Learning Forum

[joseph.becar]

In Classic, I frequency look at the sum of forces and moments in a cross-section of material - those familiar with Abaqus will recognize the analogy to their "Free-body Cut" feature. I select a cross-section of nodes, and the attached elements on one side. Then I set the moment summation point to be the centroid of the section, and run the "FSUM" command.

In Mechanical, it is impossible to natively get the same kind of result without adding in a contact pair or joint. The force reaction probe lists a limitation in the Geometry Scoping method that "when the scoping of a Force Reaction or Moment Reaction probe is applied to a geometry entity (Location Method = Geometry Selection) that shares more than one body. The (unscoped) elements that are adjacent to the scoped body contribute to the probe's results." I would like to overcome that limitation if possible. While it is straight-forward enough for me to open the *.rst in Classic and get the result there, I would like to have the capability to stay within Mechanical if possible.

I have been looking into an ACT extension that could get the capability, but I'm unfamiliar with how the nodal forces are treated in the API. I was able to access the IResultReader object and "GetNodeValues" for the "F" result (which I assume to be the nodal forces), but I cannot specify which elements should contribute to the nodal force summation, and the value it does give back is many orders of magnitude too high (and is identical for all nodes).

Has this problem been attempted in the past? Any tips on trying to replicate this functionality in Mechanical? My idea is to have two geometry scopings in the custom result object - one for the node selection of the cross-section, and one for the elements that should contribute to the summation of nodal forces. I would also include an X, Y, Z input for the moment summation point (or possibly a node selection for summation point).

If an ANSYS rep reads this, please, we need this capability natively in Mechanical!

Thanks,

Joe

[dlooman]

You can scope a Force Reaction and a Moment Reaction to a Surface (Construction Geometry) to get the force and moment at an arbitrary location without creating contact or a joint.  You will need to set Nodal Forces output to Yes.  For the Moment Reaction, specify Orientation to the coordinate system name used to locate the Surface and Summation to Orientation System.

[joseph.becar]

Dave,

Thank you for your response! I've somehow missed this capability for years! I will note that since it is dependent on the "Surface" Construction Geometry, it is limited to planar sections (you cannot, for example, query the summed forces and moments on a curved surface or a surface with multiple angles). This does get me through 80% of the use cases I run into on a daily basis, though, so that is great!

Joe