• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.130-134
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• 2007

I present a novel curvature profilometer devised fur the profile measurement of aspheric and free-form surfaces on the nanometer scale. A profile is reconstructed from measuring the curvature of a test part of the surface at several locations along a line. For profile measurement of free-farm surfaces, methods based on local part curvature sensing have strong appeal. Unlike full-aperture interferometry they do not require customized null optics. The measurement accuracy of the curvature profilometer was assessed by comparison with a well-calibrated interferometer in NIST. Experimental results prove that the maximum discrepancy turns out to be 37 nm on the 28 mm measurement range for the spherical mirror.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.191-200
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• 1994

사각형 유체저장탱크의 바닥에 놓여져 있는 사각형 블럭의 크기 및 위치가 자유수면의 유동진동수와 모드형상에 미치는 영향에 대하여 선형파이론을 적용하여 검토하였다. 유체의 영역을 3부분으로 나누고 각 영역에서의 속도포텐셜을 입사파와 블럭으로 인해 발생되는 반사파 및 전달파의 항으로써 표현하였다. 그리고 블럭에 의한 파의 반사율과 전달율은 유체영역의 경계에서 속도포텐셜과 유체입자의 속도가 연속인 조건을 사용하여 구하였다. 연구결과 블럭의 높이와 폭은 자유수면의 고유진동수에 크게 영향을 미치며 높이와 위치는 모드형상에 주로 영향을 준다. 블럭이 높고 폭이 넓을수록 고유 진동수는 감소하며 블럭이 높고 탱크의 벽면으로 이동할수록 모드형상은 크게 변한다.

• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.71-73
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• 2016

기존 우산의 단점을 보완한 발명품, 공기우산이 개발되었다. 하지만 공기우산의 단점인 짧은 사용시간을 보완하기 위해 강우량에 따라 적절하게 공기 분사압을 변화시키는 것뿐만 아니라 공기우산의 사용인원의 조절을 위해 압력비와 분사구 형태에 따른 우산의 효과를 알아보는 것이 실 사용에 중요한 요소일 것이다. 이에따라 본 연구에서는 우산 앞 부분의 분출구 형상과 자유류와의 분사 압력비에 따른 자유류의 방어 능력을 확인해 보았다. 평면 분사구에서 압력비가 1.3, 1.5인 구간에서는 우산의 효과를 나타낼 수 없었고 압력비가 1.5인 구간부터 삼각형 분사구와 육각형 분사구에서 우산의 형태가 나타남을 알 수 있었다. 압력비가 2.0인 구간에서 육각형 분사구의 경우 통상적인 우산의 형상을 보이기 시작하는 것을 알 수 있다.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.107-112
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• 1997

본 연구는 자유표면 인삭을 위한 실험 기법 개발에 관한 연구이다. 2차원 수중익에 의해 발생되는 자유표면파를 연구대상으로 삼았다. 실험은 회류수조에서 행하였다. NACA 0012 수중익을 여러가지 길이와 2가지양각에 대해서 실험한 결과 생기는 비선형 자유표면 파를 인식할 수 있도록 영상처리 기술을 도입하였다. 실헙결과 얻은 자유표면 형상을 다른 연구자의 결과와 비교하였다. 비교결과 영상처리의 기법이 자유표면을 인식하는데 대단히 유용한 도구임을 알 수 있었다.

• The Journal of the Korea Contents Association
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• v.10 no.8
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• pp.426-432
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• 2010

A level-set finite-element method is employed to investigate the free surface flow of two conceptual fish passage designs. While one design has a right-angled entrance from the reservoir to the fish passage chute, the other has a curved-shaped entrance. The numerical results are validated with hydraulic experiments through comparison of the free surface location and the pressure distribution in the spillway. It is observed that the right-angled design yields a curved free surface and pressure distribution in the vicinity of the entrance due to large strains, whereas the curved-shaped design yields a smooth flow transition with small strains. The subatmospheirc pressure distributions near the spillway ogee crest for both designs exhibit similar flow patterns. It is concluded that the curved-shaped design is more favorable for fish passage because of the feature of a smooth flow transition with small strains.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1237-1242
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• 2011

Calcium phosphates are very interesting materials for use as scaffolds for bone tissue engineering. These materials include hydroxyapatite (HA) and tricalcium phosphate (TCP), which are inorganic components of human bone tissue and are both biocompatible and osteoconductive. Although these materials have excellent properties for use as bone scaffolds, many researchers have used these materials as additives to synthetic polymer scaffolds for bone tissue regeneration, because they are difficult to manufacture three-dimensional (3D) scaffolds. In this study, we fabricated 3D calcium phosphate scaffolds with the desired inner and outer architectures using solid freeform fabrication technology. To fabricate the scaffold, the sintering behavior was evaluated for various sintering temperatures and slurry concentrations. After the fabrication of the calcium phosphate scaffolds, in-vitro cell proliferation and osteogenic differentiation tests were carried out.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.519-527
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• 2002

Shell structures have become critical in the design of pressure vessels, submarine hulls, ship hulls, airplane structures, concrete roofs, containers for liquids, and many other structures. This study presented the feature of the free vibration of anisotropic laminated conical shells according to transverse shear deformation effects. Composite materials are composed of two or more different materials in order to produce desirable properties for structural strength. Since their behavior is very complex, it is almost impossible to solve the analytical solutions. This effects of subtended and vertex angles and other geometric parameters on vibration were investigated in a comprehensive parametric study. Selected vibration mode shapes were illustrated, to enable the physical understanding of vibration of laminated composite conical shells.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.740-745
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• 2003

The so-called boundary node method (or NDIF method) that was developed by the authors has been extended for free vibration analysis of arbitrarily shaped plates with free edges. Since the proposed method is based on the collocation method, no integration procedure is needed on boundary edges of the plates and only a small amount of numerical calculation is required. A special coordinate transformation has been devised to consider the complicated free boundary conditions at boundary nodes. By the use of the special coordinate transformation, the radius of curvature involved in the free boundary conditions can be successfully dealt with. Finally, verification examples show that natural frequencies obtained by the present method agree well with those given by exact method and other analytical methods.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.10
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• pp.821-827
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• 2003

The so-called boundary node method (or NDIF method) that was developed by the authors has been extended for free vibration analysis of arbitrarily shaped plates with free edges. Since the proposed method requires no interpolation functions. no integration Procedure is needed on boundary edges of the plates and only a small amount of numerical calculation is involved, compared with FEM and BEM. In order to explain tile reason why spurious eigenvalues are generated when the NDIF method is applied to free plates, the NDIF method has been considered for free vibration analysis of both a fixed string and a free beam. Finally, verification examples show that natural frequencies obtained by the present method agree well with those given by an exact method or a numerical method (ANSYS).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1105-1114
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• 2010

Ice shapes accumulated on the aircraft surfaces are categorized into rime and glaze ice, which are highly dependent on various parameters such as ambient temperature, liquid water contents (LWC), mean volumetric droplet diameter and freestream velocity. In this study, quantitative analyses on the ice accretion have been attempted in a systematical manner and the key findings are as follows. First, the increase of freestream velocity can cause tremendous change in the ice accumulation such as the growth of ice accretion area, ice heading direction and maximum thickness of ice horn. Second, LWC is found to be linearly proportional to the ice accretion area. Third, the effects of ambient temperature on incoming water mass seem to be relatively small in comparison with LWC and freestream velocity. Finally, it was shown that MVD has only a little influence on ice shapes. However, it may increase the ice accretion area by increasing the droplet impacting range.