• 대한수학회논문집
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• 제38권4호
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• pp.1153-1162
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• 2023

In this paper, for the bounded solution of the non-densely defined non-autonomous evolution equation, we present the condition for asymptotic periodicity by using the circular spectral theory of functions on the half line and the extrapolation theory of non-densely defined evolution equation.

• 대한기계학회논문집B
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• 제26권11호
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• pp.1585-1596
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• 2002

The objectives of the present study are to numerically and experimentally investigate the steady and pulsatile flow phenomena in the circular tubes, to quantitatively compare the flow characteristics of Newtonian and non-Newtonian fluids, and to find meaningful hemodynamic information through the flow analysis in the human blood vessels. The particle image velocimetry is adopted to visualize the flow fields in the circular tube. and the results from the particle image velocimetry are used to validate the results of the numerical analysis. In order to investigate the blood flow phenomena in the circular tube. constitutive equations, which are suitable to describe the rheological properties of the non-Newtonian fluids. are determined, and the steady and pulsatile momentum equations are solved by the finite volume prediction. The velocity vectors of the steady and pulsatile flow in the circular tube obtained by the particle image velocimetry arc in good agreement with those by the numerical analysis. For the given mass flow rate. the axial velocity profiles of the Newtonian and the non-Newtonian fluids appear differently. The pulsatile flow phenomena of the Newtonian and the non-Newtonian fluids are quite different from those of the steady flow.

• 복합신소재구조학회 논문집
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• 제1권2호
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• pp.36-43
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• 2010

본 연구는 원형 및 비원형(타원형)단면을 갖는 복합폐합쉘의 좌굴하중 및 모드형상을 비교 분석하였다. 이때, 면내 회전자유도를 갖는 평면응력 요소와 추가변형률과 대체전단변형률을 도입한 휨 요소를 결합한 4절점 쉘 요소(4EAS-FS)를 작성하여 좌굴해석을 수행하였다. 해석모델의 매개변수는 기하학적 형상, 종횡비 및 화이버 보강각도로 설정하여 그에 따른 영향을 고찰하였다. 본 연구에서 제시한 원형 및 비원형 단면을 갖는 폐합쉘의 임계좌굴하중과 모드형상에 대한 폐합쉘 길이, 두께, 단면계수 및 화이버 보강각도 등 설계변수의 영향을 비교 분석하였다.

• 대한기계학회논문집
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• 제13권5호
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• pp.807-819
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• 1989

본 연구에서는 Donnell과 Flugge 셸 이론을 이용하여 단순지지된 비원형 단면을 가진 angle-ply 적층원통셸의 좌굴과 진동해석을 Soldatos의 해석과정을 따라 수행하고, 적층방법(stacking sequence)과 섬유각(fiber angle)의 변화에 따른 고유진 동수와 좌굴하중의 변화를 고찰하였으며, 초기 축하중을 받는 경우에 대한 고유진동수 의 변화에 대해서고 고찰하였다.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.411-427
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• 2006

The Discrete Element Method, DEM, is increasingly used in fracture studies of non-homogeneous continuous media, such as rock and concrete. A 2D circular rigid DEM formulation, developed to model concrete, has been adopted. A procedure developed to generate aggregate particles with a given aspect ratio and shape is presented. The aggregate particles are modelled with macroparticles formed by a group of circular particles that behave as a rigid body. Uniaxial tensile and compression tests performed with circular and non-circular aggregates, with a given aspect ratio, have shown similar values of fracture toughness when adopting uniform strength and elastic properties for all the contacts. Non-circular aggregate assemblies are shown to have higher fracture toughness when different strength and elastic properties are set for the matrix and for the aggregate/matrix contacts.

• Structural Engineering and Mechanics
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• 제58권5호
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• pp.783-797
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• 2016

Exact solutions for stresses, strains, and displacements of a perforated rectangular plate by an arbitrarily located circular hole subjected to both linearly varying in-plane normal stresses on the two opposite edges and in-plane shear stresses are investigated using the Airy stress function. The hoop stress occurring at the edge of the non-central circular hole are computed and plotted. Stress concentration factors (the maximum non-dimensional hoop stresses) depending on the location and size of the non-central circular hole and the loading condition are tabularized.

• 한국자동차공학회논문집
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• 제19권2호
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• pp.117-124
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• 2011

Valve springs with non-circular cross-section are widely used in automotive engines. Because of the reduced height, the oval cross-section provides some merits in its install height and stress distribution. This paper introduces a new method to generate optimal shape of the non-circular cross-section. For given width and height, arbitrary shape of the cross-section are described using the Hermite spline curves. Cross-section area and maximum stress level are chosen as performance indices, and nonlinear optimization problems are formulated with inequality constraints. Compared to a production spring wire, cross-section area can be reduced about 2.4 [%] without increasing maximum stress level. In addition, the other approach gives an optimum cross-section which reduces maximum stress level of 2.0 [%] without increasing cross-section area.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.57-58
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• 2006

A Simulation model is developed to minimize the path tracking errors when the non-circular cutting is done by a VCM(voice coil motor) driven tool. The relationship between PWM(Pulse Width Modulation) duty ratio and velocity of voice coil motor is theoretically derived from combining the circuit equation for the coils and the motion equation for the magnetic rod of the voice coil motor. The path tracking errors are showed differently according to the rotational speed, the number of segments and the control period in digital control. Given a required accuracy in the non-circular cutting, the optimal values for those parameters are determined based on the developed simulation model.

• Structural Engineering and Mechanics
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• 제88권3호
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• pp.287-299
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• 2023

This article describes experimental and numerical analyses of eccentrically loaded over the axially loaded circular concrete filled double-skinned steel tubular (CFDST) short columns. Tests on circular CFDST short columns under eccentric and concentric loading were conducted to assess their responses to the frequent intensity of 5-30 mm at the interval of each 5 mm eccentric loading conditions with constant cross-sectional proportions and width-to-thickness ratios of the outside and internal tubes. The non-linear finite-element analysis of circular CFDST short columns of eccentrically loaded over the axially loaded was performed using the ABAQUS to predict the structural behavior and compare the concentric loading capacity over the various eccentric loading conditions. The comparison outcomes show that the axial compressive strength of the circular CDFST short columns was 2.38-32.86%, lesser than the concentrically loaded short column with the inner circular section. Also, the influence of computer simulation employed is more efficient in forecasting the experimentally examined performance of circular CFDST stub columns.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.677-682
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• 2003

The non-linear dynamic characteristics of a semi-circular pipe conveying fluid are investigated when the pipe is clamped at both ends. To consider the geometric non-linearity for the radial and circumferential displacements, this study adopts the Lagrange strain theory for large deformation and the extensible dynamics based on the Euler-Bernoulli beam theory for slenderness assumption. By using the Hamilton principle, the non-linear partial differential equations are derived for the in-plane motions of the pipe, considering the fluid inertia forces as a kind of non-conservative forces. The linear and non-linear terms in the governing equations are compared with those in the previous study, and some significant differences are discussed. To investigate the dynamic characteristics of the system, the discretized equations of motion are derived form the Galerkin method. The natural frequencies varying with the flow velocity are computed fen the two cases, which one is the linear problem and the other is the linearized problem in the neighborhood of the equilibrium position. Finally, the time responses at various flow velocities are directly computed by using the generalized- method. From these results, we should to describe the non-linear behavior to analyze dynamics of a semi-circular pipe conveying fluid more precisely.