• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.753-757
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• 1994

In control system design, whether the various subsystems are in discrete time or continuous time, the state space is usually regarded as a continuum. However, when the system is implemented, some subsystems may have a state space which is a subset of finite computer arithmetic. This is an important concern if a subsystem has chaotic behaviour, because it is theoretically possible for rich and varied motions in a continuum to collapse to trivial and degenerate behaviour in a finite and discrete state space [5]. This paper discusses new ways to describe these effects and reports on computer experiments which document and illustrate such collapsing behaviour.

• 전산구조공학
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• 제8권4호
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• pp.107-115
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• 1995

지하 방사성 폐기물 저장소의 오랜기간동안의 거동은 지반의 파괴와 변형에 영향과 암염의 비선형변형의 예측은 어려운 실정이다. 따라서 본 연구는 암염의 비선형파괴 메커니즘과 비선형 연속체거동의 유한요소모델을 개발하였다.

• Korea-Australia Rheology Journal
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• 제21권4호
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• pp.245-268
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• 2009

Recent developments in dilute polymer solution rheology are reviewed, and placed within the context of the general goals of predicting the complex flow of complex fluids. In particular, the interplay between the use of polymer kinetic theory and continuum mechanics to advance the microscopic and the macroscopic description, respectively, of dilute polymer solution rheology is delineated. The insight that can be gained into the origins of the high Weissenberg number problem through an analysis of the configurational changes undergone by a single molecule at various locations in the flow domain is discussed in the context of flow around a cylinder confined between flat plates. The significant role played by hydrodynamic interactions as the source of much of the richness of the observed rheological behaviour of dilute polymer solutions is highlighted, and the methods by which this phenomenon can be incorporated into a macroscopic description through the use of closure approximations and multi scale simulations is discussed.

• 천문학회지
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• 제48권3호
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• pp.203-206
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• 2015

The masses of supermassive black holes in active galactic nuclei (AGN) can be derived spectroscopically via virial mass estimators based on selected broad optical/ultraviolet emission lines. These estimates commonly use the line width as a proxy for the gas speed and the monochromatic continuum luminosity, λL_λ, as a proxy for the radius of the broad line region. However, if the size of the broad line region scales with the bolometric AGN luminosity rather than λL_λ, mass estimates based on different emission lines will show a systematic discrepancy which is a function of the color of the AGN continuum. This has actually been observed in mass estimates based on Hα/Hβ and C_IV lines, indicating that AGN broad line regions indeed scale with bolometric luminosity. Given that this effect seems to have been overlooked as yet, currently used single-epoch mass estimates are likely to be biased.

• 천문학회보
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• 제41권2호
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• pp.29.4-29.4
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• 2016

The relations between star formation and properties of molecular clouds are studied based on a sample of star forming regions in the Galactic Plane. Sources were selected by having radio recombination lines to provide identification of associated molecular clouds and dense clumps. Radio continuum and mid-infrared emission were used to determine star formation rates, while 13CO and submillimeter dust continuum emission were used to obtain masses of molecular and dense gas, respectively. We test whether total molecular gas or dense gas provides the best predictor of star formation rate. We also test two specific theoretical models, one relying on the molecular mass divided by the free-fall time, the other using the free-fall time divided by the crossing time. Neither is supported by the data. The data are also compared to those from nearby star forming regions and extragalactic data. The star formation "efficiency," defined as star formation rate divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all the molecular gas.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.135-142
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• 2000

A framework alternative to that of classical slope stability analysis is developed, wherein the soil mass is treated as a continuum and in situ soil stresses and strengths are computed accurately using inelastic finite element methods with general constitutive models. Within this framework, two alternative methods of stability analysis are presented. In the first, the strength characteristics of the soil mass are held constant, and the gravitational loading on the slope system is increased until failure is initiated by well-defined mechanisms. In the second approach, the gravity loading on the slope system is held constant, while the strength parameters of the slope mass are gradually decreased until well-defined failure mechanisms developed. Details on the applying both of the proposed methods, and comparisons of their characteristics on a number of solved example problems are presented.

• 한국해양공학회지
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• 제16권4호
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• pp.32-36
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• 2002

In this paper, a numerical methodology for health monitoring of weldment was proposed using finite element method coupled with continuum damage mechanics. The welding-induced residual stress distribution of T-joint weldment was calculated using a commercial finite element package SYSWELD+. The distribution of latent damage was evaluated from the stress and strain components taken as the output of a finite element calculation. Numerical examples were given to demonstrate the usefulness of this so-called "post-processing approach" in the case of welding-induced damage assessment.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.497-502
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• 2003

This study intends to provide the analytical and experimental damping characterization of carbon nanotube/epoxy composites. A constitutive model based on continuum mechanics is employed to describe epoxy and the perfectly bonded and partially bonded nanotubes. An interfacial stick-slip between the nanotubes and epoxy is considered to characterize the damping of the composites. For experimental estimation, beam-type specimens are prepared with a variation of nanotube concentration from 0.5% to 2% in weight. An ultrasonic agitation method is employed for enhancing the nanotube dispersion within epoxy. Damping of the composites is characterized in terms of the strain and the nanotube concentration. Results show that the nanotube concentration significantly affects the damping characteristics of the nanocomposites. A good correlation is found between the analytical prediction based on the stick-slip and the experimental measurements.

• 한국기계가공학회지
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• 제8권1호
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• pp.43-47
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• 2009

Recently, an approach for nano-scale material deformation has been developed that couples the atomistic and continuum approaches using Finite Element Method (FEM) and Molecular Dynamics (MD). However, this approach still has problems to connect two approaches because of the difference of basic assumptions, continuum and atomistic modeling. To solve this problem, an alternative way is developed that connects the QuasiMolecular Dynamics (QMD) and molecular dynamics. In this paper, we suggest the way to make and validate the MD-QMD coupled model.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.90-95
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• 2001

A continuum-based shape design sensitivity analysis (DSA) method is presented for the acoustic radiation from thin body. The normal derivative integral formulation is employed as an analysis formulation and differentiated directly by using material derivative to get the acoustic shape design sensitivity. In the acoustic sensitivity formulation, derivative coefficients of the structural normal velocities on the surface are required as the input. Thus, the shape design sensitivities of structural velocities on the surface with respect to the shape change are also calculated with continuum approach. A simple disk is considered as a numerical example to validate the accuracy and efficiency of the analytical shape design sensitivity equations derived in this research. This research should be very helpful to design an application involving thin body and to change its acoustic characteristics.