Dynamic Property of a Floating Multi-Body System for Dual Barge Float-Over Operation With a Mechanical TLS (Topside Lifting System)

Abstract

Abstract TLS (Topsides Lifting System) utilization is a modern fast lifting technology developed for offshore platform installation. The positive prospects have seen from its sound and efficient performance at the offshore operation. To improve the feasibility of dual barge float-over operations, two new individual barges are designed in application with TLS. The targeting TLS system is equipped with motion compensation system that consists of several sets of lifting beams. Because the flexible mechanical couplings and the hydrodynamic interactions between bodies, the dynamic characteristics of system will be more complex. Some of the eigen modes might be excited by wave loads and could potentially lead to large responses. To demonstrate the dynamic properties of the new operation mode, a mechanical and hydrodynamic coupled multi-body model is established. Each lifting beam is modeled as a rigid body with X and Y degree of freedom relative to the barge. The motion compensation system is considered with a passive mode, and a spring-damper model is used to simulate its property. The coupled hydrodynamic forces of two barges are analyzed first. The eigen value analysis is conducted to identify the natural periods and eigen modes of the coupled multi-body system. A strong coupling of roll and sway motions of barge, and the heave motion of topside is observed. The sensitivity study about the parameters of lifting beams for system natural periods are carried out. The motions of barges and topside and the global dynamic loads acting on topside in regular waves are also presented. The results indicate that the heave motions decrease but the roll and pitch motions increase at their natural frequency compared with motions of the rigid connected system. The global dynamic loads acting on topside are decreased. The analyzed dynamic properties provide an initial cognition reference of the new operation system and help with the system design especially for TLS.