• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.12
• /
• pp.931-939
• /
• 2013

In this paper, we try to find the lifting-line method which is applicable to the conceptual design of aircraft wings, and analyze the accuracy and coverage of the method. Two methods that are extended from the lifting-line theory of Prandtl are selected. One of the methods is Weissinger's method which imposes the velocity boundary condition at the control points located at the quarter chord, and the other is Phillips's method which combines the three-dimensional vortex lifting law. Calculations are performed for an elliptic wing, a swept back wing, and a tapered unswept wing with dihedral angle and geometric twist. The aerodynamic data of the potential flow such as spanwise distributions of circulation and downwash, lift and induced drag are obtained through calculations, and these data are compared with theoretical results and wind tunnel test data. As a result, Weissinger's method showed good accuracy and reliability regardless of wing shapes, but Phillips's method revealed inaccurate results for a swept back wing.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.517-521
• /
• 2009

A unsteady internal ballistic analysis model was proposed to take account for the variance of local variance of pressure and velocity along the grain surface of a hybrid rocket combustor. The model of concern in the study was fairly comparable with the test result. The local variation of the oxidizer mass flow rate along grain surface results in chamber pressure, regression rate, and gas velocity change along its flow direction.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.484-488
• /
• 2010

In this study, combustion experiments of the End-Burning Hybrid Propulsion System using $GN_2O$(Gas Nitrous oxide)/HDPE were performed and the results were compared to those of the combustion experiments using GOX/HDPE. The regression rate of the solid fuel using $GN_2O$ is lower than that of the solid fuel using GOX since oxidizer inlet velocity of $GN_2O$ is lower than that of GOX. However, in case of using $GN_2O$, the characteristic velocity is higher than those of the GOX. The combustion chamber pressure and thrust were relatively kept constant during combustion.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.19 no.1
• /
• pp.7-14
• /
• 2011

In this study, the measurement uncertainty of combustion experimental system and experimental parameters for hybrid rocket were evaluated by B type evaluation method. The measurement uncertainty of all experimental parameters was lower than 3%. The highest value of expanded uncertainty was characteristic velocity efficiency with 2.83% and the expanded uncertainty of regression rate which is the design and performance parameter was indicated to 0.03%. These results shown that the reliability of hybrid combustion system was located within allowed limits.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.4A
• /
• pp.529-536
• /
• 2008

The failure behavior of structures is changed under different loading rates, which might arise from the rate dependency of materials. This phenomenon has been focused in the engineering fields. However, the failure mechanism is not fully understood yet, so that it is hard to be implemented in numerical simulations. In this study, the numerical experiments to a brittle material are simulated by the Molecular Dynamics (MD) for understanding the rate dependent failure behavior. The material specimen with a notch is modeled for the compact tension test simulation. Lennard-Jones potential is used to describe the properties of a brittle material. Several dynamic failure features under 6 different loading rates are achieved from the numerical experiments, where remarkable characteristics such as crack roughness, crack recession/arrest, and crack branching are observed during the crack propagation. These observations are interpreted by the energy inflow-consumption rates. This study will provides insight about the dynamic failure mechanism under different loading rates. In addition, the applicability of the MD to the macroscopic mechanics is estimated by simulating the previous experimental research.

• Journal of Wetlands Research
• /
• v.15 no.3
• /
• pp.423-430
• /
• 2013

An algorithm to allow shoreline movement during numerical experiment on sediment transport, deposition or resuspension for general coastal morphology is proposed here. The bed slope near shoreline, i.e. mean sea level, is influenced by bed material, tidal current, waves, and wave-induced current, but has been reported to remain within a stable range. Its annual variation is not large, either. The algorithm is adjusting the bathymetry, if the largest bed slope within shoreline band exceeds a given bed slope due to continuous erosion at zones below the shoreline. This algorithm automatically describes retreat of shoreline caused by erosion, when used within a numerical system. The algorithm was tested to a situation which includes a continuous dredging at a point, and showed satisfactory development of concentric circle contours. Next, the algorithm was tested to another situation which includes sinking of eroded part of bed plate, and produced satisfactory results, too. Finally, the algorithm was tested to a movable-bed laboratory experimental conditions. The shoreline movement behind detached breakwater was reasonably reproduced with this algorithm.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.7 no.3
• /
• pp.30-37
• /
• 2003

Spray angle of dual swirl injector is established according to the velocity ratio at orifice exit. Due to the internal mixing at recess and lack of correlation for the combined two fluid injection, prediction of spray angle is very difficult. This study deal with experimental work and numerical simulation on spray angle with different recess length. Among the multiphase flow models, the VOF model was selected to simulate the spray angle. Feasibility of numerical analysis are confirmed by comparing the results with the experimental data, and the effect of recess on spray angle are analyzed for single and combined spray case.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.27 no.1
• /
• pp.135-145
• /
• 2000

It is well known that there are different craniofacial skeletal groups in the same malocclusion types. The present study was performed to determine morphologic sub-groups in Korean children with Class III malocclusions, and to find out morphological differences between subgroups by means of a cross-sectional longitudinal cephalometric study. In this study, 135 children aged 6 to 14 year-old with untreated Class III malocclusions were selected. The samples were divided into two groups depending on the angulation of middle cranial fossa (MCF). That is, when the MCF of an individual was measured smaller than 40.3, he/she was tossed into mandibular protrusive-effect group(MREG), while when an individual was measured larger than 40.3, he/she was tossed into mandibular retrusive-effect group(MREG). Thereafter, the grouped samples were divided into 4 age groups(7, 9, 11 and 13 year-old). Thirty four linear and angular measurements on the tracings of lateral cephaloradiographs were measured, and the morphological characteristics and differences were compared and analysed by means of Wilcoxon test. It was found that Korean children with Class III malocclusions were divided into two groups, in which 39.3% were belonged in the MREG and 60.7% were in the MREG. In the MREG, anterior-posterior length of cranial base, nasomaxillary complex, maxilla and mandible were larger than the MREG. And although there was no difference in the total length of mandible (Co-Gn), mandibular body length (Go-Gn) was larger in the MREG during the majority of the observed periods. These results would suggest that a majority of the samples, 60.7%, demonstrated many of configurations of craniofacial skeletal relationships that can be found in the leptoprosopic faceform.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.914-918
• /
• 2008

연안지역의 갑작스런 개발은 예상치 못한 여러 가지 문제들을 발생시키고 있다. 이와 같은 문제들 중에서 가장 심각한 문제는 해안침식이다. 해안침식은 어떤 원인에 의해 토사의 평형이 손상되어 퇴적되는 양보다 더 많은 양이 유실되면서 해안선이 점점 후퇴하는 현상이다. 해안에 쌓여 있는 모래는 태풍과 폭풍해일로부터 육지를 보호하는 완충지대의 역할을 하고, 또한 관광자원으로도 그 활용가치가 증가하고 있기 때문에 침식현상을 분석하고 침식의 발생 및 진행을 억제하기 위한 연구가 반드시 필요하다고 하겠다. 본 연구에서는 해안침식을 제어하기 위한 기초적인 연구의 일환으로 연안류에 따른 연안표사의 분포특성에 대하여 살펴보았다. 연안류는 표사 이동이 가장 활발한 쇄파대로부터 해안선 사이에서 발생하는 흐름으로 파랑에 의해 발생한다. 일정경사를 갖는 해빈에 대해 연안류를 계산하고 계산된 연안류를 Komar(1977)가 Bagnold(1963) 모형을 이용하여 파의 응력과 흐름속도의 곱의 함수로 연안표사의 분포를 나타나낸 식에 대입하여 연안류에 따른 연안표사의 분포를 계산하였다.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
• /
• 2008.10a
• /
• pp.173-174
• /
• 2008

해안 침식이 진행되고 있는 부산 해운대 해수욕장을 중심으로 해수면 상승에 따른 해안선 변화에 대한 분석을 실시하였다. 1947년부터 2008년까지 항공사진을 활용하여 해안선을 추출하였는데 사진촬영시간에 따라 해안선의 위치가 현저히 변화하기 때문에 위치만으로는 비교할 수 없고, 평균적인 해안선 부근의 경사와 촬영시의 조수상태를 고려한 수심별 해빈 면적 산정 공식을 활용하여 해안선 면적을 구하였다. 또한 조위자료를 통하여 40년 동안의 해수면 상승량을 산출하고, 이를 바탕으로 미래의 해안선 후퇴거리를 계산해 보았다. 그 결과 3008년도 해빈 면적은 1947년도와 비교하면 약 29% 면적이 감소하였고, 1992년도에는 일시적으로 해빈 면적이 상승하는데 이는 양빈 사업으로 인한 것으로 이후 다시 감소현상을 보인다. 그리고 조위자료 분석 결과 해수면은 연평균 2.462mm/year의 속도로 상승하였다.