313 



Test 99 

 Measuring Time : 

 tm = 20.0 i sec 

 So = 12 N/cm3 



103.1 RPM 

 22.ikn 



Test 100 

 Meas. Time . 



20 40 50 



6-12-1977; Gulf of Aden 



K N/cm3 



n = 102 3 RPM 

 Vs = 22.2 kn 



Test 101 

 Meas. Time ■ 

 tm = 22.06sec 

 ?0 = l1N/cm3 



n =102.8 RPM 

 \] Vs = 22.3kn 



100 /u-m 

 Diameter 



FIGURE 24. Nuclei and particle distributions on 

 shallow water. 



shown in Figures 21 and 22. In the second case the 

 "Sydney Express" was ballasted with 5,160 tons of 

 water. In both series it should be noted that with 

 decreasing speed the number Co of nuclei per cm^ 

 increases. At the lowest speed of ca. ¥3= 12 kn 

 the bubble range of a diameter between 20 and 40 

 ym contains the absolute maximum number of biibbles. 

 The differences between the two cases are, however, 



20 40 60 80 —~ D 

 7-12-1977; Bab-el-Mandab 



FIGURE 25. Analog output of memory. 



[fxm] 



small. The differences between the drafts were 

 obviously not sufficient to provide stronger differ- 

 ences between the nuclei spectra. 



The two measurement series shown in Figures 23 

 and 24 were made under ideal weather conditions, 

 tihe one 7 hours later than the other. The spectra 

 from Figure 23 were obtained in deep water in the 

 Gulf of Aden; the spectra shown in Figure 24 were 

 obtained from shallow water at the entrance of the 

 Red Sea at Bab-el-Mandab. With these two series 

 it was intended to clarify the point that the 

 propeller excited vibrations which occur on shallow 

 water result (apart from the shallow water effect) 

 to a higher extent from a stronger instationary 

 cavitation, which arises on occount of an increased 

 nuclei concentration in shallow water. It must be 

 said that this question could not be answered. On 

 the other hand a comparison of these two measurement 

 series shows tiiat the number of nuclei per cm^ 

 (nuclei concentration Co) increases from a Co of 

 11 to 14 N/cm^ in deep water to a Co of 155 to 270 

 N/cm in shallow water. This will be described in 

 the following Section. The absolute maximum of Co 

 is here again in the range between the nuclei 

 diameter of 20 to 40 ym. In this connection it 

 should be noted that hardly any nuclei with a 

 diameter of above 60 ym were detected. 



7. DISCUSSION OF THE RESULTS OF NUCLEI SPECTRA 

 AND COMPARISON WITH OTHER INVESTIGATIONS 



Simultaneously with the nuclei measurements in 

 shallow water - Figure 24 - water samples have been 

 taken. The results of the tests carried out with 

 these water samples with the Aminco scattered light 

 device appear in Figure 10. These samples from the 

 shallow water region at Bab-el-Mandab showed a 

 Relative Intensity of 0.4 for the difference between 

 unfiltered and filtered water. Even after six 

 hours the unfiltered sample still showed a Relative 

 Intensity of 0.28. From this it can be concluded 

 that the suspended particles, existing at this 

 coastal strip, settled in the samples within six 

 hours . From this Aminco scattered light measurement 

 it can further be concluded that the high nuclei 

 concentration shown by the LSL measurement - of the 

 shallow water measurement series. Figure 24 - results 

 mainly from suspended particles . There were probably 

 also solid particles concerned (it is likely to be 

 sand at the coast of Arabia) which show no inclusion 

 of gas. This is assumed because the cavitation did 

 not increase in the shallow water. The corresponding 

 propeller excited pressure fluctuations in deep and 

 in shallow water show practically no difference. 

 Figure 7. 



In Figure 26 the results of the laser-scattered- 

 light technique and the Aminco scattered light 

 measurement for investigations in shallow water 

 (Test 105) are shown together. Figures 27 and 28 

 (in the diagrams marked with "Sydney Express") show 

 further results of the Aminco-scattered-light 

 measurements and the LSL measurements . In the 

 Aminco scattered light investigations the differences 

 between unfiltered and filtered water were equal 

 to zero [A (Rel.-Int. ) = ] in these cases. This 

 means that the concentrations of t±ie suspended 

 particles were imperceptibly small; they were in 

 any case below the response level of the device. 



In each top diagram of Figures 27 and 28, results 

 of the investigations of suspended particles from 



