• 한국전산구조공학회논문집
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• 제30권4호
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• pp.329-334
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• 2017

다양한 산업 분야의 구조물은 여러 부구조의 조합으로 구성되며, 시스템의 자유도 또한 무수히 많다. 높은 복잡성을 가지는 구조물의 해석 및 계산 효율을 향상시키기 위해서 해석 모델의 단순화 및 자유도 축소가 요구된다. 지난 50여 년 동안 규모가 큰 공학적 문제를 단순화하기 위해 다양한 부분구조화 기법들이 개발되어 왔다. 이러한 부분구조화 기법들은 Newton-Raphson 알고리즘 등과 같은 반복계산을 동반하는 비선형 구조해석 문제 해석에 매우 효과적이다. 본 논문에서는 기 개발된 비선형 부분구조화 기법 중의 하나인 모드미분(modal derivatives)을 이용하여 기하비선형 보의 모델 축소에 적용하고자 한다. 모드미분은 모드 기반 축소 기저의 2차항의 형태로, 선형모드의 조합으로 근사 가능한 변위벡터를 미소변위에 대한 Taylor 급수를 통해 확인할 수 있으며, 시스템의 고유치 문제를 모드 좌표로 미분을 함으로써 얻어진다. 모드미분에는 비선형 접선 강성행렬의 미분을 포함하고 있으며, 이는 유한차분법 등의 근사를 통해 계산할 수 있다. 제안된 방법론은 기하학적 비선형 문제에 우수한 성능을 보이는 동시회전 유한요소법에 적용하였다. 수치예제를 통해 보의 경계가 수평으로 움직일 수 있는 문제에서는 기존의 모드축소기법이 매우 비효율적임을 알 수 있었다. 한편 모드미분을 이용한 축소기법은 다양한 경계조건에 대하여 우수한 성능을 보임을 확인하였다.

• 한국전산구조공학회논문집
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• 제31권4호
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• pp.183-190
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• 2018

본 논문에서는 보의 대변형 및 비틀림 변형을 고려한 인간동력항공기 주익 main spar 질량 최적화 과정을 소개한다. 순차적 이차 프로그래밍 기법(sequential quadratic programming)을 최적화 기법으로 선정해 구조 최적설계에 적절한 최적화 알고리즘을 수행하였다. Main spar 내부 직경, 적층 두께 등을 설계변수로 설정하였다. 목적함수에는 질량 최소화, 굽힘 변형 변위 일정, 그리고 비틀림 변형 각도 일정 등의 요소를 포함하였다. 굽힘과 비틀림 변형 계산엔 대변형 해석에 적합한 기하학적 정밀 보 모델을 도입하였으며, 기하학적 정밀 보 모델에 필요한 단면 물성은 Variational Asymptotic Beam Sectional Analysis(VABS) 단면 해석프로그램를 통해 계산하였다. 그 결과 main spar의 굽힘 변형 및 비틀림 변형을 최대 1.45% 이내로 유지한 채로 7.88%의 질량 감소를 이루는 최적설계를 도출하였다, 이후 응력복원 및 변형률 복원을 통해 최적설계의 구조적 안정성과 최적화 과정의 타당성을 검증하였다.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2011년도 임시총회 및 하계학술연구발표회
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• pp.96-98
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• 2011

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.313-316
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• 2001

This paper shows performance of smart antenna systems with various adaptive algorithms. Geometrically based single bounce elliptical model (GBSBEM) is generated and the SMR performance of various adaptive algorithms are analyzed. According to the SINR, the system capacity of each algorithm are calculated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.57-58
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• 2011

• Structural Engineering and Mechanics
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• 제52권2호
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• pp.221-238
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• 2014

A four-noded curved shell finite element for the geometrically non-linear analysis of beams curved in plan is introduced. The structure is conceived as a sequence of macro-elements (ME) having the form of transversal segments of identical topology where each slice is formed using a number of the curved shell elements which have 7 degrees of freedom (DOF) per node. A curved box-girder beam example is modelled using various meshes and linear analysis results are compared to the solutions of a well-known computer program SAP2000. Linear and non-linear analyses of the beam under increasing uniformly distributed loads are also carried out. In addition to box-girder beams, the proposed element can also be used in modelling open-section beams with curved or straight axes and circular plates under radial compression. Buckling loads of a circular plate example are obtained for coarse and successively refined meshes and results are compared with each other. The advantage of this element is that curved systems can be realistically modelled and satisfactory results can be obtained even by using coarse meshes.

• Steel and Composite Structures
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• 제18권1호
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• pp.51-69
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• 2015

In recent years, the use of fiber reinforced polymer composites has increased because of their unique features. They have been used widely in the aircraft and space industries, medical and sporting goods and automotive industries. Thanks to their beneficial and various advantages over traditional materials such as high strength, high rigidity, low weight, corrosion resistance, low maintenance cost, aesthetic appearance and easy demountable or moveable construction. In this paper, it is aimed to determine and compare the geometrically nonlinear static and dynamic analysis results of footbridges using steel and glass fiber reinforced polymer composite (GFRP) materials. For this purpose, Halgavor suspension footbridge is selected as numerical examples. The analyses are performed using three identical footbridges, first constructed from steel, second built only with GFRP material and third made of steel- GFRP material, under static and dynamic loadings using finite element method. In the finite element modeling and analyses, SAP2000 program is used. Geometric nonlinearities are taken into consideration in the analysis using P-Delta criterion. The numerical results have indicated that the responses of the three bridges are different and that the response values obtained for the GFRP composite bridge are quite less compared to the steel bridge. It is understood that GFRP material is more useful than the steel for the footbridges.

• Design & Manufacturing
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• 제2권5호
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• pp.16-20
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• 2008

Almost all injection molds have multi-cavity runner system for mass production, which are designed with geometrically balanced runner system in order to accomplish filling balance between cavity to cavity during processing; However, even though geometrically balanced runner is used, filling imbalances have been observed. In these day, the CAE has been used widely in injection molding. However, CAE with fusion mesh can't indicate such as jetting, flow mark and filling imbalance in multi cavity mold. In this study, we investigated the filling imbalance according to runner shapes by CAE analysis. As a result in CAE, in case of binary branch runner system, filling imbalance was indicated between cavity to cavity, but the flow pattern of each cavity uniformed in unary branch runner system.

• Advances in nano research
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• 제8권3호
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• pp.255-264
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• 2020

Buckling and post-buckling cases are often occurred in aorta artery because it affected by higher pressure. Also, its stability has a vital importance to humans and animals. The loss of stability in arteries may lead to arterial tortuosity and kinking. In this paper, post-buckling analysis of aorta artery is investigated under axial compression loads on the basis of Euler-Bernoulli beam theory by using finite element method. It is known that post-buckling problems are geometrically nonlinear problems. In the geometrically nonlinear model, the Von Karman nonlinear kinematic relationship is employed. Two types of support conditions for the aorta artery are considered. The considered non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. The aorta artery is modeled as a cylindrical tube with different average diameters. In the numerical results, the effects of the geometry parameters of aorta artery on the post-buckling case are investigated in detail. Nonlinear deflections and critical buckling loads are obtained and discussed on the post-buckling case.

• 천문학회지
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• 제28권1호
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• pp.97-107
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• 1995

The stability of the geometrically thin, two-temperature hot accretion disk is studied. The general criterion for thermal instability is derived from the linear local analyses, allowing for advective cooling and dynamics in the vertical direction. Specifically, classic unsaturated Comptonization disk is analysed in detail. We find five eigen-modes: (1) Heating mode grows in thermal time scale, $(5/3)({\alpha}{\omega})^{-1}$, where alpha is the viscosity parameter and w the Keplerian frequency. (2) Cooling mode decays in time scale, $(2/5)(T_e/T_i)({\alpha}{\omega})^{-1}$, where $T_e\;and\;T_i$ are the electron and ion temperatures, respectively. (3) Lightman-Eardley viscous mode decays in time scale, $(4/3)(\Lambda/H)^2({\alpha}{\omega})^{-1}$, where $\Lambda$ is the wavelength of the perturbation and H the unperturbed disk height. (4) Two vertically oscillating modes oscillate in Keplerian time scale, $(3/8)^{1/2}\omega^{-1}$ with growth rate $\propto\;(H/\Lambda)^2$. The inclusion of dynamics in the vertical direction does not affect the thermal instability, adding only the oscillatory modes which gradually grow for short wavelength modes. Also, the advective cooling is not strong enough to suppress the growth of heating modes, at least for geometrically thin disk. Non-linear development of the perturbation is followed for simple unsaturated Compton disk: depending on the initial proton temperature perturbation, the disk can evolve to decoupled state with hot protons and cool electrons, or to one-temperature state with very cool protons and electrons.