An Improved Process for Mapping Aeroelastic Loads Across Structural Meshes
Douglas J. Neill, Jack F. Castro, Patricia E. Jones
MSC.Software Corporation
Agenda
• Typical loads processes and issues• Proposed process• The ADB/AEDB collections• Methodology• Results• Summary
An Aeroelastic Loads Process
CFD or WT
“Panel Code”
Rigid Aero Loads
AIC
“Flexibility” FE
Corrected LoadsOn
Coarse FE
Corrected LoadsOn
Internal Loads FE
AeroelasticSolver
LoadsTransfer
Tools
Critical Loads SurveyStress GroupOther tools
Issues with Typical Process
• 2 common approaches to transfer coarse loads to the internal loads model– Smearing component integrated loads
• Heuristic• Prone to error• Slow, engineer-in-the-loop • Loss of balance during smear• Re-balancing is itself heuristic and slow
– “Common Loads Points”• Difficult to coordinate• Tends to degrade FE model quality• Degrades computational performance
Issues with Typical Process
• The outlined approach works, but it’s a problem in many organizations– Too slow
• Cannot keep up with critical loads survey needs
– Too easy to make mistakes– Cannot be repeated reliably
• Too many engineer-in-the-loop heuristics• Too easy to lose the association of loading event (on
coarse FE) to critical load (on internal loads FE).
The Proposed Process
• “Remember” the elastically corrected loads on the aerodynamic mesh– As MSC.FlightLoads does now on the ADB and
AEDB
• Re-evaluate the mapping of these load increments onto the new structural FE– Re-use standard coupling methods
• Gather the loads onto an updated AEDB for use downstream– Downstream tools don’t realize a two-step
process was applied upstream
The Proposed Process
MSC.FlightLoads“AEDB”
(Coarse FE)
CFD or WT
“Panel Code” MSC.FlightLoads“ADB”
“Flexibility” FE
AeroelasticSolver New
MappingTool
“Internal Loads” FE
SplineTo
New FE
MSC.FlightLoads“AEDB”
(Internal Loads FE)
Critical Loads SurveyStress GroupOther tools
Can be applied recursively
The ADB/AEDB Collections
• The ADB contains the aerodynamic model– Mesh topology– Rigid aerodynamic loads
• The AEDB contains the ADB and “flexible increments” (FI)– FI include forces and displacements– Forces arise from rigid and from the
displacements passing thru the AIC– All forces (except rigid inertial) are on both the
aero and structural meshes– These are “unbalanced”, but all balanced
states are a linear combination
Mapping Methodology
• From equations of motion for static aeroelasticity1. rigid load + AIC deformation2. AIC * deformation elastic increment force3. rigid load + elastic force corrected load
• From 2 on the aero mesh, we map to the new structural FE via DMAP alter (for now)– From these loads, a statics solution on new FE
yields deformations on new FE– Restore inertial loads (rigid) from new FE– Proceed with normal AEDB creation to complete
the AEDB collection
Advantages
• No heuristic methods– Two mappings of the same kind– Repeatable– Recursively applicable
• Full vehicle balanced loads are immediately available– Trim on the new structure– Using mass of the new structure
• BUT using inertial aeroelastic correction of the original FE
• FASTER for superior FIDELITY
An Example
The common aero mesh
The built-up structure
The beam-stick structure
Cases• All analyses represent a 1g Level Flight
Trim at M=0.4, Sea Level• 3 variants were run
– Aero + Beam FE– Aero + Built-up FE– Starting with Aero + Beam, Map to Built-up FE
and then trim• Model Sizes
– Aero: 554 Boxes– Beam FE: 141 nodes– Built-up FE 3171 nodes
• All runs were made on NEC laptop, Pentium II
Results and Timing Summary
Beam FE Solution Built-up FE Solution Beam Solution Mapped to Built-up
ANGLEA1.740 degrees
1.702 degrees 1.740 degrees
SIDES 0.300 degrees 0.338 degrees 0.211 degrees
RUDDER -0.552 degrees -0.623 degrees -0.603 degrees
ELEV 8.311 degrees 8.159 degrees 8.310 degrees
AILERON(s) 0.450 degrees 0.292 degrees 0.463 degrees
CPU (ADB/Mach) 13.1 13.1 0 (taken from ADB)
CPU (Structural) 22.2 32.3 29.1
CPU (AEDB/Mach&Q) 13.4 128.8 16.7
CPU (Total) 49.0 174.4 46.5
Results and Timing Summary
0500
10001500200025003000350040004500
CPU
1 2 3 4
Increasing Mach/Q Pairs
Comparison of CPU Growth
Total Direct
Total Remapped
1/1 2/2 2/6 5/30
Number of Mach/M-Q Pairs
Qualitative Results
Trimmed ForcesOn
Aero Mesh
Trimmed ForcesOn
Beam Mesh
Qualitative Results (cont.)
Trimmed ForcesOn
Aero Mesh
Trimmed ForcesOn
Built-up Mesh
Quantitative Results
Comparison of Bending Moment
-20000
0
20000
40000
60000
80000
100000
120000
0.00 50.00 100.00 150.00 200.00
Span Station
Ben
din
g M
om
ent
Aero Mesh BendingMoment
Beam Bending Moment
Refined FE BendingMoment
Zoom into Tip Area
Quantitative Results
Comparison of Tip Bending Moment
-500
0
500
1000
1500
2000
150.00 155.00 160.00 165.00 170.00 175.00 180.00 185.00
Span Station
Ben
din
g M
om
ent
Aero Mesh BendingMoment
Beam BendingMoment
Refined FE BendingMoment
Summary of New Approach
• Costs– It approximates the inertial aeroelastic effect – It requires two spline models
• Benefits – It is computational (not heuristic)– It preserves full-vehicle balance– It is faster (process) and uses less CPU, too
• CPU savings accumulate as more Mach/Q pairs are used
– It creates fully reusable databases • easy to generate new trim states• able to recursively map the “mapped” solution to
other models