Dear all,

We are trying to change the thickness of the NREL 5 MW–Baseline Wind Turbine cross section and run FAST again. While checking the tower of this turbine according to Eurocodes it actually occurred that the given cross section is insufficient in some cases.

From what I can tell, there is no way to change directly the thickness of the tower in ElastoDyn’s input file or tower’s dat file. Instead, the new bending stiffness and the mode shapes should be introduced in order to make this change.

For this purpose, I tried to run BMODES. I changed the tower_section_properties file but I’m not sure if values Ixx_tip, Iyy_tip etc. in the section ‘’Tower_top_mass_properties’’ of the bmi file should also be changed when changing the thickness.

Apart from the above, I would like to ask what else is needed in order to achieve such thing and how do you suggest I continue.

Thank you in advance for your help.

Best regards,

Gia

Dear Gia,

The tower-top mass/inertia properties of the NREL 5-MW turbine are documented in the following forum topic: http://forums.nrel.gov/t/using-aggregate-mass-in-adams-to-check-nrel-cs-monopile-bmi/696/1.

Your understanding of how to change the tower thickness of a FAST model is correct–that is, re-derive the distributed tower mass and bending stiffness and recomputed the tower-bending modes (via BModes).

Best regards,

Dear Jason,

With reference to the previous discussion, I came to an understanding the tower-top mass properties for BModes can be determined using other software or “Aggregate Mass” tool in MSC.ADAMS. Also, you provided an output of WindPACT1.5-MW and 5-MW turbine cases.

I am having trouble running the ADAMS2AD, is there any other way of obtaining the mass moment of inertia of a monopile turbine model? If this concern had been discussed, could you please redirect me to that forum page?

Regards,

Jharna

Dear Jharna,

In addition to using the “Aggregate Mass” functionality of MSC.ADAMS, you can also use the linearization functionality of FAST v7 to calculate the tower-top mass and inertia–see e.g. the following forum topic for more information: http://forums.nrel.gov/t/ansys-model-tower/1722/6.

Best regards,

Thank you.

You suggested me to use FAST v7 for the linearization, but I am using FAST V8 for my simulation. Can I use FAST8 for linearization? or is it different there?

I am changing dimensions of WT towers in my analysis, apart from distributed tower properties do I have to change anything else? I have adjusted tower diameters and heights.

Your help is appreciated.

Jharna

Dear Jharna,

The linearization analysis in FAST v8 only functions in first-order form (e.g. generating state matrix A). The linearization analysis in FAST v8 does not generate second-order form (in terms of M,C,K), so, the mass matrix (M) is not directly output. However, the linearization analysis in FAST v7 can function in both first- and second-order forms, where the mass matrix can be output in the latter.

If you are changing the tower diameter and height, I would expect that you’d need to change the distributed tower properties and tower mode shapes in ElastoDyn, and the distributed tower properties in AeroDyn (if you’ve enabled tower effects in AeroDyn).

Best regards,

I changed the tower properties based on requirements in AeroDyn and ElastoDyn, but have to work on the tower mode shapes and properties.

I have another concern, so if I have to change blade length (Roter diameter), is it sufficient if I change RNodes and DRNodes in AeroDyn based on hand calculation (I followed the previous discussion on that), or should I have to perform linearization analysis as well?

Thanks,

Jharna

Dear Jharna,

If you change the blade length, I would expect that you’d have to change the distributed blade properties and blade mode shapes in ElastoDyn, and the distributed blade properties in AeroDyn. You may also need to change the controller properties.

Best regards,