Problem with transient analysis

[hexa2016]

Dear all,

I am running a transient analysis on rubber bearing which tested with compression + horizontal loading. The vertical pressure applied on top surface for 6 MPa, then cyclic load at 0.5Hz for 25mm displacement. Bottom surface is fixed at all dof. I defined the load pattern as triangular wave and the analysis is using multiple load-steps.

solu
antype,4
trnopt,full
nlgeom,1
deltim,0.5
solcontrol,on
outres,all,all

timint,on
time,3
kbc,0
asel,s,area,,1
nsla,s,1
d,all,all !fixed bottom surface
allsel

asel,s,area,,182
nsla,s,1
sf,all,pres,6 !6 MPa on top surface

allsel
lswrite !ls1


!Time at 3.125
time,3.125
asel,s,area,,182
nsla,s,1
d,all,ux,6.25
allsel
lswrite !ls2


!Time at 3.25

time,3.25
asel,s,area,,182
nsla,s,1
d,all,ux,12.5
allsel
lswrite !ls3

......continue to final loadstep


at loadstep1, I set the initial condition (6MPa vertical pressure + set the bottom surface fixed at all dof)for 3 seconds . And the cylic load on horizontal direction started in loadstep 2.

But I problem in the first step, where the vertical pressure keep going up and down for few times in the first load-step. In experimental work, the pressure is is applied for 6MPa, then under 6Mpa vertical vertical the lateral cyclic load is applied.

How can i solved this?


thanks

 

[Erik Panos Kostson]

I would do this in a different and probably easier way. Define two time tables (arrays), containing one ramped load and then constant for the pressure and one that is constant and then oscillating for the displacement.

Say if we have a pressure (table cr) with 20E6 Pa ramped and then constant assigned to face two, and an oscillating ux displacement on face 1 (-0.002 to 0.002) (cs) it would be like this (total simulation time is 4 sec in this example).

*dim,cr,table,9,,,time
cr(1) =0,10000000,20000000,20000000,20000000,20000000,20000000,20000000,20000000
cr(1,0) = 0,0.5,1,1.5,2,2.5,3,3.5,4

*dim,cs,table,9,,,time
cs(1) = 0,0,0,0,0,0.002,0,-0.002,0
cs(1,0) = 0,0.5,1,1.5,2,2.5,3,3.5,4

d,1,ux,%cs%
sf,2,pres,%rc%

That is it.