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    • Collection Down  5 Views  9
      At present, the further missions of China's planetary exploration projects to Venus, Jupiter has also begun, and their key technical researches have been carried out. However, these planets all have dense atmospheres and higher atmospheric pressures, which are significantly different from the atmospheric environments of Earth and Mars. In successful planetary explorations in the past, it has been found that the aerodynamic deceleration process in such complex planetary atmospheric environments requires multi-stage parachutes to complete and parachute opening and operation under transonic/supersonic conditions. It should be noted that the nominal diameter of the first stage guide parachute is significantly smaller than the main parachute and smaller than the forebody diameter. The fluid structure interaction mechanism and aerodynamic characteristics between two-stage parachutes of different sizes and the forebody are still unclear, till now, there are very few related research reports. In this study, based on conical ribbon parachutes and disk-band-gap parachutes suitable for dense atmospheric planetary exploration missions, the fluid structure interaction mechanism of flexible parachutes in different planetary atmospheric environments is numerically studied using the immersion boundary method, and the aerodynamic characteristics under different freestream Mach numbers, canopy types, atmospheric components, and parameter to diameter ratios are investigated in details. As a result, it was found that in the atmospheric environment of Titan, the conical ribbon canopy (its diameter ratio is 0.3) steadily descends at transonic speeds, and the projected area of the canopy gradually increases over time. The drag coefficient reaches its maximum at Mach 1.5, but its fluctuation monotonically increases with the increase of Mach number. In addition, at Mach number 0.95, the canopies exhibit extremely severe oscillation when the diameter ratios are 0 and 1.0. By comparison, in the atmospheric environment of Jupiter, when the freestream Mach number is transonic, the change in projected area of the conical ribbon canopy becomes smaller over time. The drag coefficient and its fluctuation will monotonically increase with the increase of Mach number, and the lateral force coefficient and its fluctuation reach their maximum at Mach 1.5. Finally, a comparison was made between the stable descent process of parachutes in the atmospheric environments of Titan, Venus, and Jupiter, and it was found that the conical ribbon canopy in the Jupiter atmospheric environment has the best performance, larger drag coefficient, and better stability.
    • Collection Down  5 Views  7
      To further advance the development of dual synthetic jet (DSJ) based anti-icing/de-icing technology, an experimental setup for con-trolling the trajectory characteristics of droplets using DSJ was established. The effects of the actuator’s driving voltage and driving signal phase on the trajectory of droplets, when the actuator was stationary relative to the droplet and when there was relative motion, were studied using high-speed photography. The horizontal velocity increment of the droplet (named as Vxdroplet) 375 μs after being affected by the jet was used as an index to assess the impact of the jet on the trajectory characteristics of the droplet. When there was no relative motion between the actuator and the droplet (the turntable was stationary), Vxdroplet increased linearly from 0.65 m/s at a driving signal amplitude of 60 V to 2.29 m/s at 165 V. The phase of the jet at the time of droplet generation had a significant impact on the trajectory of the droplet. With a driving signal amplitude of 165 V, Vxdroplet varied from 1.11 m/s to 4.98 m/s at different initial phases φ of the jet. When the actuator approached the droplet at a linear speed of 4.4 m/s (achieved by rotating the turntable), Vxdroplet increased from 1.57 m/s at a driving signal amplitude of 60 V to 3.67 m/s at a driving amplitude of 165 V. Moreover, the rotation of the turntable itself had little effect on Vxdroplet. Additionally, when the turntable was rotating, the change in Vxdroplet with the initial phase φ of the jet had a time lag compared to when the turntable was stationary, but the overall trend was similar, and the corresponding Vxdroplet was larger when the turntable was rotating. The results indicate that the jet could rapidly increase the velocity of the droplet to a level close to the velocity of the jet in the area where the droplet was generated (O(m/s)). Even when the turntable rotated at higher speeds (with a maximum relative linear velocity of 22 m/s between the actuator and the droplet in the ex-periment), the dual synthetic jet still significantly affected the trajectory of the droplet.
    • Collection Down  4 Views  14
      Aircraft starter/generator, meeting the lightweight and high integration requirements of more electric aircraft for aircraft power supply system, has been widely studied. Fault diagnosis of its components is crucial to ensuring the safe, stable and efficient operation of aircraft power supply system. As the most prone component to failure, rotating rectifier’s fault diagnosis is of great practical significance. This paper systematically reviews current researches on rotating rectifier fault diagnosis methods. Firstly, the development status is summarized both domestically and internationally from four perspectives: fault modeling, fault signal processing, intelligent algorithm application and industrial fault detection technology. Secondly, the common di-ode faults and fault transfer path in rotating rectifier are introduced, along with some difficult points of fault diagnosis in practice. Then, analyzing fault mechanism and starting from the different ways to acquire fault electrical signal, existing fault diagnosis methods of rotating rectifier are classified and summarized. Their advantages, disadvantages and application scope are discussed in depth. Finally, a comprehensive outlook on the future development trends of rotating rectifier fault diagnosis is provided to offer insights and references for colleagues interested in this field.
    • Collection Down  8 Views  12
      In order to analyze the influence of unsteady pulsating high pressure in the air-breathing rotating detonation engine combustor on the flow characteristics of inlet and guide the design of the inlet, the spatio-spatial characteristics of the pressure in the outlet section of inlet were considered, the propagation process and flow characteristics of moving shock wave in the inlet were simulated by adopting three-dimensional unsteady numerical simulation method. The configuration characteristics, propagation velocity, pressure and other key parameters of the moving shock wave were analyzed, the flow loss was obtained, and the influence of the angular frequency, peak and time-average values of the pulsating back pressure on the flow characteristics was obtained. The moving shock wave leads to the flow characteristics of low-pressure airflow pressurization and deceleration and high-pressure airflow decompression and acceleration in the inlet, and compared with the steady back pressure condition, the influence boundary of pulsating back pressure is more upstream; the higher the frequency, the longer the circumferential length, the more times the flow passes through the shock wave, however, the average total pressure loss of outlet at different frequencies basically remains unchanged; the time average pressure ratio are kept constant at 12000rad/s and 19.1, respectively, when the pressure peak value ranges from 0.5MPa to 1Mpa, the average total pressure loss of the outlet varies from 43% to 46%; the angular frequency and peak pressure ratio are kept constant at 12000rad/s and 49.5, respectively, when the time-average pressure increases from 0.22MPa to 0.32MPa, the average total pressure loss of the outlet decreases from 52% to 40%, compared with the steady back pressure condition, the total pressure loss is 2%~8% larger. The results show that the unsteady pulsating back pressure leads to the big differences between the flow characteristics of the air-breathing rotating detonation engine inlet and the traditional engine inlet, the flow loss is larger, and the influence boundary of shock wave is closer to the upstream.
    • Collection Down  14 Views  32
      Spatial-temporal constrained guidance is a method that simultaneously meets impact angle and time constraints. A spatial-temporal constrained guidance law with precise control capability is designed for the homing guidance problem in this paper. First, based on the time-to-go estimation of the optimal impact angle constrained guidance law, a varying-gain impact angle constrained guidance law whose time-to-go can be precisely predicted is inversely derived without any small angle approximation. Second, an impact-time error feedback term is added to the above guidance law to obtain the singularity-free spatial-temporal guidance law for simultaneously precise control of impact angle and time. Third, by introducing the remaining trajectory length as an independent variable, the proposed spatial-temporal guidance law is extended to practical scenarios with missile speed variation. Finally, the effectiveness and advantages of the proposed guidance law are verified through several numerical simulations.
    • Collection Down  8 Views  22
      Under the pressure of hypersonic inflow, the surface of an inflatable deceleration structure will deform on the wind-ward side, thereby changing the flow field. Based on the thermochemical non-equilibrium reaction model, simulations are conducted for the flow past an inflatable deceleration structure before and after surface deformation, analyzing the influence of surface deformation on the flow. The shape of inflatable deceleration structure is a blunt nosed cone with a radius of 2.4m and a half cone angle 60°, consisting of a rigid head face and 6 inflatable rings. The numerical model adopts a 5-component dual-temperature thermochemical reaction model, and the wall catalytic conditions include non-catalytic and fully catalytic. The influence of surface deformation on flow characteristics, heat flux, and pressure under different attack angles is investigated. The results show that surface deformation can lead to periodic temperature and pressure fluctuations in the shock layer of the inflatable deceleration structure, as well as non-uniform distribution of dissociated components. The influence of surface deformation on flow variables weakens as the attack angle increas-es. After the surface deformation, the change in velocity leads to increase in the heat flux and decrease in the pres-sure at inflatable rings, as well as decrease in the heat flux and increase in the pressure at the concavities between inflatable rings. The effect of surface deformation on the pressure is weaker than that on the heat flux. There is no significant change in the aerodynamic coefficients of the front face of the inflatable deceleration structure after defor-mation.
    • Collection Down  9 Views  14
      Abstract: This paper investigates the asymptotic tracking control problem of hypersonic flight vehicle with unknown model. In the absence of model prior knowledge, although the traditional intelligent control algorithm based on neural network/fuzzy system can achieve stable tracking of the expected instructions by reconstructing and compensating the unknown dynamics in the model, it cannot obtain accurate tracking results due to the existence of reconstruction errors. To solve the problem of as-ymptotic tracking control of hypersonic flight vehicle under unknown model, a modified Lyapunov function (MLF) is construct-ed by introducing the concept of error accumulation factor, and a new fuzzy adaptive control algorithm is designed based on the MLF. By ensuring the boundedness of modified Lyapunov function, the algorithm can achieve the asymptotic tracking performance without extra processing of the fuzzy reconstruction error. The stability of the closed-loop system is proved by means of Lyapunov stability theory, and the effectiveness of the control algorithm is verified by comparative simulation.
    • Collection Down  5 Views  10
      The supply chamber can be internal carried in the unmanned aerial vehicle (UAV), separated in the target area by deploying a deceleration parachute swiftly. The agility and cost-effectiveness ratio of the airdropping can be improved significantly in this concept. However, the supply chamber is snugly assembled in internal bay of UAV the and has comparable mass with UAV, which leads to stronger aerodynamic interference in the separation flow field and different from the separation of internal weapons from combat aircraft. During the separation, the inflation and deployment of the deceleration parachute will cause highly unsteady flow fields and aerodynamic interference with the supply cham-ber and UAV. This makes it difficult for traditional methods to analysis the impact of the deployment for the decelera-tion parachute on the separation dynamic characteristics, which is described based on the Arbitrary Lagrangian-Eulerian (ALE) method. In this paper, an equivalent parachute developing method based on the combination of infla-tion time method and wall assumption is proposed. By combining with Computational Fluid Dynamics (CFD) coupled with the 6 Degree of Freedom (6DOF) equation method, an equivalent model of multi body separation accompanied by parachute deployment under Eulerian description is constructed. The integrated simulation analysis of the internal separation with parachute deployment process for supply chamber is achieved, and the impact of separation trajectory parameters and aerodynamic interference for the supply chamber is explored. Result shows that, the proposed equiv-alent method can effectively analyze the deployment of the deceleration parachute. The trajectory of the supply chamber is relatively stable, while the UAV is affected by significant pitching interference during separation and para-chute deployment. The impact of the analyzed variables on separation dynamics is nonlinear, and it is necessary to optimize the separation scheme further. Works in this paper can be the foundation for the design of UAV systems and separation schemes.
    • Collection Down  12 Views  17
      A distributed predefined time adaptive sliding mode control method is proposed for the tracking control prob-lem of a second-order fixed-wing unmanned aerial vehicle(UAV) system with stochastic switching communi-cation topologies structure. Firstly, a three degree of freedom mathematical model for fixed-wing UAV cluster is established and transformed into a second-order integrator model with disturbances. Based on the model established above, a suitable sliding surface is selected, and a distributed predefined time tracking controller is designed on this basis. Considering the interference problem faced by the UAV system during flight, an adaptive control strategy was proposed to handle it. In addition, this article cites a predefined time theorem and proves through Lyapunov stability theory that the second-order UAV system can achieve stability within the predefined time. Finally, numerical simulations have demonstrated the feasibility of the proposed tracking control strategy for a fixed-wing UAV system with stochastic switching topologies.
    • Collection Down  6 Views  11
      The orbital game between spacecraft has significant importance for space safety. Compared to the classical "one-to-one" orbital game problem, the "many-to-one" orbital game faces challenges such as high-dimensional state parameters, undefined roles of pursuers, and variable terminal conditions, making traditional differential strategy methods difficult to solve. To overcome these challenges, this paper proposes a geometric method for the "many-to-one" orbital game based on the reachable set of spacecraft. Firstly, the reachable set equivalence representation of Nash equilibrium points in the orbital game is established based on the theory of reachable sets of spacecraft. Then, the envelopment of the reachable set of spacecraft at any time is accurately solved using a grid point search method. Subsequently, the relative geometric relationship between the reachable sets of spacecraft in-volved in the game is determined by computing the solid angle of the triangulated closed surface. Finally, the binary search method is used to determine the terminal time of the game, satisfying the geometric conditions of the reachable set of Nash equi-librium points, thereby determining the spatial position coordinates of the spacecraft at the end of the game and completing the solution to the "many-to-one" orbital game problem. Simulation results demonstrate that for a typical "three-to-one" orbital game scenario, the traditional differential strategy method takes over 2 hours on an ordinary personal computer. In contrast, the pro-posed geometric method can provide the same solution within 8 minutes.
    • Collection Down  11 Views  23
      The key indicator for measuring the combat performance of an aircraft carrier is the sortie rate of carrier-based aircraft, which depends on the support station matching strategy of carrier-based aircraft. Existing works mainly use sequence matching and batch matching methods to match suitable stations for carrier-based aircraft. However, both methods have certain limi-tations, and it is difficult to ensure both real-time and quality of station matching at the same time. Facing the complex and time-varying support environment, it becomes extremely difficult to determine a reasonable support operation matching strategy. Therefore, in this paper, we propose a novel adaptive batch matching decision-making method for carrier-based aircraft support operations based on the batch matching method. First, the optimal time window division strategy is solved by constructing a reinforcement learning method for multi-dimensional environmental state encoding. Then, a highly effi-cient batch matching algorithm is applied within each time window to find the best matching solution for support opera-tions and support stations. The results of multiple sets of simulation experiments based on the publicly available Nimitz aircraft carrier data show that our proposed method can effectively respond to dynamic changes in the support environment, and can quickly solve high-quality support operation assignment plans while meeting real-time requirements.
    • Collection Down  13 Views  27
      Unmanned Combat Aerial Vehicle (UCAV) is usually a continuous and multi-round missile attack and defense confrontation process. In the process of evading incoming air-to-air missiles, UCAV should comprehensively consider the impact of maneuvers on the entire air combat confrontation mission, instead of just focusing on security factors. In this paper, the UCAV autonomous evasive maneuver strategy generation method is proposed under the coupling of tactical requirements such as miss distance, energy consumption and terminal situation advantage. The three-dimensional pursuit and escape model of UCAV-missile and the state space, action space and reward function model of UCAV autonomous avoidance are established. LSTM- Dueling DDQN (Long Short-Term Memory-Dueling Double Deep-Q Network) algorithm is proposed for this model. The algorithm fuses Double DQN (Double Deep-Q Network) and Dueling DQN (Dueling Deep-Q Network) network models, and uses LSTM network to extract timing features. Aiming at the demand conflict problem in the local coupling process, the Chebyshev method is constructed to intuitively target the Pareto strategy solution set for different local demand emphasis levels, reflecting the contradiction and coupling of local demands in air combat maneuver avoidance. Simulation experiments and result analysis show that the proposed method has good convergence speed and learning effect, and it is feasible and effective to solve the problem of autonomous evasive maneuvers in air combat for the multiple tactical requirements. The obtained evasive maneuvers can reflect different evasive tactical requirements while ensuring UCAV's own safety.
    • Collection Down  6 Views  22
      Airborne multi-aperture panoramic image compositing technology generates panoramic images with high resolution and rich details by stitching images from multiple sub-aperture or sensors, which plays an important role in many key fields such as national defense and security, agriculture and forestry, and digital surveillance. This paper introduces the development background of airborne multi-aperture panoramic image compositing technology, expounds the basic concepts and steps of panoramic image compositing, combs through the classification and development of its core parts - image registration technology and image fusion technology, and summarizes the characteristics and limitations of the current mainstream methods. Finally, combined with the current development status of air-borne multi-aperture panoramic image compositing technology, the bottleneck problem of airborne multi-aperture panoramic image compositing technology is revealed. In addition, the future research direction and possible technical ways to solve these problems are also prospected, which provides useful enlightenment for the technological progress and application expansion in related fields.
    • Collection Down  10 Views  22
      A long-wave infrared polarization imaging method was designed and experimentally verified using liquid crystal polari-zation grating as a novel beam splitting element while the fabrication of liquid crystal polarization grating was achieved. The effective imaging angle of view and grating period was analyzed to optimize the grating period and maximize an-gle of view corresponding to the optical path parameters on the basis of the designed polarization imaging method based on liquid crystal polarization grating. The transformation of polarization states were derived using Mueller matrix and parameters of the time division polarization imaging method were designed and optimized. Liquid crystal polariza-tion gratings available for long-wave infrared have been manufactured using liquid crystal material on double-side AR coated ZnSe substrates with photo-alignment technology, whose diffraction efficiency achieves 90% at 10μm wave-length. Birefringence index and transmittance of the liquid crystal material were respectively measured under 10-12μm band and 7.5-12μm band with wave-plates manufactured using same materials. Experimental polarization imaging system was constructed with the prepared long-wave liquid crystal polarization grating and wave-plate to accomplish polarization imaging and imaging processing that calculate the polarization states. A measurement error of less than 1 degree was achieved by comparisons between the preset values and measured values.
    • Collection Down  10 Views  22
      In recent years, the development of Carbon Fiber Reinforced Polymer (CFRP) in the aviation industry has attracted much attention. Quantitative evaluation of its fracture process and damage prediction has become the key of the research. An experimental system for measuring interlaminar crack strain field of CFRP cross-ply laminate samples based on sampling moiré method is established. The system consists of a three-point bending test loading device, a microscope, an industrial camera and a CFRP sample with a nanoim-print grating. In this paper, the system is used to measure the strain field in the loading process of the specimen, and the strain con-centration degree before the specimen begins to bend to crack initiation is quantitatively evaluated. The results show that the initiation of interlayer cracks in CFRP is directly related to strain concentration, and obvious strain concentration occurs before crack initiation. Compared with the region around the crack, the strain concentration in the crack center is more obvious before the crack initiation, and with the increase of bending load, the strain concentration in the central region increases significantly, while the strain concentra-tion in the surrounding region does not change significantly. The experimental method developed in this paper can accurately meas-ure the strain field of CFRP laminates before crack initiation and predict the location of crack initiation effectively.
    • Collection Down  13 Views  31
      Undesirable model vibration often occurs in a conventional wind tunnel force test. Large amplitude model vibrations may affect test data adversely and even threaten the safe operation of equipment. It is of great importance to fully understand the mechanism of model vibration occurrence and reduce the vibration amplitude by effective means in wind tunnel tests. The harms of model vibration are introduced at first. Then the types of model vibrations are summarized. The status and progress of reducing model vibrations by various methods are presented. The key points and technical difficulties involved in the active control method are analyzed. The existing literature shows that the active control method with the piezoelectric stack as the actuator can best meet the requirements of the engineering practice, and the vibration damping effect is better than other methods. Finally, several suggestions regarding future research of model vibration control in the large-scale wind tunnel are also presented.
    • Collection Down  5 Views  17
      Triply surface period Minimal surface (TPMS) lattice structures have a wide range of lightweight design prospects due to their lightweight, high strength and energy absorption properties, but are difficult to manufacture by traditional methods. Using Ti-6Al-4V powder as material, two lattice samples with different porosity of Gyroid and Primitive and solid tensile samples were prepared by selective laser melting (SLM) technique, and the mechanical properties and microstructure were analyzed. The results show that the mechanical properties of TPMS tend to decrease with the increase of porosity, and the plasticity of Primitive structure is better than that of Gyroid structure, but the overall strength is lower than that of Gyroid structure. The compressive yield strength and tensile strength of TPMS lattice structure reach 498MPa and 373MPa, and the mechanical properties of TPMS lattice structure are better than those based on bar diameter class (BCC, FCC), and the elongation of lattice structure is 2.8%~14% higher than that of solid sample. The fracture mode of the two lattice structures is a mixture of toughness and brittleness, and there are porosity and unfused powder on the surface of the lattice structures, which does not affect the failure mechanism. The tensile strength and elongation of the solid tensile sample prepared under the same process parameters reach 1050MPa and 17.5%, which is superior to the mechanical properties of traditional cast Ti-6Al-4V alloy.
    • Collection Down  10 Views  30
      Ceramic matrix composites combine the performance advantages of carbon/carbon materials and ceramic materials, and become important thermal structural materials in the aerospace field. The reactive melt infiltration method is the main process for the preparation of ceramic matrix composites, in which the high-temperature melt enters the carbon/carbon preform through capillary action, and the chemical reaction with the carbon matrix is formed into the ceramic phase and embedded in the pores, so as to achieve efficient densification. However, due to the high temperature and high activity and short-term intense thermophysicochemical interactions in the infiltration process, it is challenging to observe the experiment and control the process parameters. In this paper, based on the characteristics of the reactive infiltration process, considering the channeling characteristics between different pores, and distinguishing the microstructure characteristics of the precast with single-hole structure and two-hole structure, a multi-physics model of reactive infiltration is constructed that is closer to the pore structure of the real preform, and the error between the predicted temperature value and the experimental value of the model is within 3%, and the error between the predicted value and the experimental value in the early stage of the reaction is within 3%, and the overall prediction accuracy is much better than that of the Washburn equation and its modified form. Finally, the influence of the pore structure mode on the temperature distribution and reaction rate distribution of the reactive infiltration process is discussed, and it is found that the two-hole structure mode is more conducive to the infiltration of reactive melts. This study provides a multi-physics coupling method for the permeation process of reactive melt in porous carbon media, which provides a theoretical basis for the optimization of the reactive infiltration process of ceramic matrix composites.
    • Collection Down  9 Views  25
      Aiming at the requirements of high precision and high completeness in navigation and positioning of spacecraft in the environment of satellite rejection, a robust filtering method for multi-source autonomous navigation is proposed, which combines strapdown inertial navigation, satellite navigation and barometric altimeter. In a short period of time after measurement interruption, this method can accurately quantify the state space model in the compact integrated navigation model through the filter estimation of the measurement uncertainty and nonlinear error model. Based on the in-depth analysis of the action mechanism of the measurement anomaly vector on the filter state output, a robust volume Kalman filter design is introduced. The suppression effect of error covariance matrix is effectively improved, and the stability of filter and the estimation accuracy of state equation are improved in the process of multi-source autonomous navigation interpretation. The simulation results show that compared with the traditional volume Kalman filter, the zero bias accuracy of gyroscope and accelerometer is improved by about 31%, the positioning accuracy of autonomous navigation system is improved by about 23.77%, the attitude Angle error is suppressed to a certain extent, which provides a reference for the terminal application of multi-source autonomous navigation system under the new generation of national integrated PNT system.
    • Collection Down  3 Views  18
      In order to realize the absolute heading angle acquisition, an absolute heading angle solution method based on simplified solar azimuth is proposed. By inputting the position information of the observation place and the observation time infor-mation, the solar declination angle and the solar time angle are obtained, so as to calculate the solar azimuth angle under the geographic due north coordinate system. Then using the polarization distribution characteristics of the sky, combined with the polarized light navigation and orientation algorithm based on the solar meridian extraction, the absolute heading angle information can be solved to achieve the purpose of navigation. The results of computer simulation and field experiments show that the rms error of solar azimuth is less than 0.01°, the rms error of outdoor static heading angle solving is less than 0.2°, and the rms error of dynamic heading angle solving is 0.53°, which basically meets the requirement of the measurement accuracy for navigation in most of the scenarios.

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Total visits: 6658907 Today visits: 1341All copyright © editorial office of Chinese Journal of Aeronautics

All copyright © editorial office of Chinese Journal of Aeronautics

Total visits: 6658907 Today visits: 1341