3차원 분자 모델을 사용한 재료내의 저장 에너지 계산에 관한 연구

최덕기,유한규 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.5

This paper addresses a theoretical approach to calculate the amount of the stored energy during a deformation using atomistic level simulation. During a deformation, only a small percent of the energy input is stored in the material, and most of input energy is converted into heat. The cause of the temperature rise within materials is traditionally credited to dislocations, vacancies and other defects. An atomistic material model for fcc such as copper is used to calculated the stored elastic energy. The potential energy is obtained by a molecular dynamics (MD) simulation. Two different states are considered for comparison: one is a perfect state and the other is a state with dislocations. The calculated potential energies in these two states are compared. The difference in the potential energies is considered the amount of the stored elastic energy of dislocations. The conversion factor, i.e., the fraction of the input energy that is stored as elastic energy within a material is then calculated. (Received December 22, 2003)

Chemical Composition and Phytoestrogen Analysis of Iranian Black Pomegranate Juice Concentrate and Seeds

Choi,One-Kyun,Kim,Yong-Seong,Yu,Hye-Kyoung,Lee,Chan,Bang,Hyo-Pil,Yang,Deok-Chun,Kim,Young-Kee 한국자원식물학회 2003 Plant Resources Vol.6 No.1

In this study, as preliminary research for the development of natural estrogen supplement the chemical properties of Iranian black pomegranate juice concentrate and seeds were evaluated. Proximate compositions of pomegranate juice concentrate and seeds were as follows; crude lipid 0.4% and 8.2%, moisture 39.9% and 6.6%, crude protein 0.9% and 12.2%, ash 1.4% and 1.7%, and carbohydrate 42.0% and 84.5% respectively. Major amino acids are glutamic acid (1310.0ppm) and aspartic acid (896.2ppm) in juice concentrate, and glycine (611.1ppm) and arginin (401.6ppm) in seeds. Ascorbic acid has the highest concentration of 20.0mg/l00g in juice concentrate and 0.23mg/l00 in seeds. The compositions of unsaturated fatty acids such as linoleic acid and linolenic acid were higher than those of saturated fatty acids such as stearic palmitic acid. Major minerals were potassium, calcium and sodium, potassium was highest in both juice concentrate and seeds. Vitamins were composed of ascorbic acid (20.0mg/l00g), vitamin B$_1$ 수식 이미지(0.12mg/100g) and niacin (0.80mg/l00g) in juice concentrate, and only ascorbic acid(0.23mg/l00g) in seeds. Organic acids such as citric and L-malic acid were detected only in pomegranate juice concentrate. The contents of total polyphenols were 4.55g/L in juice concentrate and 3.5mg/l00g in seeds, respectively. Phytoestrogens detected in pomegranate juice concentrate and seeds were daidzein, quercetin, genistein and 17β-estradiol.

변형률 에너지 밀도 이론을 사용한 3차원 균열 진전각 계산에 관한 연구

최덕기,이상진 단국대학교 2001 산업기술연구 Vol.2 No.-

It is not uncommon to see a fracture of material by loading, force, or natural environment. Scholars have paid a good attention to fracture mechanics to predict the fracture of materials, and researched a number of fracture theories. These theories, however, can not predict where crack propagation angles extendunder mixed mode.

Quasimolecular Dynamics Simulation of Crack-Tip Growth

Choi, Deok kee 단국대학교 1997 敎授 論文集 Vol.31 No.-

Motion Tracking of Four-Wheeled Mobile Robots in Outdoor Environments Using Bayes’ Filters

Deok-Kee Choi 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.5

The demand for outdoor wheeled mobile robots (WMRs) is rapidly growing to assist humans in outdoor environments such as transportation, exploration, rescue, security, agriculture, military, etc. To effectively control outdoor WMRs, we need motion models applicable in such unknown environments. Conventional modeling mainly concerns physics laws or equations of motion, such as kinematics, dynamics, terrains, and wheel-ground interactions. Modeling WMRs on unstructured ground is more complicated than in a well-developed indoor environment. To alleviate such difficulties, we looked at a data-driven approach instead. We built a four-wheeled mobile robot with wheel encoders installed, with which the forward and inverse differential kinematic solutions were derived. Then, we performed more than a thousand test runs in outdoor environments, having the robot run on normal, icy, and sandy roads, including test runs under constraints partially blocked by brick and grid-type holes. We employed Bayes’ filter because the robot’s tri-variate states (two linear velocities and the rotation) are not directly measurable through wheel encoders. With such uncertainty, Bayes’ filtering technique of the Kalman filter and a newly developed unscented Kalman filter were applied to infer how each wheel’s speed affects the robot’s velocity. We established a probabilistic motion model, where the differential kinematic solutions are combined with uncertainty from outdoor environments. Consequently, we could closely track the robot’s motion. This modeling technique can be used to develop better outdoor WMRs.

Calculation of Stress Intensity Factors Using Three - Dimensional Molecular Dynamics Simulation

Choi, Deok Kee,Kim, Jih Woon 대한금속재료학회(대한금속학회) 1998 METALS AND MATERIALS International Vol.4 No.4

Molecular dynamics simulation is emerging with recent advent of high-performance computers. This paper addresses an application of molecular dynamics simulation to calculation of stress intensity factors (SIF) of a material using a three-dimensional molecular model. Since the popular molecular models such as Lennard-Jones model fails to compute behaviors of materials correctly, in this paper the embedded atomic model (EAM) was utilized. A copper plate with a single edge crack is considered to calculate SIFs in opening mode. More than ten thousand of molecules were used for the simulation and due to a large amount of computation, a super computer CRAY C90 was employed. The results show good agreement with the theoretical SIF values.

Application of computer algebra system to finite element modeling of engineering problems

Choi, Deok-kee 단국대학교 1994 論文集 Vol.28 No.-

정확성과 편리성을 장점으로 하는 유한요소해석법이 널리 이용되고 있음에도 불구하고, 그것을 이용하여 실제로 공학문제를 해석하기 위해서는 상당히 많은 노력이 필요하다. 본 연구에서는 컴퓨터 대수 프로그램을 사용하여, 소요되는 시간과 노력을 줄여줄 수 있다는 것을 입증하였다. 컴퓨터 대수 프로그램은 이미 많은 공학 및 자연과학 분야에서 사용되고 있으나, 아직 그 응용에 관한 연구는 활발하지 않다. 본 연구에서는 어떠한 방법으로 컴퓨터 대수 프로그램을 이용하여 시간과 노력을 줄일 수 있는가를 예제를 통하여 증명하였다. Beam의 강성 matrix를 계산하기 위해 컴퓨터 대수 프로그램 Mathematica를 사용하였다. 첫번째 예제는 Euler-Bernouilli beam의 강성 matrix에 관한 것이고, 두번째는 Timoshenko beam의 강성 matrix에 관한 것이다. 본 연구는 크게 두 부분으로 나눌 수 있다. 앞 부분은 interpolation함수를 구하는 것이고, 뒷 부분은 구한 함수를 이용하여 유한요소모델과 강성 matrix를 계산하고 그것을 FORTRAN 프로그램의 형식으로 출력하게 하는 것이다. 손으로 일일이 계산해야될 부분들을 자동적으로 컴퓨터로 처리했을 뿐 아니라, 그 결과를 FORTRAN 프로그램형식으로 자동적으로 출력하게 하여 시간과 노력을 줄이고, 다른 공학문제들에 대한 컴퓨터 대수 프로그램을 이용한 유한요소해석에의 응용가능성을 보였다.

Atomistic Simulation of the Effect of Dislocations on Temperature Rise during High-Strain-Rate Deformation

( Deok Kee Choi ),( Han Kyu Ryu ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 METALS AND MATERIALS International Vol.12 No.4

Materials generate heat due to plastic work. The resultant temperature rise can be significant, changing the properties of the material in many aspects during high-strain-rate deformation. The deformation process can be assumed to be adiabatic, and hence the heat generated remains within the material. It is well known from experiments that only a small percent of the energy input is stored in the material, and most of the input energy is converted into heat. The temperature rise within materials is traditionally credited to dislocations, vacancies, and other defects. It is, however, difficult to explain the phenomenon using macroscopic material models. In the present study, an fcc crystal structure is used for atomistic material simulations. The energy calculation is performed by a molecular dynamics (MD) simulation, using the Lennard-Jones potential. The main purpose of the paper is to evaluate the role of dislocations in the temperature rise during high-strain-rate deformation. To this end, two different atomistic models are used: a perfect model that has no dislocations, and another model that includes the dislocations` movements. Comparison of the potential energy calculated from the two models confirms that dislocations play an important role in raising the heat during high-strain-rate deformation.

Quasimolecular Dynamics Simulation of Crack-Tip Growth

Choi, Deok-kee 단국대학교 1997 論文集 Vol.31 No.-

본 논문에서는 분자 동역학을 이용한 재료에서의 균열 단 성장에 대한 정상적인 컴퓨터 시뮬레이션 방법을 제시하고 있다. 준 분자란 방대한 컴퓨터 계산량과 시간을 즐기기 위하여 사용하는 실제의 분자가 아닌 다수의 실제 분자로 구성된 가상적인 분자를 말한다. 본 연구에서는 분자 동역학 시뮬레이션의 타당성을 검토하기 위하여 구리로 된 균열이 있는 2차원 시편을 계산에 사용하였다. 균열 단 성장에 대한 과정을 컴퓨터 상에서 모사하기 위하여 변위 경계 조건을 사용하였다. 준 분자 동역학을 사용한 재료 시험에 대한 컴퓨터 시뮬레이션은 정상적으로 볼 때 실제의 균열 단 성장과 비교하였을 때 정상적으로 타당함을 알 수 있었다.

A Study on Distribution of Plastic Region near a Crack Tip Using Three - Dimensional Molecular Dynamics Simulation

Choi, Deok Kee,Kim, Jih Woon 대한금속재료학회(대한금속학회) 1998 METALS AND MATERIALS International Vol.4 No.4

The estimation of the size of the plastic zone in the vicinity of the crack tip is of great interest. An attempt using molecular dynamics simulation is made to determine a plastic zone near the crack tip. The embedded atom method (EAM) model is employed for the potential energy. All the simulations were carried out on the supercomputer CRAY C90 at SERI (System Engineering Research Institute, Korea). Compared with the theoretical value based on the linear elastic fracture mechanics (LEFM), the present result shows good agreement.