Large scale LNG Sloshing Model Tests

The motion of the LNG fluid inside gas carriers is normally restricted by the loading condition of the vessel, i.e. the vessel is operated at either near empty condition or at fully loaded condition. In this way, the resonance or sloshing effects of the fluid on the ship’s hull are limited. However, nowadays the LNG carriers are considered to be operating at intermediate loading conditions as well. Subsequently they will be sailing with partially filled LNG tanks. In this condition the LNG fluid is more likely to be induced into resonance due to wave action and roll motions. This resonance or sloshing behavior of the LNG fluid will lead to high-impact pressures on the thermally insolated ship’s hull. Due to the different physical properties of the LNG fluid with respect to water in terms of density and viscosity, little is known of the behavior of the LNG fluid in resonance condition. Day-to-day practice in retrieving sloshing loading data is based on relatively small-scale model tests, e.g. 1:20 or 1:30. A disadvantage here is that, because any air pressure effects are not modeled, hydroelastic phenomena cannot be modeled at this scale. A way around this is to reduce the ambient air pressure when running scaled model tests. This by itself is not trivial to do. In this paper, however, we will describe a study of model test experiments on a large scale 2-dimensional section (scale 1:10) of an LNG carrier in various loading conditions without depressurization. Using high-speed video observations the wave front formed by the bore of the LNG in resonance is related to measured impacts on the tank hull. Also measured is loading on a hydroelastic panel as part of the hull, with the correctly scaled structural properties. Significant influence of the stiffness on the pressure pulse was observed.

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