Modal Continuity within Flexible Bodies (SE) in ADAMS
Transcript of Modal Continuity within Flexible Bodies (SE) in ADAMS
MSC NASTRAN 2013 SOL400 Adams MNF Export:
Accurate representation of Preloaded Flexible Components in
Multi-body system
Sukhpreet Sandhu
Background
• Adams represents deformation in flexible bodies through CB modes
• MNF files consists of these modes (besides other information…)
• CB modes respect BC’s and have the “richness” of vibration modes
Critical in forming joints: Capture exact motion of interface points (a-set)
MNF can be exported in either:
• Undeformed configuration
• Deformed / loaded configuration (includes
prestressing effects)
Why, SOL 400 MNF?
• Leverage SOL 400’s advanced modelling capabilities:
– Advanced elements: Material nonlinearity, large deformation
– Nonlinear offsets
– Complex physical phenomenon: Contact
– Large displacement RBEs
• One step procedure to generate MNF with nonlinear preload
– SOL 103 requires restart from SOL 106/SOL 129 to generate MNF with
nonlinear preload
• Better representation of Flex/bodies
• More accurate multi-body simulations
Work Flow / Typical Analysis NASTRAN SOL 400 ADAMS
•Nonlinear static step: To get to the
deformed configuration
•Modal step: NASTRAN transforms
Nodal DOFs to CB Modal Coords
• Export MNF
• Import MNF into the MBS to
represent the Flexbody:
•Define the loads and Joints on
the Flexbody
•Conduct the Simulation
Tip Displacement
Helicopter Rotor Blade
Model
Windshield Wiper Model
Typical SOL 400 Input File for MNF Export
Helicopter Rotor Blade Model
Windshield Wiper Model
$ Exec. Control Section
SOL 400
CEND
$ Case Control Section
ADAMSMNF flexbody=yes, psetid=all,
outgstrs=yes, outgstrn=yes
SUBCASE 1
$ Preload
STEP 10
$ Static load and support for preload
SUBTITLE = PRELOAD
ANALYSIS = NLSTATICS
NLSTEP = 110
LOAD = 120
SPC = 130
BCONTACT = 140
SPCF = ALL
$ Generate stress and strain grid shapes
STRESS(PLOT) = ALL
STRAIN(PLOT) = ALL
GPSTRESS(PLOT) = ALL
GPSTRAIN(PLOT) = ALL
$ Modal loading and MNF Output step
STEP 20
ANALYSIS = MODES
$ Select real Eigen Value Parameters
METHOD = 300
$ Turn residual vectors on
RESVEC = COMPONENT
...
$ Bulk section
BEGIN BULK
GRID ...
CHEXA ...
SPC1 ...
FORCE1 ...
NLSTEP ...
EIGR, 300, LAN, , , , 20
$ SPOINT are required in Main bulk
SPOINT,100001,THRU,100020
$ ADAMS REQUIRES DTI, UNITS
DTI, UNITS, 1, LBM, LBF, IN, SEC
$ If Required, turn on gridpoint weight generator
PARAM, GRDPNT, 0
$ If Required, use WTMASS, Default value = 1.0
PARAM, WTMASS, 0.00259
$ FLEXBODY Bulk section
BEGIN BULK FLXBDY=10
$ Attachment point and component mode (A-SET)
selection
ASET1,123456,1,11,111,121
QSET1,0,100001,THRU,100020
Some Guidelines
• The ASET and QSET, must only, appear in the FLXBDY bulk data section
• For contact, friction option should be turned on:
– $ Select bilinear Coulomb friction for all subcases
– BCPARA, 0, FTYPE, 6
• In ANALYSIS=MODES STEP, the SPC constraint should be removed
• During preload the structure should be statically supported and follower loading
must be applied as a self equilibrating load set
Simple Example: Plate Model
• Plate model with geometric nonlinearities.
• Step 1, nonlinear static step: Preloads the plate under simple tension
• Step 2, modal step: MNF is exported.
SOL 103 Restarted from SOL 106 SOL 400
29.2195 29.2195
47.848 47.8296
62.8388 62.8474
86.5278 86.5278
124.855 124.855
141.29 141.29
150.832 150.832
Validation
Helicopter Rotor Blade System
Helicopter Rotor Blade System
• Generation of Sol 400 MNF:
• Step 1, the blade is preloaded:
• Self Weight
• Axial tensile loading of 4.224e+5 N (centrifugal loading at 2000 deg/s)
• Step 2, modal step: MNF is exported
• Rayleigh damping included (Parameters a1 = 2508 and a2=-1.276e-5)
• Cantilevered modes of Blade:
• Unloaded SOL 103 Model: 2.658 Hz and 8.454 Hz
• Preloaded SOL 400 Model: 3.108 Hz and 8.769 Hz
Helicopter Rotor Blade System
• Three blades attached to the rotor
head through fixed joints
• Rotor shaft speed linearly ramped to
2000 deg/s at t = 25s
• Impulsive load applied at t = 26s: F = 1.0e+5 N in z-direction, Dt = 0.01s
Helicopter Rotor Blade System
Translational Deformation (+z) at Blade Tip
Helicopter Rotor Blade System
Von Mises Stress at t = 26.029s
Concluding Remarks
• A new capability of exporting MNF in NASTRAN SOL 400 has
been added
• The capability leverages SOL 400’s advanced modeling
capabilities to enable better representation of flexible bodies
in ADAMS
References
Quick Reference Guide
• MSC Nastran 2013 Quick Reference Guide: See ADAMSMNF case control
command documentation
Release Guide
• MSC Nastran 2013 Release Guide: See Section 4, Support for Export of
Adams MNF file in SOL 400