In order to improve the performance of satellite selection algorithm, the Particle Swarm Optimization (PSO) satellite selection algorithm based on artificial fish swarm algorithm is proposed. Using the global convergence characteristics of artificial fish swarm algorithm, the algorithm can overcome the shortcomings of PSO algorithm that is easy to fall into local optimum. The improved algorithm treats each satellite combination as a particle in space, and the Geometric Dilution of Precision (GDOP) is chosen as the fitness function. The particle updates its position based on the optimization principle of the particle swarm optimization algorithm and artificial fish swarm algorithm, and the optimal satellite combination and GDOP value are obtained. The algorithms are verified and compared with real data, and the results show that the improved satellite selection algorithm not only guarantees the efficiency of the satellite selection, but also the accuracy of the satellite selection result is better than that of the satellite selection algorithm based on the PSO.

In this paper, a statistical algorithm based on polynomial chaos expansion and dipole approximation for electromagnetic radiation calculation of interconnected cables with random parameters is proposed.In this method, orthogonal polynomials are used to expand the equation of the multi-conductor transmission line with random coefficients, the current along the transmission line is obtained by combining the boundary conditions, and then the electric dipole approximation and the mirror image method are used to calculate the total radiation caused by the current of the transmission line. Simulation results verify the accuracy of the proposed method, and the computational efficiency is greatly improved compared with the traditional Monte Carlo method. This method has certain reference value for predicting cable radiation field with random parameters, evaluating cable electromagnetic radiation and testing system performance index.

Aimed at the problems of lacking the theoretical research on the spiral winding deformation for soft gripper and the traditional soft gripper having a low load capacity, the research on the spiral deformation characteristics and the closed capture form of the fiber-reinforced bionic soft gripper was carried out. First, a bionic soft gripper was designed, which is composed of a software holding device, a soft clamping sleeve, a fixing sleeve and a connecting device. Secondly, a nonlinear mathematical model of the driving pressure and the torsion angle of the soft driver end face is established based on the Mooney-Rivlin model. And the end-closing characteristics of the soft gripper were analyzed. Then, the simulation and experiment of the unit spiral wound drive were carried out. The results prove the correctness of the theoretical model. Finally, the closed grabbing experiment of the bionic soft gripper was carried out. Experimental results show that the closed bionic soft gripper has a large load capacity and good target adaptability.

Simultaneous Localization and Mapping (SLAM) is one of the key technologies in visual navigation, and loop closure detection is a basis of SLAM. An efficient and accurate loop closure detection algorithm is proposed to solve the problem of low accuracy rate of SLAM loop closure detection. The loop closure detection algorithm consists of bag of words module, structure checking module, and tracking module. First, we design the bag of words model and structure checking module, combining local features with holistic features. The bag of words model compares the image similarities using visual words to obtain the closed-loop candidate frame. Then, structure checking module grayscales and normalizes the current image and the closed-loop candidate image. The normalized images are directly used as the patch of local feature to obtain holistic feature. Whether the closed-loop candidate frame is a valid closed loop is determined by the holistic descriptor. To address the problem that time consumption increases rapidly with the increase of image numbers, we design the tracking module to improve the computational efficiency. The comparative experiments with DBoW algorithm show that the proposed algorithm improves the accuracy by more than 20% and also has better real-time performance.

In order to solve the problem of electromagnetic characteristic parameters of periodic structures, an INBC-FDTD calculation method based on network analysis method and vector fitting method is:introduced in this paper, which can be used to quickly solve the electromagnetic characteristic parameters of low-profile periodic structures.In this method, the two-port frequency domain impedance parameter curve of the metal layer is firstly fitted with rational fractions by the vector fitting method, and then the time domain transform is carried out to embed the FDTD formula to complete the update of the electric field and the magnetic field. The proposed method fully considers electro-magnetic fields transmitted in the metal layer, and its two-port network impedance parameter fully considers the mutual coupling between the ports.

Aiming at the problem of human eye detection in complex scenes, indirect methods and direct methods have certain limitations.A direct human eye detection method which is independent of face detection is proposed. The proposed method detects eyes under multiple scales especially small scale in complex scenarios. The improvement of the proposed method consists of improving small-scale human eye detection ability by reducing the down-sampling factor and adding extended residual units; ensuring the accuracy of multi-scale human eye detection by concatenating the multi-scale features; improving human eye detection efficiency by reducing the number of feature output channels to simplify the complexity of the model. The experimental results show that the proposed model can distinguish the left and right eyes effectively under small scale and has good performance with infrared data. The training and test on DIF dataset show that the human eye detection precision of the proposed method is 82.59%, and the detection rate is 30.5 fps.

This paper proposes a novel Moving Path Following (MPF) control method by improving the time-varying vector field method. Moreover, it is applied to the automatic carrier landing problem of carrier-based aircraft. Based on the nonlinear model of carrier-based aircraft, backstepping method is used as the main frame. Besides, the path following error is defined in the time-varying vector field. In addition, Lyapunov function is designed for the defined virtual control variable to achieve fast and accurate tracking for the heading angle and the climb angle, and the path of the aircraft is ensured to follow the desired moving path. The stability analysis proves that the following error converges to a small region, and the simulation results show that the control method has good performance in carrier landing.

Traditional aero-engine Remaining Useful Life (RUL) model cannot objectively describe the multi-stage degeneration process, and the accuracy of RUL prediction is low. To solve this problem, a new multi-stage RUL prediction model for RUL prediction is proposed, including super statistics theory, mutation point detection, Unscented Kalman Filter (UKF) and nonlinear prediction. In the paper, a Multi-stage Segmentation Filtering based on Super statistics (BS-MSF) theory algorithm is proposed. In this algorithm, first, super statistics theory is used to conduct mutation point detection and divide the health data of aero-engine into multiple degradation phases. Then, UKF is used to filter the fused time-varying parameters. Finally, the real RUL of the aero-engine is estimated by nonlinear fitting. nonlinear fitting, and the aero-engine data was released by National Aeronautics and Space Administration. Simulation results show that the presented method has better adaptability in predicting engine performance degradation, smaller fitting error, and more accurate prediction of RUL. The prediction accuracy is 5.5% higher than that of single-stage method.

Scale Adaptive Simulation (SAS) is used to study the flow around a circular cylinder at Reynolds number 3 900. SAS predictions are compared with the popular Detached Eddy Simulation (DES) and existing experimental data. The effect of grid resolution and spanwise domain size on SAS model performance are systematically analyzed, time-averaged turbulent statistics and instantaneous distributions of the von Karman length scale in the wake region are discussed in detail. It is concluded that the recirculation length of SAS is smaller than that of Large Eddy Simulation (LES) under the same grid resolution, indicating an earlier onset of instability in shear layer. Velocity magnitude inside the recirculation bubble increases and the peak value of Reynolds stress decreases with grid refinement for SAS simulation, which are in good agreement with the experimental data of Lourenco & Shih. Additionally, changing the spanwise domain size with the same resolution has little effect on SAS predictions. The investigations on the influence of grid resolution and the spanwise domain size on SAS model performance can provide guidance for industrial applications of the SAS method in future.

Lift-type hybrid airship is an important choice of long-distance and large-load transportation. With the development of global trade, it has gradually become a research hotspot at home and abroad. As a new concept aircraft combining aeronautical science and technology, new energy technology and high-performance material technology, multiple disciplines should be considered and optimized in the design process of hybrid airship comprehensively. To introduce the Multidisciplinary Design Optimization (MDO) method into the conceptual design of hybrid airship, it is decomposed into energy subsystem, aerodynamic and propulsion subsystem, and structure and weight subsystem. On the basis of building subsystem model, a Concurrent Subsystem Optimization algorithm based on Response Surface (CSSO-RS) with the self-adaptive ability is put forward. The weight balance and energy balance are set as the constraints to achieve long-distance transportation. Meanwhile, a multi-stage task profile with climb, day cruise, gliding and night cruise is proposed to make full use of solar energy battery, fuel cell and lithium batteries and realize the optimal design of hybrid airship. The optimization results show that the adaptive optimization algorithm has obvious advantages in accuracy and computational efficiency, and the weight distribution results also put forward higher requirements for lightweight design and energy system design of hybrid airships.

For complex systems with newly developed products and less failure data, a competitive failure model in which natural degradation and external shocks are independent of each other in an uncertain environment is proposed. Considering that the system suffers from natural degradation and external shocks at the same time, the continuous natural degradation is described by an uncertain process, and the time interval of the shock arrival and the damage to the system caused by each shock are described by two different uncertain variables. Using the uncertainty theory, the system belief reliability is studied under the extreme shock model, cumulative shock model, and δ shock model. The results show that in the case of newly developed products and complex systems with less failure data, the method of uncertainty theory is more appropriate to describe the model, and numerical analysis shows the effectiveness of the model.

Aimed at Cooperative Multi-Task Assignment Problem (CMTAP) of Unmanned Aerial Vehicle (UAV) formation, considering the situation of cooperative detection and attack of two aircraft, combining the constraint conditions of time constraint, time sequence constraint, time interval constraint, ammunition constraint and task capability constraint, the model of cooperative multi-task assignment is extended, and a mixed Differential Evolution (DE) and Guo Tao (GT) algorithm, Discrete Particle Swarm Optimization (DPSO) algorithm and Simulated Annealing(SA) algorithm are fused to propose a DE-DPSO-GT-SA algorithm to solve the cooperative multi-task assignment problem. The performance of DE-DPSO-GT-SA algorithm and that of other algorithms are compared. Simulation results show that DE-DPSO-GT-SA algorithm has better convergence performance than other algorithms.

In the maneuvering process of air-breathing hypersonic vehicles, the aerodynamic characteristics show strong unsteady characteristics due to the complicated configuration. Traditional flight simulations based on database or aerodynamic models cannot exactly describe the complex aerodynamic characteristics and motion characteristics in the maneuvering process. To solve this problem, a numerical virtual flight simulation platform is established based on the distributed and modular development trend of modern software. With this coupled platform, longitudinal maneuvering simulations of an X-51A-like aircraft is carried out and the results are compared with those of the engineering method. It is found that For the X-51A-like air breathing hypersonic vehicle, the results given by the engineering method may not fully reflect the influence of unsteady effects when it pitches up longitudinally. In this case, the more accurate virtual flight method should be used to study the closed-loop response characteristics of the vehicle.In addition, the influence of the rudder loop time constant on the control system is also studied with the aid of the simulation platform, which provides a certain reference for the design of the control law.

Neutron is one of the important radiation factors that affect the safety of spacecraft and astronauts. It is difficult for neutron measurement to optimize the neutron detector, improve the measurement efficiency, and improve the inversion accuracy. A neutron detector based on a new type of neutron detection material Cs2LiYCl6:Ce (CLYC) scintillator will be installed on the space station in China. This detector has the characteristics of measuring thermal neutrons and fast neutrons simultaneously, and has high detection efficiency, etc. For the neutron spectrum inversion of this detector, the response characteristics of different energy neutrons in the detetor are analyzed, and the advantages and disadvantages of the probabilistic iterative method and Non-Negative Least Square (NNLS) method commonly used in neutron spectrum inversion are analyzed, considering the disadvantages of these two methods in the inversion application of CLYC detector, a Non-Negative Least Square method based on the Augmented Matrix (AM-NNLS) is proposed. The numerical experiment results show that the AM-NNLS method has the characteristics of high inversion operation efficiency and small inversion relative error, which verifies the effectiveness of the method.

In this paper, grid-search method is introduced into artificial neural network model incorporating spatial structure, which is a new method of model estimation, to do out-of-sample prediction. This method is based on the artificial neural network algorithm, is combined with the idea of spatial autoregressive model, and introduces the spatial lag term in the model to consider the spatial effect of variables. Meanwhile, instead of maximum likelihood method, it uses the method of grid-search for the optimal solution to estimate and model the spatial autoregressive coefficient. Then, combined with the out-of-sample data and spatial structure, the spatial matrix is extended and the new model is brought in to make out-of-sample prediction, which gives full play to the strong generalization ability of the neural network model. Finally, the simulation results show that, compared with ordinary artificial neural network, the prediction effect of the new model is significantly improved when the spatial effect is considered reasonably, and the prediction accuracy is better than that of the spatial autoregressive model when there is a nonlinear relationship between spatial variables.

The method based on the piezoelectric impedance method using statistical parameters as the damage index to evaluate loose bolt has a wide range of applications. However, most of the test objects adopting this method are structures such as plates under laboratory conditions, which are not real structures. Therefore, for real flange structures, whether these damage indexes are still applicable and whether these damage indexes need to be improved need further study. The rules between different damage indexes and loose bolt of flange structure are obtained through experiments:the larger the degree of bolt looseness is and the closer the position is, the larger the values of the Root Mean Square Deviation (RMSD), the Mean Absolute Percent Deviation (MAPD), and the Correlation Coefficient Difference (CCD) are, and R_y/R_x is not suitable to be used as a damage index for evaluating the loose bolt of flange structures because it has not a significant rule. The comparison of results shows that the structural difference affects the first three damage indicators to different degrees, and the improved damage index Root Mean Square of Change Rate (RMSCR) is only related to the position and degree of the loose bolt of flange structures, which is barely affected by the structural difference. Hence, the RMSCR has a crucial practical significance:when any piezoelectric sheet is damaged, it only needs to be replaced with a piezoelectric sheet of the same type without updating the damage index library. Finally, verification experiments verify the correctness of the above results and the applicability of the detection method for loose bolt of flange structure based on RMSCR.

In this study, several sets of experiments were carried out to evaluate the characteristics of micro milling holes in high-strength elastic alloy 3J33B material using an ultra-precision machine tool. The milling forces were measured using a Kistler 9119AA2 dynamometer, and the sizes and surface burrs on the machined holes were measured using a Keyence 3D laser scanning microscope. Furthermore, tool wear was examined using a Scanning Electron Microscope (SEM) and an Energy Dispersive Spectrometer (EDS). Experimental results indicate that the force in Y direction is always greater than the force in X direction regardless of the cutting speed variation. High cutting speeds or high spindle speeds may affect the machining dimensional accuracy during micro milling holes. The most serious region of tool wear is the tool tip of cutting edge in micro milling holes, and the wear is mainly concentrated on the whole cutting edge roundness and the flank which is near the cutting edge roundness. Abrasive wear is the main form of tool wear at a low cutting speed, and the effect of oxidation wear on tool wear increases with the increase in the cutting speeds. The elastic recovery of the machined surface aggravates the wear of the flank wear and affects the cutting stability.

On one hand, it is difficult to establish an accurate dynamical model description reflecting structural characteristics of a real-world complex structure with freeplay nonlinearity because of the inconvenience or impossibility of measuring the gap. On the other hand, even though the freeplay has been estimated, the modal parameters of the nominal linear system of the structure are still out of reach. Therefore, in this paper, nonlinear system identification was performed by the usage of conditioned reverse path method and time-domain nonlinear subspace identification method to obtain the parameters of freeplay nonlinearity as well as the frequency response function of the nominal linear system of the nonlinear structure. A 2-DOF wing section was chosen as a demonstration, on which the numerical experiments of ground vibration tests were performed. Nonlinear system identification was carried out by applying the conditioned reverse path method and time-domain nonlinear subspace identification method. Consequently, the nominal linear system can be accurately estimated by both methods, and the identified parameters of freeplay nonlinearity can also be obtained by smooth function approximation in conditioned reverse path method and by reconstruction via a series of piecewise linear functions in time-domain nonlinear subspace identification method.

A new ISAR imaging algorithm for high-speed maneuvering target is proposed to solve the Doppler ambiguity problem under Migration Through Range Cells (MTRC). First, the algorithm transforms the original signal to the image domain, then extracts the strongest scattering point, estimates the chirp rate of the point, and estimates the Doppler ambiguity number based on the maximum contrast criterion of the image. The next step is reconstructing the echo signal, correcting the MTRC, and using CLEAN technology to reduce computation and the impact of noise on imaging results. Finally, a high-resolution ISAR image without ambiguity for high-speed maneuvering target is obtained. The simulation results prove the algorithm's effectiveness and strong robustness under conditions of low signal-to-noise ratio.

In the field of Synthetic Aperture Radar (SAR) image analysis, as an important target, aircraft detection has attracted more and more attention. In order to solve the problem that traditional aircraft detection algorithms need to design hand-crafted features and have poor robustness, this paper proposes an aircraft detection algorithm based on improved Faster R-CNN. In this paper, a SAR Aircraft Dataset (SAD) is made. With Faster R-CNN as the detection framework, the improved k-means algorithm is used to design a more reasonable prior anchor frame to adapt to the characteristic of aircraft size. Based on the idea of inception module, multiple convolution kernels of different sizes are designed to expand the network width and enhance the expression of shallow features. By analyzing the residual network, the feature-map of Layer5 has a larger receptive field, and feature fusion is carried out after upsampling to make use of more context information. Meanwhile, the RoI Align unit proposed in Mask R-CNN algorithm is introduced to eliminate the mapping deviation between the feature-map and the original image. The experimental results show that, compared with the original Faster R-CNN algorithm, the proposed algorithm improves the average detection accuracy by 7.4% on the SAD, while maintaining a fast detection speed.

In the Global Navigation Satellite System (GNSS), a channel compensation technique based on BDS/GPS Kalman Based Least Mean Square estimation (KBLMS) is proposed to address the problems that the single system cannot locate in the city canyon, the signal cannot be captured after locking, and the tracking performance is poor. Firstly, a dual system model is established. Secondly, the delay estimation module based on the minimum mean square error of Kalman estimation is designed to compensate the multipath distortion on the received signal. Finally, the Line-of-Sight (LOS) optimal estimation block is designed to generate a control error signal in the feedback loop for adaptively updating the filter coefficients. The performance of KBLMS channel compensation multipath mitigation algorithm is analyzed through measured data and experimental simulation. The results show that, compared with Least Mean Square (LMS) algorithm, the KBLMS channel compensation multipath mitigation technology can fast converge in the multipath channel, the code tracking error in ENU three dimensions reduces by 0.1 chip, carrier tracking error decreases by about 0.125 cm, the error due to multipath effect effectively reduces, and the final residual error decreases by 0.035 chip. This shows that the multipath algorithm can do more accurate estimation, which verifies the effectiveness of the algorithm.

With the increase of space camera resolution, the requirements for temperature stability and uniformity of the optical system and the main load-carrying construction become higher and higher. It is a big challenge for the high-precision thermal control design of the Geostationary Orbit (GEO) camera due to the complicated space environment. According to the difficulties and characteristics of the GF-4 satellite camera's thermal control design, based on the design concept of integration thermal control design, thermal control technologies such as heat flow shield at the optical entrance, indirect radiation thermal control and coupled heat radiating surfaces are adopted to achieve high-precision temperature control; the temperature data of the camera in orbit for four years and the corresponding conditions are analyzed, the correctness of the camera's thermal control design is verified, and optimization suggestions are proposed based on the operation conditions in orbit. The thermal design methods also provide support for further improving the temperature control accuracy and reducing the thermal control resources of the geostationary orbit cameras.