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2-step static analysis

Posted Jun 30, 2018, 8:28 p.m. EDT Structural & Acoustics, Geomechanics, Studies & Solvers Version 5.3a 3 Replies

Ramin Ziaei
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Hi all,

I have been struggling with this issue like for ever! let's say we have a vertical rectangle, the bottom of which is fixed. there is a downward load and a horizontal load on top of it. First, I want to analyze the model based off of that downward load, and use the the results as the initial values for the next step which is considering the horizontal load. This is what I do:

Defining both loads in just one "Solid Mechanics" and defining 2 studies. In the first study, I go to Study1 "Modify model configuration for the study step" and disable the horizontal load since the first step is supposed to be based off of the vertical load. Then, in Study2, I disable the vertical load since we want to use the its results from the previous step. Also, I go to "Values of dependent variables" and under "Initial variables of variables solved for "I choose "User control-solution-study1-automatic". But, at the end, in the plots of study2, I don't see any effects from the vertical load. I know I am doing sth wrong but Idk where.

Thanks in advance for your time. Ramin

3 Replies Last Post Jul 3, 2018, 2:28 a.m. EDT
Josh Thomas Certified Consultant
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Posted: 6 years ago Jul 2, 2018, 1:27 p.m. EDT

Ramin-

A couple points:

1) If you want to include the effect of the vertical load in Study2 then you should not disable it in that study.
2) If your analyses are linear (i.e. no geometric or material non-linearities) then there is no benefit of initializing subsequent studies with initial values of variables solved for.

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Best regards,
Josh Thomas
AltaSim Technologies
Ramin- A couple points: 1) If you want to include the effect of the vertical load in Study2 then you should not disable it in that study. 2) If your analyses are linear (i.e. no geometric or material non-linearities) then there is no benefit of initializing subsequent studies with initial values of variables solved for.
Ramin Ziaei
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Posted: 6 years ago Jul 2, 2018, 2:21 p.m. EDT

Ramin-

A couple points:

1) If you want to include the effect of the vertical load in Study2 then you should not disable it in that study.
2) If your analyses are linear (i.e. no geometric or material non-linearities) then there is no benefit of initializing subsequent studies with initial values of variables solved for.

Dear Josh,

Thanks for your response.

It's just a simple model to see how 2-step analysis works and is not the real model that I'm working on.

About the first point you mentioned, the purpose of having a 2-step analysis is to use the results of the first step (or study) as initial values of the second study/step. Then, why should we include the vertical load in the second study anaig? This is the same problem that I have with "Tunnel excavation" example. I have already asked few questions regarding that example but haven't received any response. Maybe, if you had some free time, you could please take a look at these 3 issues.

1- In this example, for initialization, we are using External Stress in solid2 and step#2 (from gravity analysis in solid and step#1), but solid2 again considers gravity! If we are using stresses from the gravity analysis in step1, shouldn't we remove gravity from solid2?! Having both External Stresses and gravity in solid2 does not double the response? 2- For initialization, we are just considering external stress?! What about displacement (strains)? 3- And finally, in the results part, everything is based on sol1 (Data/Data set/study 1/solution 1 (sol1). What about sol2? shouldn't "after excavation" results be based on sol2? If not, then what is the point of having sol2 in the drop-down menu of Data/Data set?

Thanks in advance. Regards, Ramin

>Ramin- > >A couple points: > >1) If you want to include the effect of the vertical load in Study2 then you should not disable it in that study. >2) If your analyses are linear (i.e. no geometric or material non-linearities) then there is no benefit of initializing subsequent studies with initial values of variables solved for. Dear Josh, Thanks for your response. It's just a simple model to see how 2-step analysis works and is not the real model that I'm working on. About the first point you mentioned, the purpose of having a 2-step analysis is to use the results of the first step (or study) as initial values of the second study/step. Then, why should we include the vertical load in the second study anaig? This is the same problem that I have with "Tunnel excavation" example. I have already asked few questions regarding that example but haven't received any response. Maybe, if you had some free time, you could please take a look at these 3 issues. 1- In this example, for initialization, we are using External Stress in solid2 and step#2 (from gravity analysis in solid and step#1), but solid2 again considers gravity! If we are using stresses from the gravity analysis in step1, shouldn't we remove gravity from solid2?! Having both External Stresses and gravity in solid2 does not double the response? 2- For initialization, we are just considering external stress?! What about displacement (strains)? 3- And finally, in the results part, everything is based on sol1 (Data/Data set/study 1/solution 1 (sol1). What about sol2? shouldn't "after excavation" results be based on sol2? If not, then what is the point of having sol2 in the drop-down menu of Data/Data set? Thanks in advance. Regards, Ramin
Henrik Sönnerlind COMSOL Employee

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Posted: 6 years ago Jul 3, 2018, 2:28 a.m. EDT

Hi,

A quick remark on the data sets: 'dset1' is the final solution. 'dset2' corresponds to 'sol2' which is the solution after the first step ('Solution Store 1' in the solver sequence).

About the precedure, Josh is (as usual) right.

Regards, Henrik

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Henrik Sönnerlind
COMSOL
Hi, A quick remark on the data sets: 'dset1' is the final solution. 'dset2' corresponds to 'sol2' which is the solution after the first step ('Solution Store 1' in the solver sequence). About the precedure, Josh is (as usual) right. Regards, Henrik

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