• Journal of Advanced Marine Engineering and Technology
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• v.27 no.7
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• pp.862-871
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• 2003

In this paper, we addressed a modeling for the magnetic levitation stage. This planar magnetic levitator employs four permanent magnet liner motors. Each motor generates vertical force for suspension against gravity, as well as horizontal force for propulsion. Therefore. this stage can generate six degrees of freedom motion by the combination of forces. We derived a mechanical dynamics equation using Lagrangian method and electromechanical dynamics equation by using Co-energy method. Based on the derived dynamics, we can analyze the stage motion that is subject to the input currents and forces.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.351-366
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• 2014

We assumed the situation where an eruption column had been formed by the explosive Plinian eruption from Mt. Baekdu and that the collapse of eruption column had caused pyroclastic density currents to occur. Based on this assumption, we simulated by using a Titan2D model. To find out about the range of the impacts of pyroclastic density currents by volcanic eruption scenarios, we studied the distance for the range of the impacts by VEIs. To compare the results by each volcanic eruption scenario, we set the location of the vent on the 8-direction flank of the outer rim and on the center of the caldera, the internal friction angle of the pyroclastic density currents as $35^{\circ}$, the bed friction angle as $16^{\circ}$. We set the pile height of column collapse and the vent diameter with various VEIs. We properly assumed the height of the column collapse, the diameter of the vent, the initial rates of the column collapse and the simulation period, based on the VEIs, gravity and the volume of the collapsed volcanic ash. According to the comparative analysis of the simulation results based on the increase of the eruption, the higher VEI by the increase of eruption products, the farther the pyroclastic density currents disperse. To the northwest from the vent on the northeast slope of the outer rim of the caldera, the impact range was 3.3 km, 4.6 km, 13.2 km, 24.0 km, 50.2 km, 83.4 km or more from VEI=2 to VEI=7, respectively. Once the database has been fully constructed, it can be used as a very important material in terms of disaster prevention and emergency management, which aim to minimize human and material damages in the vicinity of Mt. Baekdu when its eruption causes the pyroclastic density currents to occur.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.570-574
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• 2009

벽 근처에서의 흐름(near wall flow)을 해석하기 위한 낮은 레이놀즈수 수정(low-Reynolds number modification)을 포함하는 통계학적 난류모형을 이용한 3차원 비정상 레이놀즈-평균 나비어-스톡스 (URANS) 계산을 실시하여 사각형 수로에서의 중력류를 모의하였다. 3차원 계산 결과를 2차원 URANS 모의에 의한 계산 결과 그리고 실험결과와 비교하였다. 이 연구 결과는 적정 시 공간적 수치해상도를 가지고 벽 근처에서의 흐름을 주의 깊게 직접 해석하는 3차원 URANS 수치모의는 2차원 계산으로는 해석할 수 없는 대규모 Kelvin-Helmholtz 와구조 (vortical structure)의 붕괴(breakdown) 그리고 중력류 선단부에서 발달하는 Lobe-and-Cleft 흐름 불안정 등을 포함하는 중력류의 동적 특성을 높은 정확도로 재현할 수 있음을 보여준다.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.689-692
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• 2004

Hydrographic data obtained from several ship experiments have shown that internal waves are frequently observed in the East (Japan) Sea, mostly in the continental slopes located along the western side of the East Sea. It is well known that oceanic internal waves can be detected well in synthetic aperture radar (SAR) images. Interactions between surface capillary-gravity waves and horizontally varying surface currents induced by internal waves produce variations in sea surface roughness which can be detected by SAR. C-band SAR images from ERS, ENVISAT ASAR and RADARSAT have been used to study the characteristics of internal waves in the East Sea. The observed properties of internal waves from many SAR images were compared and verified from in-situ measurements and theories.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.4
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• pp.481-496
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• 1996

The last Sea is a typical bark-arc basin consisting of basins, plateaus, ridges, and seamounts. The Ulleng Basin, located in the southwestern corner of the last Sea, contains thick Neogene sedimentary sequence. Analysis of over 2,500 km of single-channel seismic reflection data suggests that hemipelagic sedimentation prevailed over much of the basin during the late Miocene and pelagic sedimentation became more dominant during the Pliocene. During the Pleistocene terrigeneous sediments transported by turbidity currents and other gravity flows, together with continuous hemipelagic settling, resulted in well-stratified sedimentary layers. Influx of terrigenous sediments during the Pleistocene formed depocenters in the western and southern parts of the basins. In the Ulleung Interplain Gap, where the Ulleung Basin joins the deeper Japan Basin, sediment waves suggesting bottom current activities are seen.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1145-1158
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• 1994

A three-dimensional, finite difference, numerical model with free surface was developed on ${\sigma}$-coordinate. A semi-implicit numerical scheme in time has been adopted for computational efficiency. The scheme is essentially independent of the stringent stability criteria (CFL condition) for explicit schemes of external surface gravity wave. Implicit algorithm was applied for vertical shear stress, Coriolis force and pressure gradient terms. The reliability of the model with vertically variable grid system was checked by the comparison of simulation results with analytic solution of wind-driven currents in a one-dimensional channel. Sensitivity analysis of differencing parameters was carried out by applying the model to the calculation of wind-driven currents in a square lake.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.9 no.1
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• pp.1-12
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• 2004

Sedimentary facies and high-resolution echo facies were analyzed to elucidate sedimentation pattern of the late Quaternary glacial-marine deposits in the northern continental margin of the South Shetland Islands. Six sedimentary facies are classified, based on grain texture and sedimentary structures in gravity cores. The high-resolution (3.5 ㎑) echo characters are classified into 6 echo facies on the basis of clarity, continuity, and shape of bottom and subbottom echoes together with seafloor topography. Distribution of the echo and sedimentary facies suggest that there was a significant change in sedimentation pattern between the Last Glacial Maximum (LGM) and subsequent glacier-retreating period. When the grounded glaciers extended to the present shelfbreak during LGM, coarse-grained subglacial tills were widespread in the shelf area, and deep troughs in the shelf were carved beneath the fast-flowing ice steam. As the glacial margin retreated landward after LGM, dense meltwater plumes released from the retreating ice-front were funneled along the glacier-carved troughs, and accumulated channel- or cannyon-fill deposits in the shelf and the upper to mid slope. At that time, slope sediments seem to have been reworked by slope failures and unsteady contour currents, and further transported by fine-grained turbidity currents along the South Shetland Trench. After the glacial retreat, sediments in the shelf and slope areas have been mainly introduced by persistent (hemi) pelagic settling, and fine-grained turbidity currents frequently occur along the axis of the South Shetland Trench.

• Journal of Korea Water Resources Association
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• v.32 no.1
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• pp.83-94
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• 1999

In continental margins, turbid underflows which are not confined to a given channel, are free to spread laterally as well as longitudinally. Lateral spreading can reduce substantially the run out distance of flows along continental shelves and slopes. Laboratory experiments with a large tank, employing saline density currents as surrogates for fine-grained turbidity flow, coupled with dimensional analysis, have been used to develop a simple expression for lateral spreading rates of two-dimensional flows on sloping beds. characteristic length and time are determined by the flow discharge and buoyancy flux at the inlet. By knowing the initial width of the flow, the spreading law can be used to estimate the maximum width of the current at different times as well as the longitudinal spreading rate. Predictions for flows compare favorably against observations.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.98-98
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• 2019

중력류 또는 밀도류는 주변 유체에 비해 상대적으로 밀도가 큰 유체가 밀도차에 의한 추진력으로 흐르는 것이다. 중력류의 수치모델링에는 두 가지 어려움이 있다. 즉, 적합한 지배방정식을 구성하여 적용하는 것 그리고 난류의 영향을 합리적으로 반영하는 것이다. 기존 중력류 해석을 위한 지배방정식들은 유체의 연속방정식과 운동량 방정식 그리고 밀도 또는 농도의 이송방정식을 조합하여 구성된다. 이들 지배방정식을 이용한 연구들은 대부분 두 유체 사이의 밀도차가 충분히 작아서 밀도 변동(variations)의 영향은 오로지 부력항에서만 유지된다는 Boussinesq 근사에 근거를 둔다. 그리고 이송방정식에서 밀도 또는 농도의 확산계수을 점성계수의 함수로 표현하기 위해서 Schmidt 수를 이용한다. 수치모델링에서 Schimdt 수는 상수값을 적용하지만, 이 값은 밀도의 연직방향 경사에 근거한 부력빈도(buoyancy frequency)와 난류량의 따라 큰 차이를 보이는 것으로 알려져있다. 한편, 표준 통계학적 난류모델과 벽함수를 적용한 수치모델링은 초기 중력에 의해서 무너지는(slumping) 단계를 넘어 관성력으로 추진되는 단계와 점성 효과가 지배적인 단계에서는 정확도에 현저히 낮아지기 때문에 대부분 큰와모의(large-eddy simulation, LES) 또는 DNS(direct numerical simulation)수준의 고해상도(high-resolution) 해석기법을 적용하여 공학적인 문제에 적용하는 데는 한계가 있다. 이 연구에서는 Boussinesq 근사와 Schmidt 수를 사용하지 않으며, LES 보다 적용이 용이한 DES (detached-eddy simulation)기법을 조합한 다상흐름 수치모델을 적용하여 중력류를 해석을 시도하였다. 수치해석결과를 실험값과 함께 기존 수치모델링 기법으로 구한 수치해와 비교분석하여 이 연구에서 개발 및 적용된 수치모델링 기법의 적용성을 평가한다.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.177-184
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• 2003

Numerical simulation on marine wind and sea surface elevation was carried out using both three-dimensional hydrostatic and non-hydrostatic models and a simple oceanic model from 0900 LST, August 13 to 0900 LST, August 15, 1995. As daytime easterly meso-scale sea-breeze from the eastern sea penetrates Kangnung city in the center part as basin and goes up along the slope of Mt. Taegullyang in the west, it confronts synoptic-scale westerly wind blowing over the top of the mountain at the mid of the eastern slope and then the resultant wind produces an upper level westerly return flow toward the East Sea. In a narrow band of weak surface wind within 10km of the coastal sea, wind stress is generally small, less than l${\times}$10E-2 Pa and it reaches 2 ${\times}$ 10E-2 Pa to the 35 km. Positive wind stress curl of 15 $\times$ 10E-5Pa $m^{-1}$ still exists in the same band and corresponds to the ascent of 70 em from the sea level. This is due to the generation of northerly wind driven current with a speed of 11 m $S^{-1}$ along the coast under the influence of south-easterly wind and makes an intrusion of warm waters from the southern sea into the northern coast, such as the East Korea Warm Current. On the other hand, even if nighttime downslope windstorm of 14m/s associated with both mountain wind and land-breeze produces the development of internal gravity waves with a hydraulic jump motion of air near the coastal inland surface, the surface wind in the coastal sea is relatively moderate south-westerly wind, resulting in moderate wind stress. Negative wind stress curl in the coast causes the subsidence of the sea surface of 15 em along the coast and south-westerly coastal surface wind drives alongshore south-easterly wind driven current, opposite to the daytime one. Then, it causes the intrusion of cold waters like the North Korea Cold Current in the northern coastal sea into the narrow band of the southern coastal sea. However, the band of positive wind stress curl at the distance of 30km away from the coast toward further offshore area can also cause the uprising of sea waters and the intrusion of warm waters from the southern sea toward the northern sea (northerly wind driven current), resulting in a counter-clockwise wind driven current. These clockwise and counter-clockwise currents much induce the formation of low clouds containing fog and drizzle in the coastal region.