• 한국정밀공학회지
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• 제21권5호
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• pp.158-165
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• 2004

Up to now, many crack repair techniques have been developed for inhibiting crack growth in structural components. However, the simplest way for inhibiting crack growth is to apply a indentation at the crack tip or at some distance ahead of the expected crack growth path so as to produce residual compressive stresses that can reduce the effective stresses around the crack tip. In spite of its importance to the aerospace industry, little attention has been devoted to evaluation of the indentation residual stress effect on the fatigue crack initiation life quantitatively. Therefore, in the present work, the magnitude and distribution of the indentation residual stresses were investigated in order to estimate the beneficial effect on fatigue crack initiation by using finite element method. Furthermore, to examine the validity of finite element analysis results, residual stress distribution in the indented specimen was measured by using X-ray diffraction technique, and fatigue crack behavior at fastener hole in aluminum alloy 7075-T6 before and after indentation processes was investigated.

• Structural Engineering and Mechanics
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• 제5권2호
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• pp.137-148
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• 1997

In computing eigenvalues for a large finite element system it has been observed that the eigenvalue extractors produce eigenvectors that are in some sense more accurate than their corresponding eigenvalues. From this observation the paper uses a patch type technique based on the eigenvector for one mesh quality to provide an eigenvalue error indicator. Tests show this indicator to be both accurate and reliable. This technique was first observed by Stephen and Steven for an error estimation for buckling and natural frequency of beams and two dimensional in-plane and out-of-plane structures. This paper produces and error indicator for the more difficult problem of three dimensional brick elements.

• 한국공작기계학회논문집
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• 제12권5호
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• pp.24-33
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• 2003

This study proposed a technique for inverse problem, linear approximation of contact position and loading in single and double meshing of transmission contact element using 2-dimension model considered near the tooth by root stress. Determination of root stress is carried out far the gear tooth by finite element method and boundary element method. Boundary element discretization near contact point is carefully performed to keep high computational accuracy. The predicted results of boundary element method are good accordance with that of finite element method.

• 한국전산구조공학회논문집
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• 제12권3호
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• pp.437-445
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• 1999

본 논문에서는 다지지점 가진에 의한 구조물의 동적응답을 구하기 위하여 유한요소모형을 수정하고 등가하중을 도입하는 간단한 기법을 제안하였다. 제안방법은 다지지점 입력에 대한 해석기능이 있는 기존의 범용구조해석 S/W를 이용한 선형 및 비선형 해석결과와 비교하여 검증하였다. 이 기법은 다지지점 입력에 대한 해석기능이 없는 범용유한요소해석 S/W 및 비선형 구조해석을 위하여 특별히 개발되었던 전산프로그램을 이용하여 다지지점 입력에 대한 지진응답해석을 수행할 때 유용하게 활용될 수 있을 것으로 기대된다.

• 한국항공우주학회지
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• 제31권4호
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• pp.35-43
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• 2003

본 논문에서는 새로 제안된 절점 활성화 기법을 실제 구현하기 위한 효율적 계산법을 소개하고 각종 수치실험을 수행한다. 포아송 방정식, 2차원 탄성문제, 3차원 탄성문제에 대하여 다양하게 수행된 수치실험을 통하여 절점활성화 이론의 타당성, 수렴성, 및 효율성을 고찰한다. 수렴성, 패치 테스트 등이 포함된 각종 수치실험 결과로부터 절점활성화 기법을 이용하면 정확도의 큰 손실 없이도 많은 수의 유한요소 절점 중 관심이 있는 일부 절점만을 선택, 활성화시켜 이들만을 미지수로 이용하여 효율적으로 문제를 해석할 수 있음을 입증한다.

• 대한기계학회논문집B
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• 제28권4호
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• pp.395-405
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• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among four filling patterns at each triangular control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Using the proposed numerical technique, the collapse of a water dam has been analyzed to predict flow phenomenon of fluid and the predicted front positions with respect to time have been compared with the reported experimental results.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1921-1930
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• 1997

This paper presents the effective technique to design a six-axis load cell by using experimental design with an orthogonal array. A binocular structure is used as a basic sensing element for a load cell instead of the parallel plate structure. The finite element method is adopted to obtain strain distributions of the sensing element, and by doing the analysis of variances, its results are utilized in determining the factor which is more influential to the output strain. Calibration test results show that the developed six-axis loa cell with the maximum capacities of 196 N in forces and 19.6 N. m in moments is evaluated to be useful with the coupling error less than 2.5%.

• 한국해안·해양공학회논문집
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• 제26권1호
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• pp.9-15
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• 2014

암석과 같은 입자들로 구성된 구조체의 거동을 일반적인 요소망을 이용한 유한요소해석으로 구현하기 어렵다. 이는 입자로 구성된 구조체의 거동 해석시 입자간의 상호작용을 무시할 수 없기 때문이다. 본 연구에서는 입자로 구성된 구조체(rock-berm)의 분할에 Smooth Particle Hydrodynamics (SPH) 기법을 이용하여 충돌해석을 수행하고 이를 기존의 Lagrange 기법을 사용한 해석결과와 비교하여 SPH 기법의 적용 가능성을 알아보았다. 결과적으로 SPH 기법이 입자로 구성된 구조체의 충돌해석에 사실적인 모사가 가능한 것으로 파악되었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.91-94
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• 2004

Preform design techniques have been investigated in efforts to reduce die wear and forming load and to improve material flow, filing ratio, etc. In hot forging processes, a thin deformed part of a workpiece, known as a flash, is formed in the narrow gap between the upper and lower tools. Although designers make tools that generate a flash intentionally in order to improve flow properties, excessive flash increases die wear and forming load. Therefore, it is necessary to make a preform shape that can reduce the excessive flash without changing flow properties. In this paper, a new preform design technique is proposed to reduce the excessive flash in a metal forging process. After a finite element simulation of the process is carried out with an initial billet, the flow of material in the flash region is traced from the final shape to the initial billet. The region belonging to the flash is then easily found in the initial billet. The finite element simulation is then carried out again with the modified billet from which the selected region has been removed. In several iterations of this technique, the optimal preform shape that minimizes the amount of flash without changing the forgeability can be obtained.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1417-1426
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• 2009

Various types of damper are usually applied to reduce noise and vibration for mechanical systems. Especially, for washing machines, the free-friction stroke damper is installed. The behavior of the free-friction stroke damper has nonlinear characteristics such as hysteresis and viscoelastic properties because of its foam material. First of all, the dynamic experiments were carried out by using a MTS machine to find characteristics of the free-friction stroke damper. And the simulation model of the free-friction stroke damper and characteristics of a foam material were evaluated by using optimization technique. To make a good simulation model which can show the dynamic characteristics, it is important to understand the working mechanism of the damper. The Finite Element Method (FEM) technique can help us instinctively understand the damping phenomenon under operating conditions, because we can observe the condition of damper at every step in the simulation by using it. Also, by changing factors, we can comprehend the variation of characteristics of damper. So, in this paper, a study on the dynamic characteristics of free-friction stroke damper by FEM is focused on. Finally, the possibility which physical experiments can be replaced into simulations is shown.