Abstract: In order to study the three-dimensional and four-directional braided composites on the basis of an improved unit cell model with rectangular cross-section, the relationship between the geometric properties of the cells and the braiding parameters were deduced with considering the effects of adhesive layers between adjacent yarns. The ANSYS software was used to build a finite element model (FEM) and obtained equivalent elastic performance parameters. The effects of the main process parameters on the elastic properties were discussed. The calculation results by the finite element model coincide well with the experimental data, which can relatively truly reflect the micro-structure of this material. They have the certain reference value for the three-dimensional braided composites design and technology.
Abstract: If only one limb of the parallel mechanism was driven, this limb can't move in full stroke because of the constraints from other limbs. In order to analyze the essential cause of single limb motion limit in parallel mechanism, the method of screw reciprocal product was adopted to calculate the axial velocity component. According to the result, when the axial velocity changes into zero, the single limb motion arrives boundary. The parallel mechanism is in single limb motion singularity from input space. At the same time the parallel mechanism is in configuration singularity from workspace. So the single limb motion singularity is equal to configuration singularity in parallel mechanism. By analyzing the input and output velocity at the moment, the parallel mechanism got to the boundary of input space. Finally the general strategy of single limb motion was given.
Abstract: The node triggering and data transmission in wireless sensor network(WSN) shows an activity pattern. A clustering algorithm activity-aware clustering protocol(AACP) was put forward based on this activity pattern. Sensor nodes were divided into a plurality of clusters by AACP, and then activities were predicted with clustering results and nodes' historical trigger data. Based on this predication and some other impacts, including energy balance, nodes' residual energy and transmission consumption, activity-aware and energy balanced routing protocol(AEBRP) was proposed. The real trigger data were used for simulation experiments to compare AEBRP with protocols low energy adaptive clustering hierarchy(LEACH), hybrid clustering for multitarget tracking in wireless sensor networks(HCMTT) and power efficient gathering in sensor information system(PEGASIS). The experimental results show that AEBRP has obvious advantages in maintaining the balance of energy consumption and prolong the network life cycle.
Abstract: The thermal coupling models were established on the positive plate collector, the negative plate collector and the battery plate, which based on the Bernardi heat generation rate model of a single battery. The heat transfer model of battery group was founded as well. In the natural ventilation environment, the heat generation characteristics of a single battery LiFePO4 was simulated by using Fluent software. The performances of heat generation and dissipation of battery group were simulated under the condition of forced air convection cooling. The effect of air-outlet position on battery temperature was analyzed. The effect on battery temperature was analyzed based on air-outlet position. In different discharge ratio, the battery temperature was calculated. The calculated results show that the pole ear temperature is higher than polar balde, and the postive ear temperature is greater than negative ear at the end of constant current discharging; The thermal performance of battery could meet the demands of the safe operating temperature in forced cooling conditions; The air-outlet position directly affests the air velocity profile and battery temperature field; The below air-outlet contributes to improve the consistency in thermal state. The error in calculating and testing result is less than 5% at the feature points, which could meet the needs in engineering.
Abstract: A control method for a 3-DOF spherical motor was introduced. The 3-DOF spherical motor had three-dimensional orientation measurement ability. Considering the mechanical structure of the spherical motor, XYZ Euler angle was used for the construction of the kinematics model. The dynamic model was established by the Lagrange's equation. Because of the dynamic modeling error, friction and external disturbances, the approximation neural network system model was applied to the spherical motor's control. The simulation results show that comparing to the traditional method, the proposed method can significantly improve the motion performance. The results can serve as a basis for the future precision motion control research and experiment.
Abstract: Surface analysis methods, a mass loss method, and electrochemical tests were employed to investigate the corrosion behavior of steel Q235 under the synergistic effect of Thiobacillus thiooxidans(T.t) and Bacillus. Scanning electronic microscopy (SEM) results reveal that a densest biofilm was formed in the mixed bacteria culture; The surface of the sample immersed in the mixed culture appeared circular corrosion poles which much different from the ones in the single-bacteria cultures. Mass loss method results indicate that the corrosion rate in the (T.t)-Bacillus system was between the single-bacteria system. Electrochemical impedance spectroscopy (EIS) show that there were two time constants existed in the T.t-Bacillus system after 2 d immersion, the corrosion resistance of the film performed as initially enhanced then weakened.
Abstract: In a dynamic process, the fiber-optic gyroscope (FOG) generates a nonreciprocal error easily. After analyzing the reason of the FOG generating dynamic error, the principle that structural material performance has a significant influence on the FOG dynamic performance was proposed. Applied different structural materials in the structural body that as FOG the major part, the finite element models were made respectively. The ratio stiffness of structural material impacting on the FOG dynamic performance was qualitatively analyzed through modal analysis and harmonic response analysis. Random vibration and sine sweep vibration experiments were also executed for confirmation with finite element model. The results show that the first resonance frequency of the FOG is increased from 1 454 Hz to 2 213 Hz by applying beryllium aluminum alloy which has higher ratio stiffness instead of aluminum alloy. FOG dynamic accuracy is significantly improved with the resonance frequency increasing. Deserve to mention that beryllium aluminum alloy makes the FOG become lighter and more suitable for use in a small and light FOG.
Abstract: With the developing of integrated technology of mechanical, electrical, hydraulic and control and the developing of digital hydraulic technology, a new integrated digital hydraulic actuation system (IDA) was put forward based on digital cylinder and edropump(electric-hydraulic-pump). The system composition and operating principle were analyzed. The mathematical models of the edropump, digital cylinder and the whole system were built in AMESim. Then, from the aspects of displacement response, overflow, motor speed and control valve opening and so on, it was simulated and compared with servo valve controlled hydraulic actuator (SHA) which was supplied by the centralized hydraulic oil source. Finally, the advantages and drawbacks of the integrated digital hydraulic actuation system were put forward.
Abstract: Trailing edge slots are important cooling structures in turbine blade. In order to realize the precise modeling of these structures in bowed-twisted turbine blade and improve the modeling efficiency, a rapid generative modeling method was proposed, including the tool body creation step and the slot windows creation step. Firstly, the tool body with the same or similar bowed-twisted condition as the blade was created via the matching algorithm of inside and outside blade profiles and the direction determining algorithm of pressure and suction sides. Then the groups of slot windows with different sizes were created by employing specific data structure to store the window groups information. Finally, a rapid trailing edge slots modeling program was de-veloped based on UG Open API, and the modeling result validates the feasibility of the method.
Abstract: The UH-60A helicopter nonlinear flight dynamic model suited to evaluate the flying qualities was built. Trim calculation of the model was conducted, stability and controllability derivatives were calculated, and the agreement between the computational results and the referenced data indicated that the model is feasible and effective. The open-loop flying qualities of the UH-60A helicopter were studied by using flying qualities specification of military helicopter (GJB902—90). According to the requirements, the change of the UH-60A dynamic response characteristics and the control characteristics were computed and compared when the selected aerodynamic configuration parameters were adjusted, the flying qualities sensitivities with respect to the parameters were analyzed. The results show that, changing the rotor height has a significant impact on each quality, the decrement of tail rotor height can improve roll attitude change level, and the tail rotor longitudinal position is a major factor affecting yaw attitude change and yaw attitude response.
Abstract: To the synthetic aperture radar (SAR) imaging system which uses compressive sensing (CS) technology, radio frequency interference (RFI) would undermine the priori sparse condition and cause deterioration of image quality, making the subsequent reconstruction algorithm complete the imaging process incorrectly. A RFI suppression method of CS SAR was proposed. The greedy algorithm combined with minimum description length (MDL) criteria was used to estimate the RFI components sparsity, according to the RFI sparse characteristics in the frequency domain. For each pulse data, the RFI signal components were estimated and filtered in the time domain directly. Then conventional CS SAR reconstruction algorithm can be applied to achieve imaging output. The simulation results of L-band SAR data verify the effectiveness of this method.
Abstract: To completely meet the requirements of reliability design in the product designing, an axiom-based designing-in reliability approach was proposed. In light of the axiomatic design principles, products were designed preliminarily to establish their functional requirements, so that according to these the preservation requirements were augmented (the functions preserving requirements constitute a functional requirement preserving domain that is included in functional domain), which derived the parameterized solution for reliability design systematically. Subsequently, the design parameters were augmented and optimized to achieve the functions preserving requirements. Mapping model of the augmented functional domain, the physical domain was established. And a solutions evaluation approach based on independence axiom was proposed. Being exemplified by the design of a temperature sensor, the present study demonstrates that all approaches are feasible, efficient, and could be applied in real engineering scenarios.
Abstract: To solve the problem of high requirements for efficiency and reliability of air ammunition support, on the basis of analyzing impact of each activity on completing assignment in program evaluation and review technique(PERT) networks of support process, activity criticality index, crucial index and complete probability on time of activity were collected to establish evaluation indexes system of support crew allocation scheme, which was indicated as the form of evaluation function. Simulation of PERT networks based on Monte Carlo method was taken as the core, and optimal allocation model of support crew was established to optimize the scheme in the framework of genetic algorithm. Example analysis shows the validity and application of the proposed method with which optimal allocation scheme of support crew is found, and critical activities with focus are evaluated.
Abstract: Considering morphing vehicles with alterable sweep wings, control design and synthesis within full flight envelope was researched. The morphing vehicle model based on switched polytopic systems was established. In this framework, the stability analysis was accomplished by Lyapunov functions. The presented approach can guarantee the flight stability of the morphing vehicle within full flight envelope. A technique using the small convex hull algorithm was provided to select operating points from the 3-D flight envelope. Optimal control laws were also designed for linear models of operating points. To inherit the advantage of traditional methods, a specific interpolation method was proposed to make the control synthesis within the 3-D flight envelope brief and practical. Simulation results show that the proposed approach can guarantee flight performance during the fast reshaping of the morphing vehicles within full flight envelope.
Abstract: A kind of disturbance rejection sliding mode control based on backstepping method was studied for trajectory tracking control problem of hypersonic flight vehicle in the presence of uncertain parameters and external disturbances. The nonlinear hypersonic vehicle dynamics model was translated into the strict feedback form under reasonable hypothesis. Sliding-mode control was used in the design of each step. The parameters uncertainty and external disturbances were regarded as disturbance to the system. Directed at the disturbances problem, the estimate method using extended state observer was put forwards. The disturbances were compensated in the controller based on the value estimated. The estimate value of disturbance from extended state observer was in a small neighborhood of the true value, so that the compensating effect can be guaranteed. The simulation based on the nonlinear model under 0.5° additional angle and 25% aerodynamic coefficient offset validates the disturbances rejection ability and good tracking performance of the closed loop system.
Abstract: Mental workload is one of the most important factors that affect flight safety. Objective measurement for pilot mental workload is of great significance for the ergonomics evaluation and optimal design of mental tasks in aircraft cockpit display interface. On the basis of event related potential (ERP) technology, measurement and evaluation of three levels of mental workloads during flight simulation task were carried out. Mismatch negativity (MMN) and P3a components were recorded and selected as evaluation indices under three stimulus "oddball" paradigm. Experiment results show that the peak amplitudes of MMN and P3a are both sensitive to mental workloads. Increased MMN and decreased P3a were found under the high mental workload condition, indicating a more engaged change-detection and much reduced involuntary orienting of attention. Compared with the amplitudes of MMN and P3a elicited by novel stimulus, the ones elicited by task-irrelevant deviant stimulus had better sensitivity to mental workload related to flight task and can be available for further mental workload classification.
Abstract: The dynamic model of hose-drogue aerial refueling system is unduly predigested in the research of autonomous aerial refueling, while high cost, computational complexity and inextensible limitation of hose are not solved by the available modeling methods. In order to overcome above problems, a dynamic modeling of hose-drogue aerial refueling system was presented based on the lumped parameter method. The hose was modeled by a series of variable length pendulums-connected rigid links. A set of governing equations of hose 3-D motion was derived subject to reeling in/out of hose, tanker motion, gravity and aerodynamic loads accounting for the effects of steady wind, atmospheric turbulence and tanker wake. The linear algebraic equations for the hose tensions was obtained from restrictions of pendulum's length. Reasoning from the equations, stability and applied bound for model were determined. Numerical simulations show a good correlation of the model's steady-state characteristics, including drag, position of drogue, compared with previously reported test data. Also the dynamic characteristics of the drogue assembly resulting from reeling out of hose, a typical roll maneuver of the tanker, tanker wake and the process of hose whip phenomenon were investigated. Finally, the simulation results show the effectiveness of the model.
Abstract: In the face of the phenomenon of low overpressure of military airplane cockpits in our country, the design thought of high overpressure cockpits was proposed to realize high work efficiency and comfortable cockpit environment. To solve the contradiction between cockpit weight and environmental efficiency, a solution of using composite material to replace aluminium alloy was put forward and then the cockpit optimization was performed by means of the First-Order Radio optimization algorithm. The overpressure value increased by 37.5% from 44 kPa to 55 kPa, and the cockpit weight decreased by 26.1%. Based on the constitutive relation describing material properties, finite element models analyzing the effect of material property parameters on structures were established, also, sensitivity analysis algorithm of Morris was introduced to model parameters analysis. The results show that the major parameters that affect structures are elasticity modulus and Poisson ratio of skin and circumferential reinforcing ribs. And then some suggestions about material design were proposed based on analysis results and the conclusion can provide reference for the design of high overpressure cockpit.
Abstract: Based on the deterministic basis of the surface accuracy for the antenna, computational modeling with the semi-optical path difference as minimum value was established. As a result, a software program for surface measurement and adjustment of reflector antenna was developed. The surface accuracy of the high-precision reflector antenna was measured and antenna feed was positioned using free fixing. The surface accuracy of central zone for the large parabolic reflector antenna is 26 μm. Electrical performance test results show that the compact range has excellent electrical performance in the frequency of 26~110 GHz, and verify the correctness of the mechanical accuracy test results. This technique not only improves the efficiency of mechanical alignment significantly, but also possesses potential applicable value in engineering.
Abstract: In order to apply high level architecture (HLA) in some real time systems, real-time performance of run-time infrastructure (RTI) must be guaranteed. Because of precedence constraints of correlated tasks between federates, it is hard to provide predictable response for all tasks, and it is also difficult to ensure the real-time performance of all tasks, especially aperiodic ones. The double-earliest deadline first (D-EDF) strategy of how to schedule overall periodic and aperiodic tasks inside a federate was discussed from the point view of task scheduling theory. The policy can not only discard some redundant data to ensure the periodic tasks completed effectively before their deadlines, but also schedule aperiodic ones running regularly to improve their real-time responding speed. It makes the system effectively handle the tasks with precedence constraints and consequently improves the real-time performance of RTI. The feasibility of the D-EDF scheduling strategy was proved.
Abstract: Sneak circuit analysis is an important reliability analysis step in circuit design. With the scale enlargement of the circuit system, analyzing the circuit integrally increased the analysis time as well as the space occupied by the analysis process. While using sneak circuit analysis in complex circuit network, it was divided into several subnet modules using the spectral bisection method based on the Laplace matrix. Making each subnet module equaled to special device by the depth-first method's application according to the combination state of its internal element. Through the sneak circuit analysis of each subnet module and the whole analysis of the simplified circuit, the system's sneak circuit analysis was completed. The electric circuit analysis model was simplified by using the sneak circuit partition analysis method. What's more, the intelligent and automation level of sneak circuit analysis was improved.
Abstract: A kind of multi-missile distributed cooperative guidance and control method for coordinated attacking maneuvering target in three-dimensional space was proposed based on the principle of network synchronization. A kind of suitable three-dimensional position synchronization algorithm was designed. The target was seen as a leader and made up a "leader-followers" topology with missiles. The synchronization algorithm gave out the speed commands of each missile in three directions. Velocity and trajectory angle commands which can be tracked by autopilot were got based on the coordinate transformation theory. Switching control method was used in designing autopilot, which realized closed loop simulation. The simulation results demonstrate the effectiveness of this method.
Abstract: In order to solve the regression problems of nonlinear data and nonlinear function, the support vector machine (SVM) sequential minimal optimization (SMO) algorithm was adopted. The original SMO algorithm has deficiencies such as low training speed and instability training results. To accelerate the training process of SMO algorithm and promote training stability of the solution, the SMO algorithm was improved by updating the optimization multipliers method, using double threshold values, caching kernel function outputs, adding stop criterion. Simulation results show that the improved algorithm performs well for regression of nonlinear data and nonlinear function, and it has faster training speed and better training result stability than original SMO algorithm.
Abstract: Considering relatively higher requests of complexity of decoding algorithms due to the demand of higher decoding speed in some telecommunication systems, a multistage decoding algorithm was given based on the multilevel structure of block coding modulation (BCM). Each stage of the algorithm refers to decoding of each component code in BCM: From the first component code to the last one, each component code was decoded by a soft-decision decoder based on the judgment of the maximum likelihood progressively, thus the decoding complexity was decreased. As is illustrated in the results of the simulation, the error performance of the system applying this algorithm is approximately the same as the error performance of the system applying the Viterbi decoding algorithm, and the former is even much better than the latter when the signal-noise ratio is relatively lower, while the decoding complexity of the former is much lower than that of the latter.
Abstract: How the tool wear and milling parameters influence the work hardening in the process of face milling TB6 was studied to figure out the principles of work hardening. The results show that among the parameters selected in the experiments, the work hardening degree ranges from 107% to 112% and the depth of work hardening ranges from 18 μm to 36 μm. The work hardening degree decreases with the increasing of velocity of milling, while the changes of feed and depth of cut show no obvious impacts on it. The amount of flank wear(VB) influences the work hardening a lot. The depth of work hardening changes from 30 μm to 55 μm, when VB increases from 0 to 0.2 mm, while it increases to 130 μm when VB reaches to 0.35 mm. The material softens not deep below the surface and it is more apparent when VB is increasing.
Founded: 1956 (
Sponsor: Ministry of Industry and Information Technology of the People's Republic of China
Sponsored by: Beijing University of Aeronautics and Astronautics