Trending of Vibration Spectrum in Marine Diesel Engine, Marine Gear Box and Variations with Rotational Speeds

Abstract

Noise and vibration on board ships may cause discomfort to passengers and crew. It may also impair the efficient execution of the crew’s duties, be the cause of damage to sensitive equipment, structural parts of the ship and cargo, and even compromise the safety of the vessel. In military scenario, this may influence the combat readiness of the vessel too. Nowadays, people on board are less willing to accept discomfort due to noise and vibration, leading to increasingly strict requirements. As these are usually not easily met, noise and vibration have become important factors in ship design. Noise and vibration levels are determined by the characteristics of source, transmission and receptor. Low frequency noise and vibration are difficult to damp and addition of mass and stiffness in the ‘remedial’ design stage is costly, and an effort multiplier. Therefore, noise and vibration problems must be avoided through identification and treatment of the major sources as and when found. It is appropriate that the principal vibration exciting sources be addressed first, since with high excitation levels excessive vibration can occur almost independently of system structural characteristics. In general, the major sources are the high-speed diesel main engine and the propeller (impeller). Hull excitations are generally considered to give less excitation than diesel engines. Thus, in this section, attention is paid to the excitation of the high speed main diesel engine. The main source of vibration generator is the propulsion system for a ship. Correct identification of its signature and spectrum with the trending behaviour is a better method to predict whole ship’s vibration levels. In order to identify the same, a fast attack craft fitted with 02 Nos 2000 hp each engines were earmarked to conduct trials. Sea trials at following conditions had been carried out. Sea State : 1-2, 2-3; Loading Condition : Full Load, Half Load; Wind Condition : Moderate< 15 knots; Sea Direction : Ahead, Astern