Constraint data in a transient analysis

[lbl18]

Dear all,
i'm doing a transiet analysis on ansys,
I can plot by the "Time History Variables" the "DOF" of "nodal solution",
but i'm not able to plot the "reaction force"
how i can do to obtain the reaction force?

Any help is appreciated.

Thanks
lbl18

 

[Drej]

What do you mean "not able to plot"? Are you trying to plot the RF at an unconstrained node? If so, of course there will be zero RF.


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[lbl18]

thanks Drej,

i mean that if i select the constrained node (master node) and i plot the "reaction force" i obtain that all the value of each step is equal to zero; I think that the problem is the memorization of the value of "reaction force" at each step.

lbl18

I attach the editor file:



finish
/clear
/TITLE, Dynamic Analysis
/FILNAME,Dynamic111,0 ! This sets the jobname to 'Dynamic'
/PREP7 ! Enter preprocessor
!OUTRES,RSOL,all
K,1,0,0 ! Keypoints
K,2,1,0 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
L,1,2 ! Connect keypoints with line
ET,1,BEAM3 ! Element type
R,1,0.0001,8.33e-10,0.01 ! Real constants
MP,EX,1,2.068e11 ! Young's modulus
MP,PRXY,1,0.33 ! Poisson's ratio
MP,DENS,1,7830 ! Density

LESIZE,ALL,,,10 ! Element size
LMESH,1 ! Mesh the line
FINISH

/SOLU
ANTYPE, TRANS ! Transient analysis
TRNOPT,REDUC, ! reduced solution method
DELTIM,0.0001 ! Specifies the time step sizes

allsel
M,All,ALL
allsel

! al tempo 0
D,1,ALL
F,2,FY,-100
LSWRITE

! al tempo 0.0001

D,1,ALL
TIME,0.0001
KBC,0 ! carico a gradino
FDELE,2,ALL
LSWRITE

! al tempo 10
D,1,ALL
TIME,10
KBC,0
LSWRITE

LSSOLVE,1,3,1 ! solve multiple load steps
FINISH

/POST26
rforce,2,1,f,y,forza

 

[JoshPlumSE]

If you solve a static load, then would you be able to obtain a reaction at that node / DOF? The reason why I ask is because there are different ways to specify a joint constraint.

The most straight forward way is to remove that degree of freedom from the stiffness matrix (because it's deflection will always be zero). The only problem with that is that you cannot get reaction or displacement resutls for that DOF.

Some programs get around this issue by assigning an extremely rigid spring whenever you specify a boundary condition. That way, there is still a finite (but near zero) displacement at that joint and you can determine the joint reaction.

I'm not sure what Ansys is doing, but if they are using the first method above, then it may not be possible for them to report a reaction.