As part of collaboration with space industry players, we got a feature request to calculate the force and the torque exerted by molecular hits on either individual facets or on an object that consists of multiple facets. This is now implemented in the 2.9.8 beta, released today. It works with both static and time-dependent simulations.

The source of the molecular force is the impulse change of an incoming molecule on the surface of the facet:

Since the particle undergoes an impulse change, by definition the opposite impulse change is exerted to the facet. Since MolFlow+ simulates a flux of particles (in steady-state), the impulse change rate can be converted to a force:

And, if the user defines a global reference point in the geometry, the torque relative to that point can also be calculated:

To enable measurement (that comes at a ~5% performance impact, and somewhat larger file sizes), and to extract the measured data, see the dedicated page in documentation.