Dynamics of machines

A: A tempts you because damping does narrow peaks, and in many shop tests that’s how borderline rotors sneak through. The miss is that API intent isn’t about peak width; it’s about where the critical sits relative to continuous speed. C sounds practical and production-friendly, but it confuses vibration acceptance with separation margin — you can balance a rotor beautifully and still sit on a critical. D assumes geometry change is the only fix; sometimes mass or stiffness tweaks elsewhere move the mode enough, but the current state still fails the margin call.

A: A lines up with how standards writers think: separate rotor quality from installation variables. B feels right if you’ve been burned by bad foundations, but standards don’t dismiss vibration — they just don’t anchor balance quality to it. C overreaches; unbalance control helps, but stress still depends on geometry and speed. D sounds advanced, yet unbalance primarily drives 1× response; higher harmonics come from other sins.

A: A ignores that usable energy is only the small Δω window, not total KE. B follows the chain: KE = ½Iω², allowable ΔKE ≈ 2×Δω/ω of total, which lands you around 10 kg·m². C pads for losses without checking scale — an easy trap under time pressure. D is imported intuition from huge stamping lines, not this energy and speed range.

A: A catches a classic documentation trap: cam angle versus output motion isn’t one-to-one once you include ramps. B is plausible in a messy lab, but a 25% error would be obvious elsewhere. C sounds physics-heavy, yet expansion effects are tiny at these angles. D happens in real life, but you’d usually see profile mismatches beyond dwell alone.