Wang P.,National University of Defense Technology |
Liu Q.J.,Science and Technology on Space Physics Laboratory
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016
A six-degree-of-freedom near-space hypersonic vehicle model is developed for control studies. This vehicle model has fast variability, is highly nonlinear, multivariable, and coupled, and includes parametric uncertainties. To improve the robustness of the attitude control system, a terminal sliding mode control is proposed and used for the design of attitude controller of a near-space hypersonic vehicle. Because the sliding surface is identical to zero, the approach process of SMC does not exist, which insures that the closed-loop control system is steady and has robustness along all system trajectories. In order to guarantee the performance of the control system, simulations are conducted for the responses of the commands of pitch angle, yaw angle, and rolling angle. The simulations demonstrate that the proposed attitude controller is robust with respect to the parametric uncertainties and atmospheric disturbances. © 2016 IEEE.
Guo Z.,Beijing University of Chemical Technology |
Lu T.,Beijing University of Chemical Technology |
Liu B.,Science and Technology on Space Physics Laboratory
Journal of Thermal Science | Year: 2017
Turbulent penetration can occur when hot and cold fluids mix in a horizontal T-junction pipe at nuclear plants. Caused by the unstable turbulent penetration, temperature fluctuations with large amplitude and high frequency can lead to time-varying wall thermal stress and even thermal fatigue on the inner wall. Numerous cases, however, exist where inner wall temperatures cannot be measured and only outer wall temperature measurements are feasible. Therefore, it is one of the popular research areas in nuclear science and engineering to estimate temperature fluctuations on the inner wall from measurements of outer wall temperatures without damaging the structure of the pipe. In this study, both the one-dimensional (1D) and the two-dimensional (2D) inverse heat conduction problem (IHCP) were solved to estimate the temperature fluctuations on the inner wall. First, numerical models of both the 1D and the 2D direct heat conduction problem (DHCP) were structured in MATLAB, based on the finite difference method with an implicit scheme. Second, both the 1D IHCP and the 2D IHCP were solved by the steepest descent method (SDM), and the DHCP results of temperatures on the outer wall were used to estimate the temperature fluctuations on the inner wall. Third, we compared the temperature fluctuations on the inner wall estimated by the 1D IHCP with those estimated by the 2D IHCP in four cases: (1) when the maximum disturbance of temperature of fluid inside the pipe was 3°C, (2) when the maximum disturbance of temperature of fluid inside the pipe was 30°C, (3) when the maximum disturbance of temperature of fluid inside the pipe was 160°C, and (4) when the fluid temperatures inside the pipe were random from 50°C to 210°C. © 2017, Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg.
Zhang L.,Shanghai JiaoTong University |
Wu G.-H.,Shanghai JiaoTong University |
Wang S.-H.,Science and Technology on Space Physics Laboratory |
Ding W.-J.,Shanghai JiaoTong University
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2012
The effects of cooling conditions on the microstructure of semi-solid AZ91 slurry produced via ultrasonic vibration process were investigated. AZ91 melts were subjected to ultrasonic vibration in different temperature ranges under different cooling rates. The results show that fine and spherical α-Mg particles are obtained under ultrasonic vibration at the nucleation stage, which is mainly attributed to the cavitation and acoustic streaming induced by the ultrasonic vibration. The reduction of lower limit of ultrasonic vibration temperature between the liquidus and solidus increases the solid volume fraction and average particle size. Increasing cooling rate increases the solid volume fraction and reduces the average shape factor of particles. The appropriate temperature range for ultrasonic vibration is from 605 °C to 595 °C or 590 °C, and the suitable cooling rate is 2-3 °C/min. © 2012 The Nonferrous Metals Society of China.
Cao L.,Shanghai JiaoTong University |
Liu W.-C.,Shanghai JiaoTong University |
Li Z.-Q.,Shanghai Aviation Precision Machinery Research Institute |
Wu G.-H.,Shanghai JiaoTong University |
And 3 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2014
The microstructure, mechanical properties and fracture behavior of sand-cast Mg-10Gd-3Y-0.5Zr alloy (mass fraction, %) under T6 condition (air cooling after solid solution and then aging heat treatment) were investigated. The optimum T6 heat treatments for sand-cast Mg-10Gd-3Y-0.5Zr alloy are (525 °C, 12 h + 225 °C, 14 h) and (525 °C, 12 h + 250 °C, 12 h) according to age hardening curve and mechanical properties, respectively. The ultimate tensile strength, yield strength and elongation of the Mg-10Gd-3Y-0.5Zr alloy treated by the two optimum T6 processes are 339.9 MPa, 251.6 MPa, 1.5% and 359.6 MPa, 247.3 MPa, 2.7%, respectively. The tensile fracture mode of peak-aged Mg-10Gd-3Y-0.5Zr alloy is transgranular quasi-cleavage fracture. © 2014 The Nonferrous Metals Society of China.
Liu W.,Shanghai JiaoTong University |
Jiang L.,Shanghai JiaoTong University |
Cao L.,Shanghai JiaoTong University |
Mei J.,Shanghai JiaoTong University |
And 5 more authors.
Materials and Design | Year: 2014
In this study, the tensile properties, high cycle fatigue behavior and plane-strain fracture toughness of the sand-cast Mg-10Gd-3Y-0.5Zr magnesium alloy were investigated, comparison to that of sand-cast plus T6 heat treated magnesium alloy which named after sand-cast-T6. The results showed that the tensile properties of the sand-cast alloy are greatly improved after T6 heat treatment, and the fatigue strength (at 107cycles) of the sand-cast Mg-10Gd-3Y-0.5Zr magnesium alloy increases from 95 to 120MPa after T6 heat treatment, i.e. the improvement of 26% in fatigue strength has been achieved. The plane-strain fracture toughnesses KIC of the sand-cast and sand-cast-T6 alloys are about 12.1 and 16.3MPam1/2, respectively. In addition, crack initiation, crack propagation and fracture behavior of the studied alloys after tensile test, high cycle fatigue test and plane-strain fracture toughness test were also investigated systematically. © 2014 Elsevier Ltd.
Di X.-G.,Harbin Institute of Technology |
Kong Q.-X.,Harbin Institute of Technology |
Yu Y.,Science and Technology on Space Physics Laboratory
Yuhang Xuebao/Journal of Astronautics | Year: 2013
Considering the low efficiency of aerodynamic fins for the reentry hypersonic vehicle, the compound control actuators with moving masses and aerodynamic fins are introduced and the control allocation problem between them is researched. Besides, against strong nonlinearity and uncertainty of the vehicle, the adaptive dynamic inverse attitude control system based on the neural network (NN) is designed. Firstly, the principle of the configuration of masses and the compound control-oriented model are given. Secondly, in order to obtain a good control allocation accuracy and low energy consumption of actuators, a control allocation strategy is provided on the basis of the quadratic programming method. Thirdly, to approximate the system uncertainty and compensate the dynamic inversion error, the nonlinear dynamic inversion attitude control system based on NN with weights updating is designed. Finally, the simulation results show the effectiveness of the control allocation strategy and the adaptive dynamic inverse method in their application of attitude control of the hypersonic vehicle.
Kang L.,Science and Technology on Space Physics Laboratory |
Ting X.,CCID Consulting Co.
2015 International Conference on Logistics, Informatics and Service Science, LISS 2015 | Year: 2015
Cloud computing has officially entered the commercial application stage, which puts forward higher requirements on network load balancing. Leveraging effective load distribution and traffic scheduling algorithm to reasonably allocate the request data between every processing nods to achieve optimal processing capacity of the system is one of the effective ways to improve the utilization of network resources. The unique self-directed learning and reconfiguration capabilities of cognitive network  enable the load balancing to become more effective. Based on research of the existing traffic scheduling algorithm, this paper improves the weighted least connections scheduling algorithm, and designs the Adaptive Scheduling Algorithm Based on Minimum Traffic (ASAMT). ASAMT conducts the real-time minimum load scheduling to the node service requests and configures the available idle resources in advance to ensure the service QoS requirements. Being adopted for simulation of the traffic scheduling algorithm, OPNET is applied to the cloud computing architecture. Experimental results show that, under the premise of no large network cost, the load condition of this algorithm is better than that of the unmodified weighted least connection scheduling algorithm. © 2015 IEEE.
Lu K.,Science and Technology on Space Physics Laboratory |
Xing T.,IDC Beijing Co
International Journal of Computer Science and Applications | Year: 2016
In the era of cloud computing and big data, the demand for real-time data processing and availability poses higher requirements for network load balancing. Cognitive network has unique self-learning and re-configuration abilities that can improve the effectiveness of load balancing. Based on the existing traffic scheduling algorithms, this article will discuss the possibility of improving weighted least-connection scheduling algorithm by leveraging cognitive network. A dynamic load balancing algorithm (NNPMA,Neural Network Prediction Model Algorithm) will be developed on the basis of traffic prediction model. NNPMA can enable least load scheduling in real time for service request from node and configure available idle resources upfront to ensure compliance with QoS. This traffic scheduling algorithm will be simulated with OPNET and it will be applied to cloud computing architecture. The test results indicate that this algorithm can achieve loading performance better than the unimproved weighted least-connection scheduling algorithm without significantly increasing network overhead. © Technomathematics Research Foundation.
Yu P.,Science and Technology on Space Physics Laboratory |
Duan Y.,Science and Technology on Space Physics Laboratory |
Chen J.,Science and Technology on Space Physics Laboratory
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2015
Transition, laminar flow separation and aerodynamic error band are some aerodynamic issues which should be paid more attention to for hypersonic flight. The aerodynamic properties may be influenced obviously and with some uncertainty by transition and laminar flow separation. And how to determine the aerodynamic error band reasonably is also a key for hypersonic flight. These issues and their influences are discussed in this paper mainly from the view point of engineering design. To fulfill the need of hypersonic flight, we should further develop the relevant theoretical analysis and digital simulation technology and raise the technical level of ground tests at wind tunnel. Besides, aerodynamic flight tests should also be emphasized. ©, 2014, AAAS Press of Chinese Society of Aeronautics and Astronautics. All right reserved.
Wang Y.,Science and Technology on Space Physics Laboratory
Proceedings - 8th International Conference on Internet Computing for Science and Engineering, ICICSE 2015 | Year: 2015
This paper analyzes the ablation in a liquid rocket combustion chamber's high altitude simulation tests. Based on the characteristic of combustion chamber and the history of the malfunction, our proposed corrective measure of the chamber and relevant product reliability validation tests were conducted. The validation tests showed that our corrective measure is feasible and relevant reliability met our requirements. The investigation of purchased products should start during the phases of product manufacturing, especially for the design of combustion chamber cooling. © 2015 IEEE.