Abstract:Aimed at the problems that the accuracy of energy acquisition process is low and the design parameters are difficult to be optimized in the overall design of small longendurance solar powered unmanned aerial vehicle (UAV), an optimization method of the overall design in small lowaltitude longendurance solar powered UAV is put forward based on the principle of energy balance. In order to accurately characterize the solar radiation intensity, the atmospheric mass and atmospheric transparency coefficient are introduced. A solar radiation model of the UAV is established with direct radiation intensity and scattered radiation intensity. Based on the principle of solar energy, combining with solar radiation model and energy relationship, statistical analysis of UAV mass distribution and parametric modeling, the energy balance model is established and verified. A concept of remaining time after crossnight flight is proposed, and the optimal design parameters and schemes are obtained by using the genetic algorithm to optimize the maximum remaining time after crossnight flight. Taking the flying in Xi’an in June 22nd as an example, the optimal design is carried out, and the prototype is developed to carry out flight test. The result shows that the prototype has the ability of crossnight flight.

Abstract:In the view of the influence of different unstructured mesh types on the fluid calculation efficiency and convergence on premise of the same surface mesh size and body mesh unit number, the computational efficiency and convergence of tetrahedral mesh, hexahedral mesh and polyhedral mesh in CFD calculation are compared. The result shows that under the conditions of same surface mesh size, the convergence of hexahedral mesh is better than that of the others. Besides, the time and RAM for calculation of hexahedral mesh are less than that of the others. The convergence rate of polyhedral mesh is much better, but the computational efficiency of polyhedral mesh is a little lower than that of tetrahedral mesh. The computational efficiency and convergence of tetrahedral mesh is worse than that of the others. Under the conditions of body mesh unit number, the convergence precision of hexahedral mesh is better. The computational stability of tetrahedral mesh is better. For the convergence rate, polyhedral mesh is as well as tetrahedral mesh. Besides, the convergence precision and the computational stability of polyhedral mesh is much better. So the application range of polyhedral mesh is superior to the others in comprehensive comparison.

Abstract:In order to research on collision risk of parallel runway with simultaneous instrument approach mode, First, through the investigation into the control process of Beijing Capital Airport controllers, the paper analyzes the moving state process of aircraft in simultaneous instrument approach mode. Secondly, based on the position error model, the equations of motion state of two aircraft with simultaneous instrument approach mode are established, and then the parallel runway collision risk model in simultaneous instrument approach mode is established. The key of the position error and velocity parameters in the model are based on the actual operation ADSB data, and the other parameters are ICAO recommended values or controllers experience values. Finally, the paper utilizes MATLAB software for simulating the collision risk of per moment in the whole process of simultaneous instrument approach mode, thus, obtaining the variation trend of the whole process, which provides support for the practical operation and future optimization of simultaneous instrument approach mode.

Abstract:Numerical simulation of stage 35 with bulk swirl is carried out using CFD technology for the convenience of analyzing the instability mechanism of transonic compressor. The key factors triggered instability of the compressor are discussed such as leakage vortex and radial vortex at different rotation speed and swirl distortion condition. The results show that positive bulk swirl restrains flow separation of suction side, the leakage vortex, volume of radial vortex of compressor are decreased in positive bulk swirl. The flow separation, radial and leakage vortex and blocking area are increased with low rotation speed in negative bulk swirl. At high rotation speed, negative bulk swirl has little influence about leakage vortex, but the volume of radial vortex is greatly increased to drive flow gathered on blade tip to cause large low speed area in the tail of suction side, causing the instability of compressor strictly.

Abstract:The traditional single specular reflection model enables to formulate the basic features of the multipath error, but this model fails to characterize the combined effect of multiple reflection signal in realistic environment finely. In view of LOS, this paper proposes a new multipath analysis model based on PLLB, deduces an estimating method of multipath error, and researches correlation of pseudorange multipath error between the epochs and random noise characteristic of dynamic carrier phase multipath error. The results of experiment test show that the pseudorange multipath has the correlation between the epochs, the paper utilizes this correlation between the epochs for correcting the pseudorange multipath error to make the double difference pseudorange error decrease by 52.7％, and due to the random noise characteristic, the dynamic carrier phase error will increase.

Abstract:For a material, the design of a reasonable surface roughness structure is a main method to increase the contact angle between it and the liquid, increasing the hydrophobic of the material. In this paper, the two contact state relationships and contact angle on the solid surface, including Wenzel and Cassie states, are analyzed theoretically, and the effect of the fractal structure on the two contact models is compared. A good hydrophobic effect can be obtained by modifying the rough structure of Cassie contact state. The influence of nofractal structure and the existence of twolevelfractal structure on the contact angle of Cassie state are analyzed by using molecular dynamics model. The contact angles of the two contact states increase with the modification of fractal structure, especially the increase of Cassie state. The simulation results show that when the two dimensional fractal structure exists on the solid surface, the contact angle increases by 5°compared with the surface without fractal structure. The error between simulation value and theoretical value is about 1％. A good hydrophobic effect can be obtained by modifying the rough structure of Cassie contact state by using fractal structure in certain fractal series.

Abstract:Aimed at the problems that the existing air combat situation assessment model is lack of the overall performance analysis of fighters, this paper references the superiority function, takes the feature of threedimensional space into consideration, and improves combat power field model. The model of combat power field is constructed in aspects of attack, detection, maneuverability, countermeasure and alert.Based on the existing model, based on the change of equipment, the attack ability is calculated based on the situational advantage function. Change radar system coefficient, reflect the multitavget tracking abitity of modern radar. Increasing the consideration of radar lower visual ability highlights the 3D space characteristics. The paper restructures the function of combat power field based on the existing model and the change of equipment. The combat power field theory is applied in analysis of situation assessment and operations guidance. The paper verifies the effectiveness of the model. The result of research shows that threedimensional combat power field can reflect the air combat situation visually and bring the basis to maneuvering decision.

Abstract:On the basis of the logarithm method, an operational effectiveness evaluation method is put forward. Through calculating the radar detection range to know whether there is an earlywarning aircraft in cooperation with or not, a specific expression of the change of the target ability parameters is given. Based on the Lanchester equation, an air combat model is established under the condition of the cooperation of the earlywarning aircraft. And the air combat process is simulated under five given conditions, the air combat process is simulated, and the simulation data and loss charts are given. The results show that after the installation of the data chain under condition of the earlywarning aircraft cooperative combat, so long as the military strength of our side exceeds a foe by 77.3％, our side will surely win victory.

Abstract:Aimed at the problems that the performance is poor, the adaptability of SNR is weak, and the high computation is complex in the carrier synchronization for the CPM signal, a novel carrier synchronization algorithm based on the code assist is proposed in this paper. Firstly, a synchronization system model with CPM modulated signals is established, and in view of the above the log likelihood function of the carrier phase is deduced. Then, the parameter estimation and carrier synchronization are realized through utilizing the mean value of the posterior probability. And the estimation precision and the estimation range of phase offset are analyzed in theory. Finally, the effectiveness of the proposed algorithm is verified by the MonteCarlo simulation. The theory analysis and simulation results show that the new algorithm is good in performance in carrier synchronization of CPM signals and the adaptability of SNR, and suitable for the circumstances of large frequency offset or phase offset. Simultaneously, the algorithm is superior to the EM algorithm in the computational complexity.

Abstract:When there is mainlobe interference, the adaptive beamforming based on eigenprojection preprocessing (EPB) can effectively suppress the mainlobe interference and sidelobe interference. However, when the power of mainlobe interference becomes stronger, the ability of the algorithm to suppress sidelobe interference is greatly decreased, and the sidelobe interference fails to be suppressed effectively. In accordance with EPB, an algorithm based on eigenprojection preprocessing and augment of null depth is proposed in this paper. Firstly, the eigenprojected data is projected on the interference signal subspace which removes the main lobe interference. Secondly, the data after projection is weighted appropriately and then added to the data after eigenprojection preprocessing to enhance the power of the sidelobe interference signal. Thirdly, the output of the modified weight vector can be calculated by the new covariance matrix which is formed by the sampled data after interference enhancement. Fourthly, the output of the adaptive beamforming can be calculated by the modified weight vector, and the signal to interference plus noise ratio of the algorithm is analyzed briefly. The simulation results show that the proposed algorithm in this paper can form deeper nulls in the direction of sidelobe interference, and obtain still greater sidelobe suppression effect in the case of higher power of the mainlobe interference.

Abstract:Aimed at the problems that the spatial distribution of interruptedsampling and repeater jamming is not ideal, and the traditional frequency shift methods are hardly utilized for dealing with characteristics of interference, a spectrum spread and compression (SSC) algorithm is used to change this situation. This paper analyzes the expression of fake target based on ambiguity function. Then a SSC algorithm is used to produce advance interferences. The theory and simulation results show that this proposed method is able to improve the spatial distribution of this kind of interference. What’s more, compared with the direct frequency shift, this method can be effectively confronted by the frequency modulation slope agility radar without prior knowledge.

Abstract:This paper builds a mixed logical model for a new inverter, and treats it as a predictive model in order to research the predictive direct power control for inverter. In order to achieve the aviation power supply requirements and reduce the switching losses, the zero vector improves to the original 3+3 voltage vector control sequence method. By calculating the active and reactive components of the output voltage at the next time, the action time of each voltage vector is obtained on the basis of minimizing the objective function value to complete the control of the circuit. The method reduces the output voltage THD, 4+4 voltage vector sequence method is good in dynamic and in static characteristics, and stable in switching frequency. The result shows that the method is feasible and valid.

Abstract:The inservice Ferromagnetic Doublecasing Pipe (FDP) is prone to Subsurface Corrosion (SSC) in the rigorous environments. It is necessary to evaluate SSC periodically. On the premise of defect classification in quantitative evaluation and maintenance, the realtime classification of SSC is of great importance. In light of this, this paper proposes a stacked AutoEncoder Artificial Neural Network (SAEANN) classification method for classification of SSC in FDP in conjunction with Pulsed Remote Field Eddy Current (PRFEC) and Pulsed Eddy Current (PEC). By choosing appropriate eigenvalue as the input layer, 3 SSC scenarios (corrosion on external surfaces of inner and outer casing pipes; corrosion on the internal surface of the outer casing pipe) can be identified. The accuracy can reach 97.5% and the result shows that the proposed method is capable of identifying the localized SCC without much loss in accuracy.

Abstract:Aimed at the problem that crack is very hard to be evaluated quantitatively in the riveted structure at aircraft fuselage, pulsed remote field eddy current testing technology is used to detect the crack of riveted structure. The cracks quantitative evaluation in riveted structures are studied by utilizing the advantages rich in the pulsed spectrum components and more information. Firstly, a threedimensional model of remote field eddy current riveted structure is established to detect crack so as to get crack position. Then, the influence of crack type and size on detection signal is analyzed and the classification of surface and subsurface cracks is realized according to the different relation between direct coupling component and crack depth. Finally, the quantitative detection of crack depth is realized by zero cross time changes. Under the premise of knowing crack depth, direct coupling component amplitude and indirect coupling component amplitude are used for quantitative evaluation of the crack length on surface and subsurface respectively.

Abstract:Aimed at the problem that the defects of surface and subsurface are very hard to detect on the ferromagnetic components, the pulsed electromagnetic testing model is established. The physical mechanism of a method composed of the pulsed magnetic flux leakage (PMFL) and pulsed magnetic reluctance (PMR) under the surface and subsurface defect is revealed. Both the simulation and experimental results indicate that the magnetic flux leakage exists in the surface defect of ferromagnetic, but the subsurface defect detecting signal is the change of the pulsed magnetic resistance. For the different depth of the surface defects, the pulse leakage magnetic response signal picked by GMR sensor is better linearity and higher sensitivity; For the different subsurface defects of ferromagnetic components, the relationship between the characteristic value of the pulse magnetoresistance response and the depth of the defects is similar to the linear growth relationship, and the discrimination degree is larger and the detection performance is better.

Abstract:Aimed at the problems that the prediction accuracy is low and the dependability of software reliability model is weak based on single neural network, a Real BP-AdaBoost based on weighted information entropy (WIE) is proposed. First, the Real BP-AdaBoost is established by taking BP neural network as the base classifier of Real AdaBoost. Then, the weighted method of base classifier of Real BP-AdaBoost is improved by utilizing the product of the overall weights of the classifier for training samples and individual weight of the classifier to test samples as the final weight, and the WIE Real BP-AdaBoost is produced. Finally, the proposed algorithm is compared with SVM, BP neural network, Elman neural network and Real BP-AdaBoost with respect to two real software failure data. The mean square error of WIE Real BP-AdaBoost of the forecasted two sets data is 0.442 87 and 0.284 71 respectively, both are below the mean square error of the four comparison models. The result shows that WIE Real BP-AdaBoost is higher in prediction accuracy and reliable in dependability.

Abstract:In order to prevent the uneven frost heave deformation of pavement structure of gravel soil subgrade, this paper presets the condition and reasons for the occurrence on the uneven frost heave of pavement structure. According to the grain size analysis test and the measured value of silt content and moisture, the paper designs five schemes of pavement structure and compared them, then put forward a new antifreezing design measurement. Based on checking computation of frost resistance, the cost analysis and the actual application effect, the optimization program of integration of runway and the shoulder not only avoid the damage of uneven frost heave, but also meet the needs of frost resistance, and simultaneously have a certain economic applicability. Finally, the results show that actual measurement, checking computation and engineering practice, engineering measures are put forward. The result shows that the effectiveness of the practical application is good.

Abstract:For a class of nonlinear systems with mismatched uncertainties, a fuzzy adaptive backstepping sliding mode control method is proposed. In the process of backstepping design, the paper utilizes the fuzzy logic system for approximating the unknown nonlinearity of the system, introduces the “differential explosion” phenomenon in requiring repeatedly the derivation of the virtual control in the backstepping method into the loworder filter, and simultaneously restrains interference with the nonmatching uncertainties. Finally, the paper designs an integral terminal sliding mode control to solve some singularity problems in the control process, speed up the convergence of the system state far away from the equilibrium position, ensure the convergence accuracy of the system and weaken the traditional sliding mode control in the presence of chattering phenomenon. Lyapunov stability analysis proves that the designed controller can ensure the finitetime convergence of closedloop system. The simulation results show that the system state tracking is good in effect and the control input chattering is weakened significantly, and the method is valid.