Iveco Marine Diesel Engines, Installation Handbook

Page: 49 / 132

MARCH 2004 DRIVE
3.49
MARINE ENGINES INSTALLATION
The torsional vibrations usually are not perceived as they do not always come out in the form of noise,
anyway they are not less dangerous.They regard those systems made up of shafts and rotating masses
with big inertia and can arise when these systems undergo a pulsating twisting moment or anyway vari-
able at regular intervals.
They consist in flexible angle oscillations of a general section of the system compared to a reference
section and overlap with the normal rotating movement.
As for linear vibrations, also with the torsional ones, when the frequency is close to or coincides with
the system frequency, there is resonance.The resulting effect is an additional torsional stress compared
to the regular drive stress, with the possibility of exceeding the stability limits and the resulting breaks
due to torsion.
At design stage it is necessary to analyse the risks deriving from the critical speeds in order to foresee
the required remedies (snap joints, variation of shaft diameter, balancing of rotating masses, etc.).
Additional power takeoffs can compromise the torsional balance of the involved parts.
The analyses of the torsional vibrations of the whole application shall be carried out by the builder
fitter-out.
IVECO Technical Bodies can make suggestions about the engine data which are needed for the cal-
culation.
3.4 TORSIONAL VIBRATIONS