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Open AccessArticle

Capturing the Motion of the Free Surface of a Fluid Stored within a Floating Structure

School of Engineering, Institute for Energy Systems, FloWave Ocean Energy Research Facility, The University of Edinburgh, Max Born Crescent, Edinburgh EH9 3BF, UK
Unit of Hydraulic Engineering, University of Innsbruck, Technikerstraße 13, 6020 Innsbruck, Austria
Author to whom correspondence should be addressed.
Water 2019, 11(1), 50;
Received: 6 December 2018 / Revised: 19 December 2018 / Accepted: 22 December 2018 / Published: 29 December 2018
(This article belongs to the Special Issue Advances in Hydraulics and Hydroinformatics)
Large floating structures, such as liquefied natural gas (LNG) ships, are subject to both internal and external fluid forces. The internal fluid forces may also be detrimental to a vessel’s stability and cause excessive loading regimes when sloshing occurs. Whilst it is relatively easy to measure the motion of external free surface with conventional measurement techniques, the sloshing of the internal free surface is more difficult to capture. The location of the internal free surface is normally extrapolated from measuring the pressure acting on the internal walls of the vessel. In order to understand better the loading mechanisms of sloshing internal fluids, a method of capturing the transient inner free surface motion with negligible affect on the response of the fluid or structure is required. In this paper two methods will be demonstrated for this purpose. The first approach uses resistive wave gauges made of copper tape to quantify the water run-up height on the walls of the structure. The second approach extends the conventional use of optical motion tracking to report the position of randomly distributed free floating markers on the internal water surface. The methods simultaneously report the position of the internal free surface with good agreement under static conditions, with absolute variation in the measured water level of around 4 mm. This new combined approach provides a map of the free surface elevation under transient conditions. The experimental error is shown to be acceptable (low mm-range), proving that these experimental techniques are robust free surface tracking methods in a range of situations. View Full-Text
Keywords: free surface measurement; optical motion capturing; tank test; wave gauge; sloshing free surface measurement; optical motion capturing; tank test; wave gauge; sloshing
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Gabl, R.; Steynor, J.; Forehand, D.I.M.; Davey, T.; Bruce, T.; Ingram, D.M. Capturing the Motion of the Free Surface of a Fluid Stored within a Floating Structure. Water 2019, 11, 50.

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