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
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:
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:
When I run the .fst-file I get an AeroDyn error:
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…
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…
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…
thank you very much for your explanation and your hints!