Satellite autonomous navigation based on landmark information can be used for all kinds of satellites which can periodically obtain images of earth surface for its high accuracy and independence. This method has been restricted by landmark selection method and the establishment strategy of landmark library, which affect the navigation precision and hinder the popularization and application of this navigation method. To solve these problems, a method for establishing global high-performance landmark library is proposed. The global landmark library could be automatically generated by using global landmark control areas to select high-quality global landmark samples. To verify the feasibility of the proposed method, a simulation program was designed. The results show that the position error of the landmark navigation system based on the new landmark library is about 99 m, and velocity error is about 0.08 m/s. The proposed method can provide high-precision autonomous navigation for spacecraft fast and accurately.

A parallel micro-positioning platform with folded beams was designed, which has characteristics of large stroke and low resistance. Stiffness was solved by transfer matrix method. First, transfer matrix of flexible subunit was established. The transitivity characteristics became available by taking advantage of the common node belonging to adjacent elements. Finally, the stiffness matrix between input force and output displacement of flexible mechanism was solved according to the force balance equation and compatibility equation of deformation. A method to solve the stiffness of compliant folded beam and compliant prismatic pair considering full flexibility was put forward. The result of deformation error is less than 20.5% compared with finite element analysis. On this basis, this method ignored the correlation between the subunits because the modular stiffness analysis method regarded each subunit as independent. A modified method considering each subunit dependency was put forward, which reduced the error to less than 10% and made the results better meet the actual engineering needs.

Under the condition of multimodal travel choices in large cities, there is a close relationship of traffic demands among subway, buses and private cars. In order to explore the coupling relationship and time-varying feature among multimodal traffic demands, with road congestion index representing the traffic demands of private cars, this paper adopts the time-varying parameter vector autoregressive (TVP-VAR) model to analyze one-month travel demands of subway, buses and road congestion index on weekdays. The empirical results of two traffic zones demonstrate that:Depending on different land use types, the relationship among subway demand, bus demand and private car demand does not significantly change in trend, but varies in time scale; In urban traffic zones, there is an interactive relationship among traffic demands of subway, buses and private cars. As subway demand increases, less passengers will switch to buses. When bus demand increases, subway demand will increase correspondingly. The increase of private car travel demand will increase the subway travel demand but reduce the bus travel demand. The research is helpful to understand the coupling relationship among different travel modes in our country at the present stage, and thus to better cope with the issue of urban traffic congestion.

Topographic correction is critical to the accuracy of the earth's surface quantitative remote sensing. Traditional topographic corrective models are not so suitable for high-resolution remote sensing images. In order to address the problem, this paper proposes a topographic correction method based on radiation transfer model and strict control over error sources. High-resolution panchromatic and multispectral images of ZY3-01 satellite were taken as examples to conduct relevant experiments, and the topographic correction of high-resolution remote sensing images was realized with subjective and objective analysis and evaluation. The analysis results show that the problems of poor correction effect without absolute radiometric calibration coefficient in topographic correction of panchromatic remote sensing images can be effectively solved and the detail of high-resolution remote sensing images can also be maintained by the proposed model and method. So it is more suitable for high-resolution remote sensing images than traditional methods.

Atomic spin gyroscope is the latest type of gyroscope, which has ultra-high theoretical precision. Alkali vapor cell is the sensing element of atomic spin gyroscope, which carries the atomic spin effect. Electric heating makes alkali attain saturated vapor pressure, which will introduce electromagnetic interference and other noises, thereby affecting the accuracy and sensitivity of atomic spin gyroscope. To reduce the influence of heating chamber electromagnetic noise on the atomic spin gyroscope, the electromagnetic noise suppression experiment was studied from two aspects of heater structure and heating driving signal. A special shaped heating film with magnetic noise suppression was designed. A high frequency sine wave was designed as the heating driving signal. In addition, a non-magnetic heating system of alkali vapor cell was constructed. The test results show that the equivalent magnetic noise is within 17 fT/Hz^1/2, and the temperature stability of the alkali vapor cells is within ±0.006℃, which provides a reliable guarantee for the performance improvement of atomic spin gyroscope.

Recently the avionics system is quickly transferring to integrated modular architecture. To prevent the mutual interference between different applications, IMA software usually adopts partition mechanism. Due to the "time partition", the traditional real-time schedulability analytical method is not applicable. This paper researches a class of special partition system, which is called harmonic-period partition system on uniprocessor platform. This paper gives the formalized definition of harmonic-period partition system and the necessary and sufficient condition of schedulability of tasks in harmonic-period partition system. On this basis, this paper proposes an algorithm, which is called time windows distribution algorithm. This algorithm distributes multiple time windows for each partition in the main time frame. This algorithm must be able to find a feasible schedule table for a harmonic-period partition system if this system is schedulable theoretically, and all tasks in partitions will not timeout if the global scheduler schedules partitions according to this schedule table. The algorithm proposed in this paper can be applied to practical engineering.

The maximum forward speed for helicopter increases by adopting rigid coaxial rotor system, while the vibration load in rotor system obviously increases. In order to analyze the vibration characteristics of high-speed rigid coaxial rotor system, it is necessary to investigate unsteady aerodynamic loads of rigid coaxial rotor with aerodynamic interaction. Therefore, a rotor reverse flow aerodynamic model is established based on an unsteady panel method through satisfying boundary conditions of blade leading-edge and trailing-edge to reflect the influence of the reverse flow on the retreating side of the high-speed coaxial rotor. Moreover, a rigid coaxial rotor tip-vortex-blade aerodynamic model is added to describe the influence of aerodynamic interaction between the coaxial rotors. Coupling those models with the wake model of coaxial rotor based on a viscous vortex particle method, an unsteady aerodynamic analysis method under aerodynamic interaction of high-speed rigid coaxial rotor is established. The aerodynamic load at characteristic span of X2 rigid coaxial rotor is simulated during forward flight, and compared with the results of PRASADUM and CFD/CSD based on NASA OVERFLOW and CREATE AV Helios to validate the effectiveness of the present unsteady aerodynamic analysis method. Compared to PRASADUM, the present method better describes the variation characteristics of unsteady airloads of the upper and lower rotors on the advancing and retreading sides, and the results agree better with the computational results of CFD/CSD. Finally, the influence of aerodynamic interaction between the X2 upper and lower rotors on the unsteady aerodynamic loads is analyzed, and the difference of unsteady aerodynamic load between the single rotor and coaxial rotor is also investigated. It is shown that the unsteady aerodynamic load of rigid coaxial rotor is affected obviously by the tip vortex of coaxial rotor at low speed, while it is influenced by coaxial rotor blade at high speed. The characteristic of aerodynamic load of coaxial rotor is radial distribution with number of blades at high speed.

Land clutter power exerts a strong impact on the performance of low-altitude surveillance radar. Especially in urban areas, skyscrapers and atmosphere conditions complicate the radar signal propagation and the electromagnetic scattering from land surfaces. This paper presents a land clutter power map modeling approach for low-altitude surveillance radar in urban areas by using the parabolic equations (PE). It could theoretically contribute to the performance prediction and field deployment of such radar systems as well as the analysis of urban clutter characteristics. The proposed approach exploits wide-angle PE to take into account the reflection, diffraction, refraction and multipath effects in low-grazing-angle radar propagation related to tall buildings and atmosphere conditions. After the 3D approximation of aforementioned 2D wide-angle PE, the propagation factors could be obtained in the 3D environment. Then according to the radar equation, the power in every clutter cell is calculated. Finally, numerical simulations are carried out to demonstrate the influence of different architectural appearances and urban skyscrapers on radar signal propagation and land clutter powers.

Nacelle design has a significant effect on aerodynamic performance of blended-wing-body (BWB) aircraft with distributed propulsion. To clarify the effect and its reason of primary nacelle design parameters on aerodynamic performance of BWB aircraft with boundary layer ingestion (BLI) effect, a detailed study was conducted by computational fluid dynamics (CFD) method and Morris sensitivity analysis method. Sensitivity order and coupled effect of primary design parameters on aerodynamic performance were obtained. Flow details of higher sensitivity and greater coupled effect parameters were analyzed under baseline and alternative condition. The results show that the relatively most significant parameters are the maximum thickness of section 2 and 3. The main reason is that local thickness and camber increase, and pressure distribution of whole nacelle surface is changed. Leeward local stall will occur as the maximum thickness increases configuration when mass flow rate decreases and inlet location along the chord direction moves forward. The coupled effect of the maximum thickness of section 2 and 3 on aerodynamic performance is relatively significant.

Aimed at the problem that frequency-stepped synthetic aperture radar (SAR) images obtained by classic inverse Fourier transform method have a limit on unambiguous range, a new model which takes the pulse sequence of frequency-stepped SAR as an along-track virtual array radar signal and its corresponding imaging method for frequency-stepped SAR were proposed. Meanwhile, unambiguous imaging using modified back-projection method is realized. The virtual array model for frequency-stepped SAR signal was established and the synthesis method of high resolution range profile based on this model was presented. By embedding range migration correction and secondary phase compensation into original back-projection algorithm, a precise two-dimensional image of the target was also obtained. All the results show that the virtual array model based imaging method for frequency-stepped SAR is not restricted by the theoretical limit of frequency-stepped signal's unambiguous range and can get images without range ambiguity for wide swath imaging rapidly.

As flying wing UAV lacks manipulating ability, a control strategy combined with fluidic thrust vectoring-turbocharged engine (FTV-E) technology is proposed. In this paper, the control scheme is designed:the inner loop compensator is used to eliminate the negative coupling term of system; the outer loop compensator used backstepping tracking algorithm; the particle swarm optimization (PSO) compensator to compensate the disturbance and coupling term that cannot be modeled. The control structure's stability is proved. Based on the traditional backstepping control methods, the proposed controller increases the inner loop compensator. The proposed inner loop compensator retains the aerodynamic damping term which is favorable to flight. This compensator not only can reduce the conservatism of the outer loop controller, but also is convenient for engineering realization. The simulation results show that the proposed control scheme is effective.

In order to study the progress of the cryogenic propellant during atmospheric ground parking, a visualization liquid nitrogen tank experiment system was designed. The experiment researched how the filling rate and ambient temperature affected the evaporation mass of liquid nitrogen, and measured the fluid inside tank and the wall temperature outside tank which changed with the time and location. The experimental results show that during atmospheric ground parking the phase transition mainly happens in the wall and gas-liquid interface, air pillow zone has temperature levels, and the air pillow temperature increases with the decrease of the distance from the exit. The liquid stays in the saturated state with almost consistent temperature, and the outer wall temperature distribution of the tank is significantly different in the axial direction and lower in liquid zone. The heat and mass transfer between liquid and gas is deduced from the Hertz-Knudsen equation based on the molecular dynamics theory. According to the temperature boundary conditions acquired from the experiment, physical process of 30 min in liquid nitrogen tank during atmospheric ground parking was simulated using mixture model. The simulation results show that the deviation of volume vaporization rate between simulation and experiment is within 5%, and the deviation of temperature simulation and experiment in the liquid zone is about 0.15 K.

Global navigation satellite system-reflectometry (GNSS-R) is a new remote sensing way which is passive radar and could be used to improve the retrieval precision of the sea surface salinity (SSS). The model of brightness temperature and the scattering power model of GNSS-R were reviewed, and the spaceborne simulation scenario was developed in this paper. Based on those, the performance of GNSS-R aiding radiometer to determine SSS was first explored. Although it is possible to decrease the mass and power consumption of spaceborne equipment by sharing the antenna and radio frequency font-end between GNSS-R and radiometer working on the frequency of GPS L1 1 575.42 MHz, when SSS is larger than 25 psu, the sensitivity of brightness temperature to SSS reduces by about 0.1 and 0.08K/psu for the vertical and horizontal polarization signal respectively. The distortion of reflected GPS L1 signals on the measurement of the brightness temperature was analyzed. It is found that under the condition of the simulation scenario for 1 K variation of brightness temperature, reflected GPS L1 signals introduce error less than 2.5×10^-4 K. Subsequently, the sensitivity of the GNSS-R observable to the brightness temperature variation for the vertical and horizontal polarization signal was explored. The results show that when incidence angle increases, the sensitivity of the horizontal and vertical polarization signal show falling and rising tendency respectively. Finally, the relationship between the sensiti-vity of the observable to the brightness temperature variation and the spatial resolution was analyzed. The conclusion is that the study of retrieval algorithm having high accuracy and spatial resolution is crucial for spaceborne GNSS-R aiding radiometer to determine SSS.

Financial fraud behavior, network intrusion and suspicious social actions can be detected by structural anomaly detection in graphs. The existing anomaly detection algorithms require high computational complexity and cannot process large-scale dynamic graphs. So an incremental and parallel algorithm is proposed to discover and detect abnormal patterns in dynamic graphs effectively and efficiently. The whole graph was partitioned into subgraphs by time sliding windows. N subgraphs in time sliding windows were processed in parallel by minimum description length (MDL) principle to discover both normal and abnormal patterns. Structural outliers can be detected gradually in parallel based on normal patterns. The results of experiments conducted in multiple large-scale graphs show that the precision rate for detecting the abnormal patterns of dynamic graph reaches 96%, recall rate reaches 85%, and running time reduces by an order of magnitude. The impact of the size of sliding windows and the number of parallel on running time of the algorithm is also discussed.

In the application of global navigation satellite system-reflection(GNSS-R) technology, the GNSS-R signal simulator is needed to test the reflection signal receiver in order to reduce costs. A modeling method of global navigation satellite system (GNSS) sea surface reflection signal based on the principle of bistatic radar is presented. First, the remote sensing principle of GNSS-R bistatic radar was analyzed. Then, according to the distribution characteristics of the delay and the Doppler frequency on the sea surface, the reflection points of the sea surface were selected, and the area of corresponding reflection units was calculated. Subsequently, the calculation of the scattering coefficient was carried out. Finally, the simulation verification of the multiple combined signals was conducted. The simulation results indicate that the correlation coefficient of the simulated ocean reflection signal's correlation power curve and the theoretical curve of the ZV model is better than 0.92, which can be used to generate the GNSS ocean reflection signal effectively.

Error correcting output codes (ECOC) is a decomposition framework, which can transform a complex multiclass classification problem into a series of two-class classification problems. It can complete one multiclass classification task efficiently. To improve its generalization performance, we studied the design of its base classifier, which is also known as model selection in ECOC. The key point is how to estimate the generalization error of ECOC. Leave-one-out (LOO) error is an almost unbiased estimator of generalization error, so we studied how to estimate the LOO error bounds for ECOC. First, we provided the definition of LOO error for ECOC. And then, based on this definition, upper bound and lower bound of LOO error for ECOC was given under the condition that base classifiers were support vector machines (SVM) and decoding method was linear loss function. The experiments on synthetic dataset and UCI dataset show that the upper bound of LOO error for ECOC leads to good estimates of parameters in base classifiers, and designing base classifiers can improve the generalization performance of ECOC. Furthermore, we also report that training error is one lower bound of LOO error for ECOC, and the application of this lower bound should be studied in the future.

Fiber metal laminates, as a new-type composite material, have been applied in aerospace field. Digital optical strain method is used to realize strain measurement of metal layer instead of traditional method of strain measurement. Meanwhile, in order to predict the stress distribution in metal layer accurately, the global stiffness matrix obtained from classic laminate theory is modified by the equivalent stiffness matrix from sub-laminate stiffness theory. Taking 2/1 and 3/2 laminates of glass fiber reinforced Al-Li alloy as an example, the stress distribution in metal layer of the laminates is determined based on the measured strain, finite element analysis, classical laminate theory and modified method. The comparison of stress distributions obtained from the measured strain and finite element analysis shows that the maximum errors are only 2.12% and 3.68% for 2/1 and 3/2 laminates, respectively, which verifies the accuracy and practicability of the optical strain method. By comparing the stress distributions from the optical strain method and laminate theory, the prediction accuracy of the modified model increases by 2.91% and 5.83% compared with that of original model for 2/1 and 3/2 laminates, respectively, which proves the effectiveness and advancement of the modified model.

A novel object tracking algorithm based on convolution representation in Fourier domain is proposed for object tracking. Object tracking question can be treated as a convolution representation model. By finding the best filters, which reconstruct the target function with minimum loss, fast and robust object tracking can be realized. When the optimal multi-channel convolution representation model is mapped to the Fourier domain, it is equal to solving the least squares solution to linear equations. First, all solutions of the system of linear equations can be expressed through the theory of pseudo inverse, which provide a general format of convolution filters. Then, filters updated in the previous frame and feature templates extracted from current frame are used to generate current filters, and the pseudo inverse can be obtained fast through the full rank algorithm. Finally, tracking filters are updated and applied in both translation and scale. Experimental results on the object tracking benchmark (OTB) database show that our algorithm performs better than some state-of-the-art tracking methods in terms of accuracy and offers a general format to design filters.

In order to obtain a more realistic mesoscopic analysis model of closed-cell aluminum foam, a new methodology for the finite element modeling based on computed tomography (CT) images is presented. First, the optimal threshold between base material and air was developed using Otsu algorithm by analyzing the images obtained from the CT scanning of closed-cell aluminum foam. Then, the mesoscopic finite element model was directly established based on the thought of mapping grid. As a result, the reconstruction of three-dimensional mesoscopic analysis model of metal foams is achieved. Finally, the numerical simulations of quasi-static compression and dynamic test of closed-cell foam are carried out respectively based on the mesoscopic analysis model. The results demonstrate that the internal deformation of closed-cell aluminum foam distributes throughout the whole specimen, which is closely bound up with their 3D structure under quasi-static compression, while it is close to the loading end and remarkably behaves with localization under dynamic compression. The methodology of modeling can describe mesoscopic structure realistically and provide a more detailed simulation analysis on the stress state, deformation and failure of closed-cell aluminum foams under quasi-static and dynamic loading.

Recovering pulse template is one key technology of X-ray pulsar-based navigation system. Its precision is closely related to the pulsar angular position. First, this paper briefly introduced the theory of recovering standard profile. Then, the impact of pulsar angular position error on pulse template was analyzed and its analytical formula of annual mean value and the integral for any arc segment were derived. Finally, we proposed a feasible way that can significantly decrease the impact of pulsar angular position error. These research conclusions and simulation analysis verify the effectiveness of error compensation method, which could provide reference for optimizing observation task of X-ray pulsars and recovering X-ray pulse template.

A new integrated navigation method based on inertial sensor, optical flow and visual odometry is proposed for self-navigation indoor in GPS-denied environment. An ORB optical flow based method is also proposed for estimating real-time three-axis velocity of the UAV. The algorithm improves the traditional pyramid Lucas-Kanade method using sparse optical flow based on feature points. The tracking of feature points is made more accurate by applying forward-backward tracking and random sampling consensus strategies. For position estimation, a visual odometry method with integrated vision/inertial navigation is adopted, which uses the artificial icon method, visual optical flow information and inertial navigation data. Finally, the velocity and position estimations from the proposed method are validated via actual flight test and via comparison with velocity measurement information from a PX4Flow module and a Guidance module and with locating information from movement capture system.

Cracks often initiate at the chamfering for sagging holes. The initial fatigue quality (IFQ) of this type of crack needs to be determined prior to economic life assessment. Firstly, finite element models with and without chamfering are developed so as to investigate the effect of chamfering on the stress intensity factors at the crack front. The results show that the chamfering imposes great influence on the stress intensity factors of relatively small crack. Secondly, in order to characterize the IFQ of sagging holes, a circular-front crack initiated at the intersection of the chamfering and specimen surface is taken as the initial flaw, with the radial distance of crack front from the initiation site as the crack size. Finally, the crack growth equation for relatively small cracks is employed to characterize the crack growth behavior, and the equivalent initial flaw size (EIFS) distribution is obtained through back-extrapolation. Statistical analyses show that the EIFS distribution parameters obtained by using the proposed crack size definition are independent of stress levels.

In order to represent the movement of the shoulder skeletal system, a spatial hybrid mechanism model is proposed, which describes the articulation between the scapula and thorax as a kinematic constraint similar to a cylinder-plane pair. Firstly, types of joints in shoulder are determined, and thus the degrees of freedom of the shoulder girdle and shoulder mechanism can be analyzed. After the definition of local coordinate systems attached to each skeleton, the vector theory method and homogeneous coordinate transformation are used to establish the position analysis equation of the shoulder mechanism, and the closed-form solutions of joint positions are obtained subsequently. Finally, to verify the validity of the mechanism model, the skeletal posture dataset obtained from a shoulder movement experiment is used to inversely drive the model, the calculation results of the scapular posture are compared with the experimental data. The results indicate that the mechanism model has achieved a good consistency in predicting the skeletal movement of the shoulder complex. Furthermore, this model can be adapted for different individuals' geometric skeletal characteristics by scaling.

Cross entropy method is an efficient and adaptive stochastic optimization method and has immense potential in complex optimization problems with high dimension and nonlinear constraints. However, the traditional cross entropy method is lack of accuracy. In this study, both the concepts of current elite samples and global elite samples are introduced to extract more useful information from the whole iterative history. Then, a new parameter updating strategy is established based on these two concepts. New adaptive smoothing strategy and mutation operation are also applied to improve its computing performance. The proposed algorithm is illustrated by three numerical examples. The computational results indicate that the improved cross entropy method has higher calculation accuracy and better global search capability.