Abstract
An active vibration isolation system is retrofitted to a diesel generator set in a tugboat to determine the effectiveness of such a system in a realistic practical environment. The system consists of six bespoke inertial actuators chosen to make minimal modifications to the machinery arrangement, and a DSP-based controller. Six accelerometers are collocated with the actuators on the top of six isolators to act as error sensors, and six accelerometers are placed below the isolators to give a measure of the global vibration of the ships structure below the generator set. A hydrophone is also placed in the water to give an indication of the underwater noise due to the generator. The control strategy employed is six-input and six-output decentralized adaptive feedforward control with the reference signal being derived from the signal from an optical tachometer on shaft between the engine and the generator. To suppress the vibration at all the dominant forcing frequencies, an electrical circuit generated the half engine orders required from the measured reference signal. The experimental results show that the combination of the active control system and the passive isolators is effective in reducing the global vibration and the acoustic pressure at the hydrophone position.
Highlights
Vibration generated by propulsion machinery, ships’ services, and auxiliary machinery, for example diesel generators, is one of the five principal groups of radiated noise sources in ships [1].Much of this noise stems from vibration, which propagates through the structure as structure-borne noise
The results show that in general, the half engine orders dominate the spectrum, with the active control system being effective at some frequencies but has a detrimental effect at others
It can beelectrodynamic seen that all vibration levels and the vibration. This system consisted inertial actuators and a DSPchanges to the existing machinery layout. It thusofeffectively complemented the existing passive sound level have marginally increased at 12.5 Hz, which corresponds to the first half-order
Summary
Vibration generated by propulsion machinery, ships’ services, and auxiliary machinery, for example diesel generators, is one of the five principal groups of radiated noise sources in ships [1]. Secondary vibration sources (actuators), generate control forces to counteract the primary vibration transmission They are often installed in series or parallel with passive resilient isolators. Electromagnetic type actuators are widely used in active vibration control since they are compact and have a wide bandwidth An example of such a device to control the transmission of vibration from a diesel engine was described in [7]. An inertial shaker (or proof-mass actuator) is another kind of electrodynamic actuator which only has to be connected at one point on the structure as it generates a force by vibrating the proof-mass [2,8,10,11] It is most effective at its natural frequency, but it can be used over a range of frequencies with less efficiency.
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