How to output a modal force?

Hi Luca,

What do you mean with ”modal force”? Is it a sin-force applied to the model or is it a reactional force you want to have the modal content from?

If it’s a reactional force, you will get this in the time-domain and have to manually FFT this signal using HyperGraph.

Here is a link to the fftmag() function used in HyperGraph.

https://help.altair.com/hwdesktop/hwd/topics/reference/math/fftmag.htm?zoom_highlight=fftmag

Best regards

/Erik

Hi Luca,

What do you mean with ”modal force”? Is it a sin-force applied to the model or is it a reactional force you want to have the modal content from?

If it’s a reactional force, you will get this in the time-domain and have to manually FFT this signal using HyperGraph.

Here is a link to the fftmag() function used in HyperGraph.

https://help.altair.com/hwdesktop/hwd/topics/reference/math/fftmag.htm?zoom_highlight=fftmag

 

Best regards

/Erik

Usually it's used in combination with the fold() function:

Hello Erik, I remember you did an excellent course on MotioSolve. Let me thank you.

Modal force is:

so a generalized force coming from a load distribution projected on the modal base.

I do not find a way to export it (it's a vector).

Hello Erik, I remember you did an excellent course on MotioSolve. Let me thank you.

Modal force is:

so a generalized force coming from a load distribution projected on the modal base.

I do not find a way to export it (it's a vector).

Hi Luca,

I'm not sure if you can measure this modal force directly, as it modifies/enables an already defined load case in the FlexBody file.

I was able to find this tutorial (https://2020.help.altair.com/2020/hwdesktop/mv/topics/tutorials/mv/tut_mv_2040_t.htm) which is a great example for the use of modal forces within MotionView. It looks like you are still using the classic interface so this 2020 example should align with your current model version. 

The applied load case is a pressure distribution to the bodywork of an aircraft, defined in HyperMesh, and enabled using the modal force in MotionView. The effect of the modal force assertion is plotted at the end to see the change in piston force vs fore canard angular position with it turned on. 

Hope this helps!

Adam Reid

Hello Adam,

yes I was testing that tutorial indeed. BUT I am modying the tutorial to provide directly the generalized force using a python function for MFOSUB. That's because my model will not have a load which can be simply scaled in time or due to one variable. I have a load which changes in space with time. MFOSUB allows indeed to provide directly the generalized force without having to assume a pre-defined shape.

The goal is to allow for aeroelastic analysis for my flex body. I can provide directly the generalized forces from the aerodynamic system via FMU. MS provides to the FMU the generalized coordinates to evaluate how aero loads are affected. Generalized forces are calculated and sent to MS. 

My question was indeed to find a way to check MS is correctly taking my forces and the python function does what it is supposed to. it seems to work. I use that tutorial and set a high value of generalized forces and I can see the canard well deformed