Modes v2.2 Read Me File ----------------------- by Marshall L. Buhl, Jr. National Wind Technology Center National Renewable Energy Laboratory 16-August-2000 INTRODUCTION ------------ Modes was a program that was originally created by Dr. Robert Wilson and his colleagues at Oregon State University. They used it to create the mode shapes that their FAST program needed for flexible blades and towers. While verifying FAST_AD, a derivative of FAST, against other codes, I used Garrad Hassan's BLADED for Windows to generate mode shapes. As the time approached to release the newly debugged version of FAST_AD, I realized we needed something we could distribute with it for generating its mode shapes. I got a copy of Modes and tried to use it, but I couldn't get it to compile with the Compaq Visual Fortran (CVF) compiler we normally use at the NWTC. As I started to debug it, I found it was difficult to read and it used nomenclature and variable names I was not familiar with. It was also written long ago in FORTRAN 77 and had fixed limitations on arrays. I decided to go ahead and modernize it to Fortran 95 standards, convert the main routines to free-form Fortran, dynamically allocate the arrays, add some input checking, simplify and streamline some algorithms, rework the output, and change some of the variable names to ones that were meaningful to me. I left the canned eigen solution routines alone except for dimensioning the arrays to the actual sizes instead of to a value of 1. I had to do this because the subscript bounds checker in the CVF compiler kept complaining about the arrays. VERIFICATION ------------ Alan Wright of the NWTC generated some mode shapes with a MatLab program he had and also made some hand calculations of frequencies for uniform beams under rotation. I compared his numbers to those coming from Modes and they agreed fairly well. The differences were not large compared to the differences Modes produced when I used different numbers of interpolated beam stations. These verification tested did not include cases with non-zero end masses. I hope to make such tests later when I get a chance. I believe Gunjit Bir has a program I can verify it against. CERTIFICATION TEST ------------------ Before using Modes, you should run the certification testing program. It is a DOS batch file called "CertTest.bat" and can be found in the "Test" directory. To test the installation, edit "CertTest.bat" and set the environment variables found near the top of the file to settings compatible with your system. You will probably have to change only the "Editor" variable. Then, open up a command window, go to the Test directory, and enter "CertTest". Modes will run twice. The test procedure will compare the new results to those stored in the "Test\TstFiles" directory. The procedure will write the differences between the output files to a file called "CertTest.out". The test procedure will automatically open this file with the editor you specified with the "Editor" variable. Scan through the file; the only differences should be the date and time stamps in the headers of the files. If you recompiled Modes with another compiler, there may be some slight differences in the last digit of many of the numbers. COMPILING MODES --------------- You should not need to compile Modes unless you want to make changes to the code. The archive contains code primarily for the CVF compiler. All of the compiler-specific code should reside in files called "SysCVF.f90" and "ModCVF.f90". If you want to port Modes to another platform or compiler, you should have to change only these two files. All source code resides in Modes' "Source" directory. USING MODES ----------- To run Modes, enter "modes []", where the is optional. Examples: modes This will start Modes and open "modes.inp". This is equivalent to entering "modes modes". It will generate "modes.mod". modes myroot This will start Modes and open "myroot.inp". It will generate "myroot.mod". INPUT FILE ---------- The input file is well commented and should be self explanatory. Samples can be found in the Test folder and are called "Tower.inp", and "Blade.inp". TRANSFORMATIONS --------------- When generating mode shapes for blades, you can enter blade twist and flatwise and edgewise stiffness in addition to mass density. The input stiffness is assumed to be aligned with the local principal axes. By using the twist distribution and pitch, the program can convert the input stiffness to values that are aligned with the out-of-plane (OoP) and in-plane (IP) directions. If you set the twist distribution and the pitch to zero, Modes will compute mode shapes in the local chord reference frame. FAST_AD requires the modes shapes to be done this way, so set the twist and pitch to zero if you want to export the results to it. If you want to see the mode shapes and frequencies in the in-plane and out-of-plane directions, then use the correct twist distribution and pitch setting. When doing the transformation, Modes' first step is to transform the local stiffnesses to global stiffnesses. This eliminates the blade twist so that all stiffnesses are aligned with the nominal flatwise and edgewise directions associated with the blade zero-pitch reference. The stiffness adjustment factors are applied to these values. Normally, when one applies these adjustment factors, it is to tune the properties to get the first blade frequencies to match either finite-element predictions or test data. In order to transform from the zero pitch orientations to the pitched OoP and IP directions, one needs the stiffness associated with the product of inertia (EIxy). In the original principal axes, this term is zero, but once we've transformed to the zero-pitch coordinate system, it is no longer zero. Unfortunately, we do not input adjustment factors for this term. To compute it, we transform the adjusted stiffnesses back into the principal axes. We then compute EIxy from the transformation back into the blade zero-pitch reference system. We then use EIxy to transform to the pitched OoP/IP system. USING WITH FAST_AD ------------------ As I said earlier, when exporting blade mode shapes to FAST_AD, you must use a zero pitch and use no twist distribution. Another issue is whether to export rotating or non-rotating blade mode shapes. I've found only small differences between the two, but if I normally use rotating mode shapes. I am NOT sure which is correct. Maybe someone can enlighten us on this issue. LIMITATIONS ----------- o You are limited to a maximum of 9 mode shapes. o Towers have the same stiffness in all directions. o The order of the first polynomial coefficient must be greater than 1. KNOWN BUGS ---------- o The centrifugal stiffening for blades is done the same for the in- plane mode as it is for the out-of-plane modes. This is not correct and we hope to fix it in the near future. o Code needs to check that the first polynomial coefficient is > 1. POSSIBLE FUTURE ENHANCEMENTS ---------------------------- o Output the stiffness distributions for the out-of-plane/in-plane system when processing blades with pitch and or twist. o Check to make sure Modes gives the same answers as FAST_AD. o Move the setting of the version number to a subroutine instead of using a data statement. This will eliminate the need to recompile all the routines when the version number changes. CAVEATS ------- NREL makes no promises about the useability or accuracy of Modes, which is essentially a beta code. Nor does NREL have the resources to provide full support for this program. YOU MAY USE MODES FOR EVALUATION PURPOSES ONLY. ACKNOWLEDGEMENTS ---------------- Funding for Modes' enhancement came from the US Department of Energy under Contract No. DE-AC36-98-GO10337 to the National Renewable Energy Laboratory. It was performed under task WE00.1210 which is managed by Alan Wright of the NWTC. FEEDBACK -------- If you have problems with Modes, please contact Marshall Buhl. If he has time to respond to your needs, he will do so, but please do not expect an immediate response. Please send your comments or bug reports to: Marshall L. Buhl, Jr. Mail Code 3811 National Wind Technology Center National Renewable Energy Laboratory 1617 Cole Blvd Golden, CO 80401-3393 United States of America http://wind2.nrel.gov/designcodes mailto:marshall_buhl@nrel.gov Voice: (303)384-6914 Fax: (303)384-6901