應用計算方法研究波浪對螺槳性能之影響

STUDY OF THE WAVE EFFECTS ON PROPELLER PERFORMANCE BY COMPUTATIONS

In this paper, the effects of ship motion on propeller performance are studied. The influences are divided into two different factors. The first one is the influence due to ship positions in seaway and the induced velocity due to wave itself, and the second one is the interaction between the ship hull and the propeller. The influence of the ship motion on the propeller performance is then the sum of these two factors, and they are assumed to be independent to each other in this research. In this paper, the first factor is considered as mainly the potential flow factor, and the second one is considered as mainly the viscous flow factor. For the effects of ship positions and the influence of wave itself, a potential flow propeller unsteady flow boundary element method is used with a ship motion prediction program for computations. For computing the interactions between the ship hull and propellers, the viscous flow RANS method is adopted. Instead of using the real propeller geometry in RANS computations, the body forces are used to represent the propeller effects, and it is called the body force method. In this paper, the ship motion computational method, the propeller boundary element method, and the viscous flow RANS method are integrated to evaluate the propeller performance in waves. The applications of the present method including speed loss, propeller effects on the ship wake, and wave effects on propeller performances are shown in the paper, and computational examples are demonstrated. For wave effects on propeller performances, we found that the effect of ship motion on propeller performance is obvious, and the unsteady flow computation example in the paper shows that the unsteady flow effect due to the ship wake is more important than that due to the ship motion. 本論文探討船舶運動對螺槳性能之影響，相關的效應分為兩個不同的因素，一是船舶運動姿態以及波浪誘導速度的影響，一是波浪中船殼與螺槳互動對於螺槳性能的影響，而此兩個因素將假設為相互獨立。第一個因素主要考慮勢流的效應，將利用螺槳非定常流邊界元素法以及勢流船舶運動程式計算；而第二個因素則主要考慮黏性流的效應，將利用黏性流RANS方法以及代表螺槳受力的體積力方法進行計算。論文中，整合船舶運動計算程式，螺槳邊界元素法以及RANS方法來研究波浪對於螺槳性能的影響，應用的計算範例包含失速的計算，螺槳對於船艉跡流的效應，以及波浪中船艉跡流對於螺槳受力的效應。計算結果可看出波浪對於螺槳性能的明顯效應，同時在我們所應用非定常流計算範例中，也發現船艉跡流對於螺槳性能所造成的影響要大於船舶運動的影響。