• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.209-216
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• 2002

How to estimate the shape of trawl net and ropes of a midwater trawl on full scale was described by implementing a three-dimensional semi-analytic treatment of a towing cable system with the field experiments obtained with the Scanmar system. The shape of trawl net from wingend to the beginning of codend was assumed to be of form $\chi$$^2$/ae$^2$+ y$^2$/be$^2$=(z - c)$^2$/c$^2$, and that of the ropes attached behind otter boards be of form yr = $A\chi$rB. In case of warp length 300m long, the volume of trawl net, the ratio of net height to net width at the mouth of the trawl net, and the inclination angle of float rope were estimated according to the change of towing speed. The volume and the distance between wingtips were increased with increasing towing speed. And the inclination angle of float (or ground) rope was slightly decreased with increasing towing speed.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.35-47
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• 1996

A surface panel method treating a boundary-value problem of the Dirichlet type is presented to design a three dimensional body with free surface corresponding to a prescribed pressure distribution. An integral equation is derived from Green's theorem, giving a relation between total potential of known strength and the unknown local flux. Upon discretization, a system of linear simultaneous equations is formed including free surface boundary condition and is solved for an assumed geometry. The pseudo local flux, present due to the incorrect positioning of the assumed geometry, plays a role f the geometry corrector, with which the new geometry is computed for the next iteration. Sample designs for submerged spheroids and Wigley hull and carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. For the calculation of the wave resistance, normal dipoles and Rankine sources are distributed on the body surface and Rankine sources on the free surface. The free surface boundary condition is linearized with respect to the oncoming flow. Four-points upwind finite difference scheme is used to compute the free surface boundary condition. A hyperboloidal panel is adopted to represent the hull surface, which can compensate the defects of the low-order panel method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but by experiment.