Abstract
The limitations of existing wave basins present a significant challenge when modelling offshore deepwater systems, particularly due to the basin’s relatively shallow depth. Numerical simulation thus becomes valuable in predicting its behaviour during operation at sea. The coupled dynamic analysis is preferred over the traditional quasi-static method, as the former enables the inclusion of damping and added mass properties of the complete mooring line system, which becomes increasingly prominent at greater water depths. This paper investigates the motions and mooring line tensions of a turret moored Floating Production Storage Offloading (FPSO) platform using three numerical models, i.e. a dynamic system, quasi-static system and linear spring system subjected to unidirectional random wave condition. Analysis is carried out using a commercial software AQWA. The first two numerical models utilise a complete system of the same setup and configuration, while the linear spring system substitutes the mooring lines with equivalent linear springs and attempts to match the total mooring line restoring forces with that of the coupled dynamic analysis. The study demonstrates the significance of coupled dynamic analysis on the responses of an FPSO in deepwater. The numerical model of the FPSO is validated against the results of a published work.
Highlights
Floating platforms play an important role in the offshore oil and gas industry. Vessels such as the ship-shaped Floating Production Storage Offloading (FPSO) are commonly used in the production of oil and gas in offshore deepwater regions
The results were validated against a published physical test and numerical analysis
The same model was compared with an equivalent quasistatic system and a linear spring system, under unidirectional wave condition
Summary
Floating platforms play an important role in the offshore oil and gas industry. Vessels such as the ship-shaped FPSOs are commonly used in the production of oil and gas in offshore deepwater regions. The mooring lines are commonly modelled using some mechanical means (e.g. springs) at the cut-off section. This approach ignores the dynamic effects of the mooring line and has been proven to yield conservative results. To account for the truncated portion, Stansberg et al [1] combined physical modeling with numerical simulations to assess the viability of passive hybrid model testing for floating structures [1]. The study used a single mooring line to demonstrate the principles of HydeMoor, in which the effect of the lower portion below the cut-off point was simulated using a numerical modeling run on a computer, and applied to the upper physically modeled portion of the line at the truncation point by means of an actuator. The same model is later compared with two statically equivalent numerical simulations, a quasi-static analysis and a linear spring system
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