Abstract:The development status and tendency of drag-free satellite formation flying are analyzed,and its dynamic modelling and system control are discussed.The application foreground and related key technologies to be solved are addressed,which provide a basis for space environment observation and space weather detection in the future.

Abstract:In this paper,a wavelet based backstepping sliding mode controller for rotational maneuver is proposed for an orbiting three-axis stabilized spacecraft,taking the actuator saturation into account.Wavelet networks,which have superior learning capability in comparison to conventional neural network,are used for approximation of unknown system dynamics.This proposed controller comprises of a wavelet based saturation compensator and a robust backstepping sliding mode controller,and the latter one is designed to achieve the desired performance by attenuating the effect of approximation error caused by wavelet identifier.Lyapunov stability analysis shows that the resulting closed-loop system is globally asymptotically stable.To study the effectiveness of the corresponding control scheme,traditional methods are also developed for the control system.Both analytical and numerical results are presented to show the theoretical and practical merit of this approach.

Abstract:This paper deals with the problem of attitude regulation control of rigid satellite subject to control input constraints.A nonlinear controller based on the saturation function is designed to deal with the control input saturation and angular velocity constraint.Lyapunov theory is employed to prove the global asymptotic stability of the zero equilibrium points of the closed loop system and both attitude and angular velocity will tend to be zero asymptotically.The controller is derived independent of satellite inertia matrix,and the control scheme is model independent.Simulation results demonstrate the feasibility and effectiveness of the control scheme under control input constraints.

Abstract:This paper presents a simple and rapid algorithm for small body surface triangulations and physical properities calculation based on 3-D arbitrary points.In order to avoid destroying the original topology due to the non-convex boundary,the arbitrary points are first mapped on the unit sphere and then mapped on a 2-D plane to complete the triangular mesh generation.Based on this,the volume integral can be transformed into polyhedron vertex computation,and the processes of integral reduction using Green formula can be simplified by decomposing the polyhedron into a series of tetrahedrons.Thus the physical properties such as volume,surface aera,center of mass,moment of inertia,principal axis of intertia,gravitational potential,gravitational field intensity of the small body can be computed.Simulation shows the relationship between points number and the calculation accuracy as well as the correctness of the algorithm.

Abstract:A control design method based on nonsmooth switching surfaces is proposed for a class of second-order systems in order to enhance the flexibility of system design.Firstly,the self-stable region(SSR) with linear Lipschitz boundary surfaces is constructed by utilizing the notion of SSR.Then,the control law is derived and the convergence of the closed-loop system is proved by the contingent cone criteria,which is used to determine the relation between the solution of a differential equation and a nonsmooth surface.The results show that the control design method developped in this paper allows us to construct the SSR in a more general sense,and the flexibility of system design can be improved.Finally,the correctness and effectiveness of the control design method presented are illustrated by a numerical example.

Abstract:In order to analyze the effects of flywheel disturbance on dynamic characteristics of satellite frame structure,the dynamics model of satellite thin plate was established by travelling wave method in this paper,and then the travelling wave dynamics model of satellite frame structure was established by combining travelling wave method and sub-structure technique.The simulation on dynamics characteristic of the satellite frame structure was carried out,and simulation results were compared with FEM results.It is showed that travelling wave method is accurate and effective in calculating the dynamic response of satellite frame structure,and it is more accurate than FEM results at mid to high frequencies.

Abstract:The merit of ducted fan UAV is addressed through the illustration of recent researches on it.The flight mechanism of ducted fan vehicles is probed,then a mathematical model of the vehicle is constructed based on the analysis of aerodynamic characters for all the components of the vehicle.The controller is designed and implemented in the flight testing.The results show that the ducted fan UAV has good character of hovering,and there is little cross-coupling between the roll and pitch channels in hovering and maneuvering at a small pitch angle,which can be ignored.

Abstract:In this paper,the autonomous navigation method based on the earth sensor and the star sensor on passive section during the multi-satellites mission is studied.The orbit prediction is given by the initial state which is determined by least square method.Digital simulations are conducted to analyze the influence of sampling period,measured arc length,accuracy of measurement,reference star positions and installation errors on the position accuracy.It is indicated that the effect of measuring errors is greater than the installation errors.

Abstract:In order to realize the optical characteristics calculation of space targets with complex shape,an optical characteristics calculating method for space targets was presented based on the general idea of surface mesh-creation.The mathematical models of standard geometries for targets,mesh-creation methods,visibility of the target,and the luminance calculation were given.The software calculating optical characteristics of space targets was designed and compiled.For several satellite targets,optical characteristics calculations were conducted with this method,and the results were compared with those of analytic method and experiments.It is showed that the mesh-creation method is better than the analytic method in precision,and the errors are less than one apparent magnitude compared with experimental results,so this method can be applied in practice.

Abstract:To study the change of bifurcation properties of the system with structural parameters,a method to find the main bifurcation parameter of the dynamic system is presented in this paper.After disturbing the eigenvalue of Frechet matrix,the main bifurcation parameter is found.Different algorithms are given for different eigenvalue forms.The bifurcation parameter which has appreciable effect on dynamic characteristics of the system can be effectively identified from multiple parameters.And the unfolding parameters can be identified as well according to the effects of parameters on the system.This method can not only be used in autonomous systems,but also in nonautonomous systems.

Abstract:To reconstruct high-resolution(HR) images from a sequence of low-resolution(LR) compressed images,this paper proposes a novel algorithm focused on super-resolution reconstruction of H.264 compressed video,which is based on the integer DCT transform-domain quantization noise.Firstly,models of compressed video and integer DCT transform-domain quantization noise are surveyed.Then the reconstruction algorithm under the POCS theory is proposed.Experimental results demonstrate that this algorithm has a great improvement in subjective visual quality and low computation complexity,in which PSNR can reach 30 dB and iterations are less than 5 times.

Abstract:To improve the narrow band interference(NBI) rejection performance of the adaptive wavelet packet modulation(WPM) system,an optimal wavelet packet tree(WPT) selection algorithm based on tone interference is proposed in this paper.The proposed algorithm makes use of the bit error rate(BER) and the limited transmitted signal power to construct cost function for WPT nodes,which transforms the optimal tree selection problem into the minimization of Lagrange cost function,and the optimal tree is selected by tree pruning method.Analysis and simulation results show that the proposed algorithm can accurately find the optimal tree in NBI environment and performance of the adaptive WPM system is greatly improved without sending the periodic training data.

Abstract:In order to compute the change of system saturation throughput in cognitive network,a three dimensional Markov chain model was presented to analyze the saturation throughput of cognitive users,with the assumption of finite number of cognitive users and ideal channel conditions.The model was applied to two access mechanisms proposed by IEEE 802.11 to compute the theoretical value of saturation throughput between cognitive users.A multi-channel simulation platform was built by NS2 to compute the actual saturation throughput.Compared with simulation results,the model is extremely accurate in predicting the system throughput and the system throughput increases linearly with the number of cognitive users’ channels.

Abstract:In order to solve the problem of conveying logging tools from the surface into horizontal well,a stroke & retract-type tractor is designed.In virtue of overrunning clutch principle and three types of inchworm unit,continuous movement of the tractor is realized.By adopting hydraulic powered scheme,the tractor automatically unlock with the well wall in the event of power failure.The structural composition and working principle of the tractor are introduced,the walking mechanism is designed,and the schematic diagram of hydraulic system is presented.A virtual prototype of the tractor including hydraulic valve and pipeline is built in Pro/e and ADAMS software.The motion simulation on it is conducted,which proves the feasibility and rationality of the tractor.

Abstract:To solve the problems of the simulation in time domain and the consistent movement between waves and ships,based on frequency-spectrum analysis method,a novel method for calculating the ship oscillation movement is proposed,in which directional spectrum is used instead of using ocean wave spectrum.Mathematic expressions and the relationship between wave spectrum and directional spectrum are introduced and the long-crested wave spectrum and ITTC directional spectrum suitable for ship oscillation movement analysis are selected.The ocean wave is decomposed using Gerstner model,and then the simulation model of ship movement in the waves is built.The relationship between encounter wave surface and ship movement is described by response amplitude operator method.With the linear superposition assumption,the results of ship oscillation movements in frequency domain and time domain are obtained.

Abstract:In order to provide a usable blade model for special machining software of a blade,a parametric blade design software is developed based on the features.According to the characteristic of a turbine blade,the blade is divided into five master features:blade-root,root-surface,blade-coronal,coronal-surface and blade-body,while blade-body is divided into four child features:surface of back arc,circular arc surface of stream coming in,surface of inner arc and circular arc surface of stream coming out.3D model of the turbine blade based on features can be generated automatically by the system with blade parameters input by users.The results of machining simulation show that different cutting speeds and cutting steps can be given for different parts of the blade-body and overcut can be avoided.The paramatic blade model based on features can provide a practical base model for a blade machining software.

Abstract:To help shipborne aircrafts take off with the aid of the power of carrier engine the pulse stepless shafts are used as constant power stepless gearbox instead of the present used decelerator for carrier power.When shipborne aircrafts take off,the shafts transmit power to the drum set,around which the cables tow to accelerate the take off shipborne aircrafts.To improve the performance of pulse stepless shafts,point touches in overrunning clutches are converted into face touches,which can be realized by means of hydrostatic pressure lubricating technology.The take off weight can be increased greatly.Using pulse stepless shafts to replace decelerators can improve the cruise performance as well as the combat capibilit and the take off expenses can be reduced.

Abstract:Fluid pressure in spatial domain was solved by means of finite element method,and the distribution of fluid pressure was analyzed for different gaps in the straight-wall and the flange in hydro-mechanical deep drawing(HDD).Based on the distribution of fluid pressure in the flange,the minimum blank holding force was given in HDD.A method to select the gap and determine the minimum blank holding force was presented.The condition of the uniform pressure below the die corner was discussed.The results indicate that the gap ratio bet ween the straight-wall and the flange determines the distribution of fluid pressure.Larger the gap ratio will result in more homogeneous distribution of fluid pressure in the straight-wall and the die corner.

Abstract:The finite element analysis method was applied to the simulation of quenching process of a cylindrical specimen of 9Cr18Mo steel.The cooling curve of quenching process,the variation curve of residual stress with the time,the distribution of residual stress along the axial dimension and the axial deformation of the specimen were obtained.It is found that the stress state in the specimen during quenching is complicated due to the thermal stress and the structure stress.In the end of the process,the stress state mainly relies on the structure stress.The calculated results of residual stress on the surface and the axial deformation of the specimen agree well with experimental results.

Abstract:In order to exactly reflect the effect of the radiant tube size on the combustion performance,thermal parameters on uncork-cylinder radiant tube gas-fired combustor were measured using different radiant tubes under three kinds of loads,and the relatively suitable matching relationship among the load,the length and the diameter of radiant tube was obtained,thus the optimization design on the combustor structure was achieved.It is found that 219 mm is the appropriate radiant tube diameter in the test load range,950 mm,1000 mm and 1100 mm are the appropriate radiant tube lengths under loads of 50 kW,75 kW and 100 kW.

Abstract:This work suggested a new multi-ACO algorithm by introducing the basic idea in the particle swarm optimization(PSO) into solution information exchange between ant colonies.The new algorithm takes much less cost for exchanging solution information than those existing methods.The new algorithm was used to solve the VRPTW benchmark instances and was compared with one existing algorithm.The results show that the new algorithm out performs the existing methods.Exploiting the idea of individual moving in the swarm intelligence to design the rule of information exchange between ant colonies can improve the performance of multi-ACO algorithm.

Abstract:To solve the fixed direction problemin traditional medical imaging technologies and satisfy the clinical medicine requirement of observing the organ in term of the whole or sections from different viewpoints,a three dimensional visualization method of the cardiac MRI data to display the whole heart volume and the arbitrary-cut sections is proposed.Using VC6.0 and VTK,the ray casting method is adopted to realize the threedimensional visualization of total and partial cardiac MRI data and the virtual sections from arbitrary viewpoint.Simple interactive operations such as scaling,translation and rotation can be realized in real time.The experimental results show that the presented method can assist doctors to observe the organ tissue and sections from different viewpoints,which is valuable in disease prevention,medical diagnosis,surgical planning and postoperative evaluation.

Abstract:Aimed at the problem that the traditional phrase extraction method is strictly dependent on word alignments,and is not pruned to alignment errors,a loose phrase extraction method,which does not strictly depend on word alignments.In this method,constraints are posed on alignment points to avoid ill-formed phrase pairs.Three constraint strategies are proposed based on word similarities:Dice coefficient,Phi-square coefficient and log-likelihood ratio.Experiments were carried out on the corpus of IWSLT 2004.Results show that the BLEU scores of the best results of loose phrase extraction can be improved by 15.14%,compared with the baseline system Pharaoh.

Abstract:To improve the coding efficiency of EZW algorithm,the interval-successive-reduction approximation quantization is adopted to simplify the coding of subordinate pass,and then the improved EZW algorithm of bit successive approximation quantization for subordinate pass is presented by combining the feature of binary-bit of the significant coefficient and the interval-successive-reduction approximation quantization.This improved approach can output the binary-bit of the data in subordinate pass list directly,which discards the fussy constructing for quantizer and simplifies the coding process.Experimental results show that the improved EZW algorithm can reduce the coding time about 20%,which proves its effectiveness.

Abstract:Numerical analysis method of membrane secondary buckling was developed.Arbitrary initial flaw was introduced into membrane by applying outside disturbance,and the phenomenon of membrane secondary buckling was analyzed.It is indicated that in the process of membrane post-buckling,the phenomenon of membrane secondary buckling appears because of initial flaw,wrinkle configuration is instable,and new wrinkles are produced.Post-buckling equilibrium path presents the multistage characteristic.In the case of different initial flaws and loading processes,the phenomenon of continuous secondary buckling emerges in the process of membrane post-buckling.It is concluded that membrane can be stable or not in the course of secondary buckling,which depends on initial flaw and loading process.

Abstract:A new definition of fuzzy entropy of interval-valued fuzzy sets is proposed and applied to the image thresholding segmentation.A fuzzy parameter is determined according the histogram of image.The image is represented by an interval-valued fuzzy set through selecting an appropriate primary membership function.Then a new method of image thresholding segmentation based on fuzzy entropy of interval-valued fuzzy sets is proposed.Numerical examples show the rationality and practicality of the new method in threshloding segementation of images with noises.

Abstract:Aimed at the poor usability and low efficiency of UML modeling for enterprise software and application(ESA),an ESA oriented platform-independent model(ESA-PIM) based on extended UML is proposed to solve the problem.First,an integrated multi-view PIM model based on business objects was constructed by analyzing the characteristics of ESA.Then using the extended mechanism of UML,the new meta-classes,stereotypes and tagged values that describe the concepts and relationships in ESA-PIM were added into UML2.0 meta-model,and they were divided into different viewpoints in the extended UML meta-model.The ESA-PIM proposed in this paper realizes the semantic-based integration between various UML diagrams through the richsemantic business objects,which improves the usability of UML and enhances the modeling efficiency of ESA.The feasibility and effectiveness of ESA-PIM were verified by an application case.

Abstract:To investigate the influence of Songhua River on Harbin and its surrounding areas during summer and winter and present a theoretical support for correct utilization and optimization of the urban river,a ground data collecting approach combined with remote sensing data collecting is used to analyze the remote sensing images of January 25 and June 1 in 2004.This method based on the reach of Songhua River confirms the impact of Songhua River Basin on its adjacent areas according to the distributions of temperature and moisture in summer and winter.The results reveal that in summer the temperature inside the city is abnormally higher than that in the suburb area and there is a tendency of surface temperature increase from water area to both banks,moreover,that in the northern side is more manifest than that in the southern facet.While the suburb humidity value is comparatively low and the distribution of relative humidity is centered as the Songhua River and its adjacent areas,meanwhile,the influenced radius of northern bank is larger.In winter,the temperature inside the city is approximately 4 ℃ higher than that in the suburb area and the distribution of temperature along either side of Songhua River differs a lot.The surface temperature of the frozen river resembles that of southern bank,while it is 2 ℃ higher than that of northern bank.With urban humidity about 1% lower than that in the suburb,it is reasonable that the distribution of humidity of Harbin accords with the dry island effect in winter.This study lays a data base and a technical support for the pointing observation and moving measurement in the future.

Abstract:In order to improve the operation capacity of an underactuated prosthetic hand,the static grasp model and the force based impedance control strategy of the finger were constructed based on the underactuated mechanism.According to the static grasp model,the precise relationship between the actuation torque and the support force from phalanges can be obtained corresponding to any grasp attitude.The force based impedance control strategy realizes the force control of base joint.According to experiments,the finger can stably grasp a slippery,fragile,complicated and comparatively heavy object such as an egg.Its success ratio reaches 80%,which can not be achieved only through the force control of base joint(the success rate was only less than 20%).Therefore,the hand can realize complex operation with the construted static grasp model and the force based impedance control strategy.

Abstract:To effectively evaluate the performance of checkpoint handoff scheme for mobile computing system,a model of process state in the mobile system is presented,and then a performance evaluation model for the checkpoint handoff scheme is proposed,according to the characteristics of mobile computing system.The simulation experiments for three existing logging checkpoint recovery schemes have been implemented by the proposed performance evaluation model.The result shows that the performance evaluation model is consistent with practical cases,which proves its validity.By the proposed model of performance evaluation,the proper checkpoint handoff scheme can be determined for a specific mobile computing environment.

Abstract:Aimed at the problem that the mean shift algorithm sometimes can not compute large volumes of image data,or the data-computing speed may be very slow,by analyzing the principle of the mean-shift image segmentation,this paper presents an image-segmentation idea by processing the data in parallel computing environment,i.e.Data Partition Method with Buffer(DPMB),then we can compute different parts of data separately.By this method,we can avoid the limit of data amounts and memory errors problem of computer,which improves the efficiency of data segmentation.

Abstract:In order to take the rotating effect into consideration and predict the fatigue life of wind turbine system exactly,a fatigue life prediction model based on the rotationally sampled spectrum is proposed in this paper.Firstly,the rotationally sampled spectrum taking the rotating effect into consideration is deduced through the Fourier transformation and compared with the Von Karman spectrum(fixed point spectrum).Based on the rotationally sampled spectrum,a fatigue life prediction model which derives from the Palmgren-Miner(P-M) linear damage model is provided.Then the fatigue life analysis of a 1.25 MW wind turbine system is carried out.The results show that the energy of the rotationally sampled spectrum transforms significantly from the low frequency region to the high frequency region.Besides,multi-peaks also appear in the high frequency region because of the energy shift.The fatigue life prediction model based on the rotationally sampled spectrum can predict the fatigue life and evaluate the security of the wind turbine structure more exactly compared with the one based on the Von Karman spectrum,which will overestimate the fatigue life and is unsafe for the fatigue life prediction of wind turbines.

Abstract:In order to improve the precision of parameter estimation of reliability model,based on the analyses of traditional reliability model,the limitations of least square method and gradual linear approximation because of their hypothetical distribution to random variable are pointed out,and the parameter estimators of point and interval are given by bootstrap method.The calculating results show that the estimated interval,standard error of parameter and the standard residual errors of the model are both less than those estimated by traditional method.Bootstrap method can approximate the actual value quickly than traditional way when increasing simulative times,so this method is feasible and effective and has a better accuracy than the latter.

Abstract:In order to obtain the spatial directivity of ship radiated noise at far field in shallow water,a new method is presented to compute the corresponding sound field distribution at far field.Firstly the sound pressure data measured by hydrophone array at near field was used to obtain the equivalent intensity and positions of multi-pole structure model for ship radiated noise,then the spatial directivity of far field radiated noise is computed by normal modes.A comparison between simulation results of far field spatial directivity of ship noise obtained by this method and the result obtained from direct computation using assumed data of sound sources show that the method presented in this paper can give an acceptable spatial directivity of far field.

Abstract:In this paper,the non-steady-state heats transfer behavior of metal honeycomb sandwich panel under aerodynamic heating was studied.Based on high temperature heat transfer theory and mechanism analysis,one-dimensional transient heat transfer mathematical physics model of honeycomb sandwich panel taking the combination of heat conduction and radiation into account was given.The control volume method and Monte Carlo method were adopted and then a numerical computation method was developed to calculate the coupling problem of heat conduction and radiation.Computation methods for effective thermal conductivities of honeycomb sandwich panel,the transient temperature field and heat response of non-heated surface under typical boundary conditions were given as well.An experiment was designed to validate this computation method.The result shows that the numerical computation model given in this paper is valid to predict the thermal performance of honeycomb sandwich structures and the values calculated are more precise than those calculated by Swann-Pittman semi-empirical relationship.

Abstract:To solve the scheduling problem in flexible assembly system(FAS),the method combining hierarchical timed-delay Petri net(HTPN) model with ant colony optimization algorithm(ACOA) is adopted.In this method,the FAS is divided into a number of subassemblies and then into many flexible assembly units.With building sub-model for each unit separately and assembly scheme being traversed,the final model is determined.The method has combined the strongpoint of ACOA and HTPN and solved the problems of assembly modeling and facilities assignments optimization of FAS.The experiments show that the method is effective and can be used to guide the assembly system design.

Abstract:In order to be applied to electromagnetic(EM) radiation problems,a novel time-domain finite element method(TDFEM) on the basis of quadratic B-spline temporal basis functions is proposed.The formulation time-domain finite element methods is reviewed first.Then two TDFEM schemes based on quadratic B spine temporal basis functions are presented:conditional stability and unconditional stability.They are validated via canonical cases.The efficiencies of the two schemes in precision level and run time are compared.The stability analysis of the proposed formulations is summarized and then verified through numerical results.