Nonlinear dynamic analysis of float-over deck installation for a GBS platform based on a constant parameter time domain model

Abstract Float-over deck installation has become a reliable and cost-effective method of installing heavy integrated decks for various types of offshore platforms, such as the jacket and GBS platforms. This operation involves a number of inherent complexities such as the strong nonlinear interactions between the multi-body system and environment. Therefore, dynamic modelling of the float-over system during the deck load transfer stage is a challenging task. Particularly, the wave-induced impacts among the deck, barge and platform substructure may generate strong nonlinear dynamics that cannot be accurately investigated by the current standard simulation packages. This study develops a constant parameter time domain model (CPTDM) based on Cummins equation and state-space model for analysing the nonlinear dynamics arising from the float-over deck installation of a GBS platform. Frequency domain hydrodynamic analyses of the installation barge carrying the deck with and without the presence of the GBS are both carried to identify hydrodynamic interactions. A code-to-code verification is performed to verify the accuracy and efficiency of the developed CPTDM by comparing the present results with ANSYS-AQWA. Based on the verified model, the nonlinear dynamics of the GBS platform at different load transfer stages are investigated by using Poincare maps, bifurcation diagrams and phase trajectories.