Man B&W S50ME-B9.3-TII, Project Manual

Page: 275 / 337

MAN B&W 17.05
Page 2 of 3
MAN Diesel
MAN B&W ME-B engines 198 79 87-0.2
As the deflection shape for the Htype is equal
for each cylinder, the N
th
order Htype guide force
moment for an Ncylinder engine with regular fir-
ing order is:
N × M
H(one cylinder)
For modelling purposes, the size of the forces in
the force couple is:
Force = M
H
/L [kN]
where L is the distance between crankshaft level
and the middle position of the crosshead guide
(i.e. the length of the connecting rod).
As the interaction between engine and hull is at
the engine seating and the top bracing positions,
this force couple may alternatively be applied in
those positions with a vertical distance of (L
Z
).
Then the force can be calculated as:
Force
Z
= M
H
/L
Z
[kN]
Any other vertical distance may be applied so as
to accomodate the actual hull (FEM) model.
The force couple may be distributed at any
number of points in the longitudinal direction. A
reasonable way of dividing the couple is by the
number of top bracing and then applying the forc-
es at those points.
Force
Z, one point
= Force
Z, total
/N
top bracing, total
[kN]
Xtype Guide Force Moment (M
X
)
The Xtype guide force moment is calculated
based on the same force couple as described
above. However, as the deflection shape is twist-
ing the engine, each cylinder unit does not con-
tribute with an equal amount. The centre units
do not contribute very much whereas the units at
each end contributes much.
A socalled ‘Bimoment’ can be calculated (Fig.
17.05.01):
‘Bimoment’ =
Σ
[forcecouple(cyl.X) × distX]
in kNm
2
The Xtype guide force moment is then defined as:
M
X
= ‘BiMoment’/L kNm
For modelling purpose, the size of the four (4)
forces can be calculated:
Force = M
X
/L
X
[kN]
where:
L
X
is the horizontal length between ‘force points’.
Similar to the situation for the Htype guide force
moment, the forces may be applied in positions
suitable for the FEM model of the hull. Thus the
forces may be referred to another vertical level L
Z
above the crankshaft centre line. These forces can
be calculated as follows:
Force
Z, one point
=
M
x
× L
_____
L
x
× L
x
[kN]
In order to calculate the forces, it is necessary
to know the lengths of the connecting rods = L,
which are:
Engine Type L in mm
S60MEB8 2,540
G50ME-B9 2,500
S50ME-B9 2,214
S50ME-B8 2,050
S46ME-B8 1,980
S40ME-B9 1,770
S35ME-B9 1,550
*) Available on request