• The Journal of the Korea Contents Association
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• v.10 no.10
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• pp.451-455
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• 2010

Hydraulics usually deals with flows with free surface. When the surface curvature is small, the assumption of hydrostatic pressure distribution is enough. However, in the case, when the curvature is big, the non-hydrostatic pressure distribution should be taken into account and the Navier-Stokes equations should be employed instead of the depth-averaged shallow water equations. For the simulation of two immiscible fluids with different characteristics (e.g. water and air, water and oil), the level set method is selected for this purpose. The developed model is applied to classical dam break problem and the computational results are compared with the experimental data. The effectiveness of the developed model is confirmed.

• Journal of Biomedical Engineering Research
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• v.28 no.5
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• pp.665-675
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• 2007

The morphological change of ECG is the important diagnostic parameter to finding the malfunction of a heart. Generally ST segment deviation is concerned with myocardial abnormality. The aim of this study is to detect the change of ST in shape using a polynomial approximation method and the reference ST type. The developed algorithm consists of feature point detection, ST level detection and ST shape classification. The detection of QRS complex is accomplished using it's the morphological characteristics such as the steep slope and high amplitude. The developed algorithm detects the ST level change, and then classifies the ST shape type using the polynomial approximation. The algorithm finds the least squares curve for the data between S wave and T wave in ECG. This curve is used for the classification of the ST shapes. ST type is classified by comparing the slopes of the specified points between the reference ST set and the least square curve. Through the result from the developed algorithm, we can know when the ST level change occurs and what the ST shape type is.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.455-458
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• 2006

This study has numerically modelled the combustion processes of the turbulent swirling premixed lifted flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially- injected air jets induce the turbulent swirling flow which plays the crucial role to stabilize the turbulent lifted flame. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flame let model. Two-dimensional and three-dimensional computations are made for the various swirl numbers and nozzle length. In terms of the centerline velocity profiles and flame liftoff heights, numerical results are compared with experimental data The three-dimensional approach yields the much better conformity with agreements with measurements without any analytic assumptions on the inlet swirl profiles, compared to the two-dimensional approach. Numerical clearly results indicate that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling stoichiometric and lean-premixed lifted flames in the low-swirl burner.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1107-1116
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• 2006

The droplet ejection process driven by an evaporating bubble in a thermal inkjet printhead is investigated by numerically solving the conservation equations for mass, momentum and energy. The phase interfaces are tracked by a level set method which is modified to include the effect of phase change at the interface and extended for multiphase flows with irregular solid boundaries. The compressibility effect of a bubble is also included in the analysis to appropriately describe the bubble expansion behaviour associated with the high pressure caused by bubble nucleation. The whole process of bubble growth and collapse as well as droplet ejection during thermal inkjet printing is simulated without employing a simplified semi-empirical bubble growth model. Based on the numerical results, the jet breaking and droplet formation behaviour is observed to depend strongly on the bubble growth and collapse pattern. Also, the effects of liquid viscosity, surface tension and nozzle geometry are quantified from the calculated bubble growth rate and ink droplet ejection distance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1093-1100
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• 2004

Numerical analysis of the heat transfer associated with droplet impact on a hot solid surface is performed by solving the equations governing conservation of mass, momentum and energy in the liquid and gas phases. The deformed droplet shape is tracked by a level set method which is modified to achieve volume conservation and to include the effect of contact angle at the wall. The numerical method is validated through the calculations for the cases reported in the literature. Based on the numerical results, the heat transfer rate is found to depend strongly on the droplet spread radius. Decreased advancing/receding contact angles enlarge the splat radius and in turn enhance the wall heat flux. The effect of impact velocity on the droplet spread is reduced as the droplet size decreases. Also, droplet atomization is observed to significantly enhance the heat transfer rate and the effect is pronounced for a smaller size of droplet. An existing model equation to predict the maximum spread radius is improved for application to a micro droplet.

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.21-25
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• 2007

A general purpose program NUFLEX has been extended for two-phase flows with topologically complex interface and cavitation flows with liquid-vapor phase change caused by large pressure drop. In analysis of two-phase flow, the phase interfaces are tracked by employing a LS(Level Set) method. Compared with the VOF(Volume-of-Fluid) method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. Also, the cavitation process is computed by including the effects of evaporation and condensation for bubble formation and collapse as well as turbulence in flows. The volume-faction and continuity equations are adapted for cavitation models with phase change. The LS and cavitation formulation are implemented into a general purpose program for 3-D flows and verified through several test problems.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.583-592
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• 2005

The turbulent free surface flow around a self-propelled KRISO 138K LNG Carrier is numerically simulated using the finite volume based multi-block RANS code, WAVIS developed at HRISO. The realizable k-$\varepsilon$ turbulence model with a wail function is employed for the turbulence closure. The free surface is captured with the Level-Set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. In order to obtain an accurate free surface solution and stable convergence, the computations are executed with a proper fine grid refinement around the free surface and with an adoption of implicit discretization scheme for the Level-Set formulation. The computed velocity vectors at the several stations and wave patterns show a good agreement with the experimental results measured at the KRISO towing tank.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.2
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• pp.132-143
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• 2008

The sloshing phenomena in a two-dimensional rectangular tank are investigated using a level set method based on finite volume method. The code validations are performed by comparing between the present results and previous numerical results, which gives a good agreement. We present the streamlines pattern, free surface shape, maximum free surface elevation and pressure fluctuation patterns in the tank under the pitch and surge motions with various frequencies. These two different motions cause the different flow structures in the tank. The time variations of surface elevation and pressure at the different locations in the tank strongly depend on the exciting frequency of tank moving.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.4
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• pp.29-34
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• 2002

In this paper, we present a new geometric active contour model based on level set methods introduced by Osher and Sethian for detection of object boundaries or shape and we adopt anisotropic diffusion filtering method for removing noise from original image. In order to minimize the processing time, we use the narrow band method which allows us to perform calculations in the neighborhood of the contour and not in the whole image. Using anisotropic diffusion filtering for each slice, we have the result with reduced noise and extracted exact shape. Volume rendering operates on three-dimensional data, processes it, and transforms it into a simple two-dimensional image.

• Advances in aircraft and spacecraft science
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• v.6 no.4
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• pp.333-348
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• 2019

Low fuel regression rate is the main drawback of hybrid rocket which should be overcome. One of the improvement techniques to this problem is usage of a solid fuel grain with a complicated geometry port, which has been promoted owing to the recent development of additive manufacturing technologies. In the design of a hybrid rocket fuel grain with a complicated geometry port, the understanding of fuel regression behavior is very important. Numerical investigations of fuel regression behavior requires a capturing method of solid fuel surface, i.e. gas-solid interface. In this study, level set method is employed as such a method and the preliminary numerical tool for capturing a hybrid rocket solid fuel surface is developed. At first, to test the adequacy of the numerical modeling, the simulation results for circular port are compared to the experimental results in open literature. The regression rates and oxidizer to fuel ratios show good agreements between the simulations and the experiments, after passing enough time. However, during the early period of combustion, there are the discrepancies between the simulations and the experiments, owing to transient phenomena. Second, the simulations of complicated geometry ports are demonstrated. In this preliminary step, a star shape is employed as complicated geometry of port. The slot number effect in star port is investigated. The regression rate decreases with increasing the slot number, except for the star port with many slots (8 slots) in the latter half of combustion. The oxidizer to fuel ratio increases with increasing the slot number.