Design Wave Based Verification of Global Strength on an Unconventional FLNG Design

摘要

One proposal FLNG uses tri-lobe tanks to store the LNG. This tank is supported by two cradles. Between the cradle and the tank loads are only transferred by the parts in contact. The contact area changes due to loading of the LNG tank, motions and deformation of the vessel. This paper gives an overview of the challenges in structural analysis resulting from this non-linear behavior and how to resolve them without loss of fidelity of the solution. For spectral analysis the contact is to be linearized for the calculation of the stress RAOs and the response conditioned design waves. In performing the final structural analysis where loads from the hydrodynamic analysis are used, the contact problem is to be included. This results in an impractical processing time on one computer when considering all load cases. A superelement solution reduces the size of the model involved in the contact problem which for multiple solutions gives shorter wall times. However, these wall times are still impractical. The comparison of the linearized model and the model containing the contact shows that the effect of the non-linear contact is localized. This opens the way for a staggered approach. The linearized model is used for a brute force evaluation of the structure taking all possible relevant time instances into account. A local model, one compartment with two tanks including the contact problem, is used to determine the stresses using loads and boundary displacements from the global linearized model.