Sloshing Response of LNG Tank

Abstract

Static and dynamic stress analyses of Mark III insulation system for LNG containment considering sloshing impact pressures have been carried out. Various time and spatial characteristics of the loading was considered. A direct implicit time integration method was used for the dynamic analysis. Two structural models were applied, one in which the steel structure was modeled with a realistic flexibility and one in which the insulation was supported on a rigid foundation. The main focus was on the vertical stresses in the lower fiber of R-PUF, bottom plywood and mastic ropes. It was found that the static stress level of the lower part of the Mark III system based on the rigid steel plate support differed from one that based on the flexible steel plate support. The static stress level of the lower part of the Mark III system supported by a flexible steel structure varied and was higher above the stiffeners and less over the middle part of the plate. The largest natural period is about 1.5–8 milliseconds and, based upon the experimental results, the sloshing pressure is approximated by triangular function in time, with a characteristic duration of a few milliseconds. The effects of sloshing impact rise time and load patch on the maximum dynamic stress level of the lower part of the Mark III system based on the rigid and flexible steel plate support have been investigated. The results are presented in the form of the dynamic amplification factor. For impulse type sloshing pressures relative to the steel plate, the steel plate behaves as a rigid support, resulting in vertical responses that exhibit a limited variation over the area.