which, assuming roughly half of the power supplied is used for thrust, 

 requires approximately 750 hp for the cushion flow. Since the target 

 cable burial system is half the size of the concept described in Reference 

 26, a WCV cable burier would require on the order of 375 hp for cushioning. 

 Because the pressure is very low, the flow must be large, and there may 

 be a significant problem with scouring under the vehicle. Although a 

 WCV may provide a means of eliminating vehicle frame /soil resistance, 

 it is an unproven concept, requires large amounts of power, may have 

 stability problems, and its low (6-inch) ground clearance will cause 

 problems in negotiating obstacles. 



CONCEPT SELECTION 



To make the concept selection from the various combinations of ex- 

 cavation, propulsion, and running gear subsystems, parameters were 

 identified for comparing the combinations. Each parameter was also assigned 

 a criticality or importance factor. Each system or subsystem was judged 

 on its capability to meet the design parameters, and this capability 

 was then weighted by the importance factor. In general, the higher the 

 score, the better the system. 



The importance factors were given the following values: 



4: Essential for the system to meet its mission requirements. 



3: Important from the standpoints of feasibility and meeting target 

 design parameters. 



2: Desirable, to increase reliability, probability of success, and 

 to keep development time and costs within reason. 



1: Little impact on the probability of success, but still important 



to system reliability, efficient performance, and ease of operation. 



The performance and design parameters are discussed below in their 

 order of importance. Score ranges are shown for each parameter in Tables 7 

 through 1 1 . 



Cable Damage Probability - (Weighting Factor: 4). An essential feature 

 of a cable burial system is that it bury the cable without damaging it. 

 Scores are biased to reflect that even a moderate chance of damaging 

 the cable is unacceptable. 



Total Power -(Weighting Factor: 3). The power to be supplied through 

 an umbilical was calculated, and each concept rated according to its 

 power level . 



Force Requirements - (Weighting Factor: 3). The total motion resis- 

 tance, including cable drag, soil resistance, and other drag forces, 

 was calculated, and each concept rated according to its force level. 



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