Finite Element Based Structural Analysis to Build Better Offshore Tower Systems

By girish gs,

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The development of offshore structures has been phenomenal over the last few decades. The key driver for such development is primarily due to the constant urge to explore deep waters due to the ever-increasing oil demands.

The continuous rise in the need of deep water developments and exploitation of shallow water reserves has invoked a new range of offshore structures. These tower systems must withstand extreme wind and wave loading conditions apart from land-based loading conditions. As such their structural integrity is based on multiple factors making its design complex and often time consuming. Measuring the effect of extreme waves and its impact on these structures is of paramount importance and is often done experimentally.

Finite element method is a useful approach in such situations, helping design engineers to identify some of the critical design parameters that require quick attention to overcome excessive stress and deformation that may lead to catastrophic failure. The cost-effectiveness and safety of the offshore structure design is mainly dependent on the response demands in terms of wind and wave loads, bending moment and deformation. The design of these offshore structures is site specific and hence it is crucial to identify loads accordingly to ensure a prolonged useful life of the structure.

Developing a finite element model of tower systems can be improvised by utilizing beam elements for the tower legs. It is however important to determine the amount of accuracy required in the results. In many cases, full solid elements are required to capture stress details accurately.

The hydrodynamic loads are dynamic in nature; however, static pressure loads can be assumed to be used in performing structural analysis. The forces are usually calculated using Morison’s formula and stream function theory. Once the hydrodynamic and wind loads are identified, these forces can be applied on the finite element model. The structural analysis results can be further utilized to calculate local stress development on bolts and bracket supports to determine the periodic inspection intervals more accurately.

Finite element based structural analysis can help in obtaining quick design change information prior to actual application. The virtual simulation allows reducing the design costs significantly, while also reducing the prototyping trials needed. The cost of repetitive maintenance can be lowered by designing towers with a prolonged life.

Although, experimental validations are to be treated as a gold standard for any design change, the reduction in prototype test trials make finite element analysis a blessing in disguise for an industry that is constantly striving to explore deep waters for oil reserves.


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