302 



Laser — p 



Photomultiplier 



c Laser beam 



Scatlered 

 — Laser 



Light ,, 



Cross 

 Section 



10 



Longitudinal 

 cross section 



Frame 

 12 13 U 



PhotomJ^Gser 



Lense 



Window 



FIGURE 2. Arrangement of test setups. 



The results of the pressure fluctuation measure- 

 ments for the Tests No. 1-4, 11 and 13-16 are given 

 in Figure 3 showing the dimensionless pressure 

 amplitudes of the blade frequency for the pressure 

 pick-ups PI, P3, P4, and P6 . They have been 

 harmonically analysed on the HP-computer in the 

 measuring container. As usual with right-hand 

 propellers the pressure pick-up on the starboard 

 side (here: P3) clearly shows higher values than 

 that on the port side (P4) . Figure 4 shows the 

 amplitudes measured by these two pressure pick-ups 

 up to the 15th harmonic. The harmonic analysis has 

 been carried out for a "representative" revolution, 

 resulting from the average of 60 propeller revolu- 

 tions . 



Figure 5 shows the pressure fluctuations measure- 

 ments versus propeller rpm for the pick-ups P3 and 

 P4 for two drafts applied during the voyage in the 

 Indian Ocean. At t±iis point in time the propeller 

 was already damaged. Further data of tihese measure- 

 ment runs can be found in the Tables 3a to 3h. 

 Examples of the results of harmonic. analyses up to 

 the 15th harmonic order for the pressure pick-ups 

 P3 and P4 are shown in Figure 6. In Figure 7 a 

 comparison is given of the pressure amplitudes of 

 these harmonic orders for the pick-up P4 (port) in 

 shallow and deep water. In shallow water the 

 pressure amplitudes are only slightly higher (5.8%) 

 than that in deep water. Witih the pick-up P3 

 (starboard) the difference was even smaller (1.0% 

 increase) . 



80 90 



Undamaged Propeller 

 Mediterranean 



FIGURE 3. Pressure fluctuations. 



The lower pressure amplitudes of the blade 

 frequency in the Indian Ocean (Figures 5 and 6) 

 compared with that in the Mediterranean (Figures 



3 and 4) are to be attributed to a significantly 

 stronger, but mainly stationary cavitation of the 

 damaged blade (No. 3) . A comparison between Figures 



4 and 6 shows that due to the damage the pressure 

 amplitudes of the "not-blade-number" frequencies 

 have been strongly increased in opposition to the 

 blade frequency. It should be noted that the ship 

 superstructure vibrated strongly after the propeller 

 had been damaged. This damage resulted from a ground- 



10 



15 



TEST NO 15 J7-10-1977 Harmonic Order n 



n = 100.4 RPM ; Vs =21.3Kn 



FIGURE 4. Harmonic components of pressure fluctuations. 



