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Precise Determination of Reachable Domain for Spacecraft with Single Impulse

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2014年第6期37卷 1767-1779页

作者： Wen, Changxuan Zhao, Yushan Shi, Peng Beihang Univ Sch Astronaut Beijing 100191 Peoples R China

Reachable domain refers to the collection of all positions accessible for a spacecraft under a given initial orbit and fuel constraint with free time of flight. In this study, the fuel constraint is conveniently expressed by a single available velocity impulse. To solve the envelope of the reachable domain, the radius of an accessible target position in a given direction is formulated. By evaluating the extreme values of the accessible radius in the given direction, two reachable boundaries and a reachable line segment are solved. The reachable domain in three-dimensional space is determined by rotating the direction and tracing all the reachable boundaries. The proposed method successfully solves the envelope of the reachable domain for the remaining two unresolved scenarios: the reachable domain with an arbitrary maneuver point and arbitrary impulse direction and the reachable domain with an arbitrary maneuver point and fixed impulse direction. This is the first time the accurate envelope of the reachable domain has been described in three-dimensional space. Acomparison of the results of the proposed numerical simulations with those of the existing method demonstrates the accuracy of the proposed method.

关键词： Maneuverable Spacecraft numerical Simulation Elliptical Orbit Perifocal Coordinate System Keplerian Orbit Earth Orbital Elements numerical algorithms Terminal Velocity Newton's Method

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Dislocation glide in Fe-carbon solid solution: From atomistic to continuum level description

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INTERNATIONAL JOURNAL OF PLASTICITY 2014年第0期62卷 34-49页

作者： Khater, H. A. Monnet, G. Terentyev, D. Serra, A. Assiut Univ Dept Phys Fac Sci Assiut 71516 Egypt MMC EDF R&D F-77818 Moret Sur Loing France SMA NMS SCK CEN Struct Mat Modelling & Microstruct Unit B-2400 Mol Belgium Univ Politecn Cataluna ES-08034 Barcelona Spain

The role of interstitial carbon impurities on the dislocation glide in bcc iron is investigated by means of molecular dynamics simulations. The local stress induced by carbon atoms, interaction energy map for the a(0)/2 < 111 >{110} and a(0)/2 < 111 >{112} edge dislocations and the dynamics of dislocation carbon interaction is assessed. The local stress exerted on the dislocation due to the carbon atoms and computed by atomistic simulations is used to describe the interaction strength on the continuum level. The derived here analysis of the atomistic data enabled the determination of the activation enthalpy and volume as a function of stress. Having that information, a comparative study demonstrates that at finite temperature, the resistance to the dislocation glide induced by the carbon atoms is lower in {112} than in {110} slip systems. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Dislocations Impurities Strengthening mechanisms Crystal plasticity numerical algorithms

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Analytical Solutions to Two-Impulse Nondrifting Transfer Problems for Rendezvous in Elliptical Orbits

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2014年第3期37卷 775-788页

作者： Peters, Thomas V. Noomen, Ron Colmenarejo, Pablo GMV ES-28760 Madrid Spain

This paper develops the analytical solution to the nondrifting transfer problem for rendezvous in elliptical orbits. The transfer algorithm generates a nondrifting, passively safe trajectory between two spacecraft states by finding the appropriate maneuvers and transfer time. The nondrifting solution is derived first for Cartesian state vectors, which is useful for transferring to a terminal approach point that is defined in terms of such a Cartesian state vector. Next, the transfer problem is solved in terms of differential orbital elements. This second solution lends itself well to perform close-range rendezvous in elliptical orbits.

关键词： Orbit Determination Geostationary Transfer Orbit Orbital Period Orbit Rendezvous Automated Transfer Vehicle Flight Path Angle Kepler's Equation Propellant numerical algorithms Satellites

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Flow stress model for IN718 accounting for evolution of strengthening precipitates during thermal treatment

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COMPUTATIONAL MATERIALS SCIENCE 2014年 82卷 531-539页

作者： Fisk, M. Ion, J. C. Lindgren, L. -E. Malmo Univ Fac Technol & Soc SE-20506 Malmo Sweden Lulea Univ Technol Dept Sci & Engn SE-97187 Lulea Sweden

A flow stress model describing precipitate hardening in the nickel based alloy Inconel (R) 718 following thermal treatment is presented. The interactions between precipitates and dislocations are included in a dislocation density based material model. Compression tests have been performed using solution annealed, fully-aged and half-aged material. Models were calibrated using data for solution annealed and fully-aged material, and validated using data from half-aged material. Agreement between experimental data and model predictions is good. (C) 2013 Elsevier B.V. All rights reserved.

关键词： Dislocations Strengthening mechanisms Metallic material Mechanical testing numerical algorithms Inconel 718 Gamma double prime

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Multi-Objective Optimization of Node-Based Spacecraft Radiator Design

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JOURNAL OF SPACECRAFT AND ROCKETS 2014年第5期51卷 1695-1708页

作者： Kim, Hui-Kyung Jo, Yeongmin Choi, Seongim Korea Adv Inst Sci & Technol Dept Aerosp Engn Taejon 305701 South Korea

An efficient multi-objective optimization method is proposed for node-based spacecraft radiator design. In contrast to a conventional manual approach to node-based radiator design with a thermal model, the proposed approach finds an optimum design solution for radiator node combinations through an optimization algorithm. The important parameters of radiator design are radiator size and topology, represented by discrete binary design variables allocated to each node division in the candidate radiator region. The optimization problem is formulated as a multi-objective problem with two or more objectives to minimize the number of radiator nodes and temperature margins of unit boxes, and a genetic algorithm suitable for multi-objective optimization is used. A small thermal model (verification thermal model) was developed to verify the proposed multi-objective optimization of the node-based spacecraft radiator design method, and test problems for this thermal model were defined. The numerical optimal solutions for test problems show good agreement with the analytic optimal solutions. Therefore, the applicability and feasibility of the multi-objective optimization of node-based spacecraft radiator design method to practical radiator design were confirmed.

关键词： Spacecraft Radiators Radiators Thermal Analysis numerical algorithms Genetic Algorithm Thermal Control Thermal Performance Mathematical Models Mathematical Optimization Optical Properties

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Free surface lattice Boltzmann with enhanced bubble model

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COMPUTERS & MATHEMATICS WITH APPLICATIONS 2014年第2期67卷 331-339页

作者： Anderl, Daniela Bogner, Simon Rauh, Cornelia Ruede, Ulrich Delgado, Antonio Univ Erlangen Nurnberg Lehrstuhl Stromungsmech D-91058 Erlangen Germany Univ Erlangen Nurnberg Lehrstuhl Syst Simulat D-91058 Erlangen Germany

This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid-gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Lattice Boltzmann Free surface Volume of fluid Interface capturing Bubbly flow numerical algorithms

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Petascale large eddy simulation of jet engine noise based on the truncated SPIKE algorithm

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PARALLEL COMPUTING 2014年第9期40卷 496-511页

作者： Situ, Yingchong Martha, Chandra S. Louis, Matthew E. Li, Zhiyuan Sameh, Ahmed H. Blaisdell, Gregory A. Lyrintzis, Anastasios S. Purdue Univ Dept Comp Sci W Lafayette IN 47907 USA Purdue Univ Sch Aeronaut & Astronaut W Lafayette IN 47907 USA

With the emergence of petascale computing platforms, high-fidelity computational aeroacoustics (CAA) simulation has become a feasible, robust and accurate tool that complements theoretical and empirical approaches in the prediction of sound levels generated by aircraft airframes and engines. Differentiating itself from the broader discipline of computational fluid dynamics, CAA is particularly challenging as it demands high accuracy, good spectral resolution, and low dispersion and diffusion errors from the underlying numerical methods. Large eddy simulation based on space-implicit high-order compact finite difference schemes has been shown to meet such stringent requirements. In this paper, we discuss a new, scalable parallelization scheme with a three-dimensional computational space partitioning. Unlike many traditional multiblock computational fluid dynamics (CFD) methods, our partitioning is non-overlapping. We use the truncated SPIKE algorithm to solve the governing equations accurately and limit one-sided biased differentiation to just the physical boundaries. We present experimental performance data collected on Kraken and Ranger, two near-petascale computing platforms. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Computational fluid dynamics Large eddy simulation Finite difference methods Parallel algorithms Linear systems numerical algorithms

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Modeling of damage in unidirectional ceramic matrix composites and multi-scale experimental validation on third generation SiC/SiC minicomposites

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2014年第1期63卷 298-319页

作者： Chateau, C. Gelebart, L. Bornert, M. Crepin, J. Caldemaison, D. Sauder, C. CEA DEN DMN SRMA F-91191 Gif Sur Yvette France Univ Paris Est Lab Navier UMR 8205 CNRSENPCIFSTTAR F-77455 Marne La Vallee France Mines ParisTech Ctr Mat CNRS UMR 7633 F-91003 Evry France Ecole Polytech Solid Mech Lab CNRS UMR 7649 F-91128 Palaiseau France

The purpose of this paper is to experimentally validate a ID probabilistic model of damage evolution in unidirectional SiC/SiC composites. The key point of this approach lies in the identification and validation at both local and macroscopic scales. Thus, in addition to macroscopic tensile tests, the evolution of microscopic damage mechanisms - in the form of matrix cracks and fiber breaks - is experimentally analyzed and quantified through in-situ scanning electron microscope and computed tomography tensile tests. A complete model, including both matrix cracking and fiber breaking, is proposed on the basis of existing modeling tools separately addressing these mechanisms. It is based on matrix and fiber failure probability laws and a stress redistribution assumption in the vicinity of matrix cracks or fiber breaks. The identification of interfacial parameters is conducted to fit the experimental characterization, and shows that conventional assumptions of 1D probabilistic models can adequately describe matrix cracking at both macro- and microscopic scales. However, it is necessary to enrich them to get a proper prediction of ultimate failure and fiber break density for Hi-Nicalon type S fiber-reinforced SiC/SiC minicomposites. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Fracture mechanisms Ceramic material Fiber-reinforced composite material In-situ mechanical testing numerical algorithms

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Robust and efficient overset grid assembly for partitioned unstructured meshes

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JOURNAL OF COMPUTATIONAL PHYSICS 2014年 260卷 1-24页

作者： Roget, Beatrice Sitaraman, Jayanarayanan Univ Wyoming Dept Mech Engn Laramie WY 82071 USA

This paper presents a method to perform efficient and automated Overset Grid Assembly (OGA) on a system of overlapping unstructured meshes in a parallel computing environment where all meshes are partitioned into multiple mesh-blocks and processed on multiple cores. The main task of the overset grid assembler is to identify, in parallel, among all points in the overlapping mesh system, at which points the flow solution should be computed (field points), interpolated (receptor points), or ignored (hole points). Point containment search or donor search, an algorithm to efficiently determine the cell that contains a given point, is the core procedure necessary for accomplishing this task. Donor search is particularly challenging for partitioned unstructured meshes because of the complex irregular boundaries that are often created during partitioning. Another challenge arises because of the large variation in the type of mesh-block overlap and the resulting large load imbalance on multiple processors. Desirable traits for the grid assembly method are efficiency (requiring only a small fraction of the solver time), robustness (correct identification of all point types), and full automation (no user input required other than the mesh system). Additionally, the method should be scalable, which is an important challenge due to the inherent load imbalance. This paper describes a fully-automated grid assembly method, which can use two different donor search algorithms. One is based on the use of auxiliary grids and Exact Inverse Maps (EIM), and the other is based on the use of Alternating Digital Trees (ADT). The EIM method is demonstrated to be more efficient than the ADT method, while retaining robustness. An adaptive load re-balance algorithm is also designed and implemented, which considerably improves the scalability of the method. (C) 2013 Elsevier Inc. All rights reserved.

关键词： numerical algorithms Overset methods Computational Fluid Dynamics

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Dividends in finite time horizon

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APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY 2014年第2期30卷 172-182页

作者： Cardoso, Rui M. R. Univ Nova Lisboa Fac Ciencias & Tecnol CMA P-2829516 Caparica Portugal Univ Nova Lisboa Fac Ciencias & Tecnol Dept Matemat P-2829516 Caparica Portugal

In this paper, we consider the classical risk model modified in two different ways by the inclusion of a dividend barrier. For Model I, we present numerical algorithms, which can be used to approximate or bound the expected discounted value of dividends up to a finite time horizon, t, or ruin if this occurs earlier. We extend this by requiring the shareholders to provide the initial capital and to pay the deficit at ruin each time it occurs so that the process then continues after ruin up to time t. For Model I, we assume the full premium income is paid as dividends whenever the surplus exceeds a set *** our Model II, we assume dividends are paid at a rate less than the rate of premium income. Copyright (c) 2012 John Wiley & Sons, Ltd.

关键词： surplus process dividend payments finite time numerical algorithms Markov chains

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