水中を動く網地が受ける水の抵抗-III : 網糸の種類による流水抵抗の違い
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概要
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The previous report1) has proved that coefficient of plane net resistance against vertical flow of water is different in accordance with forms of knots. In the present study an experiment has been carried out for finding differences in coefficient of the resistance among sample nets of various kinds of fibers. Of the nets used for experiment some were made of natural fibers such as cotton, manila twine, and straw rope, the others were of synthetic fibers including Amilan (polyamid), Tevilon (vinyle chloride), Silklon (polyvinyle alcohol), Cremona (polyvinyle alcohol), Kurehalon (vinylidene chloride) and Saran (vinylidene chloride). Most of them had trawler knot with the specifications as shown in table 1. The net was stretched on a frame, 1×1 meters, of alminum bar, 0.6 centimeter in diameter, with shrinkage of 30 per cent so as to let each of meshes form a square. Towing tests for hydraulic resistance of the net were carried out at the rate of 4 to 40cm/sec., the experimental facilities being described previously. The coefficient of net resistance was calculated from the formula R=kv2 as same as performed in the preceding study, where R is the resistance of a net piece (gr.) and v the towing speed (cm/sec. ). In this case, k becomes nearly constant when the value of Reynolds number (v•d/v) is greater than 3×102 (Fig. 1), where d is the diameter of the netting cord (cm.) and v the kenematic coefficient of viscosity (cm2/sec.). Thus, the relationships between k and d/l in different kinds of fibers are shown in Fig. 2, where l is the mesh size (cm.). As is obvious in the figure the value of k is larger in natural fibers than in synthetic fibers with considerable differences even between synthetic fibers. It is interesting to observe the net made of cut-fiber of polyvinyle shows the value of k higher than that of the net made of endless fiber of polyamid, vinyle chloride and vinylidene chloride. From these results it may be concluded that the value of k is greatly affected by roughness en the surface of nettingg cord.
著者
関連論文
- 水中を動く網地が受ける水の抵抗-III : 網糸の種類による流水抵抗の違い
- 水中を動く網地が受ける水の抵抗-IV : 網糸の吹かれ
- 水中を動く網地が受ける水の抵抗-II. 網目の形状の変化と流水抵抗
- 定置網の網地の使用中に起こる抗張力の減退と使用限界張力に関する研究
- 水中を動く網地が受ける水の抵抗 (I) : 本目蛙又及び無結節網地の流水抵抗の違い
- 二重刺網の形状におよぼす波浪の影響 : 波の進行方向と平行に網地を入れた場合について
- 二重刺網の基礎実験
- イワシ刺網の長さの方向における罹網分布に及ぼす縫目の影響
- 底曳網の模型實驗
- 底曳網の網成りと抵抗
- 漁具資材並びに網の構造に関する技術的動向 (昭和45年度日本水産学会秋季大会シンポジウム) -- (定置網漁業に関する研究の現状とその問題点)