Nowadays, underwater robots play a significant role in many aspects of industry such as mine hunting, sea floor mapping, sub-sea pipeline construction and pipe surveys. Ever increasing demand on better control systems of underwater robots ignites engineers on modeling the systems for perfection. Since they are the lowest chain of the control problem, yet the most important ones. Thrusters are the most crucial parts of the underwater robot actuation. The need for maneuvering precision, for small and fast dynamic positioning, for precise motion and position control and for station keeping made developments of thruster modeling inevitable.

The fundamental difficulty in modeling of a thruster is that axial flow velocity is an unmeasurable state, yet the model depends on that variable. This work addresses this difficulty. It explores the dynamics of in-line pump jet thrusters which are used for underwater robotic actuation. This work uses impeller geometry characterization, fluid flow analysis through impeller blades and through pump jet, thrust modeling and DC motor modeling. The main contribution of this work is incorporation of axial flow velocity into thruster modeling in order to resolve the unmeasurable state problem, thanks to the dynamical properties of impeller geometry and flow conditions through impeller blades.