Research On The Influence Of Twin-propeller On Propeller Exciting Force

The intense vibration of the hull can not only destroy the structure and reduce the safety, but also affect the comfort, even threatening the physical and mental health of the crew and passengers. Propeller exciting force is one of the main excitation sources of the ship vibration, which is a key factor to de termine the quality of ships. At the same time, with the demand of tonnage and speed increasing, a considerable number of ships use twin-propeller propulsion, especially military ships. Therefore the research on twin-propeller exciting force has extremely important practical significance.With the help of the CFD software of ANSYS-CFX, the influence of the twin-propeller behind ship on exciting force without considering the cavitation was researched by the mean of numerical simulation, Details are as follow s:1) Propeller open water test was simulated and the verification of the calculation method in this paper was completed. At the same time, the influence of geometry and mesh density of the rotation field on the curve of thrust coefficient and torque coefficient was researched.2) The ship flow trace of the entire hull and half hull model was calculated and analyzed. By comparison, the flow trace is very similar, which proves the feasibility of the half hull model instead of the entire hull to generate the ship flow trace.3) Through changing arrangement of the ship propellers, the bearing force and water pressure of monitoring points of left single propeller and inward propeller were calculated. By comparison, it is found that exciting force of the left si ngle propeller and the inward propeller in the axial direction has a large difference, but there is a little difference in the other direction on the bearing force; the fluctuating pressure coefficient of the inward left propeller greater than that of the left single propeller. But due to different monitoring points, this gaps are different on the surface force.4) The influence of the different arrangement of the twin-propeller on exciting force was researched. By comparing the exciting force of the inward left propeller and outward left propeller, it is found that, on the bearing force, the first order magnitude dimensionless value of outward left propeller in the X direction greater than that of the inward left propeller 17.02%, however the former value i s slightly larger than the latter one on the other components; on the surface force, the fluctuating pressure coefficient of the outward left propeller greater than that of the inward left propeller, the greatest different of which is that the former one i s 1.48 time the latter.The influence of the phase difference on outward propeller exciting force was researched. On the bearing force, with the phase difference increasing, the difference of the first order magnitude of the excitation is also increased, while the difference of the other components of the bearing force is small; on the surface force, with the phase difference between increasing, the difference of the first order magnitude of the excitation force is also increased. The minimum difference i s about 3:2. The maximum ratio of the fluctuating pressure coefficient of 0 ° and 45 ° is 2/3 and the minimum ratio is 1/2.