11:00 AM - 1:00 PM
[AOS19-P02] Evaluation of mixing effects due to coastal marine structures
Keywords:Eddy, Mixing, Marine structure
Eddies and associated mixing phenomena have been observed around coastal marine structures. Eddies due to island mass effects are known to affect oceanic ecosystems through enhanced mixing. In this study, numerical experiments were conducted by using a high-resolution numerical simulator, SUNTANS, to evaluate physical structures associated with eddies and vertical mixing around cylinder type offshore structures with a diameter of 500m. Three types of cylinder layouts were considered: (1) single cylinder, (2) two cylinders parallel to the flow direction and (3) two cylinders perpendicular to the flow direction. Two types of flow were considered: (1) unidirectional steady state flows and (2) oscillating flows with a tidal frequency (M2). The Reynolds number were set between 100 and 5000 for the numerical studies.
Vortex motions were enhanced when the number of cylinders increased under the steady flow condition. The eddy kinetic energy for the two cylinders cases was 1.4 time higher than that for the single cylinder case when Re = 5,000. Vertical mixing was enhanced when cylinders were placed perpendicular to the flow direction. The averaged vertical eddy diffusivity around the two-cylinders case was approximately 6.6 × 10-5 m2/s when Re = 5,000, which was approximately three times larger than the other cases. In the all model cases, vortex motions and vertical mixing were enhanced on the lee and flank sides of the cylinders, respectively. When the model was forced by oscillatory flows (M2 tides), vortex motions were higher for the two-cylinders cases than those for the single-cylinder cases. The eddy kinetic energy remarkably increased when the cylinders were placed parallel to the flow directions when the model was forced by tidal flows. On the other hand, vertical mixing was enhanced when cylinders were placed perpendicular to the flow direction. The averaged vertical eddy diffusivity for the two cylinders placed perpendicular to the flow direction was approximately three times as large as when the cylinders were placed parallel. This study suggests that the number and the type of layout for marine structures largely influence on the formation of eddies and mixing conditions.
Vortex motions were enhanced when the number of cylinders increased under the steady flow condition. The eddy kinetic energy for the two cylinders cases was 1.4 time higher than that for the single cylinder case when Re = 5,000. Vertical mixing was enhanced when cylinders were placed perpendicular to the flow direction. The averaged vertical eddy diffusivity around the two-cylinders case was approximately 6.6 × 10-5 m2/s when Re = 5,000, which was approximately three times larger than the other cases. In the all model cases, vortex motions and vertical mixing were enhanced on the lee and flank sides of the cylinders, respectively. When the model was forced by oscillatory flows (M2 tides), vortex motions were higher for the two-cylinders cases than those for the single-cylinder cases. The eddy kinetic energy remarkably increased when the cylinders were placed parallel to the flow directions when the model was forced by tidal flows. On the other hand, vertical mixing was enhanced when cylinders were placed perpendicular to the flow direction. The averaged vertical eddy diffusivity for the two cylinders placed perpendicular to the flow direction was approximately three times as large as when the cylinders were placed parallel. This study suggests that the number and the type of layout for marine structures largely influence on the formation of eddies and mixing conditions.