This section is available on request - MAN Diesel & Turbo

MAN B&W 17.02
2nd Order Moments on 5 or 6-cylinder Engines
50MC
60MC
70MC
80MC
90MC
MAN B&W S70ME�C/ME�GI, L70ME�C, S65ME�C/ME�GI,
S60ME�C/ME�GI, L60ME�C, S50ME�B/ME-C, S40ME-B, S35ME-B
Cycles/min.*)
300
250
200
150
100
50
Natural frequency
cycles/min.
2 node
MAN Diesel
5 node
3 node
4 node
20000 40000 60000
*) Frequency of engine moment
M2V = 2 x engine speed
Fig. 17.02.01: Stat<strong>is</strong>tics of vertical hull vibrations in tankers and bulk carriers
The 2nd order moment acts only in the vertical
direction. Precautions need only to be considered
for 5 and 6-cylinder engines in general.
Resonance with the 2nd order moment may occur
in the event of hull vibrations with more than
3 nodes. Contrary to the calculation of natural
frequency with 2 and 3 nodes, the calculation of
the 4 and 5-node natural frequencies for the hull
<strong>is</strong> a rather comprehensive procedure and often
not very accurate, despite advanced calculation
methods.
A 2nd order moment compensator compr<strong>is</strong>es two
counter�rotating masses running at twice the engine
speed. 2nd order moment compensators are
not included in the basic extent of delivery.
Several solutions are <strong>available</strong> to cope with the
2nd order moment, as shown in Fig. 7.03.02, out
of which the most cost efficient one can be chosen
in the individual case, e.g.:
80000
dwt
Page of 2
178 06 92�4.1
) No compensators, if considered unnecessary
on the bas<strong>is</strong> of natural frequency, nodal point
and size of the 2nd order moment.
2) A compensator mounted on the aft end of the
engine, driven by chain, option: 4 4 3 233
(ME/ME-C/ME-GI except type 50 as well as
type 60 with TC on aft end) while not applicable
for ME-B.
3) A compensator mounted on the fore end,
driven from the crankshaft through a separate
chain drive, option: 4 3 243 (ME/ME-C/ME-GI
except type 50) while not applicable for ME-B.
As standard, the compensators reduce the external
2nd order moment to a level as for a 7-cylinder
engine or less.
Briefly speaking, solution ) <strong>is</strong> applicable if the
node <strong>is</strong> located far from the engine, or the engine
<strong>is</strong> positioned more or less between nodes. Solution
2) or 3) should be considered where one of
the engine ends <strong>is</strong> positioned in a node or close
to it, since a compensator <strong>is</strong> inefficient in a node
or close to it and therefore superfluous.
198 42 20�8.5