Vehicle Dynamics in Currents

Vehicles operating in non-uniform flow fields are subject to forces and moments that are not captured by kinematic motion models. These effects are even greater when the mass of the displaced fluid is commensurate with the mass of the vehicle, as is the case for maritime vehicles and airships. Following along the lines of a recent paper by Thomasson, this report presents a dynamic model for the motion of a rigid vehicle in a non-uniform flow. The flow field is assumed to be irrotational, comprising a steady, non-uniform component and an unsteady, uniform component. As Thomasson suggests, rotational flow effects can be incorporated by modifying the vehicle's angular rate when computing viscous forces and moments. These equations have a variety of applications for modeling, simulation, and design, a few of which are listed at the end of the report.