Hydrodynamic characteristics of plane minnow netting made of high-strength polyethylene (Dyneema)

Abstract

The hydrodynamic characteristics of minnow netting composed of high-strength polyethylene (Dyneema) with diŠerent types of twine diameter and mesh size were evaluated through experiments conducted in a ‰ume tank. The drag coe‹cient C D90 of Dyneema minnow netting set normal to the water ‰ow was 8 and 25 smaller than that of minnow netting made of the conventional materials of polyamide and polyvinyl alcohol, respectively.The drag coe‹cient C D0 of minnow netting set parallel to the water ‰ow showed a slight diŠerence between the materials. Additionally, C D90 and C D0 were expressed as functions of Reynolds number and mesh factor a. Furthermore, the drag and lift coe‹cients of minnow netting set at various angles to the water ‰ow were estimated by empirical equations as functions of C D90 , C D0 and attack angle u. Table 1 に示す。

Hydrodynamic characteristics of knotted and knotless purse seine netting panels as determined in a flume tank

“…For drag coefficient when the netting is normal to the flow, the empirical formulae from Milne [ 12 ] and Aarsnes et al [ 13 ] only depended on solidity ratio, thus the two constants were shown in Fig 12 under different ranges of Reynolds number. The formulae proposed by Fridman and Danilov [ 14 ], Balash et al [ 6 ], and Kumazawa et al [ 8 ] were related to solidity ratio and Reynolds number, but the predicted drag coefficients were greater than the results of this study. But the formula developed by Hosseini et al [ 7 ] as a function of Reynolds number resulted in lower predictions than our results.…”

“…We deduced the following formula for the drag coefficient of knotless nylon netting based on Tauti’s theoretical formula and Kumazawa et al [ 8 ] formula: Based on Tauti’s theoretical formula, the inclined lift coefficient formula was proposed: …”

“…The dimensionless coefficients C D (drag coefficient) and C L (lift coefficient) of plane netting were calculated using following expressions [ 8 , 10 ]: where F D and F L are the measured drag and lift forces acting on the netting panel; ρ is density of water; V is flow velocity; α is solidity ratio; S 0 is the outline area of netting panel. α S 0 represents the projected area of the netting panel.…”

“…Hosseini et al [ 7 ] obtained drag and lift coefficients of nylon knotted netting from flume experiments to simulate the sinking behavior of a purse seine, and found that hydrodynamic coefficients depended on Reynolds number and attack angle. Kumazawa et al [ 8 ] evaluated hydrodynamic characteristics of knotless netting panels made of three materials (Dyneema, polyamide, and polyvinyl) through flume tank experiments, and found that the drag coefficient depended on Reynolds number based on mean hydraulic depth and solidity ratio.…”

“…In general, combined effects of twine material, knot type, structural pattern, surface roughness and strand arrangement and other factors of netting attributes determine hydrodynamic characteristics of netting. However, previous studies only documented Reynolds number, solidity ratio, and attack angle as factors affecting the hydrodynamic coefficient [ 4 – 8 ].…”