Torsional vibration calculation (TVC)

A torsional vibration calculation models the engine, shafting, flexible coupling, and propeller as a chain of inertias and torsional stiffnesses to find natural frequencies and the resulting cyclic stresses across the speed range. Class societies require it for the propulsion train and impose barred speed ranges where a resonance would overstress the crankshaft or shafting. The crankshaft deflection check and shaft alignment work alongside it to keep the running gear within limits.