APPENDIX A 

 PREDICTED HYDRODYNAMIC PERFORMANCE CURVES 



The forces produced by the depressor along with cable parameters provide the 

 necessary input for calculating the configurations and forces of the towcable. The 

 depressor tension characteristics measured during the basin experiment are presented 

 in Figure 9. In addition, the towcable angle at the depressor must be known. Tow- 

 cable angle has not been measured. However, an estimate based on data from another 

 depressor of similar design is presented in Figure 17. 



Predicted depressor depth as a function of depressor coefficient of tension 

 is presented in Figure 18 for various towcable wetted lengths and towing speeds; 

 the predictions assume that the remote sensors are positioned along the towcable at 

 locations 10 and 20 m above the depressor. Figure 18 allows selection of a towcable 

 length to satisfy a given depth requirement. It also provides an indication of the 

 tension variation (flap angle variation) required to achieve a desired depth profile. 



Data from the at-sea evaluation also are plotted in Figure 18 for comparison 

 with the predictions. For the cable lengths and speeds evaluated, the measured depth 

 values are consistently deeper than the predicted values by 5 to 10 m. This differ- 

 ence is possibly related to the previously discussed discrepancy between the set 

 depth and measured depth; or it may be the result of predictive errors. 



The accuracy of using Figure 18 to predict cyclic depth variation will degrade 

 as oscillation frequency increases. An indication of this degradation is shown in 

 Figure 19. Dynamic data from the at-sea evaluation in conjunction with the static 

 depth predictions of Figure 18 were used to obtain the cyclic depth attenuation 

 factor of Figure 19. The attenuation factor k is define to be 



^1 

 K = 7^ (4) 



where A^ is the measured dynamic depth variation corresponding to various cycle 

 frequencies, towcable lengths, and flap deflection ranges; and 



A is the static depth variation for the same towcable lengths and flap 

 deflection ranges (predicted using Figure 18) 



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