Abstract:For solar sail spacecraft with control vanes,solar sail attitude dynamics equations considering elastic vibration and vibration equations were deduced.The solutions of solar sail spacecraft dynamics equations were achieved by utilizing the concepts of unconstraint modes.The PD controller with Bang-Bang control strategies was designed considering the problems of yaw axis earth-pointing of solar sail on super-synchronous transfer orbit.Numerical simulation shows that the designed controller based on control vanes is capable of controlling the yaw axis earth-pointing fast and accurately.

Abstract:An enhanced adjoint method for solving two point boundary value problems is proposed and applied to trajectory optimization problems for a rocket based high speed suborbital launch vehicle,and smooth control serials are obtained indirectly.The first order Taylor Expansion is used to the nominal trajectory which is calculated by the enhanced adjoint method.High robust,high accurate tracking result is obtained under disturbance boundary constrains by receding horizon control technology which is featuring prediction ability.The simulation results demonstrate the capacity and reliability of this proposed method.

Abstract:The static output feedback control problem is studied for a class of discrete-time switched linear systems with polytopic uncertainties subject to actuator saturations.Based on a parameter-dependent discontinuous switched Lyapunov function and some basic lemmas,a switched robust H-infinity static output-feedback controller is designed to guarantee the locally exponential stability of the resulting closed-loop system under average dwell-time switching scheme by using a convex optimization problem subject to linear matrix inequalities(LMI) constraints.Finally,a numerical example is given to illustrate the effectiveness of the proposed design approach.

Abstract:To study the characteristics of impact loads on the tails of supercavitating projectiles undergoing tail-slaps,a simple model for fluid region based on the Logvinovich’s Principle was presented,and the FSI method was employed.The effects of initial disturbance angular velocity,mass of projectiles,position of centroid and rigidity of projectiles on the impact loads of tail-slaps were investigated by simulations.The results showed that the greater the projectile’s mass and initial angular velocity and the smaller the elastic modulus,the greater the impact loads.The impact times increase with the increasing of initial angular velocity,however the impact times decrease,while the impact durations increase,with the mass increase and the center of mass moving back.As result,tail-slap forces which could destroy the structure and the moving stability of the projectiles can be lessened by smaller initial angular velocity,lower density,and larger elastic modulus of the bodies.

Abstract:Based on RANS equations,the wall effect and scale effect of ventilated supercavity has been simulated using inhomogeneous model and SST turbulence model with consideration of gas-water interaction and gravity effect.The influence of different turbulence models to gas ventilation coefficient has been investigated.The developing process of ventilated supercavity under different ventilation rates is shown through numerical simulation,and the cavity shape and resistance differences at different scale and in unbounded flow field are compared.The results show that the cavity length and diameter of the small-scale model are greater than that of the large-scale model.But the extent of the upper cavity drift of the small-scale model is less than that of the large-scale model.The length,diameter and the extent of the upper cavity drift at the unbounded flow field are greater than that of in the wall effect condition.In the drag-reducing,the maximum drag reduction of the small-scale model is greater than that of the large-scale model.The maximum drag reduction of the unbounded flow field is smaller than that of in the wall effect condition.

Abstract:The interaction of atoms in the Si/Ge superlattice is described by using Stillinger-Weber potentials yield intermolecular energy and the heat transport system for Si/Ge superlattice is built up.The dependences of Si/Ge superlattice thermal conductivity on period length,number of periods and temperature are investigated by non-equilibrium molecular dynamics(NEMD) simulation.The results of calculations show that the thermal conductivities increase with an increase in period length and the number of periods.Because of the effects of thermal boundary resistance offered by interfaces,the temperature drop across the interface closest to the hot reservoir is the highest.In addition,the thermal conductivities also increase with the increasing of temperature within the range from 200 K to 600 K.Compared with that of the corresponding SiGe alloy,the thermal conductivities of Si/Ge superlattice are much smaller.

Abstract:This work proposed a method to separate the low-frequency magnetic interference induced by the electrical equipment during geomagnetic navigation process.Firstly,the branches of a circuit are divided into several independent interference source based on electrical analysis,and the attitude of the carrier is regulated to make sure that the total strength measured along each sensor’s axis is the linear superposition of all field components(including geomagnetic field and interferences).Secondly,to compensate the ambiguity drawbacks of Independent Components Analysis(ICA) method,the absolute value of correlation coefficient is proposed to perform map matching.Both theoretical deduction and simulation results have proved the efficiency of the method.

Abstract:System level analysis and design of a single-loop fourth-order sigma-delta(ΣΔ) accelerometer is presented to reduce quantization noise and enhance resolution of the micromachined accelerometer.Stability of the system is analyzed by root locus method based on the linear model established in this work.Theoretical analysis indicates that the forth-order ΣΔ micromachined accelerometer has good performance in noise,dead zone and idle tone.Based on the analysis and discussion of the system level,the transistor level design of the interface circuit is implemented,the circuit is fabricated in 0.5 μm two poly two metal CMOS process,and the tested results indicate that the sensitivity is 1.2 V/g,nonlinearity is 0.2%,open-loop noise density is 12 μg/Hz1/2,closed-loop noise density is 80 ug/Hz1/2 and the power dissipation is 40 mW.

Abstract:To overcome the influence of multi-path fading in single carrier frequency domain equalization,this paper proposed "Equalization and Forward" method.In this method the partner equalizes the receiving signal in frequency domain and forward to destination.In addition,the "Equalization and Forward" and "Decoded and Forward" methods are combined to improve the performance,and the impact on cooperative performance of partners’ channel state information is analyzed.The simulation results show that the cooperative diversity can reduce error probability,and the combining method can provide larger diversity gain than single method.Partners’ channel state information determines the diversity gain,so various parameters should be considered to obtain best performance.

Abstract:Without enough measured data of channel statistics,studies on broadband satellite mobile channel modeling are still in the phase of exploring both at home and abroad.This paper analyzed the reasons of selective fading along broadband satellite mobile channel in time domain and frequency domain,and created a phase variable simulation model of wideband satellite mobile channel according to the multiple-point scattering theory.Verified with the statistics of the measured data from German Aerospace Center(DLR),under three kinds of typical environments,the model is proved to simulate the real transmission environment well.

Abstract:By extending Bueckner’s principle suited for a crack to a hole crack problem in infinite plate in tension,here,the original problem(the hole crack problem in infinite plate in tension) is divided into a homogeneous problem(the one without hole crack) subjected to remote loads and a hole crack problem in an unloaded body with applied tractions on the surfaces of hole and crack. Numerical results illustrate that the approach is very simple and effective for analyzing the hole crack problem in infinite plate in tension and by which a crack emanating from a triangle hole in infinite elastic plate in tension is analyzed in detail.The effect of hole geometry parameters on the stress intensity factors is revealed.It is found that a hole has a shielding and an amplifying effect on the stress intensity factors of crack emanating from the hole,and the shielding and amplifying effects varied with hole geometry parameters.

Abstract:The selection of interval of ISAR ship target includes selection of time position and selection of length of the time window.A definition of image contrast is given and a fast algorithm to select the time position and the length of the time window which bases on image contrast is proposed in this paper.According to the features of ISAR ship imaging,a simplified algorithm to determine optimal time position of top view or side view ship images is presented.Integrated echoes from that time,the optimal coherent time will be obtained by making the image contrast maximum.The effectiveness and practicability of the method are proven by real data processing.

Abstract:To study the reason of low dynamic response characteristics of direct drive volume control electro-hydraulic servo system and to widen the application of the system,mechanical models of motor control,hydraulic power mechanism,hydraulic actuator and other sub-structures of DDVC electro-hydraulic servo system are established.Furthermore a mathematical model of direct drive volume control electro-hydraulic servo actuator is set up,and based on MATLAB software,a relatively comprehensive numerical simulation analysis on main parts of the system is carried out.Simulation results show that the basic reason of low system dynamic characteristics is due to the low dynamic characteristics of pump-control power mechanism.The dynamic characteristics of each component part of the system are summarized so that the measures and strategies to improve the system performance are brought forward.

Abstract:To solve the problem that general optimize algorithms couldn’t effectively calculate the designed variables with complex restrictions,a hydraulic pump/motor displacements and their rotate speed restrictions rule based knowledge-base(RKB) was proposed,and the RKB adaptive simulated annealing genetic algorithm(ASAGA) was introduced to optimize the main components and system parameters of wheel drive hydraulic hybrid vehicle(WDHHV) driving system.The energy saving and propulsion characters of the optimized WDHHV were analyzed by simulation,and simulated experiments of the WDHHV with a start-stop-start working cycle according to the corresponding energy were carried out.All the simulation and simulated experiments results show that the proposed RKB ASAGA is reasonable and effective,and the energy saving and propulsion characters of the optimized WDHHV are all better than that of the traditional vehicle.

Abstract:To investigate the influence of different damper parameters(position,number and size) on the change of attitude angle of satellite during the locking process,based on the model of wing system of satellite,the attitude dynamics of the deployment of solar wing process is simulated by the MSC.ADAMS software.The change of attitude angle of satellite and the wallop between the wings during deployment process are investigated,and the influence of different damper parameters is analyzed.The result demonstrates that the damper imposed between the yoke and panel can effectively reduce the wallop and the change of attitude angle of satellite during the locking process.Finally,a selecting method of damper parameters is put forwards.

Abstract:Programming model has become one of the handicaps in multi-core era.To counter to this bottleneck,a novel multi-core architecture,namely Metric(Method centric),is proposed in this paper,which attempts to bring the concept of procedure in programming model into computer architecture design.Basing on Metric multi-core,a slice partitioning compilation pass which tries to divide procedures into finer grains of similar size,namely slice,is investigated in details.Preliminary experiment results validate its effectiveness,and the algorithm is of great importance to Metric compiler tool chain and simulator setup.

Abstract:In order to layer ventricular tissue accurately,a linear layered fill method is proposed in this paper.This method is based on the high-resolution DT-MRI imaging data of human heart and the linear relationship between the rotation angle of the muscle fibers and ventricular cell types,and it has been used to sort the ventricular cells and reconstruct the 3D structure of ventricular tissue for further simulation of heart electrophysiological activities.The pseudo ECG simulation based on the Ten Tusscher model of single ventricular cell and this 3D ventricular structure is used to test the validity of the layering method.The simulation results show that the pseudo-ECG is similar to the real ECG in morphology,the Q-T interval and QRS-wave direction.Therefore the proposed approach for the layering of ventricular tissue is valid,and can be applied to the researches on the modeling and simulation of cardiac physiology and pathology related issues.

Abstract:A multi-level grayscale-image enhancement method based on fuzzy technique is proposed to improve the contrast between homogeneous areas while saving textures.Nonlinear continuous stepped function based on statistical properties of the image is applied as membership function in fuzzy processing.The nonlinear enhancement is implemented by combining enhancement on each fuzzy sets.Comparing with classical methods,the results show that the image has higher contrast,enhance fine detail of image feature without enhancement,and it is better to representing the medical image processing,

Abstract:Wireless sensor networks are composed of sensor nodes which are limited in computational capabilities,power and memory resources,and they are susceptible to a variety of security threats.Security issues in WSNs have are the research focus in academy and industry.First,the early existing research results in wireless sensor network security was briefly surveyed,and then the security issues in WSNs were classified into five categories: cryptography algorithms and key management,secure routing,secure data aggregation,secure location,and privacy preservation.The mechanisms and characteristics of various techniques of these issues were described,while the focus was put on these new techniques that had been developed in recent three years.Finally on the basis of a comprehensive comparison and analysis of these existing techniques,it is points out that the heterogenous WSNs,inside attack and defensive techniques as well as privacy preservation techniques are the hot topics and future research trends in WSNs.

Abstract:In-network data aggregation is a useful technique for applications that require periodic dissemination of information to a large region.For applications on VANETs,destination node requires different degrees of data accuracy according to the distance from it to source node that generates data.Therefore,data aggregation scheme should adjust the aggregation factor to satisfy the different requirements of data accuracy from different applications.Based on this,we formalize adjustable data aggregation on one node on VANETs problem,and prove that it is NP-Hard,and we also propose an adjustable data aggregation approximate algorithm ESAS based on greedy.Simulation experiments make it clear that ESAS has a sharp decrease on the amount of communication data compared with that based on fuzzy logic aggregation scheme(FBAS).

Abstract:To enhance the property of YG8 hard alloy,two elements of carbon and vanadium were implanted into its surface by using Metal Vapor Vacuum Arc(MEVVA) source with several different doses.The structure of sample surface is characterized and analyzed with metallurgical microscope,X-ray diffraction and Raman spectrum,respectively.The results show that there exist new phases of C,VC,and V7O3 in the sample surface,and that C+V ion implantation actively promotes the formation of DLC structure.Moreover,it can be found that the performances of sample surface(such as microhardness,coefficient of friction and corrosion resistance) are evidently improved.In conclusion,the surface modification of YG8 hard alloy by C+V ion implantation is not only affected by the appearance of new phase,but also related to the implantation mechanism.

Abstract:To study the mechanical stability of the superconducting coupling solenoid magnets in the MICE(Muon Ionization Cooling Experiment) channel,stress analysis by a finite element model has been performed and presented for the whole process of coil winding,cooling down and charging.According to the simulation results,the stress within the coil assembly is relatively high due to high magnetic field and large size of the coupling magnet.The shear stress is the critical factor for the instability of the coil package.In the region of shear stress concentration,crack of epoxy resin in the direction of principal stress and the maximum shear stress will cause a quench or coil training

Abstract:To accurately evaluate the jamming effect on terminal guidance radar under active jamming,according to the working process of terminal guidance radar and the characteristic of counteractive active jamming,the ratio of detecting-target-time and the ratio of tracing-error were adopted as indexes,and the relationship between indexes and influence factors and the evaluation methods were analyzed briefly.The indexes were treated by unitary quantification and weighted summation to get the synthetic results.The simulation results show that the evaluation indexes are scientific and easy to be measured,and the evaluation method is simple and effective.

Abstract:In order to regulate discharging energy of a single pulse availably,a MAO flyback switching power supply made of several current pulse units connected in parallel was proposed.The load characteristics of MAO power supply was analyzed briefly and the equivalent circuit model during energy exchanging between primary winding and secondary winding of coupled inductors was established.Based on the model,the effect of energy exchanging of coupled inductors on current pulse waveform and pulse energy was analyzed,and simulation and experiments were carried out.The results show that the current pulse waveform is mainly affected by parameters and residual voltage of the MAO load,the leakage inductors of primary/secondary winding and the peak current of primary winding,and the pulse energy could be out of control if peak current of primary winding is excessive.

Abstract:To reduce the vibration and noise of double helical gears transmissions,its dynamic behavior was studied.Considered the internal dynamic excitation produced by stiffness excitation,error excitation and mesh impact excitation,a bending-torsional-axial coupling dynamic model of double helical gears was established by the method of concentrated parameter.The dynamic equation of this system was deduced by the Newton method.The effect of excitations and tooth modification on dynamics behavior was discussed,and the corresponding conclusions were obtained.Finally,a test was carried out and the result agrees well with the theory analysis,which validates the correctness of the dynamic model.

Abstract:A repairable system approach of reliability assessment for multi-NC machine tools with time truncation based on stochastic point process is proposed,and a non-homogeneous Poisson process(NHPP) model for failure time is built.The point and confidence interval(CI) estimators of model parameters and reliability indices,such as accumulated mean-time-between-failure(MTBF) and failure intensity at truncated time,are all given by Fisher Information Matrix(FIM) method.The values of Akaike information criterion(AIC) show that repairable system approach has advantage over statistical distribution method when failure times of NC machine tools with minimal repair have monotonic trend in reliability analysis.The proposed model is passed by trend testing,renewal process testing and goodness-fit-test respectively.

Abstract:A control structure consisting of nonlinear feedforward and linear feedback is adopt and the optimal ascent trajectory is generated by the adjoint method.The output feedback control law and output tracking control law are designed,the conditional asymptotically stabilization is proved and optimal ascent tracking is established for the hypersonic flight vehicle.The system is separated by the observables so that the sensors are easier to be chosen.Simulation results demonstrate that the maximum energy climbing could be realized by the proposed method for the hypersonic flight vehicle and the optimal ascent trajectory could be asymptotically tracked.

Abstract:To improve the accuracy of Chinese chunking and utilize the semantic information of words,a new Chinese chunking method is proposed based on conditional random fields and semantic classes.Through the analysis of Chinese chunking task and its sequential characteristics,conditional random fields that could incorporate various types of features were applied to overcome the label bias problem.Semantic features were utilized to improve the chunking performance.Experimental results show that the algorithm achieves impressive accuracy of 92.77% in terms of the F-score.A further experiment indicates the effects of feature template selection and training data′s scales on the aspect of chunking performance.

Abstract:Due to off-normal images,the number of alignment iterations will be increased and the collimation efficiency will be decreased.To overcome this difficulty,by analyzing the characteristics of off-normal images,a Bayesian classifier is designed to achieve image classification,and the distortion images are detected by the shape factor of beam image.Experimental results show that: by setting reasonable class condition and shape determination standard,the off-normal image classification and examination filtration can be effectively realized.As a consequence,the collimation cycle-index and alignment defeat′s probability due to the off-normal images is decreased,i.e.the total alignment efficiency is dramatically increased.In addition,the preliminary reason causing the off-normal images is analyzed,which supports the breakdown fast localization.

Abstract:In this paper,a maneuvering penetration optimization for trajectory of lift reentry vehicle is researched.At first,a model for this problem is proposed and its trajectory optimization theory is studied,and then the multi-constraints and multi-phases trajectory optimization is unified in an optimization algorithm.The direct method and sequential quadratic programming algorithm are used to solve the trajectory optimization problem,and finally the maneuvering penetration optimization trajectory which satisfies corresponding constraint is obtained.The simulation results show that the model proposed in this paper is reasonable and feasible with good results.