Some of the results obtained in these experiments are plotted in Fig. 3.11. The attached masses 

 in all cases were one or two aluminum sensor housings attached at various locations along the 4.57 mm 

 (0.18 in.) diameter steel cable span of 4.42 m (14.5 ft). It can be seen from the results in the figure 

 that the cable was tested at various conditions in the resonant, cross flow strumming regime during the 

 experiments. It should be noted that the attached masses did not deter or diminish the strumming, but 

 instead the system consisting of a bare cable plus attached masses reached higher cross flow displace- 

 ment amplitudes than the bare cable alone. It should be noted that the conditions of MAR's bare cable 

 reference experiment were at the onset of the resonant strumming regime while the attached mass 

 experiments reached well into the resonant region as shown in Fig. 3.11. All of the tests were con- 

 ducted in the range of cable and attached mass properties where hydrodynamic effects dominate (the 

 left-hand portion of Fig. 2.2), and even the addition of concentrated masses does little to deter large- 

 displacement cross flow strumming effects. All of the frequency spectra plotted in reference 51 give 

 clear evidence of cross flow strumming at a single resonant frequency. Many of the dynamic properties 

 of marine cables with attached masses can be calculated from the results of a study by Chung (52). 

 Further studies of the behavior of cables with attached masses are continuing as part of the 

 NAVFAC/CEL cable dynamics program. 



3.3 Small-Scale Field Experiments. Field studies of the strumming behavior of marine cables were 

 conducted over several summers at Castine Bay, Maine by staff members of the Ocean Engineering 

 Department at MIT. The field test layout is shown in Fig. 3.12. Sections of faired and unfaired cables, 

 nominally 23 m (76 ft) in length, were positioned normal to a spatially uniform tidal current which 

 ranged in magnitude from to 0.7 m/sec (0 to 1.36 kt). The earlier experiments have been reported in 

 detail (53). The most recent experiments, performed during 1976, were concerned with detailed meas- 

 urements of the strumming response of both unfaired and faired marine cables in an ocean environ- 

 ment (54). As with the DTNSRDC cables, measurements of the natural frequencies (in-air and in- 

 water), the added mass, and the fluid dynamic damping of the cables were made at NRL and are dis- 

 cussed in Appendix C. 



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