• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.09a
• /
• pp.28-29
• /
• 2005

• Journal of Korea Water Resources Association
• /
• v.50 no.1
• /
• pp.55-64
• /
• 2017

This study presents a numerical model for simulating turbidity currents using the ULTIMATE scheme. For this, the layer-averaged model is used. The model is applied to laboratory experiments, where the flume is composed of sloping and flat parts, and the characteristics of propagating turbidity currents are investigated. Due to the universal limiter of the ULTIMATE scheme, the frontal part of the turbidity currents at a sharp gradient without numerical oscillations is computed. Simulated turbidity currents propagate super-critically to the end of the flume, and internal hydraulic jumps occur at the break-in-slope after being affected by the downstream boundary. It is found that the hydraulic jumps are computed without numerical oscillations if Courant number is less than 1. In addition, factors that affect propagation velocity of turbidity currents is studied. The particle size less than $9{\mu}m$ does not affect propagation velocity but the buoyancy flux affects clearly. Finally, it is found that the numerical model computes the bed elevation change due to turbidity currents properly. Specifically, a discontinuity in the bed elevation, arisen from the hydraulic jumps and resulting difference in sediment entrainment, is observed.

• Coupled systems mechanics
• /
• v.8 no.4
• /
• pp.339-350
• /
• 2019

A numerical simulation of the incompressible multiphase hydraulic jump flow was performed to compare the interface prediction through the use of the three RANS turbulence models: $k-{\varepsilon}$, $RNGk-{\varepsilon}$ and SST $k-{\omega}$. A three dimensional no submerged hydraulic jump and a two dimensional submerged hydraulic jump were modeled. Both the geometry and the mesh were created using the open source Gmsh code. The project's geometry consists of a rectangular channel with length and height differences between the two dimensional and three dimensional simulations. Uniform hexahedral cells were used for the mesh. Three refining meshes were constructed to allow to verify simulation convergence. The Volume of Fluid (abbr. VOF) method was used for treatment of the air-water surface. The turbulence models were evaluated in three distinct set up configurations to provide a greater accuracy in the flow representation. In the two-dimensional analysis of a submerged hydraulic jump simulation, the turbulence model RNG RNG $k-{\varepsilon}$ provided a better interface adjust with the experimental results than the model $k-{\varepsilon}$ and SST $k-{\omega}$. In the three-dimensional simulation of a no-submerged hydraulic jump the k-# showed better results than the SST $k-{\omega}$ and RNG $k-{\varepsilon}$ capturing the height and length of the ledge with a better fit with the experimental results.

• International Journal of Aeronautical and Space Sciences
• /
• v.3 no.1
• /
• pp.95-104
• /
• 2002

Numerical solution of the full Navier-Stokes equation as well as the energy equation has been obtained for the unsteady natural convection in a rectangular enclosure. One side wall was maintained at very high temperature simulating fires. Especially the effect of surface radiation was taken into account. While the enclosed air was assumed to be transparent, the internal walls directly interacted one another through the surface radiation. Due to a significant temperature difference in the flow field, the equation of state was used instead of the Boussinesq approximation. It was found that the rapid heating of the adiabatic ceiling and floor by the incoming radiation from the hot wall made the evolution at thermo-fluid field highly unstable in the initial period. Therefore, the secondary cells brought about at the floor region greatly affected the heat transfer mechanism inside the enclosure. The heat transfer rate was augmented by the radiation, resulting in requiring less time for the flow to reach the steady state. At the steady state neglecting radiation two internal hydraulic jumps were clearly observed in upper/left as well as in lower/right comer. However, the hydraulic jump in the lower/right comer could not be observed for the case including radiation due to its high momentum flow over the bottom wall. Radiation resulted in a faster establishment of the steady state phenomena.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.151-151
• /
• 2011

평활입자동역학법(SPH, Smoothed Particle Hydrodynamics)은 도수, 댐붕괴류, 쇄파 등과 같이 수면 변동이 큰 유체 역학 문제를 해결하기 위한 무격자법 중의 하나이다. SPH법을 이용하여 1.5에서 8.0 범위의 여러 가지 Froude 수에 대하여 도수를 모의하였다. 또한, SPH의 모의 결과와 비교 검토하기 위해 실험실 수로에 물리모형을 구축하였다. 도수 전면의 위치와 도수 후의 수심을 대상으로 수리실험과 수치모의 결과를 비교하였다. 그 결과 Froude 수가 5 미만일 때, 수치모의결과는 물리 모형과 비교적 잘 일치하였으나, Froude 수가 클 때는 오차가 커지는 경향을 보였다. 이처럼 수치 모의의 결과가 물리 모형과 차이를 보이는 주요 이유는 점성의 처리와 난류에 따른 와도와 관련이 있는 것으로 알려져 있다. 따라서, 이 문제는 난류모형을 도입하면 어느 정도 개선될 수 있을 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.1
• /
• pp.149-155
• /
• 2013

In this study, factors that affect the air entrainment within a closed conduit by air drawn in through an air vent are investigated using a hydraulic scale model, which represents a gated circular conduit system connected to the intake tower of an irrigation reservoir. In addition, using data obtained during the hydraulic experiments, experimental equations are developed to estimate the amount of air drawn in through the air vent. In case of pressurized flow conditions downstream of hydraulic jumps, the relationships between $\frac{Q_a}{Q_w}$ and $Fr_g-1$ of the data form a experimental equation, $\frac{Q_a}{Q_w}=0.0304(Fr_g-1)^{1.0622}$; in case of free surface flow conditions, $\frac{Q_a}{Q_w}=0.0271(Fr_g-1)^{1.8205}$. Comparing two data sets observed under the two flow regimes with the results of previous researchers, patterns of the data sets are similar to the results estimated using the equations presented previously, and this indicates that the quality of the data obtained during the hydraulic experiments is ensured. In addition, it is revealed that air entrainment phenomena in the regions close to air vents are affected by the characteristics of supercritical flows downstream of gates. Finally, it is concluded that the equation developed for pressurized flow conditions can be applied to design of air vents.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.29 no.1
• /
• pp.1-8
• /
• 2021

Low level wind shear, which often occurs at Jeju International Airport, is a phenomenon that occurs when the topological location and topographical characteristics of Jeju Island are combined with weather characteristics. Low level wind shears, which are caused by rapid changes in wind direction and wind speed, pose a threat to aircraft safety and also cause abnormal situations, such as aircraft go-around, diversion, and cancellation. Many meteorological studies have been conducted on weather patterns, occurrence periods and frequency of low level wind shears. However, researches related to aircraft operations are limited where here we study the similarities and differences between strong southwest winds and bidirectional tailwind type low level wind shears based on aircraft go-around cases at Jeju International Airport. The results are expected to be used to enhance safety when operating to Jeju International Airport, which includes pilot training that reflects the characteristics generated by wind changes, pilot prior notification, providing pilots with latest trends, and increasing extra fuel.