• 한국방재학회 논문집
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• 제7권5호
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• pp.61-71
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• 2007

Navier 해 및 유한요소 해를 두께 방향으로 재료의 성질이 변하는 점진기능재료 판 및 쉘의 해석을 위해 제시하였다. 판과 쉘의 두께를 따라 완만하게 변하는 등방성 구조물의 두께방향에 따른 역학적 특성을 고려하기 위하여 S 형상 함수를 적용한 점진기능재료를 고려하였다. 비선형 9 절점 요소기저 Lagrangian 쉘 요소의 정식화를 기하학적 비선형 해석을 위해 제시하였다. 자연 좌표계에 의한 변형률이 본 연구의 쉘요소에 사용된다. 1차 전단변형이론에 의한 수치 해석 예제로 상면과 하면의 탄성 계수의 변화, 하중조건, 형상 비 그리고 폭-두께 비에 따른 역학적 거동을 연구하였다. 또한 거듭제곱 매개 변수의 변화에 따른 점진기능재료 구조물의 결과들을 조사하였다.

• 한국가스학회지
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• 제12권3호
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• pp.24-30
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• 2008

본 본문에서는 유한요소법과 다구찌의 최적설계법을 사용하여 헬멧의 모체 구조물에 대한 응력과 변형률 특성을 소재의 특성치, 헬멧의 두께, 보강뼈대의 수량과 두께의 함수로 각각 해석하였다. 소방관과 가스 작업자의 안전성 확보를 위해 필요한 헬멧에 대한 최적화 설계연구는 외부에서 작용하는 충격력에 대한 강도안전성을 높이고, 충격에너지 흡수력을 강화시킬 수 있는 데이터를 제공하기 때문에 대단히 중요하다. 따라서 헬멧 모체 구조물의 균일한 두께는 헬멧 모체의 중량을 감축하고 변형률 에너지를 높여 준다는 측면에서 줄여야 하지만, 헬멧의 보강뼈대의 수량과 두께는 헬멧의 충격강도를 높여준다는 측면에서 늘려주는 최적화 설계가 추진되어야 헬멧의 안전성은 확보된다는 해석결과를 제시하였다.

• Structural Engineering and Mechanics
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• 제7권4호
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• pp.401-412
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• 1999

The purpose of this paper is to show how the Evolutionary Structural Optimization (ESO) algorithm developed by Xie and Steven can be extended to optimal design problems of thin shells subjected to thermal loading. This extension simply incorporates an evolutionary iterative process of thermoelastic thin shell finite element analysis. During the evolution process, lowly stressed material is gradually eliminated from the structure. This paper presents a number of examples to demonstrate the capabilities of the ESO algorithm for solving topology optimization and thickness distribution problems of thermoelastic thin shells.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.395-410
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• 2006

This paper reports the result of an investigation into wave propagation in orthotropic laminated piezoelectric cylindrical shells in hydrothermal environment. A dynamic model of laminated piezoelectric cylindrical shell is derived based on Cooper-Naghdi shell theory considering the effects of transverse shear and rotary inertia. The wave characteristics curves are obtained by solving an eigenvalue problem. The effects of layer numbers, thickness of piezoelectric layers, thermal loads and humid loads on the wave characteristics curves are discussed through numerical results. The solving method presented in the paper is validated by the solution of a classical elastic shell non-containing the effects of transverse shear and rotary inertia. The new features of the wave propagation in laminated piezoelectric cylindrical shells with various laminated material, layer numbers and thickness in hydrothermal environment and some meaningful and interesting results in this paper are helpful for the application and the design of the ultrasonic inspection techniques and structural health monitoring.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.447-461
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• 2006

Here, the axisymmetric free flexural vibrations and thermal stability behaviors of functionally graded spherical caps are investigated employing a three-noded axisymmetric curved shell element based on field consistency approach. The formulation is based on first-order shear deformation theory and it includes the in-plane and rotary inertia effects. The material properties are graded in the thickness direction according to the power-law distribution in terms of volume fractions of the constituents of the material. The effective material properties are evaluated using homogenization method. A detailed numerical study is carried out to bring out the effects of shell geometries, power law index of functionally graded material and base radius-to-thickness on the vibrations and buckling characteristics of spherical shells.

• 대한조선학회지
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• 제22권1호
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• pp.1-8
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• 1985

The buckling characteristics of cylindrical shells with a circular hole, under axially compressed loads, have been analyzed and the results have been compared with existed experimental results. Deflection function with decay factor is assumed, and stress distribution around a circular hole in tensioned infinite plate is used for formulating buckling energy function. Applying Rayleigh Ritz procedure to this energy function, characteristic equation of eigenvalue problem is determined. Buckling load is defined by the minimum value of eigenvalues calculated according to several decay factors, and as the radius ratios of a circular hole (a/R) and shell thickness ratios (R/t) are varied, the reducing characteristics of buckling load are studied. As a result, buckling loads are reduced by about 50% according to some radius ratios ($a/R{\geq}0.15$) of circular hole and are not nearly affected by shell thickness ratio(R/t).

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.539-544
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• 2013

$Ag@SiO_2@SiO_2$(FITC) nanocomposites were prepared by the simple polyol process and St$\ddot{o}$ber method. Fluorescence enhancement of fluorescein moiety (fluorescein isothiocyanate, FITC) was investigated in the presence of silver nanoparticles in $Ag@SiO_2@SiO_2$(FITC) system with varying thickness (X nm) of first silica shell. Maximum enhancement factor of 4.3 fold was achieved in $Ag@SiO_2@SiO_2$(FITC) structure with the first silica shell thickness of 8 nm and the average separation distance of 11 nm between the surface of silver nanoparticle and fluorescein moiety. The enhancement is believed to be originated from increased excitation rate of fluorescein moiety due to concentrated local electromagnetic field which was improved by interaction of light with silver nanoparticles.

• Geomechanics and Engineering
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• 제35권5호
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• pp.465-473
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• 2023

The higher order shear deformable model and an exact analytical method is used for analytical bending analysis of a cylindrical shell subjected to mechanical loads, in this work. The shell is modelled using sinusoidal bivariate shear strain theory, and the static governing equations are derived using changes in virtual work. The eigenvalue-eigenvector method is used to exactly solve the governing equations for a constrained cylindrical shell The proposed kinematic relation decomposes the radial displacement into bending, shearing and stretching functions. The main advantage of the method presented in this work is the study of the effect of clamping constraints on the local stresses at the ends. Stress, strain, and deformation analysis of shells through thickness and length.

• 농업과학연구
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• 제18권1호
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• pp.10-20
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• 1991

본(本) 연구는 한국재래오골계(韓國在來鳥骨鷄)의 난구성분(卵構成分) 및 난질(卵質)에 대한 유전력(遺傳力) 및 유전상관(遺傳相關)을 추정(推定)하여 닭의 효율적(效率的)인 개량을 위한 육종목표(育種目標)의 설정(設定)과 선발(選拔)을 수행하는데 필요한 기초자료을 얻고자 충남대학교(忠南大學校) 농과대학(農科大學) 부속동물사육장(附屬動物飼育場)에서 1987연 6월 18일부터 1989년 4월 6일까지 500일 동안 부가계(父家系) 20수와 모가계(母家系) 150수에서 생산된 450수의 자손으로부터 생산된 계란(鷄卵) 38,320개의 난구성분(卵構成分)을 조사하여 얻어진 결과는 다음과 같다. 1. 난구성분(卵構成分)의 유전력추정치(遺傳力推定値)는 부분산성분(父分散成分), 모분산성분(母分散成分) 및 부모분산성분(父母分散成分)에서 난백중(卵白重)은 각각 0.620 - 0.723, 0.206 - 0.300 및 0.413 - 0.511이었고, 난황중(卵黃重)은 각각 0.439, - 0.737. 0.484 - 0.544 및 0.492 - 0.615이었으며, 난각중(卵殼重)은 각각 0.172 - 0.387, 0.412 - 0.642 및 0.309 - 0.503이었다. 2. 난질(卵質)의 유전력추정치(遺傳力推定値)는 부분산성분(父分散成分), 모분산성분(母分散成分) 및 부모분산성분(父母分散成分)에서 난각(卵殼) 두께는 각각 0.197 - 0.279, 0.557 - 0.819 및 0.428 - 0.508이었고, 난백고(卵白高)는 각각 0.202 - 0.394, 0.119 - 0.678 및 0.256 - 0.440이었으며, Haught units는 각각 0.108 - 0.443, 0.237 - 0.698 및 0.244 - 0.399이었다. 3. 난구성분간(卵構成分間)의 유전상관(遺傳相關) 및 표현형상관(表現型相關)은 난백중(卵白重)과 난황중간(卵黃重間)에 각각 0.089 - 0.564, 0.084 - 0.235이었고, 난백중(卵白重)과 난각중간(卵殼重間)에는 각각 0.396 - 0.925, 0.225 - 0.544이었으며, 난황중(卵黃重)과 난각중간(卵殼重間)에는 각각 0.220 - 0.375 및 0.098 - 0.358이었다. 4. 난질간(卵質間)의 유전상관(遺傳相關) 및 표현형상관(表現型相關)은 난각(卵殼)두께와 난백고간(卵白高間)에 - 0.082 - 0.346, - 0.163 - 0.060이었고, 난각(卵殼)두께와 Haught units간(間)에는 각각 - 0.076 - 0.167 및 - 0.185 - 0.010이었으며 난백고(卵白高)와 Haught units간(間)에는 각각 0.338 - 0.604 및 0.154 - 0.285 이었다. 5. 난구성분(卵構成分)과 난질간(卵質間)의 유전상관(遺傳相關)에서 난백중(卵白重)과 난각(卵殼)두께, 난백고(卵白高), Haught units간(間)에는 각각 - 0.380 - - 0.002, 0.239 - 0.381 및 - 0.279 - 0.127이었고, 난황중(卵黃重)과 난각(卵殼)두께, 난백고(卵白高) 및 Haught units간(間)에는 각각 - 0.294 - 0.133, - 0.049 - 0.133 및 - 0.196 - - 0.136이었으며, 난각중(卵殼重)과 난각(卵殼)두께, 난백고(卵白高), Haught units간(間)에는 각각 0.127 - 0.476, 0.140 - 0.273 및 0.038 - 0.223 이었다.

• Advances in concrete construction
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• 제13권5호
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• pp.367-376
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• 2022

Theoretical study of vibration distinctiveness of rotating cylindrical are examined for three volume fraction laws viz.: polynomial, exponential and trigonometric. These laws control functionally graded material composition in the shell radius direction. Functionally graded materials are controlled from two or more materials. In practice functionally graded material comprised of two constituent materials is used to form a cylindrical shell. For the current shell problem stainless steel and nickel are used for the shell structure. A functionally graded cylindrical shell is sanctioned into two types by interchanging order of constituent materials from inner and outer side for Type I and Type II cylindrical shell arrangement. Fabric composition of a functionally graded material in a shell thickness direction is controlled by volume fraction law. Variation of power law exponent brings change in frequency values. Influence of this physical change is investigated to evade future complications. This procedure is capable to cater any boundary condition by changing the axial wave number. But for simplicity, numerical results have been evaluated for clamped- simply supported rotating cylindrical shells. It has been observed from these results that shell frequency is bifurcated into two parts: one is related to the backward wave and other with forward wave. It is concluded that the value of backward frequency is some bit higher than that forward frequency. Influence of volume fraction laws have been examined on shell frequencies. Backward and forward frequency curves for a volume fraction law are upper than those related to two other volume fraction laws. The results generated furnish the evidence regarding applicability of present shell model and also verified by earlier published literature.