• Interaction and multiscale mechanics
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• v.2 no.4
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• pp.353-374
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• 2009

A new seamless multiscale simulation was developed for coupling the continuum model with its molecular dynamics. Kriging-based Finite Element Method (K-FEM) is employed to model the continuum base of the entire domain, while the molecular dynamics (MD) is confined in a localized domain of interest. In the coupling zone, where the MD domain overlaps the continuum model, the overall Hamiltonian is postulated by contributions from the continuum and the molecular overlays, based on a quartic spline scaling parameter. The displacement compatibility in this coupling zone is then enforced by the Lagrange multiplier technique. A multiple-time-step velocity Verlet algorithm is adopted for its time integration. The validation of the present method is reported through numerical tests of one dimensional atomic lattice. The results reveal that at the continuum/MD interface, the commonly reported spurious waves in the literature are effectively eliminated in this study. In addition, the smoothness of the transition from MD to the continuum can be significantly improved by either increasing the size of the coupling zone or expanding the nodal domain of influence associated with K-FEM.

• KIISE Transactions on Computing Practices
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• v.20 no.10
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• pp.534-542
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• 2014

Multiscale modeling is a new simulation approach which can manage different spatial and temporal scales of system. In this study, as part of multiscale modeling research, we propose the way of combining two different simulation methods, molecular dynamics(MD) and stochastic rotation dynamics(SRD). Our conceptual implementations are based on LAMMPS, one of the well-known molecular dynamics programs. Our prototype of multiscale modeling follows the form of the third party implementation of LAMMPS. It added MD to SRD in order to simulate the boundary area of the simulation box. Because it is important to guarantee the seamless simulation, we also designed the overlap zones and communication zones. The preliminary experimental results showed that our proposed scheme is properly worked out and the execution time is also reduced.

• Nuclear Engineering and Technology
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• v.36 no.3
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• pp.229-236
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• 2004

Radiation hardening is a multiscale phenomenon involving various processes over a wide range of time and length. We present a multiscale model for estimating the amount of radiation hardening in pressure vessel steel in the environment of a light water reactor. The model comprises two main parts: molecular dynamics (MD) simulation and a point defect cluster (PDC) model. The MD simulation was used to investigate the primary damage caused by displacement cascades. The PDC model mathematically formulates interactions between point defects and their clusters, which explains the evolution of microstructures. We then used a dislocation barrier model to calculate the hardening due to the PDCs. The key input for this multiscale model is a neutron spectrum at the inner surface of reactor pressure vessel steel of the Younggwang Nuclear Power Plant No.5. A combined calculation from the MD simulation and the PDC model provides a convenient tool for estimating the amount of radiation hardening.

• Interaction and multiscale mechanics
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• v.4 no.3
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• pp.173-185
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• 2011

A multiscale modeling scheme that addresses the influence of the nanoparticle size in nanocomposites consisting of nano-sized spherical particles embedded in a polymer matrix is presented. A micromechanics-based constitutive model for nanoparticle-reinforced polymer composites is derived by incorporating the Eshelby tensor considering the interface effects (Duan et al. 2005a) into the ensemble-volume average method (Ju and Chen 1994). A numerical investigation is carried out to validate the proposed micromechanics-based constitutive model, and a parametric study on the interface moduli is conducted to investigate the effect of interface moduli on the overall behavior of the composites. In addition, molecular dynamics (MD) simulations are performed to determine the mechanical properties of the nanoparticles and polymer. Finally, the overall elastic moduli of the nanoparticle-reinforced polymer composites are estimated using the proposed multiscale approach combining the ensemble-volume average method and the MD simulation. The predictive capability of the proposed multiscale approach has been demonstrated through the multiscale numerical simulations.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.11-20
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• 2009

Radiation effects on materials are inherently multiscale phenomena in view of the fact that various processes spanning a broad range of time and length scales are involved. A multiscale modeling approach to embrittlement of pressure vessel steels is presented here. The approach includes an investigation of the mechanisms of defect accumulation, microstructure evolution and the corresponding effects on mechanical properties. An understanding of these phenomena is required to predict the behavior of structural materials under irradiation. We used molecular dynamics (MD) simulations at an atomic scale to study the evolution of high-energy displacement cascade reactions. The MD simulations yield quantitative information on primary damage. Using a database of displacement cascades generated by the MD simulations, we can estimate the accumulation of defects over diffusional length and time scales by applying kinetic Monte Carlo simulations. The evolution of the local microstructure under irradiation is responsible for changes in the physical and mechanical properties of materials. Mechanical property changes in irradiated materials are modeled by dislocation dynamics simulations, which simulate a collective motion of dislocations that interact with the defects. In this paper, we present a multi scale modeling methodology that describes reactor pressure vessel embrittlement in a light water reactor environment.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.547-550
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• 2004

We present a multiscale scheme which describes the dynamic pictures of atoms in the multiple length-scale systems. Large-scale atomic systems are reduced to coarse grained system by the quasicontinuum, of which the dynamic pathways are rendered by the action-derived molecular dynamics proved effective for multiple time-scale problems such as rare events. Adatom diffusions on the metal (001) surface are selected for our numerical examples. The energy barriers of the diffusions and the real dynamic trajectories of the adatoms are calculated.

• Computers and Concrete
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• v.33 no.3
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• pp.325-340
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• 2024

The growing demands for sustainable and high-performance construction materials necessitate a deep understanding of their physicochemical properties by that of these heterogeneities. This paper presents a comprehensive review of the state-of-the-art hierarchical multiscale modeling approach aimed at predicting the intricate physicochemical characteristics of construction materials. Emphasizing the heterogeneity inherent in these materials, the review briefly introduces single-scale analyses, including the ab initio method, molecular dynamics, and micromechanics, through a scale-bridging technique. Herein, the limitations of these models are also overviewed by that of effectively scale-bridging methods of length or time scales. The hierarchical multiscale model demonstrates these physicochemical properties considering chemical reactions, material defects from nano to macro scale, microscopic properties, and their influence on macroscopic events. Thereby, hierarchical multiscale modeling can facilitate the efficient design and development of next-generation construction.

• Interaction and multiscale mechanics
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• v.1 no.4
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• pp.437-448
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• 2008

This paper examined the stability of high-dense dislocation substructures (HDDSs) associated with martensite laths in High Cr steels supposed to be used for FBR, based on a series of dislocation dynamics (DD) simulations. The DD simulations considered interactions of dislocations with impurity atoms and precipitates which substantially stabilize the structure. For simulating the dissociation processes, a point defect model is developed and implemented into a discrete DD code. Wall structure composed of high dense dislocations with and without small precipitates were artificially constructed in a simulation cell, and the stability/instability conditions of the walls were systematically investigated in the light of experimentally observed coarsening behavior of the precipitates, i.e., stress dependency of the coarsening rate and the effect of external stress. The effect of stress-dependent coarsening of the precipitates together with application of external stress on the subsequent behavior of initially stabilized dislocation structures was examined.

• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.582-590
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• 2007

In view of the analysis of the phenomena and the prediction of the performance, mathematical modelling and simulation of a high temperature pilot reactor for water gas shift reaction (WGSR) has been carried out. Multiscale simulation incorporated computational fluid dynamics (CFD) technique, which has the capability to deal with the reactor shape, fluid and energy transport with extensive degree of accuracy, and process modeling technique, which, in turn is responsible for reaction kinetics and mass transport. This research employed multiscale simulation and the results were compared with those from process simulation. From multiscale simulation, the maximum conversion of was predicted approximately 0.85 and the maximum temperature at the reactor was calculated 720 K, resulting from the heat of reaction. Dynamic simulation was also performed for the time transient profile of temperature, conversion, etc. Considering the results, it is concluded that multiscale simulation is a safe and accurate technique to predict reactor behaviors, and consequently will be available for the design of commercial size chemical reactors as well as other commercial unit operations.

• Interaction and multiscale mechanics
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• v.3 no.1
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• pp.1-22
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• 2010

In this paper one introduces a method of multiscale modelling called collection of dynamical systems with dimensional reduction. The method is suggested to be an appropriate approach to theoretical modelling of phenomena in mechanics of materials having in mind especially dynamics of processes. Within this method one formalizes scale of averaging of processes during modelling. To this end a collection of dynamical systems is distinguished within an elementary dynamical system. One introduces a dimensional reduction procedure which is designed to be a method of transition between various scales. In order to consider continuum models as obtained by means of the dimensional reduction one introduces continuum with finite-dimensional fields. Owing to geometrical elements associated with the elementary dynamical system we can formalize scale of averaging within continuum mechanics approach. In general presented here approach is viewed as a continuation of the rational mechanics.