Hi Mohammed,

Did you try to just add another study to the same file, you can compute the transient study (study 2) after the stationary one (Study 1), I think COMSOL can take the solution from Study 1 as an initial step to Study 2.

I guess you can save the model with a different name, then go to the study section. From "Add Study" tab, you can add a new transient study to your model. you can delete the previous stationary study or keep it as it is depending on your preference.

Thank you so much Waranatha for your quick answer,

In fact, now I can change the situation from "stationary to transient"  BUT still it  does not make sense because I could not able to make plots (lines or surfaces) at specific time that I want ! While if I start the problem again from scratch, I can do these plots at any  time I would like to.

This should not be the case. Once you added a transient study and solved it, usually the plots will be available. Check if you are still using your old stationary solution as the data source for your plot group.

You need to set a particular time step and save data files, where you want to need data for analysis. You need not to save it again and again, just set the particular step and software will automatic write the data files and you can use these all data files at later stage for comparison and analysis.

You most likely have two solutions under the Data Sets node: one stationary and one time dependent. This is probably the cause for your confusion. When creating new plots, you have to choose the time dependent solution.

Thank you guys for your responses,

My problem was solved initially as a stationary problem as the top picture (1) of the attached file shows, then I tries to resolve it as transient one, by changing the step 1 : stationary to step 1 : time dependent ,but the results are the same, I can not make plots at specific times, even I placed a range for the times as shown in the bottom picture(2). In fact, if you look at the bottom picture, even it was changed to time dependent, you will see under "" Dependent variables "" the stationary solver 1 exactly like the top pic. for the basically stationary problem!

I have solved another problem as a time dependent problem and it shows me under "" Dependent variables "" time - dependent solver 1 as shown in the picture 3.

So, should I start from scratch to resolve the stationary problem as time dependent one?

Thank you in advance for your helping!

Hi Mohammed,

Did you try to just add another study to the same file, you can compute the transient study (study 2) after the stationary one (Study 1), I think COMSOL can take the solution from Study 1 as an initial step to Study 2.

Sallal is right,

you can use solution from Study 1 as an initial value in Study 2. Go to "Step 1: Time Dependent" under Study 2, and check box "Initial values of variables solved for" from "Values of Dependent Variables".

There you can set that use solution frrom Study 1.

Thank you Sallal and Antti for your answers,

Now, how can I add another study (study 2) to the one that I have already (study 1) for stationary solution, please? Should I repeat the previous steps of the stationary solution by adding new physics and this time will be as a transient study or there is another way to add study besides the old one?

This is quite easy:

Right click on Study, Study steps.....and choose the type of study you want to add...COMSOL will then add it and name it as Study 2

I followed what Sallal mentioned and I can add '' step 2: time dependent''  BUT under the tab STUDY 1, so I'm still inside '' study 1'' and my last post was asking how to get STUDY 2 so I can use the time dependent step below it. 

I added  '' step 2: time dependent'' under the tab STUDY 1, then I followed what Antti said in his last post, after that I got exactly the same results of the stationary solution, NO BENEFIT from creating time dependent under just STUDY 1, where I can not find my results at'' specific times'' that I desire and basically this  should be the aim of time dependent problem.

Sallal, I think there is big difference between adding '' step 2: time dependent'' under the tab STUDY 1  and named it STUDY 2 than creating real STUDY 2.

Thank you guys for understanding my long conservation.

Not under Study1

From the study node...you should add a new study..which is named Study2

Right click on Study not on Study 1......you can add more than just one study...

Sallal, can you show me where the study node is, please?

Thanks

Mohammed,

I dont know if you are using an old or a new version of COMSOL, mine is 4.3, but i guess it is the same. Go to the Model Builder to the right of the screen, if you already have saved the file, then the file name will be the first icon in the tree of the Model Builder, if not, it will be named as "Untitled.mph"........right click on this icon (it takes the shape of the COMSOL icon"......from the list choose "Add study"....then from the "Select Study Type" window (to the right)....choose the study type you want, the new study will be created in the Model Builder. if you have more studies, just repeat the same procedure.

Thank you so much Sallal and all of you guys,

Now, it works perfectly, but i am not really sure about the results. Anyway, I have to check them next time.

Dear Mohammed,

The stationary solution can be used as the initial values for the time-dependent solver, according to the given instructions.

Another problem is that, if one does so, it seems that the transient solution is just the same as the steady solution.

I wonder if you guys have met this kind of problem.

Thanks.

Regards,

Bill