Coupled Atomistic/Discrete Dislocation Simulations of Nanoindentation at Finite Temperature

2005 ◽  
Vol 127 (4) ◽  
pp. 358-368 ◽  
Author(s):  
Behrouz Shiari ◽  
Ronald E. Miller ◽  
William A. Curtin
Keyword(s):  
Finite Temperature ◽  
Computational Cost ◽  
Computational Method ◽  
Atomistic Simulations ◽  
Computational Framework ◽  
Reflected Waves ◽  
Indentation Process ◽  
Discrete Dislocation ◽  
Atomistic Region ◽  
System Temperature

Simulations of nanoindentation in single crystals are performed using a finite temperature coupled atomistic/continuum discrete dislocation (CADD) method. This computational method for multiscale modeling of plasticity has the ability of treating dislocations as either atomistic or continuum entities within a single computational framework. The finite-temperature approach here inserts a Nose-Hoover thermostat to control the instantaneous fluctuations of temperature inside the atomistic region during the indentation process. The method of thermostatting the atomistic region has a significant role on mitigating the reflected waves from the atomistic/continuum boundary and preventing the region beneath the indenter from overheating. The method captures, at the same time, the atomistic mechanisms and the long-range dislocation effects without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. Results and the deformation mechanisms that occur during a series of indentation simulations are discussed.

Multiscale modeling of solids at the nanoscale: dynamic approach

2008 ◽  
Vol 86 (2) ◽  
pp. 391-400 ◽  
Author(s):  
B Shiari ◽  
R E Miller ◽  
D D Klug
Keyword(s):  
Computational Cost ◽  
Atomistic Simulations ◽  
Process Variables ◽  
Dynamic Approach ◽  
Multiscale Models ◽  
Major Class ◽  
Dislocation Plasticity ◽  
System Temperature ◽  
Cyclic Indentation ◽  
Insight Into

One major class of multiscale models directly couples a region described with full atomistic detail to a surrounding region modeled using continuum concepts and finite element methods. Here, the development of a new dynamic approach to such coupled atomistic-continuum models is discussed with insight into the key ideas and features, with emphasis on fundamental difficulties involved in dynamic multiscale models. Simulations of nanoindentation in single crystals are performed to demonstrate the power of the developed method in capturing both long-range dislocation plasticity and short-range atomistic phenomena during single or cyclic loading without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. The deformation mechanisms and the surface evaluation that occur during a series of single and cyclic indentation simulations are discussed. PACS Nos.: 81.07.–b or 73.22.–f

Development of a Fast Fluid Dynamics Model Based on PISO Algorithm for Simulating Indoor Airflow

2021 ◽  
Author(s):  
Sibo Li ◽  
Hongtao Qiao
Keyword(s):  
Fluid Dynamics ◽  
Real Time ◽  
Computational Cost ◽  
Flow Simulation ◽  
Building Design ◽  
Energy Performance ◽  
Computational Effort ◽  
Computational Method ◽  
Dimensional Case ◽  
Time Flow

Abstract Real-time or faster-than-real-time flow simulation is crucial for studying airflow and heat transfer in buildings, such as building design, building emergency management and building energy performance evaluation. Computational Fluid Dynamics (CFD) with Pressure Implicit with Splitting of Operator (PISO) or Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm is accurate but requires great computational resources. Fast Fluid Dynamics (FFD) can reduce the computational effort but generally lack prediction accuracy due to simplification. This study developed a fast computational method based on FFD in combination with the PISO algorithm. Boussinesq approximation is adopted for simulating buoyancy effect. The proposed solver is tested in a two-dimensional case and a three-dimensional case with experimental data. The predicted results have good agreement with the experimental results. In the two test cases, the proposed solver generates lower Root Mean Square Error (RMSE) compared to the FFD and at the same time, the proposed method reduces computational cost by a factor of 10 and 13 in the two cases compared to CFD.

scholarly journals A geometric diffuse-interface method for droplet spreading

2020 ◽  
Vol 476 (2233) ◽  
pp. 20190222
Author(s):  
Darryl D. Holm ◽  
Lennon Ó Náraigh ◽  
Cesare Tronci
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Computational Cost ◽  
Computational Method ◽  
Diffuse Interface ◽  
Precursor Film ◽  
Droplet Spreading ◽  
Wetting Fluids ◽  
Thin Film Equation ◽  
Wetting Fluid

This paper exploits the theory of geometric gradient flows to introduce an alternative regularization of the thin-film equation valid in the case of large-scale droplet spreading—the geometric diffuse-interface method. The method possesses some advantages when compared with the existing models of droplet spreading, namely the slip model, the precursor-film method and the diffuse-interface model. These advantages are discussed and a case is made for using the geometric diffuse-interface method for the purpose of numerical simulations. The mathematical solutions of the geometric diffuse interface method are explored via such numerical simulations for the simple and well-studied case of large-scale droplet spreading for a perfectly wetting fluid—we demonstrate that the new method reproduces Tanner’s Law of droplet spreading via a simple and robust computational method, at a low computational cost. We discuss potential avenues for extending the method beyond the simple case of perfectly wetting fluids.

scholarly journals A Sequential Approach to Numerical Simulations of Solidification with Domain and Time Decomposition

2019 ◽  
Vol 9 (10) ◽  
pp. 1972 ◽  
Author(s):  
Elzbieta Gawronska
Keyword(s):  
Parallel Computing ◽  
Computational Cost ◽  
Fixed Time ◽  
Simulation Software ◽  
Computational Method ◽  
Computational Time ◽  
Time Step ◽  
Sequential Approach ◽  
Time Partitioning ◽  
Physical Phenomena

Progress in computational methods has been stimulated by the widespread availability of cheap computational power leading to the improved precision and efficiency of simulation software. Simulation tools become indispensable tools for engineers who are interested in attacking increasingly larger problems or are interested in searching larger phase space of process and system variables to find the optimal design. In this paper, we show and introduce a new approach to a computational method that involves mixed time stepping scheme and allows to decrease computational cost. Implementation of our algorithm does not require a parallel computing environment. Our strategy splits domains of a dynamically changing physical phenomena and allows to adjust the numerical model to various sub-domains. We are the first (to our best knowledge) to show that it is possible to use a mixed time partitioning method with various combination of schemes during binary alloys solidification. In particular, we use a fixed time step in one domain, and look for much larger time steps in other domains, while maintaining high accuracy. Our method is independent of a number of domains considered, comparing to traditional methods where only two domains were considered. Mixed time partitioning methods are of high importance here, because of natural separation of domain types. Typically all important physical phenomena occur in the casting and are of high computational cost, while in the mold domains less dynamic processes are observed and consequently larger time step can be chosen. Finally, we performed series of numerical experiments and demonstrate that our approach allows reducing computational time by more than three times without losing the significant precision of results and without parallel computing.

Interface Conditions for Coupled Atomistic and Continuum Models of Solids for Dynamics Problems at Finite Temperature

2006 ◽  
Vol 978 ◽  
Author(s):  
Xiantao Li ◽  
Weinan E
Keyword(s):  
Molecular Dynamics ◽  
Boundary Conditions ◽  
Finite Temperature ◽  
Langevin Equations ◽  
Continuum Models ◽  
Interface Conditions ◽  
System Temperature ◽  
Dynamics Simulations ◽  
Dynamics Problems ◽  
Generalized Langevin Equations

AbstractWe will present a general formalism for deriving boundary conditions for molecular dynamics simulations of crystalline solids in the context of atomistic/continuum coupling. These boundary conditions are modeled by generalized Langevin equations, derived from Mori-Zwanzig's formalism. Such boundary conditions are useful in suppressing phonon reflections, and maintaining the system temperature.

scholarly journals Finite-temperature elasticity of fcc Al: Atomistic simulations and ultrasonic measurements

2011 ◽  
Vol 84 (6) ◽  
Author(s):  
Hieu H. Pham ◽  
Michael E. Williams ◽  
Patrick Mahaffey ◽  
Miladin Radovic ◽  
Raymundo Arroyave ◽  
...  
Keyword(s):  
Finite Temperature ◽  
Atomistic Simulations ◽  
Ultrasonic Measurements

Finding the Shortest Path on a Polyhedral Surface and Its Application to Quality Assurance of Electric Components

2004 ◽  
Vol 126 (6) ◽  
pp. 1017-1026 ◽  
Author(s):  
Masaru Kageura ◽  
Kenji Shimada
Keyword(s):  
Product Design ◽  
Shortest Path ◽  
Shortest Paths ◽  
Computational Cost ◽  
Computational Method ◽  
Polyhedral Surface ◽  
Global Optimality ◽  
Shortest Path Algorithm ◽  
Suzuki Method ◽  
Polyhedral Surfaces

This paper presents a computational method for finding the shortest path along polyhedral surfaces. This method is useful for verifying that there is a sufficient distance between two electrical components to prevent the occurrence of a spark between them in product design. We propose an extended algorithm based on the Kanai-Suzuki method, which finds an approximate shortest path by reducing the problem to searching the shortest path on the discrete weighted graph that corresponds to a polyhedral surface. The accuracy of the solution obtained by the Kanai-Suzuki method is occasionally insufficient for our requirements in product design. To achieve higher accuracy without increasing the computational cost drastically, we extend the algorithm by adopting two additional methods: “geometrical improvement” and the “K shortest path algorithm.” Geometrical improvement improves the local optimality by using the geometrical information around a path obtained by the graph method. The K shortest path algorithm, on the other hand, improves the global optimality by finding multiple initial paths for searching the shortest path. For some representative polyhedral surfaces we performed numerical experiments and demonstrated the effectiveness of the proposed method by comparing the shortest paths obtained by the Chen-Han exact method and the Kanai-Suzuki approximate method with the ones obtained by our method.

Scaling Evaluations on the Drag of a Hub System

2013 ◽  
Vol 58 (3) ◽  
pp. 1-13 ◽  
Author(s):  
Rajiv Shenoy ◽  
Marlin Holmes ◽  
Marilyn J. Smith ◽  
Narayanan M. Komerath
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Computational Cost ◽  
Wind Tunnel Test ◽  
Complex Model ◽  
Computational Method ◽  
Component Level ◽  
Grid Adaptation ◽  
Magnus Effect ◽  
Match Model

Parasite drag on rotorcraft can become a crucial factor in forward flight, especially during high-speed flight. Prior evaluations of the ability of computational methods to predict hub drag have focused on the ability of these solvers to match model-scale experimental data, but the results have not typically been examined for full-scale conditions. Using an unstructured computational method, the sources of hub drag on a moderately complex model are examined at different Reynolds number scales. Correlations with a 1/3.5-scale wind tunnel test and empirical data are provided to confirm the accuracy of the computations. Unlike prior efforts, grid adaptation that crosses overset mesh boundaries permits grid refinement where needed while minimizing the computational cost. For the moderately complex hub evaluated, utilization of the same grid is permissible, provided the boundary layer grid is tailored for the highest Reynolds number studied and that grid adaptation is applied. Drag evaluation illustrates that the drag of each component should be estimated at the component-level Reynolds number before consideration of the interference effects. Estimation of the interference drag for rotating hubs should additionally account for the Magnus effect, which influences the nonlinearities observed in scaling the drag and the wake.

scholarly journals Atomistic Simulations of Dislocations in Confined Volumes

MRS Bulletin ◽  
2009 ◽  
Vol 34 (3) ◽  
pp. 184-189 ◽  
Author(s):  
P.M. Derlet ◽  
P. Gumbsch ◽  
R. Hoagland ◽  
J. Li ◽  
D.L. McDowell ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Time Scale ◽  
Finite Temperature ◽  
Atomistic Simulation ◽  
Dislocation Nucleation ◽  
Atomic Scale ◽  
Atomistic Simulations ◽  
Complementary Role ◽  
Nanocrystalline Structures ◽  
Strength And Ductility

AbstractInternal microstructural length scales play a fundamental role in the strength and ductility of a material. Grain boundaries in nanocrystalline structures and heterointerfaces in nanolaminates can restrict dislocation propagation and also act as a source for new dislocations, thereby affecting the detailed dynamics of dislocation-mediated plasticity. Atomistic simulation has played an important and complementary role to experiment in elucidating the nature of the dislocation/interface interaction, demonstrating a diversity of atomic-scale processes covering dislocation nucleation, propagation, absorption, and transmission at interfaces. This article reviews some atomistic simulation work that has made progress in this field and discusses possible strategies in overcoming the inherent time scale challenge of finite temperature molecular dynamics.

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