Predefined announced variables give zero results

Dear All,

I am working on the formation of ultrasonic-standing wave using a piezoelectric device acting on a fluid domain which contains suspended particles that is surrounded by PMMA walls.

I have 3 domains and 4 physics:
Transducer domain - piezoelectric device physics
PMMA domain - structural mechanics physics
Fluid domain - pressure acoustics + euler model physics

On the boundary load condition of PMMA wall structural mechanics I used an acoustic load per unit area (acpr/pam1).
On the normal acceleration boundary condition, I used Acceleration (solid/lemm1).

While computing it, it gave me zero results, why is that?

Thanks.