Regard Bruhn problem 2

[GopalPartha]

Actually iam intrested to solve book problems into FEA Model, for that I took one of Landing Gear Problem from Bruhn Book
I have modeled those truss with Beam Element in NX nastran, Iam getting results but result not converged with Text book result.
Find the attachment for the FEA model as well Book problem.
Please let me know anyone can solve the issue.
Regards,
Gopal Parthasarathy

Nastran Deck

$**********************
INIT MASTER(S)
NASTRAN SYSTEM(442)=-1,SYSTEM(319)=1
ID Landing,Femap
SOL SESTATIC
TIME 10000
CEND
TITLE = NX Nastran Static Analysis Set
ECHO = NONE
DISPLACEMENT(PLOT) = ALL
SPCFORCE(PLOT) = ALL
OLOAD(PLOT) = ALL
FORCE(PLOT,CORNER) = ALL
STRESS(PLOT,CORNER) = ALL
SPC = 2
LOAD = 1
BEGIN BULK
$ ***************************************************************************
$ Written by : Femap with NX Nastran
$ Version : 11.0.0
$ Translator : NX Nastran
$ From Model : C:\Gopal\Bruhn_Problems\Landing_gear_12.modfem
$ Date : Tue Feb 25 20:31:57 2014
$ Output To : C:\Gopal\Bruhn_Problems
$ ***************************************************************************
$
PARAM,POST,-1
PARAM,OGEOM,NO
PARAM,AUTOSPC,YES
PARAM,K6ROT,100.
PARAM,GRDPNT,0
CORD2C 1 0 0. 0. 0. 0. 0. 1.+FEMAPC1
+FEMAPC1 1. 0. 1.
CORD2S 2 0 0. 0. 0. 0. 0. 1.+FEMAPC2
+FEMAPC2 1. 0. 1.
$ Femap with NX Nastran Load Set 1 : Load
FORCE 1 6 0 1. 5000.8660.254 0.
$ Femap with NX Nastran Constraint Set 2 : support
SPC1 2 13456 3
SPC1 2 123456 4
SPC1 2 123456 5
$ Femap with NX Nastran Property 1 : ROD
PROD 1 2 .1 .1 0. 0.
$ Femap with NX Nastran Property 2 : BAR ELement
$ Femap with NX Nastran PropShape 2 : 5,0,0.2,0.,0.,0.,0.,0.
$ Femap with NX Nastran PropOrient 2 : 5,0,0.,1.,2.,3.,4.,-1.,0.,0.
PBAR 2 3 .125664.0012566.0012566.0025112 0. +
+ 0. -.2 .2 0. 0. .2 -.2 0.+
+ .8861727.8861727 0.
$ Femap with NX Nastran Property 3 : Beam Element
$ Femap with NX Nastran PropShape 3 : 5,0,1.25,0.,0.,0.,0.,0.
$ Femap with NX Nastran PropOrient 3 : 5,0,0.,1.,2.,3.,4.,-1.,0.,0.
PBEAM 3 24.9087391.9174761.917476 0.3.831723 0.+
+ 0. -1.25 1.25 0. 0. 1.25 -1.25 0.+
+ YESA 1. +
+ .8861771.8861773
$ Femap with NX Nastran Material 2 : AISI 4130 Steel (DEFAULT CARD)
MAT1 2 2.9+7 .327.3315-4 6.6-6 70.
MAT4 25.5555-4 40.537.3315-4
$ Femap with NX Nastran Material 3 : 6061-T651 Al Plate .25-2. (DEFAULT CARD)
MAT1 39900000. .332.5388-4 1.265-5 70. +
+ 35000. 35000. 27000.
MAT4 3.0020602 81.1442.5388-4
GRID 1 0 0. 12. 0. 0
GRID 2 0 0. 24. 0. 0
GRID 3 0 0. 36. 0. 0
GRID 4 0 12. 36. 0. 0
GRID 5 0 -12. 36. 0. 0
GRID 6 0 0. 0. 0. 0
GRID 7 0 0. 24. 0. 0 3456
GRID 8 0 0. 12. 0. 0 3456
GRID 9 0 0. 12. 0. 0
GRID 10 0 0. 24. 0. 0
RBE2 1 9 12 1 8
RBE2 2 10 12 2 7
CBEAM 4 3 4 7 0. 0. 1.
CBEAM 5 3 3 2 0. 0. 1.
CBEAM 7 3 2 1 0. 0. 1.
CBEAM 10 3 1 6 0. 0. 1.
CBEAM 11 3 5 8 0. 0. 1.
ENDDATA e951db54

 

[rb1957]

remove 456 freedoms from the SPCs

use CROD elements for the brace struts (pinned ends, axial loads only)

Quando Omni Flunkus Moritati

 

[GrandpaDave]

Yes... It's the old garbage-in garbage-out problem.

 

[GopalPartha]

Yes, I agreed that's old problem, But I need solution...
Could you help me if you can
regards,
Gopal Parthasarathy

 

[GopalPartha]

Yes I did with CROD, When I use CROD Iam not getting any magnitute for the Rc Reaction.
Becasue 10000lbs applied into two direction that Fx-5000lbs; Fy = 8660.564.
CROD Not resisting any bending stiffness there is Stiffness issue came, So we have to use PARAM, BAILOUT, -1
But Y direction it's taking as CROD take Axial Load. That's what I used BEAM to take Fx Load.
Please chexk the problem.
Regards,
Gopal Parthasarathy

 

[GopalPartha]

Nastran file for the ref
Regards,
Gopal Parthasarathy

 

[rb1957]

the main fttg (connecting to Rc) needs to be a beam, 'cause it's taking bending.

the brace struts are designed to take axial load only, and should work with CROD.

remove the fixity of the constraints (this creates redundancies that Bruhn would not have solved for); his reactions are clearly pinned. if this problem is all in-plane you need to consider the out-of-plane freedom ... you constraints need to constrain the 6 rigid body motions.

i imagine that this problem is meant to be solvable by three equations of equilibrium (three unknowns) ... looking carefully at D there is no moment constraint. But FEA is not as smart as we are ... we know this is an in-plane problem, so we know how to solve it; FEA needs to solve the full 3D problem, the constraints to solve the problem react 3 rigid body motions, so you need to provide the other three constraints (Fz, Mx, My) at D.

be Very Very careful using PARAM, BAILOUT, your model shouldn't need it ... maybe use it to get your model to run to see what's the problem and fix the problem so it runs without BAILOUT.

Quando Omni Flunkus Moritati

 

[GopalPartha]

Really Thanks for the solution.
I got the result as same as book result
regards,
Gopal Parthasarathy

 

[rb1957]

what, no LPS ?

Quando Omni Flunkus Moritati

 

[GopalPartha]

May I Know what is meaning of LPS ?

regards

Gopal parthasarathy

 

[rb1957]

Little Purple Star as in "like this post? Star it!" (button about 2" from this text) ...

Quando Omni Flunkus Moritati

 

[GrandpaDave]

GoPal,
Sorry I could not help because I've been retired too long.
But I had to ping you with that GIGO. Everyone is guilty of
GIGOs. I'm assuming you are a university student going through
learning curves. You have chosen a good approach of checking out Bruhn.
His book(s) has(have) many errors and there are correction sheets (errata sheets)
on the web.
G-pa Dave