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Control Allocation of Solar Sail Tip Vanes with Two Degrees of Freedom

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2016年第8期39卷 1857-U239页

作者： Choi, Mirue Damaren, Christopher J. Univ Toronto N York ON M3H 5T6 Canada Univ Toronto Inst Aerosp Studies 4925 Dufferin St N York ON M3H 5T6 Canada BlackBridge Kurfurstendamm 22 D-10719 Berlin Germany AIAA Reston VA USA

A method for solving the control allocation problem posed by four 2-DOF vanes on a square solar sail was presented. numerical examples were provided that demonstrated the feasibility of the algorithm. The algorithm presented is not complete because there are other factors that must be taken into account. One such factor is the nonlinearity of the reflective surface of the vane, which would change the shape of the attainable moment set (AMS) and render the analytic solution to the single-vane problem invalid. The change in AMS will be static and hence can be accounted for from the ground-testing phase. Another factor is the structural dynamics of the booms to which the vanes are attached, which would render the AMS time-dependent. This is a critical issue that could render the derived solution useless because the AMS will need to be recalculated on the fly or the initial derivation of the estimated AMS will somehow need to include the structural dynamics factor.

关键词： Degrees of Freedom Solar Sail Center of Pressure numerical algorithms Structural Dynamics Control Moment Gyros Solar Radiation Astronomical Unit Convex Optimization Reaction Wheels

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An incremental micro-macro model for porous geomaterials with double porosity and inclusion

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INTERNATIONAL JOURNAL OF PLASTICITY 2016年 83卷 37-54页

作者： Shen, W. Q. Shao, J. F. Hubei Univ Technol Coll Civil & Architecture Engn Wuhan Peoples R China Univ Lille CNRS UMR 8107 Lab Mech Lille F-59655 Villeneuve Dascq France

This paper is devoted to micro-mechanical analysis of heterogeneous rock-like materials with two populations of pores as well as mineral inclusions. This work is an extension of the previous works devoted to materials with a single population of pores in (Shen et al., 2012, 2013a,b). A three-step homogenization procedure is developed. During the first step, the effective plastic yield function is determined in an analytical form for a porous medium constituted of Drucker-Prager solid matrix and microscopic pores. An analytical effective plastic yield function is then obtained by the second homogenization step for a porous materials containing a porous matrix and mesoscopic pores. During the last step, the macroscopic plastic behavior of heterogeneous materials is determined by considering effects of mineral grains and by using an incremental approach. In parallel, the effective elastic properties of heterogeneous materials are also estimated by the three-step homogenization procedure with a Mori-Tanaka scheme by considering effects of two populations of pores and inclusions. A non-associated plastic potential is also postulated. The proposed model is applied to two typical heterogeneous rock-like materials, claystone and mortar. Comparisons between numerical results and experimental data show that the micro-mechanical model is able to capture main features of a class of rocic-like materials with complex micro-structures. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Microstructures Voids and inclusions Constitutive behaviour Elastic-plastic material numerical algorithms

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Novel approach to FE solution of crack problems in the Laplacian-based gradient elasticity

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MECHANICS OF MATERIALS 2016年第Apr.期95卷 28-48页

作者： Skalka, Petr Navratil, Petr Kotoul, Michal Brno Univ Technol Inst Solid Mech Mechatron & Biomech Tech 2 Brno 61669 Czech Republic

Stress/strain concentration around a crack tip in ceramic foam-like structures, where the characteristic size of the foam cell is comparable with a typical length over which field quantities change significantly, is analysed. It is convenient to replace the foam structure by an effective continuum which retains all necessary characteristic features of the foam. To this end a homogenized cracked open cell ceramic foam is analysed using the strain/stress model based upon an implicit dependence of the non-local stress and strain on the local stress and strain in the form of an inhomogeneous Helmholtz equation which is solved together with the equilibrium equations. To preserve the advantage of the uncoupled system of equations, which means that one set of equations is solved prior the other one and that two sets of shape functions can be chosen independently, a recurrent sequence of well posed boundary value problems is constructed which can be solved using a classical 8-nodes isoparametric element for 2-D problems. The key idea behind the suggested procedure consists in replacing the scale parameter l by a parameter increment Delta l chosen arbitrarily small. The given small disturbance causes a redistribution of the local stress/displacement field. After the new local stress/displacement field is known, another disturbance is introduced and so on. The procedure is stopped when the solution, exhibiting boundary layer behaviour, leads to the cohesive-like zone with length reaching a value uniquely related to the scale parameter l. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Ceramic material Foam material Gradient elasticity Stress concentrations Finite elements numerical algorithms

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Stationary state distribution and efficiency analysis of Langevin dynamics in physical and unphysical regions

Stationary state distribution and efficiency analysis of Lan...

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第十三届全国量子化学会议

作者： Dezhang Li Xu Han Yichen Chai Cong Wang Jian Liu Jiushu Shao Beijing National Laboratory for Molecular Sciences Institute of Theoretical and Computational ChemistryCollege of Chemistry and Molecular EngineeringPeking University College of Chemistry and Center for Advanced Quantum Studies Key Laboratory of Theoretical and Computational PhotochemistryMinistry of EducationBeijing Normal University

Langevin dynamics is a typical thermostat for canonical MD simulations. Various schemes may be proposed for numerical integration of the Langevin equation. Accuracy and efficiency of the simulation strongly replies on the numerical algorithm employed to solve the Langevin equation. In this article, we study twelve useful schemes for Langevin dynamics. For both the stationary state distribution and the characteristic correlation time of the one-dimensional harmonic system, we introduce two approaches to investigate the twelve schemes. They include a direct approach that is based on the trajectory of Langevin dynamics, and an indirect approach that employs the mean value and the phase space propagator. All the schemes are employed in the MD simulations of two model systems(harmonic potential and quartic potential).

关键词： Langevin dynamics numerical algorithms stationary state distribution characteristic correlation time

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Online Parameter Estimation for Model-Based Force Control in Milling Processes

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IFAC-PapersOnLine 2016年第12期49卷 634-639页

作者： Petruck, Henning Schlick, Christopher M. Stemmler, Sebastian Abel, Dirk Adams, Oliver Klocke, Fritz Institute of Industrial Engineering and Ergonomics RWTH Aachen University Germany Institute of Automatic Control RWTH Aachen University Aachen Germany Laboratory for Machine Tools and Production Engineering RWTH Aachen University Aachen Germany

In order to adapt to a milling machine's changing behavior while operating due to changing tool-workpiece contact conditions adaptive controllers are an advantageous approach to control the machine's feed rate. Otherwise inaccuracies can occur leading to poor quality. In this paper Model Predictive Control (MPC) is used to control the feed rate of the machine. By applying a parameterized model to the current state of the milling process its future trend can be predicted. An n-th order system with delay time is used to model the behavior of the milling machine's velocity control loop. By continually re-estimating the model parameters at run time, the controller adapts to the current machine behavior. We developed solutions of the maximum likelihood estimators of the model's independent parameters for a state-space representation that can be numerically efficiently calculated. These estimators can be used to estimate the parameters of the n-th order system and the delay time iteratively based on the collected process data. Two validation studies, one emulating an online estimation based on real data from the five-axis machining center Mazak Variaxis 630II-T, and one simulation study with a simulated machine, were carried out to validate the iterative parameter estimation algorithm. In these studies, the time variant model, whose parameters are re-estimated on the basis of the developed estimators, is compared to a time invariant model, for which the controller does not adapt to changing machine behavior. © 2016

关键词： Parameter estimation Adaptive control systems Controllers Identification (control systems) Iterative methods Least squares approximations Machining centers Maximum likelihood estimation Milling (machining) Milling machines Model predictive control numerical methods Predictive control systems State space methods Adaptive Control Least squares methods Model based controls numerical algorithms State space models

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AIAA policy statements and manuscript review process

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Journal of Aircraft 2017年第1期54卷 8-10页

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Construction of continuous and piecewise affine Lyapunov functions via a finite-time converse

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IFAC-PapersOnLine 2016年第18期49卷 13-18页

作者： Steentjes, Tom R.V. Doban, Alina I. Lazar, Mircea Department of Electrical Engineering Eindhoven University of Technology Netherlands

A novel numerical Massera-type approach for the computation of Lyapunov functions (LFs) for nonlinear continuous-time systems is presented. The construction is enabled by verifying a finite-time decrease condition for a candidate function, which is allowed to be any K∞function of the norm of the state, and applying a converse Lyapunov theorem. In the construction we make use of approximated system trajectories and we obtain a continuous and piecewise affine (CPA) LF. By optimization, the obtained CPA LF is verified and an estimate of the domain of attraction is obtained. Several examples are presented for illustration and demonstration of the effectiveness of the proposed approach. © 2016

关键词： Continuous time systems Computation theory Computational methods Lyapunov functions Lyapunov methods Nonlinear systems numerical methods Approximated system Converse Lyapunov theorem Domain of attraction Nonlinear continuous time systems numerical algorithms Piecewise affines Stability analysis Stability domains

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Stationary state distribution and efficiency analysis of Langevin dynamics in real dynamics and virtual dynamics regions

Stationary state distribution and efficiency analysis of Lan...

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第十五届全国化学动力学会议

作者：李德彰 Xu Han Yichen Chai Cong Wang Jian Liu Jiushu Shao Beijing National Laboratory for Molecular Sciences Institute of Theoretical and Computational ChemistryCollege of Chemistry and Molecular EngineeringPeking University College of Chemistry and Center for Advanced Quantum Studies Key Laboratory of Theoretical and Computational PhotochemistryMinistry of EducationBeijing Normal University

关键词： Langevin dynamics numerical algorithms stationary state distribution characteristic correlation time

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An Analysis of the Matrix Equation AX + <(Xover bar>B = C

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COMPUTATIONAL MATHEMATICS AND MATHEMATICAL PHYSICS 2016年第9期56卷 1536-1539页

作者： Ikramov, Kh. D. Moscow MV Lomonosov State Univ Fac Computat Math & Cybernet Moscow 119992 Russia

The matrix equation AX + XI"B = C, where XI"B is obtained by the entry-wise conjugation of X, is examined. On the basis of analogy with the Sylvester matrix equation, special cases are distinguished where the former equation corresponds to normal and self-adjoint Sylvester equations. Efficient numerical algorithms are proposed for these special cases.

关键词： Sylvester matrix equation BHH-equation normal matrix conjugate-normal matrix unitary similarity unitary congruence numerical algorithms

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Online Parameter Estimation for Model-Based Force Control in Milling Processes

Online Parameter Estimation for Model-Based Force Control in...

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8th IFAC Conference on Manufacturing Modelling, Management and Control (MIM)

作者： Petruck, Henning Schlick, Christopher M. Stemmler, Sebastian Abel, Dirk Adams, Oliver Klocke, Fritz Rhein Westfal TH Aachen Inst Ind Engn & Ergon Aachen Germany Rhein Westfal TH Aachen Inst Automat Control Aachen Germany Rhein Westfal TH Aachen Lab Machine Tools & Prod Engn Aachen Germany

In order to adapt to a milling machines changing behavior while operating due to changing tool-workpiece contact conditions adaptive controllers are an advantageous approach to control the machines feed rate. Otherwise inaccuracies can occur leading to poor quality. In this paper Model Predictive Control (MPC) is used to control the feed rate of the machine. By applying a parameterized model to the current state of the milling process its future trend can be predicted. An n-th order system with delay time is used to model the behavior of the milling machines velocity control loop. By continually re-estimating the model parameters at run time, the controller adapts to the current machine behavior. We developed solutions of the maximum likelihood estimators of the models independent parameters for a state-space representation that can be numerically efficiently calculated. These estimators can be used to estimate the parameters of the n-th order system and the delay time iteratively based on the collected process data. Two validation studies, one emulating an online estimation based on real data from the five-axis machining center Mazak Variaxis 630II-T, and one simulation study with a simulated machine, were carried out to validate the iterative parameter estimation algorithm. In these studies, the time variant model, whose parameters are re-estimated on the basis of the developed estimators, is compared to a time invariant model, for which the controller does not adapt to changing machine behavior. (C) 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

关键词： Adaptive Control Iterative Methods Least-Squares Method numerical algorithms Parameter Identification Model Based Control State-Space Models System Identification

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