User's Guide to BModes (Software for Computing Rotating Beam-Coupled Modes)

This guide explains data preparation and execution with BModes, a finite-element code that provides dynamically coupled modes for a beam. The beam can be a rotating or non-rotating rotor blade or a tower, and it can have arbitrary distribution of structural properties and geometry along its length. A coupled mode implies presence of coupled flexural, axial, and torsion motions in a natural modeof vibration. Knowledge of flap-lag-torsion-axial coupled modes is crucial to several applications. Examples are: accurate modeling of major flexible components for modal-based aeroelastic codes such as FAST (Fatigue, Aerodynamics, Structures, and Turbulence), validation of flexible component models using experimental data, modal-based fatigue analysis, and interpretation ofaeroelastic-stability behavior of turbines. Our plan is to eventually integrate BModes with FAST to provide tower and blade modes as rotor speed and blade pitch control settings change during a simulation. This guide provides step-by-step instructions on how to prepare input files (specify blade geometry, section properties, and finite-element discretization), how to execute the code, and how tointerpret the outputs.