inertia relief in linear static analysis · 2019-05-01 · femap, nx nastran, fibersim, nx, solid...
TRANSCRIPT
5/22/2012
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IN THIS WEBINAR:
• What is inertia relief?
• Setting up a static analysis with inertia relief in FEMAP
• Recovering OLOAD data from Nastran output
Inertia Relief in Linear Static
Analysis
Nick Mehlig
Aerospace Stress Engineer
Structural Design and Analysis
PRESENTED BY:
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• Assumptions:
– Linear
– Static equilibrium
– No Rigid Body Motion (singular matrix)
• Constraint is required
• Breakout models are useful for sizing and
analyzing assemblies
• Full vehicle models are used for internal
loads
Static Analysis in Finite Element Method
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Examples
Airbus Vahana
Source: vahana.aero
Hubble space telescope in orbit.
Source: NASA
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What is Inertia Relief?
• An accelerating aircraft has a net force acting on it and an equal and opposite force due to the
aircraft mass.
– This equal and opposite force is the inertial loading on the aircraft
• Example: Increased lift bends the wings up while the inertial loading “relieves” some of the
bending
www.scienceabc.com
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Importance of Inertial Effects
• Inertial forces will “relieve” wing bending
• A standard linear static run would show larger internal loads in the wing
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
0 50 100 150 200
Win
g L
oad
Span
Total Lift Weight Fuel
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Inertia Relief in Static Analysis
• Inertia Relief allows a static analysis to be run without constraints.
• Applied loads are balanced out by accelerations applied to nodes.
• Rigid Body Acceleration is canceled out leaving a state of static equilibrium.
• Supported for NASTRAN Linear Static SOL101
– Linear Static portions of SOL 105, 200
• GRAV Cards cannot be used
– The acceleration from a GRAV card will be completely canceled out by the Inertia
Relief accelerations
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FEMAP Demo
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Manual vs. Automatic Inertia Relief
• Manual (PARAM, INREL, -1)
– SUPORT entry is required
– SUPORT card contains the rigid body DOFs which will
be balanced out
– Ground point (PARAM,GRDPNT,*) determines where
inertia relief calculations are summed about
• Automatic (PARAM, INREL, -2)
– No SUPORT entry required
– Ground Point (PARAM,GRDPNT,*) only affects GPWG
and OLOAD output
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Recovering Data from .f06 file
• Grid Point Weight Generator (GPWG)
• OLOAD Resultant
• User Information Message 3035 (for Manual Inertia Relief only)
– Epsilon
– Strain Energy
• Intermediate Matrix, [QRR] - total rigid body mass of the structure
• QRL Matrix - the resultant of the apparent reaction loads
• URA Matrix - rigid body acceleration matrix computed from the applied loads
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Grid Point Weight Generator (GPWG)
• Summed about GRDPNT
• Origin by default (PARAM, GRDPNT, 0)
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OLOAD Resultant
• Section 1 shows the resultant of applied
loads summed about the GRDPNT
• Following 6 sections are the necessary
loads required for unit acceleration
2
4
5
3
6
7
1
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User Information Message 3035
• Manual Inertia Relief only
– Epsilon
– Strain Energy
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Intermediate Matrices
• QRR Matrix - total rigid body mass of the structure
• QRL Matrix - the resultant of the apparent reaction loads
• URA Matrix - rigid body acceleration matrix computed from the applied loads
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How is the Data Helpful?
• Verifying that the correct load factor is being applied
• Verifying correct mass of FEM
• Verifying the quality of the model & results
• Using acceleration data outside of NASTRAN
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Structural Design and Analysis (Structures.Aero)
Structural Analysis
• Team of stress engineers that help our clients
design lightweight and load efficient structures.
• We service aerospace companies and other
industries that require high level analysis.
• Specialty in composites and lightweight
structures
• Tools used include hand analysis, HyperSizer,
Femap, NX Nastran, Fibersim, NX, Solid Edge,
Simcenter 3D, LS Dyna, and LMS.
Software Sales and Support
• Value added reseller providing software, training,
and support for products we use on a daily
basis.
• Support Femap, NX Nastran, Simcenter 3D,
Fibersim, Solid Edge, and HyperSizer.
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For questions on the material covered
today, please contact Nick Mehlig.
For questions about pricing, or to see a
demo, please contact Marty Sivic.
Questions?
Marty SivicDirector of Sales
724-382-5290
Nick MehligAerospace Stress Engineer
703-935-2881