NX NASTRAN Rotodynamics

Creator
Creator

Hello NASTRAN users,

 

I have a question that I hope someone can help me with. I am trying to perform a NASTRAN Rotordynamics analysis on a generic Laval Jeffcot Rotor with very stiff bearings and flexible shaft. The model has a disk in the middle of the shaft and is supported at either end of the shaft by the bearings.  The model is described as follows:

 

Bearings K = 1E10 lbf/in (With negligible damping)

Mass of disk = 0.259 lbf-s^2/in (10lbm)

Ip disk = 0.207 lbf-s^2-in (80 lbm-in^2)

Id disk = 0.129 lbf-s^2-in (50 lbm-in^2)

L = 10 in

Shaft diameter = 0.375 in

Shaft E = 3E7 psi

 

I am using the template from example rotor091.dat and modified it to the values described above. When I run the file, I am getting results that do not make sense since I expectd the second FWD mode to increase and the BWD mode to decrease with increasing rpm due to gyroscoping stiffening/softening effect. Can you guys point me to what I may be missing? 

 

Here is the input file, Thanks in advance.

 

NASTRAN $

$

assign output4='OUTDIR:Ch4.2.gpf',unit=22, form=formatted
assign output4='OUTDIR:Ch4.2.csv',unit=25, form=formatted
$
SOL 110
$
TIME 20000
DIAG 8
$
CEND
$
SPC = 1
$
SET 1 = 1006
$
DISP = 1
$
RMETHOD = 99
$
$
METHOD = 1
CMETHOD = 2
$
$
BEGIN BULK
$
$ Units for GPF and CSV files
$
PARAM ROTGPF 22
PARAM ROTCSV 25
$
ROTORG 11 1001 THRU 1024
$
$ SID RSTART RSTEP NUMSTEP REFSYS CMOUT RUNIT FUNIT
ROTORD 99 0.0 100.0 100 FIX -1.0 RPM HZ +ROT0
$ ZSTEIN ORBEPS ROTPRT
+ROT0 1.0E-6 +ROT1
$ RID1 RSET1 RSPEED1 RCORD1 W3-1 W4-1 RFORCE1
+ROT1 11 1.0 1
$
$ . . . . . . .
EIGRL 1 4 1
EIGC 2 CLAN 4
$
$ Coordinate system for definition of rotor axis of rotation
$
CORD2R 1 0. 0. 0. 0. 0. 1. +XCRD001
+XCRD001 1. 0. 0.
$
$ Shaft stiffness. here a flexible massless shaft is used
$
PBAR 1000 1000 0.11039 9.707-4 9.702-4 0.001941 +P00V8AA
+P00V8AA 0. 0.1875 0.1875 0. 0. -0.1875 -0.1875 0. +P00V8AB
+P00V8AB 0.9 0.9
MAT1 1000 3.000+7 0.3 0.0
$
$ Nodes
$
GRID 1001 0. 0. -5.
GRID 1006 0. 0. 0.
GRID 1011 0. 0. 5.
$
$ Elements
$
CBAR 1001 1000 1001 1006 1. 0. 0.
CBAR 1010 1000 1006 1011 1. 0. 0.
$
$ Mass and inertia of the rotor disk
$
CONM2 1106 1006 0.02590 +C1106
+C1106 0.12950 0.12950 0.207205
$
$ Bearing points on the support side (non rotating)
$
GRID 101 0. 0. -5.
GRID 111 0. 0. 5.
$
$ Bearing points on the rotor side (coincident with the rotor nodes)
$
GRID 201 0. 0. -5.
GRID 211 0. 0. 5.
$
$ Bearings
$
CELAS1 101 101 101 1 201 1
CELAS1 102 102 101 2 201 2
$
CELAS1 111 111 111 1 211 1
CELAS1 112 112 111 2 211 2
$
PELAS 101 1.0+10
PELAS 102 1.0+10
PELAS 111 1.0+10
PELAS 112 1.0+10
$
$ Damping of the bearings
$
CDAMP1 301 301 101 1 201 1
CDAMP1 302 302 101 2 201 2
$
CDAMP1 311 311 111 1 211 1
CDAMP1 312 312 111 2 211 2
$
$ here the damping is not considered. Small values are used in order to avoid
$ numerical problems
$
PDAMP 301 1.0-6
PDAMP 302 1.0-6
PDAMP 311 1.0-6
PDAMP 312 1.0-6
$
$ Connection of rotor points to bearing
$
RBE2 201 1001 123456 201
RBE2 211 1011 123456 211
$
$ constraints of rotor axial motion ands rotation
$
SPC1 1 36 1001
$
$ Constraints of the bearings
$
SPC1 1 123456 101 111
$
ENDDATA