In the present paper, a new fully coupled simulator based on DeepLines™ software is described in order to address floating wind turbines dynamic simulation. It allows its user to take into account either separately or together the hydrodynamic and aerodynamic effects on one or several floating wind turbines. This simulator includes a non linear beam finite elements formulation to model the structural components — blades, tower, drivetrain, mooring lines and umbilicals — for both HAWT and VAWT layouts and advanced hydrodynamic capabilities to define all kinds of floating units and complex environmental loadings. The floating supports are defined with complete hydrodynamic databases computed with a seakeeping program. The aerodynamic loads acting on the turbine rotor are dynamically computed by an external aerodynamic library, which first release includes BEM (blade element moment for HAWTs) and SSM (single streamtube method for VAWTs) methods. The integration in time is performed with an implicit Newmark integration scheme.
The accurate modeling of offshore flexible risers behaviour remains a great challenge because of (i) their complex internal structure, (ii) the variable nature of the loads along the pipe (tension, curvature, internal and external pressures), (iii) and the interactions with structures used to limit the pipe curvature. Technip and IFP have been codeveloping for many years models dedicated to stresses calculation in the armour wires, to assess the flexible lifetime. These models must account for a large number of potential inner contacts (contacts between upper and lower layers, lateral contacts between adjacent armour wires in the same layer) as well as external contacts (bend stiffener, arch, bellmouth or other curvature limitation setup). The paper presents a comparison between 3 models with different level of complexity and realism. The first one is a in house model, whereas the two others were developed on the basis of the commercial FE code Abaqus. The first model, Life6, is based on some simplified assumptions in particular the fact that periodic solutions are assumed (given constant curvature in the pipe) and uses analytical solutions of equilibrium of wires on a torus (the bend pipe). The effect of non uniform curvature (in particular end-fitting proximity) is not considered in this model. The second model, namely 3D/Periodic model, is still based on a periodic assumption, but can cope with severe loadings (such as large curvature of the pipe or compression) leading to specific wires contact interactions. Abaqus Standard (Implicit scheme) is used. The third model, called 3D/Explicit model, is a full length model, as it includes end fittings effects, outer structure (like stiffener) interactions and any curvatures variations along the pipe. All contacts interactions are considered. The number of DOFs involved in the analysis requires the use of an explicit integration scheme (Abaqus Explicit) running on a parallel platform. These models are cross validated on a dedicated case study that consisted of a pressurized pipe cyclically bent with constant curvature. The validation of the model results is very satisfying even when lateral contacts between wires occur. Finally, a comparison of the 3D/Explicit model results with experimental data is presented. This model provides a very good estimation of the flexible behavior and of the end fitting effects.
The paper focuses on a Finite Element (FE) model developed at IFPEN, denominated 3D-Periodic, which is dedicated to flexible riser studies. It takes full advantage of the geometric and loading periodicities to reduce the model length and the CPU cost. The model is developed in a commercial FE software with dedicated pre- and post-treatment packages. The model can represent standard cyclic bending with internal pressure and axial tension as well as external pressures load cases to investigate the risk of lateral buckling of tensile armors or of pipe collapse.
The present paper describes the validation and the modeling capabilities of a new fully coupled floating wind turbine simulator based on DeepLines™ software. A first validation, based on code comparison with NREL-FAST software, is presented and shows very good correlation on a rigidly founded 5MW wind turbine in various wind conditions despite the different modeling techniques and assumptions of the two softwares. This benchmark, in addition to the extensive validation on various offshore projects, makes us confident on DeepLines capabilities to assess founded and floating wind turbine behaviour in a complex offshore environment. Furthermore, some simulation results on jacket and floating founded wind turbines, defined in the frame of IEA OC4 project, are presented and highlight the versatility of our simulator to perform offshore and floating wind turbine optimal design.
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