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Adams-to-Nastran
Jose L Ortiz, PhD.Adams User MeetingMunich - May 19, 2011
Agenda
• Overview
• Manual and Scripted Translation
• Theoretical Background
• Implementation Details
• Example
• Q&A
5/26/2011 2
• Overview– Introducing Adams-to-Nastran
• Manual and Scripted Translation
• Theoretical Background
• Implementation Details
• Example
• Q&A
Agenda
5/26/2011 3
Overview
• There is a need for model translation from Adams to FEA
5/26/2011 4
Multibody Dynamics System modelAdams
Finite Element Analysis modelFEA
Overview
• Introducing Adams-to-Nastran
– Performs an automatic model translation (export) from Adams to FEA
– Available for the past 2 releases
– As of today, an MD license and a LINEAR license are required
– Available only in the Adams/Solver C++
5/26/2011 5
Overview
• Introducing Adams-to-Nastran (cont.)
– The export process creates a set of fully editable *.bdf files
– Old “black box” option still available
– Minor limitations in the type or complexity of the Adams model• Models with non holonomic constraints
– Tool can be used from shell and from Adams/View
5/26/2011 6
Overview
• Introducing Adams-to-Nastran (cont.)
– There is no need to modify the Adams model
– There is no need to change your processes
– Export job can be triggered at any operating point
– Export job is a high fidelity translation• Accurate kinematics• Matching eigenvalues (static cases only)
5/26/2011 7
Overview
• Introducing Adams-to-Nastran (cont.)
– Users can use an optional configuration file to fine tune translation
– Current release exports to linear FEA codes
5/26/2011 8
Overview
• Example CAE process
5/26/2011 9
Motion analysis
FEA
translation
Create Adams model
Adams
NVH Optimization
• Overview
• Manual and Scripted Translation– Problems– Limitations
• Theoretical Background
• Implementation Details
• Example
• Q&A
Agenda
5/26/2011 10
Manual and Scripted Translation
• Manual translation – Error prone– Time consuming (300 man hours for chassis prototype)– Inaccurate
5/26/2011 11
Manual and Scripted Translation
• Manual translation – Error prone– Time consuming (300 man hours for chassis prototype)– Inaccurate
• Scripted (user-written script)– Limitations. Cumbersome– Inaccurate
5/26/2011 12
Manual and Scripted Translation
• Why inaccurate?– Kinematic configuration is hard to reproduce
5/26/2011 13
Manual and Scripted Translation
• Why inaccurate?– Kinematic configuration is hard to reproduce
– Eigenvalues computed by FEA code do not matcheigenvalues computed by Adams
5/26/2011 14
3.78
MBD FEA
7.23
Manual and Scripted Translation
• Why inaccurate?– Kinematic configuration is hard to reproduce
– Eigenvalues computed by FEA code do not matcheigenvalues computed by Adams
– Structural coupling can be compromised
5/26/2011 15
Manual and Scripted Translation
• Why inaccurate?– A thorough theoretical study showed that
(1) High fidelity translations require mathematical informationnot available to users
5/26/2011 16
Manual and Scripted Translation
• Why inaccurate?– A thorough theoretical study showed that
(1) High fidelity translations require mathematical informationnot available to users
Example:
MOTION/1, JOINT=2, FU=DX(7,8)-DZ(11,23)
5/26/2011 17
Manual and Scripted Translation
• Why inaccurate?– A thorough theoretical study showed that
(1) High fidelity translations require mathematical informationnot available to users
(2) Linear FEA codes use linear constraint equations
5/26/2011 18
• Overview
• Manual and Scripted Translation
• Theoretical Background– Overview– Governing equations in Adams– Governing equations in Nastran– Example
• Implementation Details
• Example
• Q&A
Agenda
5/26/2011 19
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
5/26/2011 20
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
Command:
SIMULATE/DYN, END=1.0, STEP=10LINEAR/EXPORT, TYPE=WHITEBOX, FILE=abc.nas
5/26/2011 21
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
Adams/View:
5/26/2011 22
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
Adams/View:
5/26/2011 23
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
– Accurate. Exact kinematics
5/26/2011 24
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
– Accurate. Exact kinematics
– Overcomes FEA limitations
5/26/2011 25
Theoretical Background
• Overview
– Automatic. The translation is another simulation job
– Accurate. Exact kinematics
– Overcomes FEA limitations
– Matching eigenvalues guaranteed for static cases
5/26/2011 26
Theoretical Background
• Basic idea
– Linearize the Adams model at the operating point
5/26/2011 27
Theoretical Background
• Basic idea
– Linearize the Adams model at the operating point
– Linearize the Adams model using Nastran coordinates
5/26/2011 28
Theoretical Background
• Basic idea
– Linearize the Adams model at the operating point
– Linearize the Adams model using Nastran coordinates
– Identify inertia elements, constraint equations and forces
5/26/2011 29
Theoretical Background
• Basic idea
– Linearize the Adams model at the operating point
– Linearize the Adams model using Nastran coordinates
– Identify inertia elements, constraint equations and forces
– Will the equations assembled by Nastran match?
5/26/2011 30
Theoretical Background
• Basic idea
– Linearize the Adams model at the operating point
– Linearize the Adams model using Nastran coordinates
– Identify inertia elements, constraint equations and forces
– Will the equations assembled by Nastran match?
– Need to examine the equations of motion in more detail
5/26/2011 31
Theoretical Background
• Governing equations in Adams– Simplified version
5/26/2011 32
Nastran coordinates
used!
Non linear equations!
Theoretical Background
• Governing equations in Adams (cont.)– Simplified version
– Partitioning
5/26/2011 33
Theoretical Background
• Governing equations in Adams (cont.)– Simplified version
– Partitioning
– Defining P
5/26/2011 34
This P is non linear!
Theoretical Background
• Governing equations in Adams (cont.)– Eliminating Lagrange multipliers
5/26/2011 35
Non linear equations!
Theoretical Background
• Governing equations in Adams (cont.)– Eliminating Lagrange multipliers
– Differentiating constraints
5/26/2011 36
Non linear equations!
Theoretical Background
• Governing equations in Adams (cont.)– Eliminating Lagrange multipliers
– Differentiating constraints
– Dependent accelerations
5/26/2011 37
Theoretical Background
• Governing equations in Adams (cont.)– Reduced ODE
• First and second derivatives of dependent states can be found from constraint equations
• Linearization done in terms of Nastran coordinates
5/26/2011 38
Theoretical Background
• Governing equations in Adams (cont.)– Reduced ODE
• First and second derivatives of dependent states can be found from constraint equations
• Linearization done in terms of Nastran coordinates
– Exact linearization of ODE. In variational form
5/26/2011 39
Linearized equations!
Theoretical Background
• Governing equations in Nastran– Partitioned equations of motion (linear)
5/26/2011 40
Theoretical Background
• Governing equations in Nastran (cont.) – Partitioned equations of motion (linear)
– Constraints (linear)
5/26/2011 41
Theoretical Background
• Governing equations in Nastran (cont.)– Partitioned equations of motion (linear)
– Constraints (linear)
– Defining P (this P is a constant)
5/26/2011 42
This P is a constant!
Theoretical Background
• Governing equations in Nastran (cont.)– Dependent accelerations
5/26/2011 43
Theoretical Background
• Governing equations in Nastran (cont.)– Dependent accelerations
– Reduced ODE
5/26/2011 44
Theoretical Background
• Governing equations in Nastran (cont.)– Dependent accelerations
– Reduced ODE
– Final form
5/26/2011 45
Theoretical Background
• Adams and Nastran equations
5/26/2011 46
Adams
Nastran
This P is a constant!
This P is non linear!
Theoretical Background
• Linearized Adams and Nastran equations
5/26/2011 47
Adams
Nastran
uuv
TTTT
fffMMvMMMMvMMMM
PPPPPPPPPPP
δδδδδδ
++=Ψ+++++++++
))(()()(
13
24132413
uvTT ffvMMMM δδδ PPPPP +=+++ )( 2413
P is now a constant!
Theoretical Background
• Linearized Adams and Nastran equations (cont.)
5/26/2011 48
Adams
Nastran
uvTT ffvMMMM δδδ PPPPP +=+++ )( 2413
uuv
TTTT
fffMMvMMMMvMMMM
PPPPPPPPPPP
δδδδδδ
++=Ψ+++++++++
))(()()(
13
24132413
Theoretical Background
• Eigensolutions will match only in static cases
5/26/2011 49
Adams
uuv
TTTT
fffMMvMMMMvMMMM
PPPPPPPPPPP
δδδδδδ
++=Ψ+++++++++
))(()()(
13
24132413
Zero in static configuration
Exported as DMIG
Theoretical Background
• Example Windmill– Model provided by NREL– Blades 63.5 m radius
5/26/2011 50
Theoretical Background
• Example Windmill (cont.)– Model provided by NREL– Blades 63.5 m radius
– Static simulation followed byeigensolution
– Model exported to Nastran
5/26/2011 51
Theoretical Background
• Example Windmill (cont.)– Exported model imported into
Patran
– Run SOL 107
5/26/2011 52
Theoretical Background
• Eigenvalue comparison
5/26/2011 53
Theoretical Background
• Eigenvalue comparison (cont.)
5/26/2011 54
• Overview
• Manual and Scripted Translation
• Theoretical Background
• Implementation Details– Inertial elements– Force elements– Constraints– Configuration file
• Example
• Q&A
Agenda
5/26/2011 55
Implementation Details
• Miscellaneous issues– By default, exports model for SOL 107
$ Force = N (newton)$ Time = s (second)$ UCF = 1000$ Export type: Whitebox$ Configuration file used: a2n_config.txt $$......1.......2.......3.......4.......5.......6.......7.......8.......SOL 107CENDTITLE = ADAMS2NASTRAN Export UtilitySUBTITLE = Adams operating point at time t=2.000000e+000ECHO = NONECMETHOD = 101
5/26/2011 56
Implementation Details
• Miscellaneous issues (cont.)– Files are organized using three optional styles and included in main
exported file
$$-------------------------------------------------------------------------------$ Model$-------------------------------------------------------------------------------INCLUDE 'results/a2n_01_w.bdf.nas’INCLUDE 'results/a2n_01_w.bdf_DMIGS.bdf’INCLUDE 'results/a2n_01_w.bdf_GRAPHICS.bdf’$ENDDATA
5/26/2011 57
Implementation Details
• Miscellaneous issues (cont.)– Every MARKER is exported as a GRID and a CORD2R:
PART/2MARKER/3
$ PART_2.MARKER_3CORD2R* 107 1.970978041D-11-3.519613300D+02* -3.938151830D-14 1.971010203D-11-3.519613300D+02 1.000000000D+00* 1.970903015D-11-3.529613300D+02-3.938151830D-14$ PART_2.MARKER_3GRID* 11 107 0.000000000E+00 0.000000000E+00* 0.000000000E+00 107
5/26/2011 58
Several numbering conventions
Implementation Details
• Miscellaneous issues (cont.)– GRIDs are RBE2’d to the CM of the corresponding PART:
$ PART_2RBE2 7 3 123456 16 17 18 19 20
21 22 23 24 25 26 27 2829 30 31 32 33 34 35 36
5/26/2011 59
Implementation Details
• Inertial elements– Adams model is linearized without constraint equations. This makes easier
to identify the inertia properties of all elements
5/26/2011 60
3
2
1
MM
M
Implementation Details
• Inertial elements (cont.)– PART and POINT_MASS are translated as CONM2
$PART_1GRID* 1 5.563508327E-01 1.690524981E-01* -1.224646799E-16$$PART_1CONM2* 1 1 0 3.000000000E+00** 4.000000000E+00 2.220446049E-16 4.000000000E+00-3.790727274E-32* -1.702149213E-32 4.000000000E+00
5/26/2011 61
Implementation Details
• Inertial elements (cont.)– FLEX_BODY are translated as SPOINT and three DMIG (M, K, and B)
$ FLEXIBLE_BEAMSPOINT 9999 THRU 10006$$ FLEXIBLE_BEAMDMIG MGMYFLX 0 6 2 0DMIG* MGMYFLX 9999 0* 9999 0 2.950000000D+00DMIG* MGMYFLX 10000 0* 10000 0 2.950000000D+00DMIG* MGMYFLX 10001 0* 10001 0 2.950000000D+00
5/26/2011 62
Implementation Details
• Force elements– All forcing elements (GFORCE, VFORCE, SPRING, etc.) are translated as
CBUSH, PBUSH cards plus a residual DMIG
5/26/2011 63
VFORCE CBUSH
+ DMIG
uuv fff PP δδδ ++
• Force elements (cont.)– PBUSH properties and residual DMIG computation
Matrix is full and not symmetric !
Implementation Details
5/26/2011 64
UKF u=
uK
Adams linearization
(damping not shown for clarity)
• Force elements (cont.)– PBUSH properties and residual DMIG
Implementation Details
5/26/2011 65
?URKRUK pT
u =
• Force elements (cont.)– PBUSH properties and residual DMIG computation
Desired PBUSH propertymust be diagonal
Standard FEA transformation
• Force elements (cont.)– PBUSH properties and residual DMIG
Implementation Details
5/26/2011 66
rpT
u DKRKR +=
• Force elements (cont.)– PBUSH properties and residual DMIG computation
Exported PBUSH property.Diagonal matrix
Residual DMIG.Residual DMIG could be zero!
Implementation Details
• Force elements (cont.)– Typical output (residual DMIG not shown)
$ I: PART_1.MARKER_4, J: PART_9.MARKER_8$ Grid coincident with marker I but located on PART_9GRID* 10 1000004 0.000000000E+00 0.000000000E+00* 0.000000000E+00 1000004RBE2 11 9 123456 10$$SPRING_1PBUSH* 1000000 K 5.500000000E+01 1.424819004E-14** 1.221245327E-14 0.000000000E+00 0.000000000E+00 0.000000000E+00** B 0.000000000E+00 0.000000000E+00** 0.000000000E+00 0.000000000E+00 0.000000000E+00 0.000000000E+00$CORD2R* 10 1.112701665D+00-6.618950039D-01* -2.449293598D-16 1.112701665D+00-6.618950039D-01 1.000000000D+01* 1.054919334D+01 2.647580015D+00-2.449293598D-16$ I: PART_1.MARKER_4CBUSH 6000000 1000000 1000004 10 10
5/26/2011 67
Implementation Details
• Force elements (cont.)– Residual DMIG can be split into a symmetric and a non symmetric parts
– Without splitting
SET 1 = KGt00001K2GG = 1
– With splitting
SET 1 = KGt00001SET 2 = KPt00001K2GG = 1K2PP = 2
5/26/2011 68
Symmetric residual
Non symmetric residual
Implementation Details
• Force elements (cont.)– Residual non symmetric DMIG can be manually removed
from exported files
– Removal of non symmetric DMIG allows running SOL 103 and other solutions requiring symmetric matrices only
5/26/2011 69
Implementation Details
• Constraint elements– Whenever possible, JOINT and JPRIM are exported using RJOINT
$----------------------------------- TrnJnt ------------------------------------$$JOINT_3000$ I: PART_3000.MARKER_3001, J:PART_9000.MARKER_9003GRID* 9010 1003001 0.000000000E+00 0.000000000E+00* 0.000000000E+00 1003001 $JOINT_3000RJOINT* 9010 1003001 9010 12456$$----------------------------------- FxdJnt ------------------------------------$$JOINT_1000$ I: PART_1000.MK_REF1, J:PART_9000.MARKER_9001RJOINT* 9011 1001001 1009001 123456
5/26/2011 70
Implementation Details
• Constraint elements (cont.)– Whenever possible, JOINT and JPRIM are exported using RJOINT
– UNIVERSAL and HOOKE are exported as combination of RJOINT
– Other constraints (GCON, MOTION, etc.) are exported as MPC cards
5/26/2011 71
Implementation Details
• Constraint elements (cont.)– Constraint MPC are obtained by computing
– Matrix is exported as MPC
5/26/2011 72
Implementation Details
• Differential elements– DIFF, LSE, GSE, and TFSISO are exported as SPOINT and DMIG
– Given
5/26/2011 73
),,(0)(
),(
tqzhzq
zqfqM Tq
==Φ
=Φ+
λDIFF, LSE, GSETFSISO
Implementation Details
• Differential elements (cont.)– Linearization finds
05/15/11 74
Exported as DMIG
=
zqq
AAAAQP
I
zqq
432
1
00
Implementation Details
• Graphic elements– Alpha version
5/26/2011 75
CONM2, DMIG, GRID, SPOINT
Implementation Details
• Graphic elements (cont.)– Current version
5/26/2011 76
Implementation Details
• Graphic elements (cont.)– All GRAPHIC elements are exported as constrained CQUAD4 or CTRIA3
elements with zero mass
5/26/2011 77
Implementation Details
• Graphic elements (cont.)– All GRAPHIC elements are exported as constrained CQUAD4 or CTRIA3
elements with zero mass
– FLEX_BODY graphics are exported fixed in space (to be enhanced)
– All exported graphics can be removed before starting Nastran solutions
– Debugging tool. Does not affect results.
5/26/2011 78
Implementation Details
• Configuration file (cont.)– An optional configuration file can be supplied
LINEAR/EXPORT, TYPE=WHITEBOX, FILE=abc.nas, CONFIG=myconfig.txt
– Configuration file is a plain text file with directives
– Allow fine tuning the export process
5/26/2011 79
Implementation Details
• Configuration file (cont.)– Users may:
Modify numbering schemes, choose solution number, modify defaults, create channels for FRF solution in Nastran, remove damping, etc.
– Easy to add new directives
5/26/2011 80
Implementation Details
• Configuration file (cont.)– Example configuration
$ Setting FRF analysis for SOL 108
actuator_swept_sine {phase_angle = 90 magnitude = 77name = test01
}
force_input_channel {name = f1marker_id = 3001dof = ryactuator_name = test01
}
displacement_output_channel {name = d1marker_name = model.PART_1000.MK_REF1
}
05/15/11 81
Comments
Implementation Details
• Configuration file (cont.)– Example configuration (cont.)
frequency_response_subcase {number = 101input_channel_names = f1output_channel_names = d1
}
export_all_markers = nompc_set = 77grid_offset = 1spoint_offset = 9999solution_number = 108forces_dmig_name = ADMS1differentials_dmig_name = ZZ3matrix_entry_zero_tolerance = 1.e-8
05/15/11 82
• Overview
• Manual and Scripted Translation
• Theoretical Background
• Implementation Details
• Example– Full chassis model
• Q&A
Agenda
5/26/2011 83
Example
• Chassis model prototype (courtesy of BMW Group)
5/26/2011 84
Example
• Exported model loaded in SimXpert
5/26/2011 85
Example
• Eigenvalues comparison
5/26/2011 86
Chassis - Frequency error vs. Mode number
-0.2000
0.0000
0.2000
0.4000
0.6000
0.8000
1.0000
1.2000
1.4000
1.6000
0 50 100 150 200 250 300Mode number
% E
rror
Example
• Observations– Matching eigenvalues for static cases only
– FEA model has exactly the same kinematic configuration as in Adams
5/26/2011 87
• Overview
• Manual and Scripted Translation
• Theoretical Background
• Implementation Details
• Examples
• Q&A– Acknowledgments– Q&A
Agenda
5/26/2011 88
Q&A
• Acknowledgments
– MSC.Software Italy
– Dr. Daniel Heiserer (BMW Group)
– MSC.Software Germany
5/26/2011 89