Magnetohydrodynamic Propulsion for Sea Vehicles 



(10 V.045)^ = 471, or B need only be 37.4 gauss. Fields this size can easily 

 be arranged to travel along coils. It is unfortunate that the sea does not have 

 such an enhanced conductivity. Liquid metal pumps of this type, however, can 

 operate with very reasonable fields. 



Since pressure forces are conveniently created in liquid metals, consider 

 the possibility of using electromagnetic fields to pump a liquid metal which 

 then pumps the sea water. One needs the liquid metal to transfer the momen- 

 tum from the electromagnetic fields to the sea water. Consider a flexible 

 elastic tube filled with a liquid metal. It is well known that a pressure pulse 

 in such a system will be propagated as a wave along the tube. Consider the 

 possibility of pushing a solid ring along the tube with the pulse, the pulse being 

 driven and sustained if necessary by our traveling electromagnetic wave. The 

 device might resemble that depicted in Fig. 4. 



Fig. 4 - Electromagnetic wave 

 propagation along plastic tube 

 filled with liquid metal (ring is 

 propelled forward by the pulse) 



Of course, the elastic properties of the tube wall must be chosen so that 

 the wave velocity and the phase velocity Vp are the same, or nearly so. The 

 magnetic field B drives the pressure pulse in the liquid metal ahead of it. Now 

 consider the possibility of replacing the solid ring by sea water. The water 

 would, unfortunately, flow around the bulge if it were not prevented from doing 

 so. The sea water to be pumped can be prevented from flowing around the 

 bulge by providing another wall or sealing surface. The whole propulsion con- 

 figuration might then look as in Fig. 5. In Fig. 5 the radial position of the 

 water "ring" and liquid metal have been interchanged. 



The magnetic field traveling along the coil will tend to deform the liquid 

 metal so as to conform to the field configuration. How successful it is in do- 

 ing this is governed by the magnetic Reynolds number previously discussed. 

 The magnetic pressure is transformed to fluid pressure in the liquid metal, and 

 the pressure is transmitted to the sea water across the flexible diaphragm. The 

 pressure pulse will also propagate along the interface, and the whole system is 

 designed so that the magnetic field configuration, the pulse in the material, and 



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