The measured array responses were to be employed in a validation of analytical cable design models and 

 computer codes (57). A second goal of the SEACON II experiment was to demonstrate and evaluate 

 new developments in ocean engineering which were required to design, implant, operate, and recover 

 fixed undersea cable structures. 



The SEACON II structure consisted of a delta-shaped module with three mooring legs. It was 

 implanted in 885 m (2900 ft) of water in the Santa Monica Basin by the Civil Engineering Laboratory 

 during 1974 and was retrieved during 1976. The top of the cable structure was positioned 137 m (450 

 ft) below the water surface. The mooring legs were 1244 m (4080 ft) long and each arm of the delta 

 was 305 m (1000 ft) long. An artist's view of the completed structure is shown in Fig. 3.19. Two 

 mooring legs were attached to explosive anchors embedded in the sea floor and the third leg was 

 attached to a 5680 kg (12500 lb) clump anchor. The entire cable structure was instrumented in order 

 to collect water current and array position data. 



The data were used to validate the computer code DECELl (previously called DESADE). This 

 code was developed at NRL (58) and is discussed elsewhere in this report. The delta cables experi- 

 enced uniform currents over their respective lengths and often were subject to cable strumming. These 

 strumming oscillations led to increased steady drag coefficients and static deflections as discussed 

 further in Section 4 of this report and by Skop, Griffin and Ramberg (59). Details of the SEACON II 

 implantation, design and recovery are given by Kretschmer, Edgerton and Albertsen (57). 



The drag coefficient Co of the SEACON II cable was measured in two series of tests conducted 

 for CEL. These measurements are plotted in Fig. 3.20. The tests conducted at the Naval Postgraduate 

 School utilized a short segment of the cable that was restrained from oscillating. An average value of 

 Co = 1.55 was obtained. The DTNSRDC tests were conducted with a 4.6 m (15 ft) long cable seg- 

 ment. The resonance in the drag versus Reynolds number data in Fig. 3.20 was caused by cable strum- 

 ming. The drag resonance is similar to that measured by Dale and McCandless (47) and plotted in Fig. 

 3.3. 



63 



