FLOW VELOCITY DISTRIBUTION AROUND SILT CURTAIN USED FOR DRILLING SEA FLOOR METHANE HYDRATES AT DEEP WATER

Abstract

 Standing silt curtains would be used to reduce the diffusion of turbidity generated during mining of methane hydrate on the deep sea floor. The purpose of this study is to simulate the flow field around these curtains in a slow and uniform flow in the deep sea by numerical calculation as a basic research for the development of these curtains that can be applied to the unique environmental conditions of the deep sea. Hydraulic experiments were carried out at a finite depth for the same slow steady-state flow as in the deep sea, and the boundary conditions between the bottom surface of the numerical calculation and the curtains surface were determined from the results. Numerical calculation shows that the drag coefficient of the curtain does not change with water depth when the depth-to-curtain height ratio is more than 20 times (preferably more than 30 times), resulting in an external flow where the drag coefficient of the curtain does not change with water depth. The external flow simulations confirm that the flow returns to the lower layer in front of the curtain.