Abstract:A user-experience-based handoff decision method towards Integrated Satellite and Terrestrial Network (ISTN) is proposed to guarantee the user session continuously. It selects the network with the lowest user experience difference, so each user can access to the most appropriate network. Meantime, a speed perception module is designed based on fuzzy method for the purpose of decreasing handoff times with high mobility. Simulation performance proves the superiority in reducing the probability of handoff failure and new call blocking. Moreover, the system can maintain a higher average network load to serve more users, which indicates the superiority of resource allocation among the whole network.

Abstract:In order to improve the transmission rates of cognitive radio (CR) and primary user (PU), the cooperative communication scheme between CR and PU and the optimal sub-band power allocation are proposed respectively. If the presence of the PU is detected, the scheme allows CR to use half of the frame to transmit data while using the left half to help PU with cooperative transmission. The proposed power allocation based on the scheme can make CR achieve higher rate without influencing PU. Simulation results show that compared with the conventional non-cooperative communication, the proposed scheme can make improvements on the rates of both PU and CR.

Abstract:To improve the bit error rate (BER) performance of physical-layer network coding (PNC) in asymmetric two-way relay communication systems, a new PNC scheme named combined orthogonal physical-layer network coding (COPNC) is proposed. In the scheme, the two source nodes employ orthogonal carriers; then the relay node employs orthogonal combination and broadcasts the combined signal to the two destination nodes. Analytical and simulation results show that COPNC can provide better BER performance when the channel conditions in the systems are asymmetric. Especially when the two uplink channels have different signal to noise ratio (SNR), BER of COPNC is lower about 3 dB than PNC. As a result, COPNC is very suitable to be used in two-way relaying communication systems with asymmetric uplink channels.

Abstract:To evaluate an ultra-lightweight blockcipher Piccolo’s ability to counteract Power Analysis Attack (PAA), an attack model, which focuses on the first round of Piccolo, was proposed and Correlation Power Analysis (CPA) was conducted on this cipher based on a power simulation acquisition platform. Due to the whiten keys and round permutation for the first round of Piccolo, attacking keys including RK0L, RK0R, WK₀ and WK₁ were divided into six sub-keys, which were disclosed one by one. This approach can reduce the 80-bit primary key search space from 2⁸⁰ to (2×2²⁰+2×2⁴+2×2⁸+2¹⁶) and make it possible to recover the primary key. The attack results show that 500 power traces are enough to recover Piccolo’s 80-bit primary key. It is concluded that the hardware implementation of Piccolo without any countermeasure is vulnerable to CPA and some countermeasures should be used. This work is the first known report about the security of Piccolo against PAA.

Abstract:For the reentry terminal guidance problem of ballistic missile with constraint of impact angle, a nonlinear suboptimal guidance law that not only precisely attacks the ground target, but also satisfies the requirement of the terminal angle is designed based on the model predictive static programming technology proposed recently. The flight scenes that the ballistic missile attacks against stationary targets and maneuvering targets are simulated in this paper. The simulation results show that the designed guidance law spends less energy than the APN law. Compared with other guidance laws with impact angle constraint, the designed guidance handles the nonlinear problem as it is (without linearization), and the computational complexity is significantly lower than the guidance law with the angle constraint based on optimal control theory.

Abstract:The inflatable wing with inflated pressure has a large deflection which leads to a deviation compared with target shape. Such deviation has a great influence on the aerodynamic shape of the inflatable wing, which decreases the precision of structural analysis. In this paper, we proposed a novel inverse iterative method to obtain the accurate 3D initial shape of the unpressured inflatable wing. The initial shape of the Lattice Inflatable Wing is then obtained accurately by combining the inverse iterative method and the APDL program. The non-contact tests are performed to validate the inverse iterative method in the end. The results reveal that the proposed inverse iterative method is an accurate and effective method which may be used to obtain the 3D initial shape of inflatable wing with zero pressure. This method has high computation efficiency, good convergence and reliable characteristic.

Abstract:To provide precise simulation for the flow field of steam turbine last stage, the calculation method for the vapor-liquid two-phase non-equilibrium condensing flow was developed based on the two-fluid model. The numerical simulation of moisture removal slot on the surface of a steam turbine last stage blades was carried out, and the influence of different moisture removal slot structures on the non-equilibrium condensing flow of turbine cascade was analyzed. The results show that the moisture removal slot set on the blade suction surface can effectively reduce the nucleation rate of water droplets near the throat region of cascade,therefore decrease the loss of non-equilibrium condensation caused by phase transition,significantly reduce the number of larger diameter water droplets at the outlet of the blade cascade. Due to larger inflow width and more reasonable moisture removal structure, the scheme II is more beneficial to improve the suction effect of the water film on the surface of long blade in the wet steam stage.

Abstract:Based on Matlab heat transferring program and combined with CFX three-dimensional temperature field of thermal conductivity for calculation, included design of pipe network computing plan and three dimensional heat transferring calculation, a guiding blade of high pressure turbine is researched and the cooling structure is designed according to the characteristics of the guiding blade. A high temperature zone about 1 700 K appears on the blade, but the average temperature is about 1300 K, because the trailing edge vortex cooling structure enhances heat transfer coefficient. A good cooling structure design and verifying calculation of temperature distribution in 3 D can be completed on the cooling structure design platform.

Abstract:To obtain the detailed distribution of three dimensional magnetic flux leakage (MFL) from wire rope defect, and to improve the accuracy of the quantitative recognition, Hall sensor array was used to detect the three dimensional magnetic flux leakage. In the detection process, variation of lift-off, the magnetic excitation heterogeneity and other factors will cause the dissimilarity of MFL signals obtained from the Hall sensor array, which is not conducive to quantitative inversion of wire rope defects. In this paper, a method combined with baseline estimation and normalization of peak-peak value of MFL signals is presented, by which the dissimilarity of each channel is compensated and the signal-noise ration of MFL signal and the contrast of MFL image are improved. The experimental results show that the defects are inspected more accurately with the channel-equalized MFL image.

Abstract:The strap-down inertial/stellar refraction integrated navigation method (SINS/RCNS) was proposed in this paper based on high precision of starlight refraction indirect sensitive horizon. The outputs posture of the star sensor correct gyro drift, and combined with the atmospheric refraction model, the starlight refraction angle can be got which is used to correct the position and velocity error. The observation model of the integrated navigation system was derivated, and it's observability was analyzed, finally the Kalman filter (KF) was used for state estimation. The simulation result indicated that the proposed method was able not only to estimate the gyro drift exactly, but also to correct the navigation error caused by the accelerometer bias, the divergence of the speed and position error was bated ulteriorly, therefore it was a practical method to improve the positioning accuracy. 

Abstract:A fuzzy recurrent neural network controller with fault tolerable thrust allocation control strategy has been proposed for Remote Operated Vehicles (ROV). Extended functional link is issued for fuzzy recurrent neural network controller to improve the ability of identification and response. Online training algorithm is developed based on gradient descent method. The learning rate parameters are determined according to particle swarm optimization, hence the whole network convergence is guaranteed. On the aspect of force allocation, a model has been established according to thruster positions for open frame remote operated vehicles based on which the fault tolerable problem has been transformed into dual optimization problem. The energy function concerning ROV control has been established so as to obtain thrust optimal allocation under fault conditions. Experiments have demonstrated that the controller can improve the ROV capacity to handle nonlinear characteristics and strong disturbance, reduce control errors. When one of main or side thrust fails, the controller can still accomplish precise horizontal position control through thrust optimization allocation strategy. Therefore, the reliable operation of ROV for the long time-span has been improved.

Abstract:To study the effects of COF on wear of high pair, a wear prediction model of cylinder-on-flat configuration was established with the finite element method (FEM) and the commercial FE software ANSYS. The wear volume is computed by a modified Archard equation, and the material loss caused by wear is simulated by moving contact boundary nodes in FEM model. The simulation results, which have been verified by experiments, show that the lower COF would generate the larger contact pressure and slip that produces more wear volume. The larger COF would accelerate the generation of fatigue.

Abstract:Temperature and thermal stress analyses of receiver can provide theoretical guidance to the suppressing of thermal stress. Coupled-field element method is adopted to conduct temperature and thermal stress field analyses of tube receiver under non-uniform and intermittent concentrated solar irradiation. During the temperature analyses of tube receiver, angle relationships between incident direction of solar rays and surface elements of tube receiver are calculated, and the relationships multiplied by magnitude of concentrated solar irradiation are used as the secondary boundary condition of temperature analyses. The secondary derivative of temperature field along length direction of tube receiver is also investigated to clarify the thermal stress distribution along length direction. The numerical results indicate that axial stress and tangential stress have much higher influence on thermal stress field than radial stress, and the inflexion of secondary derivative of temperature distribution will induce an inflexion of thermal stress distribution.

Abstract:To predict hydraulic transients of operating processes of control valve of LO₂ delivery pipes for space vehicle, mathematical models of rigid pipe, corrugated pipe, LO₂ tank and control valve were established on consideration of the influences of unsteady friction and corrugated pipe elastic deformation, numerical computation was carried out by method of characteristics to solve first order partial differential equation and method of linear theory to solve second order non-linear equation with single variable. Different influence to transient flow is discussed by changing flow characteristic, motion index and motion time of control valve. Calculations show that pressure surge in transient flow caused by operation of valve with equal percentage flow characteristic (VWEPFC) is significantly weaker than that of valve with quick opening flow characteristic(VWQOFC). The total accuracy of LO₂ delivery is more easily controlled on operation of VWEPFC opposite to VWQOFC. Extending the closing time of VWEPFC could reduce the pressure surge efficiently, but the effect of extending the closing time of VWQOFC is mainly delayed arrival time rather than reduction of water hammer wave. Valve motion index of VWEPFC equal 1.0 and fast-opening along with slow-closing program is optimum to transient control of LO₂ delivery pipes. 

Abstract:For liver segmentation on abdominal CT images, a novel algorithm is proposed which is based on the threshold method and modified GGVF-Snake model. Firstly, the CT image is converted into grayscale by using Window-Leveling algorithm, and then Modified Curvature anisotropic diffusion filter is applied. Secondly, a threshold method is used to obtain the initial contour of liver. Finally, the accurate liver boundary is obtained by using a modified GGVF-Snake model. Experimental results show that the proposed algorithm can be applied to the segmentation of liver on abdominal CT images effectively.

Abstract:To optimize the properties of gypsum wallboards incorporated with Composite Phase Change Material (CPCM), orthogonal test was used, and according to the practical conditions, the mechanical properties and thermal performance of gypsum wallboards incorporated with CPCM were studied. The results show that, the compression and flexural strength of gypsum board decreases with the increase of CPCM content, and increases with the increase of steel fiber content or moisture content. Under different temperature conditions, the influence of various factors on the thermal conductivity is in a different order. Increasing internal relative humidity and steel fiber dosage, leads to increase in the thermal conductivity, but increasing the CPCM content leads to decrease the thermal conductivity. The thermal conductivity of gypsum board is dependent on the initial board temperature. The maximum thermal conductivity appears in the phase transition temperature interval of CPCM.

Abstract:To implement the uniform load distribution of the power-split transmission, a pseudo static model is built. First, according to the method of theoretical analysis of tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA), the actual meshing process of each gear pair is simulated, and the fitting curves of time-varying mesh stiffness are obtained, which can improve the numerical precision. Next, according to the closed-loop characteristic of system power flow, the conditions for deformation compatibility of torsion angle are proposed, which are then combined with the torque equilibrium conditions and elastic support conditions to calculate the transmission torque of each gear pair. Finally, the load-sharing coefficient of the system is obtained, and the influence of the floating pinion based on spline clearance floating and constrained by the radial spacing ring is analyzed. The results show that the errors collectively influence the load sharing characteristics, only reducing a certain error never fully reach the perfect loading sharing characteristics. The floating component can significantly improve the load sharing characteristics. By comparing the theoretical data with the experimental data, the correctness of the method proposed is verified.

Abstract:A new method of hyperspectral imagery band selection is proposed based on artificial physics optimization algorithm. In this method, the combination between classes separability and information of band groups is used as fitness function, and subspace division is used to deal with hyperspectral imagery before band selection to reduce the correlation and redundancy of the output band of hyperspectral imagery. AVIRIS imagery is used for experiment with the proposed algorithm and other classical algorithms which are ant colony algorithm, genetic algorithm and particle swarm optimization, and it turns out that this algorithm is more effective in both band chosen performance and computing time consumption than others. 

Abstract:To solve the problem that the manipulator of single-arm space robot has limited accuracy of positioning and attitude determination during on orbit servicing, a precision synergy control algorithm for multi-arm space robot was proposed. This method researched space robot (SR) with three arms each of them has seven degrees of freedom. The kinetic equations include the body and arms were built based on Kane method. Moreover, according to Lyapunov function, a trajectory tracking algorithm was designed for each arm to reduce motion jitter while capturing target. Simulation results show that the presented method can ensure the manipulators move along the desired paths and improve the position and attitude precision of manipulators.

Abstract:Using a quasi-one-dimensional election gas model, we investigate the plasma excitation of quasi-one-dimensional nanostructure systems. The Eigen-equation of plasma oscillation in the quasi-one-dimensional systems is deduced based on the linear-response and electromagnetic theory. Numerical calculation for the plasmon spectrum is presented. The results show that the excitation spectrum of the finite-scale systems is discrete and depending on the size of systems strongly. As the size of system increases, the number of plasmon increases, the excitation spectrum decreases, and the mutual spacing becomes denser. In addition, the excitation spectrum increases with the electron density of the systems increasing, which is qualitatively consistent with the conclusion of macroscopic systems.

Abstract:As far as the stereo images, the matching between the left and right image and the disparity should be considered, and the matching and the resizing of disparity are fused on the retargeting of the stereo images. A resizing method by using stereo extension of seam carving is proposed, which can keep the image content more precise during adjusting the size of the image, adjust the size of disparity, and ensure the consistency between the left and right images.

Abstract:The preparation method of oil perforating bullet body by repressing and resintering powder is introduced. The influence of pressing pressure, time of holding pressure, forming way on texture and density distribution are studied. The results show that when the initial pressure is 600 MPa and repressing pressure is 800 MPa, the compaction structure and density is appropriate. When the compaction density exceeds 7.4 g/cm³, it does not increase with the pressure addition. High density powder metallurgy bullet body that has a certain density gradient distribution can be acquired by adopting extrusion strengthening compact compensation process, the average density of bullet body reaches 7.3 g/cm³, tensile strength and elongation are 647 MPa and 3.78％ respectively. The implosion contrasting results of different bullet body indicate that the penetration value and aperture of powder metallurgy bullet body exceeds the standard value on steel target and concrete target, the penetration value is higher than that of 20＃ steel bullet body and has a prominent debrital property.