In the environment where global navigation satellite system (GNSS) signals are not available, positioning based on low Earth orbit (LEO) satellites signals of opportunity (SOP) is an effective positioning solution. At present, positioning based on the single LEO constellation SOP is faced with problems such as insufficient constellation configuration or less visible satellites. While, fusion positioning based on the multi-LEO constellations can effectively solve this problem, as it can improve the positioning accuracy, enhance the positioning reliability and availability, and make full use of the on-orbit non-navigational satellites that can be used for positioning. Based on the analysis of instantaneous Doppler positioning principle, the Iridium and ORBCOMM SOPs fusion positioning model is established, and the weighted least squares algorithm based on Helmert variance estimation is introduced to further improve the positioning accuracy. The experiment results show that the positioning accuracy of Iridium and ORBCOMM SOPs fusion based on Helmert variance estimation is better than 70 m, which verifies the feasibility and effectiveness of multi-LEO constellation SOPs fusion positioning.

The background pressure in vacuum chamber is an important parameter that affects the performance evaluation and plume field parameter diagnosis of electric thruster during ground tests. In this paper, a simulation analysis was made on the background pressure establishment method used in the numerical simulation of the plume field parameters of LIPS-200 ion thruster. The hybrid particle in cell (PIC) method and the direct simulation Monte Carlo (DSMC) method were used to deal with plasma motion and particle collisions in plume field. The electric propulsion plume was numerically simulated by using virtual particles and computed particles respectively, and compared with the vacuum environment. The results show that the number densities of neutral particles and charge-exchange ions are more than one order of magnitude higher than those in the vacuum environment due to the existence of background pressure. The virtual particles can greatly improve the computational efficiency, and the charge-exchange ion distribution in the plume field obtained is similar to that of the computed particle. However, the neutral particle distribution is quite different, so the influence of the wall and vacuum pump cannot be characterized by virtual particles.

Crank judgement is an important link in kinematic analysis of mechanisms, which determines the motion state of the mechanism. The existing Grashof theorem and N-bar rotation theorem can well solve the problem of crank judgement of single closed-loop linkage with only R joints, but there is no general and effective solution for crank judgement of complex multi-loop linkage widely used in aerospace. A branch graph identification method for determining the crank of complex multi-loop linkage is proposed. This method first determines the first sufficient condition for the existence of the crank through the inequality of the link relationship of each loop in the complex multi-loop linkage, and then determines the second sufficient condition for the existence of the crank by combining the branch graph of the linkage with the rotation range of the movable joint. On the basis of summing up the sufficient conditions, this method is used to analyze the planar 4R and 5R linkages, and the outcomes are compared with the existing recognized results, verifing the effectiveness of this method. Finally, the crank judgment is carried out on a complex multi-loop Stephenson six-bar linkage with only rotating pairs, which proves the feasibility of the method.

Very low Earth orbit (VLEO) has unique advantages in Earth observation and scientific research due to their low orbital altitude; however, the knowledge of the atmospheric density variation in these orbits is insufficient. A preliminary analysis and discussion of the in-situ results of atmospheric density in VLEOs in China is carried out, based on the description of the history and current status of in-situ exploration of VLEO atmospheric density, and on the summary of the existing in-situ detection techniques of atmospheric density. The results show one order of magnitude difference in atmospheric density between 250 km and 350 km altitudes during the quiet period of the space environment in October 2020. During the orbit ascent and descent, the atmospheric density of VLEOs decreases by 0.025×10^-12 kg/m³ and 0.041×10^-12 kg/m³ per kilometer, respectively, each 0.5 times less than that of the NRLMSISE00 model. At 40°N, the atmospheric density in the ascending section at midnight (~250 km) is 11.2 times higher than that in the descending section at noon (~420 km), and the effect of altitude is greater than that at local time. At different latitudes, the daily mean ratio of the observed values to the model values decreases from 0.49 at high latitudes to 0.39 at low latitudes, with the NRLMSISE00 model values being larger. At the VLEO, the observed values are generally smaller than the NRLMSISE00 model values, which can provide basic data for atmospheric physical studies and applied research.

Lithium-ion batteries have been used in high-altitude areas and airports in China, and therefore it is urgent to investigate their cycle performance and aging mechanism in high-altitude and low-pressure environments. The aging behavior of NCM523 pouch lithium-ion batteries is analyzed in terms of electrochemical characteristics such as battery health status, charging energy, direct current internal resistance, electrochemical impedance spectroscopy, capacity increase and differential voltage curves under 96 kPa-25℃ (normal temperature and pressure) and 60 kPa-25℃ (normal temperature and low pressure). The results show that the low pressure of 60 kPa accelerates the aging process of lithium-ion batteries. The internal structure of the battery is affected by low pressure, which increases the ohmic resistance and charge transfer resistance of the battery by 6.22% and 45.76%, respectively, compared with those under normal pressure. In addition, the lithium deintercalation reaction is limited, and the kinetic properties of the battery interface are reduced. Due to the increase of the battery impedance, the cycle capacity decays rapidly, determined by the loss of active Li⁺ of the cathode. The attenuation rate of the battery health state is higher by 3.08% than that under atmospheric pressure.

The discontinuous Galerkin (DG) method has been widely studied and applied because of its high-order accuracy and applicability to the unstructured grid. However, it still has problems such as poor convergence and limited robustness in numerical simulation flowfield with strong discontinuity. This problem is exacerbated by the uniformly distributed grid, which results in poor shock resolution. In order to solve the problem, an r-grid adaptive method was developed to aggregation and refinement grids in process of DG numerical simulation. The normalized pressure of grid points was taken as an important weight to calculate the driving force of grid points. At the same time, the ratio of the displacement variation of grid points to the initial distance between grid points was taken as another important weight. A Venkatakrishnan limiter suitable for DG was developed. Numerical results of interaction between two parallel NACA0012 airfoils and interaction between two parallel cylinders showed that the DG method based on r-grid adaptation can capture shock clearly and sharply, improve simulation accuracy, and has good convergence and robustness.

Control moment gyro (CMG) is the actuator for the attitude control of large spacecraft. In order to evaluate the performance degradation state of CMG, a convolutional neural network (CNN) and residual power consumption-based degradation feature extraction method is proposed. The high-precision control of the CMG control system makes it difficult to extract degradation features from the operational state of the CMG rotor. To solve this problem, a CNN model is introduced to establish the mapping between CMG operating state parameters and motor power consumption, and the degradation feature is defined as the residual error between the model output and actual power consumption of the motor in the degraded state. For approach validation, an accelerated life test dataset of a real CMG was used. The results show that the constructed degradation feature can reflect the performance degradation of the CMG rotor bearing.

To satisfy the requirements of satellite navigation spoofing, a satellite navigation signals purification method is proposed based on the optimal design of the array digital beamforming. Firstly, a new covariance matrix is constructed and the disparity between the max eigenvalue and the minimum eigenvalue of the covariance matrix of the array received data is expanded by combing the direction information of non-object satellites, the layout information of the received array and the covariance matrix of the array received data. Secondly, the spatial filter weights that make the object satellite signal distortion-free while nullifying any non-object satellite signals are computed by using the constructed covariance matrix. At last, the purified satellite signals are obtained by weighting the array of received data. The correctness and effectiveness of the method proposed in this paper are validated by computer simulations.

To study the internal flow process of the multi-stage pressure drop valve and the influencing factors and influence laws of the pressure drop of pressure-drop-stage, based on the numerical calculation method of the Mixture two-phase flow model and the Schnerr-Sauer cavitation model, the calculation model of the flow field of a multi-stage inside the valve was established. The flow characteristics inside the pressure drop valve are obtained through numerical simulation calculation, and the impact of various pressure differences and various opening degrees of the valve on the pressure drop of each pressure-drop-stage is analyzed and discussed. Numerical calculation results show that there are a large number of vortices in the valve due to the vigorous mixing and shear of multiple fluids when the fluid flows through the throttle element of the valve. The pressure drop of each pressure-drop-stage is different, and the degree of cavitation of the third stage sleeve is the largest, cavitation is more likely to occur at the valve seat. The pressure drop of the working fluid along each pressure-drop-stage exhibits the same changing trend at the same opening degree of the valve under various pressure differences. The pressure drop of the third pressure-drop-stage rises when the opening degree of the valve is reduced. The average pressure drop of the 3rd pressure-drop-stage reaches 8 MPa at the opening degree of 25%. The velocity of working fluid in the small hole of the pressure-drop-stage also increases under the condition of the same mass flow rate. This paper provides the theoretical basis and reference value for the designs of the pressure reducing valve.

The nursing robot's arm does not meet the PIEPER criterion and is constructed with a high degree of coupling and complexity. The standard genetic algorithm is difficult to accurately solve its inverse kinematics. As a result, the pose error of the end of the robot arm is relatively large. In order to solve the problem that premature and poor local search ability in the standard genetic algorithm solution process, the following methods are proposed. Firstly, use equal partitions to replace the initial population of individuals generated by random commands. Divide 5 small areas to improve the dispersion of the population and search efficiency. Secondly, introduce variable weight factors in the fitness function. The change value of the pose error is used as the variable of the variable weight factor. The weight factor varies between 0.5-1.0 during the evolution process. And effectively assign position and attitude error weights. Finally, verified by simulation and experiment. The results show that the improved genetic algorithm can greatly improve the accuracy and speed of convergence, achieve precise control of position and attitude at the same time, and greatly reduce the pose error of the robot arm.

From the perspectives of the current verification work there are a few issues need to be addressed, such as the top-level planning is not enough, the interfaces between the development organization and test organization are not well defined, the sufficiency of the verification activities is difficult to be determined. By combining the verification scenario modeling in civil aircraft development process based on system engineering and revolving around the verification requirements, a novel methodology of verification work process is introduced in this paper. Firstly, based on the product design requirements, the identification of stakeholders in the verification scenario is conducted, the activities and the time sequence of events associated with the scenario model are studied. Secondly, all the contained elements associated with the verification requirements are defined, the verification requirements capturing from the model is described, and the mapping traceability among the design requirements, the verification methods, and the verification requirements are constructed. At last, the methodology for defining the verification planning and the verification procedure based on the verification scenario model is investigated. Using the landing gear system of an aircraft as an example, a complete approach is demonstrated by proceeding from design requirements to verification requirements and then to verification procedures. The proposed technical method can ensure the completed traceability from product design requirements to verification activities, effectively facilitates the integration between the verification process and the product design process in civil aircraft development. Moreover, the method introduced here provides a valuable example for planning the verification activities in the early stage of civil aircraft development.

In order to guarantee the security of wireless sensor networks, a federated intrusion detection algorithm Fed-XGB based on fog computing is proposed. The Fed-XGB algorithm extends the edge of the network by introducing fog computing nodes, reduces communication delay, improves the accuracy of joint learning of global and local models, and reduces the transmission bandwidth and the risk of privacy leakage. By improving the approximate calculation method based on the histogram, this algorithm can adapt to the characteristics of unbalanced data in wireless sensor networks. Through the introduction of the TOP-K gradient selection, the number of uploads of model parameters is minimized, and the interaction efficiency of model parameters is improved. Experimental results show that the detection accuracy of the Fed-XGB algorithm is above 0.97, and the false alarm rate is below 0.036, which is better than other comparison algorithms. The results also show that, in the face of poisoning attacks and noisy data, the detection and classification performance are still stable and has strong robustness.

In order to solve the coupling nonlinear dynamics problem of the mechanical system and pneumatic system in the process of a new air-cooled launch device, an analysis method and optimization design method for the air-cooled launching dynamic characteristics of folding-rotor unmanned aerial vehicle (UAV) were proposed to satisfy the requirements of its structural form and launching technology. Taking a folding-rotor UAV as the research object, the dynamics model of the compressed gas launch system of UAV was established based on co-simulation, and the test prototype of the cold air launch system was built, the compressed gas launch experiment was completed to verify the accuracy of the simulation model. The effect of the main system parameters of UAV and air-cooled launcher on the dynamic performance of UAV launch is analyzed. Finally, the parameter optimization design is carried out for the system. Results show that the volume of the air cylinder and the inflation pressure are the key parameters influencing the dynamic characteristics of the UAV air conditioning launch, with air cylinder volume and air pressure, the largest launch speed and overload increasing, air cylinder volume increased from 15 L to 30 L, the largest launch speed increased by 52.7%, the largest launch overload grew by 60.9%, were positively correlated; When the charging pressure increases from 0.4 MPa to 0.7 MPa, the maximum launch velocity increases by 50.5% and the maximum launch overload increases by 69.9%. The launch angle has little effect on UAV launch performance and can be ignored.

An effective dimension reduction method for multivariate functional data is developed within the theoretical framework of regularized generalized canonical correlation analysis. Functional data in square integrable spaces is first projected in an integral form to a series of numeric variables, and those variables are then used for simultaneously determining the related projection directions of functional features by maximizing a kind of global correlation measure, which achieves the featured information extraction and rapid dimension reduction of multivariate functional data as traditional numeric variables. A general basis function system is used to create the iterative computing algorithm for the optimal functional projection weights, which is independent of the specified basis functions. A large number of simulation results for infinite samples show that the proposed method is able to detect the correlation among multivariate functional data and obtain consistent estimates for the associated functional projection weights. The real-data study on the gait of Parkinson's patients indicates the interpretability of the numeric featured information derived from the original functional data and the utility of the proposed method.

The stratospheric wind field environment has an important influence on the flight performance of near space low speed aircraft. In this paper, the modeling and prediction methods of stratospheric regional wind field are investigated based on PSO-BP neural network. Firstly, the principal component analysis method is implemented to reduce the dimensions of the historical wind field data. Then, the BP neural network, which is trained by the processed data to predict the wind field, is optimized with particle swarm optimization (PSO) algorithm. Finally, the Biharmonic spline surface interpolation method using multi-point prediction wind fields is studied to construct the regional prediction wind field. Taking the 5-year historical wind field data of a certain place, comparative study of the wind field prediction model based on BP neural network and PSO-BP neural network is conducted. The results show that PSO algorithm, which is characterized global optimization, can improve BP neural network by avoiding the disadvantage of easily falling into local optimization, and enhance the prediction accuracy. The integration method of PSO-BP neural network prediction and Biharmonic spline surface interpolation can provide the prediction of the regional wind field. The proposed method can provide high precision regional prediction wind field for trajectory planning and station keeping of near space low speed aircraft.

The attitude control of hypersonic morphing flight vehicles cause problems of large uncertainties, such as time-varying parameter perturbation, difficulty in modeling deformation process, and complex "lumped disturbances". To address these problems, a control-oriented model for variable-sweep wing hypersonic flight vehicles is established, and a finite-time control scheme is proposed. Firstly, a three-degree-of-freedom model is established for attitude control, which can reflect the influence caused by deformation. Secondly, the aerodynamic characteristics of the hypersonic morphing flight vehicle in some typical states are analyzed, and a feasible method for the key aerodynamic data of continuous deformation is developed. Thirdly, a finite-time control scheme is designed for the continuously deformable vehicle, and the system stability is demonstrated. Further, the finite-time convergence filter is designed, considering the command differentiation term used in the control law. An extended state observer is also used to estimate the unmeasurable states and the "lumped disturbances". Finally, numerical simulations are performed with complex disturbances, and the results show that the proposed control scheme can solve the attitude control problem for the vehicle with complex disturbances at different deformation rates.

Aiming at the integrated design and manufacturing of micro-channel structure parameters for printed circuit heat exchanger (PCHE), the performance optimization research of heat exchangers considering manufacturing constraints is carried out. Through fluid simulation, the influence of flow channel width, depth, and aspect ratio on temperature distribution, pressure loss, and heat transfer coefficient is analyzed. A multi-objective genetic algorithm (MOGA) is used to establish a multi-variable and multi-objective optimization simulation model for heat transfer performance. The results of the performance simulation are used to establish the microchannel structure rolling forming process, and the manufacturing constraints are obtained. The manufacturing constraints are fed back to the performance optimization simulation model. Consequently, the micro-channel design parameters with a width of 0.29 mm and a depth of 0.39 mm are obtained, and the feasibility of the optimization method was verified by the roll-to-roll (R2R) process test. The designed method of heat-exchanger optimization considering manufacturing constraints introduce process constraints in the stage of performance optimization design, and is proved an effective measure to achieve the integrated design and manufacture of heat exchangers.

One of the key technologies of precision-guidance weapons is the anti-ship missile's ability to strike vital parts of a warship with pinpoint accuracy. Aiming at the problems of low detection accuracy, insu-fficient ability in feature extraction and the processing of the generated-anchors reduces the detection speed in anti-ship missile seekers, a warship's vital parts detection algorithm based on a lightweight Anchor-Free network with multi-scale feature fusion is proposed. Due to the multi-scale and multi-angle characteristics of the vital parts detection data, the multi-scale feature fusion module is introduced to optimize the feature extraction by comprehensively using the detection information of different receptive fields. To boost the detection accuracy and reduce the total parameters of the algorithm, the skip connections in Hourglass are enhanced by using the efficient and lightweight attention mechanism. The transfer-learning is used to improve the convergence of this algorithm effectively. Experiments were carried out on the dataset of the warship's vital parts and the PASCAL VOC. Experimental results show the mAP is increased by 4.41% and 5.57% respectively. The algorithm's parameters and the computation are analyzed. The module ablation experiments are designed to demonstrate the effectiveness of the algorithm.

Considering the underactuated hypersonic flight vehicles with strong uncertainty of the dual channel attitude control strategy, practical feedback-based dual-channel control schemes are given and the robustness analysis method based on the bounded perturbation analysis of eigenvalues is proposed. Firstly, two control schemes, namely the pole-assignment schemes and modes-decoupling scheme, are given to improve Dutch roll dynamics based on the approximate linearization approach and engineering constraints. Then, to evaluate the robustness of the closed-loop system for the uncertain parameters, the eigenvalue sensitivity matrix, the eigenvalue bounded-perturbation-matrix and eigenvalue bounded-perturbation index are proposed. Finally, simulations and analysis of the proposed schemes and methods are given based on the closed-loop six degree-of-freedom model with nominal parameters and perturbed parameters, respectively. Simulation results demonstrate that both schemes could solve the dual-channel control issue. The results also show that the perturbation analysis of eigenvalues could precisely evaluate the system robustness.

XNOR/OR-based fixed polarity Reed-Muller (FPRM) circuit area optimization is one of the current research hotspots in the field of integrated circuit design. However, the existing XNOR/OR-based FPRM circuit area optimization method has problems such as poor optimization effect and low optimization efficiency. Since XNOR/OR-based FPRM circuit area optimization is a combinatorial optimization problem, a binary adaptive bacterial foraging algorithm (BFA) is first proposed. The algorithm adds a probability model to the replication operation to improve the diversity of the population, and uses fuzzy rules to modify the replication probability and migration rate to improve the convergence speed of the algorithm. This algorithm allows bacteria to search in the neighborhood, replacing the repulsion operation in the quorum sensing mechanism of bacteria, and bacteria no longer need to sense the influence of other individual positions on it. In addition, an XNOR/OR-based FPRM circuit area optimization method is proposed. This method uses the proposed binary adaptive bacterial foraging algorithm to search for the FPRM circuit with the smallest circuit area. The experimental results based on the MCNC Benchmark circuit show that the maximum area optimization rate reaches 18%, and the maximum time saving rate reaches 46%.

The airborne hollow fiber membrane inerting system of a helicopter is taken as the research subject.in this paper. Two temperature control systems using an electric valve and a frequency conversion fan have been designed. Based on the AMESim platform and the calculated data of the separation membrane mathematical model, an airborne inerting system was built. Under the flight mission, the temperature control effect of the two systems, the variation of the performance of the inerting system at different flight stages, and the influence of key parameters were all studied. The results show that: the system with an electronic valve can maintain the bleed air temperature at the desired level of 90℃ throughout the flight. After take-off, the nitrogen concentration of nitrogen enriched air (NEA) is maintained between 91.5%-96.4%, the required bleed air flow rate is maintained between 40 kg/h-243 kg/h, and the oxygen volume fraction on ullage can be reduced to 9% within 180 s and kept below 9% throughout the flight. Under the premise of the heat exchanger selection that meets the temperature control and inerting requirements during the high temperature stages such as climb, acceleration, and descent, the bleed air is overcooled to about 0℃ during the cruise stage of the system with the variable frequency fan, although the required bleed air flow rate dropped to 26 kg/h, the concentration of NEA is greatly reduced to 81%, and the oxygen volume fraction on ullage rose to 18%. The larger the flying speed, the greater the temperature drop of bleed air and the lower the cruising altitude, the lower the minimum cruising speed required to meet the temperature control effect are all valid during the cruise phase of the system with the variable frequency fan.

To meet the needs for collaborative decision making (CDM), the dynamic collaborative sequencing of departure flights in both crowded and uncrowded scenarios was systematically studied with the demands of air traffic control units, airlines and airports being taken into consideration. With a deep analysis of the operation characteristics of departure flights, a dynamic sequencing method was designed based on scheduled off-block time (SOBT) and estimated off-block time (EOBT) data of the departure flights. Several optimization objectives of departure flight sequencing were set for each of the parties. Meanwhile, an evaluating indicator of airline delay fairness was proposed to ensure the sequencing fairness, the priority of uncontrolled departure flights was divided into three categories, the maximum acceptable delay time and maximum position offset were set for all categories of uncontrolled departure flights, and thus the collaborative sequencing model for departure flights based on traffic state was established. Further, a fast non-dominant sorting genetic algorithm with elite strategy (NSGA-Ⅱ) was designed to find the optimal solution to dynamic collaborative sequencing for departure flights. Simulation results show that, compared with first come first served (FCFS) method, the proposed method adds a variety of sequencing schemes in each sequencing stage in both scenarios, the total delay of departure flights is reduced by more than 50%, and the airline delay fairness is improved in uncrowded scenarios. The proposed method can optimize the sequencing of departure flights, significantly reduce flight delays, effectively improve fairness, and fit in with the concept of collaborative decision making, thus realizing tripartite collaborative sequencing.

Aiming at engineering application problems, the multi-degree-of-freedom angular momentum envelope model of magnetically suspended control and sensing gyroscope (MSCSG) is studied. Based on the mechanical structure of MSCSG, the characteristics of radial universal deflection of magnetic suspension rotor are analyzed. Axial 1-DOF Flywheel torque and radial 2-DOF gyroscope torque output mechanism of MSCSG are clarified. Based on the Lorentz force magnetic bearing (LFMB) principle, the linear relationship between the radial deflection torque and the control current is analyzed, which reveals the advantages of the MSCSG torque with high precision, high bandwidth and small amplitude. Considering rotor speed saturation, the MSCSG angular momentum envelope model is constructed based on deflection reconstruction and rotation matrix. The simulation shows that although radial deflection torque has a high bandwidth, small amplitude, and axial flywheel torque has a high precision and large magnitude. High bandwidth performance test of the MSCSG deflection torque is carried out, showing that MSCSG can output radial deflection torque whose frequency is greater than 100 Hz. It is shown that MSCSG has the prospect of strong micro-vibration suppression under high dynamic conditions and high precision attitude control.

The echo signal of the target is the most important way for radio fuze to obtain target information. This research employs bispectral analysis to examine the echo properties of terahertz wave at different heights of plateau in shrub terrain in order that the front-end of terahertz band fuze can be implemented into the plateau battle field in the future and adapt to the different landform environments of the plateau. In order to reduce the classification time, the bispectral data is integrated to obtain the bispectral slice features of the actual signal, and then the k-nearest neighbor algorithm is used for classification. Empirical mode decomposition (EMD) is used to extract the intrinsic mode function features of the original data, and the classification results are compared with the previous group. Through a series of data classification, the results show that using one-dimensional integrated bispectral information can effectively extract the features of 2 m, 3 m, 4 m, 5 m from the ground and classify them, empirical mode decomposition can also effectively improve the success rate of classification, the success rate can reach more than 90%.

The conducted electromagnetic interference of the wireless charging system with the bilateral LCC structure of electric vehicles is studied. According to the standard SAE J2954, a high-frequency circuit model of the conducted electromagnetic interference of the wireless charging system with a power of 3.7 kW is constructed. A method combining measurement and theoretical calculation is used to extract the high-frequency parasitic parameters of the coupling coil, cable and compensation circuit components. The modeling and simulation analysis of the conducted interference of the system are carried out by using the software ANSYS Maxwell and Simplorer. Simulation results show that the common mode interference is more significant than the differential mode interference in the frequency band of 150 kHz-30 MHz. The accuracy of the simulation model is verified by the conducted emission experiment of the wireless charging system.