双桨船Lucy Ashton轴系附体阻力的尺度效应

本文对Lucy Ashton带附体美人架和轴包架的几何相似船模试验结果重加分析。分别将带附体的和相应裸体的船模阻力试验结果绘成以C_r为纵坐标对C_F为横坐标的Froude数等值线。假定: C_r=(1 k)C_F C_W可发现全部Froude数等值线都是直线。可见三因次外插法可推广应用于带轴系附体的船模。 带轴系附体船模与相应裸体船模的1 k之差,乘以足足C_F后,可认为是轴系附体的粘性阻力系数。带轴系附体船模与相应裸体船模的C_w之差可认为是轴系附体的兴波阻力系数。以上粘性阻力系数和兴波阻力系数之和可认为是足尺轴系附体的总阻力系数。 由此三因次外插法计得的足尺轴系附体总阻力系数与由实船试验测得者间的最大误差可发现小于10％。假定船的附体阻力为裸船体阻力的10％,则最大误差小于裸船体阻力的1％。可见应用三因次外插法预估轴系附体阻力可给出十分满意的结果。

SCALE EFFECT FOR SHAFT APPENDAGE RESISTANCE OF TWIN-SCREW VESSEL LUCY ASHTON

This paper reanalyzes resistance test results of Lucy Ashton geosims with both shaft brackets and shaft bossings. The resistance test results of models with shaft appendages and their corresponding naked hulls are plotted separately as iso-Froude lines with CT as the ordinate and CF as the abscissa. AssumingCT=(1 k)CF CWit is found that all iso-Froude lines are straight lines. It is thus evident that 3-dimensional extrapolation method can be extended to models with shaft appendages.The difference in 1 K between models with shaft appendage and their corresponding naked hulls, when multiplied by full-scale CF, can be regarded as viscous resistance coefficient of shaft appendage. The difference in CW between models with shaft appendage and their corresponding naked hulls can be regarded as wave making resistance coefficient of shaft appendage. The sum of viscous and wave making resistance coefficients can be regarded as the total resistance coefficient of full-scale shaft appendage.The maximum error between the full-scale shaft appendage resistance obtained by 3-dimensional extrapolation me thod and the measured shaft appendage resistance on the ship is found to be less than 10%. If the ship appendage resistance is 10% of the naked hull ship resistance, the maximum error is then less than 1% of the naked hull ship resistance. It is evident that 3-dimensional extrapolation method can give very satisfactory results for shaft appendage resistance estimation.