Active Vibration Isolation in Ships: A Pre-Analysis of Sound and Vibration Problems

Document type: Journal Articles
Article type: Original article
Peer reviewed: Yes
Author(s): Mathias Winberg, Sven Johansson, Lars Håkansson, Ingvar Claesson, Thomas L Lagö
Title: Active Vibration Isolation in Ships: A Pre-Analysis of Sound and Vibration Problems
Journal: International Journal of Acoustics and Vibration
Year: 2005
Volume: 10
Issue: 4
Pagination: 175-196
ISSN: 1027-5851
Publisher: IIAV
Organization: Blekinge Institute of Technology
Department: School of Engineering - Dept. of Signal Processing (Sektionen för teknik – avd. för signalbehandling)
School of Engineering S- 372 25 Ronneby
+46 455 38 50 00
http://www.tek.bth.se/
Authors e-mail: mathias.winberg@bth.se, lars.hakansson@bth.se
Language: English
Abstract: Engine-induced sound and vibration levels in boats for professional and leisure use are in many cases unacceptably high in terms of comfort and environmental disturbance. Classical methods for passive treatment are normally less efficient due to the low frequency content and often lead to a substantial increase in weight. The requirements for lower weight which would increase the maximum speed of the boat as well as improve fuel economy have to be considered. More efficient vibration damping methods must therefore be found. With, for example, active engine mounts, it is possible to achieve a decrease in the vibrations even for cases when the hull is not very stiff. This is especially important in marine applications, since the engines are usually mounted on flexible and light structures. The project Active Vibration Isolation In Ships (AVIIS) aims at investigating the effects of using a type of Active Noise and Vibration Control system (ANVC) in this type of marine application.
This article presents the analysis of the sound and vibration problems in one particular leisure boat from an ANVC point of view. A very thorough investigation is carried out, the main noise and vibration sources are established as well as the transmission paths of the noise into the boat. Answers are found from this investigation as to where the actuators should be positioned, which kind of ANVC approach that would be preferable to use and the expected interior noise reduction. This is the kind of pre-analysis that is needed for a complex structure such as found in a marine vessel for the successful implementation of ANVC. An optimized engine mount was also designed and evaluated resulting in a 10 dBA saloon sound level reduction compared to the standard engine mounts. Additionally, with the optimized engine mounts, the vibration levels at the hull were also reduced by up to 15 dB at the main harmonic components.
This paper also presents a feasible way to estimate the performance of a potential active control system based on feedforward narrowband control of engine and propeller harmonics. Secondary sources inertial mass actuators are proposed and for error sensors, accelerometers or microphones or a combination of the two are used. In the low frequency range, below 300 Hz, a further reduction of engine orders and propeller BPFs in the order of 5-10 dB are predicted.
Subject: Signal Processing\Active Noise and Vibration Control
Keywords: actve control, vibration analysis, actuators
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