Sesam software to design floating offshore wind foundations
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Supporting the development of floating offshore wind turbine foundations
Floating offshore wind foundation structural design
Sesam software for FOWT design and analysis is based on decades of experience in engineering of offshore structures. It provides a tailor-made solution for structural strength analysis of floating offshore wind support structures, such as wind turbine semisubmersibles, spar buoys, barges and substations. It can be used for conceptual and detailed design of the primary structure, as well as for the structural design of cables, mooring lines and secondary steel. Besides this, Sesam can perform other lifecycle analyses such as transportation, lifting, and corrosion protection. Sesam also supports the structural design of fixed offshore wind foundations.
Sesam offers analysis methodologies in both frequency and time domain. The frequency domain method is very fast to use and is the standard industry method for offshore floaters. It has been used for decades and in Sesam engineers can check for plate ULS (DNV-RP-C201), member ULS (ISO, API, Norsok), plate and member fatigue (DNV-RP-C203) as well as to find the envelope of stresses or other structural responses. For FOWT it can be used for conceptual studies where the coupled effects from the wind turbine often can be ignored.
For early and detailed design, it is more common to use a time domain coupled analysis to cover the non-linear interactions between the floater, the turbine and the mooring and cable arrangement. A coupled analysis process includes the use of a non-linear time domain solver where the turbine and mooring/cables lines are modelled in detail and the hull is represented as a rigid body with stiffness, damping and hydrodynamic coefficients. This often leads to many Design Load Cases where each will typically represent a 3 hour simulation with 0.1 – 0.2 second time step. Because of this, Sesam supports cloud computations in addition to desktop for faster analysis. Sesam is fully integrated with Bladed and Sima for the coupled analysis. The results from coupled analysis are converted to pressure loads on the hull (inclusive of the time series loads from the turbine) for structural analysis and subsequent fatigue analysis. Finally, the fatigue results (screening and multidirectional hot-spot according to DNV-RP-C203) can be viewed graphically and tabular.
Sesam comes with a pre-defined workflow for doing time domain fatigue analysis of FOWT, see below. It is also possible to make your own workflows where the load reconstruction is based on other data than Sima and Bladed.
Floating wind turbine design
For floating wind turbine design, Sesam provides state of the art numerical tools for simulations of floating offshore wind turbines through the module Sima. Sima can perform a fully coupled analysis where the effects of wind, waves and current are combined with the effects of the wind turbine and the dynamic effects due to elastic response of slender structural members like the rotor blades, the tower, and the mooring lines.
If the structure is modelled by slender members only and the loads can be computed by Morison's equation, Sima will be a self-contained complete solution. For more general cases hydrodynamic coefficients can be computed up-front by the hydrodynamic analysis tool, HydroD, and the results from the coupled analysis can be read back into the general Sesam for floating structures solution for a full-fledged structural analysis of any type of floater including the coupling effects from the wind turbine.
Sima can also handle marine operations, which means that it will cover all phases in the life cycle of the floating offshore wind turbine, i.e. towing, installation, in-place and decommissioning. Transportation on a barge or heavy-lift vessel can be analyzed by Sesam for floating structures.
More detailed information about SIMA can be found at SINTEF.
Sesam also supports:
- Substations (monopiles, jackets, floating)
- Jack-up vessels
- Crew transport vessels (CTV)
- Service operation vessels (SOV)
- Marine operations (installation, lifting turbine parts, towing floating wind turbine)