어업용 PES 무결절 망지의 유체역학적 특성

Abstract

PES netting is importantly used in purse seine gear, set net gear and so on in fishery. In particular, at least ten kinds of nettings are used in the large purse seine gear. And PES is made from various types of mesh according to fish species and size in cage culture. There are many examples of studies on the hydrodynamic characteristics of the various nettings in fisheries. There is also a single netting experiment on the resistance coefficient of the netting used in fisheries. In this study, the characteristic of resistances were analyzed for fourteen kinds of PES knotless nettings. So, in order to understand the interaction between the knotless nettings when using them together, we connected two different nettings and measured the moment due to the resistance in the fluid. Experiment were carried out in the circulating water channel of the National Institute of Fisheries Science. In the resistance test, one netting was attached to on frame at a hanging ratio of 70.7 %. Then attack angle was varied from 0 to 90 degrees by 10 degrees according to the current speed of 0.4 m/s and 0.5 m/s. In the moment test, two nettings were attached to one frame at a hanging ratio of 70.7 %. The attachment criteria were set for the case of the same diameter, the case of the same length of bar, and the case d/l similar. In the case of a netting of the same diameter, a smaller mesh size netting was attached to the left of the half of the frame. And when the length of bar is the same and d/l is similar, the larger diameter is attached to the left side. The ratio of diameter to length of bar is d/l and the drag coefficient is Cd. It can be expressed as Cd=3.71499(d/l)+0.76595 at a current speed 0.4 m/s and Cd=4.30324(d/l)+0.69056 at a current speed 0.5 m/s. Also, The larger the diameter, the larger the moment(Mz), and the longer the length, the smaller the moment(Mz). The results of this study clearly clarify the characteristics of the PES knotless nettings which is widely used in the fisheries sector. Therefore, it can be helpful to use the netting according to the purpose.