NWTC

Dear Damba,

I'm assuming you recompiled FAST for use in Simulink? When doing so, set the compiler directive COMPILE_SIMULINK to avoid getting that error.

Best regards,

Dear Jason,

Thank you for your replay. Yes i recompiled FAST. I will set the compiler directive in the next days.

Best regards
Damba

Dear Jason,

I must rectify my declaration before: i just recompiled FAST without changing for Simulink. Now i found that COMPILE_SIMULINK is involved in the files ServoDyn.f90, FAST_Mods.f90 and FAST_Subs.f90. I don't know how to set it. could you give me some directives to do that please?

Best regards
Damba

Dear Damba,

I don't know what compiler you are using, but you should set the COMPILE_SIMULINK preprocessor directive in your linker dependencies. The FAST ReadMe file explains how to do this when using Intel Fortran with Visual Studio: https://wind.nrel.gov/nwtc/docs/README_FAST8.pdf.

Best regards,

Dear Jason,

Thanks for the replay and file. The compiler i am using is gfortran/gcc. i think my problem is that my FAST is running on Window and Linux at the same time. My new FAST doesn't contain the "dependencies" order any more. I recompiled to obtaine the FAST_Library_glin32.so and some modifications in FAST_SFunc.c for linux.
for window system the control from simulink is working well. But the same control mode doesn't work on Linux computer with the same recompiled FAST. Maybe i have to include the "dependencies" again.

Best Regards
Damba

Dear Damba,

I'm sorry, but I don't personally have experience with the gfortran/gcc compiler. I suggest you review the documentation of that compiler to figure how to set compiler directives.

Best regards,

Dear Jason,

You are right. I have to know more about recompiling FAST.

Best regards,

Dear all,

I derived the natural Eigenfrequencies for the OC3-Hywind FOWT Modell in FAST v7.02 and in Bladed v4.4
Attached a picture of the EF for 1st flw- Blademodes.

The asymmetric Modes behave different in FAST and Bladed.
Especially the regressive mode EF in Bladed is decreasing slower from 6 rpm on than in FAST and for the progressive Mode the other way around.
Does anybody has an idea what the reason could be for this?

The small bumps are not seen in FAST results due to the lack of points in this range.

With best regards,

Simon

Dear Simon,

I'm not sure, but are the operating point rotor speeds at each wind speed from which the linearizations were obtained the same between FAST and Bladed? (Differences in the operating point rotor speed can result in differences in the resulting eigenfrequencies.)

Best regards,

Dear Jason,

Yes, the operation points are almost the same as you can see in the picture.
Are there any other ideas for the differences?

Best regards,

Simon

Dear Jason,

I just reviewed your derived Campbell diagram for the land-based 5 MW baseline wind turbine. It was in your post from Thu Sep 22, 2016 8:24 am.

Furthermore I reviewed the tower section 6 in Jonkman, J., Butterfield, S., Musial, W., and Scott, G: Definition of a 5-MW Reference Wind Turbine for Offshore System Development. February 2009.

In this section 6 on page 15 in the second paragraph, one writes:

We based the distributed properties of the land-based tower for the NREL 5-MW baseline wind turbine on the base diameter (6 m) and thickness (0.027 m), top diameter (3.87 m) and thickness (0.019 m), and effective mechanical steel properties of the tower used in the DOWEC study (as given in Table 9 on page 31 of Ref. [14]) ... Because the REpower 5M machine had a larger tower-top mass than the DOWEC wind turbine, we scaled up the thickness of the tower relative to the values given earlier in this paragraph to strengthen the tower. We chose an increase of 30% to ensure that the first fore-aft and side-to-side tower frequencies were placed between the one- and three-per-rev frequencies throughout the operational range of the wind turbine in a Campbell diagram....

This sounds like the wall thickness of the baseline tower is driven by its first two eigenfrequencies. But when I go back to your Campbell diagram I see, that these tower eigenfrequencies are very close to the three-per-rev frequencie at cut-in rotational speed. In fact, neglecting the proposed wall thickness increasement of 30 % would decrease the tower eigenfrequencies to about 0.282 Hz and a larger distance to the exciting three-per-rev frequency can be obtained. Note, that it would still have enough distance to the one-per-rev excitation frequency of 12.1 1/min / 60 s/min * 1.05 = 0.21 Hz.

What do you think about this?

Best regards,
Achim

Dear Achim,

What you say sounds reasonable.

If I recall correctly (although this was over 10 years ago now), I think the cut-in speed dropped a bit over the course of the NREL 5-MW development and perhaps the tower thickness was set before this and not later updated.

I agree that the final first tower fore-aft and side-to-side mode frequencies are bit close to the 3P frequency at the cut-in rotor speed. That said, I don't recall finding a problem with resonance of the tower from 3P excitation.

Best regards,

Dear Jason,

I need some clarification with the Campbell diagram (Excel file) of the land-based NREL 5-MW turbine that you posted here (viewtopic.php?f=3&t=1056&hilit=campbell) in the forum on Sep 22, 2016. I think that the values for the 2nd blade regressive and progressive modes in rows 14 and 16 in the “CampbellDiagram” worksheet are reversed. Based on the data (natural frequencies) for the 1st blade flapwise regressive and progressive modes (6th and 8th row) on the CambellDigram worksheet, I understand that data corresponding to the 1st blade regressive and progressive modes was chosen from the rows 20 and 19 of the worksheets with names 0 RPM to 14 RPM. Likewise, the 1st blade edgewise regressive and progressive data was chosen from the rows 23 and 22 respectively. However, the reverse was done for 2nd flapwise regressive and progressive modes i.e. data from rows 25 and 26 are chosen for regressive and progressive modes shown in the rows 14 and 16 on the CambellDigram worksheet. Was this a mistake or do you have any particular explanation for doing this for only the 2nd blade regressive and progressive modes?

Regards,
Srinivasa

Dear Srinivasa,

This is simply a naming convention. By "regressive", I mean the asymmetric mode that reduces in frequency with increasing rotor speed. By "progressive", I mean the asymmetric mode that increases in frequency with increasing rotor speed.

Best regards,

Dear Jason,

Thanks for the clarification.

Regards,
Srinivasa