This paper presents magnetohydrodynamics (MHD) as applied to electromagnetic marine propulsion, the history of its development, and some recent accomplishments. The focus of the paper is confined to the efforts in the US and Japan. The merit of current accomplishments with respect to the development of practical electromagnetic thrusters for surface, and underwater vehicle propulsion, and the challenges such as: management of the excessive stresses and magnetic signatures, superconducting magnet design, problems associated with low conductivity, bubble formation and transport and the associated problems in current transport, noise and signatures, and electrode erosion, are discussed. The state-of the- art and future efforts needed for this technology to reach fruition as a potential candidate for marine propulsion are described.
Magnetohydrodynamics or MHD is the science of conducting fluids interacting with electric and magnetic fields. This interdisciplinary science dates back to the early eighteen hundreds for its inception. However, it has received attention from the research community only in the past few decades. The principle of MHD (power generation) is illustrated in Fig. I. The MHD generator transforms the internal energy of a gas into electric power in much the same way as a piston engine generator or a turbogenerator does, and the basic physical phenomena is the same. In the first two devices, the energy of the gas is converted into the motion of solid conductors in a magnetic field. In the MHD generator, the gas itself is the conductor. As this conducting gas moves (by expansion through the nozzle) through a magnetic field, an electromotive force is generated and current flows according to Faraday's laws of induction. The seawater enters a rectangular duct (could be circular or annular), with continuous electrodes on the top and bottom (could be on the sides), placed in a magnetic field.
