BModes is a finite-element code that provides dynamically coupled modes for a beam.  The beam can be a rotor blade, rotating or non-rotating, or a tower.  Both the blade and the tower can have a tip attachment. The tip attachment is assumed to be rigid body with mass, six moments of inertia, and a mass centroid that may be offset from the blade or tower axis. Examples of tip attachments are aerodynamic brakes for blades and nacelle-rotor subassemblies for towers. In addition to the tip inertia, the tower can also have tension-wire supports. Both the tip inertias and tension support wires can substantially influence the coupled modes mentioned earlier, especially for a tower.

Wind turbine designers may use coupled modes for several applications such as modal-based modeling of blades and tower for (FAST uses this approach), validation of flexible-component models using experimental data, modal-based fatigue analysis, and interpretation of aeroelastic-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.

BModes requires specification of rotor speed, blade geometry, precone, pitch control setting, and structural properties distribution along the blade as inputs.  These properties may be obtained from experimental tests, blade manufacturer, or a properties-extractor code, such as PreComp or BPE.  The current version of BModes can handle only metallic or isotropic composite blades.

The code and downloadable draft user's guide assume the user has basic familiarity with coupled modes.  Please note that due to budgetary and time constraints, the code has not yet been fully commented or documented.  Therefore, we will not be able to entertain any questions on the source code.  However, questions on the code usage or the guide may be directed to Gunjit Bir. Following upgrades of BModes to handle additional boundary conditions, we will put a final edited version of user's guide on this website.

You may download the following files from our server:

• BModes Change Log (v3.00.00, 2 KB, 20-March-2008)

  This is a list of changes made to the code.  Look at this text file to see if we've made worthwhile changes since you received your previous version of BModes.

• BModes User's Guide (v1.03, 178 KB, 27-September-2007)

  This is a draft of the BModes User's Guide.  Please refer to it when trying to understand how the program works.

• BModes Archive (v3.00.00, 675 KB, 20-March-2008)

  This is a self-extracting archive of BModes.  It contains the BModes executable file, sample input files, installation-verification test procedure, change log, and user's guide.  It runs on all 32-bit Windows® platforms.  We created the executable file with Intel Visual Fortran® v10.0.3718.2003.

If you want to refer to the BModes website in a report, here is a reference you can use:

NWTC Design Codes (BModes by Gunjit Bir).  http://wind.nrel.gov/designcodes/preprocessors/bmodes/.  Last modified 20-March-2008; accessed 20-March-2008.