Determine the Zero-Stress State

The CAD geometry used to create the finite element mesh corresponds to the heart at 70% diastole—a pressurized/loaded state. However, when the geometry is meshed, the resulting elements are stress and strain free. Therefore, an inverse problem must be solved to calculate an initial stress state corresponding to 70% diastole. SIMULIA has solved this problem and determined an initial set of nodal locations that correspond to what would be a zero-stress state (a "deflated mesh") for the baseline model. When this mesh is pre-loaded during the simulation, it brings it back to very closely matching the original CAD geometry.

You must repeat this inverse procedure if you do any of the following.

• Create new elements. For example, when you remesh any part of the heart.
• Change any loads or boundary conditions during the PRE-LOAD step.
• Change any of the mechanical properties of any portion of the model including any properties related to the blood flow model.

If you are working with the Heart Model on premises, you can execute one of the simulation process experiences supplied with the model to determine a new zero-stress state. For more information, see The Heart Model Simulation Processes.