• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• Computers and Concrete
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• 제7권4호
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• pp.347-364
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• 2010

Since its invention in the $19^{th}$ century, Reinforced Concrete (RC) has been widely used in the construction of a lot of different structures, as buildings, bridges, nuclear central plants, or even ships. The details of the mechanical response for this kind of structures depends directly upon the material behavior of each component: concrete and steel, as well as their interaction through the bond-slip, which makes a rigorous engineering analysis of RC structures quite complicated. Consequently, the practical calculation of RC structures is done by adopting a lot of simplifications and hypotheses validated in the elastic range. Nevertheless, as soon as any RC structural element is working in the inelastic range, it is possible to obtain the numerical prediction of its realistic behavior only through the use of non linear analysis. The aim of this work is to develop a new kind of Finite Element: the "Enhanced Solid Element (ESE)" which takes into account the complex composition of reinforced concrete, being able to handle each dissipative material behavior and their different deformations, and on the other hand, conserving a simplified shape for engineering applications. Based on the recent XFEM developments, we introduce the concept of nodal enrichment to represent kinematics of steel rebars as well as bonding. This enrichment allows to reproduce the strain incompatibility between concrete and steel that occurs because of the bond degradation and slip. This formulation was tested with a couple of simple examples and compared to the results obtained from other standard formulations.

• 한국지반공학회논문집
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• 제28권4호
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• pp.67-78
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• 2012

철지반의 비선형성을 고려한 말뚝지지 전면기초의 3차원 해석기법(YSPR)을 개발하였다. 전면기초는 6개의 자유도를 가진 평면쉘 요소로, 말뚝은 보-기둥 요소로 모델링하여 전면기초와 결합하였다. 또한 말뚝두부 및 지반의 강성은 $6{\times}6$ 강성행렬로 모델링 하였으며, 전면기초-말뚝-지반의 상호작용은 비선형 하중전이함수를 이용하여 선형/비선형거동의 모사가 가능하도록 하였다. 기존의 단순해석기법, 유한요소해석 및 현장계측값과의 비교 분석 결과, 본 해석기법이 대단면 말뚝지지전면기초에서 말뚝의 축하중 분포와 침하량을 비교적 정확히 산정하는 것으로 판단되며, 이러한 검증을 토대로 실제 대단면 기초설계에 대한 적용 가능함을 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.899-916
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• 2015

Upgrading or strengthening of existing reinforced concrete (RC) infrastructure is an emerging demand nowadays. Near Surface Mounted (NSM) technique is very promising approach for flexural strengthening of RC members. However, premature failure such as concrete cover separation failure have been a main concern in utilizing this technique. In this study, U-wrap end anchorage with carbon fiber reinforced polymer (CFRP) fabrics is proposed to eliminate the concrete cover separation failure. Experimental programs were conducted to the consequence of U-wrap end anchorage on the flexurally strengthened RC beams with NSM-steel. A total of eight RC rectangular beam specimens were tested. One specimen was kept unstrengthened as a reference; three specimens were strengthened with NSM-steel bars and the remaining four specimens were strengthened with NSM-steel bars and U-wrap end anchorage using CFRP fabrics. A 3D non-linear finite element model (FEM) was developed to simulate the flexural response of the tested specimens. It is revealed that NSM-steel (with and without end-anchors) significantly improved the flexural strength; moreover decreased deflection and strains compared with reference specimen. Furthermore, NSM-steel with end anchorage strengthened specimens revealed the greater flexural strength and improve failure modes (premature to flexure) compared with the NSM-steel without end anchorage specimens. The results also ensured that the U-wrap end anchorage completely eliminate the concrete cover separation failure.

• 한국강구조학회 논문집
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• 제18권2호
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• pp.123-135
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• 2006

이 연구에서는 원형기둥-상자형보 접합부의 다이아프램 형상에 따른 거동특성과 다이아프램 설계방법에 관한 것이다. 강재 원형기둥-상자형보 접합부의 다이아프램은 상자형보 하부플랜지로부터 전달되는 집중력을 지지하게 되며, 보와 기둥의 강도 뿐만아니라 접합부의 거동에 큰 영향을 미치게 된다. 기존의 연구에서는 부정정 곡선보 모델로부터 유도된 다이아프램의 응력계산식이 제시되어 있으나, 설계식으로 활용되기에는 계산과정이 난해하고 유도과정이 비합리적이다. 또한 접합부 강도에 대한 다이 아프램의 역할을 고려하지 않음으로써 다이아프램의 합리적인 설계가 이루어 지지 못하고 있다. 따라서 이 연구에서는 접합부 다이아프램의 설계변수에 대한 비선형 유한요소 해석을 수행하여, 다이아프램의 형상에 따른 강도특성을 검토하였다. 또한 원형기둥-상자형보, 접합부 다이아프램의 이론식이 접합부의 실제 거동과 큰 차이를 나타냄을 확인하였고, 보와 기둥 및 다이아프램 강성을 고려한 강재 원형기둥 접합부 다이아프램의 설계방법을 제안하였다.

• 대한기계학회논문집A
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• 제37권1호
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• pp.83-88
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• 2013

연쇄붕괴는 충격이나 폭발 등의 비정상 하중에 의하여 구조물의 하중 전달요소가 제거됨으로써 구조물의 일부 또는 전체가 연쇄적으로 붕괴되는 형상을 말한다. 예상외의 하중이 기둥부재에 작용할 경우, 좌굴이 발생하며 내력저하가 급격히 진행되어 붕괴에까지 이르게 된다. 하지만 좌굴 후 에너지를 흡수할 수 있는 잔존내력이 충분하면 붕괴를 막을 수 있다. 따라서, 구조물이 최종 붕괴상태에 도달되는 전 과정에 대한 기둥부재의 하중-변형관계를 명확히 파악할 필요가 있다. 본 논문에서는 비선형유한요소해석을 실시하여 H 형 강재기둥의 단부 구속조건이 고정일 경우 잔존내력의 변화추이를 파악하였다. 또한, 처짐이론을 기반으로 이론식을 도출하여 해석값과의 적합성을 검토하였다.

• Composites Research
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• 제22권2호
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• pp.30-36
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• 2009

본 논문에서는 헬리콥터 착륙장치를 위한 복합재료 토크링크를 개발하기 위한 설계 기법을 제시하였다. 복합재 토크링크는 헬리콥터 착륙장치의 충격흡수부의 정렬을 위해 장착되는 장치로서 가벼우면서도 강성이 커서 외부하중에 대해 최소의 변형량을 가져야 한다. 또 가격적인 측면을 고려한 복합재 구조물 제조 공정(RTM: 수지충전공정)이 반영되어 대량생산이 가능한 구조 및 형태를 가져야 한다. 본 논문에서는 복합재 구조물 제조 공정과 동일한 공정으로 시편을 제작하여 설계에 필요한 기계적 특성을 얻었으며, 유한요소해석을 통하여 복합재 토크링크에 대한 최적 형상설계를 수행하였다. Lug 형태를 가지는 두꺼운 복합재료 구조물인 복합재료 토크링크의 설계를 위해서는 ABAQUS의 3D Layered Solid 요소로 구성된 유한요소모델을 활용하여 복합재료의 두께방향을 포함한 강도해석을 수행하였으며, Rigid-Deform 구속조건의 접촉문제를 고려한 비선형 정적 해석을 반복적으로 수행하여 주어진 정강도 요구조건을 만족시키는 복합재 토크링크를 설계하였다.

• 대한토목학회논문집
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• 제37권1호
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• pp.83-91
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• 2017

말뚝지지 전면기초에서 침하량을 산정할 경우 기초판-말뚝-지반간 상호작용을 고려해야 하며, 단순 해석법으로는 이러한 복잡한 상호작용을 고려하여 해석하는 것이 어렵다. 본 연구에서는 말뚝지지 전면기초의 침하량 해석을 위해 기초판-말뚝-지반간 상호작용을 고려한 근사해석법(HDPR)을 개발하였다. 기초판은 Mindlin 판이론을 이용하여 유한요소로 모델링 하였고, 지반 및 말뚝은 기초판에 연결된 스프링으로 모델링되었다. 지반 스프링의 경우 다층지반을 고려한 선형 스프링을 적용하였고, 말뚝은 비선형 스프링을 적용하였으며, 각각의 스프링은 기초판-말뚝-지반간 상호작용이 반영되었다. 본 연구에서의 해석기법 검증을 위해 3차원 유한요소해석, 기존에 개발된 근사해석방법 및 실제 현장 계측결과와 비교분석을 수행하였다. 그 결과, 개발된 기법이 말뚝 및 기초판의 침하량을 합리적으로 예측하는 것으로 나타났다. 이를 통해 실제 말뚝지지 전면기초 해석 및 설계 시 실용적인 측면에서 적용이 가능함을 확인할 수 있었다.

• Restorative Dentistry and Endodontics
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• 제19권2호
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• pp.345-371
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• 1994

Restorative procedures can lead to weakening tooth due to reduction and alteraton of tooth structure. It is essential to prevent fractures to conserve tooth. Among the several parameters in cavity designs, cavity isthmus and depth are very important. In this study, MO amalgam cavity was prepared on maxillary first premolar. Three dimensional. finite element models were made by serial photographic method and cavity depth(1.7mm, 2.4mm) and isthmus (11 4, 1/3, 1/2 of intercuspal distance) were varied. linear, eight and six-nodal, isoparametric brick elements were used for the three dimensional finite element model. The periodontal ligament and alveolar bone surrounding the tooth were excluded in these models. Three types model(B, G and R model) were developed. B model was assumed perfect bonding between the restoration and cavity wall. Both compressive and tensile forces were distributed directly to the adjacent regions. G model(Gap Distance: 0.000001mm) was assumed the possibility of play at the interface simulated the lack of real bonding between the amalgam and cavity wall (enamel and dentin). When compression occurred along the interface, the forces were transferred to the adjacent regions. However, tensile forces perpendicular to the interface were excluded. R model was assumed non-connection between the restoration and cavity wall. No force was transferred to the adjacent regions. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, von Mises stress, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as follows: 1. G model showed stress and strain patterns between Band R model. 2. B model and G model showed the bending phenomenon in the displacement. 3. R model showed the greatest amount of the displacement of the buccal cusp followed by G and B model in descending order. G model showed the greatest amount of the displacement of the lingual cusp followed by B and R model in descending order. 4. B model showed no change of the displacement as increasing depth and width of the cavity. G and R model showed greater displacement of the buccal cusp as increasing depth and width of the cavity, but no change in the displacement of the lingual cusp. 5. As increasing of the width of the cavity, stress and strain were not changed in B model. Stress and strain were increased on the distal marginal ridge and buccopulpal line angle in G and R model. The possibility of the tooth fracture was increased. 6. As increasing of the depth of the cavity, stress and strain were not changed in B and G model. Stress and strain were increased on the distal marginal ridge and buccopulpal line angle in R model. The possibility of the tooth fracture was increased.

• Restorative Dentistry and Endodontics
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• 제20권2호
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• pp.432-461
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• 1995

The basic principles in the design of Class II amalgam cavity preparations have been modified but not changed in essence over the last 90 years. The early essential principle was "extension for prevention". Most of the modifications have served to reduce the extent of preparation and, thus, increase the conservation of sound tooth structure. A more recent concept relating to conservative Class II cavity preparations involves elimination of occlusal preparation if no carious lesion exists in this area. To evaluate the ideal ClassII cavity preparation design, if carious lesion exists only in the interproximal area, three cavity design conditions were studied: Rodda's conventional cavity, simple proximal box cavity and proximal box cavity with retention grooves. In this study, MO amalgam cavity was prepared on maxillary first premolar. Three dimensional finite element models were made by serial photographic method. Linear, eight and six-nodal, isoparametric brick elements were used for the three dimensional finite element model. The periodontal ligament and alveolar bone surrounding the tooth were excluded in these models. Three types model(B option, Gap option and R option model) were developed. B option model was assumed perfect bonding between the restoration and cavty wall. Gap option model(Gap distance: $2{\mu}m$) was assumed the possibility of play at the interface simulated the lack of real bonding between the amalgam and cavity wall (enamel and dentin). R option model was assumed non-connection between the restoration and cavty wall. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as followed. 1. Rodda's cavity form model showed greater amount of displacement with other two models. 2. The stress and strain were increased on the distal marginal ridge and buccopulpal line angle in Rodda's cavity form model. 3. The stress and strain were increased on the central groove and a part of distal marginal ridge in simple proximal box model and proximal box model with retention grooves. 4. With Gap option, Rodda's cavity form model showed the greatest amount of the stress on distal marginal ridge followed by proximal box model with retention grooves and simple proximal box model in descending order. 5. With Gap option, simple proximal box model showed greater amount of stress on the central groove with proximal box model with retention grooves. 6. Retention grooves in the proximal box played the role of supporting the restorations opposing to loads.