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51st AIAA aerospace Sciences Meeting including the New Horizons Forum and aerospace Exposition 2013

作者： Zheng, Borui Wang, Zhongyi Gao, Chao Fang, Hong Xiong, Juntao Liu, Feng Luo, Shijun Northwestern Polytechnical University Department of Fluid Mechanics Xi'an 710072 China Beijing University of Aeronautics and Astronautics Department of Fluid Mechanics Beijing 100191 China Northwestern Polytechnical University National Key Laboratory of Science and Technology Aerodynamic Design and Research Xi'an 710072 China Beijing Institute of Nearspace Vehicle's System Engineering Department of Fluid Mechanics Beijing 100076 China University of California Department of Mechanical and Aerospace Engineering Irvine CA 92697-3975 United States

ISBN: (纸本)9781624101816

High angle of attack flows over a 20° conical forebody are computed by the commercial CFD code ANSYS CFX in this paper. The free-stream velocities are 10 to 70 m/s, the Reynolds number based on the forebody base diameter varies from 0.1×106 to 0.7×106, and the angle of attack ranges from 10° to 35°, the boundary layer is under free transition. The C-O structured meshes are used to compute the entire flow field. The axial and radial grid numbers are 81 and 121, respectively, while the circumferential grid points uniformly distributed with different grid number of 120, 180, 240 and 360, respectively. The pressure distributions over the forebody surface have been computed by three computational models, and the results computed by the transitional model agree well with the experimental data, which were measured over 40 roll angles with equal intervals for each test condition. The computed total pressure coefficient and axial vorticity distributions over the cross-flow section are studied. The three vortex pairs, i.e., the primary, secondary and tertiary vortex, separated from the forebody boundary layer at angle of attack of 15°-35° and wind speed of 10-70m/s are captured. The approximate conical flow features of pressure distribution and primary vortex location are identified. © 2013 by The Authors.

关键词： Angle of attack

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Effect of the scaling of the mechanical properties on the performances of ZnO piezo-semiconductive nanowires

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AIP Conference Proceedings 2014年第1期1603卷

作者： R. Araneo A. Rinaldi A. Notargiacomo F. Bini F. Marinozzi M. Pea G. Lovat S. Celozzi Electrical Engineering Division of DIAEE University of Rome Sapienza Rome via Eudossiana 18 - 00184 Italy University of L'Aquila International Research Center for Mathematics & Mechanics of Complex System MEMOCS Via S. Pasquale 04012 Cisterna di Latina LT Italy and ENEA Research Center Casaccia Via Anguillarese 301 Santa Maria di Galeria 00 Italy Institute for Photonics and Nanotechnology - CNR Via Cineto Romano 42 00156 Rome Italy Mechanical and Aerospace Engineering Department - DIMA University of Rome Sapienza Rome via Eudossiana 18 - 00184 Italy Institute for Photonics and Nanotechnology - CNR Via Cineto Romano 42 00156 Rome Italy Electrical Engineering Division of DIAEE University of Rome Sapienza Rome via Eudossiana 18 - 00184 Italy

Zinc Oxide piezoelectric nanowires may offer unprecedented functional properties for piezotronics and piezoelectrics due to their electrical properties combined to the increased strength. Conventional "bulk" modeling used so far has suggested that "the smaller, the better" is the design tenet to obtain stronger and more reliable systems with higher piezopotential and efficacy. However, prior work has never addressed the interaction between electrical and mechanical size-effects of ZnO NWs, particularly the effect of the mechanical stiffening on the piezoelectric potentials and mechanical-to-electrical conversion efficacy of a NW. In this paper we propose a refined "size-dependent" modeling based on a "double power-law scaling" for the mechanical size-effects, which reveals, though consistent simulations based on the Finite Element Method, that stiffening effects can indeed collide with the electrical size-effects in very small NWs, thus meaning that minimizing the NW diameter does not yield always the best piezo-performance, as purported by standard bulk modeling. Our computations support that the elastic size-effects need to be carefully accounted in the design of ZnO NWs piezo-technology.

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A Terrain Referenced Precision Approach based on LiDAR for Lunar Landing

A Terrain Referenced Precision Approach based on LiDAR for L...

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International Conference on Control, automation and systems

作者： Wonhee Lee Young Min Yoo Sun Min Lee Chan Gook Park School of Mechanical and Aerospace Engineering Seoul National University School of Mechanical and Aerospace Engineering/Automation and Systems Research Institute Seoul National University

ISBN: (纸本)9781467322478

Terrain Referenced Navigation, referred to as TRN, is the one of the multi-sensor integrated navigation systems. And it has recently gained the interest as a backup system of conventional navigation methods due to widespread availabilities. In TRN, the terrain height measurement is correlated with terrain database to correct the position error. TRN is a powerful navigation method in the moon where does not have position fixing methods like GNSS. The terrain height information is used to achieve the navigation performance for precise lunar landing approach. The terrain height information of TRN is obtained using high performance ranging sensor LiDAR (Light Detection And Ranging). LiDAR is well developed showing its potential for TRN. Especially, LiDAR can make the height information which has high accuracy, resolution and update rate. This paper explains the component of TRN based on LiDAR. And we discuss the configuration of precise terrain referenced approach based on LiDAR height measurement for landing on the moon.

关键词： TRN LiDAR Lunar Landing

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Fault tolerant sliding mode control for a nanosatellite

Fault tolerant sliding mode control for a nanosatellite

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International Conference on Control, automation and systems ( ICCAS)

作者： Miri Shin Chul Woo Kang Junkyu Lim Chan Gook Park School of Mechanical and Aerospace Engineering Seoul National University Seoul South Korea School of Mechanical and Aerospace Engineering/Automation and Systems Research Institute Seoul National University Seoul South Korea

This paper describes a nanosatellite attitude control being able to perform fault tolerant control to increase a reliability of a nanosatellite. A fault-tolerant sliding mode controller is used for a nanosatellite using four reaction wheels as a set of actuators. The fault-tolerant sliding mode controller is designed to perform the rest-to-rest maneuver of a satellite system. The actuator fault reflects the degradation of the actuation effectiveness. The Lyapunov theorem is used to analyze the system stability. In computer simulations, we use SNUSAT-1 made in Seoul National University as an applied nanosatellite. The control scheme of a nanosatellite is verified under the actuator fault situation that one reaction wheel of four reaction wheels is fault as well as the normal situation that four reaction wheels are healthy.

关键词： Wheels Actuators Fault tolerance Fault tolerant systems Attitude control Satellites Sliding mode control

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Online Learning Algorithm for Stackelberg Games in Problems with Hierarchy

Online Learning Algorithm for Stackelberg Games in Problems ...

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IEEE Annual Conference on Decision and Control

作者： K. G. Vamvoudakis F. L. Lewis M. Johnson W. E. Dixon Center for Control Dynamical-systems and Computation (CCDC) University of California Automation and Robotics Research Institute University of Texas at Arlington NASA Ames Research Center Department of Mechanical and Aerospace Engineering University of Florida

ISBN: (纸本)9781467320658

This paper presents an online adaptive optimal control algorithm based on policy iteration reinforcement learning techniques to solve the continuous-time Stackelberg games with infinite horizon for linear systems. This adaptive optimal control method finds in real-time approximations of the optimal value and the Stackelberg-equilibrium solution, while also guaranteeing closed-loop stability. The optimal-adaptive algorithm is implemented as a separate actor/critic parametric network approximator structure for every player, and involves simultaneous continuous-time adaptation of the actor/critic networks. Novel tuning algorithms are given for the actor/critic networks. The convergence to the closed-loop Stackelberg equilibrium is proven and stability of the system is also guaranteed. A simulation example shows the effectiveness of the new online algorithm.

关键词： Stackelberg games Hierarchical control problems adaptive optimal control Social Hierarchy Game theory e-learning infinite horizon Best value algorithms

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Finite element modelling and experimental investigation of low frequency electromagnetic technique in pipeline defect detection

Finite element modelling and experimental investigation of l...

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International Conference on Automatic Control and Artificial Intelligence, ACAI 2012

作者： Li, Junru Zhong, Shuncong Yang, Xiaoxiang Gong, Lingzhu Guo, Jinquan Chen, Shiwang Chen, Xiaohan Lin, Tong Ye, Feifei Wen, Zhenxing Yang, Tianxue School of Chemistry and Chemical Engineering Fuzhou University Fuzhou 350108 China School of Mechanical Engineering and Automation Fuzhou University Fuzhou 350108 China Key Laboratory of Safety Science of Pressurized System of Ministry of Education East China University of Science and Technology Shanghai 200237 China Fujian Key Lab of Medical Instrument and Pharmaceutical Technology Fuzhou 350002 China Special Equipment Inspection and Research Institute of Fujian Fuzhou 350001 China

ISBN: (纸本)9781849195379

Finite Element (FE) models of LFET were employed to investigate Low Frequency Electromagnetic Technique (LFET) in pipeline defect detection. Two-dimensional and three-dimensional LFET simulations were carried out using the ANSYS Parametric Design Language (APDL). Magnetic Flux Leakage (MFL) signals of different defects were obtained from the established models. From the simulations and experimental results, the practicality of LFET-based pipe defect detection was demonstrated, therefore, it could be recommended for the applications in non-destructive testing of pipelines such as boiler water wall etc.

关键词： Nondestructive examination

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Improvement of a low cost MEMS inertial-GPS integrated system using wavelet denoising techniques

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International Journal of Aeronautical and Space Sciences 2011年第4期12卷 371-378页

作者： Kang, Chang Ho Kim, Sun Young Park, Chan Gook School of Mechanical and Aerospace Engineering Automation and Systems Research Institute/The Institute of Advanced Aerospace Technology Seoul National University Seoul 151-744 Korea Republic of

In this paper, the wavelet denoising techniques using thresholding method are applied to the low cost micro electromechanical system (MEMS)-global positioning system(GPS) integrated system. This was done to improve the navigation performance. The low cost MEMS signals can be distorted with conventional pre-filtering method such as low-pass filtering method. However, wavelet denoising techniques using thresholding method do not distort the rapidly-changing signals. They can reduce the signal noise. This paper verified the improvement of the navigation performance compared to the conventional pre-filtering by simulation and experiment. © The Korean Society for Aeronautical & Space Sciences.

关键词： MEMS

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An extended scalar adaptive filter for Mitigating sudden abnormal signals of guided missile

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International Journal of Aeronautical and Space Sciences 2011年第1期12卷 37-42页

作者： Lim, Jun Kyu Park, Chan Gook School of Mechanical and Aerospace Engineering The Institute of Advanced Aerospace Technology/Automation and Systems Research Institute Seoul National University Seoul 151-744 Korea Republic of

An extended scalar adaptive filter for guided missiles using a global positioning system receiver is presented. A conventional scalar adaptive filter is adequate filter for eliminating sudden abnormal jumping measurements. However, if missile or vehicle velocities have variation, the conventional filter cannot eliminate abnormal measurements. The proposed filter utilizes an acceleration term, which is an improvement not used in previous conventional scalar adaptive filters. The proposed filter continuously estimates noise measurement variance, velocity error variance and acceleration error variance. For estimating the three variances, an innovation method was used in combination with the least square method for the three variances. Results from the simulations indicated that the proposed filter exhibited better position accuracy than the conventional scalar adaptive filter. © The Korean Society for Aeronautical & Space Sciences.

关键词： Adaptive filters

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Evaluation of crash energy absorption capacity of a tearing tube

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2010 Annual Conference on Experimental and Applied Mechanics

作者： Ko, Younki Ahn, Kwanghyun Huh, Hoon Choi, Wonmok Jung, Hyunseung Kwon, Taesoo School of Mechanical Aerospace and System Engineering KAIST 335 Gwahak-ro Yuseong-gu Daejeon 305-701 Korea Republic of Railway System and Safety Research Department Korea Railroad Research Institute 301-1 Wulam-dong Uiwang-si Gyeonggi-do 437-757 Korea Republic of

ISBN: (纸本)9781441994974

This paper deals with the numerical prediction of energy absorption capacity of a tearing tube, which can absorb the crash energy through expanding and axial splitting processes. It is important to consider the dynamic material behavior and fracture characteristics of tube material in order to simulate the deformation behavior of a tearing tube accurately. Uniaxial tensile tests are performed in order to obtain the flow stress curve and the fracture strain of a tube material according to the strain rate. Quasi-static tensile tests were carried out in the range of strain rates from 0.001/sec to 0.01/sec using a static tensile testing machine. Dynamic tensile tests were conducted at strain rates ranged from 0.1/sec to 300/sec using a high speed material testing machine. These dynamic material properties are utilized to finite element analysis through a user material subroutine of ABAQUS/Explicit. Especially, ductile fracture criteria are adopted in order to describe the fracture characteristics of a tube material during axial splitting process. Dynamic tearing cases are simulated and the reliability of numerical results is verified by comparing them with the experimental results in dynamic tearing tests. The simulated results accurately predict the onset of fracture in axial splitting process and the energy absorption capacity has a good agreement with experimental results. ©2010 Society for Experimental Mechanics Inc.

关键词： Strain rate

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Helicopter aeroelastic analysis in forward flight using dynamic wake model

Helicopter aeroelastic analysis in forward flight using dyna...

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29th AIAA Applied Aerodynamics Conference 2011

作者： Lee, Joonbae Oh, Sejong Yee, Kwanjung Yoo, Seung-Jae Jeong, Min-Soo Lee, In Kim, Deog-Kwan Department of Aerospace Engineering Pusan National University San30 Jangjeon-dong Geumjeong-gu Busan 609-735 Korea Republic of School of Mechanical Aerospace Engineering Korea Advanced Institute of Science and Technology 335 Gwahangno Yuseong-gu Daejeon 305-701 Korea Republic of Department of Rotor System Korea Aerospace Research Institute 115 Gwahangno Yuseong-gu Daejeon 305-333 Korea Republic of

ISBN: (纸本)9781624101458

In this study, the aeroelastic analysis of rotorcraft in forward flight has been performed using dynamic wake model to handle unsteady aerodynamics. The quasi-steady airload model based on the blade element method has been coupled with dynamic wake model developed by Peters and He. The nonlinear steady response to periodic motion is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim for stability analysis. The aerodynamic and structural characteristics of dynamic wake model are validated against other numerical analysis results by comparing induced inflow and blade tip deflections(flap, lag). In addition, mechanism of aeroelastic instability will be investigated by evaluating the aeroelastic stability using different linear inflow and dynamic wake models at a low advance ratio. As the influences of nonlinearity result in significant differences in the blade deflection behavior and aeroelastic characteristics, an appropriate analysis is required to capture these attributes. The dynamic wake model is more accurate than the linear inflow model is at low advance ratios (0.0 ≤ μ ≤ 0.15) yet more time-effective than 3-D aerodynamic models. Thus it is most suitable for aeroelastic analysis in the preliminary design of a helicopter.© 2011 by the American institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Nonlinear equations

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