178 57 45-6.0
Fig. 17.03.01: MAN B&W external electrically driven
moment compensator, RotComp, option: 4 31 255
If annoying 2nd order vibrations should occur: An
external electrically driven moment compensator
can neutralise the excitation, synchronised to the
correct phase relative to the external force or mo-
ment.
This type of compensator needs an extra seating
fitted, preferably, in the steering gear room where
vibratory deflections are largest and the effect of
the compensator will therefore be greatest.
The electrically driven compensator will not give
rise to distorting stresses in the hull and it offers
several advantages over the engine mounted solu-
tions:
• When placed in the steering gear room, the
compensator is not particularly sensitive to the
positioning of the node.
• The decision whether or not to install compen-
sators can be taken at a much later stage of a
project, since no special version of the engine
structure has to be ordered for the installation.
• Compensators could be retrofit, even on ships
in service, and also be applied to engines with a
higher number of cylinders than is normally con-
sidered relevant, if found necessary.
• The compensator only needs to be active at
speeds critical for the hull girder vibration. Thus,
it may be activated or deactivated at specified
speeds automatically or manually.
• Combinations with and without moment com-
pensators are not required in torsional and axial
vibration calculations, since the electrically
driven moment compensator is not part of the
mass-elastic system of the crankshaft.
Furthermore, by using the compensator as a vi-
bration exciter a ship’s vibration pattern can easily
be identified without having the engine running,
e.g. on newbuildings at an advanced stage of
construction. If it is verified that a ship does not
need the compensator, it can be removed and re-
used on another ship.
It is a condition for the application of the rotating
force moment compensator that no annoying lon-
gitudinal hull girder vibration modes are excited.
Based on our present knowledge, and confirmed
by actual vibration measurements onboard a ship,
we do not expect such problems.
Balancing other forces and moments
Further to compensating 2nd order moments,
electrically driven balancers are also available for
balancing other forces and moments. The avail-
able options are listed in the Extent of Delivery.
Electrically Driven Moment Compensator
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