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