Active Vibration Isolation System for Seawater Pumps

Seawater pumps in cooling systems are the main noise and vibration sources in modern vessels, especially at cruising speed while the propulsion system is in low noise status. The measuring results show that the noise level radiated by a single pump is about 140dB in frequency range from 100 to 20kHz, whose energy mainly locates in low frequency domain with obviously periodical characteristics. So it is important to reduce the pump vibration. A hybrid control isolation mounting is constructed in the laboratory at the Harbin Engineering University and used to isolate the vibration of a typical seawater pump for vessels. The main intension of the work described here is to experimentally investigate the use of active vibration control to minimize the vibration of the intermediate mass in vertical direction, thereby also minimize the vibratory energy transmitted to the hull. This approach involves the use of two electromagnetic actuators, mounted on the intermediate mass, to produce the canceling vibration. The controller used in the real-time experiments is based on the filtered x-LMS algorithm with online secondary path modeling. It is demonstrated here that active vibration control of the intermediate mass of the seawater pump mounting is a practical way of reducing the main components (about 100Hz and 300Hz) of the vibration transmission.