선망의 침강 저항 해석 - 2. 망지재료와 침자량이 다른 모형망의 경우 -
An Analysis on the sinking Resistance of Purse Seine - 2. In the Case of the Model Purse Seine with Different Netting Material and Sinkers
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선망의 침강 저항 특성을 해명하기 위한 기초 연구로서, 망지의 재료가 다르고 침자량이 동일한 선망 모형의 침강특성을 해석하였다. 실험에 사용한 선망은, 그물실의 직경 및 발의 길이가 같은 폴리프로피렌사 (밀도 0.91g/㎤), 폴리아미드사 (밀도 1.14g/㎤) 및 폴리에스터사 (밀도 1.39g/㎤)의 매듭 없는 망지를 사용하여, 뜸줄의 길이 420cm, 그물의 폭 85cm가 되도록 제작하였다. 이 그물들의 발줄에 침자를 25g, 45g, 60g의 3단계로 바꾸어 9종류의 모형그물을 만들고, 각각 PP-25, PA-25, PES-25, PP-45, PA-45, PES-45, PP-60, PA-60 및 PES-60 그물이라고 이름을 붙였다. 회류수조의 수로 위에 투망장치를 설치해서 정지상태의 수중에 투망하고, 관측부 전면에 설치한 비디오 카메라를 이용하여 촬영 녹화하였다. 그리고, 그물에 표시한 측정점의 좌표를 화상해석장치로 읽고 실험치를 구하였다. 여기서, 선망의 수직 방향의 침강운동을 나타낸 이론식을 이용하여 수치해석을 행하였는데, 그 결과는 다음과 같다. 1. 침자량이 60g일 때, 아랫자락의 평균 침강속도는 PES 그물 12.2cm/sec로 가장 빠르고, PA 그물 11.4 cm/sec, PP그물 10.7cm/sec 순으로 늦게 나타났다. 2. 망지의 저항계수 KD는, 계산결과 KD=0.09(ρ/ρw)⁴의 관계식으로 나타낼 수 있다. 3. 그물다발의 저항계수 CR은, 계산 결과 CR=0.09(ρ/ρw)의 관계식으로 나타낼 수 있었다. 4. 선망 투망후경과시간에 따른 그물 아랫자락의 도달 수심에 대한 실험치와 계산치의 관계는 상관성이 매우 높아, 침자량이 25g 일 때 meas.=1.04cal., 45g 일 때 meas.=0.99 cal.였으며, 60g 일 때 meas.=0.98 cal.의 관계를 나타냈다.
Abstract
This study deals with an analysis on the sinking resistance for the model purse seine, in the case of different netting material and sinkers. The experiment was carried out using nine simplified model seines of knotless nettings. Dimension of model seines 420 cm for corkline and 85 cm for seine depth, three groups of models rigged 25, 45 and 60 g with the same weighted sinkers in water were used. These were named PP-25, PA-25, PES-25, PP-45, PA-45, PES-45, PP-60, PA-60 and PES-60 seine. The densities(ρ) of netting materials were 0.91g/㎤, 1,14g/㎤ and 1.39g/㎤. Experiments carried out in the observation channel in a flume tank under still water conditions, Sinking motion was recorded by the one set of TV-camera for VTR, and reading coordinate carried out by the video digitization system. Differential equations were derived from the conservation of momenta of the model purse seines and used to determine the sinking speeds of the depths of leadline and the other portions of the seines. An analysis carried out by simultaneous differential equations for numerical method by sub-routine Runge-Kutta-Gill. The results obtained were as follows : 1. Average sinking speed of leadline for the model seines rigged 60g with the same weighted sinkers in water was fastest for 12.2cm/sec of PES seine, followed by 11.4 cm/sec of PA and 10.7cm/sec of PP seines. 2. The coefficient of resistance for netting of seine was estimated to be KD=0.09(ρ/ρw)⁴.
참고문헌 (23)
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