• 한국자동차공학회논문집
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• 제11권4호
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• pp.110-116
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• 2003

In this paper, an evaluation method of fracture toughness on interface cracks has been investigated under various mixed-mode conditions of the bonded scarf joints. Two types of the bonded scarf joints with an interface crack were prepared to analyze the stress intensity factors using boundary element method(BEM) and to perform the fracture toughness test. From the results of fracture toughness experiments and BEM analysis, an evaluation method of fracture toughness on interface cracks in the bonded dissimilar materials has been proposed and discussed.

• 대한수학회지
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• 제59권3호
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• pp.519-548
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• 2022

In this paper, a stabilized-penalized collocated finite volume (SPCFV) scheme is developed and studied for the stationary generalized Navier-Stokes equations with mixed Dirichlet-traction boundary conditions modelling an incompressible biological fluid flow. This method is based on the lowest order approximation (piecewise constants) for both velocity and pressure unknowns. The stabilization-penalization is performed by adding discrete pressure terms to the approximate formulation. These simultaneously involve discrete jump pressures through the interior volume-boundaries and discrete pressures of volumes on the domain boundary. Stability, existence and uniqueness of discrete solutions are established. Moreover, a convergence analysis of the nonlinear solver is also provided. Numerical results from model tests are performed to demonstrate the stability, optimal convergence in the usual L² and discrete H¹ norms as well as robustness of the proposed scheme with respect to the choice of the given traction vector.

• 한국환경과학회지
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• 제3권2호
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• pp.129-140
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• 1994

An intermediate atmosphere-ocean coupled model appropnate for the study of El Nino has been developed. The model is not only economic to use but also contains several most important physical processes. The geometrical effects which were not confided in the previous intermediate model study of Ahn (1990), are included in the model for more realistic simulation of the event. The results show that the individual models respond appropriately to the given boundary conditions. At the same time, in the coupled model experiment, ENSO-like oceanic and atmospheric anomalies are also well simulated under an external triggering similar to the initiation forcing of ENSO. It is expected that this type of model can be effectively used for the. study and simulation of El Nido. More improvement of modeling may be Possible after inclusion of subsequent processes such as inclusion of ocean mixed layer dynamics.

• 대한기계학회논문집
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• 제16권10호
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• pp.1900-1907
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• 1992

본 연구에서는 원형평판의 경계조건을 일부분은 고정단으로 일부분은 자유단 으로 구성하여 자유단각 .alpha.(Fig.4 참조)를 0˚, 30˚, 60˚, 90˚, 120˚, 150˚, 180˚로 변화시킴에 따른 진동모드를 시간평균 홀로그래픽 간섭계(time-average holographic interferometry)를 이용해 분석하고 자유단의 변화에 따른 고유진동수의 비를 비교하였고, 레이저 도플러 유속계(LDV)를 변형한 레이저 도플러 진동계(laser doppler vibrometer)로 원형평판의 진동변위와 시간평균 홀로그래픽 간섭계로 구한 진 동변위를 비교하였다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.534-537
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• 2005

Free Vibration Analysis using Non-dimensional Dynamic Influence Function (NDIF) is extended to arbitrarily shaped plates including polygonal plates. Since the corners of polygonal plates have indefinite normal directions and additional boundary conditions related to a twisting moment at a corner along with moment and shear force zero conditions, it is not easy to apply the NDIF method to polygonal plates wi th the free boundary condition. Moreover, owing to the fact that the local polar coordinate system, which has been introduced for free plates with smoothly varying edges, cannot be employed for the straight edges of the polygonal plates, a new coordinate system is required for the polygonal plates. These problems are solved by developing the new method of modifying a corner into a circular arc and setting the normal direction at the corner to an average value of normal direct ions of two edges adjacent to the corner. Some case studies for plates with various shapes show that the proposed method gives credible natural frequencies and mode shapes for various polygons that agree well with those by an exact method or FEM (ANSYS).

• 한국주조공학회지
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• 제31권3호
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• pp.130-136
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• 2011

Effects of GBF (gas bubbling filtration) treatment conditions and scrap ratio on the electric conductivity of a commercial pure aluminum for diecasting were investigated using by specific gravity and electrical conductivity measurement system, hydrogen gas analyzer, XRD, and EDS. Electrical conductivities of specimen mixed Al scrap ratio until 60% from 0% were decreased with increasing the precipitates amount and size of AlFeSi ternary intermetallic compound on the grain boundary as well as amount of porosity in the grain. On the other hand, electrical conductivities was reincreased gradually in spite of scrap ratio increase from 80% to 100%. Size of AlFeSi compound formed on the grain boundary were coarsened with the increament of scrap ratios untill 80% and GBF treatment time simultaneously.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제23권4호
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• pp.367-380
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• 2019

A 1kW-class horizontal axis wind turbine (HAWT) rotor blade is taken into account to investigate elastic characteristics in 2-D. The elastic blade field is composed of symmetric cross-ply laminated composite material. Blade element momentum theory is applied to obtain the boundary conditions pressuring the blade, and the plane stress elasticity problem is formulated in terms of two displacement parameters with mixed boundary conditions. For the elastic characteristics a fair of differential equations are derived based on the elastic theory. The domain is divided by triangular and rectangular elements due to the complexity of the blade configuration, and a finite element method is developed for the governing equations to search approximate solutions. The results describe that the elastic behavior is deeply influenced by the layered angle of the middle laminate and the stability of the blade can be improved by controlling the layered angle of laminates, which can be evaluated by the mathematical approach.

• Steel and Composite Structures
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• 제39권5호
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• pp.493-509
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• 2021

There is not enough mixed finite element method (MFEM) model developed for static and dynamic analysis of functionally graded material (FGM) beams in the literature. The main purpose of this study is to develop a reliable and efficient computational modeling using an efficient functional in MFEM for free vibration and static analysis of FGM composite beams subject to high order shear deformation effects. The modeling of material properties was performed using mixture rule and Mori-Tanaka scheme which are more realistic determination techniques. This method based on the assumption that a two phase composite material consisting of matrix reinforced by spherical particles, randomly distributed in the beam. To explain the displacement components of the shear deformation effects, it was accepted that the shear deformation effects change sinusoidal. Partial differential field equations were obtained with the help of variational methods and then these equations were transformed into a novel functional for FGM beams with the help of Gateaux differential derivative operator. Thanks to the Gateaux differential method, the compatibility of the field equations was checked, and the field equations and boundary conditions were reflected to the function. A MFEM model was developed with a total of 10 degrees of freedom to apply the obtained functional. In the numerical applications section, free vibration and flexure problems solutions of FGM composite beams were compared with those predicted by other theories to show the effects of shear deformation, thickness changing and boundary conditions.

• Advances in nano research
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• 제6권2호
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• pp.163-182
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• 2018

Based on the Reissner mixed variational theorem (RMVT), the authors present a nonlocal Timoshenko beam theory (TBT) for the nonlinear free vibration analysis of multi-walled carbon nanotubes (MWCNT) embedded in an elastic medium. In this formulation, four different edge conditions of the embedded MWCNT are considered, two different models with regard to the van der Waals interaction between each pair of walls constituting the MWCNT are considered, and the interaction between the MWCNT and its surrounding medium is simulated using the Pasternak-type foundation. The motion equations of an individual wall and the associated boundary conditions are derived using Hamilton's principle, in which the von $K{\acute{a}}rm{\acute{a}}n$ geometrical nonlinearity is considered. Eringen's nonlocal elasticity theory is used to account for the effects of the small length scale. Variations of the lowest frequency parameters with the maximum modal deflection of the embedded MWCNT are obtained using the differential quadrature method in conjunction with a direct iterative approach.

• 대한기계학회논문집
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• 제8권3호
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• pp.232-240
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• 1984

본 논문에서는 Stern이 제시한 경로적분식을 기본방정식으로 하여 예리한 임 의 노치내각을 가진(크랙의 경우 0˚), 즉 r$^{.lambda.}$ 형태의 특이점을 포함한 모우드-I 및 II 응력확대계수를 위한 특성해 및 보조해를 규정하고 선택모형문제로 예리한 노치 내각을 달리한 대칭 하중의 인장문제와 끝단 전단력하중하의 일단 고정보의 비대칭문 제의 응력확대계수를 기존의 재래식 유한요소법과 결합하여 계산하였다. 또한 각각 의 경우 적분경로 및 요소분할을 달리하여 수치해의 안정성 및 경로 독립성을 검토하 였다.