Vibration Analysis of A 3-Bladed Marine Propeller Shaft for 35000DWT Bulk Carrier

Vibration Analysis of a 3-bladed Marine Propeller shaft for 35000 DWT Bulk Carrier was carried out. The objectives of the analysis were mathematically designing the 3-bladed propeller shaft, carrying out computer aided design of the shaft and numerically performing vibration analysis. The methodology include mathematically designing the marine propeller and the corresponding shaft, manual calculation of the natural frequency of the shaft, using solidworks to design the shaft and numerically performing vibration analysis on the designed shaft using Analysis System (ANSYS) software. Hub (boss) diameter of 0.17m was calculated. The hollow shaft has external and internal diameters of 0.10m and 0.09m respectively. Torques of 202Nm2 and 384.72Nm2 were obtained at the driver and driven shafts respectively. The natural frequency calculated manually was 249Hz while that of the ANSYS was 280Hz which gives an error of 12%. However, the numerical analysis carried out with ANSYS software also showed that a phase difference of 1800 occurs at the frequency of 280Hz which is a signal of possible misalignment of shaft. At this frequency, the displacement of the shaft has a maximum value of 7.87 . Reaction forces from the components of the shaft were also observed to play major role in the vibration of the propeller shaft. These reaction forces, which cause wearing of the stern tube and intermediate bearings due to friction, are represented by phase angles closer to zero degree. Wear due to friction is a major source of shaft misalignment.