A non-linear pendulum model is developed to represent the motion of a sloshing fluid in real time. The forces imposed by the sloshing fluid are identified using multiphase RANS CFD simulations and subsequently included in the pendulum sloshing model. The pendulum sloshing model was used to simulate sloshing induced by linear and angular motions at and near resonance. Good agreement between the CFD data and the pendulum sloshing model was observed. A blind simulation with multiple surge excitation components is carried out and the pendulum sloshing model agrees with the RANS CFD result. Typically, the computational time of the pendulum is approximately 1/700th of real time.
Sloshing occurs when a tank is partially filled with a fluid and subjected to an external excitation force (Olsen, 1976). Ships with large ballast tanks and liquid bulk cargo carriers, such as very large crude carriers (VLCCs), are at risk of exposure to sloshing loads during their operational life (Rizzuto and Tedeschi, 1997). The inclusion of structural members within the tanks dampens the sloshing liquid sufficiently in all but the most severe cases. However, this approach is not used for Liquefied Natural Gas (LNG) carriers and the accurate calculation of the sloshing loads is an essential element of the LNG tank design process (Bass et al., 1980; Knaggs, 2006). Recent increases in vessel size have renewed interest in methodologies for the simulation of the sloshing loads experienced by the containment system. While the sloshing response depends on the amplitude and frequency of the excitation force, history effects can be of significance as well. Waterhouse (1994) observed the hard and soft spring-type behavior of a sloshing flow. The offset of the response peak from the resonant excitation was found to depend on the tank filling level.
