A multimodal dynamic vibration absorber for controlling longitudinal vibration of propulsion shafting system

The pulse force generated by the propeller excites the hull through the propulsion shafting system, which is the primary source of vibration and noise of ships. In order to control the transmission of longitudinal vibration of ship shafting, a multimodal dynamic vibration absorber (MDVA) with broadband vibration control performance is proposed. A magnetorheological elastomer (MRE) was prepared and used as an elastic element to construct a semi-active dynamic vibration absorber (SDVA), designed spiral flexible springs and embedded SDVA into the proposed MDVA. An equivalent propeller propulsion shaft system model was established, and its first three longitudinal vibrations were controlled based on the MDVA. Furthermore, the stiffness and damping of the MDVA were optimized by fixed point theory. A design scheme for the MDVA considering the changes in oil film stiffness of thrust bearings under different propeller speed conditions was proposed. The results indicate that the MDVA has excellent vibration transmission control performance at the first three natural frequencies. The proposed MDVA also has a broader frequency band for controlling vibration near first-order resonance than the traditional single degree of freedom DVA, which has excellent vibration control performance under variable speed conditions.