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hGAST

hGAST is a hydro-servo-aeroelastic code developed at the National Technical University of Athens. It is a multibody finite element method code. Timoshenko beam elements are used for the wind turbine components (blades, shaft, tower and monopile or jacket) and truss elements (only subjected to axial loading) for the mooring lines. The aerodynamic loads are estimated either using the Blade; Element Momentum theory or the free wake vortex code GenUVP, both applying the ONERA dynamic stall model. The hydrodynamic loading for bottom mounted support structures is exclusively based on Morison's equation. In case of floating wind turbines is based either on Morison's equation or on the linear potential theory, including the modeling of the quadratic difference loads through Newman's approximation method and the viscous drag term from the Morison's equation. The loading on the dynamic mooring line model accounts for inertial, gravitational and hydrodynamic loading based on Morison's equation. Any controller can be externally loaded, while a standard built-in variable speed / variable pitch controller is also available.

Latest version

hGAST v1

Submitted by Marinos Manolesos on August 26, 2015 - 5:47pm
Main hypothesis
hGAST is an advanced, nonlinear hydro-servo-aero-elastic simulator for WTs. It performs time domain simulations, modal analysis as well as stability analysis. The structure (blades, shaft, tower and support structure) is divided into a number of interconnected bodies and sub-bodies based on the multi-body formulation. Each deformable body is modeled as a Timoshenko beam subjected to combined bending in 2 directions including shear, torsion and extension and solved using the FEM. A dynamic mooring line model defines the mooring contribution based on nonlinear, co-rotational truss elements following the FEM context. The floater is either modeled as a rigid body or as a multi-membered FEM structure. The aerodynamic loads are estimated either using the standard BEM method including corrections and add-on's or the 3D free wake vortex particle method GenUVP. Both methods apply the ONERA dynamic stall model. The hydrodynamic loads are estimated either using potential theory (linear and Newman's approximation) or Morison's equation.
Software
Solver
hGAST
License
Structural dynamics
Turbine
Platform
Aerodynamics
Mooring lines
Structural dynamics
Added mass coefficient
accounted for using Morison's equation
Normal drag coefficient
accounted for using Morison's equation
Tangential drag coefficient
accounted for
Seabed contact model
using stiffness and damping terms
Seabed-line friction model
not included at the moment
Wave kinematics
Wave theory
Airy theory for regular and irregular waves or stream function theory
Free surface correction
Wheeler Stretching method, applied in the Airy wave theory
Wave spectrum
Jonswap, Pierson-Moskowitz or any other user defined
Hydrodynamics
References

Manolas, D., Development of simulation tools for the integrated analysis of offshore wind turbines. PhD Thesis, NTUA, Athens,  2015

Voutsinas, S.G., Vortex methods in aeronautics: how to make things work. International Journal of Computational Fluid Dynamics, 2006. 20(1): p. 3-18.

Riziotis, V. and S. Voutsinas. GAST: A general aerodynamic and structural prediction tool for wind turbines. in EWEC CONFERENCE. 1997. Dublin Castle, Ireland

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