Underwater vehicle control and estimation in nonuniform currents

While ocean and atmospheric vehicles often operate in time-varying, nonuniform currents, the effects of flow accelerations on vehicle dynamics are typically ignored in motion models used for control and estimation. Vehicle dynamics are either ignored entirely (the kinematic particle model), the vehicle is treated as a point mass (the dynamic particle or “performance” model), or the flow is assumed to be uniform. As applications for autonomous ocean and atmospheric vehicles expand into more constrained, dynamic environments, such as shallow water or urban airspace, the benefits of using more precise motion models for control and estimation become more compelling. Forces and moments due to flow gradients are strongest when apparent mass effects are important and flight paths are most sensitive to these disturbances when flow-relative velocities are small. The paper presents a dynamic model for a streamlined underwater vehicle in a nonuniform flow. To illustrate the utility of the full dynamic model, open- and closed-loop numerical motion predictions are compared with those of simpler models for a variety of nonuniform flow fields. We also demonstrate the application of the full dynamic model for flow estimation using an observer.