Overturning moment at tower base - 15MW turbine

[Heike.vonWaaden]

Dear reader,

I disregarded the wind and wave loads to check the overturning moment at the tower base (since the CoG of the RNA mass is in front of the tower axis).
Here you can see the longitudinal bending moment at the tower base:

I assume the moment is oscillating since the gravity is internally ramped up, right?
But why is the deflection of the first moment positive? That would mean that the structure bends backwards first…

I found the total mass here -

but I’m not sure where to find the “RNA center of mass relative to the nacelle attachment point on the tower”…

I know it’s a basic question, maybe another beginner user can give me a hint

BR,
Heike

[Jason.Jonkman]

Dear @Heike.vonWaaden,

OpenFAST does not ramp up gravity at the start of the simulation. Rather, the transient dynamic response you are seeing is the start-up transient associated with the initial condition solution, which will depend on what initial conditions you have set (like initial rotor speed and initial blade and tower deflections).

ElastoDyn does not directly compute the center of mass of the RNA. But you can calculate that through an OpenFAST linearization analysis, e.g., as discussed in the following forum topics:

RNA Inertia FASTv7

Dear Dr. Jonkman, I try to calculate the moments of inertia for the RNA of an onshore reference turbine (130-3.4MW, see nrel.gov/docs/fy19osti/73492.pdf). Therfore, I followed the steps described in post Ansys model tower - #4 by Jason.Jonkman. I converted the input files of the WT to the FASTv7-Format. I created the following files: 130_lin.fst 130_AD.ipt Blade_NoDamp.dat Tower_NoDamp.dat Platform.dat Linear_130.dat (Control) When I run the .fst-file I get an AeroDyn error: I checked…

Openfast Linearization for RNA moments of inertia

Hi all, I am trying to find the RNA characteristics (center of gravity, inertia moments) of the UMaine Semi from the last updated files of the on the IEA-15-240-RWT github, by following the procedures described on this forum ([url]OpenFast 2nd order Linearization - #2 by Jason.Jonkman] ; [url]Ansys model tower - #4 by Jason.Jonkman] ) using openfast v 2.4. I manage to run the linearization, but in the linearization file I get the D matrix for floater motions is only composed of zeros… I set a…

OpenFast 2nd order Linearization

Hi Jason After reading some posts and a quick scan of the user guide, my understanding of the FAST/OpengFast linearization capability is that, at the current stage, only FAST V7 is able to do a 2nd order Linearization (e.g. output MCK matrix). Whether the above is correct or have I missed something? It would be apricated if you can help to clarify this. If the above statement is correct, is there any plan of implementing the 2nd order linearization into a future OpenFast version? The 2nd order…

Rotor and Nacelle Mass moment of Inertia Tensors

Dear Dr. jason Jonkman I am trying to determine the inertia tensors of rotor and nacelle separately. I was able to find the combine (RNA) inertia values (Ixx, Iyy, Izz, Ixy, Izx, Iyz) of the 5MW wind turbine on this forum. However, i could not find separately the inertia values of rotor and nacelle. I will highly appreciate if you can guide me on the calculation procedure of these values separately or if you can provide me some values. Link for combine RNA values: Tower Eigenfrequencies of NRE…

Best regards,

[Heike.vonWaaden]

@Jason.Jonkman

Dear Jason,

thank you very much for your explanation and your hints!

BR,
Heike

[Alberto.Utrera]

Dear @Garrett.Barter,

I have a couple of questions regarding the IEA-15MW wind turbine:

Regarding the IEA-15MW-tabular excel, why the RNA mass does not have the same value as the sum between 3 blades and the nacelle? Is there any more term that makes the summation be the same as the RNA mass?

Since the 15 MW WT is CLASS IB, is it advisable to run a simulation with a reference speed of 50 m/s and reference turbulence intensity of 0,14 (These are the data associated with class IB WT)

I am comparing some graphs: Why YAWBRTDYP and Q_TFA1 are not the same??

Thank u very much
Alberto

[Garrett.Barter]

Hi Alberto,

On the RNA mass summary, I think you are missing the inclusion of the Hub System, which includes not just the spherical shell of the hub, but also the pitch systems.

Perhaps I don’t understand your question about running a reference speed of 50m/s and reference TI. You are welcome to run any sort of DLC according to the IEC guidelines, and yes some of the DLC inputs are dependent on the turbine class.

On your last question, I’ll tag another to address that one.

[Jason.Jonkman]

Dear @Alberto.Utrera,

Q_TFA1 is the first fore-aft bending mode degree of freedom, which should be close to YawBrTDxp (not YawBrTDyp), except for the contribution of the second fore-aft bending mode degree of freedom.

Best regards,