PreComp is a code that provides span-variant structural properties for composite blades.  These properties include cross-coupled stiffness properties, inertia properties, and offsets of the blade shear center, tension center, and center of mass with respect to the blade pitch axis.  Analysts need these properties to properly model the major flexible components of a wind turbine—blades, tower, and drivetrain shaft.  Almost every aeroelastic code (FAST, ADAMS, BLADED, etc.) requires these properties as inputs.  Designers need these properties to rapidly evaluate alternate composite layouts and their effects on blade properties and material strains.

Salient features of PreComp are accurate computation of blade torsion stiffness and cross-stiffness properties.  The cross-stiffness properties (flap-torsion, lag-torsion, flap-lag, axial-torsion, flap-axial, and lag-axial stiffness) arise if an anisotropic (unbalanced) layup of composite laminates is used.  These properties couple flap, lag, axial, and torsion motions of the blade and can substantially influence the turbine performance, loads, and aeroelastic stability.  Accurate estimates of cross-stiffness properties are of interest to the wind industry members who tailor composites to mitigate turbine loads and enhance performance.  Computation of torsion stiffness and cross-stiffness properties can be tricky even with 3-D finite element approaches.  We therefore merged a modified classic laminate theory with a shear-flow approach to reliably compute these properties.

PreComp requires description of blade external shape and the internal layup of composite laminates as inputs.  The external shape is specified in terms of the chord, twist, and airfoil geometry variation along the blade.  The internal structural layup is specified in terms of the laminates schedule, orientation of fibers in each laminate, and the laminate constituent properties.  The code allows for a general layup of composite laminates, both spanwise and chordwise, and an arbitrary number of webs.

The code and downloadable draft user's guide assume the user has a modest knowledge of composites and laminates schedule typically used in blades. 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.

Please note that there is a bug in the program; we will sort it out as soon we get time. Meanwhile, use caution—make sure results make physical sense. Report any problems.

You may download the following files from our server:

• PreComp Change Log (v1.00.02, 1 KB, 26-March-2007)

  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 PreComp.

• PreComp User's Guide (v1.01, 383 KB, 04-August-2006)

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

• PreComp Archive (v1.00.02, 621 KB, 26-March-2007)

  This is a self-extracting archive of PreComp.  It contains the PreComp 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 Compaq Visual Fortran® v6.6.0.

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

NWTC Design Codes (PreComp by Gunjit Bir).  http://wind.nrel.gov/designcodes/preprocessors/precomp/.  Last modified 26-March-2007; accessed 26-March-2007.