Hydrodynamic Optimization for Pod Propulsion System using Real-coded Genetic Algorism

本文从水动力的角度出发，研究了螺旋桨-吊舱-支撑系统的优化计算方法。采用实数编码遗传算法作为优化技术。首先，为了减少优化的计算时间，开发了完全原创的并行计算系统。利用所提出的螺旋桨优化计算方法，对原螺旋桨进行了改进，使空泡面积减小到原来的一半。通过实验验证了优化结果。空泡面积没有明显减小，螺旋桨效率下降。造成这种失败的主要原因可能是对空化的严格限制。通过实验验证了吊舱螺旋桨水动力计算方法的准确性。测量了五个不同吊舱的水动力。计算结果与实验数据吻合较好。为了减小吊舱螺旋桨所受的侧向力，通过实验研究了支板与吊舱的附着角对其的影响。发现存在一个使侧向力接近于零的最佳附着角。横向力的计算结果与试验结果有相似的趋势。作为本研究进一步发展的初步实验，对吊舱下方安装小翅片的效果进行了研究。有可能使横向力几乎为零，也防止在推进方向上作用在吊舱螺旋桨上的力的增量。通过合理选择桨片的尺寸和形状、最佳桨片数量和最佳附着位置，可以研制出具有优良水动力性能的新型吊舱螺旋桨。

In the present study, calculation methods for optimizing propeller and pod-strut system in hydrodynamic aspect were developed. Real-coded genetic algorism was used as an optimization technique.At first, completely original parallel computing system was developed in order to reduce the computing time for optimization.Improvement to reduce the cavitating area to half on an original propeller was attempted using presented calculation method for propeller optimization. Experiments were conducted to confirm the optimization results. The cavitating area did not reduce remarkably and the propeller efficiency declined. The main reason of this failure may be caused by the strict restriction for cavitation.Experiments to confirm the accuracy of the calculation method for hydrodynamic forces acting on the pod propeller were conducted. Hydrodynamic forces on five different pods were measured. Calculated results agreed well with the experimental data. In order to reduce the lateral force on the pod propeller, the effect of the attachment angles of the strut to the pod was investigated by experiment. It was found that there was an optimum attachment angle to make the lateral force nearly zero. Calculated results about lateral force had the similar tendency to the experimental results.As the preliminary experiments for the further development of the present study, the effect of small fin mounted under the pod was investigated. There is the possibility to make the lateral force nearly zero and also to prevent the increment of the force acting on the pod propeller in the advancing direction. If we choose size and shape of the fin, optimum number of the fin and optimum position of attachment appropriately, we can create a new type pod propeller which has excellent hydrodynamic performance.