연안역에서의 취송류의 3차원 확산특성

A Study on the 3-D Wind-Induecd Flow in Coastal Area

연안부근의 흐름을 지배하는 요인으로서는 조석에 의한 조류와 바람에 의한 취송류로 크게 분류할 수 있다. 조석 등과 같이 주기가 긴 장파에 의한 연안해역에서의 흐름은, 연안해역의 수평스케일이 연직스케일에 비해 상당히 크기 때문에 연직방향으로 수심 평균한 평면 2차원 흐름으로 평가한다. 그러나, 취송류의 경우, 수심방향의 유속분포는 수면에서 최대이며 수심이 깊어짐에 따라 대수적으로 감소(加藤始 等, 1976; Bains, etal., 1965)하며, 풍속, 풍향, 수심, 지형, 바람의 지속시간 둥 그 기구가 복잡하여 연안과 같이 수심과 지형이 크게 변하는 곳에서는 기존의 방법으로 오염물질 확산거리를 해석하면 현상을 과소평가할 가능성이 있으며, 확산방향도 연안해역의 지형적 복잡성 때문에 잘못 평가할 가능성이 있다. 특히 기름과 같은 부유성 오염물질의 이동을 해석하는 경우, 수심방향으로 평균한 평면 2차원흐름으로 해석하면 현상을 과소평가할 가능성이 있다. 이에 본 연구에서는 취송류를 지배하는 풍속, 풍향, 수심, 지형 등을 고려하여 연안해역에 적용할 수 있는 취송류의 3차원 모델을 제시하였다.

The analysis of the movement of tidal current has been carried out with an assumption that tidal current is to be a 2-D plane flow in the averaged depth. Insofar as wind-induced flows, however, 3-D analysis has to be applied since wind-induced flows shows the characteristics of logarithmic velocity profile from the water surface to the bottom. The Vertical distribution of wind-induced flows mostly depends upon the vertical eddy viscosity. For this reason, Ekman's calculation does not have inertia and horizontal viscosity terms. This method of calculation has formed a basis in the study of this field. Application of this model to a region where changes of water depth and geographical features are not prominent does not hinder a higher accuracy. However, a problem of a certain degree may arise if we apply this model to a region where the changes of water depth and geography are prominent such as nearshore zones, for the inertia and horizontal viscosity terms in equation of motion are not included in the Ekman's model. Therefore, this study has aimed at quantifying the equation of motion with particular attention to the inertia and horizontal viscosity terms in question and, further, proposing a 3-D model which is capable of being applied to nearshore zones. In order to verify the 3-D characteristics of wind-induced flows due to geographical changes, a model test was performed in the wind flume, as shown in Fig. 4. and Fig. 5. The applicability of the proposed model to the Port of Ulsan was confirmed with the following results: 1. The experiment gives good results in comparison with the numerical analysis, when a structure is placed. The surface flow over the boundary of the structure is found an inverse flow against the surface. Therefore, the proposed model can be used even in the region where a structure is placed or changes of geographical changes are prominent. 2. When the proposed model was applied to the Port of Ulsan where the gradient of water depth was relatively high, it was found that the Vertical distribution of the flow exhibits the characteristics of an inverse flow.