• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.331-336
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• 2002

Recently the critical nozzles with small diameter are being extensively used to measure mass flow in a variety of industrial fields and these have different configurations depending on operation condition and working gas. The curvature radius of the critical nozzle throat is one of the most important configuration factors promising a high reliability of the critical nozzle. In the present study, computations using the axisymmetric, compressible, Navier-Stokes equations are carried out to investigate the effect of the nozzle curvature on critical flows. The diameter of the critical nozzle employed is D=0.3mm and the radius of curvature of the critical nozzle throat is varied in the range from 1D to 3D. It is found that the discharge coefficient is very sensitive to the curvature radius(R) of critical nozzle, leading to the peak discharge coefficient at R = 2.0D and 2.5D, and that the critical pressure ratio increases with the curvature radius.

• 한국추진공학회지
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• 제12권2호
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• pp.66-73
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• 2008

본 논문에서는 환형 관에서의 데토네이션 파의 전파 특성을 살펴보았다. 이전의 연구에 이용된 수치 기법과 이동 계산 창 기법을 본 연구에 이용하였으며, 관 폭의 값으로 무차원화 된 곡률 반경을 유일한 기하학적 변수로 고려하여 일련의 해석을 수행하였다. 곡률 반경이 작은 환형 관에서 데토네이션 파는 불안정하여 정규적인 데토네이션 셀 구조가 나타나지 않으며 셀 구조가 유지될 수 있는 임계 곡률 반경이 존재함을 알 수 있었다. 곡률의 효과로 관의 내벽 및 외벽은 압력 차가 발생하며, 외벽 쪽에 서는 overdriven 데토네이션의 경향을 가진다. 예상할 수 있는 바와 같이 곡률 반경이 커지면서 직선관의 결과에 수렴한다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.119-124
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• 2001

In this study, a vision system with image processing method have been introduced to find the edge radius of curvature. It was applied to inspect the edge quality of the deburring process product with brush grinding. Size of data was found to be critical in calculating the radius of curvature. Results using laser measurement system were compared.

• 한국자동차공학회논문집
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• 제14권1호
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• pp.79-85
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• 2006

CFRP(Carbon Fiber Reinforced Plastics) of the advanced composite materials as structural materials for vehicle, has a wide application in light-weigh structural materials of airplanes, ships and automobiles because of high strength and stiffness, However, there is a design variable to be considered in practical application of the laminate composite materials, these materials are vulnerable to transverse impact. This paper is to study the effects of stacking sequence and curvature on the penetration characteristics of composite laminate shell. They are stacked to $[0_3/90_3]S,\;[90_3/0_3]s\;and\;[0_2/90_3/0]s,\;[90_2/0_3/90]s$ and their interlaminar number two and four. They are manufactured to various curvature radius (R=100, 150, 200mm and $\infty$), When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determing the time for it to pass two ballistics-screen sensors located a known distance apart. The critical penetration energy of specimen A and B with less interfaces were a little higher than those of C and D. As the curvature increases, the critical penetration energy increases linearly because the resistance to the in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. The specimen A and C have higher critical penetration energy than B and D because of different stacking sequences. We examined crack length through a penetration test. For the specimen A with 2interfaces, the longest circumferential direction crack length were observed on the first interface from the impact point. For the specimen B 4-interface, the longest circumferential direction crack length were observed on the second interface from the impact point.

• 한국응용과학기술학회지
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• 제23권1호
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• pp.54-62
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• 2006

Kelvin equation is revisited, which accounts for important phenomena observed frequently in nano-dispersion systems. They include vapor pressure increase for curved interfaces, nucleation, capillary condensation, Ostwald ripening and so on. The smaller the radius of curvature is, the more significant Kelvin equation becomes. Therefore, its meaning, curvature effect, and importance are examined and discussed.

• 한국지반공학회논문집
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• 제37권4호
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• pp.5-17
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• 2021

본 논문은 만곡부 제방에 대해 곡률각도, 곡률반경에 따라 3차원 해석을 실시하여 침투특성을 규명하였다. 제방만곡부에서 동수경사는 2차원 해석 결과에 비해 외측제방에서는 감소하였고, 내측제방에서는 증가하였다. 곡률각도와 곡률반경이 작을수록 2차원 해석 대비 동수경사의 변화가 큰 경향을 나타내었으며, 곡률각도보다는 곡률반경이 동수경사에 미치는 영향이 큰 것으로 나타났다. 한계동수경사에 의한 파이핑 안전율 산정결과, 2차원 해석에 대비하여 안전율은 외측제방에서는 2~5%가 증가되었고, 내측제방에서는 4~12%가 감소되었다. 이 감소폭을 고려해 볼 때 제방만곡부에 대해 2차원 해석을 실시하고 파이핑에 대한 허용안전율 Fs=2.0보다 0.1~0.3정도 더 크게 설계하면 만곡부의 안전율은 약간 감소되지만 안정성 확보에는 무리가 없는 것으로 판단되었다.

• 한국정밀공학회지
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• 제22권2호
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• pp.164-171
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• 2005

This study aims to examine an effect of stacking sequence and curvature on the penetration characteristic of a composite laminated shell. For the purpose, we manufactured specimens with different stacking sequences and curvatures, and conducted a penetration test using an air-gun. To examine an influence according to stacking sequence, as flat plate and curvature specimen had more plies, their critical penetration energy was higher, Critical penetration energies of specimen A and C with less interfaces somewhat higher than those of B and D with more interfaces. The reason that with less interfaces, critical penetration energy was higher is pre-impact bending stiffness of composite laminated shell with less interfaces was lower than that of laminated shell with more interfaces, but bending stiffness after impact was higher. And it is because interface, the weakest part of the composite laminated shell, was influenced by transverse impact. As curvature increases, critical penetration energy increases linearly. It is because as curvature increases, resistance to in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. Patterns of cracks caused by penetration of composite laminated shells include interlaminar crack, intralaminar crack, and laminar fracture. A 0$^{\circ}$ply laminar had a matrix crack, a 90$^{\circ}$ply laminar had intralaminar crack and laminar fracture, and interface between 0$^{\circ}$and 90$^{\circ}$laminar had a interlaminar crack. We examined crack length and delamination area through a penetration test. For the specimen A and C with 2 interface, the longest circumferential direction crack length and largest delamination area were observed on the first interface from the impact point. For the specimen B and D with 4 interface, the longest crack length and largest delamination area were observed on the third interface from the impact point.

• Journal of the Korean Wood Science and Technology
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• 제37권2호
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• pp.128-136
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• 2009

Curved glued laminated timber (glulam) is rapidly coming into the domestic modern timber frame buildings and predominant in building construction. The radial stress is frequently occurred in curved beams and is a critical design parameter in curved glulam. Three models, Wilson equation, Exact solution and Approximation equation were introduced to determine the radial stress of curved glulam under pure bending condition. It is obvious that radial stress distribution between small radius and large radius was different due to slight change of neutral plane location to center line. If the beam design with extremely small radius, it should be considered to determine the exact location of maximum radial stress. The current standard KSF 3021 was reviewed and would be considered some adjustment determining the optimum radius in curved glulam. Current design principle is that the stress factor is given by the curvature term only in constant depth of the beam, but like tapered or small radius of beams, the stress factor by Wilson equation was underestimated. So current design formula should be considered to improvement for characterizing the radial stress factor under pure bending condition.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.274-279
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• 2004

Currently, carbon-fiber reinforced plastics(CFRP) are widely used in both space and civil aircraft due to their superior stiffness and strength to weight ratios compared to conventional metallic materials. This paper is to study the effects of curvature and stacking sequence on the penetration characteristics of composite laminated shell. And were performed to investigate the penetration characteristics of composite laminated shells by the oblique impact. They are stacked to [0$_3$/90$_3$]s, [90$_3$/0$_3$]s and [0$_2$/90$_3$/0]s, [90$_2$/0$_3$/90]s their interlaminar number two and fore. They are manufactured to varied curvature radius (R=100, 150, 200mm and $\infty$). When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determining the time for it to pass two ballistics-screen sensor located a known distance apart. In general, the critical penetration energy interface decrease and slope angle on the impact surface increased. [0$_3$/90$_3$]s and [0$_2$/90$_3$]s specimens higher than [90$_3$/0$_3$]s and [90$_2$/0$_3$/90]s specimens.

• 한국전산유체공학회지
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• 제19권1호
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• pp.57-63
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• 2014

This study performed numerical analysis for the characteristics of flow-induced forces and the flow instability depending on the cross-sectional shape of the cylinder in laminar flow. To implement the cylinder cross-section, we adopted an Immersed Boundary Method with marker particles. We analyzed flow characteristics based on the radius of corner curvature. Main parameters are corner radius and Reynolds number (Re). With Re = 40, 50, 150 we calculated the flow field, drag coefficient, RMS of lift coefficient, pressure coefficient and Strouhal number in conjunction with the corner radius variation. Also, we calculated critical Reynolds number ($Re_c$) depending on the corner radius variation.