Updated NWTC Design Codes Available on Our Web Site

Hello, Design-Codes Users.

It is with great excitement that we announce the release of new versions of several of our NWTC Design Codes, which we’ve uploaded to our Web site:

FAST v7.00.00a-bjj (wind.nrel.gov/designcodes/simulators/fast/),
ADAMS2AD (A2AD) v13.00.00a-bjj (wind.nrel.gov/designcodes/simulators/adams2ad/),
AeroDyn v13.00.00a-bjj (wind.nrel.gov/designcodes/simulators/aerodyn/), and
NWTC Subroutine Library v1.02.00 (wind.nrel.gov/designcodes/miscel … nwtc_subs/).

Many of the changes to the codes are a result of (1) a new interface to AeroDyn and (2) linking FAST, AeroDyn, and A2AD with the NWTC Subroutine Library. Other changes include

  • additional strain gage outputs are available in FAST and A2AD,
  • TurbSim’s “.bts” wind files can be used,
  • the source code for the FAST S-Function for MATLAB/Simulink is included in the FAST archive,
  • hydrodynamics, which is a hidden feature in FAST and A2AD (until it can be documented), has been included,
  • an tower-influence model, which is a hidden feature in AeroDyn, has been included,
  • the codes can be compiled with the Intel Visual Fortran compiler for Windows, and
  • much, much more!

As we have not had the time to remove each of these code’s respective change comments and update their user’s guides, we have temporarily left the codes as “alpha” versions. We have created a document to guide you through the major changes in the updated codes and to document the updated AeroDyn interface. We encourage you to read it. You can access it here: wind.nrel.gov/designcodes/simula … erface.pdf. For a full list of changes included in these codes, please see the “ChangeLog.txt” files in their respective archives.

Despite their “alpha” status, we feel the codes have been thoroughly tested. For those using prior alpha or beta versions of these codes, we encourage you to upgrade.

Happy Modeling!

Jason & Bonnie Jonkman

Dear NREL Team:

The expanded capabilities of the software for offshore applications that are described in the report are of special interest to me.

In the 5 MW offshore mono-pile example, the PLATFORM portion of the offshore turbine support structure is subjected to wave and current induced loads (“hydro-loads”) calculated by Morison’s Equation. I see that no mass, stiffness and damping data for the PLATFORM are provided. Also I do not see a means of applying hydro-loads to the TOWER potion of the support structure.

Therefore I wish to know:

1] Does the software treat the effects of the hydro-loads on the dynamic response of the TOWER and BLADES?

2] If stiffness information about the PLATFORM is not input (i.e. the software considers the PLATFORM as a rigid body); is it still possible to model the stiffness interaction between the PLATFORM and the seabed soil (i.e. soil-pile interactions)?

This is my first message to the Forum, so please pardon if I have made any protocol errors.

Regards,

John F. Conlon, P.E.
Tel. & Fax 609-448-7190
E-mail: jcnlon@comcast.net

Dear John,

I’m happy to hear of your interest in the new offshore features of FAST.

For monopiles, the hydrodynamic loads are distributed along the submerged portion of the support structure (what FAST calls the “tower”). As is appropriate, there are no hydrodynamic loads on the blades (but, of course, there are aerodynamic loads here). The hydrodynamics loads are calculated at each submerged tower analysis node.

Input parameter TwrDraft from FAST’s platform input file determines the length of the tower that extents below the still water level (the tower draft). The total flexible length of the tower equals TwrDraft + TowerHt - TwrRBHt, where the tower height (TowerHt) and tower rigid-base height (TwrRBHt) are input parameters defined in FAST’s primary input file. The distributed tower mass and stiffness and the tower mode shapes specified in FAST’s tower file apply to the entire flexible tower (both submerged and not), with HtFract = 0.0 at the tower base (submerged for a monopile) and HtFract = 1.0 at the tower top. The tower analysis nodes are determined by input parameter TwrNodes from FAST’s primary input file. In the current version of FAST, the elements are uniform in length, so, if you want a fine discretization of the hydrodynamic loads, you must make the entire tower finely discretized. We plan to remove this limitation in a future release of FAST. (The code itself is capable of handling a nonuniform spacing of tower elements, but FAST has no input parameter that allows one to specify the nonuniform spacing from within the input file. Consequently, without modification of the code, you must simply use a large number of uniformly-spaced tower elements.) See the FAST User’s Guide for more information on these FAST input parameters.

The monopile can be modeled in FAST with a rigid or flexible foundation. One typically models the foundation in one of four ways:

  1. Rigid foundation – no foundation flexibility
  2. Apparent fixity – mimicking only the influence of the foundation on the tower natural frequencies by modeling a fictitious portion of the tower below the mudline (the depth, stiffness, and mass of this fictitious portion can be tuned to get the overall tower with foundation’s natural frequencies correct)
  3. Coupled springs at mudline – mimicking the foundation with a set of springs (or 6x6 stiffness matrix) at the mudline
  4. Distributed springs – modelling the full flexibility of the tower and soil with a set of linear or nonlinear springs distributed along the below-mudline portion of the tower)

All of these can be run within FAST. Model (2) can be employed directly through proper settings in FAST’s platform and tower input files. For model (2), set input parameters TwrDraft, PtfmCM, and PtfmRef from FAST’s platform input file equal to the apparent fixity depth and tune the distributed tower mass and stiffness and tower mode shapes in the FAST’s tower input file accordingly. FAST has no built-in functionality for models (3) or (4); instead, platform DOFs must be enabled and the use of user-defined routines enabled through FAST’s platform input file are required. In many cases, model (2) can give very good results down to the mudline and model (2) is much easier to use than models (3) and (4).

I hope that helps.

Best regards,

Dear NREL Team:

Thank-you for informative reply to my prior query.

I have unsuccessfully tried to run the Offshore Baseline 5MW (Monopile) data in FAST v.7. It appears the file “windData\90m_12mps.??? ” is missing. More detail of my effort below. Please advise how I may locate missing file required to run the Offshore Baseline 5MW cases in Fast.

The data I am using is located at:

  1. http://wind.nrel.gov/public/jjonkman/NRELOffshrBsline5MW. Aerodyne is looking for input file: “windData\90m_12mps”. [see line 10 of the file “NRELOffshrBsline5MW_AeroDyn.ipt”]. Fast indicates a problem with the missing file extension, and assumes it should be .wnd. However, even then there is no file with the stated name.

  2. I tried to substitute wind data that was produced by an earlier version of Aerodyn (v12.5-). But the version of Aerodyn (v.13) associated with Fast v.7 does appear to be compatible with earlier Aerodyn results.

Regards,

John F. Conlon, P.E.
Tel. & Fax 609-448-7190
E-mail: jcnlon@comcast.net

Dear John,

We don’t supply the wind data with the NREL 5-MW turbine models. This is because the wind data files are large (over 10 MB each) and because you need a lot of them in order to cover a range of operational conditions. TurbSim is available from: http://wind.nrel.gov/designcodes/preprocessors/turbsim/.

I’m not sure I understand your second question. AeroDyn does not generate wind. Also, the wind files compatible with AeroDyn v12.5- should be compatible with AeroDyn v13.00.00a-bjj. It’s possible the file name should be specified differently (see the documentation here: http://wind.nrel.gov/designcodes/simulators/aerodyn/March312010UpdatesAndNewAeroDynInterface.pdf)or that the file you are trying to use is not large enough to encompass the 5-MW turbine.

Best regards,

Dear Jason,

I understand that since the required wind data have not been provided, I need to run TurbSim to obtain required Aerodyn input wind data file “90m-12mps.”for the offshore monoplile example. I searched, but could not find the appropriate TurbSim input; so please advise if you have issued the TurbSim input files for the NREL 5-MW turbine models and where it is located.

Regards,

John F. Conlon, P.E.
Tel. & Fax 609-448-7190
E-mail: jcnlon@comcast.net

John,

Here is a link to a file that I have used to create some turbulence for the NREL 5 MW Baseline Model: http://wind.nrel.gov/public/bjonkman/Samples/Sample5MWTurbSim.inp. However, I always suggest that people try to get some idea of what they are trying to generate before pushing the button to make turbulence files. The turbulence input does effect the turbine simulation output.

Appendix B in the TurbSim User’s Guide (http://wind.nrel.gov/designcodes/preprocessors/turbsim/TurbSim.pdf) contains a guide to help you get started. It lists the basic parameters that need to be set and gives some help for choosing appropriate values. I encourage you to read it.

Regards,
Bonnie

As I announced here: http://forums.nrel.gov/t/other-news/846/1, the drive.google.com/drive/folders/ … sp=sharing.