structural beam – Comsol modelling for Energy Harvester (Unimorph)

I am trying to model an energy harvester, a cantilever beam with some PZT material. After applying the geometry and BCs, I am trying to get a mechanical Power Out Vs Frequency chart to obtain the mechanical power at the natural frequency. I am stuck on the global variable part, not sure what formula to use. I have attached photos of the modelling and a similar chart I am trying to obtain. The first picture shows the geometry, the second picture shows the global variable part which I keep getting wrong. The third picture shows a similar chart, which is what I am trying to obtain.
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