Learning Forum

[Bhargava Sista]

Why the moment reaction differs in Workbench and MAPDL? n

[Hui Liu]

Moment probes which perform a moment arm calculation, Mechanical employs the undisplaced mesh. In other words, when Mechanical computes a moment arm for a node, it finds the difference between the (x,y,z) of the node and the summation point (sx,sy,sz) in the base mesh: moment_arm = (x,y,z) - (sx,sy,sz) Please note that the above formula differs from how MAPDL performs a moment arm calculation and therefore, the results between the two applications differ. MAPDL uses the FSUM command for large scale deformation analyses (NLGEOM,ON). In MAPDL, node-based displacements, where the NLGEOM,ON command is issued, are added to the (x,y,z) in the base mesh, such that: moment_arm = (x+ux,y+uy,z+uz) - (sx,sy,sz)n

[Chris Lavery]

Hi,
What settings or issues in Ansys could result in moment probes producing moment values that are 1000 times larger than expected? Details below:

I'm using a macro to extract forces and moments from a bolted joint model in Mechanical APDL Product Launder (original model/analysis created and run in Ansys 2021 R2). Both the forces and moments I extract using the macro appear to be reasonable because they compare well with the equivalent stress plots for the bolts. The macro produces moments on the order of 15 - 100 N*m. However, when I go in and create force and moment probes to verify the macro I get vastly different results. The force probes produce force values almost identical to the macro. The moment probes produce moments that are vary far off (>15000 N*m). Both the probe and the macro are producing results that are in N*m. 

 

The macro is basing the values it pulls off of key points. And it adjusts for finding the node that is closest to the center of the bolt axis.

The settings for the moment extraction are shown in this last image and I have tried adjusting the summation point from centroid to orientation system and the extraction to either side of the surface.

 

Thanks in advance for any assistance you can provide.