• Transactions of Materials Processing
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• v.21 no.6
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• pp.366-371
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• 2012

Atomistic simulations have become useful tools for exploring new insights in materials science, but the length and time scale that can be handled with atomistic simulations are seriously limiting their practical applications. In order to make meaningful quantitative predictions, atomistic simulations are necessarily combined with higher-scale modeling. The present research is thus concerned with the development of a multi-scale model and its application to the prediction of the mechanical properties of body-centered cubic(BCC) iron with an emphasis on the coupling of atomistic molecular dynamics with meso-scale discrete dislocation dynamics modeling. In order to achieve predictive multi-scale simulations, it is necessary to properly incorporate atomistic details into the meso-scale approach. This challenge is handled with the proposed hierarchical information passing strategy from atomistic to meso-scale by obtaining material properties and dislocation mobility. Finally, this fundamental and physics-based meso-scale approach is employed for quantitative predictions of the mechanical response of single crystal iron.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12S
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• pp.1157-1164
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• 2003

This paper shows the results of atomistic modeling for the interaction between spherical nano abrasive and substrate in chemical mechanical polishing processes. Atomistic modeling was achieved from 2-dimensional molecular dynamics simulations using the Lennard-Jones 12-6 potentials. The abrasive dynamics was modeled by three cases, such as slipping, rolling, and rotating. Simulation results showed that the different dynamics of the abrasive results the different features of surfaces. This model can be extended to investigate the 3-dimensional chemical mechanical polishing processes.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.6
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• pp.61-70
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• 2003

A multibody system dynamics analysis program is presented using one of the most useful programming methodologies, the object-oriented modeling, The object-oriented modeling defines a problem from the physical world as an abstract object. The object becomes encapsulated with the data and method, Analysis is performed using the object's interface, It is then possible for the user and the developer to modify and upgrade the program without having particular knowledge of the analysis program, The method presented in this paper has several advantages, Since the mechanical components of the multi-body system are converted into the class, the modification, exchange, distribution and reuse of classes are increased. It becomes easier to employ a new analysis method and interface with other S/W and H/W systems, Information can be communicated to each object through messaging. This makes the modeling of new classes easier using the inheritance, When developing a S/W for the computer simulation of a physical system, it is reasonable to use object-oriented modeling.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.2
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• pp.409-425
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• 2015

In this paper, we employ a dynamics modeling method for investigating a multi-body dynamics system of semi-submersible autonomous underwater vehicles consisting of a towing vehicle operated near the water surface, a tow cable, and a towfish. The towfish, which is towed by a marine cable for the purposes of exploration or mine hunting, is modeled with a Six-Degree-of-Freedom (6-DOF) equation of motion that reflects its hydrodynamics characteristics. The towing cable, which can experience large displacements and deformations, is modeled using an absolute nodal coordinate formulation. To reflect the hydrodynamic characteristics of the cable during motion, the hydrodynamic force due to added mass and the drag force are imposed. To verify the completeness of the modeling, a few simple numerical simulations were conducted, and the results confirm the physical plausibility of the model.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.190-197
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• 2000

A graphic vehicle modeling pre-processing program and a visualization post-processing program have been developed for AutoDyn7, which is a special program for vehicle dynamics. The Rapid-App for GUI(Graphic User Interface) builder and the Open Inventor for 3D graphic library have been employed to develop these programs in Silicon Graphics workstation. A Graphic User Interface program integrates vehicle modeling pre-processor, AutoDyn7 analysis processor, and visualization post-processor. In vehicle modeling pre-processor, vehicle hard point data for a suspension model are automatically converted into multibody vehicle system data. An interactive graphics capabilities provides suspension modeling aides to verify user input data interactively. In visualization post-processor, vehicle virtual test simulation results are animated with virtual testing environments.

• Steel and Composite Structures
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• v.10 no.2
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• pp.129-149
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• 2010

The objective of this study is to formulate a general 3D material-structural analysis framework for the thermomechanical behavior of steel-concrete structures in a fire environment. The proposed analysis framework consists of three sequential modeling parts: fire dynamics simulation, heat transfer analysis, and a thermomechanical stress analysis of the structure. The first modeling part consists of applying the NIST (National Institute of Standards and Technology) Fire Dynamics Simulator (FDS) where coupled CFD (Computational Fluid Dynamics) with thermodynamics are combined to realistically model the fire progression within the steel-concrete structure. The goal is to generate the spatial-temporal (ST) solution variables (temperature, heat flux) on the surfaces of the structure. The FDS-ST solutions are generated in a discrete form. Continuous FDS-ST approximations are then developed to represent the temperature or heat-flux at any given time or point within the structure. An extensive numerical study is carried out to examine the best ST approximation functions that strike a balance between accuracy and simplicity. The second modeling part consists of a finite-element (FE) transient heat analysis of the structure using the continuous FDS-ST surface variables as prescribed thermal boundary conditions. The third modeling part is a thermomechanical FE structural analysis using both nonlinear material and geometry. The temperature history from the second modeling part is used at all nodal points. The ABAQUS (2003) FE code is used with external user subroutines for the second and third simulation parts in order to describe the specific heat temperature nonlinear dependency that drastically affects the transient thermal solution especially for concrete materials. User subroutines are also developed to apply the continuous FDS-ST surface nodal boundary conditions in the transient heat FE analysis. The proposed modeling framework is applied to predict the temperature and deflection of the well-documented third Cardington fire test.

• East Asian mathematical journal
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• v.34 no.3
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• pp.317-330
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• 2018

We develop a mathematical model for the obesity dynamics to investigate the long term obesity trend with the consideration of psychological and social factors due to the increasing prevalence of obesity around the world. Many mathematical models for obesity dynamics adopted the modeling idea of infectious disease and treated overweight and obese people infectious and spreading obesity to normal weight. However, this modeling idea is not proper in obesity modeling because obesity is not an infectious disease. In fact, weight gain and loss are related to social interactions among different weight groups not only in the direction from overweight/obese to normal weight but also the other way around. Thus, we consider these aspects in our model and implement personal weight gain feature, a psychological factor such as body image dissatisfaction, and social interactions such as positive support on weight loss and negative criticism on weight status from various weight groups. We show that the equilibrium point with no normal weight population will be unstable and that an equilibrium point with positive normal weight population should have all other components positive. We conduct computer simulations on Korean demography data with our model and demonstrate the long term obesity trend of Korean male as an example of the use of our model.

• 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.

• Korean System Dynamics Review
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• v.8 no.1
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• pp.97-115
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• 2007

In System Dynamics, causal maps are used as a tool for analyzing dynamic problems and discussing the outcome of analyzed problems. However there are some limitations to use causal maps. In the drawing phase of causal maps, the high abstraction of variables that constitutes problems makes it difficult to find out correct information. And principles or rules to check errors on causal maps are not sufficient yet. Moreover, simulation modeling tasks are required to be concerned separately from drawing causal maps because causal maps cannot provide enough information to simulation modeling. In order to overcome these limitations, this study shows ways that ensure validity, increase power of expression of causal maps and improve the connection between causal maps and simulation modeling.

• Korean Journal of Computational Design and Engineering
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• v.14 no.4
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• pp.261-270
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• 2009

We can save a lot of efforts and time to perform various kinds of multibody system dynamics simulations if the equations of motion of the multibody system can be formulated automatically. In general, the equations of motion are formulated based on Newton's $2^{nd}$law. And they can be transformed into the equations composed of independent variables by using velocity transformation matrix. In this paper the velocity transformation matrix is derived based on a topological modeling approach which considers the topology and the joint property of the multibody system. This approach is, then, used to formulate the equations of motion automatically and to implement a multibody system dynamics simulation program. To verify the the efficiency and convenience of the program, it is applied to the lifting simulation of a floating crane.