Finite element analysis of vibrations caused by unbalance effect in boat engine shaft propeller system

Ensuring that all forces are transmitted smoothly while the rotating machine elements transfer the rotational motion will be achieved with the existence of a balanced system. As a result of the disappearance of this balance situation, unbalance problems will occur. Unbalance problems cause vibrations in rotating machine elements. In this study, the data sets obtained in a sample experiment were used to detect malfunctions that may occur due to unbalance effect, and with the data sets used, the vibration amplitudes that appeared in the time domain at the measured points were obtained. FFT transformation of vibration signals was performed to determine the modes of vibrations in the time domain that occurred at different rotation speeds where the experiment was performed. Afterwards, the system was modeled by considering only the rotational equipment of the tested system and the modal analysis of the structure was performed using finite element analysis. In the next stage, a propeller was added to the end of the shaft in the modeled system, and assuming that this version of the system could serve as an external electric motor in small boats, the vibration modes that could occur at the same measurement points during the system's operation in water were examined. The examination was carried out by taking into account various configurations such as different shaft sizes and whether the propeller was damaged or not. By performing modal analyzes of the motor shaft propeller system at different rotation speeds and with the effect of water on the propeller, it was examined which of the modes that emerged in the structure were effective at the measurement point, which was considered to be more consistent in the real experimental system. As a result, the results of the unbalance effects that occur in the damaged propeller-operated system through the natural vibration modes revealed through modal analysis tests after the addition of a propeller to the experimental system are interpreted.