| Abstrakt: |
To obtain a systematic set of data on noise and vibration due to propeller cavitation a comprehensive program of model and full-scale hydrodynamic and acoustic investigations was carried out during the years 1979-1981 on a single screw 39000 dwt Dutch ro-ro containership (speed, power, full-scale cavitation viewing, noise, and vibrations simultaneously). This paper reviews some of the acoustic results in connection with the possible application of compliant layers on the shell plates in way of the propeller. A simplified acoustic scale 1:10 model of the stern part has been constructed in steel, including proper scantlings, bulkheads, rudder and skeg, and checked for reliability by means of an electrodynamic hydrosounder located at the propeller disk. The model and full-scale ratios of sound pressure in front of the plating to velocities of the shell and of some decks agreed satisfactorily except below 20 Hz (full scale). The acoustic effect of an a priori seaworthy compliant layer, investigated by means of the model, appeared satisfactory, although it was limited by the flanking paths through rudder and skeg. The model also showed that a useful reduction of the transmission of cavitation noise by an increase of the source-to-shell-distance can only be obtained for frequencies above 25 Hz (full scale). [ABSTRACT FROM AUTHOR] |
