Extreme sloshing and whipping-induced pressures and structural response in membrane LNG tanks

Abstract

The long-term extreme pressure in the membrane LNG tank and structural response of the Mark III containment system are addressed. The effect of hull slamming-induced vibrations on the vertical acceleration is investigated and found to be important in certain situations. Determining structural response due to sloshing requires a stepwise approach considering long-term variation of the sea state, ship motion in a stochastic seaway, fluid motion in the tanks, pressures acting on the tank structure, structural load effects, and their comparison with the appropriate resistance. This paper is focused on the determination of the critical conditions to limit the number of combinations of sea states, vessel heading, and speed that need to be considered in estimating extreme sloshing pressures. In this context, an approximate method is introduced and validated. These sea states are determined by a full linear long-term analysis. The response quantiles suitable for the contour line approach are also found using simplified criteria. The effect of avoiding heavy weather in vessel operation on sloshing and whipping-induced pressures is investigated. Sloshing experiments and various scaling approaches are described. Application of the generalized Pareto distribution and correctly determining its shape parameter is discussed. Structural response of the LNG membrane tank wall is investigated. The importance of accounting for the steel flexibility in calculating sloshing response is shown. A new method for approximating the time history of sloshing impact pressure is suggested.

A set of canonical problems in sloshing. Part 2: Influence of tank width on impact pressure statistics in regular forced angular motion

“…The analysis is usually based on the collection of impact pressure samples, followed by a fitting using, typically, parameterized distributions (Weibull, Generalized Pareto, etc.) (Graczyk et al, 2007;Fillon et al, 2013). The design pressure values are then obtained by extrapolating the model distribution to specified probability levels, typically associated with specified return periods.…”

“…If the focus is put on to the statistical characterization of sloshing pressures, major contributions are due to Graczyk and Moan (2008) and Graczyk et al (2007) who provided a statistical fitting for long series of sloshing impact pressure recordings aimed at building simplified models of sloshing events load histories for structural finite element analysis.…”

The two-dimensional study of the interaction between liquid loshing and elastic structures

“…For the transportation of the general incompressible inviscid fluid, the RANS equations should be satisfied, which can be found in the general CFD books, such as the literature by Mateusz et al (2007). We deal the free surface with the VOF method as follows:…”

“…(4) Sloshing loads based on experimental results, finite element methods for structure analysis (Mateusz et al, 2007).…”

Toward a Probabilistic Approach to Determine Nominal Values of Tank Sloshing Loads in Structural Design of Liquefied Natural Gas FPSOs

“…Although a comparative assessment can provide a sound basis for certain types of LNGC designs, it offers little flex ibility for new applications: it is difficult to apply to the case of a new LNG tank that does not yet have a large enough database, because its development is based on a previous database on which safety has already been verified. The direct assessment method is based on the measured pressure from model tests, which is then expanded to full scale using Froude's scaling law and applied to the structural assessment in the form of an idealized triangle pres sure shape [14][15][16][17][18][19][20][21][22], As LNG cargo containment systems (LNG CCS) are becoming wider and larger, deterministic-based design procedures are no longer regarded as promising methods for determining sloshing design loads. Efforts have therefore been made to introduce probabilistic-based design procedures.…”