{"id":310817,"date":"2023-10-10T11:55:32","date_gmt":"2023-10-10T11:55:32","guid":{"rendered":"\/forum\/forums\/topic\/load-step-definition-for-a-transient-analysis\/"},"modified":"2023-10-10T11:55:32","modified_gmt":"2023-10-10T11:55:32","slug":"load-step-definition-for-a-transient-analysis","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/load-step-definition-for-a-transient-analysis\/","title":{"rendered":"Load Step definition for a transient analysis"},"content":{"rendered":"

Hello everyone,<\/p>\n

I am trying to perform a transient analysis of a cylindrical shell subject to a transient load in one end and fixed one the other. My goal is to see a pulse propagating along the pipe from the position of the load until the fixed end. This is the code I used to do the pre-processing:<\/p>\n

“”<\/p>\n

\/CLEAR<\/div>\n
!Parameters <\/div>\n
*SET,diameter , 85.4<\/div>\n
*SET,thick , 11 <\/div>\n
*SET,length , 100   <\/div>\n
!Geometry   <\/div>\n
\/PREP7  <\/div>\n
ET,1,SHELL181   <\/div>\n
KEYOPT,1,8,2<\/div>\n
SECTYPE,1,SHELL <\/div>\n
SECDATA,thick   <\/div>\n
MP,EX,1,2000<\/div>\n
MP,PRXY,1,0.35  <\/div>\n
MP,DENS,1,900   <\/div>\n
k,1 <\/div>\n
k,2,diameter<\/div>\n
circle,1,2  <\/div>\n
k,7,,,length<\/div>\n
l,1,7   <\/div>\n
ADRAG,1,2,3,4,,,5   <\/div>\n
!Mesh   <\/div>\n
ESIZE,0.5   <\/div>\n
amesh,all   <\/div>\n
 <\/div>\n
!* Fixed boundary condition<\/div>\n
 <\/div>\n
FLST,2,28,1,ORDE,8  <\/div>\n
FITEM,2,1   <\/div>\n
FITEM,2,-8  <\/div>\n
FITEM,2,1609<\/div>\n
FITEM,2,-1615   <\/div>\n
FITEM,2,3016<\/div>\n
FITEM,2,-3022   <\/div>\n
FITEM,2,4423<\/div>\n
FITEM,2,-4428   <\/div>\n
!*  <\/div>\n
\/GO <\/div>\n
D,P51X,ALL,0, , , , , , , , ,   <\/div>\n
 <\/div>\n
FINISH  <\/div>\n
\/SOL<\/div>\n
!*  <\/div>\n
 <\/div>\n
ANTYPE,4<\/div>\n
 <\/div>\n
!*  <\/div>\n
 <\/div>\n
TRNOPT,FULL <\/div>\n
LUMPM,0 <\/div>\n
 <\/div>\n
“”<\/div>\n
 <\/div>\n
Now, the problem I am having and trying to learn how to do properly is how to define the Load Step. <\/div>\n
 <\/div>\n
If I understood correctly, for each load step we define the time duration of that load step and in which time it starts. So for example, the following command define the load step duration of 0.0001 seconds, that happens at the time stamp of 0.0000001 second. Would that be correct?<\/div>\n
 <\/div>\n
\n
DELTIM,0.0001,0,0,ON <\/div>\n
 <\/div>\n
TIME,0.000001<\/div>\n
FLST,2,28,1,ORDE,11<\/div>\n
FITEM,2,9<\/div>\n
FITEM,2,209<\/div>\n
FITEM,2,-215<\/div>\n
FITEM,2,1616<\/div>\n
FITEM,2,1816<\/div>\n
FITEM,2,-1821<\/div>\n
FITEM,2,3023<\/div>\n
FITEM,2,3223<\/div>\n
FITEM,2,-3228<\/div>\n
FITEM,2,4429<\/div>\n
FITEM,2,-4434<\/div>\n
\/GO<\/div>\n
F,P51X,FZ,100,  %Here is the force value<\/div>\n
LSWRITE,1,<\/div>\n
 <\/div>\n
Then For the next time step I want the force value to change a then give the command <\/div>\n
 <\/div>\n
DELTIM,0.0001,0,0,ON <\/div>\n
\n
TIME,0.000002<\/div>\n
FLST,2,28,1,ORDE,11<\/div>\n
FITEM,2,9<\/div>\n
FITEM,2,209<\/div>\n
FITEM,2,-215<\/div>\n
FITEM,2,1616<\/div>\n
FITEM,2,1816<\/div>\n
FITEM,2,-1821<\/div>\n
FITEM,2,3023<\/div>\n
FITEM,2,3223<\/div>\n
FITEM,2,-3228<\/div>\n
FITEM,2,4429<\/div>\n
FITEM,2,-4434<\/div>\n
\/GO<\/div>\n
F,P51X,FZ, 25,  %Here is the new force value<\/div>\n
LSWRITE,2,<\/div>\n
 <\/div>\n
and then I repeat this process for the number of load steps I would like to have and ask to solve.<\/div>\n
The code is solved but the results appears as if this was a static load, where instead it should be an impulsive load.<\/div>\n
 <\/div>\n
I have looked the manuals and tutorials through Ansys and could not find an answer to that.<\/div>\n
 <\/div>\n
My final goal is to observe how a pulse propagates through an elastic medium, but the results I am getting are a static load beeing applied slowly to the structure.<\/div>\n
 <\/div>\n
Could anyone give me some light on this matter ? If I was not very clear I could try to reformulate my problem!<\/div>\n
 <\/div>\n
I appreciate any advice<\/div>\n
 <\/div>\n
Kind regards<\/div>\n
Pedro<\/div>\n
 <\/div>\n
P.S.:<\/div>\n
 <\/div>\n
This is the time history I am getting at one of the nodes:<\/div>\n
 <\/div>\n
<\/div>\n
 <\/div>\n
and this is the countour plot at the final time step<\/div>\n
 <\/div>\n
<\/div>\n
 <\/div>\n
See how the load gets concentrated at the point of application? Even though I set the force to zero after the tenth time step<\/div>\n
 <\/div>\n
In summary:<\/div>\n
I defined 100 load steps each with a duration of 0.000001 second<\/div>\n
The force value of each load step changes until the time step 20 when it becomes 0<\/div>\n
I would expected that the loads of the first 20 load steps would start to propagate through the structure but they dont<\/div>\n
 <\/div>\n
 <\/div>\n
 <\/div>\n<\/div>\n<\/div>\n","protected":false},"template":"","class_list":["post-310817","topic","type-topic","status-closed","hentry","topic-tag-transient-structural"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t