# Stabilize SOLIDWORKS Simulation Studies with Soft Spring and Inertial Relief

Article by Mersedeh Zandvakili updated May 27, 2019

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SOLIDWORKS Simulation offers two techniques for stabilizing self-equilibrated models: Soft Springs or Inertial Relief.

In a self-equiblibrated model, all of the applied loads are inherently balanced which means that we don’t expect the model to be unstable in any direction (or move away in any direction). For example, in the picture below, the model is exposed to an elevated temperature from original room temperature (25 degrees of Celsius) at zero strain. This is the only source of load in the model and therefore, this is a self-equilibrated model. Although we don’t expect the model to move away in any directions, we need to make sure that the model is fully constrained in x, y, and z directions. This is because the finite element method, does not recognize the fact that the model is inherently balanced and any small inaccuracy, numerical error, or mesh asymmetry may cause the model to displace uncontrollably in the directions that it is not constrained in.

The SOLIDWORKS Simulation Soft Spring and Inertial Relief options can be activated from Simulation Properties > Options > Use Soft Spring to Stabilize Model / Use Inertial Relief.

Activating Soft Spring or Inertial Relief Options

• SOLIDWORKS Simulation Soft Spring will place weak springs (with stiffness negligible compared to the model’s stiffness) to each node of the model and connected to the ground. Unbalanced forces stretch these springs until equilibrium is reached and the model is stable. This option, however, should only be used if the model is self-equilibrated.
• SOLIDWORKS Simulation Inertial Relief applies body load acceleration to the model to offset any unbalanced forces. This doesn’t account for any reaction loads at restraints that may have balanced the system. This option should not be used with the intention to stabilize an analysis where gravity, centrifugal, or some thermal loads are defined. Therefore, we don’t use inertial relief for this example.

Please note that misapplication of these options will result is unrealistic values for displacements and stresses.