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Reference map technique for finite-strain elasticity and fluid-solid interaction

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2012年第11期60卷 1952-1969页

作者： Kamrin, Ken Rycroft, Chris H. Nave, Jean-Christophe MIT Dept Mech Engn Cambridge MA 02139 USA Univ Calif Berkeley Dept Math Berkeley CA 94720 USA Univ Calif Berkeley Lawrence Berkeley Natl Lab Dept Math Berkeley CA 94720 USA McGill Univ Dept Math & Stat Montreal PQ H3A 2K6 Canada

The reference map, defined as the inverse motion function, is utilized in an Eulerian-frame representation of continuum solid mechanics, leading to a simple, explicit finite-difference method for solids undergoing finite deformations. We investigate the accuracy and applicability of the technique for a range of finite-strain elasticity laws under various geometries and loadings. Capacity to model dynamic, static, and quasi-static conditions is shown. Specifications of the approach are demonstrated for handling irregularly shaped and/or moving boundaries, as well as shock solutions. The technique is also integrated within a fluid-solid framework using a level-set to discern phases and using a standard explicit fluid solver for the fluid phases. We employ a sharp-interface method to institute the interfacial conditions, and the resulting scheme is shown to efficiently capture fluid-solid interaction solutions in several examples. Published by Elsevier Ltd.

关键词： Finite-differences numerical algorithms Finite strain Rubber material

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Micro-, meso- to macroscopic modeling of deformation behavior of semi-crystalline polymer

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INTERNATIONAL JOURNAL OF PLASTICITY 2013年 49卷 164-184页

作者： Uchida, Makoto Tada, Naoya Okayama Univ Grad Sch Nat Sci & Technol Kita Ku Okayama 7008530 Japan

To represent the elasto-viscoplastic deformation behavior of semi-crystalline polymer (SCP), which has a complicated hierarchical structure, a micro-, meso- to macroscopic computational model was developed. A laminar composite model and FE-based homogenization method were used to relate the mechanical behaviors in micro- to mesoscopic and meso- to macroscopic scales of the material. Using the proposed model, elasto-viscoplastic deformation behaviors of high density polyethylene under several macroscopic boundary conditions were computationally investigated. Material's parameters used in the constitutive equations for microstructure of SCP were defined by fitting the calculated stress-strain relation into the experimental data. Then, the effects of deformation mode and crystallinity on deformation behavior of SCP were investigated. Obtained stress-strain relations represented the experimentally observed characteristics such as an anisotropic strain hardening rate depending on the deformation mode and an increase in the Young's modulus and the flow stress with the crystallinity. Then, the neck propagation process in the uniaxial tension with different strain rate was investigated. The present model represented a development of macroscopic non-uniform deformation characterized by the mechanical response of micro- to mesoscopic deformation. (c) 2013 Elsevier Ltd. All rights reserved.

关键词： Polymeric material Layered material Finite element numerical algorithms

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The role of texture in tension-compression asymmetry in polycrystalline NiTi

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INTERNATIONAL JOURNAL OF PLASTICITY 1999年第1期15卷 69-92页

作者： Gall, K Sehitoglu, H Univ Illinois Dept Mech & Ind Engn Urbana IL 61801 USA

The purpose of the present study is to thoroughly understand the stress-strain behavior of polycrystalline NiTi deformed under tension versus compression, To do this, a micromechanical model is used which incorporates single crystal constitutive relationships and experimentally measured polycrystalline texture into the self-consistent formulation. For the first time it is quantitatively demonstrated that texture measurements coupled with a micromechanical model can accurately predict tension/compression asymmetry in NiTi shape memory alloys. The predicted critical transformation stress levels and transformation stressstrain slopes under both tensile and compressive loading are consistent with experimental results, For textured polycrystalline NiTi deformed under tension it is demonstrated that the martensite evolution is very abrupt, consistent with the Luders type deformation experimentally observed. The abrupt transformation under tension is attributed to the fact that the majority of the grains are oriented along the [111] crystallographic direction, which is soft under tensile loading. Since single crystals of the [111] orientation are hard under compression it is also demonstrated that under compression the martensite in textured polycrystalline NiTi evolves relatively slower. (C) 1999 Elsevier Science Ltd. All rights reserved.

关键词： phase transformation constitutive behavior polycrystalline material numerical algorithms textured shape memory alloy

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A return-map algorithm for general associative isotropic elasto-plastic materials in large deformation regimes

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INTERNATIONAL JOURNAL OF PLASTICITY 1999年第12期15卷 1359-1378页

作者： Auricchio, F Taylor, RL Univ Pavia Dipartimento Meccan Strutturale I-27100 Pavia Italy Univ Calif Berkeley Dept Civil Engn Berkeley CA 94720 USA

The present paper addresses a flexible solution algorithm for associative isotropic elasto-plastic materials, i.e. for materials whose elastic and plastic behaviors are described through an isotropic free-energy function, an isotropic yield function and an associative flow rule. The discussion is relative to a large deformation regime, while no hardening mechanisms are included. The algorithm is based on a combination of the operator split method and a return map scheme. Both the algorithm linearization and the requirements for the yield criterion convexity are discussed in detail. Finally, to show the algorithm flexibility and performance, the discussion is specialized to three yield criteria and some test problems are studied. (C) 1999 Elsevier Science Ltd. All rights reserved.

关键词： elastic-plastic finite strain finite elements numerical algorithms return map

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CONVEXITY PRESERVING INTERPOLATION WITH EXPONENTIAL SPLINES

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COMPUTING 1986年第4期36卷 335-342页

作者： HESS, W SCHMIDT, JW 1.Sektion Mathematik Technische Universit?t Dresden Mommsenstrasse 13 DDR-8027 Dresden German Democratic Republic

Sufficient and necessary conditions are derived under which interpolating splines are convex if the data set is in convex position. In order to select one of the interpolants, by means of a well-known objective functi... 详细信息

关键词： 65D07 41A15 90C20 Convexity conditions weakly coupled system of inequalities numerical algorithms quadratic programming unconstrained dual program with tridiagonal Hessian

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A weight function method for the assessment of partially closed three-dimensional plane cracks

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ENGINEERING FRACTURE MECHANICS 2008年第15期75卷 4486-4500页

作者： Lopez Montenegro, Hugo Pablo Cisilino, Adrian Luis Otegui, Jose Univ Mar del Plata Inst Mat Sci & Technol INTEMA RA-7600 Mar Del Plata Argentina

The interference and physical contact between mating fracture surfaces can lead, even under the action of traction loads, to the closure of a crack. A low-cost numerical tool for the assessment of three-dimensional partially closed mode-I cracks is presented in this paper. The devised tool is based on the weight function methodology and it allows computing the geometry of the open part of the crack and the stress intensity factor along the complete crack front. The accuracy and versatility of the proposed procedure is assessed by solving a number of examples and comparing the obtained results with those available in the literature. (C) 2008 Elsevier Ltd. All rights reserved.

关键词： fracture mechanics stress intensity factor three-dimensional cracks crack closure numerical algorithms surface cracks

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Vessel transform for automatic optic disk detection in retinal images

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IET IMAGE PROCESSING 2015年第9期9卷 743-750页

作者： Muangnak, Nittaya Aimmanee, Pakinee Makhanov, Stanislav Uyyanonvara, Bunyarit Thammasat Univ Sirindhorn Int Inst Technol 131 Moo 5Tiwanont Rd Muang 12000 Pathumthani Thailand

Precise localisation of an optic disk (OD) in the retinal images is one of the most important problems in the ophthalmic image processing. Although a considerable progress has been made towards a computerised solution of the problem, the numerical algorithms often fail on retinal images characterised by poor quality. Therefore, the authors propose a new method suitable for low-quality images based on exploiting the convergence of the blood vessels to the OD. The novelty of the proposed techniques includes clustering the vessels endowed with a novel correction procedure and the vessel transform (VT) which measures the distance to the main clusters. The algorithm is integrated into the scale-space (SS) analysis to detect the boundary of the OD. The integrated method is called SS algorithm with VT (SSVT). SSVT has been tested on retinal images from two databases with fair and poor images against the fuzzy convergence (FC) method and a modification of the circular transform proposed by Lu. The absolute improvement on sensitivity of SSVT against FC and Lu's are up to 12.37% and 8.18%. Bigger improvements of SSVT in terms of positive predictive value are up to 37.46% and 30.84% against FC and Lu's, respectively.

关键词： eye medical image processing blood vessels transforms fuzzy set theory biomedical optical imaging convergence of numerical methods vessel transform automatic optic disk detection retinal images ophthalmic image processing computerised solution numerical algorithms low-quality images blood vessels vessel clustering scale-space analysis integrated method SS algorithm fuzzy convergence method FC method circular transform SSVT sensitivity

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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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Modeling maneuver dynamics in air traffic conflict resolution

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2003年第3期26卷 407-415页

作者： Paielli, RA NASA Ames Res Ctr Aviat Syst Div Moffett Field CA 94035 USA

Much of the previous literature on conflict resolution is based on instantaneous maneuver models, in which speed and/or heading change dynamics are unmodeled. The effects of the actual maneuver dynamics on the resulting minimum separation are analyzed, and a simple numerical algorithm is presented to compensate for those effects. The focus is on level flight in the horizontal plane. Speed changes are modeled as periods of constant along-track acceleration or deceleration, and heading changes are modeled as steady turns of constant rate and radius. These simple kinematic (constrained point-mass) models improve on the resolution accuracy that results from modeling speed and heading changes as instantaneous, but they yield much simpler solutions than general point-mass dynamic models. The accuracy improvement is minor for most heading-change maneuvers, but it is substantial for most speed-change maneuvers. An important operational benefit of the algorithm is that it detects immediately if a conflict is too close to be resolved by a particular maneuver. A method is also outlined for determining the optimal combination of speed and heading change to resolve conflicts. With minor adaptation, the algorithms can also make use of an existing conflict probability estimation algorithm to determine maneuvers for strategic conflict probability reduction.

关键词： numerical algorithms Aerodynamics Computing Airspeed Transport Aircraft Airspace Aircraft Maneuvers Fuel Consumption Heading Angle Burning Rate

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A unified constitutive model for asymmetric tension and compression creep-ageing behaviour of naturally aged Al-Cu-Li alloy

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INTERNATIONAL JOURNAL OF PLASTICITY 2017年 89卷 130-149页

作者： Li, Yong Shi, Zhusheng Lin, Jianguo Yang, Yo-Lun Rong, Qi Huang, Bo-Ming Chung, Tsai-Fu Tsao, Cheng-Si Yang, Jer-Ren Balint, Daniel S. Imperial Coll London Dept Mech Engn London SW7 2AZ England Natl Taiwan Univ Dept Mat Sci & Engn Taipei Taiwan

A set of unified constitutive equations is presented that predict the asymmetric tension and compression creep behaviour and recently observed double primary creep of pre-stretched/naturally aged aluminium-cooper-lithium alloy AA2050-T34. The evolution of the primary micro- and macro-variables related to the precipitation hardening and creep deformation of the alloy during creep age forming (CAF) are analysed and modelled. Equations for the yield strength evolution of the alloy, including an initial reversion and subsequent strengthening, are proposed based on a theory of concurrent dissolution, re nucleation and growth of precipitates during artificial ageing. We present new observations of so-called double primary creep during the CAF process. This phenomenon is then predicted by introducing effects of interacting microstructures, including evolving precipitates, diffusing solutes and dislocations, into the sinh-law creep model. In addition, concepts of threshold creep stress o-th and a microstructure-dependant creep variable H, which behave differently under different external stress directions, are proposed and incorporated into the creep model. This enables prediction of the asymmetric tension and compression creep-ageing behaviour of the alloy. Quantitative transmission electron microscopy (TEM) and related small-angle X-ray scattering (SAXS) analysis have been carried out for selected creep-aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to creep age forming of other heat-treatable aluminium alloys. (C) 2016 The Authors. Published by Elsevier Ltd.

关键词： Creep age forming Ageing Microstructures Constitutive behaviour numerical algorithms

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