초록
종횡비, 다각형 모양에 따른 평판과 범포의 유체역학적 특성을 규명하고자 직사각형, 사다리꼴 모양으로 모형 평판과 범포를 제작하고 회류수조에서 양 ${\cdot}$ 항력 실험을 수행하였다. 그 결과를 요약하면 다음과 같다. 1. 삼각형 평판의 경우, 종횡비가 1 이하인 모형에서는 38${\sim}$42$^{\circ}$에서 최대 $C_L$이 1.23${\sim}$1.32, 1.5 이상인 모형에서는 20${\sim}$50$^{\circ}$에서 $C_L$이 약 0.85 전후였다. 역삼각형 평판의 경우, 종횡비가 1 이하인 모형에서는 영가가 36${\sim}$38$^{\circ}$에서 최대 $C_L$이 1.46${\sim}$1.56, 1.5 이상인 모형에서는 22${\sim}$26$^{\circ}$에서 1.05${\sim}$1.21 정도였다. 같은 삼각형 평판 모형에서는 전자의 모형이 후자보다 $C_L$이 작게, 양항비도 작게 나타났다. 2. 삼각형 범포의 경우, 종횡비가 1 이하인 모형에서는 영각 46${\sim}$48$^{\circ}$에서 최대 $C_L$이 1.67${\sim}$1.77, 1.5 이상인 모형에서는 20${\sim}$50$^{\circ}$에서 $C_L$이 약 1.1 전후였다. 역삼각형 범포의 경우, 종횡비가 1 이하인 모형에서는 영각 28${\sim}$32$^{\circ}$에서 최대 $C_L$이 1.44${\sim}$1.68, 1.5 이상인 모형에서는 18${\sim}$24$^{\circ}$에서 10.3${\sim}$1.18 정도였다. 같은 삼각형 범포 모형에서는 전자의 모형이 후자보다 $C_L$은 크게, 양항비는 작게 나타났다. 3. 모형에서 물의 유체력을 많이 받을 수 있는 곳에서 만곡꼭지점이 만들어지며, 삼각형 모형에서는 종횡비가 클수록, 역삼각형 모형에서는 작을수록 만곡꼭지점의 위치도 컸다. 4. 만곡도는 전 모형에서 종횡비가 클수록 컸으며, 삼각형 모형에서는 영각이 클수록 컸고 역삼각형 모형에서는 작을수록 컸다.
As far as an opening device of fishing gears is concerned, applications of a kite are under development around the world. The typical examples are found in the opening device of the stow net on anchor and the buoyancy material of the trawl. While the stow net on anchor has proved its capability for the past 20 years, the trawl has not been wildly used since it has been first introduced for the commercial use only without sufficient studies and thus has revealed many drawbacks. Therefore, the fundamental hydrodynamics of the kite itself need to ne studied further. Models of plate and canvas kite were deployed in the circulating water tank for the mechanical test. For this situation lift and drag tests were performed considering a change in the shape of objects, which resulted in a different aspect ratio of rectangle and trapezoid. The results obtained from the above approaches are summarized as follows, where aspect ratio, attack angle, lift coefficient and maximum lift coefficient are denoted as A, B, $C_L$ and $C_{Lmax}$ respectively : 1. Given the triangular plate, $C_{Lmax}$ was produced as 1.26${\sim}$1.32 with A${\leq}$1 and 38$^{\circ}$B${\leq}$42$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$${\leq}$B${\leq}$50$^{\circ}$, $C_L$ was around 0.85. Given the inverted triangular plate, $C_{Lmax}$ was 1.46${\sim}$1.56 with A${\leq}$1 and 36$^{\circ}$B${\leq}$38$^{\circ}$. And When A${\geq}$1.5 and 22$^{\circ}$B${\leq}$26$^{\circ}$, $C_{Lmax}$ was 1.05${\sim}$1.21. Given the triangular kite, $C_{Lmax}$ was produced as 1.67${\sim}$1.77 with A${\leq}$1 and 46$^{\circ}$B${\leq}$48$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$B${\leq}$50$^{\circ}$, $C_L$ was around 1.10. Given the inverted triangular kite, $C_{Lmax}$ was 1.44${\sim}$1.68 with A${\leq}$1 and 28$^{\circ}$B${\leq}$32$^{\circ}$. And when A${\geq}$1.5 and 18$^{\circ}$B${\leq}$24$^{\circ}$, $C_{Lmax}$ was 1.03${\sim}$1.18. 2. For a model with A=1/2, an increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Then there was a tendency of a very gradual decrease or no change in the value of $C_L$. For a model with A=2/3, the tendency of $C_L$ was similar to the case of a model with A=1/2. For a model with A=1, an increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. And the tendency of $C_L$ didn't change dramatically. For a model with A=1.5, the tendency of $C_L$ as a function of B was changed very small as 0.75${\sim}$1.22 with 20$^{\circ}$B${\leq}$50$^{\circ}$. For a model with A=2, the tendency of $C_L$ as a function of B was almost the same in the triangular model. There was no considerable change in the models with 20$^{\circ}$B${\leq}$50$^{\circ}$. 3. The inverted model's $C_L$ as a function of increase of B reached the maximum rapidly, then decreased gradually compared to the non-inverted models. Others were decreased dramatically. 4. The action point of dynamic pressure in accordance with the attack angle was close to the rear area of the model with small attack angle, and with large attack angle, the action point was close to the front part of the model. 5. There was camber vertex in the position in which the fluid pressure was generated, and the triangular canvas had large value of camber vertex when the aspect ratio was high, while the inverted triangular canvas was versa. 6. All canvas kite had larger camber ratio when the aspect ratio was high, and the triangular canvas had larger one when the attack angle was high, while the inverted triangluar canvas was versa.
