• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.5
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• pp.700-707
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• 1997

In order to express exactly the total resistance of bottom trawl nets subjected simultaneously to the water flow and the bottom friction, the influence of frictional force was added to the formular for the flow resistance of trawl nets obtained by previous papev and the experimental data obtained by other investigators were analyzed by the formula. The analyzation produced the total resistance R (kg) expressed as $$R=4.5(\frac{S_n}{S_m})^{1.2}S\;v^{-1.8}+20(Bv)^{1.1}$$ where $S(m^2)$ was the wall area of nets, $S_m\;(m^2)$ the cross-sectional area of net mouths, $S_n\;(m^2)$ the area of nets projected to the plane perpendicular to the water flow, B (m) the made-up circumference at the fore edge of bag parts, and v(m/sec) the dragging velocity. From the viewpoint that expressing R in the form of $R=kSv^2$ was a usual practice, however, the resistant coefficient $k(kg{\cdot}sec^2/m^4)$ was compared with the factors influencing it by reusing the experimental data. The comparison gave that the coefficient k might be expressed approximately as a function of BL only and so the resistance R (kg) as $$R=18{\alpha}B^{0.5}L\;v^{1.5}$$ where L (m) was the made-up total length of nets and $\alpha=S/BL$. But the values of a in the nets did not deviate largely from their mean, 0.48, for all the nets and so the general expression of R (kg) for all the bottom trawl nets could be written as $$R=9\;B^{0.5}\;L\;v^{1.5}$$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.4
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• pp.247-259
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• 1993

The fishing experiment was carried out by the training ship Saebada in order to analyse the mesh selectivity for trawl cod-end, in the Southern Korea Sea and the East China Sea from June. 1991 through August, 1992. The trawl cod-end used in this experiment has the trouser type of cod-end with cover net. and the mesh selectivity was examined for the five kinds of the opening of mesh in its cod-end part. A total of 163 hauls, of which having mesh size 51.2mm ; A 89, 70.2mm ; B 54, 77.6mm ; C 55, 88.0mm ; D 52 and 111.3mm ; E 20 were used respectively. Selection curves and selection parameters were calculated by using a logistic function, S=1/(1+exp super(-(aL+b)) ). The mesh election master curves were estimated by S=1/(1+exp super(-[a(L/M)+$\beta$]) ). and the optimum mesh size were calculated with (L/M) sub(50) of master curve. In these cases 'a' and '$\alpha$' are slope, 'b' and '$\beta$' are intercept. 'L' is body length of the target species of fishes, 'M' is the mesh size, and 'S' denotes mesh selectivity. In this report, the four species of compressed form fishes were taken analized according to fish shape, and 'S' denotes mesh selectivity. In this report, the four species of compressed form fishes were taken analized according to fish shape, and the results obtained are summarized as follows: 1. Red seabream Pagrus major(Temminct et Schlegel) and yellow porgy Dentex tumifrons(Temminct et Schlegel) ; Selection rate in each mesh size of A, B, C, D and E were 99.7%, 97.5%, 91.4%, 76.7% and 57.8% respectively. Selection parameters 'a' and 'b' of mesh sizes C, D and E were 2.65 and -28.62, 4.40 and -77.73, 2.31 and -46.99, and their selection factors were 1.39, 2.10, 1.83 respectively. Selection parameters of master curve '$\alpha$' and '$\beta$' were 3.05 and -5.65 respectively, and (L/M) sub(50) was 1.85. The optimum mesh size of Red seabream was 141mm. 2. Filefish Thamnaconus modestus (Gunther) ; Selection rate in each mesh size of A, B, C, D and E were 99.6%, 98.3%, 91.2%, 80.0% and 48.6% respectively. Selection parameters 'a' and 'b' of mesh sizes C, D and E were 5.82 and -55.10, 2.92 and -36.90, 3.91 and -63.09, and their selection factors were 1.35, 1.44, 1.45 respectively. Selection parameters of master curve '$\alpha$' and '$\beta$' were 3.02 and -4.32 respectively, and (L/M) sub(50) was 1.43. The optimum mesh size was 129mm. 3. Target dory Zeus faber Valenciennes ; Selection rate in each mesh size of A, B, C, D and E were 99.7%, 100%, 83.2%, 91.6% and 65.0% respectively. Selection parameters 'a' and 'b' of mesh sizes C, D and E were 3.85 and -32.46, 4.19 and -57.38, 2.45 and -40.03, and their selection factors were 1.09, 1.56, 1.47 respectively. Selection parameters of master curve '$\alpha$' and '$\beta$' were 2.64 and -3.53 respectively, and (L/M) sub(50) was 1.34. The optimum mesh size was 127mm. 4. Butterfish Psenopsis anomala (Temminct et Schlegel) ; Selection rate in each mesh size of A, B, C, D and E were 99.2%, 34.1%, 46.5%, 14.3% and 2.4% respectively. Selection parameters 'a' and 'b' of mesh sizes B, C and D were 5.35 and -71.70, 5.07 and -69.25, 3.31 and -62.06 and their selection factors were 1.91, 1.75, 2.13 respectively. Selection parameters of master curve '$\alpha$' and '$\beta$' were 3.16 and -6.24 respectively, and (L/M) sub(50) was 1.98. The optimum mesh size was 71mm.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.196-205
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• 2004

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 rectangular plate, $C_{Lmax}$ was produced as 1.46${\sim}$1.54 with A${\leq}$1 and 40$^{\circ}$${\leq}$B${\leq}$42$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$${\leq}$B${\leq}$22$^{\circ}$, $C_{Lmax}$ was 10.7${\sim}$1.11. Given the rectangular canvas, $C_{Lmax}$ was 1.75${\sim}$1.91 with A${\leq}$1 and 32$^{\circ}$${\leq}$B${\leq}$40$^{\circ}$. And when A${\geq}$1.5 and 18$^{\circ}$${\leq}$B${\leq}$22$^{\circ}$, $C_{Lmax}$ was 1.24${\sim}$1.40. Given the trapezoid kite, $C_{Lmax}$ was produced as 1.65${\sim}$1.89 with A${\leq}$1.5 and 34$^{\circ}$${\leq}$B${\leq}$44$^{\circ}$. And when A=2 and B=14${\sim}$48, $C_L$ was around 1. Given the inverted trapezoid kite, $C_{Lmax}$ was 1.57${\sim}$1.74 with A${\leq}$1.5 and 24$^{\circ}$${\leq}$B${\leq}$36$^{\circ}$. And when A=2, $C_{Lmax}$ was 1.21 with B=18$^{\circ}$. 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 gradual decrease in the value of $C_L$ and in particular, the rectangular kite showed a more rapid decrease. For a model with A=2/3, the tendency of $C_L$ was similar to the case of a model with A=1/2 but the tendency was a more rapid decrease than those of the previous models. For a model with A=1, and increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Soon after the tendency of $C_L$ decreased dramatically. For a model with A=1.5, the tendency of $C_L$ as a function of B was various. For a model with A=2, the tendency of $C_L$ as a function of B was almost the same in the rectangular and trapezoid model. There was no considerable change in the models with 20$^{\circ}$${\leq}$B${\leq}$50$^{\circ}$. 3. The tendency of kite model's $C_L$ in accordance with increase of B was increased rapidly than plate models until $C_L$ has reached the maximum. Then $C_L$ in the kite model was decreased dramatically but in the plate model was decreased gradually. The value of $C_{Lmax}$ in the kite model was higher than that of the plate model, and the kite model's attack angel at $C_{Lmax}$ was smaller than the plate model's. 4. In the relationship between aspect ratio and lift force, the attack angle which had the maximum lift coefficient was large at the small aspect ratio models, At the large aspect ratio models, the attack angle was small. 5. There was camber vertex in the position in which the fluid pressure was generated, and the rectangular & trapezoid canvas had larger value of camber vertex when the aspect ratio was high, while the inverted trapezoid canvas was versa. 6. All canvas kite had larger camber ratio when the aspect ratio was high, and the rectangular & trapezoid canvas had larger one when the attack angle was high.