Sure, let’s think of it like a musical chord in the engine. The core idea of perfect resonance is that the driving frequency—say the oscillation from the thrust cycle—matches one of the engine’s natural frequencies. That’s when the amplitudes grow because every push lands on the same part of the vibration cycle. Mathematically, you’re looking for the ratio of the driving frequency to a natural frequency to be an integer, like 1:1, 2:1, 3:1, and so on. In practice you model the engine as a set of coupled oscillators, write the differential equations, and solve for the eigenfrequencies. Then you check where the external input frequency hits one of those eigenvalues. It’s the same idea that makes a violin string produce a clear tone when you press the correct note—everything lines up. If you want to dig into the exact equations or how to damp those unwanted harmonics, let me know which part is most interesting to you.