• Interaction and multiscale mechanics
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• 제1권1호
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• pp.143-156
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• 2008

Elliptical tubes may buckle in an elastic local buckling failure mode under uniform compression. Previous analyses of the local buckling of these members have assumed that the cross-section is hollow, but it is well-known that the local buckling capacity of thin-walled closed sections may be increased by filling them with a rigid medium such as concrete. In many applications, the medium many not necessarily be rigid, and the infill can be considered to be an elastic material which interacts with the buckling of the elliptical tube that surrounds it. This paper uses an energy-based technique to model the buckling of a thin-walled elliptical tube containing an elastic infill, which elucidates the physics of the buckling phenomenon from an engineering mechanics basis, in deference to a less generic finite element approach to the buckling problem. It makes use of the observation that the local buckling in an elliptical tube is localised with respect to the contour of the ellipse in its cross-section, with the localisation being at the region of lowest curvature. The formulation in the paper is algebraic and it leads to solutions that can be determined by implementing simple numerical solution techniques. A further extension of this formulation to a stiffness approach with multiple degrees of buckling freedom is described, and it is shown that using the simple one degree of freedom representation is sufficiently accurate for determining the elastic local buckling coefficient.

• Interaction and multiscale mechanics
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• 제2권3호
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• pp.223-233
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• 2009

This paper presents a new nonlocal stress variational principle approach for the transverse free vibration of an Euler-Bernoulli cantilever nanobeam with an initial axial tension at its free end. The effects of a nanoscale at molecular level unavailable in classical mechanics are investigated and discussed. A sixth-order partial differential governing equation for transverse free vibration is derived via variational principle with nonlocal elastic stress field theory. Analytical solutions for natural frequencies and transverse vibration modes are determined by applying a numerical analysis. Examples conclude that nonlocal stress effect tends to significantly increase stiffness and natural frequencies of a nanobeam. The relationship between natural frequency and nanoscale is also presented and its significance on stiffness enhancement with respect to the classical elasticity theory is discussed in detail. The effect of an initial axial tension, which also tends to enhance the nanobeam stiffness, is also concluded. The model and approach show potential extension to studies in carbon nanotube and the new result is useful for future comparison.

• Smart Structures and Systems
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• 제13권4호
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• pp.501-515
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• 2014

This paper presents a linear computational homogenization framework to evaluate the effective (or generalized) electromechanical coupling coefficient (EMCC) of adaptive structures with piezoelectric structural fiber (PSF) composite elements. The PSF consists of a silicon carbide (SiC) or carbon core fiber as reinforcement to a fragile piezo-ceramic shell. For the micro-scale analysis, a micromechanics model based on the variational asymptotic method for unit cell homogenization (VAMUCH) is used to evaluate the overall electromechanical properties of the PSF composites. At the macro-scale, a finite element (FE) analysis with the commercial FE code ABAQUS is performed to evaluate the effective EMCC for structures with the PSF composite patches. The EMCC is postprocessed from free-vibrations analysis under short-circuit (SC) and open-circuit (OC) electrodes of the patches. This linear two-scale computational framework may be useful for the optimal design of active structure multi-functional composites which can be used for multi-functional applications such as structural health monitoring, power harvest, vibration sensing and control, damping, and shape control through anisotropic actuation.

• 한국대기환경학회지
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• 제21권1호
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• pp.49-62
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• 2005

Lake Paldang is a main resource of drinking water for 20 million people in the greater Seoul area. Dry deposition amounts of nitrogen and sulfur were estimated for three typical days in each season over the watershed of Lake Paldang. Models- 3/CMAQ (Community Multiscale Air Quality) and MM5 (Mesoscale Model) were used to predict air quality and meteorology, respectively. Aerosols as well as gaseous pollutants were considered. Nitrogen was mainly deposited in the form of HNO, while most of sulfur was deposited in the form of SO$_2$. Contribution of secondary pollutants was the largest in fall since they were transported from the greater Seoul area. However, contribution of secondarily-formed particulate pollutants to the nitrogen deposition was the largest in winter because semi-volatile ammonium nitrate favors lower temperature. Annual deposition amounts of nitrogen and sulfur were 37% and 26% of their emission amounts, respectively, over the watershed of Lake Paldang. Higher value of the nitrogen deposition showed a more influence of pollutants emitted in the greater Seoul area.

• 한국전산구조공학회논문집
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• 제24권4호
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• pp.413-419
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• 2011

나노 크기의 허니콤 구조물은 거시적 크기의 허니콤 구조물에 비해 보다 높은 부피 대비 표면적 비율을 구현하여 전기적, 화학적인 촉매로써 기능성을 극대화할 수 있다. 나노 크기의 구조물은 거시적 크기의 구조물과 다른 기계적 거동양상을 보이며 이는 표면효과에 기인한다. 이러한 표면효과는 원자 수준 전산모사(atomistic simulation)를 통해 규명할 수 있으나 나노 허니콤 구조물의 거동을 예측하는 것은 현실적으로 과도한 전산자원 및 계산시간으로 인해 불가능한 실정이다. 본 연구에서는 표면응력 탄성모델을 적용한 브리징방법을 균질화기법과 연계하여 나노 크기의 허니콤 구조물의 기계적 거동을 효율적으로 예측하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.67-70
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• 2004

An investigation was performed to study the impact damage of the laminated composite plates caused by a low- velocity foreign object with multi-scale modeling based on the concepts of Direct Numerical Simulation (DNS)[4]. In the micro-scale part, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. A micro-scalemodel was developed for predicting the initiation of the damage and the extent of the final damage as a function of material properties, laminate configuration and the impactor's mass, etc. Anda macro-scale model was developed for description of global dynamic behavior. The connection betweenmicroscopic and macroscopic is implemented by the tied interface constraints of LS-DYNA contact card. A transient dynamic finite element analysis was adopted for calculating the contact force history and the stresses and strains inside the composites during impact resulting from a point-nose impactor. The low-velocity impact events such as contact force, deformation, etc. are simulated in the macroscopic sense and the impact damages, fiber-breakage, matrix cracking and delamination etc. are examined in the microscopic sense.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.157-172
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• 2013

This paper presented an investigation of macromolecular suspension in a grooved channel by using the dissipative particle dynamics (DPD) with finitely extensible non-linear elastic (FENE) bead spring chains model. Before studying the movement and evolution of macromolecules, the DPD method was first validated by modeling the simple fluid flow in the grooved channel. For both simple fluid flow and macromolecular suspension, the flow fields were analyzed in detail. It is found that the structure of the grooved channel with sudden contraction and expansion strongly affects the velocity distribution. As the width of the channel reduces, the horizontal velocity increases simultaneously. Vortices can also be found at the top and bottom corners behind the contraction section. For macromolecular suspension, the macromolecular chains influence velocity and density distribution rather than the temperature and pressure. Macromolecules tend to drag simple fluid particles, reducing the velocity with density and velocity fluctuations. Particle trajectories and evolution of macromolecular conformation were investigated. The structure of the grooved channel with sudden contraction and expansion significantly influence the evolution of macromolecular conformation, while macromolecules display adaptivity to adjust their own conformation and angle to suit the structure so as to pass the channel smoothly.

• 대한전자공학회논문지SP
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• 제42권6호
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• pp.43-54
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• 2005

이본 논문에서는 Bayesian 영상 분할법과 SOM(Self Organization feature Map)을 이용한 텍스쳐(Texture) 분할 방법을 제안한다. SOM의 입력으로 다중 스케일에서의 웨이블릿 계수를 사용하고, 훈련된 SOM으로부터 관측 데이터에 대한 우도(尤度, likelihood)와 사후확률을 구하는 방법을 제시한다. 훈련된 SOM들로부터 구한 사후확률과 MAP(Maximum A Posterior) 분류법을 이용하여 텍스쳐 분할을 얻는다. 그리고 문맥 정보를 이용하여 텍스쳐 분할 결과를 개선하였다. 제안 방법은 HMT(Hidden Markov Tree)을 이용한 텍스쳐 분할보다 더 우수한 결과를 보여준다. 또한 SOM과 HMTseg라고 불리는 다중스케일 Bayesian 영상 분할 기법을 이용한 텍스쳐 분할 결과는 HMT와 HMTseg을 이용한 결과보다 더 우수한 성능을 보여준다.

• Interaction and multiscale mechanics
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• 제3권2호
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• pp.173-191
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• 2010

Damage detection plays a very important role to the maintenance of bridge structures. Traditional damage detection methods are usually based on structural dynamic properties, which are acquired from pre-installed sensors on the bridge. This is not only time-consuming and costly, but also suffers from poor sensitivity to damage if only natural frequencies and mode shapes are concerned in a noisy environment. Recently, the idea of using the dynamic responses of a passing vehicle shows a convenient and economical way for damage detection of bridge structures. Inspired by this new idea and the well-established tap test in the field of non-destructive testing, this paper proposes a new method for obtaining the damage information through the acceleration of a passing vehicle enhanced by a tapping device. Since no finger-print is required of the intact structure, this method can be easily implemented in practice. The logistics of this method is illustrated by a vehicle-bridge interaction model, along with the sensitivity analysis presented in detail. The validity of the method is proved by some numerical examples, and remarks are given concerning the potential implementation of the method as well as the directions for future research.

• 스마트미디어저널
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• 제8권2호
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• pp.39-45
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• 2019

딥러닝이 보편화되면서 예측 결과를 설명하는 연구가 중요해졌다. 최근 슈퍼픽셀에 기반한 다중스케일 결합 기법이 제안되었는데, 물체의 모양을 유지함으로써 시각적 공감이라는 장점을 제공한다. 이 기법은 예측 차이라는 원리에 기반을 두고 있으며, 슈퍼픽셀을 가리고 얻은 예측 결과와 원래 예측 결과의 차이를 보고 돌출맵을 구성한다. 본 논문은 슈퍼픽셀을 가리는 제외 연산뿐 아니라 슈퍼픽셀만 보여주는 포함 연산까지 사용하는 새로운 기법을 제안한다. 실험 결과 제안한 방법은 IoU에서 3.3%의 성능 향상을 보인다.