• 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.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 1992년도 수공학연구발표회논문집
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• pp.55-66
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• 1992

수로단면의 유속분포가 균일하지 않으므로, 에너지 원리의 $\alpha$값과 운동량원리의 $\beta$값 각각에 미치나, 대부분 실무에서는 이들 값을 추정하는 어려움 때문에 통상 1로 가정하여 사용하고 있다. 본 연구에서는 실용적으로 이용할 수 있는 공식을 유도하고, 기존에 사용되고있는 Prandtl-Von Karman 공식과 비교 검토하였으며, 유속분포계수 공식을 유도하기 위하여, 수로 바닥과 수 표면까지도 포함한 전 영역에서 비교적 정확한 유속분포를 나타내는 Chiu의 유속공식을 사용하였다. 또한, 실용적목적을 위해 유속데이타 없이 유속분포 계수를 구하기 위해서 Manning공식과 Chiu공식을 사용하였으며, 실험실 및 현장데이타를 위의 연구에 적용 검증하였다.

• 한국안전학회지
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• 제19권4호
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• pp.155-160
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• 2004

판의 두께에 선형적으로 변화하는 온도분포의 열하중을 받는 단순지지의 사각형 박판을 해석하였다. 열에 의한 판의 처짐이 판두께에 비해 상대적으로 과대하여 막응력이 부수적으로 발생하여 문제는 비선형 해석이 된다. 큰 처짐을 가지는 기하학적 비선형 문제를 지배하는 기본방정식은 von Karman 방정식이 사용되며 차분법으로 수치해석 한다. 차분화 하여 얻어지는 유사선형 대수방정식은 반복법을 도입하여 해석하고 결과치를 해석적으로 얻은 해와 비교 검토한다.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2008년도 춘계 학술발표회 논문집
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• pp.74-79
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• 2008

본 논문에서는 유한요소법을 이용하여 저속충격을 받는 복합적층판(Graphite/Epoxy)의 충격과도응답을 조사한다. 판의 대처짐을 고려한 von-Karman 이론에 Mindlin의 전단변형 효과와 회전관성 효과를 포함한 비선형 이론을 도입한다. 과도응답의 수렴은 정적만입실험을 통해 얻은 접촉법칙을 사용하며, 다양한 복합적층판의 두께 변화에 따른 접촉력, 변위응답, 변형률 등을 조사하여 비교 분석한다.

• Wind and Structures
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• 제12권6호
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• pp.541-551
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• 2009

This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti's formula or Maskell's theory with ${\varepsilon}$=0.96. In the super-critical regime, one should prefer using Glauert's formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the flow regimes.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.281-289
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• 2016

In this paper, a new dynamic model for modal analysis of a rotating cantilever beam with a tip-mass is developed. The nonlinear strain such as von Karman type and the corresponding linearized stress are used to consider the geometric nonlinearity, and Euler-Bernoulli beam theory is applied in the present model. The nonlinear equations of motion and the associated boundary conditions which include the inertia of the tip-mass are derived through Hamilton's principle. In order to investigate modal characteristics of the present model, the linearized equations of motion in the neighborhood of the equilibrium position are obtained by using perturbation technique to the nonlinear equations. Since the effect of the tip-mass is considered to the boundary condition of the flexible beam, weak forms are used to discretize the linearized equations. Compared with equations related to stiffening effect due to centrifugal force of the present and the previous model, the present model predicts the dynamic characteristic more precisely than the another model. As a result, the difference of natural frequencies loci between two models become larger as the rotating speed increases. In addition, we observed that the mode veering phenomenon occurs at the certain rotating speed.

• 한국구조물진단유지관리공학회 논문집
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• 제6권3호
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• pp.139-149
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• 2002

Explicit 직접적분법을 사용하여 충격하중을 받는 박판의 후좌굴거동을 해석할 수 있는 알고리즘을 제안하였다. von Karman의 대변위 판 이론과 Marquerre의 쉘 이론을 이용하여 유도한 직사각형 평판 유한요소는 박판의 초기처짐과 기하학적 비선형 거동을 고려할 수 있다. 중앙차분법을 바탕으로 해석 알고리즘을 개발하였고 이를 프로그램화 시켜, 하중형상과 재하시간이 다른 충격하중에 대하여 박판의 동적 좌굴거동을 해석 하였다. 수치해석 예제를 통하여 Explicit 직접적분법의 특성을 평가하였다.

• 한국항공우주학회지
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• 제30권1호
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• pp.36-43
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• 2002

압전적층판의 비선형 열압전탄성 거동에서의 스냅-스루 현상을 뉴튼-랩슨기법에 호길이법을 적용하여 수치적으로 규명하였다. 층별변위장이론과 von Karman 변형률-변위 관계식을 적용하여 열압전탄성 복합적층 평판에 대한 비선형 유한요소정식화를 수행하였다. 다양한 압전 작동모드에 따라 대칭 및 편심된 구조모델에 대하여 정적 및 동적 관점에서 비선형 열압전탄성 거동과 진동특성을 연구하였다. 본 연구에서는 압전 작동기를 사용하여 유연한 열적 구조물들의 성능을 향상시킬 수 있는 가능성과 새로운 현상학적인 발견인 열압전탄성 스냅핑 거동이 좌굴된 압전탄성 복합적층 평판에서 과도한 압전작동력이 작용하는 경우에 발생할 수 있음을 제시하였다.

• Wind and Structures
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• 제9권5호
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• pp.387-396
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• 2006

This paper presents the wind characteristics of Typhoon Dujuan as measured at a 50 m guyed mast in Hong Kong. The basic wind speed, wind direction and turbulent intensity are studied at two measurement levels of the structure. The power spectral density of the typhoon is compared with the von Karman prediction, and the coherence between wind speeds at the two measurement levels is found to This paper presents the wind characteristics of Typhoon Dujuan as measured at a 50 m guyed mast in Hong Kong. The basic wind speed, wind direction and turbulent intensity are studied at two measurement levels of the structure. The power spectral density of the typhoon is compared with the von Karman prediction, and the coherence between wind speeds at the two measurement levels is found to compare with Davenport's prediction. The effect of typhoon Dujuan on the response of the structure will be discussed in a companion paper (Law, et al. 2006).with Davenport's prediction. The effect of typhoon Dujuan on the response of the structure will be discussed in a companion paper (Law, et al. 2006).

• Smart Structures and Systems
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• 제18권1호
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• pp.155-181
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• 2016

In the present paper we discuss the stability and the post-buckling behaviour of thin piezoelastic plates. The first part of the paper is concerned with the modelling of such plates. We discuss the constitutive modelling, starting with the three-dimensional constitutive relations within Voigt's linearized theory of piezoelasticity. Assuming a plane state of stress and a linear distribution of the strains with respect to the thickness of the thin plate, two-dimensional constitutive relations are obtained. The specific form of the linear thickness distribution of the strain is first derived within a fully geometrically nonlinear formulation, for which a Finite Element implementation is introduced. Then, a simplified theory based on the von Karman and Tsien kinematic assumption and the Berger approximation is introduced for simply supported plates with polygonal planform. The governing equations of this theory are solved using a Galerkin procedure and cast into a non-dimensional formulation. In the second part of the paper we discuss the stability and the post-buckling behaviour for single term and multi term solutions of the non-dimensional equations. Finally, numerical results are presented using the Finite Element implementation for the fully geometrically nonlinear theory. The results from the simplified von Karman and Tsien theory are then verified by a comparison with the numerical solutions.