Loads applied to the structural analysis are equivalent to the boundary conditions in a fluid analysis. For this analysis, a fixed support is needed to hold the bottom of the reed valve in place.
Verify that each of these supports has been defined for the co-simulation.
In Mechanical's Outline, expand Transient.
Under Transient, review the supports.
Click Fixed Support.
In the Geometry pane, note that the fixed support is defined on the bottom right corner of the Valve body.
Click Fixed Support 2.
In the Geometry window, note that the fixed support is defined on the low-x face of the Stopper body.
Click Frictionless Support.
In the Geometry window, note that the frictionless support is defined on the sides of the Valve body.