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Multiscale Modeling (multiscale + modeling)

Distribution by Scientific Domains

Engineering	42%
Chemistry	42%

Selected Abstracts

Multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2010
Flavio V. Souza
Abstract Multiscale computational techniques play a major role in solving problems related to viscoelastic composites due to the complexities inherent to these materials. In this paper, a numerical procedure for multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks is proposed in which the (global scale) homogenized viscoelastic incremental constitutive equations have the same form as the local-scale viscoelastic incremental constitutive equations, but the homogenized tangent constitutive tensor and the homogenized incremental history-dependent stress tensor at the global scale depend on the amount of damage accumulated at the local scale. Furthermore, the developed technique allows the computation of the full anisotropic incremental constitutive tensor of viscoelastic solids containing evolving cracks (and other kinds of heterogeneities) by solving the micromechanical problem only once at each material point and each time step. The procedure is basically developed by relating the local-scale displacement field to the global-scale strain tensor and using first-order homogenization techniques. The finite element formulation is developed and some example problems are presented in order to verify the approach and demonstrate the model capabilities. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Multiscale modeling of hard materials: Challenges and opportunities for chemical engineering

AICHE JOURNAL, Issue 5 2000
Dimitrios Maroudas
First page of article [source]

Multiscale modeling of nucleic acids: Insights into DNA flexibility

BIOPOLYMERS, Issue 9 2008
Yannick J. Bomble
Abstract The elastic rod theory is used together with all-atom normal mode analysis in implicit solvent to characterize the mechanical flexibility of duplex DNA. The bending, twisting, stretching rigidities extracted from all-atom simulations (on linear duplexes from 60 to 150 base pairs in length and from 94-bp minicircles) are in reasonable agreement with experimental results. We focus on salt concentration and sequence effects on the overall flexibility. Bending persistence lengths are about 20% higher than most experimental estimates, but the transition from low-salt to high-salt behavior is reproduced well, as is the dependence of the stretching modulus on salt (which is opposite to that of bending). CTG and CGG trinucleotide repeats, responsible for several degenerative disorders, are found to be more flexible than random DNA, in agreement with several recent studies, whereas poly(dA).poly(dT) is the stiffest sequence we have encountered. The results suggest that current all-atom potentials, which were parameterized on small molecules and short oligonucleotides, also provide a useful description of duplex DNA at much longer length scales. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 722,731, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]

A multiscale modeling of damage and time-dependent behavior of cohesive rocks

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2009
A. Abou-Chakra Guéry
Abstract The present paper deals with a micromechanical approach to modeling the time-dependent mechanical behavior of a class of cohesive geomaterials. The considered material is Callovo-Oxfordian argillite, which is mainly composed of three constituents: an elastoviscoplastic clay matrix, elastic quartz minerals, and elastic damaged calcite grains. The macroscopic constitutive law is obtained by adapting the incremental method proposed by Hill (J. Mech. Phys. Solids 1965; 13:89,101). Its unified formulation allows a description of not only the time-dependent behavior of the argillite but also its elastoplastic damage response. The developed model is first validated by comparison with finite element solutions and then it is applied to the prediction of argillites' macroscopic responses in connection with their mineralogical compositions. The validity of the model is checked through comparisons between the model's predictions and experimental data. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks

Process intensification aspects for steam methane reforming: An overview

AICHE JOURNAL, Issue 2 2009
Shrikant A. Bhat
Abstract Steam methane reforming (SMR) is the most widely used process in industry for the production of hydrogen, which is considered as the future generation energy carrier. Having been perceived as an important source of H2, there are abundant incentives for design and development of SMR processes mainly through the consideration of process intensification and multiscale modeling; two areas which are considered as the main focus of the future generation chemical engineering to meet the global energy challenges. This article presents a comprehensive overview of the process integration aspects for SMR, especially the potential for multiscale modeling in this area. The intensification for SMR is achieved by coupling with adsorption and membrane separation technologies, etc., and using the concept of multifunctional reactors and catalysts to overcome the mass transfer, heat transfer, and thermodynamic limitations. In this article, the focus of existing and future research on these emerging areas has been drawn. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Challenges of introducing quantitative elementary reactions in multiscale models of thin film deposition

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2010
Alessandro Barbato
Abstract The implementation of detailed surface kinetic mechanisms describing the thin film growth dynamics into models of chemical vapor deposition (CVD) reactors has been a challenge for many years. In this article we review the literature concerning the study of the dynamics of the Si(100)2,×,1 surface and introduce a multiscale model that captures the main features of its reactivity. The model combines the results of ab initio calculations with an atomistic description of the Si surface, obtained using a 3D-kinetic Monte Carlo (KMC) model that explicitly accounts for the 2,×,1 surface reconstruction and the formation and diffusion of Si dimers on a hydrogenated surface. At the atomistic scale, we determined pre-exponential factors and activation energies of hydrogen desorption reactions proceeding through the 2H, 3H, and 4H mechanisms. The calculated kinetic constants were embedded in the KMC model and used to simulate literature TPD experimental data. The simulations were used to fit the activation energies of hydrogen desorption reactions, which showed that DFT calculations performed with B3LYP functionals are likely to overestimate hydrogen desorption energies by up to 9,kcal,mol,1, which was confirmed by successive ab initio calculations. Two examples of the solution of the KMC model in conjunction with a reactor scale model are provided, in which the coupling was performed adopting both a hierarchic and a two-way coupling strategy. We found that in the plasma deposition of nanocrystalline silicon performed at low substrate temperatures the growth proceeds through a layer-by-layer mechanism on a surface almost completely covered by hydrogen. The application of the same model to the simulation of the thermal CVD of Si showed that at intermediate growth temperatures, when the hydrogen surface concentration is high, a new hydrogen desorption mechanism, in which Si adatoms play an important role, is active. Length scales encountered in multiscale modeling of thin films deposition. [source]