重みづけの異なる網地の沈降特性の解析

抄録

This study deals with the sinking characteristics of weighted netting, a basic study in purse seine. The experiment was carried out using five simplified model nets in a flume tank under still water condition. The mean densities (ρ) of netting materials were 0.91g/cm³ for A net, 1.14 g/cm³ for B net, 1.38g/cm³ for C net, 1.70g/cm³ for D net, and 2.10g/cm³ for E net. A number of spherical tiny leads were attached separately on the net surface so that each of the models will have the same weight in water. The Reynolds number of nettings used ranged from 7 to 170.
Differential equations were derived from the conservation of momenta of the model nets and used to determine the sinking speeds of the depths of leadline and the other portions of nets.
The results were as follows:
1) Sinking speed was fastest for A net, followed by B, C, D, and E nets.
2) The drag coefficient of netting was estimated to be 0.025 (ρ/ρω)³.
3) The drag coefficient of netting bundle was estimated to be 0.91 (ρ/ρω).
In all nets, the calculated depths of leadline closely agreed with the measured ones.