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A two-dimensional numerical and experimental study of piston and sloshing resonance in moonpools with recess

Published online by Cambridge University Press:  19 August 2019

Senthuran Ravinthrakumar Open the ORCID record for Senthuran Ravinthrakumar [Opens in a new window] ,
Trygve Kristiansen Open the ORCID record for Trygve Kristiansen [Opens in a new window] ,
Bernard Molin Open the ORCID record for Bernard Molin [Opens in a new window]  and
Babak Ommani Open the ORCID record for Babak Ommani [Opens in a new window]
Senthuran Ravinthrakumar*
Affiliation:
Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
Trygve Kristiansen
Affiliation:
Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
Bernard Molin
Affiliation:
Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway Aix-Marseille Université, CNRS, Centrale Marseille, IRPHE, 13013 Marseille, France
Babak Ommani
Affiliation:
SINTEF Ocean, NO-7465 Trondheim, Norway Centre for Autonomous Marine Operations and Systems (AMOS), Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
*
†Email address for correspondence: senthuran.ravinthrakumar@ntnu.no
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Abstract

The piston and first sloshing modes of two-dimensional moonpools with recess are investigated. Dedicated forced heave experiments are carried out. Different recess lengths are tested from $1/4$ to $1/2$ of the length of the moonpool at the mean waterline. A theoretical model to calculate the natural frequencies is developed based on linearized potential flow theory and eigenfunction expansion. Two numerical methods are implemented: a boundary element method (BEM) and a Navier–Stokes solver (CFD). Both the BEM and CFD have linearized free-surface and body-boundary conditions. As expected, the BEM over-predicts the moonpool response significantly, in particular at the first sloshing mode. The CFD is in general able to predict the maximum moonpool response adequately, both at the piston and first sloshing modes. Both numerical methods fail to predict the Duffing-type behaviour at the first sloshing mode, due to the linearized free-surface conditions. The Duffing behaviour is more pronounced for the largest recess. The main source of damping in the proximity of the first sloshing mode is discussed.

Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 877 , 25 October 2019 , pp. 142 - 166
Copyright
© 2019 Cambridge University Press 

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