Abstract:The problem of attitude regulation control of an underactuated spacecraft is resolved by using sliding mode method. The three-axis underactuated spacecraft attitude dynamics and kinematics models are introduced. A sliding mode controller using generalized inverse and second order approaching law is designed for underactuated axis stabilization control, and the realisability of the controller is analyzed. A perturbed null-projection is constructed to guarantee the feasibility of the controller. On the basis of stabilization of the underactuated axis, a sliding mode controller is designed for another two axes as well. The proof of bounded stability is given in Lyapunov's sense. Simulation results demonstrate the availability of the proposed control algorithm. 

Abstract:The robust fault-tolerant control problem of time-delay uncertain system is studied to improve the performance of fault systems. For this class of linear uncertain time-delay systems model with actuator and sensor recoverable faults, a H∞ output-feedback controller solved by a linear matrix inequality (LMI) is designed to make sure the system can work steadily using the other elements and satisfy the system index. The simulation of an attitude control closed-loop system of satellite validates that it is effective.

Abstract:According to the application of the 2^nd generation lifting reentry vehicle, a further research and analysis was performed for the TAEM. Based on the space shuttle's trajectory and guidance of TAEM, several parameters of TAEM trajectory are analyzed, and the ground trajectory and altitude profiles of TAEM are designed by optimization. Also, the longitudinal and lateral guidance laws are given in order to make simulation verification for the reference trajectory. Simulation results satisfy all of the trajectory constraints, and the guidance algorithm has been proved effective and accurate. The guidance method validates that the guidance is feasibility and validity for TAEM of the 2nd generation lifting reentry vehicle.

Abstract:Rod and beam with fuzzy structures is modeled using sprung mass system to analyze vibro-acoustic responses of complex structures. Energy density is used as response method to simulate the structural vibration, and the simulation indicates that the fuzzy structures affect the master structure maximally around the natural frequency of the fuzzy structures. The effect acts as a frequency dependent equivalent mass. The equivalent mass is positive under the natural frequency of the fuzzy structure and negative over the frequency. The positive equivalent mass decreases, while the negative one increases the vibration energy density responses.

Abstract:A numerical prediction on wear life formation is carried out in involute spur gear. The sliding velocity and contact pressures are computed along the contact zones at each rotational gear position, then the Continuous wear process are discretized by introducing wear step. A quasi-static model instead of the nonlinear wear model in the wear step is used to simulate the gear wear problem based on a generalized Achard wear equation which takes full account of the load and speed combined effects. A gear wear life prediction model is established, and then the procedures are developed which can predict the wear life of different gears or under different operating conditions.

Abstract:The problem of distributed coordinated attitude control for multiple rigid bodies is addressed in this paper. Based on graph theory and sliding mode control theory, a sliding mode coordinated attitude control law aiming at the attitude tracking control system described by the Modified Rodrigues Parameters is proposed. First the sliding surface is designed by introducing graph Laplacian matrix and using Lyapunov stability analysis method. Then the sliding mode attitude control algorithms for multiple rigid bodies with external disturbances are designed, and the robustness of the control algorithm is studied in the presence of uncertainty inertia. Finally, numerical simulations of the algorithms are given. The results show that the sliding mode coordinated attitude control algorithm for multiple rigid bodies is feasible and effective.

Abstract:In the sight of the higher requirement about operation speed and control accuracy in satellite attitude control system, this paper analyzed the feasibility of PD attitude controller by using FPGA, and proposed a method using the input enable and the output control symbol to dominate the internal calculation module to figure out the problem of data synchronization. The paper used hardware description language to achieve the function of each module, and finally instantiated the IP core of PD controller. The result shows that the design is able to accomplish the calculation of attitude control torque by only using 34 clock pulses and the accuracy of control can reach 10-5 magnitude. The speed and accuracy meet the needs of the modern small satellite control system and lay the foundation for using FPGA implementation in small satellite attitude control system.

Abstract:To obtain the behaviors of Poly(vinylidene difluoride) (PVDF) under large tensile deformations, this paper investigates the tensile behavior of a single molecular chain of rod-like PVDF with β phase structure at zero temperature using a Density Functional Theory (DFT) calculation. We obtain the critical bond length, critical fracture energy, critical tensile force and the elastic constant when the β phase PVDF chain is stretched to break. Then a novel method is proposed to build the cell model of the amorphous polymer, which is used for the molecular dynamics (MD) simulations of uniaxial tensile of PVDF. During the simulations, two cases that the chains will never break and are permitted to break are considered. In the first case, the simulations with three different strain rates 10¹⁰ s-1, 10⁹ s-1, and 10⁸ s-1 were carried out and the strain rate dependence of the stress-strain relationship, the structure deformation were analyzed as well. In the second case, the simulations with a strain rate of 10⁹ s-1, 5×10⁸ s-1 and a quasistatic strain loading were performed and the stress-strain relationship, the cell structures before and after the breaking were researched. Some key factors to influence the simulation results and some important deformation information were analyzed. This is helpful to elucidate the inherent deformation mechanisms during the tensile procedure.

Abstract:To solve the problem of thermal error of heavy-duty CNC machine tools, a thermal error separating and modeling approach based on linear regression theory is proposed. Firstly, the thermal errors are separated from geometric error to get thermal error parameters. Secondly, based on temperature sensors optimizing distribution strategies, like main factor strategy and irrelevance strategy, the key points of thermal errors are selected. Finally, a multiple linear regression model is constructed for thermal errors, and an experiment is carried out on a TK6920 heavy-duty CNC floor-type boring and milling machine tool, and the results indicate that the thermal error of column is reduced from 0.45 mm and 0.25 mm to 0.13 mm and 0.09 mm in X and W directions, that is 71％ and 64％ of thermal error can be compensated with this model. Error compensation technology can reduce the thermal error of heavy-duty CNC machine tools, therefore the manufacturing precision can be improved.

Abstract:To meet the need on machining SiCp/Al surface with high efficiency and accuracy, with electroplated diamond grinding wheel and taking mill-grinding narrow slot as a typical example, the influence of machining parameters and mill-grinding tool on SiCp/Al machined surface roughness was experimentally investigated. The results show that the machining parameters and mill-grinding tool both have significant influence on the surface roughness. The influence of grinding speed on roughness appears saddle-shaped, i.e. decreased first, then increase while the roughness is increased as federate increasing. The grinding wheel without flutes can produce lower roughness than that with flutes. Therefore, higher grinding speed, lower federate with fluteless grinding wheel are recommended. Under the given experimental conditions, the optimum combination of machining parameters are grinding speed of 9.42 m/s and federate of 20 mm/min. And if a fluted grinding wheel will be applied to machine narrow slot, the recommended helix angle of the flutes is about 50° to achieve lower roughness.

Abstract:To investigate the impact of magnetic heads on disk in a hard disk drive, an elastic-plastic contact model for rough sphere contacting rigid flat in slip contact condition is provided. The normal load and the real contact area as functions of separation and plasticity index for the rough spherical elastic-plastic contact are investigated by mathematical modeling and MATLAB simulating. The results are compared with the perfect smooth spherical contact model, CEB (Chang-Etsion-Bogy) model and CKE (Cohen-Kligerman-Etsion) model in stick contact condition for different values of the plasticity index. It is shown that the normal load and real contact area of present model are more accurate than that of the CEB and CKE models. This is because the CEB and CKE models neglect the elastic-plastic contact and fully plastic of a single asperity, respectively, resulting in the limitation for the analysis.

Abstract:The governing differential equations of motion for flexible aerofoil, which is coupled with plunge, pitch, and camber bending motions, were derived by using the Hamilton’s principle. The nonlinear aerodynamic forces of oscillating thin aerofoil were given with consideration of camber bending. The two-dimensional aeroelastic model of flexible aerofoil was presented and the flutter characteristics of flexible thin aerofoil were investigated. Numerical results show that the single camber bending motion is instability. When the characteristic frequencies of pitch and plunge modes are given, the flutter velocity is powerfully affected by the characteristic frequency of camber bending mode. When the characteristic frequency of camber bending mode is less than one of pitch mode, the flutter is dominated by the camber bending mode and the flutter velocity is much lower than one given by the classical pitch-plunge coupled model. When the ratio of characteristic frequencies of camber bending and plunge modes is 2.5, the flutter is dominated by the camber bending and plunge modes. When the ratio is greater than 2.5, it is dominated by the plunge mode. When the ratio is greater than 6.0, the pitch-plunge-camber bending coupled aeroelastic model is agreed with the pitch-plunge model.

Abstract:Based on ray trace method, Monte-Carlo method and Simplifie-Equation iterative method, the spectral transimttance radio calculation model for semitransparent liquid was developed and two inversion methods of optical constants (extinction coefficient k and refractive index n) of semitransparent liquid were analyzed. The application range of two inversion methods were investigated. The optical constants of Heptane attained in the references were selected as the true values, and the spectral transimttance radio of the semitransparent liquid based on the direct model simulation were regarded as the experimental values. The optical constants of Heptane were achieved by the inverse models. Then the influence of measurement error on the inverse results were also investigated. The results show that the standard deviation of k calculation error by the MC and SEI inversion methods are less than 10-6, while that of n are higher than 0.1％, and the influence of measurement error on the inverse results is urgent distinctness, and inversed calculation precision of optical constants becomes lower when the measurement error are higher.

Abstract:Sample selection can speed up the training of Fuzzy Support Vector Machine(SVM). However, it is difficult to select effective sample and the selection ratio is very high. This paper proposes a new sample selection method for Fuzzy SVM based on shadowed sets. We divide the fuzzy sets into three subsets, i.e. trustable data sets, trustless data sets and uncertain data sets. The samples are only selected in trustable data sets and uncertain data sets by using the subspace selection algorithm and the border vector extraction method respectively. Experimental results show that the training time and selection ratio is significantly reduced without any decrease in generalization ability by using the samples chosen by the proposed method. Furthermore, it improves the prediction performance of the classifiers when the data sets contain noises.

Abstract:Compared with state diagram, activity diagram can be used to display the concurrent behavior of program in a more natural and intuitive way. Six primitives of initial, fork, join, flow final, activity final and activity were selected as the basis for graphical modeling and automatic code generation. A XML document format was defined to describe the activity diagram, then the XML document was parsed based on DOM, after that original activity diagram was split into separate activity sub-diagrams; and then each activity diagram was parsed into a number of processes and semaphores and codes. The methods and algorithms proposed were tested by designing and implementing a software system and good results were achieved, it showed that the methods and algorithms were right and effective.

Abstract:To improve control accuracy for the Giant Magnetostrictive Actuator (GMA), the fuzzy PID control method is proposed by the PID control method based on Preisach model. The dSpace real-time simulation system is used to build the real-time control experimental platform of GMA. The designed GMA tests for the PID control method based on the Preisach model and the fuzzy PID control method in the square-wave signal and mixed-signal tracking were carried out. The effect of real-time control of two control methods was compared and analyzed, and the results show that the fuzzy PID control method is better than PID control method.

Abstract:Because the general Markov Chain Monte Carlo(MCMC) method is easily to get trapped in some fixed state especially in the case of high SNR condition or iteration process that leads to performance degradation, in this paper, an improved MCMC algorithm is presented. Determining the initial sample value based on MMSE principle, the Markov chain is convergent rapidly. Simulation results show that the mentioned algorithm can improve the BER performance and reduce computational complexity.

Abstract:Based on in-depth analysis of the modulated signal spectrum, the waveform optimization of the continuous phase carrier modulation is developed including two methods of approximate reconstruction and analytic construction in order to get more compact power distribution without useful information loss. The modulated waveforms having very high spectral efficiency by both of the methods are more conducive to the signal acquisition and tracking using the phase-locked loop structure for future GNSS.

Abstract:To obtain high-performance simulation supporting environment that can satisfy the need of argument simulation and with super real-time operation ability, according to the characteristic of high-performance distributed simulation, a software architecture and components of integrated environment is researched for developing and running high-performance distributed simulation based on high level architecture (HLA). It Mainly includes the integrated development environment and running-monitoring management environment, and provides an integrated environment for the development, test, integration, initialization, execution, monitoring, and management of high-performance distributed simulation. The function design and key technologies of each component, especially HPC-RTI, are described in detail. A certain equipment system simulation experiment was carried out, and the experimental results show that the efficiency of large-scale simulation system is improved by 17.8 times.

Abstract:To reduce the influence of deflection and time lag of control force during the dispersion of tether on trajectory control precision, this paper designed stratospheric satellite control system. According to the system composition this paper established the trajectory control system and the longitude motion model of balloon system; Based on sliding mode variable structure control, according to deflection between the actual instruct position and instruct position in north-south direction, the methods of exponent reaching law and the flutter reduction around boundary layers are used to design the control system of trajectory controller. The simulation results have shown that the control system can overcome the disturbance and time lag caused by tether effectively, and complete the stratosphere satellite east and west direction motion control with the error of 80 m.

Abstract:By means of microstructure observation and enduring properties measurement, an investigation has been made to study the influence of the molten salt cooling temperatures on microstructure and stress rupture properties of FGH95 Ni-based superalloy. The results show that, when the alloy solution treated at 1 150 ℃ is quenched in molten salt at 650 ℃ and aged, the fine γ′ phase dispersedly precipitates in the grain, and less carbide phase distributes in the alloy. With the molten salt temperature decreases, the size of fine γ′ phase decreases gradually, but the amount of the carbides increases. When the molten salt temperature is 520 ℃ the size of fine γ′ phase decreases gradually, but the amount of the carbides increases. When the molten salt temperature is 520 ℃, the size of fine phase in the alloy decreases further, and there are more carbide particles which discontinuously precipitate in the grain and along the grain boundaries. The carbide particles are dispersedly precipitated in the grain, which improves the grain strength and makes the alloy possess longer enduring life under the experimental condition. 

Abstract:To overcome the drawback of small displacement, large pressure fluctuation and unbalanced radial force of a rotary positive displacement pump, the rotating-guide-bar and gear mechanisms assembled driving systems of differential velocity vane pump with the cranks and the guide-bars as active parts are presented in this paper. With variation of the motion characteristic coefficient on the rotating-guide-bar and gear mechanisms assembled driving systems, their motion characteristics and laws are investigated. The basic parameter equations are established and the kinematics characteristics and mechanics performance are analyzed for these two types of driving systems. The results show that the transmission performance of rotating-guide-bar and gear mechanisms assembled driving system with the guide-bars as active parts is superior to that with cranks as active parts.

Abstract:An ATP-EMTP simulation model is proposed for calculating lightning transient effects on transmission lines. Both frequency dependent of transmission line and impulse corona effect are considered in this model. The frequency dependent characteristic is analyzed by Marti line model and a user defined corona model is applied to simulate the effect of impulse corona. The expression of geometric capacitance is derived by means of image theory and the dynamic capacitance for line with corona is computed on this base. The simulation results show that the effect of corona plays a more important role than that of frequency dependent characteristic on lightning overvoltage, while it accords more with the facts to take both the effect of frequency dependent characteristic and that of impulse corona. The model presented in this paper can calculate the possible overvoltages on transmission line to provide reliable guidelines for insulating and lightning protection design of transmission line. 

Abstract:To improve the detection precision of the urban rail vehicle wheel key parameters, a new non-contact dynamic detection method based on opening up a “detect window” at the wheel/rail contact point is put forward. The image geometric mapping model of the wheel tread and the coordinate system for detection are established, and the calculation method of wheel key parameters is established on the basis of coordinate translation methods. According to the actual application regulations of urban rail vehicle wheels, the key parameters of optical section detecting window are selected. The wheel key parameters checking experiments are carried out by use of the developed test bed. The results show that the wheel key parameter error values obtained by the method are all less than 1％. By opening up the “detect window” at the wheel/rail contact point, the light source position and the camera position can remain unchanged, so the parameters detecting precision can be guaranteed effectively.

Abstract:To realize the lossless recovery of non-stationary signal in complicated noise environment, a novel design method based on fractional Fourier transform of time-frequency filter is proposed, in which the time-frequency distribution of incident signal is obtained by Gabor transform first, and then based on support vector machine (SVM) and technique of image segmentation, the regions of signal and noise on the time-frequency plane are separated and the optimal separating line is drawn, finally the order number and transfer function of the time-frequency filter can be determined by the optimal separating line equation. For the case of linearly inseparable signal and noise time-frequency distribution, the piecewise linear fitting based on global least square criterion is performed to the separating curved line, and the parallel filter banks are constructed from the linear fitting equation. To meet the real-time requirement in engineering application, the computational complexity was optimized, and the simulation results demonstrated the validity of this method.

Abstract:Because the FPGA factories presently do not offer the special testing function in their EDA tools, this paper addresses the design of a navigated mapping method used for FPGA testing. The navigated mapping tool totally controls the basic elements and exactly controls the usage of FPGA logic resource, tests some targetable logic of the FPGA and increases the coverage of each test vector effectively, implements the FPGA software defect-tolerance function. The result is well proven in test converage through 128 test cases.