Abstract:Autonomous navigation based on sequential images (ANBSI) is the key technology of pinpoint landing missions for future deep space exploration and also is one of the major development directions for deep space exploration technology. The necessity of developing ANBSI for planetary pinpoint landing is elaborated in this paper. Firstly, state-of-art developments of ANBSI are reviewed in terms of active sensing and passive sensing. Then, the key techniques applied in ANBSI for planetary landing are summarized and analyzed. Finally, according to the analysis of the key techniques, the main issues of ANBSI are raised and their future developments are overviewed.

Abstract:This paper investigates the attitude synchronization problem of multiple spacecraft without a prescribed reference attitude in the presence of disturbance. Autonomous attitude synchronization is necessary when a spacecraft formation has no external reference information. Therefore, a decentralized robust attitude control scheme is proposed to guarantee spacecraft attitude synchronization under external disturbances in the absence of a common reference attitude or any other hierarchy in formation. The proposed class of controllers is effective with a large range of communication topological structure, and is designed by using the absolute angular velocity and absolute attitude quaternion. The control scheme is robust against environmental disturbance torques. The stability the resulting closed-loop system under the controllers are proven theoretically. Numerical simulations are included to validate the analytical results.

Abstract:A fault tolerant control scheme based on integral sliding mode surface is developed for spacecraft attitude stabilization in the presence of actuator faults, misalignments, magnitude saturation and external disturbances simultaneously. This approach is based on a novel integral-type sliding mode control strategy to compensate for these un-desired issues without controller reconfiguration. Especially, it guarantees the reachability of the system states by involving adaptive control technique to relax the boundary information in advance. A sufficient condition for the controller to accommodate magnitude saturation is also presented and then the fault tolerant attitude control system can be guaranteed theoretically to be asymptotically stable by using Lyapunov method. Numerical simulation results shows that the proposed control law can quarantee the stability of the spacecraft attitude control system in the presence of actuators' failures, and it has good robust performance.

Abstract:Based on fixed-time stabilization theory, a new hovering control strategy for spacecraft in relative orbit is investigated. First, the mathematical description of the fixed-time stabilization theory is introduced. Then, the hovering control law is proposed by utilizing C-W equation. The control effects can be adjusted to desired states in which the spacecraft hovers stably and precisely in finite time by regulating the values of corresponding parameters. Numerical simulation results are provided to validate the performance of the proposed control law.

Abstract:In order to improve the autonomous ability of unmanned aerial vehicles (UAVs) and achieve the integral framework of task assignment and path planning, a mission planning system based on path prediction algorithm for multiple UAVs is presented. To model obstacles more accurately, the forbidden areas are defined as polygons. Then, the optimal path segment avoiding all obstacles between two waypoints is computed by using improved A^* path prediction algorithm. According to this path segment, the task assignment is determined by improved particle swarm optimization (PSO) algorithm. Finally, the B-spline method is adopted to smooth the flight path, which consists of the sequential path segments. Numerical results demonstrate that the proposed method can achieve the near-optimal task assignment and best flight routes with effectiveness of computation speed and precision.

Abstract:The shock waves caused by the high-speed water entry projectiles have significant effects on the trajectory and damage performance of under-water projectiles. In this paper, the light-gas gun based system was exploited to accelerate the flat and spherical projectiles into a water-filled vessel at different initial velocities horizontally. The impact induced underwater shock waves caused by the two typical projectiles were investigated on the characteristics of propagation and attenuation. The pressure history captured by the transducers installed with different distributions in water column was analyzed in terms of the attenuate characteristics according to the distances and angles. The results indicate that the peak pressure of initial shock waves undergoes an exponential decay and the pressure among the curves 1/x and 1/x2 according to the distance. The decay characteristics of pressure on the spherical surface comply with the sine curve. The attenuation experienced by the pressure for different experimental conditions are independent with initial velocity of projectiles.

Abstract:An imaging simulation system of Earth Sensor is investigated, including the imaging of earth, atmosphere, twilight lines and background stars. To improve the simulation accuracy, the outline of earth is described as an ellipsoid rather than a sphere, and the scattering of atmosphere is taken into account. Based on the simulator, a hierarchical ellipse fitting algorithm is studied, in which the ellipse model is constructed to reduce the fitting error caused by the flat rate of earth, and the orbit a priori knowledge is used to improve the fitting robustness. Numerical simulations demonstrate the effectiveness of the approach proposed.

Abstract:To test the vehicle electronic control units, an improved test case generation algorithm based on the IPO (In-Parameter-Order) strategy is proposed via the parameter correlation and combination constraints of the vehicle. An integration testing system for vehicle electronic control units is developed, in which a unified management and data sharing mechanism is enabled for the common equipments used in vehicle test. The proposed method is validated under two different kinds of vehicle electronic control units and test conditions. The results show that the proposed test case generation algorithm can achieve the same coverage with a clear reduced number of test cases. And the integrated test system can meet the test requirements of the different vehicle electronic control units, with an improved testing efficiency and accuracy.

Abstract:To improve the fluid mixing effect under micro-nano scale condition, we designed and manufactured a novel micro mixer with three-dimensional step structure based on the polymethyl methacrylate (PMMA) substrate material. The mixer was composed by one T-shaped inlet channel and six three dimensional step mixing units. The mixer was fabricated by using ultra-precision engraving machine and bonded by miscible organic solvents bonding method at the atmospheric pressure and low temperature conditions. Then, a series of numerical simulations were executed to optimize the step structures and investigate the mixing efficiency. The results showed that, when the Reynolds number was between 0.1 and 5, the concentration variance of mixing chamber cross section was less than 0.1. The reagent was close to the uniform mixture. When the flow rate within 1~20 mL/h, the mixer can achieve on precise regulation of solution pH. The micro machining technology and miscible organic solvents bonding method which were used for fabricate the 3D step micromixer are convenient and cost-effective. The mixer was conducive to the further promotion and application of microfluidic chips.

Abstract:In order to obtain modes and damping characteristics of beam-like carbon fiber composite truss, a solid finite element model is established for truss modes simulation. It is then proposed to compute the structural damping loss factors based on the simulated results, using modal strain energy damping model. To improve the effciency of modes analyzation, also, an equivalent analysis approach for truss modes is presented, which is based on beam equivalence theory. Comparisons are made among the simulated results, equivalent analysis results and actual measurement, respectively, which show that vibration shapes from equivalent analysis, simulation and the experiment agree well. In addition, errors of the simulated natural frequencies and the calculated structural damping loss factors are both less than 10%. These validate the applicability of both the presented modes simulation method and damping computation method. Finally, the equivalent analysis approach is demonstrated to be rather efficient for modes of large scale truss, based on the simulation results.

Abstract:In video tracking applications, most algorithms often fail in such conditions as object occlusion, disappearance. To address this issue, an improved L1-tracker algorithm is proposed. Expanded templates (including the fixed template and the evolved template) are applied to improve the tracking accuracy and robustness.The fixed template keeps the original features of the target, and prevents the error introduced by false tracking result with the template update. The evolved template recording the latest tracking result is used to avoid massive use of trivial templates which will lead to the false recognition of occlusion. The experimental results on a number of standard data sets prove that the application of expended templates improves the ability of L1-tracker algorithm to deal with the occlusion problem.

Abstract:To alleviate the inefficiency of the current visualization methods in skipping the empty voxels located in the hollow part, this paper presents a GPU-based ray casting method for hollow volume data. First, the volume is divided into two equal parts and reconstructed into two octrees before rendering. In this process, the empty blocks are culled synchronously from the original data, and two vertex arrays are generated consisting of valid voxels only. Then, the vertex arrays are rendered into textures which contain the start and direction information of the ray. The final images are obtained by calculating the color and opacity of the two parts with CUDA, respectively. The experimental results show that our method can speed up the rendering speed considerably on the volume data with large hollow structure without any quality loss compared with the traditional visualization methods.

Abstract:To design low energy return trajectory for unmanned lunar probe, the dynamic model of the probe is developed under the elliptical four body problem in consideration of the effect of sun's gravitation and lunar elliptical motion to the probe's orbit. The existence and the dynamical characteristics of the return trajectory are analyzed. To deal with the strong nonlinearities of the dynamic model and the local convergence in the optimal process, an adaptive genetic algorithm is proposed which can adjust the self-evolution parameters according to the fitness of the population to improve the effectiveness of the evolution of the population to the global optimal point as well as to reduce the computation burden. According to the simulation results, the algorithm works well in optimizing the energy needed for the lunar probe to return to Earth, which is only 75% of that in the traditional hyperbolic matching method.

Abstract:This paper presents a flight control scheme for the aircraft with thrust vectoring to perform the pitch maneuver at high angle of attack under unsteady aerodynamic condition. The scheme employs a disturbance observer to estimate the unsteady aerodynamic disturbances emerging in maneuvers. Complete pitching moment compensation and proper lift amendment are added to the control signals. In order to design the nominal controller and the disturbance observer, linear parameter varying (LPV) models of the aircraft and external disturbances with identical scheduling parameters are established. Maneuvers simulations show that the proposed method has excellent track to the command and effective rejection to the unsteady aerodynamic disturbance.

Abstract:For the longitudinal landing control problem of flying-wing UAV with unknown external disturbances, a backstepping L₂ gain robust control scheme based on super twisting sliding mode disturbance observer and tracking differentiator is proposed. The tracking differentiator is introduced to calculate the derivative of virtual control law which is very difficult to evaluate with the traditional backstepping control. Super twisting sliding mode disturbance observer and L₂ gain robust item are designed to increase the robustness of the control system. Simulation results show:the altitude and airspeed of UAV are tracked on control command, vertical ground speed is within the allowable range. Compared with traditional PID control scheme, the proposed control scheme has better automatical landing control performance.

Abstract:In order to enhance mission flexibility, reduce launch preparation, and achieve quick launch and precision strike, a three dimensional autonomous guidance method for lift reentry vehicle's whole flight is studied in this paper. Firstly, a method is proposed for reentry phase, whose drag acceleration profile is obtained by interpolation between upper and lower boundary of entry corridor and two reversals of bank angle. The reentry process constraints and precision can be met by adjusting interpolation factor of the drag acceleration profile and reversal point of the bank angle. Then, the hit phase guidance law is designed in the form of proportional navigation guidance law based on vehicle and target position. The vehicle can strike target exactly with certain precision by updating the guidance coefficient in real time. Lastly, the whole flight guidance method is obtained using smooth transition at the joint point control commands of entry phase and hit phase. Monte Carlo simulation results show that the guidance method can guide the vehicle to strike target exactly with certain precision and meet process constraints, and the hit deviation is less than 10 m, the angle deviation is less than 1.3°.

Abstract:To explore deformation characteristics of airship envelope with different structure resistance indexes, a numerical method was employed to analyze the deformation of a kind of typical airship envelope with different structure resistance indexes. Analytical results show:the effect of elastic modulus on deformation is nonlinear, the effect of poisson ratio on deformation is linear, and the effect of elastic modulus on deformation is obviously stronger than that of poisson ratio. Meanwhile, a square relationship between envelope length and its absolute deformation, a linear relationship between envelope length and relative deformation have been certified under the same working condition. What is more, it was testified that the curve between slenderness ratio and relative deformation was horizontal when slenderness ratio was between 4 and 5. Therefore, to reduce the relative deformation, it is beneficial to adopt envelop materials with large elastic modulus anddesign airship with appropriate length to make the slenderness radio between 4 and 5.

Abstract:In practical nonlinear system, due to the limitation of resources, the input signal is quickly refreshed, while the output signal is slowly sampled. Thus, it is difficult to identify the original nonlinear system by using the sampled data. For this purpose, the linear models of multiple characteristic points of nonlinear system are transformed into a series of consequent linear models of the fuzzy model by the lifting technique. On this basis, we propose a fuzzy identification algorithm based on competitive learning and recursive gradient descent method. And we prove that the parameters of the fuzzy model can be uniformly convergent under the condition of persistent excitation. In view of chemical pH neutralization process, the fuzzy model of the chemical system is established by using non-uniformly sampled data. By comparing the output errors between the actual data and the output data of the fuzzy model, it is shown that the fuzzy identification method can establish the process model in the real system under the condition of non-uniform sampling, which verifies the validity of the proposed method.

Abstract:In order to improve the performance of networked control system, this paper proposed a dynamic weight variable sampling period scheduling algorithm for networked control system. Firstly, each controlled loop weight is dynamically adjusted according to controlled loop data transmission error through quadratic square root mapping function, the different weight is given for each loop. Then the prediction of the new network utilization through proportional control is given based on the current network status, and least square support vector machine algorithm (LSSVM) is used for controlled loop packet transmission time prediction. Finally, under certain conditions of the network bandwidth limitation, variable sampling time for each controlled loop is determined by using dynamic weight of the controlled loop, network utilization and data transmission time, thus the system performance is optimized. The simulation results show that under the proposed variable sampling periodical scheduling algorithm, the network utilization converges to the setting value, the delay of control loop data transmission is reduced, and the output response performance and control performance of the system are improved.

Abstract:In order to sort frequency-hopping networks, identify and track signals effectively, an novel joint estimation algorithm based on spatial polarimetric time-frequency analysis is proposed as the solution for the two dimensional direction of arrival (2D-DOA) and polarization estimation of Frequency Hopping (FH) signals in underdetermined condition. First, the data model for polarization sensitive array of FH signals is built. On this basis, the SPSTFT, the extendable form of spatial polarimetric time frequency distributions, is derived. Meanwhile, a new combined time-frequency(TF) analysis method is presented to locate the auto term region of each hop in the TF plane. Consequently, the SPTFD and SPSTFT matrix for each hop is generated. Finally, depending on the spatial and polarization information getting from SPTFD and SPSTFT matrix, the 2D-DOA and polarization are estimated by two different methods. With splendid estimation precision, this novel method requires less computation burden without multiple-parameter optimization and pair-matching. Simulation results show that the proposed algorithm could estimate 2D-DOA and polarization in underdetermined condition effectively, and the SPTFD matrix method has high estimation accuracy.Besides, the collision hop could be processed.

Abstract:An evaluation model based on fuzzy theory is proposed in order to study the effectiveness evaluation of telecommunication satellites. Using ideas from fuzzy theory, a nonlinear evaluation function is established based on the analysis about properties of the assessment objects, making our model be applicable to a class of assessment objects which are evaluated by a system of index determined by a constellation of factors. These factors may be mutually dependent on each other. However, any two indices are independent. Given a number of such objects, the model is also able to classify them by using the method of fuzzy cluster analysis. Finally, the effectiveness evaluation of telecommunication satellites is considered according to the measurement data. The scores of the telecommunication satellites, Dongfanghong Ⅲ, the basic and enhanced type of Dongfanghong Ⅳ and Dongfanghong Ⅴ are 0.230-0.243, 0.470-0.536, 0.614-0.791 and 0.855-0.945 respectively, which shows that the effectiveness of Dongfanghong telecommunication satellites are growing. However, the integrated efficiency of Dongfanghong Ⅴ is not much better than that of the enhanced type of Dongfanghong Ⅳ.

Abstract:In order to deal with the lack of decision method during the evaluation of the airflow field on large ship decks, an initial evaluation index system of the airflow field was built according to the feature of similarity in all parameters. An improved TOPSIS method was proposed by combining the Deng's method and the slope grey relational method. The airflow fields on three foreign ships with same working conditions were simulated. Then, an evaluation method was presented on the basis of the takeoff and landing speeds, the change of vortex and some other related key parameters. With the method, the airflow fields on the three foreign ships were evaluated comprehensively. The results show that the improved TOPSIS method can be applied to assess ship airflow schemes according to the differences between the parameters from the evaluation index system. The present method is effective and feasible to the evaluation of airflow fields on ships.

Abstract:In order to solve the underwater explosion flow field with large discontinuities, Level Set method was applied to track the interface position of the multi-medium flow, Ghost Fluid method was used to calculate the physical parameter of both sides of the interface, time and space were discretized by Runge-Kutta Discontinuous Galerkin Method, Euler equations of the flow field were solved. One-dimensional and two-dimensional assessments were conducted by RKDG approach. The results reflect the phenomena of underwater explosion shock wave generation, propagation, reflection and explosion products expansion. Finally, the shock responses and damage characteristics of hull plates under shock load were simulated with the nonlinear FEM softeware ABAQUS. The RKDG method can be applied to simulate the hull plates response with high accuracy. The response of hull plates is inversely proportional to the blast center distance.

Abstract:For studying on start-up performance rules of fixed pitch tidal current turbine, the transient self-starting process of vertical axis hydro-turbine is numerical simulated by using CFX fluid-rigid body coupled motion calculating method. Combining static start-up torque coefficient results, the self-starting time and the angular speed stability of the turbine are analyzed in different initial azimuth angles. It is shown that, as for the three-blade fixed-pitch vertical axis hydro-turbine, the turbine has a better self-starting performance at azimuth angles of 60°~130°, but the angle of 90°is not a good choice because the static start-up torque will drop suddenly at this point. The turbine has a worse self-starting performance at azimuth angles of 140°~170°. However, the three-blade vertical axis hydro-turbine has self-starting performance at any initial position when the system damping is zero and the angular speed of the main shaft can arrive at runaway speed finally.

Abstract:In order to prove that the classical variational principles contain one principle that the reflection law is the constitutive relation, Hamilton principle of nonlinear elastodynamics is established by using the variational integral, starting from the basic equations of nonlinear elastodynamics. Then, after involutory transformation is used, Hamilton theory is converted to the constitutive variational principle with Langrange multiplier method and partial substitution method. It testifies that this variational principle reflects the constitutive relation. Taking the nonlinear material as an example, a new way to obtain the material constitutive relation is provided in this paper, which provides theoretical basis for numeral modeling. It supplements and improves the reflections of three basic rules in the classical constitutive relation:the reflection law of minimum potential energy principle is the balanced relation, the reflection law of the minimum complimentary energy principle is continuous relation, and the reflection law of constitutive variational principle is constitutive relation.

Abstract:The in-situ stress is the original stress in the geological body forming from the geological structure and gravity. It is an important factor which influences the stability and instability of the geological engineering. Due to the long geological tectonic setting and geological evolution, the in-situ stress field is a function of time and space, thus it is very difficulty for us to make accurate inversion the in-situ stress field. Taking Jinchuan mine as the engineering background and with the aid of in-situ stress measurement in Jinchuan mine, the in-situ stress field was inverted. First the 3D numerical mode of geological engineering body in Jinchuan mine was established, and the relation between in-situ stress and rock mass parameters and coefficients of horizontal pressure was obtained by orthogonal numerical analysis and genetic programming(GP). Then the optimization mode was established which takes the sum of squares of differences between the measured initial stress and calculation initial stress up to the minimum value as the objective function. The rock masses parameters and coefficients of horizontal pressure would been obtained by solving the optimization model using genetic algorithm. Finally, the initial stress field can be obtained when the 3D numerical analysis is carried out again by inputting the parameters of rock masses and coefficients of horizontal pressure. Based on comparing inverting in-situ stress with the measured values for the 4 gauging points, the maximum and minimum error of the principal stress is 16% and 0.62% respectively. The results show that the method of intelligent inversion of in-situ stress field can be applied for complicated geological engineering body to simulate in-situ stress field and the accuracy meets the engineering demand.

Abstract:According to the serious phenomenon of floor swelling during the coal mine burst in Huating coal field, measures which the transverse pressure relief (roadway cross-section) and the longitudinal pressure relief (along the roadway) were taken to eliminate the danger of rockburst. The static friction, which is caused by the horizontal stress in the borehole of roadway floor, would squeez the floor causing downward movement. The pressure of the floor was relieved through the fissure zone formed by the borehole blasting. A fracture zone in the tunnel was arranged at intervals, which played a role of " the spring body", to absorb the energy caused by the horizontal stress along the tunnel direction. The calculation results show that the energy absorption caused by the orientation controlling method was far greater than the energy level (10⁶ J) caused by mining shock hazard tested by the microseism monitoring system. Thus the orientation controlling method can have very good effects on avoiding the floor type rockburst phenomenon. Testing in a mine field, the implementation of the measures for a mine field was good and basically eliminated the phenomenon of tunnel floor swelling.

Abstract:In order to solve the serious problem of dust pollution during down-the-hole drilling in open-pit mine, based on the mechanism of foam dust removal and two phase foaming principle, a foaming generator was designed and the experimental study was made on it. The facts of poor application effect of traditional dedusting technology and large gas consumption and difficult water intaking were considered. Through the experiments of the foam flow, foaming times and half-life of the foaming generator, the major factors affecting foaming properties and the optimum operating point of the foam generator can be determined. The experimental results show that:gas flow, liquid flow (gas-liquid ratio), foam net and concentration of foaming agent are main factors affecting the foaming properties of the foam generator. When the working conditions for the foam generator were foam net 1, the concentration 1.5% of formula 2, gas pressure 0.7 MPa, liquid flow rate 18 L/min, gas flow of 30 m³/h, the foam generator reached the optimum state with the foam flow euqal to 515 L/min, the foaming times equal to 22, and the half-life equal to 65 min. Through the test, the average dust removal rate was higher than 90% using foam dedusting in the stope.

Abstract:In order to overcome the certain shortcomings of traditional methods in studying the pyrolysis process of coal, a sectioning method is proposed in this paper. Taking Xinglongzhuang coal for example, the pyrolysis process is divided into three parts based on the thought of sectioning method and the characteristics of weight loss curves. The interfacial chemical reaction model, the internal diffusion model with the constant volume of resultant and the internal diffusion model with the shrinking volume of resultant are established to fit the experimental data, respectively. The results show that experimental data can be well fitted by the established models. Finally, the corresponding kinetic parameters are calculated for each stage. The sectioning method is successfully applied to describe the pyrolysis process of Xinglongzhuang coal, which provides a theoretical guidance for the simulation and expanded production.

Abstract:Based on the data from a steel company, this paper applied life cycle assessment and GaBi 4.3 to analyze the material, energy consumption and emission during production of 1 t on steel by CML2001 method was used to perform environmental impact assessment of steel production. The results showed that the major environmental impact of BF-BOF steelmaking process includes aquatic ecotoxicity, human toxicity, fossil energy depletion and mineral resource depletion from coking, sintering, blast furnace and steel scrap recycling. And climate change, human toxicity, aquatic ecotoxicity, solid waste take up 30%, 95%, 50% and 90% of the total environmental impact, respectively. The major environmental impact of electric furnace steelmaking process includes mainly climate change, acidification and photochemical ozone formation from the molten iron and electric steelmaking processes. So a reliable basis of for decision making for iron and steel enterprises to adjust two different processes is provided. And the research helps to accurately discover energy saving, reduce the potential for environmental load in various aspects of the production process, thus contribute to iron and steel enterprises to improve or optimize production processes.

Abstract:This paper proposes a gait recognition algorithm based on three kinds of features from the image's silhouette. It extracts silhouette features by establishing dynamic information of invariant moment and percentage of frame difference, combining the modified angle distance of static information. It realizes the gait recognition via a modified K neighbor method. The experimental result shows that the recognition ratio achieves 91.94% with the static featureis only, and reaches 99.19% with the dynamic features under the improved classifier.