平面網地の流水抵抗に関する基礎的研究-4-有結節網地と無結節網地の流水抵抗特性について

概要

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The studies were carried out to measure the drag and lift components of hydrodynamical resistance of the trawl-knotted and knotless nettings, both of which were equally composed from the same size of nine meshes, made of the same polyethylene twine. The results obtained were as follows: 1. Hydro-dynamical resistance of the drag-coefficient (CD), the lift-coefficient (CL) and the frictional-drag-coefficient (CF) on both nettings were denoted by the following empirical equations. CD=CD90sin2/5θCL=CD90sin3/2θcosθ CF=CF0cosθ+Ksinθcosθ Where θ was the attack angle of the netting, CD90 was the value of drag-coefficient on 90° of θ, CF0 was the frictional-drag-coefficient on 0° of θ, and K was the constant depending on characteristic of netting. 2. The value of pressure-drag-coefficient (CD and CL) of the trawl-knotted netting was noted to be about 10% bigger than the knotless netting. The frictional-drag-coefficient (CF) of the trawl-knotted netting was equal or a little bigger than the knotless netting, and the hydro-dynamical resistance of the netting was proportional to the projective area of the netting twine.