| This thesis studies the influence of random vibration on ships to provide some powerful theoretical supports for improvements of ship’s stabilization. In order to comply with the requirements in the Ship Vibration Control Guidance GD026-2000and the IMO resolution A468(XII) code of Noise Level on board Ships, optimization of the ship construction design not only may reduce the ship’s vibration and noises, thus improving the ship design level in China to shorten the distance in the ship construction industry between our and advanced countries., but also can lower the ship construction cost to promote economic effectiveness. Nowadays, ship construction takes into consideration only the recognized vibration effects, such as from main engine, and the appropriate stabilizing measures. There has been lack of forward-looking research on effects of random vibration both at home and abroad. Instead, it is done by taking remedial measures according to the performance after ship construction. Therefore, it is necessary to develop some basic research in this field.The ship is subject to the loads of wind, wave and propeller, which are characterized as random. They influence the vibration condition and safety of the ship to a great extent. This thesis studies the effects of various loads on ship’s structural vibration at sea, analyses their contributions to ship’s structural vibration by means of theoretical modeling and numerical simulation of ship construction and trials on board, and provides a series of rapid and effective prediction methods for ship vibration engineering and new technologies for wave and vibration prevention in order to optimize ship stabilizing design and minimize vibration effects on ship’s hull.The traditional ship design mainly aims at the structural strength, watertightness and stability of the ship’s hull. In recent years, the IMO has provided more requirements for ship’s habitability, bringing the structural vibration form machinery and control and prediction of compartment air-borne noise into consideration of ship engineering personnel. Modern ships are usually provided with large-powered propulsion plant for demands in power performance. The strong structural vibration from the powerful machinery may result in fatigue of adjacent structure and influence on normal operation of other equipment. Meanwhile, the secondary sound radiation of the structural noise transmitted through ship’s hull may affect the habitability of the superstructure.Habitability mainly includes temperature, oxygen content, illumination and noise. On home made ships, the noise problem is prominent due to limits on control methods and costs. Lately, foreign countries have paid special attention to this aspect and developed a series of standards. Our research on this aspect is still behind the advanced countries.Ship’s construction consists of steel plates and beams that are closely connected to ensure strength and watertightness. This particularity in construction may cause great transmission losses in airborne noises by sound barriers of multi decks and bulkheads, but not enough for the compartment noise target. Since the steel material intrinsically has a very low loss factor, it is a good sound conductor. The structural sound can pass through structural path almost loss-free from the engine room to the superstructure and cause the secondary sound radiation which is the major reason for superstructure airborne noises. Therefore, it is necessary to analyze and study the basic principles of structural vibration transmission caused by marine propulsion and propeller plants and take proper stabilizing and denoising measures according to ship’s structural vibration strength to reduce the effects of structural sound transmission on habitability. |
PDF Full Text Request