CIMAC Congress - Schiff & Hafen

Monday, 14 June
Tuesday, 15 June
Thursday, 17 June
Wednesday, 16 June
at stern tube bearing, shaft bending moment and shaft bending
stress. The engine crankshaft values are crankshaft deflection and
bearing load. Calculation parameters are intermediate shaft bearing
height, engine bearing height and engine inclination, which are
decided by a vessel deformation and an engine thermal expansion.
The calculation procedures are as follows.
(1) A certain shaft alignment for initial condition is set.
(2) Shaft alignment after considered a vessel deformation for a
vessel draft condition and an engine thermal expansion is
calculated.
(3) Output values are calculated.
(4) Each output value is estimated whether to meet or not with
permissible values.
(5) Permissible vessel deformation and draft level is solved.
By calculating the shaft alignment including the whole range of
designed draft level, allowable shaft alignment area is able to be
solved. The validity of this method is confirmed that the already
serviced vessel data are enough for reliability within the allowable
area. It is also confirmed that the vessel deformation and engine
thermal expansion influence mainly engine aft side bearing. A stern
tube bearing performance is determined by initial installation and
is not influenced by a vessel deformation and engine thermal
expansion. Finally, it is clarified that a conventional design is
essential for the stern tube bearing, and it is necessary for engine
bearing to consider a vessel deformation. At a vessel under
construction, this method is able to indicate the allowable value of
intermediate shaft bearing height, engine bearing height and engine
inclination. And for in-service vessel, by using the inverse shaft
alignment calculation, safety margin of shaft alignment against
vessel deformation is able to be indicated.
10:30 June 16th Room Scene GH
(2–2) Fundamental Engineering –
Piston Engines – Mechanics
Comparison of crankshaft calculation
methods with reference to classification
societies’ requirements
M. Savolainen, H. Tienhaara, Wärtsilä Oy, Finland, T.
Resch, AVL List GmbH, Austria,
B. Smiljanic, AVL AST d.o.o, Croatia
Crankshaft strength analysis methods have significantly developed
since last ten years. Modern numerical methods combine flexible
multi-body dynamic simulation, Finite Element method and
multiaxial fatigue criteria to predict local stresses under realistic
boundary conditions very accurately. In parallel traditional,
analytical methods and rules as Unified Requirement M53 are still
used and have their place in large engine development due to their
stability and reliability. Therefore they are also used by classification
societies. Nevertheless, durability results between different methods
can vary significantly due to their different approaches, representation
of structures and loads, but also material data consideration and
influence factors. Modern numerical methods also have the
disadvantage that they can be considerably dependent on the tools
involved and even the user, due to high number of required input
and their deviation, as well as the complexity of the usage in general.
Due to the necessity for high reliability, especially for large engine
crankshafts, on one hand, but new demands in sense of efficiency
and costs on the other hand, which can hardly be covered by
traditional approaches, it is important to enhance the current rules
to go closer to the limits and reach the new targets, but avoid loosing
the stability of these methods. Therefore the relation between the
methods and their results is of interest to be able to connect them or
further develop the traditional ones. Within the current project
different methods for crankshaft fillet strength are analyzed and
compared. The present work is done within the CIMAC Working
Group 4 and discusses a sequence of different approaches, starting
from original UR M53 up to most complex approach using MBS,
FEM-structures and multi-axial fatigue method. Each step is based
on the previous one and differences in results are outlined to detect
the specific influences of each approach. Focus is set on the local
stresses and safety factors in pin and journal fillets of the specific
crankshaft. The target crankshaft is a modern 20-cylinder 4-stroke
ship engine crankshaft from Wärtsilä. The examined operating
condition is 600rpm with full load. Specific influences are
investigated separately. Most important are stress concentration
factors from analytical definition, via FEM based ones, up to direct
evaluation of stresses, which avoids the usage of such factors, the
load definition and the resultant local stresses. Loads are derived
from analytically calculated bending moments in combination with
torsional torque from separate torsional vibration analysis up to full
3-dimensional and transient coupled bending and torsional ones.
Effects of phasing between loads and stress components as well as
mean stress influence are worked out. Additional influences from
material definition, influence factors and the usage of different
fatigue methods are compared.
Fatigue design and optimization of diesel
engine cylinder heads
T. Gocmez, Institute for Combustion Engines VKA
RWTH Aachen University, Germany,
S. Lauer, FEV Motorentechnik GmbH, Germany
Cylinder head high cycle fatigue (HCF) and thermomechanical
fatigue (TMF) behavior has become more critical under today’s
stringent demands, where modern engines are increasingly designed
much closer to their mechanical limits. Often, the problem of critical
loading of cylinder heads is solved by a material variation and/or by
a design change - depending on the most critical fatigue mechanism.
This leads to additional design iterations and accordingly costs.
Therefore, an optimized design done in early phases of engine
development lowers the cost. This paper aims to give an insight on
optimization possibilities (production process, material selection,
design features) and a focus on integrated cylinder head design
optimization for cost effective engine development. An integrated
simulation approach covering the development needs in terms of
turnaround times, accuracy and reliability during the different
phases of cylinder head engineering process is presented. A through
understanding of fatigue mechanisms via design of experiments is
provided along with primary material and design feature selection
criteria, mathematical formulation of the design optimization
problem and cylinder head optimization roadmap. Showing that
TMF is a global problem and HCF is a local one, pre- and postoptimization
measures for the former and latter are proposed,
respectively. Emphasis is given to increased quality in entire
development process by “do it right the first time” philosophy,
where analysis of mass distribution on cylinder heads and 1D heat
transfer through the combustion chamber walls taking into account
the coolant side boiling effects are integrated to the frontloading. A
new solution for the TMF problem of heavy duty cylinder heads, by
the introduction of a groove between bore diameter and sealing
diameter on cylinder head flame deck, is presented as well. The
result is maximization of effectiveness of calculation methods on
the end product. The integrated usage of benchmark, empirical,
analytical and finite element methods, which are explained
throughout the paper, delivers an optimized dimensioning process
of valve bridge width and thickness at concept phase and removal of
local structural weaknesses on cylinder head coolant jacket side at
No. 3 | 2010 | Ship & Offshore
71