• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.3 no.1
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• pp.57-73
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• 1999

Baroclinic hydraulic model experiments on the time-varying states of the flow pattern and water exchange in Sagami Bay were carried out based on quasi-steady state experiments on the flow pattern. For the model experiments, density changes as well as time changes in the volume transport of the upper layer were executed to investigate the flow response of the bay in the case of a sudden inflow of low density water and variable volume transport into the Sagami Bay. The results of the model experiments showed that when the volume transport was increased frontal eddies or frontal wave streamers from the Kuroshio Through Flow were transferred to the inner part of the bay along with cyclonic circulation in the bay. In addition, density boundary currents appeared and flowed along the eastern boundary of the bay. As the upper layer density decreased, frontal eddies, frontal streamers and coastal boundary density currents occurred and proceeded along the eastern boundary of the bay at a high speed.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.3 no.2
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• pp.91-103
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• 1999

According to numerical experiments, the Sokcho Eddy is produced at $37 5~39.0^{\circ}N$ by strong offshore winds, whereas the Ulleung Eddy is produced at $35~37^{\circ}N$ by an inflow variation of the Tsushima Current. These locations compare well with visual observations. The nonlinear 1$1/2$-layer model showed that most of the East Korea Warm Current (EKWC) driven by the Tsushima Current form the Ulleung Eddy that is larger and stronger than the Sokcho Eddy. In contrast, the nonlinear 2$1/2$-layer model showed that most of the EKWC travels further northward due to a strong subsurface current, thereby enhancing the Sokcho Eddy making it larger and stronger than the Ulleung Eddy. The Sokcho Eddy is also produced relatively offshore due to an eastward subsurface current in the frontal region. Using the 1$1/2$-layer model, when the mass of the Tsushima Current decreases, the two eddies are weakened and produce a circular shape. In the 2$1/2$-layer model the EKWC pushes the Ulleung Eddy northward after 330 days, next the Sokcho and Ulleung eddies begin to interact with each other, and then after 360 days the Ulleung Eddy finally disappears absorbed by the relatively stronger Sokcho Eddy. This behavior compares favorably with other visual observations.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.30-35
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• 2016

In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.

• Proceedings of the KSRS Conference
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• v.2
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• pp.926-929
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• 2006

Some features of vertical structure of the frontal interaction zone of the warm Kuroshio Current and cold Oyashio Current are known from 1930 from analysis of ship data. Ship data however do not allow carrying out the area detailed survey opposite to satellite infrared (IR) observations which possess by high spatial and temporal resolution. Analysis of NOAA AVHRR IR images demonstrated that process of formation and development of the Kuroshio warm core rings is highly complex. They are formed as a result of development of anticyclonic meanders of the warm Kuroshio waters and spin off them from the current. Joint analysis of thermal infrared images and altimetry data has also indicated that interaction of eddies to the frontal zone plays a crucial role in formation of large eddies moving to the Southern Kuril region.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.6
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• pp.1044-1055
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• 1997

To find out generating mechanism of eddies in the polar frontal zone of the East Sea, we carried out a series of numerical experiments using the nonlinear $1^{1/2}-layer$ model allowing the effect of the polar front. We assumed the polar front at about $39^{\circ}N$ in zonal direction with the cold water region in the northern part and the warm water region in the southern part of the model ocean. To examine the effect of the frontal motion without the influence of the Tsushima Current from the beginning of the geostrophic adjustment, the initial state of the model ocean was assumed motionless. Eastward current was caused by the geostrophic adjustment process in the polar frontal zone that induced a steady northward coastal current along the Korean coast to satisfy the mass continuity. The overshooting of this coastal current acted as an initial disturbance of the zonal flow field which caused meanders and eddies. The spatial scales of eddies were in good agreement with the baroclinic instability theory.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.2
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• pp.267-281
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• 2019

Energetic mesoscale eddies in the East Sea (ES) associated with strong mesoscale variability impacting circulation and environments were statistically characterized by analyzing satellite altimeter data collected during 1993-2017 and in-situ data obtained from four cruises conducted between 2015 and 2017. A total of 1,008 mesoscale eddies were detected, tracked, and identified and then classified into 27 groups characterized by mean lifetime (L, day), amplitude (H, m), radius (R, km), intensity per unit area (EI, $cm^2/s^2/km^2$), ellipticity (e), eddy kinetic energy (EKE, TJ), available potential energy (APE, TJ), and direction of movement. The center, boundary, and amplitude of mesoscale eddies identified from satellite altimeter data were compared to those from the in-situ observational data for the four cases, yielding uncertainties in the center position of 2-10 km, boundary position of 10-20 km, and amplitude of 0.6-5.9 cm. The mean L, H, R, EI, e, EKE, and APE of the ES mesoscale eddies during the total period are $95{\pm}104$ days, $3.5{\pm}1.5cm$, $39{\pm}6km$, $0.023{\pm}0.017cm^2/s^2/km^2$, $0.72{\pm}0.07$, $23{\pm}21TJ$, and $588{\pm}250TJ$, respectively. The ES mesoscale eddies tend to move following the mean surface current rather than propagating westward. The southern groups (south of the subpolar front) have a longer L, larger H, R, and higher EKE, APE; and stronger EI than those of the northern groups and tend to move a longer distance following surface currents. There are exceptions to the average characteristics, such as the quasi-stationary groups (the Wonsan Warm, Wonsan Cold, Western Japan Basin Warm, and Northern Subpolar Frontal Cold Eddy groups) and short-lived groups with a relatively larger H, higher EKE, and APE and stronger EI (the Yamato Coastal Warm, Central Yamato Warm, and Eastern Japan Basin Coastal Warm eddy groups). Small eddies in the northern ES hardly resolved using the satellite altimetry data only, were not identified here and discussed with potential over-estimations of the mean L, H, R, EI, EKE, and APE. This study suggests that the ES mesoscale eddies 1) include newly identified groups such as the Hokkaido and the Yamato Rise Warm Eddies in addition to relatively well-known groups (e.g., the Ulleung Warm and the Dok Cold Eddies); 2) have a shorter L; smaller H, R, and lower EKE; and stronger EI and higher APE than those of the global ocean, and move following surface currents rather than propagating westward; and 3) show large spatial inhomogeneity among groups.

• Journal of the korean society of oceanography
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• v.31 no.2
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• pp.64-74
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• 1996

Numerical experiments of OAT (Ocean Acoustic Tomography) are carried out in the East Sea of Korea where the canonical ocean has been perturbed by a mesoscale warm eddy and a thermal front. In order to estimate the horizontal and vertical structure of water temperature of the perturbed ocean, the experimental area is divided into 16 cells with 8 pairs of sources and receivers for a horizontal slice and the water column is divided into 8 layers for a vertical slice. The inversely estimated temperature field by using SVD (Singular Value Decomposition) method reveals the eddy and frontal structure clearly. The rms errors of the two horizontal slices are less than $0.4^{\circ}C$ and $1.7^{\circ}C$ at 400 m and 200 m depths, respectively, while the error in the vertical slice is less than $1.0^{\circ}C.$ For better estimation of temperature by OAT method, particularly for the East Sea, a range-dependent ray model should be used to solve the forward problem. At the same time, improvement in computing the refracted ray path between vertical layers is required to obtain more accurate travel time information. The results of the present experiment give rise to a possibility of application of OAT in remote sensing of the ocean thermal structure.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.313-313
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• 2023

이 연구에서는 침수식생 조건에서 식생 형태 별 frontal area, solid volume fraction이 유속 분포에 미치는 영향을 분석하고, 흐름측정결과로부터 식생 형태에 따른 난류흐름특성을 분석하기 위하여 수행 되었다. 식생흐름 구현을 위하여 5 cm의 간격으로 총 257개의 모형식생을 전체 영역에 배치했다. 유속측정위치는 수위측정결과에 따라 흐름이 안정화되는 구간에서 연직방향으로 17개 지점에서 측정한 후 앙상블 평균하여 분석했다. Branch의 유무에 따라 Type I과 II로 구분하여 각 식생에 대해 유속의 연직분포를 측정한 결과, Branch가 없는 Type I에서는 유속이 지속적으로 감소하는 반면, Type 2에서는 Frontal area가 급격히 증가하는 Branch 구간에서 유속이 급격히 감소한 후 Trunk 구간에서 유속이 다시 증가하는 변화를 보였다. Velocity Spectrum 분석 결과, 모든 지점에 대해 평균한 결과 고주파수 영역에서 -5/3 law를 따르는 것으로 나타나 전체 영역에서 isotropic & homogeneous 난류흐름이 발생함을 확인했다. 난류흐름특성 계산결과, Turbulent kinetic energy(k)를 mean kinetic energy(K)로 무차원화하여 연직분포를 비교했을 때 -k/K는 모두 식생에 근접하며 증가했다. Shear production(P_s)의 계산결과로부터 전단흐름에 의한 난류운동에너지 생성영향분석결과, Type I과 II가 식생경계의 mixing interface 부근에서 급격히 증가하는 분포를 보였으며, 이는 시간평균유속분포에서 분석한 결과와 일치한다. Wake production(P_w)의 연직분포계산결과, P_s와 유사하게 식생경계 부근에서 상승하는 결과가 나타났으며, 이는 식생경계에서 발생하는 Large scale eddy로 인해 발생함을 알 수 있다. 마지막으로 x-방향 난류확산계수로부터 scale factor(α_x)의 연직분포를 계산한 결과, 식생경계부근의 mixing interface에서 증가한 후 식생영역 내에서 감소하는 분포를 나타냈다. z-방향 난류확산 계수의 scale factor(α_z)는 α_x에 비해 작게 계산되었다. 이러한 결과는 오염물질의 연직확산이 식생경계에서 증가한 후 식생 내부에서 감소하여 오염물질, 부유사 등의 축적이 이뤄질 것으로 예상된다. 이는 가지로 인해 식생저항이 증가할 경우 용존성 물질의 혼합이 감소하여 식생의 저장대 효과가 증가함을 의미한다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.2
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• pp.226-244
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• 1998

The relationship between the transport of eggs and larvae of Anchovy (Engraulis japonica) and the oceanic condition in the southern sea of Korea was examined on August and November 1996. In summer (August), when the Tsushima Warm Current is strong near to the coast, the warm waters such as warm streamers from the Tsushima Warm Current intrude into the coastal area, and cyclonic circulations are formed. The warm water intrusions also generate wakes around Komun Island, Sori Island and Koje Island. In the coastal area where the warm water intrusions occur, the nutrients, dissolved oxygen, suspended solid and chlorophyll are concentrated in probably relation to the upwelling concerned with this warm streamer and/or the wakes. Anchovy eggs and larvae are transported to the coastal area by the cyclonic circulations. The hatching and growth of anchovy larvae are increased because of high primary production in the cyclonic circulations. However, as the amount of Copepods which are a main food for anchovy larvae decrease in the coastal area, anchovy larvae seem to move to the Isushima Warm Water area for seeking a prey. In autumn (November), the Tsushima Warm Current is far away from the coast. In this season the warm water intrusions almost disappear, and the small scaled frontal eddies are formed between the coastal water and the Tsushima Warm Water. As the surface water moves towards offshore, few anchovy eggs and larvae were sampled in the survey area. Chemical and biological substances are concentrated in the leftdown sides of the small scaled frontal eddies because of eddy formation.

• Wind and Structures
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• v.11 no.4
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• pp.275-289
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• 2008

Large eddy simulations have been performed within and over different types of urban building arrays. This paper adopted three dimensionless parameters, building frontal area density (${\lambda}_f$) the variation degree of building height (${\sigma}_h$), and the staggered degree of building range ($r_s$), to study the systematic influence of building spacing, height and layout on wind and turbulent characteristics. The following results have been achieved: (1) As ${\lambda}_f$ decrease from 0.25 to 0.18, the mean flow patterns transfer from "skimming" flow to "wake interference" flow, and as ${\lambda}_f$ decrease from 0.06 to 0.04, the mean flow patterns transfer from "wake interference" flow to "isolated roughness" flow. With increasing ${\lambda}_f$, wind velocity within arrays increases, and the vortexes in front of low buildings would break, even disappear, whereas the vortexes in front of tall buildings would strengthen and expand. Tall buildings have greater disturbance on wind than low buildings do. (2) All the wind velocity profiles and the upstream profile converge at the height of 2.5H approximately. The decay of wind velocity within the building canopy was in positive correlation with ${\lambda}_f$ and $r_s$. If the height of building arrays is variable, Macdonald's wind velocity model should be modified through introducing ${\sigma}_h$, because wind velocity decreases at the upper layers of the canopy and increases at the lower layers of the canopy. (3) The maximum of turbulence kinetic energy (TKE) always locates at 1.2 times as high as the buildings. TKE within the canopy decreases with increasing ${\lambda}_f$ and $r_s$ but the maximum of TKE are very close though ${\sigma}_h$ varies. (4) Wind velocity profile follows the logarithmic law approximately above the building canopy. The Zero-plane displacement $z_d$ heighten with increasing ${\lambda}_f$, whereas the maximum of and Roughness length $z_0$ occurs when ${\lambda}_f$ is about 0.14. $z_d$ and $z_0$ heighten linearly with ${\sigma}_h$ and $r_s$, If ${\sigma}_h$ is large enough, $z_d$ may become higher than the average height of buildings.