Ultimate Load Mlife

Wind & Water Structural Analysis
1

Dear Jason,

I need to use Mlife for fatigue analysis on wind turbine tower but to do this I need to know the ultimate Load “Lult”.

Is to correct to compute Lult this way ?

  • I calculate the section moment of inertia of the tower for the section where I have the moment time history from Fast as:
    I=pi/64*(D^4-d^4) with D=external diameter of the tower and d=internal diameter of the tower.

  • I use the ultimate stress “sUlt” for the tower material and from the usual expression s=(M/I )(D/2) I will write MUlt= (2 sUltI )/D

Thank you!

2

Dear Alessandro,

Yes, that is correct for a circular section undergoing pure bending. LUlt has been discussed a bit more in the following forum topic: MLife/Interpretation of DEL and LUlt - #2 by Jason.Jonkman.

Best regards,

3

Dear Jason,

thank you for your answer!

Can you suggest me reasonable values for LUlt in Mlife for the TwrBsMxt and RootMxc1 in Test11 in Fast 7 ( 5MW wind turbine)?

From my calculations I supposed that the tower is made by Steel with density=7500 (kg/m^3) , E=2.1*10^11(N/m^2) and I found D and d for the Tower base and Blade rootby a 2-equations systems with 2 unknowns .Doing this i obtained for the Tower base D=5.26(m) and d=5.22(m) and
for the blase D=1.28(m) and d=1.18(m). With these two parameters I found the followind values for LUlt:

TwrBsMxt=> 219 125 (KNm)
RootMxc1= 29162 (KNm).

Do you find them reasonables?

thank you!

4

Dear Alessandro,

Test11 in FAST v7 is actually a model of the WindPACT 1.5-MW turbine. Do you mean the WindPACT 1.5-MW or NREL 5-MW turbine?

Best regards,

5

Dear Jason,

Sorry, I meant 1.5 MW wind turbine, Test11!

do you think my calculations are correct?

Another question! Which Test number corresponds to the NREL 5MW wind turbine? I’have never seen that in the Fast7 archive!

If it is possible I would like to know these values also for the 5MW turbine!

Thank you!

6

Dear Alessandro,

I follow your procedure, but have a few comments/questions:

  • What value are you using for the yield strength (elastic limit)?
  • The actual WindPACT 1.5-MW turbine has a tower-base outer diameter of 5.606 m and a tower-base thickness of 17.6 mm.
  • The actual WindPACT 1.5-MW turbine has a density of 7850 kg/m^3 and a Modulus of Elasticity of 2.0*10^11 N/m^2.
  • Obviously the blade-root of the WindPACT 1.5-MW turbine is not steel, but finding the true LUlt would require detailed knowledge of the blade-root design. I can’t really comment on how accurate your approach to estimate it would be.
  • The actual NREL 5-MW turbine has a tower-base outer diameter of 6 m and a tower-base thickness of 35.1 mm.
  • The actual NREL 5-MW turbine has a denisty of 8500 kg/m^3 and a Modulus of Elasticity of 2.1*10^11 N/m^2.

FAST v7 models of the NREL 5-MW turbine are available here: wind.nrel.gov/public/jjonkman/NR … Bsline5MW/. We didn’t include the NREL 5-MW models in the FAST archive until the release of FAST v8. I’m not sure why you are using FAST v7, but in most cases I’d recommend an upgrade to FAST v8.

I hope that helps.

Best regards,

7

Dear Jason ,

thank you for the answer!

I used 510 (MPa) as ultimate strength for the tower just to have reasonable values for the damage in my matlab routines that give the same results of MLife .

I’m using Fast v7 beacuse I need the Adams model generated automatically by Fast but I will learn Fast8 for others simulations!

8

Dear Jonson,
I am trying to get the FAST v7 models of the NREL 5-MW turbine, but the website is not avilable now.

FAST v7 models of the NREL 5-MW turbine are available here: wind.nrel.gov/public/jjonkman/NR … Bsline5MW/

So, could you please sent me a cope of that to me? Thank you for your time sincerely.
My Email: wbx1125666865@163.com
BRs
Wang, Baoxuan

9

Dear Wang, Baoxuan,

Given the decommissioning of the wind.nrel.gov server, these files have now been moved to my Google Drive: NRELOffshrBsline5MW - Google Drive.

Best regards,