Add a Prescribed Pressure subnode under Enclosed Cavity to apply a known pressure. This feature can be used to model a constant pressure inside the cavity, or when there is an initial overpressure in the cavity in addition to pressure changes resulting from wall deformations.

This type of analysis requires two study steps. In the first step, only the initial overpressure is applied to compute the deformed volume. In the second step, the initial overpressure must be maintained, while additional pressure changes occur due to the external deformation of the cavity. These additional pressure changes can be modeled by adding a Fluid subnode, see Fluid (Enclosed Cavity), with appropriate values for the reference pressure and reference volume. The reference volume must be equal to the deformed volume from the first step.

The Prescribed Pressure node is contributing with the Fluid node and other Prescribed Pressure nodes.

Enter the Pressure p.

Physics tab with Enclosed Cavity selected in the model tree: