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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.

Zhang Y.,Shanghai JiaoTong University | Li M.,Shanghai JiaoTong University | Zhang J.,Science and Technology on Space Physics Laboratory | Li G.,Science and Technology on Space Physics Laboratory
Journal of Mechanical Design, Transactions of the ASME | Year: 2016

Uncertainty is unavoidable in engineering design, which may result in variations in the objective functions and/or constraints. The former may degrade the designed performance while the latter can even change the feasibility of the obtained optimal solutions. Taking uncertainty into consideration, robust optimization (RO) algorithms aim to find optimal solutions that are also insensitive to uncertainty. Uncertainty may include variation in parameters and/or design variables, inaccuracy in simulation models used in design problems, and other possible errors. Most existing RO algorithms only consider uncertainty in parameters, but overlook that in simulation models by assuming that the simulation model used can always provide identical outputs to those of the real physical systems. In this paper, we propose a new RO framework using Gaussian processes, considering not only parameter uncertainty but also uncertainty in simulation models. The consideration of model uncertainty in RO could reduce the risk for the obtained robust optimal designs becoming infeasible even if the parameter uncertainty has been considered. Two test examples with different degrees of complexity are utilized to demonstrate the applicability and effectiveness of our proposed algorithm. Copyright © 2016 by ASME.

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 [1] 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.

Shao C.,Zhejiang University | Nie L.,Science and Technology on Space Physics Laboratory | Chen W.,Zhejiang University
Aerospace Science and Technology | Year: 2016

Hypersonic vehicles are enveloped by a plasma sheath that affects the data transmission and object identification. This paper develops a numerical methodology based on Magnetohydrodynamics equations to study the electromagnetic environment of hypersonic vehicles under the condition of carbon-based thermal protection material ablation. A surface ablation model considering the oxidation and sublimation ablation process is coupled with a Navier-Stokes solver by a gas-solid interaction method to simulate the ablation plasma flows. A piecewise linear current density recursive convolution finite-difference time-domain method is applied to further analyze the interaction between the incident electromagnetic wave and the plasma sheath. The computational results for an HTV-2 type vehicle indicate that both ablation and non-ablation plasma sheaths have significant effects on the electromagnetic environment of the vehicle. Compared with a non-ablation plasma sheath, ablation results in a decrease in the number of electrons and increases the number of neutral particles and therefore changes characteristic parameters of the plasma. Details of the electromagnetic scattering characteristics are reported to highlight the influences of ablation on the reflectivity, penetrability, and absorptivity of the plasma sheath for incident electromagnetic waves over different bands. © 2016 Elsevier Masson SAS.

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.

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