Reaction Forces
The simplest and most important plausibility check for any simulation.
Reaction forces are the simplest and most important plausibility check for any FEM simulation. The underlying principle is force equilibrium — the sum of all external forces (applied loads plus reactions) must equal zero.
Checking in Dr.Q
Verify that:
- The sum of reaction forces approximately equals the applied loads
- Force direction and distribution look reasonable
- For gravity loading: the reaction force should approximately equal the component's weight
Example
You apply a 5000 N force in the Z direction. The sum of all reaction forces in Z must equal 5000 N. If the model has two symmetrically placed fixed supports, each should carry roughly 2500 N.
If reaction forces don't match expectations, the simulation setup almost certainly contains an error. Check load direction and unit specification first.
Moment equilibrium
For models with eccentric loads, also verify moment equilibrium. The sum of moments about any point must also equal zero when accounting for both applied loads and reaction forces.
Why this check matters
A model with a missing boundary condition or a load applied in the wrong direction can still converge and produce a smooth-looking result — but the reaction forces will immediately expose the error. This check takes 30 seconds and is the fastest way to catch fundamental setup mistakes.