Abstract:In this paper, a neural network based on adaptive sliding mode controller for rigid spacecraft is proposed, in which the external disturbance that is caused by drift of mass’s center and thruster misalignment, uncertain parameters and actuator saturation are explicitly taken into account. More specifically, this input saturation nonlinearity is assumed to be unknown in advance and as disturbance. By using the characteristics of neural network (NN), the NN-based compensator is developed to compensate the effect of this saturation nonlinearity. Under this, a novel adaptive sliding mode controller is designed to reject the disturbance and deal with uncertainty due to the thruster misalignment and the center drift, in which the requirement of knowing the system parameters in advance is eliminated by using an adaptive updating technique. Systematic design procedure is also developed for synthesis of the NN adaptive sliding mode attitude control strategy. Simulation results show the theoretical and practical merit of the designed approach.

Abstract:The shape characteristics of gas screen in water are thoroughly studied by adopting the multiphase VOF model and the standard k-ε turbulence model. The shape, length and location of pinch-off of the gas screen have been calculated by numerical method, and the results are well consistent with the experimental results, which prove the accuracy and reliability of the numerical method. The length and pinch-off position of the gas screen gradually increase as the Mach number is increased in the process of the vertical launching technology of the gas screen when Ma<1.1. However, when Ma<1.1, the length of pinch-off position from 21 to 22 does not vary, and the shape contour of the gas screen increases as the Mach number is increased.

Abstract:In order to reveal the influence of gravity effect and tunnel blocking effect on the minimum ventilation cavitation number. In this paper, based on the two-fluid multiphase flow and SST (Shear Stress Transport) turbulence models considering gas-water interaction, the three-dimensional ventilated cavity simulation model is established. The relations between minimum ventilation cavitation number and its influencing factors are analyzed respectively in unbounded flow field and water tunnel. The simulations show that minimum cavitation number decreases with the increase of Froude number in unbounded flow field in the form of a power function.In water tunnel the minimum cavitation number increases with the blockage ratio at the same Froude number. The change range of minimum cavitation number decreases with the increase of the blockage ratio at the same Froude number range.

Abstract:To satisfy the high requirement of temperature uniformity of concentric V-grooved surface blackbody, an optimum design method based on finite element method and with axial, radial temperature uniformity and effective emissivity as constraints is proposed. Firstly, the kinds, causes and variations of temperature nonuniformity are analyzed; Secondly, the interactional relationship between temperature nonuniformity and effective emissivity is researched; Thirdly, the optimum design parameters of concentric V-grooved surface blackbody are determined based on complex constraints, and the surface blackbody is developed based on optimum parameters; Finally, the temperature uniformity of surface blackbody is tested and evaluated. The results demonstrate that the temperature uniformity can reach 0.1 K in the range from 250 K to 350 K. The structural parameters reasonable design of radiation surface and soaking disk is the key factor of ensuring temperature uniformity.

Abstract:According to the problem of sparse matrix with high complexity of LDGM codes, a low-complexity construction algorithm of LDGM codes is proposed, which can decrease the encoding complexity while keeping a good performance. Meanwhile, a serially-concatenated construction with a modified SCLDGM decoding algorithm is introduced to solve the problem of high error floor of LDGM codes. This algorithm considers the incorrect output of the inner decoder as the erasures from a BEC channel. The outer decoder uses the priori probability to initialize in the decoding process, which further reduces the residual errors. By simulations for the SCLDGM encoding and decoding system, the near-optimal combination of inner and outer coding rates and the near-optimal column weights of inner and outer codes are obtained. Simulation results show that, a good BER performance can be obtained and the error floor of LDGM codes can be decreased as well by using the proposed algorithms on the premise of keeping a low complexity.

Abstract:To improve the system fairness of Spectrum Allocation on cognitive radio system, this paper presents a spectrum allocation algorithm of combining two standards on cognitive radio system. Firstly, some subgraphs allocate spectrum by using the Collaborative Max Sum Bandwidth (CMSB) standard, after finishing spectrum allocation, then other subgraphs adopt Collaborative Max Proportional Fair (CMPF) standards. Compared with the previous improved parallel algorithm, the simulation shows that the system fairness has been improved obviously, at the same time, the channel capacities of bottleneck cognitive users have been improved greatly.

Abstract:A TEM horn antenna applied to ultra-wideband radar for human being detection is designed. The proposed TEM horn antenna is simulated by CST MICROWAVE STUDIO software. And the influences of antenna structural parameters on antenna pass band are discussed and analyzed. Finally, the prototype of the proposed antenna is manufactured and measured in the microwave anechoic chamber. The simulation and experimental results show that the working frequency of the proposed antenna is from 0.71 GHz to 3.25 GHz with reflection coefficient less than -10 dB (bandwidth ratio 4.6∶1). The antenna front-to-back ratio is greater than 14.0 dB at 2.4 GHz, and the antenna gain is greater than 9.0 dBi within the pass band. So the proposed antenna has characteristics of ultra-band, high gain, and strong directional radiation.

Abstract:To improve AP’s capability of communication services, this paper addresses the problem of efficiently downloading content when vehicles go through the limited coverage range of roadside access point(AP) in drive-thru internet. How to allocate channel resource and effectively utilize vehicle-to-vehicle communication is focused on to improve AP’s capability of service. An optimization selection problem of k forwarding nodes to maximize the number of completed file download jobs is formalized, and that it is NP-Hard is proved. Based on this, allocation of resource (APL) scheme based on the prediction of link durations of the different pair users, and the APL approximate algorithm based on greedy are proposed. Extensive simulation results show that the APL consistently outperforms competitive allocation schemes under varying workloads.

Abstract:To resolve the low-coverage problem of the statistic machine translation training corpus, a dependency parsing and sentence realization based paraphrasing method is proposed. The input sentence is first parsed into a dependency tree, and then the tree is realized into multiple natural language sentences. Although the generated sentences have the same lexical words, the expressions of word orders are re-arranged. The experiments shows that the paraphrasing method can be used to enlarge the bilingual corpus for statistic machine translation and the method efficiently relieves the low-coverage problem of training corpora without any extra resources, finally the translation quality is improved. 

Abstract:The traditional aeroengine residual life prediction method assumes that all aeroengines have the same performance deterioration pattern in a fleet, which leads to a low prediction accuracy. On the basis that the aeroengine exhaust gas temperature margin (EGTM) is analyzed, the aeroengine residual life prediction method based on performance deterioration pattern is proposed. The gross error removal of aeroengine EGTM time series data is studied. The distance measure of aeroengine EGTM time series data is defined, and performance deterioration pattern mining steps are given. Finally, the CFM56-5B aeroengine EGTM time series data is adopted to verify the proposed method. The results show that the average absolute relative error of the proposed method is reduced by 2.5％ compared to the method of average EGTM deterioration pattern in a fleet. Thus, the aeroengine residual life prediction method based on performance deterioration pattern can supply reliable support for predicting aeroengine removal deadline and making maintenance plan.

Abstract:To reduce the time of torque gap during gear shift and realize the quick gear shift for hybrid electric urban bus, based on the mass-spring-damping model, the kinematics models of parallel hybrid transmission system are established. To damp driveline oscillation when picking gear neutral, a controller is designed by LQG/LTR theory. And to minimize engine torque pulsation and satisfy the uncertainty of clutch states in variety of hybrid operate mode, an electric machine torque regulator is also designed based on MPC realizing quick synchronization. The above hybrid AMT gear shift control strategies are verified by simulation and road test, and the results show that the gear shift time is limited to 1 second and the jerk is also kept within a reasonable range. The comfort of urban bus is enhanced and the industrialization process of hybrid electric urban bus AMT system is promoted by applying the above gear shift control strategy.

Abstract:The mistuned stiffness model of bolted rotor with curvic couplings was established, and the effect of bolt preload mistuning on dynamic characteristics of the rotor was studied. At last, the dynamic response of the rotor was applied to finite element model as displacement boundary conditions to analyze the dynamic stress distribution under the condition of dynamic bending, and the influence of bolt mistuning on stress distribution of curvic couplings was obtained. The results show that the stiffness anisotropy of the rotor can be reduced when positive mistuning bolt lies on the major axis of the running orbit, or negative mistuning bolt lies on the minor axis. The stress variation of each tooth can be reduced if negative mistuning bolt is on the compression side, and it will be further increased if negative mistuning bolt is on the tensile side when dynamic bending happens, whereas the stress change tendency of curvic teeth is opposite under the positive mistuning condition.

Abstract:By software FLUENT, the influence of different double-outlet mode of wind on the electric vehicle power cabin natural wind cooling performance with different environmental temperature and charge ＆ discharge rate is researched, and the results show that the heat dissipation performance of electric vehicle power cabin natural wind cooling is improved as the vehicle speed is increased, the heat dissipation performance of up-outlet mode of wind with two hole is better than both sides outlet mode in all fields of different environmental temperature and charge ＆ discharge rate.

Abstract:To study the effect of the dynamic characteristic of brake valve on full hydraulic braking system, the working principle of the tandem dual-circuit hydraulic brake valve was introduced, the mathematic model was established and the corresponding simulation model was set up based on software AMESim. The proportional property of brake pressure, the step response characteristic and the safety of dual-circuit compared to single-circuit were simulated, and then the corresponding experiment was designed to verify the simulation. The results show that the simulation model of the brake valve is accurate and the performance of the brake valve meets the request of full hydraulic braking system exactly. The optimized hydraulic brake valve controlling spring stiffness can be better adapted to the condition that the mass of load is of great difference between no-loaded and fully-loaded status.

Abstract:A method of face gear machined by long radius disk (profile of involute) tool (hob or grinding wheel) without feed motion was proposed aiming at improvement of processing efficiency of face gear machined by such tools. By coordinate transformation the derivation of equations of working flank and fillet surfaces of tooth was based on the design of disk tool and theory analysis of applying the disk tool without feed motion in the face gear machining. To reduce the errors of working flank and even avoid flank interference caused by such method of face gear manufacturing, another motion which rotated in a small angle rang was added into the process of face gear machining. Tooth contact analysis (TCA) was applied to demonstrate the meshing performance of the face gear cut by such method. Numerical examples illustrate that disk tool of long radius with additional motion is able to manufacture face gear with high-precision working flank (the max error of working flank is 19 μm), and the meshing performance of such face gear drive demonstrated by TCA is not second to that face gear drive wit theoretic working flank.

Abstract:To improve the flight stability of quadrotor unmanned air vehicle(UAV) in different environment, a stability augmentation controller using hybrid control methods is designed. This hybrid controller contains several PID controllers, and it can choose the applicable controller according to the flight altitude and pitch/roll angle, which reduces probabilities of air crash and other potential risks. At the same time a simulation model is built with Matlab/Simulink toolbox which can simulate switching processes of quadrotor UAV in different situations contained take-off, landing, calm weather, windiness and out of control. The simulation results show that the hybrid controller is able to robustly stabilize the quadrotor UAV in different environments.

Abstract:In this paper the particle-grid hybrid numerical method is used to investigate the onset of droplet entrainment in annular flow. The flow field is solved on the grid and the motion of fluid film and droplet is solved by particles. Under large density ratio between gas and liquid the critical velocities of droplet entrainment for different flow directions, viscosities and fluid film thicknesses were obtained. The results are in good agreement with classical correlation. This method provides valuable references and guidelines for further study of the two-phase flow in nuclear reactor accident.

Abstract:To improve the trajectory optimization with Chebyshev local collocation method, we study the convergence and stability of Chebyshev local collocation method and provide a theoretical basis for its application. In this paper, the examples of Hyper-sensitive and Minimum-energy problem verify the feasibility and effectiveness of Chebyshev local collocation method which not only is convergent and stable for Hyper-sensitive problem, but also can achieve higher accuracy and faster computation speed in some degree compared with traditional interpolation method and even classic Chebyshev pseudospectral method.

Abstract:The method of calculating the flame front speed of the explosion in the pipe is researched by theoretical analysis and experiments. The model of calculating turbulent burning velocity and expansile velocity by pressure is deduced after the simplification of flame front speed to be the result of turbulent burning velocity and expansile velocity, and the method of calculating flame front speed is advanced by pressure, laminar burning velocity, turbulent burning velocity and expansile velocity. The calculating analysis and explosion experiments of the premixed mixture under the condition of the lean fuel (equivalence ratio equal to 0.967) and rich fuel (equivalence ratio equal to 1.21 and 1.45) indict that the pressure is linear with the accretion of length to diameter ratio on the longitudinal direction, and the laminar burning velocity is linear with the pressure variation, and the change rate of laminar burning velocity is larger when the equivalence ratio approaches the stoichiometric one while the laminar burning velocity is the largest at the equivalence ratio of 1.21. The effect of pressure variation and laminar burning velocity increasing on turbulent burning velocity is not apparent, but is apparent on the expansile velocity, so the pressure and laminar burning velocity is the decisive factor in expansile velocity but not in turbulent burning velocity.

Abstract:To study the temperature changing process inside roadway after coalmine explosion, this paper built a simplified mathematical physical model of roadway after coalmine explosion, analyzed the effect of convection coefficient and density on the basis of thermodynamic equation, and got the curve of air temperature changing. To avoid generating excessive error because of simplifying the convection heat transfer model, the unsteady gas-solid coupling heat transfer was analyzed with Fluent to obtain the process information of temperature changing in roadway. The two curves match each other highly. The results show that the period of high temperature inside roadway after explosion won’t last long, which provides reference for the parameter design of mine refuge chamber and rescue capsule.

Abstract:The essence of this paper is to report the computational research in a S-shaped inlet performance at different angle of attack with and without vortex generators. First, several vortex generators were set near the entry of diffuser to effectively reduce flow distortion produced in the S-shaped inlet. Several parameters, i.e. the ratio of generator blade height to local boundary layer thickness, the locating position, and the angle against centerline have been given. Second, the performance of the S-shaped inlet with and without vortex generators at different angle of attack was developed by using a computational fluid dynamics (CFD) procedure. The results show that in the ±10°angle of attack range, by using a properly designed vortex generator the total pressure circumferential distortion can be greatly reduced about 0.1 and the flow quality can be improved, but the total pressure recovery couldn't be raised. At high angle of attack, because of flow separations, the effect of the vortex generator was reduced. These results should provide valuable guidance in designing vortex generator installations in the S-shaped inlet. 

Abstract:During the powered descent phase of manned lunar lander, offset of center of mass and attitude disturbance brought by the offset are outstanding,so the combined Reaction Control System (RCS) and Thrust Vector Control (TVC) attitude control method is proposed. Based on the lunar lander's attitude kinematic and dynamic models, adaptive attitude controller and estimator of center of mass offset are developed. Stability of closed-loop attitude control system is proved via Lyapunov method, while error characteristic of RCS and TVC is imported to verify the controller's robustness. Numerical simulation results show that the proposed adaptive attitude control method is feasible, and the designed attitude controller can guarantee the attitude control system stable and possess robustness.

Abstract:To test the position and orientation’s certainty performance and movement control performance, this paper designed a Lunar Rover tracking measurement scheme based on the indoor GPS measurement system. Firstly, it introduced the structure and the measurement fundamental of the indoor GPS, then based on the Rover’s ground verifying test, the test site coordinate system establishment scheme, the Lunar Rover coordinate establishment scheme and tracking measurement scheme were designed, finally, the precision of the test measurement system was analyzed and some conclusions were obtained.