The Prediction of Sloshing Pressure in Prismatic Tanks of LNG Carriers (eBook)

Published Date

January 1984

The Prediction of Sloshing Pressure in Prismatic Tanks of LNG Carriers (eBook)

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This study looked for a correlation factor between impact pressures in model tests and in actual ships and tried to verify that specific membrane configurations are free from sloshing problems. (16pp)

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Some membrane type LNG carriers are free from sloshing problems, while others suffer from them. Liquid motion depends greatly upon the shape of the cargo tank, the filling ratio, the amplitude of the ship's motion and the relation between the period of ship motion and the natural period of liquid motion in the cargo tank. It is described in reference 8 that the impact pressure load resulting from this liquid motion differs greatly between the types of membrane system. Furthermore, it is well known that impact pressure acting upon the tank's cargo ceiling corner parts in fully loaded conditions varies widely in its value, even in the case of a tank oscillating regularly. So far, many model experiments have been done to investigate the effects of sloshing loads. However, almost all of the experiments were conducted on the basis of regular oscillation testing. Therefore, when estimates are made for ships in actual service from the results of these tests, many problems arise because such ships are usually in irregular motion. It is necessary to conduct tests by exciting models irregularly, similar to ships in service, to ensure a more practical sloshing load and especially to obtain the maximum value of impact pressure.

Test results are converted into the equivalent values of ships in actual service, applying the main laws of similarity. However, such values must be further modified by inroducing the empirical correlation factor, because we cannot simulate everything in the model tests. For this purpose, we conducted a series of simulation tests of accidents involving damage to a ship in order to find the empirical correlation factor which connects the result obtained from the experiments and the already known strength of the damaged part, on the assumption that both the result and the actual strenth are equal. Establishing the empirical correlation factor, in order to ascertain the security involved in the sloshing of a 130 000 m3 LNG carrier, we performed a series of irregular oscillation tests and tried to predict statistically the highest sloshing load on the conservative assumption that the ship concerned was running in the North Atlantic Ocean at a constant speed (18–9 knots) for 20 years continuously without stopping.

As a result of our sloshing study, we conclude that the membrane type LNG carrier with large upper chamfers and corrugated membranes is completely free from sloshing problems

Paper delivered by:
T. Tanaka
N. Umekawa (Nippon Kokan KK)

Prepared for:
Gastech Amsterdam 1984

Title: The Prediction of Sloshing Pressure in Prismatic Tanks of LNG Carriers (eBook)
Product Code: 4433g162
Published Date: January 1984

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