Abstract
A study about the effect of different configurations of stationary and movable appendages on the dynamic stability of an autonomous underwater vehicle (AUV) is presented. A new stability index that can be used to assess dynamic stability in the vertical plane is derived. It improves upon the vertical plane stability index by accurately accounting for the contribution of hydrostatic forces to dynamic stability, even at low speeds. The use of the new stability index is illustrated by applying it to a set of AUV configurations based on an AUV initially designed at Virginia Tech and built by Dive Technologies. The applicability of this index depends on the speed of the craft. The range of applicability in terms of speed is presented for the DIVE craft as an example. The baseline design of the DIVE craft has asymmetry in the vertical plane and symmetry in the horizontal plane. A virtual planar motion mechanism (VPMM) is used to obtain the hydrodynamic coefficients of the hull. Design iterations are performed on the baseline design by varying the appendages in shape and size, adding appendages and adding features on appendages. The best and the baseline design from this effort are incorporated in a 6 DOF lumped-parameter model (LPM) to compare results of a straight line maneuver. A computational fluid dynamic (CFD) tool is used to obtain the trajectory comparison of turn-circle maneuver for these two designs. A principal conclusion is the important contribution of a hydrostatic restoring force at low-moderate speeds by using GVgrav and the influence of design of control surfaces, both stationary and non-stationary, in the achievement of control-fixed course stability.
Highlights
The design of an autonomous underwater vehicle (AUV) and its control surfaces have an important role to play in the maneuverability and stability of a craft
We explore the definition of stability using hydrodynamic derivatives to include the effect of gravity
We investigate the increase in hydrodynamic stability with design changes
Summary
The design of an AUV and its control surfaces have an important role to play in the maneuverability and stability of a craft. Lambert [3] investigated the effect of change in first order stability derivatives on the dynamic behavior of a torpedo hull. The stability inequality derived in Lambert [3] is similar to the dynamic stability defined in Section 4.2 of in Lewis et al [4], and both do not address the effect of gravity. On assessing the stability of a family of vessel shapes by developing a new vertical plane coefficient that accurately accounts for the effects of hydrostatic forces. The primary aim is to demonstrate an increase in the stability of the craft in the vertical plane, calculate the corresponding stability index, and show that the change in stability is validated upon implementation in LPM and/or CFD. Our analysis highlights the importance of accounting for hydrostatic force when assessing stability at low to moderate speeds
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