Vehicle Motion in Currents

Abstract

In this paper, we present a nonlinear dynamic model for the motion of a rigid vehicle in a dense fluid flow that comprises a steady, nonuniform component and an unsteady, uniform component. In developing the basic equations, the nonuniform flow is assumed to be inviscid, but containing initial vorticity; further rotational flow effects may then be incorporated by modifying the angular rate used in the viscous force and moment model. The equations capture important flow-related forces and moments that are absent in simpler models. The dynamic equations are presented in terms of both the vehicle's inertial motion and its flow-relative motion. Model predictions are compared with exact analytical solutions for simple flows. Applications of the motion model include controller and observer design, stability analysis, and simulation of nonlinear vehicle dynamics in nonuniform flows. As illustrations, we use the model to analyze the motion of a cylinder in a plane laminar jet, a spherical Lagrangian drifter, and a slender underwater vehicle. For this last example, we compare predictions of the given model with those of simpler models and we demonstrate its use for flow gradient estimation. The results are applicable to not only underwater vehicles, but also to air vehicles of low relative density such as airships and ultralights.

Autonomous Underwater Vehicle Model-Based High-Gain Observer for Ocean Current Estimation

“…Referring to [14] and [15], the dynamic equations of an AUV in currents can be derived in terms of the flow-relative velocity as shown in Equation 5, and the explanation of these terms is not elaborated here for reasons of brevity.…”

Autonomous boat dynamics: How far away is simulation from the high sea?

“…This throws doubts on the simulated results. The presented simulation intends to provide the first steps towards a more realistic representation of the boat dynamic behaviour [6]. However, the damping coefficients, added masses, and disturbance force function adopted in the present study are speculative with the aim to illustrate the simplified modelling approach rather than any quantitative judgement.…”

Dynamical Analysis of Autonomous Underwater Glider Formation with Environmental Uncertainties

“…The Kane's equation is used to study the dynamic characteristics of the multibody system, which is 0, 1, 2, , 3N l l F F l (10) where F l is the generalized active force and l F is the generalized inertia force. The generalized force is calculated by the force associated with the generalized coordinate q l (l=1,2,…, 3N) and can be written as:…”

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