Learning Forum

[Chandra Sekaran]

Below are possible reasons given in the ANSYS theory manual ( https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/ans_thry/thy_tool7.html%23eltreactforce) that can cause apparent disequilibrium. As shown in bold below for axisymmetric structure with radial load some of the load is balanced by hoop stresses.nThe following circumstances could cause an apparent disequilibrium:nAll nodal coordinate systems are not parallel to the global Cartesian coordinate system. However, if all nodal forces are rotated to the global Cartesian coordinate system, equilibrium should be seen to be satisfied.nThe solution is not converged. This applies to the potential discrepancy between applied and internal element forces in a nonlinear analysis.nThe mesh is too coarse. This may manifest itself for elements where there is an element force printout at the nodes, such as SHELL61 (axisymmetric-harmonic structural shell).nThe TOTAL of the moments (MX, MY, MZ) given with the reaction forces does not necessarily represent equilibrium. It only represents the sum of all applicable moments. Moment equilibrium would also need the effects of forces taken about an arbitrary point.nAxisymmetric models are used with forces or pressures with a radial component. These loads will often be partially equilibrated by hoop stresses, which do not show up in the reaction forces.nShell elements have an elastic foundation described. The load carried by the elastic foundation is not seen in the reaction forces.nIn substructure expansion pass with the resolve method used, the reaction forces at the master degree of freedom are different from that given by the backsubstitution method (see Substructuring Analysis).nn