## 14.13. Mesh Deformation

Mesh deformation using either of the `Regions of Motion Specified` or `Junction Box Routine` options introduces several CPU intensive operations during each outer iteration or time step. When deformation is performed using `Regions of Motion Specified`, a Mesh Displacement equation is assembled and solved at the start of each outer iteration or timestep for steady-state and transient simulations, respectively, and the mesh coordinates are updated. When deformation is performed using a `Junction Box Routine`, you define how mesh coordinates are updated.

After updating the mesh coordinates, other mesh related quantities (such as volumes, areas, mesh quality measures, mesh velocities, and so on) are updated, and GGIs are re-intersected before advancing to solve other equations or physical models for the current outer iteration or time step. Mesh volume flows that are later used to augment mass flow rates applied in advective transport are precalculated and stored during these updates.

Depending on the complexity of the deformation and physical model (for example, the use of GGIs), adding the mesh deformation to a simulation will increase CPU usage by approximately 10% to 50% per outer iteration or time step.

Adding the mesh deformation will increase memory requirements due to the storage of: the noted mesh volume flows (one per control volume integration point), and multiple sets of mesh coordinates for transient simulations (one triplet per mesh vertex per time step that must be kept for the selected transient discretization).

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