The Altair Bushing Model for Multibody Simulation
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Transcript of The Altair Bushing Model for Multibody Simulation
The Altair Bushing Model for
Multibody Simulation
Ingo Nolden
June 25, 2014
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Development Partners
• Detailed Specifications
• Bushing Testrig Data
• Testing
• Real-World Full-Vehicle and Suspension-Models for thorough testing
(USA)
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Applications for Bushings
• Function
• Absorb shock
• Reduce vibration
• Transmit power
• Eliminate metal-to-metal contact
• Tolerate misalignment
• Industry
• Automotive (cars, trucks, buses & other variants)
• Farm equipment (harvesters, combines, etc.)
• Industrial machines
• Construction machinery
• Marine Industry (boats, ships, etc.)
• Helicopters, etc.
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Rubber Bushings In a Car
Rear knuckle
bushing
Disc brake
caliper bushings
Control arm
bushing
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Spherical Joint can be modeled as a bushing
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
How do Bushings/Joints behave?
• Bushing:
• Stiffness is nonlinear
• Damping changes with amplitude and preload, but only little with frequency
• Isotropic bushings don‘t change stiffness at different angles (coupling )
• Memory Effect
• Hydromount:
• Have large damping in a specific frequency range
• Inherit most of the rubber bushing properties due to rubber shell
• Spherical Joint:
• Is isotropic (coupling)
• Has friction on the sphere surface
• Assembly behaviour:
• Attached components are flexible
• Attached components can collide
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Ho do rubber bushings and hydromounts behave
• Rubber Bushings behavior are complex
Displacement
Fo
rce
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Ho do rubber bushings and hydromounts behave
• Separate the static stiffness from the damping
+ =
= +
• And solve with static and dynamic models
𝐹(𝑥, 𝑥 ) 𝐹𝑠(𝑥) 𝐹𝑑(𝑥 )
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One frequency/amplitude/preload
• Consider different preloads/operating points
Displacement
Fo
rce
Point of
Dynamic
Stiffness
Point of
Static
Stiffness
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Why an “Altair Bushing”
• Bushings are complex – Forces lag Displacements at steady state
DX +X
-X
DF +F
-F
DynamicStiffness=
DF
DX
∆𝑡
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Why an “Altair Bushing”
• Dynamic Stiffness and Loss Angle for different Amplitudes at the same
preload as function of the frequency
Dyn
am
ic S
tiff
ness
Frequency (Hz) 0 300
500
1100
1.0 mm
0.5 mm
0.3 mm
0.1 mm
Lo
ss A
ng
le
Frequency (Hz) 0 300
500
20°
1.0 mm
0.5 mm
0.3 mm
0.1 mm
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Why an “Altair Bushing”
• Bushings are complicated: “Operating Point” Dependence
0 100 200 300 400 500 600 -100 -200
400
600
800
Dyn
am
ic S
tiff
ness
Operating Point
10 Hz
20 Hz
40 Hz
60 Hz
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Altair Bushing Model Design Decisions
• The bushing is described by a bushing property file
• The property file defines the Bushing as „lying on the table“
• Mount conditions, DOE adjustments are NOT part of the Bushing (file)
• The software will make sure, that the above rules can be observed in
practice
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Implementation Architecture
• Solver Support:
• Available for Windows & Linux
AltairBushingCore
(.dll/.so)
Matlab/Simulink (S-Function)
MotionSolve (GSE+GFORCE)
Simpack (UFORCE)
ADAMS/Solver (GSE+GFORCE)
UserForceMethodB UserForceMethodA
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Implementation Scenarios
• Preprocessing Support
Matlab/Simulink MotionView
Simpack ADAMS/Car
• S-Function Subblock
• Combined Subblocks for
Friction + Mount Stiffness
• Full GUI support equivalent to
other modeling entities
• Substructure with Bushing
capabilities inside
• Full GUI support equivalent to
other modeling entities and for
all capabilities
• ac_bushing derived UDE
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Workflow
Fitting Tool
Test
Data
Bushing
Property
File MBD Solver
Bushing
Simulation
Model
Solver
Results
Solver
Input
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Stiffness
• Constant Stiffness (concept phase)
• The property file defines a stiffness coefficient for the direction
• Cubic Stiffness (concept phase)
• The property file defines two slopes and two force values for specific
displacements
• Spline-Stiffness (measured data)
• The property file defines a table of displacement and forces Spline
Stiffness
Cubic
Stiffness
Constant
Stiffness
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Damping
• Constant Damping (concept phase)
• The property file defines a viscous damping
coefficient for the direction
• Rubber Damping (measured data)
• The property file defines coefficient gained from a
fitting process
• Hydromount-Damping (measured data)
• The property file defines more coefficients gained
from a fitting process
Rubber Damping
Hydromount Damping
Constant
Damping
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Coupling
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
• Asymmetric, Anisotropic Example: Fy vs Y
The Altair Bushing Model: Coupling
Existing Coupling Modified Coupling
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
External Friction
• The external frictions intent is to be used with ball joints
• The external behaviour is a friction torque as a result of rotations
in the joint
• It can be used with any combination of rubber or hydromount
force methods
• The friction is using the LuGre friction model
and is defined in an on-surface translational
model (e.g. bristle stiffness and damping is
translational)
• Instead of LuGre, the Dahl model can be used
by simply setting a few parameters to zero
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Mount Stiffness
• For each of the connected bodies, one can define the local stiffness and
damping, so that flexible behaviour of those can be approximated when
flex bodies are not available or even geometry has not been designed
• This is also useful in the conceptual phase, when hardpoints are still
subject to change
• The stiffness can only be defined in the bushing local coordinate
system
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Mount Limits
• For each translational or rotational modes and for both positive and
negative direction of deflection, the motion of the bushing can be
further limited by bumpstop like forces
• The forces use an IMPACT function
• Can be used to model clash between the connected bodies of the
bushing at large deflections
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
DOE
• Since all the bushing properties are defined in a file and the files is
expected to represent a real bushing, a method for changing those
properties for a single simulation must be invented
• The Bushing Simulation Model will read a special „DOE-File“, which
contains parameter updates for the property file
• Preprocessors can provide methods to generate those file in an
automated way and interface with DOE methods in those programs
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
How does it all work together?
𝐹𝑥 = 𝐹𝑠𝑡𝑎𝑡 𝑥 + 𝐹𝑑𝑦𝑛(𝑥, 𝑥)
𝐹𝑦 = 𝐹𝑠𝑡𝑎𝑡 𝑦 + 𝐹𝑑𝑦𝑛(𝑦, 𝑦)
𝐹𝑧 = 𝐹𝑠𝑡𝑎𝑡 𝑧 + 𝐹𝑑𝑦𝑛(𝑧, 𝑧)
𝑇𝑥 = 𝑇𝑠𝑡𝑎𝑡 𝑟𝑥 + 𝑇𝑑𝑦𝑛(𝑟𝑥, 𝑟𝑥)
𝑇𝑦 = 𝑇𝑠𝑡𝑎𝑡 𝑟𝑦 + 𝑇𝑑𝑦𝑛(𝑟𝑦, 𝑟𝑦)
𝑇𝑧 = 𝑇𝑠𝑡𝑎𝑡 𝑟𝑧 + 𝑇𝑑𝑦𝑛(𝑟𝑧, 𝑟𝑧)
Couplin
g
Couplin
g
𝑥, 𝑥
𝑦, 𝑦
𝑧, 𝑧
𝑟𝑥, 𝑟𝑥
𝑟𝑦, 𝑟𝑦
𝑟𝑧, 𝑟𝑧
𝑥, 𝑥 𝐹𝑥 = 𝐹𝑙𝑖𝑚𝑖𝑡(𝑥, 𝑥) 𝐹𝑥
𝑦, 𝑦 𝐹𝑦 = 𝐹𝑙𝑖𝑚𝑖𝑡(𝑦, 𝑦) 𝐹𝑦
𝑧, 𝑧 𝐹𝑧 = 𝐹𝑙𝑖𝑚𝑖𝑡(𝑧, 𝑧) 𝐹𝑧
𝑟𝑥, 𝑟𝑥 𝑇𝑥 = 𝑇𝑙𝑖𝑚𝑖𝑡(𝑟𝑥, 𝑟𝑥) 𝑇𝑥
𝑟𝑦, 𝑟𝑦 𝑇𝑦 = 𝑇𝑙𝑖𝑚𝑖𝑡(𝑟𝑦, 𝑟𝑦) 𝑇𝑦
𝑟𝑧, 𝑟𝑧 𝑇𝑧 = 𝑇𝑙𝑖𝑚𝑖𝑡(𝑟𝑧, 𝑟𝑧) 𝑇𝑧
general_state_equation
(GSE)
Bushing &
Mount Limits
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
How does it all work together?
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
The Altair Bushing Model
• Thank You!