Theoretical and Experimental Investigation of Magneto Hydrodynamic Propulsion for Ocean Vehicles

The concept of Magneto-Hydrodynamic (MHD) propulsion can be used to implement a propeller-less propulsion system for marine vehicles. The basic principle behind MHD is to use the (Lorentz) force produced by the interaction of electric and magnetic fields to generate thrust on a conducting fluid in motion. Electrodes are lined up along the walls of the duct which act as the source of the electric field. Seawater acts as the conducting medium for the current when it passes through the duct. This medium is then subjected to a strong magnetic field within the duct, thereby producing an axial force, i.e., an axial thrust. Propulsion systems based on MHD require virtually no mechanical components, therefore a good application would be to design a propulsor which produces very little noise for small underwater vehicles. Results of a preliminary feasibility study on this application are presented in this thesis. An approximate, consistent MHD propulsion theoretical model to assess the performance of a MHD propulsor for small underwater vehicles is introduced and analyzed. The model is generalized from the hydrodynamic point of view to consider inlet and outlet diffusers. The general model is applied systematically varying the main design parameters with respect to a given autonomous underwater vehicle (AUV) size. The results show that larger magnetic fields, longer propulsor lengths and smaller inlet flow speeds are preferred to get the highest propulsion efficiency and thrust. To check the consistency of the theoretical model, experiments are conducted. The results of these experiments show an approximate relation between the theoretical equations and the actual phenomenon.