Sloshing and scaling - results from the Sloshel project

At the turn of 2007 full scale wave impact tests have been carried out by MARIN in the frame of the Sloshel project. Unidirectional breaking waves were generated in a flume in order to impact an instrumented transverse wall with embedded test structures. The main goals of these tests were to study the hydro-elastic effects associated with the NO96 membrane containment system for LNG carriers and to create a sound database for validation of numerical simulations. The preliminary results were overviewed in 2009 by Brosset et al. Since then the full scale tests have been repeated at scale 1 to 6 in order to study the scaling effects. These tests are referred to as the large scale tests. The large scale test set-up mimicked as far as possible the full scale setup. At both scales the instrumentation consisted of multiple pressure sensors, accelerometers and load cells. Special attention was paid to observe the shapes of the breaking waves while impacting. This was obtained by optical sensors at full scale and high speed cameras at large scale, both synchronized with the data acquisition systems. These recordings provided insight in the sloshing physics and enabled to determine characteristic quantities like the amount of entrapped air for air pocket impacts and the corresponding oscillation frequencies. In order to compare deterministically measured impact pressures at both scales a similarity must be ensured on the global flow from the wave paddle to the instant just before the first contact with the wall. Such a similarity has not been achieved. Reasons for that are analysed and recommendations for further tests at full scale are given. Nevertheless a comparison is proposed restrained to global parameters describing gas pocket impacts like pressure within the gas pocket, frequency of the oscillations when compressed and damping coefficient of these oscillations.

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