Abstract:The tracking problem of free-floating space manipulator system in task space with friction disturbance torque is investigated in this paper. A terminal sliding mode controller is proposed to achieve finite time stabilization of the system. Furthermore, taking into account the existence of dead-zone nonlinearity of the actuator, an adaptive compensator is designed to estimate its upper bound and thus ensure the effectiveness of the proposed controller. Lyapunov stability analysis proves that the closed-loop system is globally asymptotic stable. Numerical simulations show that this controller can effectively achieve inertia space tracking task and also be robust to external disturbances.

Abstract:Abstract: In order to reduce the influence of disturbance on the drag-free satellite, a disturbance compensation control combined with optimal control of quadratic performance based on a Kalman estimation theory is presented. Firstly, the relative dynamics of the satellite and the proof mass are modeled. Secondly, the state estimation of the drag-free satellite is given and an optimal controller is established. Finally, the control system with a feedforward loop for disturbance compensation based on Kalman filter is constructed. The simulation results in MATLAB/Simulink indicate that the disturbance compensation together with optimal control is effective to reject external disturbance, the accuracy of the drag-free satellite can be satisfied.

Abstract:To evaluate how the uncertain factors in the entry dynamics such as the navigation errors at the entry point affect the landing precision effectively, by introducing the Galerkin projection, a rapid landing error prediction method for Mars entry is proposed. In this method, the Polynomial Chaos are used to approximate the vehicle's states, and the problem is converted to a deterministic dynamical systems. Applying the method to a representative entry scenario of our country's future Mars entry mission, simulation results indicate that, compared with Monte Carlo method, the proposed method is able to predict the mean and covariance with little error and more computational efficiency.

Abstract:The initial conditions for targeted energy transfer in coupled nonlinear oscillators are investigated. First it is shown that optimal targeted energy transfer and complete energy exchange in non-conservative systems are basically the same in the system of a linear oscillator coupled with a nonlinear energy sink. An assumption and an inference are proposed that there is a proportional relationship between initial energy for inducing optimal targeted energy transfer and the cubic stiffness based on the research of slow-flow dynamics of the non-conservative system. The assumption and inference are verified by numerical simulations. The result can be applied for design of the cubic stiffness for inducing optimal targeted energy transfer in the system of a linear oscillator coupled with a nonlinear energy sink, and the method is also given in the paper.

Abstract:To improve the arc trajectory planning accuracy of manipulators passing the non-collinear three-points, a new approach for the manipulators’ position planning and orientation planning is presented by using homogeneous matrix and quaternion respectively. For the position planning, the central angle of the arc in space is normalized, the positions of interpolation points are planed according to the smooth angular velocity curve and represented by homogeneous matrix, all the interpolation points are on the demanded arc. By using circular blending quaternion curve and a piecewise rational cubic spline together, a C² continuous orientation path which smoothly interpolates the given sequence of the manipulators positions is obtained. Simulation example shows that the presented planning approach for position and orientation can guarantee the end trajectory precision of manipulator, and can be applied to the trajectory planning of the manipulators with high accuracy requirement.

Abstract:For the problem of multi-body contact and co-deformation in the stiffness analysis of angular contact thin-section ball bearings, an angular contact ball bearing 71718 is taken to investigate the axial stiffness of the thin-section bearing. Firstly, the reasonable finite element dimension is acquired based on the influence of the element dimension on the finite element analysis (FEA) results. Secondly, the finite element model of bearing 71718 is established to analyze the axial stiffness characteristics. Finally, the bearing axial stiffness test table was set up to test the axial stiffness of bearing 71718. The comparisons between test results and analysis results show that the Hertz analytical solutions has large calculation errors, the finite element results are close to real results, and the error is less than ten percent.

Abstract:To study the influence of thermo property on stress of femur-prosthesis system quantitatively, the finite element method is used to analyze the stress of femur-prosthesis system when the hip joint has been replaced, in which the prosthesis, bone cement and femur are assumed as linear elastic and isotropic materials in shape of a concentric cylinder. Considering the thermal effect, the axial stress of prosthesis, bone cement, femur and the interface shear stress along axial of the prosthesis／bone cement and bone cement／femur when the prosthesis are made of titanium alloy and cobalt-chromium alloy are acquired separately by mechanical analysis and FEM simulation.The results indicate that the interface failure is the primary failure mode of the femur-prosthesis system. The existence of thermal effect accelerates the interface failure of femur-prosthesis system and the loose of prosthesis stem. The possibility of interface failure which result in operation failure will ascend when the cobalt-chromium alloy is used, because the thermal expansion coefficient of cobalt-chromium alloys is higher than that of titanium alloy.

Abstract:To meet the need of large removal allowance and high efficiency of machining SiCp/Al surface, taking narrow slot mill-grinding as a typical example, the influence of machining parameters and mill-grinding tool on SiCp/Al machining force was experimentally investigated. The results show that the mill-grinding force is increased with the increasing speed and feedrate, and the feedrate is a significant impact on the force. In machining narrow-slot, the mill-grinding force can be reduced obviously by using the grinding tool with helix flutes. However, the mill-grinding force is fluctuant, and the fluctuant amplitude is reduced by reducing helix. Under the given conditions, the recommended helix of the wheel with flutes in mill-grinding narrow-slot is 50° which can perform a relative stabile machining process.

Abstract:To discern false modes during experimental modal analysis process and identify dense modes in axial symmetrical structures, the dynamic properties of truncated conic aluminum alloy thin shell satellite adaptor was experimental investigated. Electromagnetic vibration generators were used for exciting structures, and piezoelectric accelerometers for measuring the corresponding response. Polynomial method was applied for fitting experimental frequency response functions and identifying modal parameters. The effects of different methods between single input single output (SISO), single input multiple output (SIMO), and multiple input multiple output (MIMO) were evaluated systematically, both experimental and numerical analysis results were compared to recognize false modes. The experimental results show that the MIMO method helps in splitting dense modes in axial symmetry structures, and the former 10 modes of satellite adaptor were clearly identified. However, improper exciter fixation results in false modes in frequency response function. For experimental modal analysis of lightweight structures, special attention should be paid on additional mass and stiffness due to exciter fixation.

Abstract:To investigate the turbulent drag-reducing mechanism of drag-reducing aqueous solution, turbulent drag reduction of 30×10-6 cetyltrimethyl ammonium chloride (CTAC) aqueous solution in a channel flow was investigated experimentally and the influence of the drag-reducing additives on the flow structures was studied based on proper orthogonal decomposition, and POD was used to analyze turbulent fluctuating velocity based on PIV. The experimental results showed that at different Reynolds numbers, such as, 15×10⁴, 25×10⁴ and 35×10⁴, drag reduction (DR) rate of CTAC aqueous solution can reach up to 651％, 700％ and 330％ respectively, and the CTAC additives can inhibit the ejection motion of low-speed fluid from the wall and sweep motion of high-speed fluid towards the wall associating with turbulent bursting events, that is to say, the CTAC additives can inhibit the formation and development of turbulent coherent structures, resulting in a great decrease of turbulent contribution to frictional drag and DR.

Abstract:To deal with the problems such as high complexity and low accuracy of redundancy detection, a model of redundancy detection based on control structure analysis is proposed and implemented. This paper predigests the complexity of control structure by establishing a compound node table for tokens, which reduces the complexity of redundancy detection, and then detects the idempotent operations, dead code and redundant assignment. Experimental results of the open source code of Linux show that this model can find redundant code accurately and also has a low time-complexity. With this model, it is very convenient for developers to detect and correct these kinds of defects, and thereby to further guarantee the software quality.

Abstract:To improve the distribution properties of nanoparticles in the polymer electrolyte, micro-porous polymer electrolyte PVDF-HFP-SiO₂(OP-10) was prepared with phase inversion method by adopting nano-sized SiO₂ as the inorganic filler and OP-10 as dispersant. The morphology, crystal structure and electrochemical properties of the electrolyte were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), electrochemical impedance spectra (EIS). The results showed that the addition of nano-SiO₂ suppressed the crystallinity of polymer electrolyte and enhanced the tensile intensity. The ionic conductivity was improved, the highest ionic conductivity (20 ℃） of the PVDF-HFP-SiO₂(OP-10) polymer electrolyte was 490×10-3S·cm-1,with a high electrochemical stability window of 53 V, and the corresponding cation transference number was 083. The distribution of SiO₂ and interfacial compatibility of nanometer particles were improved by the addition of OP-10.

Abstract:To verify the impact of disaster reduction engineering on the agricultural output, we use the grey relational analysis algorithm and the measurement model to standardize many indicators in the agricultural production system, such as waterlogging control, irrigating, embankment and reservoir, and forming the assessment of the degree of the indicator association. At the same time, on the basis of the Cobb-Douglas production function, each indicator is included in the regression analysis, and the quantitative evaluation of waterlogging control and other indicators which affect the output of the agricultural production are completed. The empirical study has shown that the impact of the agricultural disaster reduction engineering on the agricultural production can be arranged from largest to smallest as waterlogging area, irrigating area, embankment length, salinization of arable land improvement area, reservoir capacity, and soil erosion control area;expanding the waterlogging control area, building the reservoir and increasing the length of the embankment can increase the total value of the agricultural output, and the waterlogging control has the greatest utility to increase agricultural output in these measures. The natural disaster hinders the development of agricultural production. And increasing the input of the disaster reduction engineering can be conducive to increase the output of agricultural production.

Abstract:Classical Bellman-Ford algorithm is improved to solve the shortest path problem with bounded edge number efficiently. Using the experience of partitioning algorithm for reference, two improved algorithms are obtained, which can decrease the number of distance labels of vertices. Since all existing improved Bellman-Ford algorithms can’t solve the shortest path problem with bounded edge number, these two improved algorithms are entirely new. In contrast to the common version of Bellman-Ford algorithm, these two improved algorithms can save storage space efficiently, and can raise computing efficiency remarkably.

Abstract:To reduce maintenance cost and improve performance after a shop visit, a decision-making method for civil aeroengine workscope under uncertain condition is proposed. Firstly, aeroengine overall performance restoration value for each module′s maintenance level is expressed as a trapezoidal fuzzy number, and then a fuzzy chance constrained programming model on module performance restoration value distribution optimization is put forward under uncertain condition. Secondly, the chance constraint of the model is transformed into a clear equivalence class. It is found that this model and the optimization model of module performance restoration value distribution under certain condition have the same structure. Thus, the solving method of the model with certain condition is adopted to achieve the model with uncertainty condition. Finally, the proposed method is validated by a real example. The result shows that the proposed method can solve decision-making problem for aeroengine maintenance workscope under uncertainty condition; the reasonable confidence level for the chance constraint of the model is essential to the decision-making result, and could be determined according to the risk of achieving the repair objectives and maintenance cost.

Abstract:In order to abstract Schumann Resonance parameters in shorter time, Prony algorithm is adopted and analyzed here to process the sampling data directly without FFT. Due to the fact that the algorithm is noise-sensitive, the minimization of correlated residuals proposed by Martin is adopted for solving the overdetermined equations and verified with simulated signals. It is proved to be feasible for SR signal processing after compared with the results from frequency domain.

Abstract:For the existing circle matching algorithms could not simultaneously meet the requirements of high-speed, low memory consumption and high accuracy, a new algorithm based on hit rate was proposed. The Ring Sample Template was introduced and its edge was used as matching information. The matching result was determined by hit rate, and the Grey Scale Correlation between source and destination was calculated to eliminate wrong destination. The result showed that the algorithm could get destination position in milliseconds, and had good performances on both memory consumption and reliability.

Abstract:The application of hyperspectral imagery (HSI) is quite limited to its low spatial resolution. A new method for super-resolution mapping of HSI is proposed using support vector machine(SVM) and wavelet transform. Firstly, spectral unmixing is processed for HSI and the fraction images are obtained. Then the wavelet decomposition is processed on these fraction images. In the local window, the relation between the three high-frequency coefficients of the center pixel and low-frequency coefficients of neighbour pixels are described by training samples, which are used for the learning process of SVM. The trained SVM models are utilized to predict the super-resolution mapping results of the coarse resolution images, i.e., the fraction images. Experiment results show that using wavelet transform can eliminate the dependence on prior information, and compared with the learning method based on BP neural network, SVM can produce higher accuracy super-resolution mapping results.

Abstract:In order to analyze the dynamic effects of elastic support on dynamic characteristics of marine planetary reducer, the dynamic model of transmission system is set up in consideration of the time-varying mesh stiffness and gear error, and the dynamic excitations of the system are calculated. The dynamic response model of the gearbox is set up by using finite element method and solved by using mode superposition method. Then the time history and spectrum of node acceleration of the gearbox are obtained, and the effect of support stiffness on vibration transfer and displacement of the gearbox are researched. The study provides useful theoretical guideline to the design of the marine gearbox.

Abstract:To calculate soot source terms the new model is presented according to recent literature data. Different models are used in deferent temperature zones in combustion chamber. When zone temperature T<1 500 K, gas-phase kinetics is considered and the soot precursors -PAHs (Polycyclic aromatic hydrocarbons) is calculated. When zone temperature T ≥1500 K, the gas-phase chemistry and soot source terms are calculated. PAHs model is the modified Frenklach-Ma model which includes formation and oxidation of PAHs. The formation of soot can be subdivided into the process of particle inception, surface growth and oxidation, particle coagulation. Temperature and excess air coefficient are the most important parameters in the new model . The soot is created only when temperature T≥1 500 K and excess air coefficient Ф<0.6. The new model is implemented into the KIVA-3V code and the results of soot with variation of injection time and variation of rail pressure between simulation and experimental data are analyzed. It gives a new way to predict soot for direct-injection diesel engine.

Abstract:Touchless fingerprint capturing can provide richer features and overcome the deficiency of 2D fingerprint recognition. In this paper, a clustering-based dynamic score selection (CDSS) algorithm is proposed for the combination of scores which are generated by different vision touchless fingerprint recognition systems. First, the scores are divided into two classes and the number of elements in each class and other statistic variables is computed. Then appropriate statistic value is chosen as the score for final decision of the whole system. The experimental results show that the performance of CDSS-based multi-vision touchless system can be enhanced efficiently compared to touchless fingerprint recognition and better than those of sum, max, SVM and Fisher linear discrimination algorithms.

Abstract:To solve the modelling problem of wheel-rail force, a modelling approach based on the genetic algorithm and radial basis function neural network method is proposed, which can predict the output of wheel-rail force using the input of track irregularities. In order to improve the accuracy of the designed neural network and relieve the computational burden, the centers, widths and weights of the neural network are determined using the maximum distance measure, the least square method and genetic algorithm, respectively. The simulation results indicate that the proposed method can predict wheel-rail force with high precision.

Abstract:To solve the problem of poor flexibility and frequent route breakage caused by dynamic topology in Ad Hoc network routing protocols, a stable ant colony routing algorithm based on Q-learning (SACRQ) is proposed, which synthesizes the Ant Colony Optimization and the Q-learning algorithm. The pheromone level is equal to the Q value to enhance the learning ability of nodes. To avoid local peak, SARCQ applies an adaptive pseudo random proportional action choice rule to select the next hop. A new robustness of the links metric is presented to calculate the probability of the route selection together with the pheromone level. The algorithm enhances the stability of the links and demonstrates high flexibility to the dynamic topology of the network. Simulation results show that SACRQ achieves better performance in terms of the number of the route discovery, the average end-to-end delay, the number of collisions and the average throughput per route discovery, which is respectively compared with the ARA and AODV.

Abstract:The dynamic spherical cavity expansion with damage and elastic area was investigated when distortion is so small that no plastic area arisen. First, by study of elastic region and initial damage, the stress distribution and the continuous conditions in the intersection of damage and elastic regions were given. Then the governing equations to solve the problem of dynamic expansion in the damage zone were deduced. Finally, numerical solutions of the non-linear differential equations were obtained by shooting method. The results show that some material parameters such as v、n、m have influence on the field quantities of elastic and damage regions.

Abstract:To improve the product quality of combined elbows and reduce the production cost, 2-axis computer control filament winding machine was designed to wind the combined elbows. Geodesic and non-geodesic theory was used to design the fiber winding trajectory of elbow and tube. The boundary condition without slippage and bridging and the overlay condition of the maximum arc on the elbow were given. The winding nodes were designed with the patch winding theory and the overlap condition of the minimum arc on the elbow was analyzed. The winding control program was written to verify the practicability of this winding method. The result shows that the winding process has the advantages of simple structure, low cost, high productivity and stable pattern. It can meet the winding requirements of all combined elbows.

Abstract:Abstract: For the nonlinearity of the system dynamic and measurement model in Tightly Coupled Integration of LEO, this article holds research on Unscented Kalman Filter (UKF). The system model and UKF method in inertial frame are introduced. The attitude is represented by modified Rodrigues parameters instead of quaternion for its unit norm constraint, and the state is predicated by the fourth Runge-Kutta technique for satellite's high speed. The performance of UKF is compared to Extended Kalman Filter (EKF) by simulations. The results indicate that UKF is better on attitude precision than EKF by one order of magnitude, equal on position and velocity precision, but higher on computation time.

Abstract:To mitigate the negative impact of varying satellite signal-to-noise ratio (SNR) on the vector lock loop (VLL) in a Global Navigation Satellite System (GNSS) receiver, an innovation based adaptive Kalman filter is employed to real-time adjust VLL measurement noise covariance matrix. Intermediate frequency data from a Global Positioning System (GPS) signal generator are post-processed using a software GPS receiver to verify the proposed method. The experimental result shows that VLL with the proposed adaptive Kalman filter outperforms under lower SNR conditions or with even insufficient amount of visible satellites comparing with the conventional scalar lock loop (SLL). Both carrier frequency tracking results and navigation solutions from the proposed method are more accurate than those from either fixed-parameter VLL or conventional SLL.

Abstract:FPGA has fixed number of I／O or CLB, which resulting in a limitation to the implementation of a very large complex system in a single FPGA. This paper addresses a partitioning method used for a multi-FPGA system implementation with partly guidance of User Constraint File and FPGA EDA flow. The partitioning method can improve the partitioning efficiency, and reduce the complexity of a multi-FPGA system design. Based on the proposed method and the multi-FPGA system architecture, a partitioning tool was implemented, which has the capability of designing a nine-chip multi-FPGA system.