• Imaging Science in Dentistry
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• 제33권1호
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• pp.35-41
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• 2003

Purpose: To aid in determining the volume of graft bone required before a maxillary sinus lift procedure and compare the alveolar bone height measurements taken by panoramic radiographs to those by CT images. Materials and Methods : Data obtained by both panoramic radiographs and CT examination of 25 patients were used in this study. Maxillary sinus volumes from the antral floor to heights of 5 mm, 10 mm, 15 mm, and 20 mm, were calculated. Alveolar bone height was measured on the panoramic images at each maxillary tooth site and corrected by magnification rate (PBH). Available bone height (ABH) and full bone height (FBH) was measured on reconstructed CT images. PBH was compared with ABH and FBH at the maxillary incisors, canines, premolars, and molars. Results: Volumes of the inferior portion of the sinuses were 0.55 ± 0041 ㎤ for 5 mm lifts, 2.11 ± 0.68 ㎤ for 10 mm, 4.26 ± 1.32 ㎤ for 15 mm, 6.95 ± 2.01 ㎤ for 20 mm. For the alveolar bone measurement, measurements by panoramic images were longer than available bone heights determined by CT images at the incisor and canine areas, and shorter than full bone heights on CT images at incisor, premolar, and molar areas (p<0.001). Conclusion: In bone grafting of the maxillary sinus floor, 0.96 ㎤ or more is required for a 5 mm-lift, 2.79 ㎤ or more for a 10 mm-lift, 5.58 ㎤ or more for a 15 mm-lift, and 8.96 ㎤ or more for a 20 mm-lift. Maxillary implant length determined using panoramic radiograph alone could result in underestimation or overestimation, according to the site involved.

• 대한기계학회논문집B
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• 제30권2호
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• pp.117-125
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• 2006

In the present study the unsteady forces acting on the pitching foils such as a flat plate, NACA0010, NACA0020, NACA65-0910 and BTE have been measured by using a six-axis sensor in a circulating water tunnel at a low Reynolds number region. The unsteady characteristics of the dynamic drag and lift have been compared to the quasi-steady ones which are measured under the stationary condition. The pitching motion is available for keeping the lift higher after the separation occurs. Especially, the characteristics of the dynamic lift are quite different from the quasi-steady one at high pitching frequency regions. As the pitching frequency deceases, the amplitude of the dynamic lift becomes closer to the quasi-steady one. However, the phase remains different between the steady and unsteady conditions even at low pitching frequencies. On the other hand, the dynamic drag is governed strongly by the angle of attack.

• 한국건설관리학회논문집
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• 제13권2호
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• pp.110-119
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• 2012

초고층 건축물의 수요가 늘어나면서 수직 양중 계획과 장비에 대한 중요성이 증대되고 있으며, 경제적이고 효율적인 리프트 사용을 위하여 무인 리프트의 사용 비중이 늘어나고 있다. 하지만 리프트의 정지위치 에러가 발생하거나 누적되는 경우 작업 효율성이 떨어지고, 문제 해결을 위해 리프트 업체가 리프트를 재 세팅 하는 동안 리프트 사용이 불가하게 되어 공사 진행에 장애가 된다. 본 연구에서는 리프트 정지위치 에러에 의한 시간 및 비용 손실을 방지하기 위해 리프트 정지위치 감지장치를 개발하였다. 실험을 통해, 정지위치 에러 발생 시 이를 보정하는 기능을 검증하였고, 정확도도 약 9.75mm 증가하는 것을 확인하였다.

• Wind and Structures
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• 제32권3호
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• pp.239-248
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• 2021

In this study, three airfoil families, NACA, FX and S, in each case three from each series with different shapes were investigated at different angles of attack using Computational Fluid Dynamics (CFD) method. To verify the CFD model, simulation results of the NACA 0012 airfoil was compared against the available experimental data and k-ω SST was used as the turbulence model. Lift coefficients, lift to drag ratios and pressure distributions around airfoils were obtained from the CFD simulations and compared each other. The simulations were performed at three Reynolds numbers, Re=2×105, 1×106and 2×106, and angle of attack was varied between -6 and 12 degrees. According to the results, similar lift coefficient values were obtained for symmetric airfoils reaching their maximum values at similar angles of attack. Maximum lift coefficients were obtained for FX 60-157 and S 4110 airfoils having lift coefficient values around 1.5 at Re=1×106 and 12 degrees of angle of attack. Flow separation occurred close to the leading edge of some airfoils at higher angles of attack, while some other airfoils were more successful in keeping the flow attached on the surface.

• 한국항공우주학회지
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• 제45권3호
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• pp.191-193
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• 2017

EFD-CFD 비교워크샵은 AIAA의 Drag Prediction Workshop과 High Lift Prediction Workshop을 참고하여 국내의 풍동실험과 전산해석기술 수준을 향상시키고 두 분야의 협력을 통해 공기역학의 기술수준을 고양하고자 조직되었다. 국내외에서 수행된 3개의 풍동실험 Case에 대한 전산해석 수행 및 비교분석을 수행하며 2015년부터 비교 워크샵이 개최되고 있다. 향후 국내 연구자들의 참여와 협력을 적극 유도하며 새로운 형상에 대한 실험과 해석 및 분석을 진행하여 국내 공기역학의 기술발전에 기여하고자 한다.

• Nuclear Engineering and Technology
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• 제34권4호
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• pp.358-369
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• 2002

Abundant information about analyses of single steam generator tube rupture (SGTR) events is available because of its importance in terms of safety. However, there are few literatures available on analyses of multiple steam generator tube rupture (MSGTR) events. In addition, knowledge of transients and consequences following a MSGTR event are very limited as there has been no occurrence of MSGTR event in the commercial operation of nuclear reactors. In this study, a postulated MSGTR event in an APR1400 is analyzed using thermal-hydraulic system code MARSI.4. The present study aims to examine the effects of affected steam generator selection. The main steam safety valve (MSSV) lift time for four cases are compared in order to examine how long operator response time is allowed depending on which steam generate. (S/G) is affected. The comparison shows that the cases where two steam generators are simultaneously affected allow longer time for operator action compared with the cases where a single steam generator is affected. Furthermore, the tube ruptures in the steam generator where a pressurizer is connected leads to the shortest operator response time.

• 항공우주기술
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• 제12권2호
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• pp.180-185
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• 2013

본 연구에서는 공기역학적 성능을 고려하여 인간의 힘만으로 이륙할 수 있는 초경량 인간동력 항공기의 개념설계를 수행하였다. 이를 위해 조종사를 포함한 항공기 전체 무게를 결정한 이후 적절한 익형을 선정하여 주날개/보조날개를 설계하였다. 설계된 비행기의 형상을 기초로 3차원 전산해석을 하였으며, 이를 통해 양력/항력 등의 성능계수 및 항공기 무게 중심(CG)에 대한 계산을 수행하였다. 그 결과 비행기의 양력 및 추력이 양력 및 추력의 제한 조건을 만족하였다. 또한 비행기의 무게 중심(CG)이 주익의 공력 중심(AC)에 위치함으로써 26%의 정적 안정성이 보장되었다.

• Journal of Mechanical Science and Technology
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• 제19권3호
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• pp.877-886
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• 2005

Two-dimensional incompressible Navier-Stokes equations are solved using SIMPLER method in the intrinsic curvilinear coordinates system to study the unsteady viscous flow physics over two-dimensional ellipses. Unsteady viscous flows over various thickness-to-chord ratios of 0.6, 0.8, 1.0, and 1.2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000. This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces. The present numerical solutions are compared with available experimental and numerical results and show a good agreement. Through this study, it is observed that the Reynolds number and the cylinder thickness affect significantly the frequencies of the force oscillations as well as the mean values and the amplitudes of the drag and lift forces.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권3호
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• pp.305-314
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• 2017

Asymmetric planing hulls are often used on high-speed catamarans. In this study, a linearized potential-flow method is applied for modeling steady hydrodynamics of single asymmetric hulls and their catamaran setups. Numerical results are validated with available experimental data and empirical correlations. Parametric calculation results are presented for the lift coefficient and the center of pressure for variable hull geometry, spacings, and speed regimes. The lift coefficient is found to increase at smaller hull spacings and decrease at higher Froude numbers and higher deadrise angles.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.131-135
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• 2006

The aerodynamic characteristics of a T-50 aircraft configuration are investigated by a subsonic panel method. Panel methods are best applicable to the lifting surfaces such as wings and airfoils. Source and doublets are used in the present code as a basic singularities of the panel technique. The panel method is first assessed by applying it to several benchmark problems for which other solutions and experimental data are available, such as a swept wing and wing body configuration. The prediction results are compared with experimental data and show good agreement in all cases considered. Finally, the method is applied to a T-50 aircraft configuration and excellent agreement with flight test data in lift coefficients is found.