Shigeru Fuwa

Fundamental study on the flow speed distribution around small traps

This study measured the flow speed distribution using actual small traps to investigate the effects of their materials and shapes by analyzing the characteristics of the water flow patterns around them. Five types of trap (netted semi-cylinder shaped, wire semi-cylinder shaped, heart shaped, box shaped, and a cylinder shaped traps) constructed from different materials were used in the experiment. The flow speed distribution around each trap was measured in a flume tank. Flow speeds in the flume tank were 0.1, 0.2, 0.3, and 0.4 m/s. The webbing of the traps was different in shape and had various diameters of twine. The diameters of twine ranged from 0.55 to 1.00 mm. The relationship between the solidity ratio of the twine and flow distribution of the traps was also analyzed. For the netted semi-cylinder shaped and cylinder shaped traps, the area of reduced flow speed extended along the downstream area and its width slightly increased with distance from the trap’s entrance. The heart shaped trap is shown to have the largest solidity ratio and this resulted in a high reduction of the flow speed downstream from the trap.

Characteristics of periodical movement of live squid (Todarodes pacificus) hooked on the branch line of a red sea bream long line

In Jeju Island, red sea bream is mainly caught by long line with a live squid as bait. The movements of artificial jigs in the fishery are supposed to be an important factor for catching the target organism as well as bait. To develop new fishing method for long line fishery, movements of the bait which was squid were tried to be characterized. In a water tank experiment, a live squid was hooked by a fish hook attached to a model long line. And then movements of squids in the water tank were recorded for 20 minutes by a video camera. Recorded movement of the squid was just periodically up-and-down moving, with a dominant frequency of 0.125Hz, and amplitude of 10.8cm.

Shape and Hydrodynamic Characteristics of Canvas Kite for Midwater Trawl.

キャンバスカイトの流体特性を明らかにするために, 形状の異なる5種類のキャンバスカイトの模型を用いて, 0.2から0.5までの4段階の異なるキャンバーと迎角30°から130°の範囲で水槽実験を行った。実験で得られた揚力と抗力から求めた最大揚力係数と最大揚抗比は, I型の反り比0.2と迎角度50°で, それぞれ1.37と2.00であった。また, 簡単な構造の拡網装置としてキャンバスカイトを用いるには, I型が最適形状であるといえた。