다변수 변분해법에 의한 비적합 8절점 육면체 요소

주상백,신효철,Ju, Sang-Baek,Sin, Hyo-Chol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.7

This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

변형률에 근거한 2-절점 곡선보 요소

유하상,신효철,Ryu, Ha-Sang,Sin, Hyo-Chol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.8

It is well known that in typical displacement-based curved beam elements, the stiffness matrix is overestimated and as a result displacement predictions show gross error for the thin beam case. In this paper, a stain based curved beam element with 2 nodes is formulated based on shallow beam geometry. At the element level, the curvature and membrane strain fields are approximated independently and the displacement fields are obtained by integrating the strain fields. Three test problems are given to demonstrate the numerical performance of the element. Analysis results obtained reveal that the element is free for locking and very effectively applicable to deeply as well as shallowly curved beams.

비압축성 문제에 대한 비적합 복합유한요소 정식화

주상백,신효철,Ju, Sang-Baek,Sin, Hyo-Chol 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.2

In the present study, we attempted to add the incompatible functions as additional variable terms to the conventional u-p formulation. It is derived from the four-field generalized variational principle that encompasses velocity, pressure, velocity strains and stress fields as independent interpolated variables. As a severe test of the present formulation, we have investigated the driven cavity with the corner velocity singularity like leaky lid. Through the test, the present element performs very well without unstable oscillation of pressure distribution.

임의 형상의 단면을 갖는 박판보의 유한요소 해석

양웅필,신효철,Yang, Woong-Pill,Sin, Hyo-Chol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.1

In this paper, a new thin-walled beam finite elcment is developed to overmome the difficulties in the analysis of real structures by existing beam elements. The element is formulated by extending Benscoter's assumption and also by adopting the concept of the curvature-based element. It is applicable to the analysis of the beams with arbitrary cross-sectional shapes. The results obtained show that the element is locking-free and the accuracy of the finite element solutions is remarkably improved.

자오 변형률에 근거한 2절검 축대칭 셸요소

유하상,신효철,Ryu, Ha-Sang,Sin, Hyo-Chol 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.6

Two shear-flexible curved axisymmetric shell elements with two nodes, LCCS(linear curvature and constant strain) and CCCS(constant curvature and constant strain) are designed based on the assumed meridional strain fields and shallow shell geometry. At the element level, meridional curvature, membrane strain and shear strain fields are assumed by using polynomials and the displacement fields are obtained by integrating the assumed strain fields along the shallowly curved meridian. The formulated elements have high order displacement fields consistent with the strain field. Several test problems are given to demonstrate the performance of the two elements. Analysis results obtained reveal that the elements are very accurate in the displacement and the stress predictions.

열-나노임프린트 공정의 점탄성 유한요소해석

김남웅,김국원,신효철,Kim, Nam-Woong,Kim, Kug-Weon,Sin, Hyo-Chol 한국마이크로전자및패키징학회 2007 마이크로전자 및 패키징학회지 Vol.14 No.4

최근 나노임프린트 리소그래피 공정이 마이크로/나노스케일의 소자 개발에 있어서 경제적으로 대량 생산할 수 있는 기술로 주목 받고 있다. 나노 스케일의 패턴을 성공적으로 전사하기 위해서는 폴리머의 기계적 거동에 대한 이해를 바탕으로, 적절한 공정 조건 즉, 압력, 온도, 시간 등의 선택이 필요하다. 본 연구에서는 열-나노임프린트 공정에서의 충전과정을 해석하기 위하여 비선형 유한요소법을 이용하였으며, 폴리머의 거동을 점탄성으로 가정하여 재료의 응력완화 효과를 고려하였다. 해석을 통하여 온도 및 몰드의 패턴형상이 열-나노임프린트 공정에 미치는 영향을 살펴보았다. Nanoimprint lithography (NIL) is an emerging technology enabling cost-effective and high-throughput nanofabrication. To successfully imprint a nano-sized pattern, the process conditions such as temperature, pressure, and time should be appropriately selected. This starts with a clear understanding of polymer material behavior during the NIL process. In this work, the squeezing of thin polymer films into nanocavities during the thermal NIL has been investigated based upon a two-dimensional viscoelastic finite element analysis in order to understand how the process conditions affect a pattern quality. The simulations have been performed within the viscoelastic plateau region and the stress relaxation effect has been taken into account.

공구끝단반경이 고려된 2차원 금속절삭에 대한 열-점소성 유한요소해석

김국원,이우영,신효철,Kim, Kug-Weon,Lee, Woo-Young,Sin, Hyo-Chol 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.1

In this paper, thermo-viscoplastic finite element analysis of the effect of tool edge radius on cutting process are performed. The thermo-viscoplastic cutting model is capable of dealing with free chip geometry and chip-tool contact length. The coupling with thermal effects is also considered. Orthogonal cutting experiments are performed for 0.2% carbon steel with tools having 3 different edge radii and the tool forces are measured. The experimental results are discussed in comparison with the results of the FEM analysis. From the study, we confirm that this cutting model can well be applied to the cutting process considered the tool edge radius and that a major causes of the "size effect" is the tool edge radius. With numerical analysis, the effects of the tool edge radius on the stress distributions in workpiece, the temperature distributions in workpiece and tool, and the chip shape are investigated.estigated.

균질화법을 이용한 충돌 최적화 기초 연구(Ⅱ)

조용범(Yong Bum Cho),신효철(Hyo-Chol Sin) 한국자동차공학회 2002 한국 자동차공학회논문집 Vol.10 No.4

The homogenization method is applied to maximize crash energy absorption for a given volume. Optimization analysis of a closed-hat type example problem is conducted with different impact velocities and thicknesses. The results show that the bending-type deformation for the original design is changed to the folding-type deformation for a new design with a hole, which is partly due to the increase of the crash energy absorption for the new design. Dynamic mean crushing loads of the original and new design are compared with those by the theoretical equation by Wierzbicki. It shows that the dynamic mean crushing loads of new designs are very close to those by Wierzbicki's equation.

전기자동차의 유럽 OFFSET 충돌 특성 기초 연구

조용범(Yong Bum Cho),신효철(Hyo-Chol Sin) 한국자동차공학회 2002 한국 자동차공학회논문집 Vol.10 No.3

European offset impact analysis of an electric vehicle was done using the robust design method. Section properties of some of the vehicle structure components which influence the european offset impact character­istics were chosen as the main factors for the design. Eight factors were considered for the analysis: one with two level and seven with three level combinations comprising the L_18(2¹ X3^7) orthogonal array. It is shown that the sensitivities of the factors and the best combination of the factors can be obtained. One of the noteworthy results is that the design with the lower stiffness of the front components of engine room than the rear components can absorb more crash energy. Also it is shown that there exist interactions between some offactors considered.

동흡진기를 사용한 광 디스크 드라이브의 진동저감

김남웅(Kim, Nam-Woong),신효철(Sin, Hyo-Chol),김국원(Kim, Kug-Weon) 한국소음진동공학회 2006 한국소음진동공학회 논문집 Vol.16 No.5

In high-speed optical disk drive, the excitation caused by rotation of a mass-unbalanced disk is a major source of vibration. The vibration can be a disturbance to the servo system, which is sufficient to cause severe failures in the reading and writing process. The vibration also causes users to feel unpleasantness. The vibration reduction is therefore essential for the reliable operation of optical disk drive. One of the approaches to reduce the vibration is a dynamic vibration absorber(DVA). In this paper, we analyze the dynamic behavior of $DVD{\pm}RW$ combo drive system with DVA through 12-dof rigid multi-body dynamic model. The effective location and the optimal frequency ratio for the DVA are obtained from the analysis. The DVA are fabricated based on the analysis and its usefulness is confirmed.