CIMAC Congress - Schiff & Hafen

CIMAC CONGRESS | BERGEN 2010
due to evolving interest in occupational health and safety issues
and tightening legislations. Wärtsilä product development
organization, in close co-operation with their partners and
contractors, has answered the challenge and expectations. Low
noise solutions suitable for the existing and future engines have
been designed. This paper describes diesel engine noise control
measures applied to Wärtsilä 4-stroke diesel engines. In the past
five years, an increasing effort has been concentrated on noise
and vibration related work in Wärtsilä R&D. The ultimate aim is
to reduce noise radiation of medium speed 4-stroke diesel
engines. This persistent hard work has resulted in knowledge of
the major engine noise sources, in a deeper understanding of
the structureborne noise transmission through the engine block
and finally, in a definition of effective noise control measures.
The measures are the heart of the newly developed noise
reduction package. The package includes various enclosure and
lagging solutions and cover structures. The solutions are based
on add-on methods and structural component design
improvements. Tonal noise from turbocharger is reduced by
means of sound and heat insulation enclosures and laggings.
Noise radiated from the side of the engine is effectively reduced
by improved structural design of the covers. The flywheel end
and the top part of the engine are enclosed in order to reduce
the noise emitted from the subsurface. The beauty of the
developed measures is that they can be adapted to any Wärtsilä
4-stroke diesel engine, existing or yet to come, large and even
larger ones. Noise control measures, as a package, enables even
5 dB(A) engine noise reduction, depending slightly on engine
configuration. Furthermore, the noise control package can be
combined with engine room acoustic design to achieve even
greater noise reduction.
Two node torsional vibration control of
the multi-cylinder two-stroke diesel
engine
S. J. Hwang, K.T. Yoo, STX Heavy Industries,
Korea, U. K. Kim, Korea Maritime University,
Korea
Marine engines have been required higher power to fit the
bigger and faster ships aiming at economical operation. To
produce higher power, cylinder bore has been larger and the
number of the cylinder has been increased. On the other hand,
it has been continuously tried to develop components which
has influence on engine power, as turbocharger, and to introduce
a new fuel injection method etc. For this reason, the shafting
system of the large scale diesel engine is getting complicated
such that it is impossible to control the vibration in a simple
way as before. By increasing the number of cylinders, the
torsional vibration encounters another problem, 2-node
torsional vibration in a crankshaft at the engine above seven
cylinders [1]. As a solution of the problem caused by 2-node
torsional vibration, a vibration damper [2] has been usually
applied. However, in the future, the vibration damper might
not be able to solve the problem by only itself because the
power of the engine will be much higher than now. If the engine
has a higher power than present engine, the size of the damper
could be bigger to have higher damping coefficient [3], which
affects bearings due to heavy weight and the damper’s life would
be shorter by the influence of the big mass moment of inertia of
the inertia ring. In this study, the methods of increasing the
crank section [4] and changing the excitation characteristics
which can be adopted as an alternative solution to cope with
the future requirements have been investigated. The basic
concepts of these methods are as follows; the first concept is to
lead to increase the modulus of section of a part of the crankshaft
by increasing the diameters of one crank. With the increased
section modulus, the torsional stress can be reduced. The second
is to have proper excitation characteristics by changing the firing
order. The firing order can influence on the sub-harmonic
resonance. Generally, 2-node vibration is problem with minor
order. So it could be effective to change the critical order. By
these concepts, the combination of the proper diameters of the
crank and the firing order has been found. To select the crank of
which section to be increased, the variation tendencies of the
torsional stress and the node position by the variation of the
crank section, flywheel and tuning wheel mass moment of
inertia have been investigated. Also, since the external force, the
external moment [5] and the guide force moment [6] by the
change of firing order can induce high excitation of engine, it
has been also confirmed. In the result of the investigation, the
node location becomes more distance from the crank which the
diameter is increased due to the stiffness increase by the
diameter change of the crank. On the other hand, the node
location approaches the wheel which the mass moment of
inertia is increased. Accordingly, the node movement by the
stiffness increase could be controlled by changing the wheel’s
mass moment of inertia, so it could make the suggested method
more effectively to control the 2-node vibration. Based on the
above results, these methods have been applied at eight cylinder
engine shafting system and the effects have been confirmed.
Modern ultrasonic quality evaluation of
large crankshafts
A. Silvonen, P. Halla-aho, Wärtsilä Finland Oy,
Finland,
T. Hakkarainen, Inspecta Oy, Finland
New developments carried out by crankshaft manufacturers in
order to fulfil more strict material strength requirements set by
engine builders is causing new challenges in crankshaft quality
control. Higher stress amplitudes in engine operation and the
fact that higher strength materials tend to have smaller allowable
flaw size against metal fatigue call for more efficient nondestructive
evaluation (NDE) of the crankshafts. Wärtsilä has
together with its partners carried out a development work with
the intention in implementing new hardware and detection
guidelines to safeguard the high-level reliability of the crankshaft
material. Introducing of ultra-clean steels already has a very
high contribution in crankshaft safety, but in parallel with that
new NDE methods are needed with improved accuracy and
detection level. The most essential applied stresses in the shaft
from the reliability point of view are highly concentrated in a
relatively small material volume in the vicinity of the crank
fillets. Finite element and fracture mechanical analyses give
essential information about the critical defect sizes in function
of applied stresses and location, and further, information about
the needed accuracy of the used NDE system. As a result of
analyses carried out it is possible to guide the ultrasonic NDE in
different phases. High performance, but more time consuming
techniques, will be applied in critical areas, and, conventional
techniques in other parts of the shaft. Based on the required
accuracy, i.e. minimum detectable imperfection size, the phased
array techniques has been used in the project as a highest
accuracy evaluation method.
This paper reports the results of the stress and strength analyses
made and material tests determining the fracture-mechanical
data of modern crankshaft steels, and, finally reports benefits of
the phased array NDE method over to conventional nondestructive
ultrasonic methods when applied in either as forged
94 Ship & Offshore | 2010 | No. 3