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Error in Combin39

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Old   May 17, 2020, 20:39
Default Error in Combin39
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Carolina Paredes
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Hello,

I am trying to simulate a steel connection of a test tube with a spring-combin39, however it gives me the following error: "The last input displacement for element x must be positive."

I tried to find a solution to the problem in a simplified model, by joining two nodes with a spring with combin39 but it keeps throwing the same error.

Here is a little part of the code (I would initially like my spring to behave "linearly" to understand its functionality, that's why I entered those Dx, Fx.):

!* Spring in the x direction

ET,101,39
keyopt,101,1,0,
keyopt,101,2,0,
keyopt,101,3,0,
keyopt,101,4,1,
!keyopt,101,6,0
R,101,-1,-300,0,0,1,300

!* Spring in the y direction
ET,102,39
keyopt,102,1,0,
keyopt,102,2,0,
keyopt,102,3,0,
keyopt,102,4,1,
!keyopt,101,6,0
R,102,-1,-300,0,0,1,300
!RMORE,102,,,,,

!* Spring in the z direction
ET,103,39
keyopt,103,1,0,
keyopt,103,2,0,
keyopt,103,3,0,
keyopt,103,4,1,
!keyopt,101,6,0
R,103,-1,-300,0,0,1,300
!RMORE,103,,,,,


n,1,0,0,0
n,2,1,0,0
allsel

d,1,ux,0,,,,uy,uz,
d,2,,0,,,,uy,uz,

r,1
real,1

! Define spring in the x direction
type,101
e,1,2
allsel

! Define spring in the y direction
type,102
e,1,2
allsel

! Define spring in the z direction
type,103
e,1,2
allsel

d,2,ux,50


I hope you can help me with this problem. Beforehand, thank you very much.
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Old   July 1, 2020, 02:23
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Gwenael H.
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Hello Carolina,

What you're missing is the real constant selection before creating the element assigned to the node set.

Additionally if you're planing to use the same keyopts for the different COMBIN39 elements you don't need to define different types. You just need to define different real constants and select them before creating the spring.

>
ET, 101, 39
KEYOPT,101, ......

R,101,-1,-300,0,0,1,300
R,102,-2,-600,0,0,1,400
R,103,-3,-300,0,0,1,200

type,101 ! Assuming you’re using the same element definition for all the springs
R,101
e,1,2 ! Define the first Combin39 spring with constant R101
R,102
e,1,2 ! Define second Combin39 spring with constant R102
R,103
e,1,2 ! Define third Combin39 spring with constant R103

allsel

continue with your script

Have fun
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