• Structural Engineering and Mechanics
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• 제66권1호
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• pp.85-96
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• 2018

This study investigates the response of functionally graded (FG) gas pipe under unsteady internal pressure and temperature. The pipe is proposed to be manufactured from FGMs rather than custom carbon steel, to reduce the erosion, corrosion, pressure surge and temperature variation effects caused by conveying of gases. The distribution of material graduations are obeying power and sigmoidal functions varying with the pipe thickness. The sigmoidal distribution is proposed for the 1st time in analysis of FG pipe structure. A Two-dimensional (2D) plane strain problem is proposed to model the pipe cross-section. The Fourier law is applied to describe the heat flux and temperature variation through the pipe thickness. The time variation of internal pressure is described by using exponential-harmonic function. The proposed problem is solved numerically by a two-dimensional (2D) plane strain finite element ABAQUS software. Nine-node isoparametric element is selected. The proposed model is verified with published results. The effects of material graduation, material function, temperature and internal pressures on the response of FG gas pipe are investigated. The coupled temperature and displacement FEM solution is used to find a solution for the stress displacement and temperature fields simultaneously because the thermal and mechanical solutions affected greatly by each other. The obtained results present the applicability of alternative FGM materials rather than classical A106Gr.B steel. According to proposed model and numerical results, the FGM pipe is more effective in natural gas application, especially in eliminating the corrosion, erosion and reduction of stresses.

• 헤리티지:역사와 과학
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• 제37권
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• pp.151-168
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• 2004

미륵사지 서탑은 현존하는 국내 최대 규모의 석탑이다. 현재까지 연구 진행된 결과에 따르면 미륵사지 서탑은 9층 석탑으로 추정되고 있다. 대규모의 건축물임에도 불구하고 이 탑에 대한 직접적인 창건 기록이 아직 발견되지 않은 상태다. 다만 미륵사의 창건기사가 "삼국유사(三國遺事), 무왕조(武王條)"에 연기설화로 나타나 있을 뿐이다. 설화적인 역사의 기록은 사실성에 대한 규명에 있어 다양한 분야에서의 연구가 필요하다. 건축사적 측면에서 평면형식의 시대 위치에 대한 고찰은 탑의 창건 연대 규명에 하나의 가시적 근거를 제공할 수 있다. 나아가서 미륵사지 서탑의 양식과 계통사 연구에 근간이 된다고 판단하여 수행코자 한다. 목조번안 석탑으로도 유명한 미륵사지 서탑은 우리나라 석탑의 시원적인 성격을 지니고 있다고 그동안의 연구에서 밝혀져 있다. 우리나라 불탑은 인도에서 발생되어 중국을 거쳐 도입되었다. 국내에서는 미륵사지 서탑보다 앞선 시기의 유례를 볼 수 없는 상태이므로 중국의 실 예를 참고하여 접근해 보고자 했다. 본 고에서는 한국(韓國)과 중국(中國)의 전석탑(塼石塔) 평면의 시대별 변천과정을 고찰하여 미륵사지 서탑의 평면형식이 7세기 초에 위치함을 결론으로 도출하였다.

• 식물조직배양학회지
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• 제21권1호
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• pp.59-63
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• 1994

세포유전적 유형이 다른 무릇 (Scilla scilloidise Coplex)의 조직배양에서 유도된 캘러스에서 염색체 변이를 조사하였다. AA유형의 캘러스에서 심한 수적, 구조적 변이가 관찰된 반면, BB 유형의 캘러스 세포에서는 상염색체의 변이가 발견되지 않았다. 이질 4배체인 AABB유형에서는 두개의 hypoploid 세포만 관찰되었으나, B게놈의 진정4배체인 BBBB유형에서는 hypoploid 세포와 함께 hyperploid 세포가 관찰되었다. 캘러스 세포에서 상염색체의 안정성은 B염색체를 지닌 식물에서 유도된 캘러스에서 더 높게 나타났다. 이는 배양세포에서 B염색체가 상염색체의 안정성에 선택적으로 기능하기 때문인 것으로 여겨진다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.211-214
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• 2001

Electronic Speckle Pattern Interferometry(ESPI) is one of optical technique to measure displacement precisely, uses CCD camera to show result image in real time. General ESPI system measures in-plane or out-of-plane displacement. Shearography is one of electronic speckle pattern interferometric methods which allow full-field observation of surface displacement derivatives and it is robust in vibration. The shearography provides non-contacting technique of evaluating defects nondestructively. In this study, the shearography was used to evaluate defects in Carbon Fiber Reinforced Plastic(CFRP). Various sizes of artificial defects were embedded in various depths of woven CFRP plate. Effects due to the variation of size and depth of defects were evaluated in this study.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2002년도 정기학술대회
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• pp.245-251
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• 2002

Electronic Speckle Pattern Interferometry(ESPI) is one of optical technique to measure displacement precisely, uses CCD camera to show result image in real time. General ESPI system measures in-plane or out-of-plane displacement. Shearography is one of electronic speckle pattern interferometric methods which allow full-field observation of surface displacement derivatives and it is robust in vibration. The shearography provides non-contacting technique of evaluating defects nondestructively In this study, the shearography was used to evaluate defects in Carbon Fiber Reinforced Plastic(CFRP). Various sizes of artificial defects were embedded in various depths of woven CFRP plate. Effects due to the variation of size and depth of defects were evaluated in this study.

• Ocean Systems Engineering
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• 제13권2호
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• pp.123-146
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• 2023

In this paper, Moore-Gibson-Thompson theory of thermoelasticity is considered to investigate the fundamental solution and vibration of plane wave in an isotropic photothermoelastic solid. The governing equations are made dimensionless for further investigation. The dimensionless equations are expressed in terms of elementary functions by assuming time harmonic variation of the field variables (displacement, temperature distribution and carrier density distribution). Fundamental solutions are constructed for the system of equations for steady oscillation. Also some preliminary properties of the solution are explored. In the second part, the vibration of plane waves are examined by expressing the governing equation for two dimensional case. It is found that for the non-trivial solution of the equation yield that there exist three longitudinal waves which advance with the distinct speed, and one transverse wave which is free from thermal and carrier density response. The impact of various models (i)Moore-Gibson-Thomson thermoelastic (MGTE)(2019), (ii) Lord and Shulman's (LS)(1967) , (iii) Green and Naghdi type-II(GN-II)(1993) and (iv) Green and Naghdi type-III(GN-III)(1992) on the attributes of waves i.e., phase velocity, attenuation coefficient, specific loss and penetration depth are elaborated by plotting various figures of physical quantities. Various particular cases of interest are also deduced from the present investigations. The results obtained can be used to delineate various semiconductor elements during the coupled thermal, plasma and elastic wave and also find the application in the material and engineering sciences.

• 조명전기설비학회논문지
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• 제25권5호
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• pp.79-84
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• 2011

In this study, breakdown characteristics of a vertical sphere-plane air gap in the presence of combustion flame were examined under the application of a.c. and d.c. high-voltages in order to investigate the effect of flame on the dielectric strength of air. Propane gas is used as the fuel of the flame, and the temperature distribution of air around the flame is measured. The polarity effects for the d.c. voltages and breakdown voltages of air when applied both of a.c. and d.c. voltages were examined in the case of the variation of the gap length and the horizontal distance between the flame and the high-voltage sphere electrode. The influence of relative air density, electrification and shape changes of the flame as factors that affect the breakdown voltages were discussed.

• Journal of Welding and Joining
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• 제21권6호
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• pp.77-83
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• 2003

The finite element analysis was performed for the cracks existing in residual stress fields in order to investigate the effects of configuration of residual stress distribution to the fatigue crack opening behaviour. And the variation of stress distributions adjacent to the crack caused by uploading was examined. The finite element model with contact elements for the crack plane and plane stress elements for the base material and the analytical method based on the superposition principle to estimate crack opening behaviour and the stress distribution adjacent to the crack subjected to uploading were used. The results of the analysis showed that crack opening behaviors and variations of stress distribution caused by uploading were changed depending on the configuration of residual stress distribution. When the crack existed in the region of compressive residual stress and the configuration of compressive residual stress distribution were inclined, a partial crack opening just behind of a crack tip occurred during uploading. Based on the above results, it was clarified that the crack opening behaviour in the residual stress field could be predicted accurately by the finite element analysis using these analytical method and model.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.247-269
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• 2020

A finite strip formulation was developed for buckling and free vibration analysis of laminated composite plates based on different shear deformation plate theories. The different shear deformation theories such as Zigzag higher order, Refined Plate Theory (RPT) and other higher order plate theories by variation of transverse shear strains through plate thickness in the parabolic form, sine and exponential were adopted here. The two loaded opposite edges of the plate were assumed to be simply supported and remaining edges were assumed to have arbitrary boundary conditions. The polynomial shape functions are applied to assess the in-plane and out-of-plane deflection and rotation of the normal cross-section of plates in the transverse direction. The finite strip procedure based on the virtual work principle was applied to derive the stiffness, geometric and mass matrices. Numerical results were obtained based on various shear deformation plate theories to verify the proposed formulation. The effects of length to thickness ratios, modulus ratios, boundary conditions, the number of layers and fiber orientation of cross-ply and angle-ply laminates were determined. The additional results on the same effects in the interaction of biaxial in-plane loadings on the critical buckling load were determined as well.

• Steel and Composite Structures
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• 제34권1호
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• pp.75-89
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• 2020

The current paper illustrates the effect of in-plane varying compressive force on critical buckling loads and buckling modes of sandwich composite laminated beam rested on elastic foundation. To generalize a proposed model, unified higher order shear deformation beam theories are exploited through analysis; those satisfy the parabolic variation of shear across the thickness. Therefore, there is no need for shear correction factor. Winkler and Pasternak elastic foundations are presented to consider the effect of any elastic medium surrounding beam structure. The Hamilton's principle is proposed to derive the equilibrium equations of unified sandwich composite laminated beams. Differential quadrature numerical method (DQNM) is used to discretize the differential equilibrium equations in spatial direction. After that, eigenvalue problem is solved to obtain the buckling loads and associated mode shapes. The proposed model is validated with previous published works and good matching is observed. The numerical results are carried out to show effects of axial load functions, lamination thicknesses, orthotropy and elastic foundation constants on the buckling loads and mode shapes of sandwich composite beam. This model is important in designing of aircrafts and ships when non-uniform compressive load and shear loading is dominated.