Input 



Table 3. Power Conversion Efficiencies 



0.39 



Cavitation Cutting and Eigh-Pvessicpe Jetting. Both of these techniques 

 use the principle of focusing moderate amounts of energy to achieve ultra- 

 high energy densities to cut, fracture, or erode materials such as rock 

 and metal. As such, they are not suitable means of excavating a trench 

 in soft materials. High-energy density water jets achieve 100,000 to 

 5,000,000 psi in a jet 1/16 inch in diameter. The optimal cutting range 

 is 20 nozzle diameters, and the jet pressure should be at least 10 times 

 the material strength [35]. Extrapolating this information to digging 

 a 3-foot-deep trench in a typical (4-psi) seafloor soil suggests a nozzle 

 size of 1-1/2 inch and jet pressure of 40 psi (minimum). Thus, it can 

 be seen that the high-pressure water jetting technique provides nominally 

 2,500 times the pressure required to cut seafloor soil, and the jets 

 are so small that only a localized area of soil would be excavated. Extra- 

 polation of high-pressure water jet theory to soil excavation leads to 

 standard (low-pressure) jetting techniques. Cavitation cutting results 

 in pressures and cutting volumes similar to high-pressure water jetting. 



Direct Insertion. Using this method, the cable is simply forced into 

 the soil with, for example, a heavy wheel. The wheel must be forced through 

 the soil while penetrating 3 feet into the bottom. Preliminary analysis 

 showed that, even if the wheel were water lubricated such that an 80% 

 reduction in frictional resistance could be attained, the forward force 

 required to push the wheel through the soil ranges from 4,400 pounds for 

 a 4-inch-thick wheel to 7,900 pounds for a 1 6-inch-thick wheel. In addition. 



15 



