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061108 – Pre and Post sales training Webex
Mieke Robijns – Product Development Engineer
What’s new in Structural Testing 7B
2 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
3 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
4 copyright LMS International - 2006
Why are inertia properties needed ?
� Verification of CoG & MoI values
� Input for simulation models
� Kinematic and dynamic prediction
(multibody dynamics calculation)
� Coupling of an FE model with smaller
“rigid” components
� Accurate Modal based modification or
Substructuring requires flexible modes +
rigid body modes
?
5 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
6 copyright LMS International - 2006
How to determine inertia properties ?
� Pendulum test� Based on measured Frequency response
functions
� Typical modal test with hammer or shaker
excitation
� At least 6 excitation locations (SDOF)
� 8 – 12 response locations (3 DOF)
� Time consuming
� Requires multiple suspensions - difficult
for complex structures
� No extra equipment is needed
� Limited measurement effort
� Highly accurate alternative to
conventional pendulum test
7 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
8 copyright LMS International - 2006
Rigid Body Properties Calculation
How does it work – Test setup
� Weigh the test item to obtain mass [kg]
� Suspend Test item (once) in free-free conditions
� Create geometry wire-frame model in global or local coordinates
� Measure FRF matrix with hammer or shaker(s)
Test Setup:
9 copyright LMS International - 2006
Rigid Body Properties Calculation
How does it work - Mass line methods
� Unchanged FRFs
� Rigid body modes and first deformation modes are sufficiently spaced
� Measured FRFs are used
� Corrected FRFs
� Rigid body modes and first deformation modes are not sufficiently spaced
� Estimate first set of flexible modes from measured FRFs
� Correct measured FRFs by subtraction of contribution of flexible modes
� Lower Residual
� No accurate FRFs are measured in the frequency range directly above rigid body modes
� Lower residuals represent the influence of the modes below the deformation modes, and are
therefore representative of the rigid body modes.
Extract mass line:
10 copyright LMS International - 2006
Rigid Body Properties Calculation
How does it work - Calculation and results
� Coordinates of centre of gravity
� Moments and products of inertia about CoG and any user defined reference
point
� Principal moments of inertia and their direction
� Synthesis of 6 scaled rigid body modes with user defined frequency and
damping for use in simulation models
� Least square solution over all measured DOFLeast squares over selected frequency band of mass-line
� Validation through animation of rigid body motion
Calculate Rigid Body Properties:
Results:
11 copyright LMS International - 2006
Rigid Body Properties Calculation
Application
Calculate Rigid body properties and
synthesis of rigid body modes
Available as Add-in in
Test.Lab Modal
12 copyright LMS International - 2006
Rigid Body Properties Calculation
Application – Data Selection
� Easy FRF selection and visualization
� Calculate sum of FRFs
� Select band with double cursor
� 3 mass line methods
� Unchanged FRFs
� Corrected FRFs
� Lower residual
� Validate FRFs selection with
� Rigid body correlation
� ODS animate at selected
frequency band
� Animate Lower Residual
� Coloring and text feedback on
validation
Solid data validation before analysis
13 copyright LMS International - 2006
Rigid Body Properties Calculation
Application - Calculate
� Extract rigid body properties
� Coordinates of CoG
� Moments and products of inertia about a reference
� Principal moments of inertia and their direction
� User defined frequency and damping for rigid body modes
� Synthesized rigid body modes
� 3 translational
� 3 rotational
� Animate rigid body modes immediately
� Automatically add CoG with principal axes orientation on geometry
Rigid body properties and rigid body modes in 1 click
14 copyright LMS International - 2006
Rigid Body Properties Calculation
Application - Results
15 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
16 copyright LMS International - 2006
Rigid Body Properties Calculation
17 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
18 copyright LMS International - 2006
Rigid Body Properties Calculation
Test Case / Demo - Frame
� Frame structure
� ANSYS finite element model
� 2272 elements
� 2347 nodes
� Test data 408 FRFs
� 34 response DOFs
� 12 excitation DOFs
� Demo
19 copyright LMS International - 2006
Rigid Body Properties Calculation
Test Case - Frame
� Rigid body modes and the first
flexible mode are sufficiently
spaced
� Comparison of the 3 mass line
methods with the FE results
� 12 references
� 34 responses
� Excellent prediction for all
the methods
20 copyright LMS International - 2006
Rigid Body Properties Calculation
Test Case - Frame
Use the inertia properties to synthesize 6 rigid body modes
21 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
22 copyright LMS International - 2006
Conclusion
�Based on classical FRF measurement
�Limited measurement effort
�Fast and accurate analysis, using least squares solution
�Compensate the effect of the first flexible mode
�Fast and easy data validation
�6 rigid body modes for modal-based substructuring
�For a wide range of applications
23 copyright LMS International - 2006
Overview
Analysis: Rigid Body Calculator
Why are inertia properties needed ?
How to determine inertia properties ?
LMS Test.Lab Rigid body properties calculation
� How does it work ?
� Application
Practical Examples
Test case
� Demo: Frame
Conclusion
Acquisition: “From Geometry” in
Modal Impact
24 copyright LMS International - 2006
Test.Lab Modal Impact 7B: From Geometry
� Allows easy editing of Point Id’s based on defined geometry
� As a side effect roving accelerometer measurements are also better supported
061108 – Pre and Post sales training Webex
Mieke Robijns – Product Development Engineer
Thank you
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