Green Water Phenomena on a Twin-Hull FLNG Concept

Abstract

This paper investigates — based on model tests and potential flow calculations — several phenomena associated with the green water problem in severe sea states. The topics investigated are: the wave characteristics of the severe and steep sea states, the behavior of the vessel in these waves, the relative motions at the bow and the height of water on deck. The green water problem is of interest since many floaters used for the oil and gas production by the offshore industry are permanently moored for typically 20 years or more, and they will experience severe storm conditions with large wave heights. The investigations concern an unusual vessel type: SBM’s innovative midscale Twin-Hull FLNG concept [1]. The floater concept is to join two (standard) LNG carriers together to obtain sufficient storage volume and process deck space. The concept is under development and one aspect, from operability point of view, is the probability for green water. For this purpose a first model test campaign has been carried out. The Twin-Hull FLNG concept has been tested in extreme sea states which are typical for offshore Brazil and East-Africa. Linear potential flow calculations were applied to predict the freeboard exceedance based on relative motion amplitude operators. The correlation to the measured data is discussed. Although the research is dedicated to the Twin-Hull FLNG vessel, the observed phenomena are considered applicable to any stationary vessel in general.