• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.140-145
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• 2000

The spectral method which is composed of an eigenfunction expansion of free modes in the wave number domain is used to produce two dimensional unsteady inviscid wave simulation such as progressive waves in a numerical pneumatic wave tank. A spatial and time dependent free surface elevation and the potential are calculated by integrating ODE derived from fully nonlinear kinematic and dynamic free surface boundary condition at each time step. The nonlinear characteristics in the waves by this method were notable as increasing wave steepness. This method is very useful and powerful in terms of saving computational time caused by rapid convergence exponentially with increasing number of nodes, even preserving accurate numerical results. Moreover, it will given us many possibilities to apply to naval and ocean engineering fields.

• Journal of Ocean Engineering and Technology
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• v.21 no.6
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• pp.47-52
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• 2007

This paper presents the design of a submerged breakwater, which functions as an eco-structure in a marine environment. Newly patented blocks were used in the submerged breakwater to both make it stable and provide an inhabitable space for fish. To investigate the wave transmission of the proposed submerged breakwater, parametric studies were conducted through two-dimensional hydraulic tests, which were carried out at the National Fisheries Research and Development Institute (NFRDI) in South Korea. Those parameters are relative crest width (B/L), wave steepness (H/L), relative crest depth (hB/H), and submerged breakwater configuration. The hydraulic experimental results can be used to predict the performance of the proposed submerged breakwater covered with the multi-function blocks.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.143-144
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• 1996

Two-component models (normal star and degenerate star components) are the simplest realization of clusters with a mass spectrum because the high mass stars quickly evolve off leaving degenerate stars behind, while low mass stars survive for a long time as main-sequence stars. In the present study we examine the post-collapse evolution of globular clusters using two-component Fokker-Planck models that include three-body binary heating. We confirm that a simple parameter ${\epsilon}{\equiv} (E_{tot}/t_{rh})/(E_c/t_{rc})$ well describes the occurrence of gravothermal oscillations of two-component clusters. Also, we find that the degree of instability depends on the steepness of the mass function such that clusters with a steeper mass function are less exposed to instability.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.5
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• pp.457-462
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• 1987

Stochastic stability criterias for ocean wave analysis add simulation are studied using the data simulated by the linear superposition method. To clarify the criterias, the effects of the simulation parameters on the variance of stochastic properties of ocean waves are investigated, and the stable conditions of the parameters are estimated through the comparative study on the stochastic properties of simulated waves and well-known ocean waves. The simulation parameters considered are high frequency cut-off, data length, and number and phase angle of component waves. Statistical characteristics analysed are wave height, period and steepness, and the formation of groups of higher waves, resonance periods, steeper higher waves and extreme run-length of the run.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1982-1988
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• 1995

Methane/Air premixed flames are studied numerically, using a detailed chemical model, to investigate the flame strech effects on the extinction in a counterflow. The finite difference method, time integration and modified Newton iteration are used, and adaptive grid technique and grid smoothing have been employed to adjust the grid system according to the spatial steepness of the solution profiles. Results show that the flame stretch, or the conventional nondimensionalized stretch having the tangential flow characteristics of the stretched flame alone cannot adequately describes the extinction phenomena. On the other hand, the local flame stretch having both the normal and tangential flow characteristics of the stretched flame can give a proper explanation to the extinction of the symmetric planar premixed flames stabilized in a counter flow. The extinction condition were found to be a constant local stretch regardless of the equivalence ratio.

• Wind and Structures
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• v.19 no.1
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• pp.75-88
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• 2014

The computational fluid dynamic is used to explore new aspects of the hill flow. This analysis focuses on flow dependency and the comparison of results from measurements and simulations to show an optimization turbulent model and the possibility of replacing measurements with simulations. The first half of the paper investigates a suitable turbulence model for determining a suitable site for a wind turbine. Results of the standard k-${\varepsilon}$ model are compared precisely with the measurements taken in front of the hilltop, The Reynolds Stress Model showed exact results after 1.0 times of hill steepness but the standard k-${\varepsilon}$ model and standard k-${\omega}$ model showed greater underestimation. In addition, velocity flow over Pha Taem hill topography and the reference geometry shape were compared to find a suitable site for a turbine in case the actual hill structure was associated with the trapezoid geometric shape. Further study of geometry shaped hills and suitable sites for wind turbines will be reported elsewhere.

• Journal of Industrial Technology
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• v.8
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• pp.3-11
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• 1988

Shock pressure of wave breaking on vertical wall is studied experimentally with beaches, which have four different slopes (1/4.02, 1/7.05, 1/10, 1 /13.5). This results is summerized as follows: 1. Maximum impact presures are occured where the wave break directly on the wall rather than breaking in front of the wall. 2. Deep water steepness, and the beach slope are the two Quantities governing the magnitude and location of maximum dimensionless impact pressure from wave breaking directly on the wall, also, the greatest pressure is produced with a beach slope of 1/10. 3. This study is clearly shown that the location of maximum pressure can be presented above still water level under respectively experimental condition. The dimensionless elevation of maximum Pressure is greatest on a beach slope of 1/10.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.1
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• pp.71-78
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• 2008

In this paper, The voltage waveshapes and the lightning parameters such as peak voltage, rise time, decay time and steepness of the front wave were statistically anal zed from the lightning-induced voltages measured on subscriber telecommunication line by lightning. Induced voltage measurement system to measure and collect the lightning-induced voltages in several regions of Korea was developed and installed in several sites. The distributions of lightning-induced voltages for Tears, regions and seasons were analyzed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.8
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• pp.878-883
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• 2008

In this paper, we propose a double rings structure to improve the balanced-port characteristics of Balun-Bandpass Filter(Balun-BPF). The conventional Balun-BPF has limitations on output symmetry and skirt steepness. We introduce a double rings structure and the suitable coupling point between the two ring resonators to solve these problems. The fabricated double rings Balun-BPF shows excellent characteristics as a Balun-BPF without the conventional limitations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.04a
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• pp.48-51
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• 2009

Excessive wavy surfaces formed by a cold or hot-rolling process in a thin plate degrade the value of the plate significantly, which is called flatness problem in the industry. It is a result of post-buckling due to the residual stress caused by the rolling process. A unique difficulty of the problem as a buckling problem is that the buckling length is not given but has to be found. a new approach is developed to solve the flatness problem by extending a classic post-buckling analysis method based on the energy principle. The approach determines the buckling length and amplitude. The new solution approach can be used to determine the condition for the maximum rolling production that does not cause the flatness problem.