link resource waste and improve the satellite-ground transmission throughput without increasing power consumption and design cost. A VCM schedule designing algorithm is illustrated for optimizing link throughput within the data transmission period. For a satellite system with foreseeable orbit and based on its dynamic link budget results, the proposed algorithm selects variable coding modulation combination under the bit error rate requirement to fit the link budget curve and keep a relatively constant link margin to achieve optimal link efficiency. Finally, on the basis of the proposed algorithm, a VCM data transmission system is designed for a LEO sun-synchronous satellite. According to the simulation results, the remarkable advantage of the proposed method is proved by comparison with traditional constant coding modulation design.

Abstract:In order to make out an objective and fine assessment on risk conduction of weapon development projects,a fuzzy cloud model algorithm is utilized to calculate the impacts that arise from single risk conduction factor upon schedule,cost and performance risk. Then the total impacts from all risk conduction factors are calculated through weighted summation. In addition,the comprehensive risk value is calculated by the ranking method of triangular fuzzy number complementary judgment matrix based on the possibility degree theory. Finally,the values of single impact factor on risk and the total risk sequence are obtained through the simulation operation on X-51 propulsion system project,which requires explicitly for strengthening the index of supervisory control and management. They also verify the validity and feasibility of the proposed identification and evaluation method for risk conduction. This method provides decision-making support for the risk conduction managers of weapon development projects.

Abstract:In order to decrease satellite attitude turnover and guarantee high-accuracy pointing for satellite optical payload,a novel method is designed for horizontal deployment experiment of satellite solar array. A multi-degree-of-freedom balance weight strategy is used to counterbalance the gravity. Firstly,the kinematics model and dynamics model are established. Then,the error analysis is deduced. Finally,the experiment is carried out. The experimental results show that the method can truly simulate the micro-gravity in-orbit environment compared with the previous method. Moreover,it is very strict with mass deviation and centroid deviation of solar array and the system frictions. The results indicate that the model and test methods are correct and meet the test requirements.

Abstract:In order to improve indoor thermal comfort and reduce the energy consumed for heating in rural residential buildings in severe cold regions of northeast China,the paper analyzed the influencing factors using field survey and software simulation and established the heating energy consumption prediction model. The paper studied the influence factors of shape coefficient,window to wall ratio,heat transfer coefficient of building envelope,orientation,absorption coefficient,thermal inertia,attached sunspace,snow cover with the help of BES-01 temperature recorder and DeST-h software. The results showed that the shape coefficient,windows to wall area ratio and heat transfer coefficient were positively correlated with heating energy consumption,the best orientation is south and southeast,absorption coefficient was negatively correlated with heating energy consumption,attached sunspace can effectively improve indoor thermal environment,and snow cover can play a role in roof insulation. The prediction model can provide design basis for rural energy-saving residential buildings. The paper can guide and improve energy efficiency design level of rural residential buildings in severe cold regions of northeast China.