Hydro- and aerodynamic analysis for the design of a sailing yacht

The results of the design analysis for a sailing yacht’s hull and sails are reported. The results were used to confirm the design of a 30 ft long sloop, which was planned, designed, and built in Korea for the first time in history. Flows around a sailing yacht above and under the free surface were analyzed separately using both computational and experimental methods. For the underwater flow analysis, turbulent flow simulations with and without free surface wave effects were carried out for the canoe hull with keel/rudder. The computed drag and side forces on the hull model were compared with the measurement data obtained from the towing tank experiments. In order to assess the sail performance, another set of computations was carried out for the flow around a sail system composed of main and jib sails with a mast. The present study demonstrates that, for the design analysis of a sailing yacht, computational fluid dynamics techniques can be utilized with a reasonable level of confidence.     

A study on the weld characteristics of 5182 aluminum alloy by Nd:Yag laser welding with filler wire for car bodies

Defects such as porosity, underfill, and magnesium loss occur during laser welding of 5182 aluminum alloy. To compensate for these problems, AA5356 filler wire was used in our present work. To investigate the weld characteristics of the filler wire, experiments were performed with laser power, welding speed, and wire feed rate as the control variables. Bead appearance, bead shape, penetration depth, tensile strength, and the Erichsen ratio were observed as weld characteristic variables. The range of full penetration was reduced as laser power decreased and welding speed and wire feed rate increased. Without filler wire, full penetration was formed under all conditions. However, with filler wire, the range of conditions necessary to form full penetration was reduced as the wire feed rate increased because the heat input was used to melt both of the filler wire and the base metal. Filler wire increased the tensile strength and the Erichsen ratio. Using analysis of variance (ANOVA), it was shown that laser power had a greater influence on tensile strength and the Erichsen ratio among the three control variables. It was also found that tensile strength was closely related to the Erichsen ratio because the coefficient of correlation was 0.899.