Unbalanced reaction with the ForceFromReaction function

[aziz_barzuk]

Dear Support,
I can't get how to use the force from reaction function.
The problem is that there is some umbalced force that makes the model move.
In particular this happens when the initialization phase is solved in transient mode.
No problem with the static mode.
I need only to remove the fixes in x direction and replace them with forces in the dynamic phase.
The only difference in comparison with the advanced tutorial about an SSI case is that I have 2 soil layers and the domain is composed by some merged surface.

Can you kindly tell me how to use it and why does the model move itself ?

I annex the simple model of a slope in which I wanted to verify the problem.
In the following image is shown the u_x displacement and it can be seen that there is a cumulated, uncontrolled x displacement.



another important effect is that by following the resolving procedure used in the file annexed I have the same effect using the ASDAbsorbingElement2D auto.
Unfortunately, because of the up element I can't initialize the model with a static analysis.

Thanks in advance

[STKO Team]

The problem is that there is some umbalced force that makes the model move.

It's not about that. It moves due to a rigid body motion in X. It may happen due to numerical integration. Not a problem since a RBM does not introduce strain.

I need only to remove the fixes in x direction and replace them with forces in the dynamic phase.

Note that it's only an approximation. More specifically it may not work well with UP elements, since the reaction forces are computed in the pseudo-static analysis, but when you run the dynamic the P DOF change and may introduce extra forces in X (expansion) not balanced with the previously computed reactions

[aziz_barzuk]

Very thank you for your answer,
I found a post about the same topic.

The user found the option -dynamic and said that that was right.

Can you confirm if the option -dynamic makes the function forceFromReaction to work properly with the up-element ?

Thanks in advance.

[STKO Team]

I found a post about the same topic.
The user found the option -dynamic and said that that was right.

Where did you find that post?
We don't have any "-dynamic" attribute in the ForceFromReaction automation

[aziz_barzuk]

These are the references:

from Prof. Scott Blog
"Reaction and Unbalance"
https://portwooddigital.com/2021/05/09/ ... unbalance/

This is the thread:
https://www.asdeasoft.net/forum/viewtop ... 9747#p9747

But maybe there is a minor bug (not related with the issue) in the Force From reaction function in the .tcl file.
In particular if I split 2 force from reaction functions one for the x direction (named FFR_X) and one for the y direction (named FFR_Y) and if I specify a FFR_x and and a FFR_y in the Load function for the analysis menù, in the .tcl code the function "reaction" is written 2 times in the same Load pattern.
The second time is wrong and need to be erased (by hand)

Than I wanted to ask you kindly if you can add a button in the ForceFromReaction function to consider the option -dynamic in the reaction function. In this way I can avoid to add it manually.

[STKO Team]

We will look into this for the next STKO release