Abstract No.C180103-097

Author name(s): Jiaying WANG, Jinfeng LIU, Fangsheng SUN

Company: Hudong-Zhonghua Shipbuilding (Group) Co., Ltd., China

This paper studies the non-synchronization vibration beating phenomenon on a 172000m3 LNG Carrier. The port/starboard propulsions controlled respectively by each engine always have slightly speed deviation which results in vibration beating phenomenon. With two slow speed main engines (6S70ME-C8.2) and a five blades propeller, the vessel has 6th H-Moment as the largest main engine resource and 1st excitation force as the main propeller excitation source. A global finite element model was built to conduct free vibration analysis at a shaft speed of 80 rpm (NCR). Two opposite phase angles (0° and 180°) of 1st excitation force between two propellers and the 6th H-moment between two engines were specially assumed and evaluated in the calculation. The forced vibration responses at main engine frame top, wheel house and bridge wing under different phase angle load conditions were predicted and studied. The R.M.S velocities at wheel house and bridge wing under different load cases were calculated and studied. The measurements were recorded continuously during manual and the automatic increase from 27 to 83 rpm. Obvious vibration beating on main engine frame can be observed, which is caused by slightly speed deviation between the two main engines. All these can be a reference for other project with similar beating phenomenon.

KEY WORDS: two propulsion vessels; LNG carrier; vibration analysis; beating phenomenon; slightly speed deviation

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