• Proceedings of the KSEG Conference
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• 2004.03a
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• pp.24001-24056
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• 2004

암반 기초에서 발생 가능한 파괴형태로는 $\circled1$전단파괴(Shear failure) $\circled2$관입파괴(punch failure) $\circled3$붕락(Collapse) $\circled4$균열파괴 (cracking) $\circled5$분쇄상파괴 (crushing) $\circled6$쐐기상파괴 (wedging)를 들 수 있다. 그림 2.4-1에서 (a)는 연암층 내에서의 전형적인 전단파괴를 나타내고, (b)는 소성암반 상부에 강성암반이 놓였을 때의 전단파괴를 보여준다. (c)는 2층으로 구성된 지반에서의 전단파괴 양상이며, (d)는 편심하중이 작용할 때의 전단파괴이다. (e)는 사면 상에서의 활동에 의한 파괴유형이다. (f)는 절리가 발달한 풍화된 암반내로 진행되는 관입파괴를 보여주고 있다. (e)는 연암지반 내부로 강성암반이 관입되어 파괴된 모습이다. (h)는 풍화된 화강암에서의 관입파괴 유형이다. (i)는 석회암층 내부의 지하공동에 의한 붕락현상을 보여주고 있으며, (j)는 지하수의 유동에 의해 형성된 공동으로 인한 붕락파괴를 나타낸다. (k)는 균열파괴, (l)은 분쇄상 파괴, (m) 쐐기상 파괴, (n)은 단층선을 따른 파괴 유형이다. (중략)

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.9-16
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• 2004

A three-dimensional numerical analysis was carried out on incompressible flows in butterfly valves by using commercial FLUENT/UNS code. Characteristics of complex flows including cavitation effect were investigated for different valve disk angles. The butterfly-valves that had different disk angles and different disk shapes were compared with each other in detail. This study focused on the flow analysis in the conventional butterfly valve and the newly designed butterfly valve in order to prevent cavitation. The newly designed valve shows great improvement on performance and endurance.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.1
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• pp.99-106
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• 2013

DME (Di-Methyl Ether) is synthetic product that is produced through dehydration of methanol or a direct synthesis from syngas. And it is able to save fossil fuel and reduce pollutants of emission such as PM and $CO_2$. In spite of its advantages it is difficult to design DME fuelled engine system because DME fuel may cause to severely generate cavitation and corrosion in fuel delivery system due to physical properties of DME. Therefore, in this study three-dimensional internal flow characteristics with consideration of cavitation were predicted in the DME injector using diesel and DME fuel. Moving grid technique was employed to describe needle motion and 1-D hydraulic simulation of injector was also simulated to obtain transient needle motion profiles. The results of simulation show that cavitations was generated at the inlet of nozzle near high velocity region both diesel and DME. And mass flow rate of DME is reduced by 4.73% compared to that of diesel at maximum valve lift because cavitation region of DME is much more larger. To increase flow rate of DME injector, internal flow simulation has been conducted to investigate the nozzle hole inner R-cut effect. The flow rates of diesel and DME increase as R-cut increases, and flow coefficient of DME fuel injector was increased by 6.3% on average compared with diesel fuelled injector. Finally, optimum shape of DME injector nozzle is suggested through the comparison of flow coefficient with variation of nozzle hole inner R-cut.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.483-488
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• 2001

In the present study a numerical simulation is performed on a natural convection inside a square cavity with a vibrating wall. The study has been conducted varying the heat transfer rate, wall excitation frequency and also the orientation of the cavity. The temperature and velocities inside the cavity was observed and also, the heat transfer coefficients on the heating wall was seen. From the results, it can be seen that the temperature inside the cavity decreases when excited with the proper frequency and the heat transfer coefficient increased with cavity inclination angle, ${\theta}$. It is also found from the results that flow resonance is occurred near the inclination angle ${\theta}=90^{\circ}$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.339-343
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• 2006

Model SCRamjet Engine intake is designed for Ground test. The designed Intake provides hot and slow flow with the combustor. Flow separation is controlled by the shock wave segregation based on the Korekegi criteria. With Kantrowitz limit analysis, side wall cut out region is also set for the self start.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.924-931
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• 2009

The two-dimensional turbulent flow around the horn-type rudder has been examined in the present study by using the commercial code FLUENT. The standard ${\kappa}-{\epsilon}$ model is used as a closure relationship. The geometry of horn rudder is based on the NACA 0020 airfoil. The simulations for various angle attack (${\alpha}$) and yaw angle(${\delta}$) are carried out. The effect of Reynolds number is also investigated in this study. The cavitation is more possible when the yaw angle is $6^{\circ}$ and it is more serious as Reynolds number increases.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.6
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• pp.50-57
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• 2007

Pressure Sensitive Paint(PSP) means a reacting paint in pressure. PSP can measure continuous pressure field by analyzing the oxygen quantity using optical method. The surface pressure of down stream after the sonic jet that injected transversely into the supersonic freestream was measured by PSP technique. Moreover the effect of various rectangular shaped cavities in front of the jet was measured by PSP technique. A comparison of the PSP results with conventional pressure tap and CFD indicates good agreement. Until now, the results of numerical analysis were compared with the discrete points such as the results of pressure tap. In this study, the whole region pressure was measured using PSP technique and its results were similar to CFD. Therefore, the flow phenonenon of cavity downstream was clearly grasped.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.4
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• pp.400-406
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• 2017

The model used in this study was reversed to analyze the cause of excessive damage that occurred inside the rotating system and pipe system of a centrifugal-type seawater pump on a ship. For this purpose, internal flow analysis on a cooling seawater pump was performed using CFD. As a result, the shape and boundary conditions of the target pump were set by reverse engineering, and pump efficiency at a design operating point of $125m^3/h$ was calculated as 85.3 % with a head of 32.0 m. The maximum efficiency point of the target pump was estimated to be 86.2 % at $150m^3/h$, but this differed from the actual operating point. At $112.5m^3/h$, which was the lowest flow point, flow was unstable due to the characteristics of the low flow point and analysis convergence was not good. The purpose of this study was to clarify the cause of ongoing cavitation in seawater pumps and piping systems in operation. Future research will be needed to clarify causes for pipe systems in the future by performing calculations for the total piping system of an inlet and outlet, in addition to measuring the flow rate of each branch pipe.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.499-505
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• 2001

The objective of the paper was to measure the pressure drop and to investigate the recirculation region of the conical orifices used in Kwang-yang Iron & Steel Company. The flow field with water used as a working fluid was the turbulent flow for Reynolds number of $2{\times}10^4$. The effective parameters for the pressure drop and the recirculation region were the conical orifice's inclined angle (${\theta}$) against the wall, the interval(L) between orifices, the relative angle of rotation(${\alpha}$) of the orifices, the shape of the orifice's hole(circle, rectangle, triangle) having the same area. It was found that the shape of the orifice's hole affected the pressure drop and the flow field a lot, But the other parameters did not make much differences to the pressure drop. The PISO algorithm with FLUENT code was employed.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.324-333
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• 2013

Recently, rudder erosion due to cavitation has been frequently reported on a semi-spade rudder of a high-speed large ship. This problem raises economic and safety issues when operating ships. The semi-spade rudders have a gap between the horn/pintle and the movable wing part. Due to this gap, a discontinuous surface, cavitation phenomenon arises and results in unresolved problems such as rudder erosion. In this study, we made a rudder model for 2-D experiments using the NACA0020 and also manufactured gap flow blocking devices to insert to the gap of the model. In order to study the gap flow characteristics at various rudder deflection angles($5^{\circ}$, $10^{\circ}$, $35^{\circ}$) and the effect of the gap flow blocking devices, we carried out the velocity measurements using PIV(Particle Image Velocimetry) techniques and cavitation observation using high speed camera in Seoul National University cavitation tunnel. To observe the gap cavitation on a semi-spade rudder, we slowly lowered the inside pressure of the cavitation tunnel until cavitation occurred near the gap and then captured it using high-speed camera with the frame rate of 4300 fps(frame per second). During this procedure, cavitation numbers and the generated location were recorded, and these experimental data were compared with CFD results calculated by commercial code, Fluent. When we use gap flow blocking device to block the gap, it showed a different flow character compared with previous observation without the device. With the device blocking the gap, the flow velocity increases on the suction side, while it decreases on the pressure side. Therefore, we can conclude that the gap flow blocking device results in a high lift-force effect. And we can also observe that the cavitation inception is delayed.