Transient analysis of magnetohydrodynamic seawater thrusters with decaying magnetic field

Abstract

ABSTRACTIn magnetohydrodynamic (MHD) seawater thrusters, a lot of energy is stored in the superconducting coil which produces the magnetic field. Although it is necessary to store this energy in the field coil to produce a constant thrust, on the way back to the beach and before mooring, this energy can be used to supply the required electricity of the ship equipment. This will lead to consumption of the field coil energy and will reduce the magnetic field intensity in the channel with a decaying exponential function. In this study, an approximate analytical solution is presented to predict the transient behaviour of the MHD thruster with decaying exponential magnetic field. Using this analysis, the maximum navigable distance and the maximum speed of a hypothetical MHD vessel are calculated as a function of Stuart number, electromagnetic interaction number, Reynolds number, and the time constant. The results show that the electromagnetic parameter and the Stuart number can be considered as measures of electromotive and counter-electromotive forces of the MHD thruster, respectively. These two parameters are the most important factors in increasing and decreasing the maximum navigable distance of the MHD vessel.