• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.3 s.258
• /
• pp.264-272
• /
• 2007

The aim of this study is to investigate the effects of nozzle orifice shapes and the nozzle length-to-diameter ratio(L/D) on the nozzle cavitation formation inside the orifice and the external flow pattern. The nozzle used in this work was tested the taper orifice nozzle and the rectangular orifice nozzle which was made from the transparent acrylic acid resin. For studying the effect of the nozzle L/D ratio, it was used to three L/D ratios of 3.33, 10, and 20. The cavitation flow of nozzle was visualized by using the ICCD camera and optical system. This work revealed that the flow rate and discharge coefficient($C_d$) of the taper orifice nozzle was larger than those of the rectangular orifice nozzle at the same injection pressure. The cavitation flow was observed in the nozzle orifice at the low injection pressure and the breakup of liquid jet was promoted as the L/D ratio is decreased. The cavitation of biodiesel fuel was formed at the lower injection pressure than that of diesel fuel because of higher viscosity and density.

• Journal of the Society of Naval Architects of Korea
• /
• v.37 no.4
• /
• pp.11-18
• /
• 2000

This paper is concerned with the generation of an optimal forward hull form by a nonlinear programming method. A Rankine source panel method based on the inviscid and potential flow approximation is employed to calculate the wave-making resistance and SQP method is also used for the optimization. The hull form is represented by a spline function. The forward hull form of a minimum wave resistance with the given design constraints is generated. In addition, the forward hull form of a minimum total resistance by considering the frictional resistance together with an empirical form factor is produced and compared with the former result.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.05a
• /
• pp.315-320
• /
• 2008

This experimental study has been conducted to investigate the effect of the flame holder on the multi-slot film cooling in the ramjet combustor. The turbulent wake which is generated by the flame holder on the entrance of the coolant flow path affects on the slot. Adiabatic film cooling effectiveness on the downstream wall of the slot exit are measured. The results show that the film cooling performance is rapidly decreased after the slot exit by shear layer and high turbulence intensity between separated flows and coolant flows.

• The Korean Journal of Rheology
• /
• v.9 no.1
• /
• pp.33-39
• /
• 1997

PCL, MDI, BD 및 DMPA를 이용, 폴리우레탄(PU)을 ionomer 및 nonionomergudxo 로 제조하였으며 이때 연질성분의 함량(SSC) 및 길이가 PU의 기계적, 동적기계적 특성은 물론 형상기억특성에 미치는 영향을 연구하였다. Ionomer는 nonionomer에 비하여 경도, 탄 성율 및 강도가 모두 우수하였으며 그 효과는 실온에서 경질성분의 함량(HSC)이 높은 PU 일수록 보다 뚜렷하였는데 이는 HSC가 증가할수록 ion 중심의 농도가 증가하며 ion 중심간 의 Coulob 력이 고온보다 실온에서 보다 큰데 기인하는 것으로 해석하였다. 반복인장하중실 험에서 ionomer는 nonionomer에 비해 회복변형이 크고 잔류변형이 작았는데 이는 ionomer 의 고무탄성율이 보다 큰 데 기인한 것으로 해석하였다. 나아가 재료의 형상기억거동은 기 본적으로 탄성율의 온도의존성에 크게 의존함을 알수있었다.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.06a
• /
• pp.620-623
• /
• 2009

여러 해양에너지 중 유체의 빠른 흐름을 이용하는 조류발전은 서해안과 남해안에 적용하기에 적합하며 해양환경의 영향을 최소화 하면서 많은 에너지를 연속적으로 생산할 수 있는 장점이 있다. 조류발전에서 1차적으로 에너지를 변환시키는 로터는 조류발전시스템의 주요한 장치중의 하나로 여러 변수에 의해 그 성능이 결정된다. 블래이드 수, 형상, 단면적, 허브, 직경 등 여러 요소를 고려하여 로터를 설계하며, 설계정보와 실험데이터를 바탕으로 수치모델을 구현하여 실험에서 직접 계측할 수 없는 로터 주변의 유체현상 및 간섭영향 등을 예측할 수 있다. 본 논문에서는 변화하는 유속에 따른 HAT 로터의 시동속도, 회전수를 측정하여 로터 형상과 허브-직경비가 다른 로터의 성능을 고찰하고, 이를 수치모델로 구현하여 로터주변 유동변화를 연구하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.10
• /
• pp.809-819
• /
• 2020

In this study, the twist angle and wing planform shapes were selected as design variables and optimized to secure the stability of the flying-wing type UAV. Flying-wing aircraft has no separated fuselage and tails, which has advantages in aerodynamic characteristics and stealth performance, but it is difficult to secure the flight stability. In this paper, the sweep back angle and twist angle were optimized to obtain the lateral stability, the static margin and wing planform shapes were optimized to improve the longitudinal stability of the flying-wing, then effect of the twist angle was confirmed by comparing the stability of the shape with the winglet and the shape with the twist angle. In the optimization formulation, focusing on improving stability, constraints were established, objective functions and design variables were set, then design variable sensitivity analysis was performed using the Sobol method. AVL was used for aerodynamic analysis and stability analysis, and SQP was used for optimization. The CFD analysis of the optimized shape and the simulation of the dynamic stability proved that the twist angle can be applied to the improvement of the lateral stability as well as the stealth performance in the flying-wing instead of the winglet.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.04b
• /
• pp.45-51
• /
• 1995

자동차 엔진의 피스톤은 핀 구멍의 복잡한 형상과 2사이클 엔진의 경우 실린더쪽 흡기 및 배기 포트의 위치에 따라 균일하지 않은 열이나 응력 등의 영향에 의한 변형을 고려하여, 상온에서의 형상이 각종 평가 시험을 거쳐 엔진마다 다양한 형상을 갖는 피스톤으로 결정된다. 본 연구에서는 컴퓨터 제어에 의한 방법으로서 타원형상을 갖는 임의의 피스톤을 고속, 고정도로 가공할 수 있는 CNC(Computer Numerical Control)선반 개발에 관하여 연구 하였다. 피스톤 데이터를 퍼스널 컴퓨터로 입력하고 CNC 제어하므로 마스터캠의 제작 불필요, Recess 등과 같은 미세가공 가능, 피스톤의 형상변경 용이, 고속가공 등으로 모방절삭 방식보다 훨씬 높은 생산성 향상이 기대된다.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.1
• /
• pp.24-40
• /
• 1997

Horseshoe vortices generated around the juncture between the ship and her appendages often lower a performance of the ship by increasing the appendage drag and making a non-uniform wake on the propeller plane. This paper investigates numerically how the fillet around the juncture of the leading edge influences the juncture flow and the appendage drag. Computation has been made by solving Navier-Stokes equations with MAC method and the flows are at the Reynolds number of 5,000. Five fillets with different height-breath ratios and curvatures are chosen as test models to find out the effects of the shape of fillets on the appendage drag and wake. Computational results show that fillets with a smaller height-breath ratio and/or with a concave curvature has smaller appendage drag and more uniform wake.

• Tunnel and Underground Space
• /
• v.14 no.5
• /
• pp.363-372
• /
• 2004

Double torsion (DT) tests were carried out to investigate the influence of the geometry of guide groove on stress corrosion index of Kumamoto andesite. The fracture toughness was measured in the constant displacement rate, which was set to 2.07 MN/m$^{3}$2/ in average regardless of crack velocity. Stress corrosion indices, n were evaluated using specimens with rectangular, circular and triangular grooves and were 37, 36 and 38 in average, respectively. The n values were constant regardless of the groove geometry, however the DT specimen with triangular groove geometry showed the largest standard deviation in the relationship between crack velocity and stress intensity factor. The DT test was found to be effective in using a rectangular-grooved specimen and the width of the groove must be greater than the average grain size of minerals.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.4
• /
• pp.169-183
• /
• 2007

Numerical analysis was performed to investigate the behavior of rammed aggregate piers (RAP) in soft ground with various interface conditions, area replacement ratio, aspect ratio and surcharge loads of pile and soil. And field modulus load test was carried out to predict the input parameters. Field prototype (unit cell) tests are in progress to compare the result of numerical analysis. Also a modified load transfer equation of RAP on soft foundation was proposed. According to the results, the behavior of RAP depended on such as interface conditions, settlement characteristics (free strain) and stress concentration ratio. On the other hand, maximun stress concentration ratio increased as area replacement ratio and aspect ratio increased, and it was remarkably affected by surcharge loads.