Large engine vibration analysis using a modular modelling approach
Dr.-Ing. Jochen Neher
Mechanics, Engine Structure
16th, October, 2018
Dr. Alexander Rieß
Mechanics, Power Train
Marko Basic
AVL-AST d.o.o. Croatia
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Large engine vs. car engine
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Agenda short
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1 Motivation
2 Established vibration analysis disciplines
3 Virtual Engine approach
4 Modular modelling
5 Reorganised interaction
6 Next steps
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Motivation 1
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Structural Requirements
Operational Safety Comfort Aspects
Vibration analysis is essential for both requirements
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Established vibration analysis disciplines
2
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Torsional Vibration Calculation (1D)
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Conceptual design crankshaft, crank star,
firing order sequence
Vibration damper and flywheel selection to
minimize torsional stress
Vibration analysis of ship propulsion
according to classification societies
Transient Load Cases: stochastic misfiring,
power fluctuations, grid events
1D Torsional Vibration Calculation(TVC):
Transient and Steady state
0
200
0 500 [°]
p [b
ar]
gas pressure curve
pe cyl, pmax cyl, ε,
1 8
3 6
2 7
4 5
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Cranktrain Simulation
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Crankcase Vibration Simulation
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Conceptual design for crankcase, oilpan,
foundation frame, charging unit
Basis for strength analysis of main and attached
components
Efficient for complete engine series
Scope
Shell model approach
zy
x
Shell free cut at cranktrain
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Engine Mounting Simulation
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Engine-plant integration
Comfort requirement
Special load cases (earthquake, shock)
Standard: Rigid body approach
Single stage mounting 2 stage mounting
F z
F y
F x
M y M z
M x
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Airborne Noise Simulation
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Comfort requirement
Component optimization
Automated FEM Workflow
fK
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Structure Borne Noise
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Comfort requirement
Combination of analytics,
simulation, measurements
Forced excitation
(low frequency approach)
v =
Y *
F
SBN Engine
Mounting
Stiffness Excitation
Force F
FE
M Model
Unitary
Excitation Admittance
Y
F =
c *
x
SBN
Frame
Mounting
Stiffness
Foundation
Stiffness
v =
v *
f
SBN
Foundation
De
cis
ion
Limit
2DOF
Check
Compliance
Modifications
Mo
un
ting
De
sig
n
Vib
ratio
n
Asse
ssm
en
t
De
sig
n
Mo
dific
ation
F0 v0
v3F3
ZF
m2
c2
m1
c1
v2F1
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Limitations
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Established vibration analysis disciplines focus on specific problems
Interaction of engine components simplified strongly (e.g. crankshaft-crankcase)
efficient, flexible
Combination of vibration analysis disciplines relevant e.g. for
2-stage-mounted engines
Structure Borne Noise
New engine technologies different engine behavior (e.g. 7th eo 12V)
Different expert tools - obstacle for knowledge exchange between engineers
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Virtual Engine approach 3
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Virtual Engine (AVL Excite)
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Project with AVL Croatia
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Inspiration
Pilot, AVL Workflow
Rollout, MAN Workflow
Pilot, MAN
Implementation
2018
2016
2015
2017
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Virtual Engine - workflow
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Nodes:
>6,000,000
Elms:
>5,000,000
Structural matrices
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Virtual Engine example: Axial bearing - setup
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Initial EXCITE model
Standard spring/damper
MAN disciplines
HD (squeeze effect only)
EXCITE model - Update
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Virtual Engine example: Axial bearing - results
Initial Update
Updated AVL significantly improved correlation of simulation and measurement
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Virtual Engine example: Axial bearing - results
Initial Update Velocity RMS – Horizontal Velocity RMS – Horizontal
Improved vibration behavior of crankcase due to updated axial thrust bearing
Nominal speed
Complete speed range
Magnitude – Velocity - Horizontal
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Virtual Engine example: Axial bearing
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- Bearing behavior with significant impact on crankcase vibration
- Cranktrain EHD (established MAN discipline) showed detailed bearing behavior
- Implementation in Excite, simplified
- Good result
Benefit:
- Identified design sensitivity
- In cranktrain MBS and crankcase FEM (MAN disciplines), this effect is not visible
- Virtual engine + experience => benefit
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Virtual Engine example: Unbalance mass - setup
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Crankshaft modified by adding mass on flywheel bolt node:
EXCITE with unbalance: m=50kg (0.17% of total mass)
RBE2 element with added CONM2 mass
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Virtual Engine example: Unbalance mass - results
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1st Engine Order
1st Engine Order
1st Engine Order
1.5th Engine Order
Significant influence on engine motion. Lower influence on crankshaft motion.
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Virtual Engine example: Unbalance mass - results
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EXCITE w/o unbalance
EXCITE with unbalance
Operation deflection shape
Nominal speed
1st engine order
Strain – directly from EXCITE
Low influence on strain Significant influence on motion
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Virtual Engine example: Unbalance mass
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- TVC: Not relevant. No bending. Inertia not effected significantly
- Crankcase FEM: Mounting not considered in detail, difference just at 1 frequency
- Mounting calculation: Only rigid body modes considered (mostly(!), this is sufficient)
- Measurement: Balancing is expensive, difficult to distinguish between elastic and rigid modes!
- Virtual Engine shows influence in detail, also at higher frequencies
- ODS enables overall engine behaviour evaluation; frequency (order) analysis being particularly beneficial
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Experience at MAN
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Launch phase still ongoing at MAN, close collaboration with AVL
Software improvements implemented by AVL (functions, interfaces)
Virtual engine …
is a platform for different vibration disciplines improved exchange
supports a better understanding of the engine behavior
virtual engine benefits from established disciplines (efficient modelling, experience, validation)
established disciplines benefits from virtual engine (interaction)
will not replace established disciplines in the near future at MAN
validation with measurements not always satisfying, overall engine simulation remains a challenge
sometimes replaces testing
Currently, time to model is too long action required “modular modelling”
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Modular modelling
4
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Crankcase intersection modelling for 6-10L
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Base TC@CCS
+1cyl
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Crankcase intersection modelling for 6-10L
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Power Unit without liner ANSYS ACT
assembly conversion to
mass point
right inertia properties,
position in cog of
assembly, only attaching
location need
Engine Assembly Engine Section CS
Engine Section Mid
Engine Section CCS
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Alignment of models for different disciplines
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Crankcase
10L crankcase vibration model
Ansys macro
30V skeleton
10L skeleton
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Crankshaft intersection modelling for 6-10L
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Parametrized CAD
3D crankshaft
Generator
e.g. 10L crankshaft
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Alignment of models for different disciplines
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Crankshaft with identical meshes for different MBS solver
192 362 Nodes
111 150 Elements
Cranktrain simulation
Virtual Engine
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Parameterized AVL Excite model (by AVL)
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AVL Excite, engine template
Definition of approx. 300 parameters
Values defined via case table
Excel with Makros case table input
Parameters
Gas pressure curve
Calculation of bearing stiffness parameters
Automated checks
8
1
Case Set Name "Case Set 1"
Joint Type of MB NONL
Config of Engine
Param. Name for Excite Unit
Crank Train Globals General Data Engine Speed Engine_Speed rpm
Engine Speed Initial Engine_Speed_Init rpm
Number of Cylnders Num_Cyl ""
Bore Bore mm
Stroke Stroke mm
Excite parameter specification
Maintenance
Run CheckerExport casetable
Reset Cell Color
Protect This Sheet
Unprotect This Sheet
Home Input data Cylinder pressure ThresholdStiffness Technical Help
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Reorganised interaction
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CAD
Coupling
Engine Frame
Alternator
Ship
Foundation
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Next steps
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Next steps
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Proceed with AVL Excite launch, collaboration with AVL
Workflow validation for component (crankcase) optimization in FEM (frequency domain)
FEM excitation analytical vs.
FEM excitation with AVL Excite results
Structure Borne Noise
interaction engine ship underwater noise
evaluation of necessary modelling depth for ship excitation
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All data provided in this document is non-binding.
This data serves informational purposes only and is especially not guaranteed in any way.
Depending on the subsequent specific individual projects, the relevant data may be subject to changes and
will be assessed and determined individually for each project. This will depend on the particular characteristics
of each individual project, especially specific site and operational conditions.
Disclaimer
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Thank you very much!
Dr.-Ing. Jochen Neher
Head of Mechanics, Engine Structure
+49 821 322-2976
16th, October, 2018