Experiences on the modelling and identification of the heave motion of an open-frame UUV

Experiences in heave motion modelling and identification of ROMEO, the latest open-frame unmanned underwater vehicle (UUV) developed at CNR-IAN are reported. The use of a vehicle's dynamic model in the heave direction can easily increase the performance of the depth motion estimator and control during typical UUV applications as bottom or ice-canopy following. Standard system identification techniques are adopted to select and identify a simplified dynamic model on the basis of experimental data acquired by inboard navigation sensors. Results suggest that in common operational conditions heave momentum drag force components arising from thrusters operating in the horizontal plane can be modelled by standard linear and quadratic heave drag coefficients. It is also shown that propeller-hull interactions in the same conditions are not negligible.