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This guide explains data preparation and execution with BModes, a finite-element code that provides dynamically coupled modes for a beam. All results, presented in terms of frequencies and mode shapes, show excellent agreement. BModes-computed modes for all models are compared with analytical modes, if possible to obtain, and with modes generated by RCAS.
#Beam element orcaflex verification
Verification begins with simple uniform beams, rotating and non-rotating, and progresses to realistic blades. This paper presents verification of the blade modal analysis capability of BModes. Examples are: modeling of major flexible components for modal-based aeroelastic codes such as FAST, validation of turbine models using experimental data, modal-based fatigue analysis, and understanding of aeroelastic-stability behavior of turbines. Coupled more » modes (implying coupling of flap, lag, axial, and torsion motions) have several applications. Allowable supports for the tower include tension wires, floating platforms, and shallow-water monopiles with elastic foundation. Examples of tip attachments are aerodynamic brakes for blades and nacelle-rotor subassemblies for towers. Both the blade and the tower allow a tip attachment, which is modeled as a rigid body with mass, six moments of inertia, and a mass centroid that may be offset from the blade or tower axis. = ,īModes is a finite-element code we developed to provide coupled modes for flexible blades, rotating or non-rotating, and for towers, onshore or offshore (supported either on floating platforms or on monopile foundations). All results in general show excellent agreement. Finally, we verified a model of a blade carrying tip mass and rotating at different speeds(verifications of other blade models, rotating or non-rotating, have been reported in another paper.) Verifications were performed by comparing BModes-generated modes with analytical results, if available, or with MSC.ADAMS results. For the monopole-supported tower, we accounted for distributed more » hydrodynamic mass on the submerged part of the tower and for distributed foundation stiffness. For the floating turbine, we accounted for the effects of hydrodynamic inertia, hydrostatic restoring, and mooring lines stiffness. Verification studies began with uniform tower models, with and without tip inertia, and progressed torealistic towers. These are also required for validation of turbine models using experimental data, modal-based fatigue analysis, controls design, and understanding aeroelastic-stability behavior of turbines. Coupled modes (implying coupling of flap, lag, axial, and torsional motions) arerequired for modeling major flexible components in a modal-based, aeroelastic code such as FAST1. BModes modeling allows for tower supports including tension wires, floating platforms, and monopiles on elastic foundations. Examples of tip attachments are aerodynamic brakes for blades and nacelle-rotor subassembly for towers. Both blade and tower models allow a tip attachment, which is assumed to be rigid body with sixmoments of inertia, and a mass centroid that may be offset from the blade or tower axis.
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The blades, which may be rotating or non-rotating, and the towers, whether onshore or offshore, are modeled using specialized 15-dof beam finite elements. This paper describes verification of BModes, a finite-element code developed to provide coupled modes for the blades and tower of a wind turbine.