Publication Detail

Numerical Predictions of the Relative Motion of a SWATH ASV and an AUV in Waves. A True Step Forward Towards Accurate L&R Simulations

Stefano Brizzolara, Chrys Chryssostomidis
2014
10 pp.
MITSG 14-33
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Two editions ago (ASNE L&R 2012) we presented at the ASNE L&R conference the design of an Autonomous Surface Vessel (ASV) for Launch and Recovery of Autonomous Underwater Vehicles (AUVs) in rough sea states. The vessel is the missing link for an effective realization of a network of underwater autonomous vehicles to persistently monitoring a sea; in fact, the unmanned surface vehicle is designed to assist (recharging, downloading data and reprogramming), deploy and recover medium size AUVs directly in the field of operation. The vessel design is based on an unconventional Small Waterplane Area Twin Hull (SWATH) with a particular shape which has been optimized to reduce the resistance (and hence propulsion power) at maximum speed.

Some preliminary predictions of the motions in waves were given in that occasion as obtained from a new CFD model based on the solution of the fully viscous unsteady free surface flow around the vessel in regular waves. The computational method is inherently non-linear, overcoming limitations present in most of the traditional linear seakeeping codes based on inviscid flow theory. In that occasion we demonstrated the superior performance of the
SWATH ASV with respect to a tradition catamaran in terms of reduced heave and pitch motions. In this new proposed paper, we adapt the numerical method to consider multiple rigid bodies and the their mutual unsteady hydrodynamic interference effects, as in this case where the underwater vehicle when it is placed inside the two underwater hulls of the SWATH vessel (see Figure 1). We will show the difference of the motion predictions obtained with the new fully non-linear viscous methods versus more traditional potential flow based linear theories. Unfortunately these last theories are still widely used to predict the capabilities of L&R of underwater vehicles from surface crafts in a sea state. We will show the limitations and the level of approximation of these low fidelity methods versus the new one. The analysis of the results of the simulations of the relative motions in different wave lengths and amplitudes will serve also to devise the best recovery system to be used in the autonomous vessel and a series of criteria for delimiting the capabilities of the ASV L&R in rough seas.

type: Presentations

Parent Project

Project No.: 2013-RU-022-LEV
Title: Underway Wireless Recharging of AUVs

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