Experimental Investigation of Invar Edge Effect in Membrane LNG Tanks

Sloshing, a violent fluid motion in tanks is of current interest for many branches of the industry, among them gas shipping. Although different methods are commonly combined for analyzing sloshing in liquid natural gas (LNG) carriers, time histories of the pressure in the tanks are most reliably obtained by experiments. Very localized pressures may be important for the structural response of the tank containment system. Moreover, the typical pressure time history duration is similar to the structural natural frequency. Therefore, pressure measurements need to be performed with due account for temporal and spatial distribution. This requires a high sampling resolution both in time and space. Fine spatial resolution becomes especially important when local pressure effects are of interest, such as pressure profile passing a membrane corrugation of Mark III containment or Invar edge of No. 96 containment. In this paper experimental approach applied by MARINTEK for analyzing sloshing phenomenon is presented. The focus is put on investigating effects of Invar edges. A transverse 2D model of a typical LNG carrier is used. Local pressure effects are investigated based on low filling level tests with different wall surfaces: smooth and with horizontal protrusions representing the surface similar to the No. 96 containment system.