• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.649-653
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• 2005

유역형상의 변화에 따라서 이동강우가 유출에 미치는 영향을 운동파이론을 적용하여 분석하였으며, 유역형상은 신장형유역과 정4각형유역 및 장방형유역에 대하여 분석하였고, 이동강우 분포형은 균등분포형, 전진형, 지연형, 중앙집중형을 사용하였다. 이와 같은 형상의 유역에 대하여 다양한 이동속도를 가진 강우가 유역내 하천의 상류방향, 하류방향, 횡방향으로 이동할 때 강우분포형에 따르는 유출수문곡선을 모의하여 그 특성을 비교분석하였다. 유출수문곡선의 모양과 첨두시간, 첨두유량은 시간적, 공간적으로 변화하는 강우와 유역형상에 의하여 크게 영향을 받는다. 횡방향의 이동강우에서는 상류방향과 하류방향의 경우보다 더 큰 첨두유량이 발생하며, 하류방향 이동강우의 첨두유량은 상류방향의 첨두유량보다 더 크게 나타났다. 신장형유역의 경우 하류방향 이동강우의 첨두시간은 상류방향과 횡방향의 경우보다 더 지체되며, 수문곡선의 총유출량과 기저시간은 강우속도가 증가함에 따라 감소하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.6
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• pp.371-378
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• 1986

In the reflection and transmission of a transverse magnetic wave(TM wave) from a dielectric plane osillating sinusoidally perpendicular to ist surface, one could assume that the boundary moves with a uniform nelocity equal to the instantaneous socillating velodity. According to the extended Lorentz transform, the reflected and the transmitted field are obatained as the function of the dielectric permittivity, the oscillating velocities, and the incident angles. The above results are analyzed graphically.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.10 no.4
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• pp.193-200
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• 1985

In the reflection and transmission of a plane wave(TE) from a dielectric plane surface oscillating sinusoidally perpendicular to its surface, one could assume that the boundary moves with a uniform velocity equal to the instantaneous oscillating velocity. The reflected and the transmitted fields are obtained as the function of the incident angles, the dielecri'c permittivity, and the oscillating velocities according to the extended Lorentz transform.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.949-949
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• 2012

유출수문곡선은 강우량, 강우강도, 강우지속시간, 강우이동방향 및 이동속도와 같은 강우발생특성과 강수대의 공간적 이류방향과 유역형상과의 상호작용에 의하여 영향을 받으며, 특히 강우의 이류과정에서 나타나는 시간적, 공간적인 분포는 유출에 영향을 미치는 중요한 인자이다. 일반적으로 유출해석 기본이론은 연속방정식과 운동방정식으로서 운동파가정(kinematic wave analogy)을 기반으로 한 집중수문모형(lumped hydrologic model)에 의하여 수행되고 있지만 집중형 모형은 한 매개변수에 여러 가지의 물리적 과정을 개념화하여 담고 있기 때문에 유출과정에 대한 섬세한 모형화의 제약으로 인하여 강우의 이류과정에 따른 유출변화특성을 모의하기가 어렵다. 본 연구에서는 완전 분포형 수문동력학적 강우-유출 모형을 사용하여 강우의 이류특성을 반영할 수 있는 유출 모델을 구성하고, 강우의 이류특성에 따른 유역 출구에서의 유출수문곡선의 변화과정을 살펴보고 상관관계를 분석하였다.

• Journal of Biomedical Engineering Research
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• v.21 no.3 s.61
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• pp.261-271
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• 2000

The present study investigated flow dynamics of a two-dimensional abdominal aortic bifurcation model under sinusoidal flow conditions considering wall motion. impedance phase angle(time delay between pressure and flow waveforms), and non-Newtonian fluid using computational fluid dynamics. The wall shear stress showed large variations in the bifurcated region and the wall motion reduced amplitude of wall shear stress significantly. As the impedance phase angle was changed to more negative values, the mean wall shear stress (time-averaged) decreased while the amplitude (oscillatory) of wall shear stress increased. At the curvature site on the outer wall where the mean wall shear stress approached zero. influence of the phase angle was relatively large. The mean wall shear stress decreased by $50\%$ in the $-90^{\circ}$ phase angle (flow wave advanced pressure wave by a quarter period) compared to the $0^{\circ}$ phase angle while the amplitude of wall shear stress increased by $15\%$. Therefore, hypertensive patients who tend to have large negative phase angles become more vulnerable to atherosclerosis according to the low and oscillatory shear stress theory because of the reduced mean and the increased oscillatory wall shear stresses. Non-Newtonian characteristics of fluid substantially increased the mean wall shear stress resulting in a less vulnerable state to atherosclerosis.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.226-233
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• 2002

In the field of research of sea keeping quality, much development has been made in recent years using the method of calculation based on the strip theory. It is very important to investigate the hull response of a fishing vessel in waves to ensure the safe navigation and fishing operation in rough seas by preserving excellent sea keeping qualities. For this purpose, the author measured various responses of three fishing vessels in waves using real sea experimental measuring system and analyzed the experimental data The results obtained can be summarized as follow. 1. The amplitudes of pitching motion in the experiments appeared low values with more than one peak occasionally in following sea and quartering sea, and the band width of those was found to be wide relatively. 2. The amplitudes of rolling motion in the experiments appeared high values with only one peak in following sea and quartering sea regardless of ship's tonnage, and the band width of those was found to be narrow relatively. 3. The comparisions of theoretical results with those of experiments for the pitching motions and rolling motion in following sea and quartering sea show that the theoretical values are higher slightly than those of experiments in both directions and the period at which the peak appears in the calculations and the experiments has good agreement approximately 4. The calculated responses of two vessels under a assumed wave of 2.2m height and 5.0sec period showed that the response of pitching motion of ship-A are 2.2 times bigger than those of ship-C in following sea and quartering sea, and the response of rolling motion of ship-A is 4.2 times bigger than that of ship-C in quartering sea.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.27-37
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• 1991

In this paper the nonlinear free surface flows for an axisymmetric submerged body oscillating beneath the free surface are solved and the forces acting on the body are calculated. A boundary integral method is applied to solve the axisymmetric boundary value problem and the Runge-Kutta 4-th order method is used for the time stepping of the free surface location. The nonlinear forces acting on the axisymmetric body are computed and compared with published results.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.2
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• pp.90-103
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• 1997

A numerical procedure is described for predicting the motion and structural responses of the very large floating offshore structures supported by multiple 3-D floating bodies of arbitrary shape in multi-directional irregular waves. The developed numerical approach taking into account of the hydrodynamic interactions among the multiple floating bodies is based on a combination of the 3-D source distribution method, the wave interaction theory, the finite element method and the spectral analysis method to get the significant values of the dynamic responses in the multi-directional irregular waves. The effects of wave interactions and directionality on the dynamic responses of a very large offshore structure, which is semisubmersible ring type, are numerically examined.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.256-256
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• 2021

Saint-Venant 방정식은 수평규모가 수심규모보다 큰 천수흐름을 기술하는 수리동역학 모형으로 지난 수십년간 공학적 분야에서 널리 이용되어 왔다. 최근에도 기후변화에 따른 도시 홍수의 위기 증대로 홍수위기관리의 관심이 높아짐에 따라 홍수파(flood wave), 도시침수(urban inundation), 돌발홍수(flash flood) 등의 신속한 예측을 위한 Saint-Venant 방정식의 연구가 활발히 진행되고 있다. 그러나 도시와 같은 인공구조물이 즐비한 상황에서 천수흐름을 해석하는 고전적인 수치해법들은 다양한 불연속 지형들의 존재로 인하여 불안정하며 지배방정식의 정해로 수치해가 잘 수렴하지 않는 문제가 있다. 지난 수년간 이를 해결하기 위해 불연속한 지형을 안정적으로 해결할 수 있는 수치기법의 연구가 진행되어 왔으나, 정해로의 수렴성, 정확성에 관하여 연구가 부족한 실정이다. 본 연구는 수치해법의 주요 구조를 구성하는 Saint-Venant 방정식의 불연속한 지형조건에 대한 리만 문제의 정해를 연구하였다. 쌍곡선형 시스템의 특징을 고려하여 요소파들(elementary waves)의 공식을 유도하였는데, 질량과 에너지의 보존법칙에 위배되지 않으며 운동량이송부의 비선형성과 지형의 불연속에 의한 비엄격성을 고려할 수 있는 조건을 제시하였다. 또한, 유도된 요소파들을 바탕으로 L-M & R-M 커브이론(Han et al. 2014)을 사용할 수 있는 조건과 당위성을 증명하였고, 이를 바탕으로 Saint-Venant 방정식의 정해법을 구성하였다. 리만문제의 다양한 초기조건들을 바탕으로 모든 경우의 정해 구조를 조사하였고, 이를 통해 불연속 지형에 대한 Saint-Venant 지배방정식의 정해가 다수해를 갖을 수 있음을 보였으며, 이를 근사할 수 있는 수치기법의 전략을 소개하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.3
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• pp.161-167
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• 1992

We consider the preparation of long finite amplitude nondispersive waves over a step bottom between two regions of finite different depths. Two dimensional motion is assumed. with the wave crests parallel to the step, and irrotational flow in the inviscid fluid is considered. To describe the transformation of finite amplitude waves we use the finite-amplitude shallow-water equations, the conditions of mass flow conservation and pressure continuity at the cut above the step in Riemann's variables. The equations define four families of curves-characteristics on which the values of the Riemann's invariants remain constant and a system of two nonlinear equations that relates the amplitudes of incident reflected and transmitted waves. The system obtained is difficult to analyze in common form. Thus we consider some special cases having practical usage for tsunami waves. The results obtained are compared with the long wave theory and significant nonlinear effects are found even for quite small amplitude waves.