Abstract:Considering overactuated satellite optimal control allocation problem with redundant reaction wheels, in order to achieve minimum total energy consumption and torque allocation deviation as a goal, an energy/torque dynamic control allocation algorithm is proposed by defining relevant optimized objective function. Also, the proposed method takes nonlinear dynamics into account and modifies the initial control allocation result. Finally, mathematical simulations are used to verify the performance of the algorithm, the result shows its feasibility and effectiveness.

Abstract:Considering the orbit design of a solar sail in the circular restricted three-body problem(CRTBP), the sail attitude and lightness parameter required for stationary solutions and the artificial libration surfaces are investigated. For there is very little intuition about the solution space of the periodic orbit near most artificial libration points, higher-order collocation is utilized to discretize the solution to the equations of motion. This approach converts the original problem to a finite-dimensional nonlinear programming problem with a finite set of variables. The calculation results demonstrate the availability of the approach in generating periodic orbits in solar sail CRTBP as well as its robustness to the initial guess.

Abstract:A Gauss pseudo-spectral method is proposed to solve optimal control problem for satellite rapid orbital maneuver, in which only one axis thruster is provided under the finite thrust. The concept of "virtual satellite" transforms the orbital maneuver of satellite into the soft rendezvous of the satellite and virtual satellite. The relative motion equations are then formulated and the maneuver time is selected as cost function for the optimal control problem, which is transformed to a nonlinear programming problem by using the Gauss pseudo-spectral method. This approach avoids the difficulties in solving boundary value problem. Finally, the optimal trajectory is solved by using MATLAB optimization toolbox. The results show that the Gauss pseudo-spectral method is very effective for solving the multiple constrained nonlinear strongly coupled equations, and it isn′t very sensitive to initial data and has certain robustness.

Abstract:Based on exposure characteristics of the wafer scanner, a segmented iterative learning control strategy is presented. The proposed method inherits the advantage of non-causal iterative learning control, which is full learning of errors. In order to improve the dynamic tracking performance, non-causal learning of errors in the last iteration is implemented during the acceleration phase, which guarantees the fast convergence of the system versus iteration domain. For the purpose of overcoming the weakness of blind learning for non-causal iterative learning control methods, errors are not learnt fully during the constant velocity so that exposure performance does not go bad. It improves the transient performance versus time. In addition, the convergence of the proposed method is analyzed and proved. Combining the numerical example, effectiveness of the method is testified.

Abstract:The trajectory characteristics of lunar return reentry are determined by cosmic velocity dynamics. The model of reentry problem is established. Based on the trajectory characteristics analysis of lunar return reentry, we obtained the following conclusions. First, entry angle has a significant effect on downrange, heating rate and g-load. A small entry angle can significantly improve heating and g-load environment. Second, bank reversal has no significant effect on downrange, heating rate and g-load, but has a significant effect on cross-range, which provides a basis for the vertical and lateral decoupling guidance. Third, the maximum heating rate always appears before the first peak g-load, and decreases with the decreasing of entry velocity. Thus, it requires the vehicle to achieve decelerating adequately and effectively in the initial descent phase and then skip out of the atmosphere to improve the heating environment.

Abstract:To solve the problem of dynamic coupling between satellite platform and antenna system, a three degree of freedom drive and measurement mechanism was utilized to interface antenna arm and satellite platform, and to control pointing of antenna. By this mechanism, the drive torque was fed forward into attitude control system to compensate reacting torque and realize decoupling control between satellite attitude and antenna pointing. Dynamic model of satellite platform and antenna with decoupled mechanism was established for large angle attitude maneuver. Using this model, large angle maneuver control law was designed and simulation was done for performance verification. Results demonstrate that the decoupling control approach could increase the stability of satellite attitude with two orders of magnitude. Decoupling control enhances vibration damping and improves satellite stability.

Abstract:Considering practical application in cognitive radio system, a graph theory algorithm is applied firstly to rapidly allocate spectrums (channels), which provides distribution fairness, and then the game theory algorithm is used to optimize first distribution spectrums (channels) and complete spectrum redistribution between cognitive users. Finally, simulation results show that the spectrum resources can be fully utilized, and under power transmission constraints, each cognitive user optimizes its own utility (rate) and distributes reasonably power. The simulation verifies that joint algorithm based on graph theory algorithm and game theory algorithm is effective. 

Abstract:This paper presents a sorting method based on cosine weighting to improve the anti-jitter ability of histogram algorithm in radar signal sorting. This method uses variable and superposed boxes, into which the collected radar pulses repetition interval (PRI) falls, and the histogram increment of these boxes are normalized weighted by cosine window smoothly. Each peak position of the histogram that exceeds threshold is the estimated PRI of radar. The histogram obtained by this method is smooth and the peak is clear. Furthermore, the sub-harmonic is well restrained. Experimental result shows that this method has good anti-jitter ability.

Abstract:The modular robot has the characteristic of diversity configuration and multi-mode locomotion. To make the robot more flexible and the control of multi-mode locomotion easier, combined with the feature of lattice and chain type self-reconfigurable robots, the UBot module based on the universal joint has been developed. According to the mutual inhibition relation of two joints in each module, combined with biological central pattern generator (CPG) principle, the CPG controller with two outputs has been designed. The two-output CPG controller can control the UBot robot's locomotion effectively by adjusting the connective weights among CPGs and two outputs' relation in each CPG and getting different phases. The control method has been used to control three motions: quadruped motion, squirm motion and multi-segmented worm motion. The simulation has been successfully done in ADAMS, besides, the experiment of the three motions have been done on the UBot modular robotic platform. The experiment results have proved the Two-output CPG phased network for modular robot locomotion control to be practical and effective.

Abstract:To reduce the pressure shock of the electro-hydraulic-servo piston hydraulic transformer with swash plate, to lower the noise and to improve the operational stability, this paper develops buffer slot in the valve plate of the hydraulic transformer based-on the fluid-structure coupling function of the software ADINA. In software Pro/E, fluid model and solid model of the flow assignment structure of valve plate are built and imported to the software ADINA for building of finite element model. The flow field of the flow assignment structure that was checked with finite element method was analyzed. A valve plate with buffer slot with triangle shape was manufactured and tested on hydraulic transformer test-bed. The results revealed that the valve plate enabled hydraulic transformer steady in operation and the minimum speed of hydraulic transformer reached 35 r/min. The noise was lower and the reliability was improved. The correctness of theoretical analysis was testified.

Abstract:The effect of convolution height and corner located on transition zone on forming precision, axial compensation capacity, anti-instability capacity, and heat transfer characteristics are analyzed one by one in this paper by experiments, theory checking and simulation. The results show that, for hydroformed corrugated tube, with the increase of corner radius there will be a better forming precision; with the increase of convolution height, there will be a good performance on axial compensation capacity and bad performance on anti-instability capacity and anti-fatigue capacity; with the increase of corner radius and convolution height, the comprehensive heat transfer friction are first increase and then decrease. When the convolution height is 2.5 mm and the corner radius is 30 mm, the hydroformed corrugated tubes have better comprehensive performance.

Abstract:Based on the failure criterion that is suitable for the undirectional composite laminates, the impact damage of fabric fiber reinforced composites is proposed to improve the fiber and matrix damage failure criterion. The impact damage of longitude fiber failure, latitude fiber failure, matrix crushing and delamination were considered for the fabric carbon fiber reinforced epoxy composites laminates. A finite element analysis model is established by using ABAQUS software combined with the sudden stiffness degradation model. Basic strength parameters of composites are used to evaluate the mechanical properties of CFRP laminates with different porosities. The impact damage area of the fabric carbon fiber reinforced epoxy composites laminates are simulated accurately.

Abstract:To study the influence of boundary effect on phonon heat transport in nanoscale material, the phonon heat transport in silicon dioxide material for rectangular geometry is simulated, in which the effect of boundary scattering on phonon mean free path is considered. The results show that the effective thermal conductivity in nanoscale material reduces more obviously for diffuse reflection than the case of specular reflection, and the effect of boundary exists at the boundary. The effective thermal conductivity reduces with the decrease of specularity factor. The increasing of boundary roughness in nanoscale material, which enhances the thermal resistance of boundary, is in favor of the reduction of the thermal conductivity.

Abstract:To improve the surface properties in solution, a series of imidazolum Gemini surfactants with methylene spacer chains were synthesized. The structure of the target product is characterized by 1HNMR. The surface tension of imidazolum Gemini surfactants was measured at 25 ℃. The results show that the synthetic imidazolum Gemini surfactants are consistent with the target structure. As the number of carbon atoms of the hydrophobic group increases, the tendency of adsorption on the gas-liquid interface increases with the fixed length of the hydrophilic spacer. The critical micelle concentration and adsorption capacity decrease while the adsorption area and pc20 increase. The effect of the hydrophobic length on the surface tension is weak with the high surface activities. In addition, the shorter the hydrophilic spacer length of imidazolum Gemini surfactants is, the higher the adsorption and surface tension with the fixed length of the hydrophobic group.

Abstract:For the operating needs of bomb-disposal robot, a set of semi-physical simulation system, which consists of a embedded control system and a 3D simulation system, is developed to simulate the typical operation tasks, such as hazardous materials detection, explosives handling, et al. Firstly, the embedded control system is developed based on a single-chip microcomputer, the actual trajectory planning and control algorithm is used, and the control instructions according to the true timing is generated. Secondly, using VC and OSG (Open Scene Graph) software, the 3D simulation system is programmed, which is composed of dynamic, geometry, binocular camera, sensor models, et al, and it can be run on a PC computer. Finally, by integrating the embedded control system and the 3D simulation system, the closed-loop control simulation of typical tasks is completed. The simulation results show the effectiveness of the system.

Abstract:To track a desired trajectory better, a CMAC neural network is added to conventional computed torque control as compensator. In the CMAC network, the inputs contain cross-coupling error composed of trajectory tracking error and synchronization error and its change rate, and the output is the compensation torque. Matlab simulations show that the tracking error and synchronization error can converge to zero with CMAC network. Compared with pure computed torque control, the trajectory tracking is more accurate with the proposed control strategy. The results show that the proposed control strategy is valid to track a predefined trajectory accurately. 

Abstract:An electric vehicle model is established based on the design parameters to match and optimize the drive system of the electric vehicle. Then the influence laws of the battery capacity for the vehicle performance are researched deeply, and a novel strategy for batteries optimization and match is proposed based on SOC-weight coefficient defined. To obtain the optimal transmission ratio and develop the vehicle dynamic performance, a new vehicle performance integration coefficient is proposed to select the most effective drive ratio for the vehicle based on the vehicle driving cycle. Finally, the motor and vehicle performance is analyzed and the simulation results show that the matched and optimized vehicle parameters greatly meet drive targets in the ECE drive cycle, and it is much significant for the electric vehicle to improve the vehicle power performance, battery efficiency and driving range.

Abstract:Two U tubes and two multi-U tubes are used to investigate the pressure drop and heat transfer characteristics of single-phase liquid nitrogen flowing in U-tubes. The diameter and curvature ratio of U tubes is from 4 to 8mm, and 8 to 15, respectively. It is found that the local heat transfer characteristics of both single U tubes and multi-U tubes in the 180° return bend are different from that of straight pipe. The wall temperature, especially the wall temperature of the latter part of the bend, decreases, and the heat transfer coefficient increases. For a single-U tube, the maximum heat transfer coefficient is at the exit of the return bend, for a multi-U tube, the heat transfer coefficient is sawtooth-type growing along the way, and reaches the maximum at the exit of the last bend. Based on Idelshik’s correlation, the new correlation for the 180°return bend friction pressure drop is proposed. The new correlation adds the centrifugal force item and agrees well with the experimental data.

Abstract:To improve the throughput and decrease the suffered interference of TDCS, the double-threshold energy detection is proposed to estimate the spectrum environment around TDCS. By comparing the detected spectrum value with the double thresholds, the spectrum with the statistic above the upper threshold is marked as 0, and below the lower threshold is marked as 1, while that between the double thresholds is marked as 0.5. The basic function at time domain is obtained by operating IDFT to the product of spectrum marker and pseudo random phase. TDCS implements communication by modulating data on the basic function with CCSK. Simulation shows that compared with the traditional single-threshold TDCS, the proposed double-threshold TDCS bears lower BER and higher throughput.

Abstract:In the paper, the concept of hyper-horizon coverage vehicle was briefly described, and the optimization of the Common Aero Vehicle (CAV) constellation was investigated. First, based on the analysis of earth coverage of a single CAV, a new method was proposed to analyze the earth coverage of CAV, which was simple and geometrical meaningful. Then a math model of the optimization of a CAV constellation was established by introducing the concept of average visit time on orbit, which was an equivalent coverage performance of CAV constellation. At last, genetic algorithm was used to optimize the parameters of CAV constellation and the results validated the proposed method and mathematical model.

Abstract:To obtain current road information quickly and to improve vehicle active safety performance accurately, a vehicle state estimation method was proposed to real-time track changes in road friction coefficient. A 7-DOF non-linear vehicle dynamic model including Pacejka 89 tire model was established. The normal force of tire was approximately calculated from the vehicle dynamic model, the tire slip and longitudinal force were estimated by a combination of tire mechanical model and UKF algorithm. Then Slip-slope of different road friction coefficient was obtained. A mapping relationship between several typical road friction coefficient and Slip-slope was built. By constructing various ground test environment with different road friction coefficient using the Road Builder in ADAMS/Car, the estimation method proposed was verified to be effective and reliable. Moreover, the simulation results indicated that Slip-slope theory is also applicable in the virtual test under the ADAMS/Car environment.

Abstract:To improve the performance of olivine LiFePO₄ positive-electrode material, the Mn-doped LiMn_xFe1-xPO₄(x=0,0.0,0.5,0.0,0.50) materials were prepared by a solid-state reaction method. The structure, electrochemical performance and lithium ion insertion-extraction kinetic of the material are investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), charge-discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the Mn-doped LiFePO₄ material powders have a uniform morphology, a small particle size and narrow particle size distribution, and LiMn_xFe1-xPO₄ materials are pure phase olivine structure. LiMn0.4Fe0.6PO₄ shows the highest discharge capacity and the best kinetic performance among all samples at different rates. The Mn doping improves the reversibility, Li+ions diffusion coefficient and discharge capacity, and reduces the charge transfer resistance, and then increase the kinetic performance of LiFePO₄ material.

Abstract:To solve the problem that the BP network training algorithm is easy to fall into local minimal point, this paper designs a set of new filled function in view of its characteristic, which can be used to replace the objective function for search and improve the SPDS algorithm. The algorithm simulation test proves that, when the SPDS algorithm falls into local minimum point, the use of the filled function instead of objective function makes the algorithm avoid the fetters of minimum problem, and accelerates convergence to the global minimum point.