Question about Moving Mesh Modelling

ashtonJ · April 16, 2014, 00:20

Dear All,
I am modelling flow in a tube with moving walls. As seen in the attached image, the middle part of tube starts to narrow from t = 0 to t = 1.0. I have done this part of modelling successfully.
Now, I want to investigate the effect of time shift on the flow behaviour. I mean, I want to start modelling from t = t1 to t = 1+t1.

I created the model of narrowing to t1 and then tried to model it; however, I’ve got overflow error. Is there any way to do the modelling from t = 0 to t = t1, and then use the narrowed geometry at t1 and run another simulation.

Regards,
AshtonJ

Lance · April 16, 2014, 05:50

Use your deformed geometry at t1 as initial condition for your next simulation. See that FAQ on what to do if you get overflow errors.

ashtonJ · April 16, 2014, 06:10

Thanks Lance. Actually, I tried it. First, I defined a transient analysis from 0 to t1, then defined another analysis from t1 to 1. In configuration, I used the the first analysis as the initial condition for second analysis. However, when I checked the second analysis results, I realized that the initial geometry is the geometry at t=0 (non-constricted pipe) not t=t1. Do you have any idea where the poblem could be?

Lance · April 16, 2014, 06:14

Quote:

Originally Posted by ashtonJ

However, when I checked the second analysis results, I realized that the initial geometry is the geometry at t=0 (non-constricted pipe) not t=t1. Do you have any idea where the poblem could be?

Yes, I have an idea.

You need to make sure that you use the geometry from the initial file and not the input file. Under initial values specification, make sure that you have specified: "Use mesh from: initial values"

ashtonJ · April 17, 2014, 04:21

Thanks Lance, it works.

ashtonJ · April 17, 2014, 05:47

Dear Lance,
I encountered with a strange problem.
I defined two transient analyses, one from 0[s] to 0.25[s] (transient 1) and the other from 0.25[s] to 1.25[s] (transient 2).
As suggested, I used the transient 1 mesh as initial condition for transient 2. However, I faced with a strange problem in transient 1 results. I attached here the wall deformation in transient 1 analysis at t=0.248[s] and t=0.25[s].
As seen, at 0.248[s], as instructed by the mesh displacement graph on the left, the middle section of pipe is narrowed. However, at t=0.25[s], the middle section of pipe is returned to its initial non-deformed state in contrast to its corresponding displacement graph shown on the left. I am confused with this, do you know why this happens?

Thanks

April 16, 2014, 00:20	Question about Moving Mesh Modelling	#1
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Dear All, I am modelling flow in a tube with moving walls. As seen in the attached image, the middle part of tube starts to narrow from t = 0 to t = 1.0. I have done this part of modelling successfully. Now, I want to investigate the effect of time shift on the flow behaviour. I mean, I want to start modelling from t = t1 to t = 1+t1. I created the model of narrowing to t1 and then tried to model it; however, I’ve got overflow error. Is there any way to do the modelling from t = 0 to t = t1, and then use the narrowed geometry at t1 and run another simulation. Regards, AshtonJ

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April 16, 2014, 05:50		#2
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	Use your deformed geometry at t1 as initial condition for your next simulation. See that FAQ on what to do if you get overflow errors.

April 16, 2014, 06:10		#3
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Thanks Lance. Actually, I tried it. First, I defined a transient analysis from 0 to t1, then defined another analysis from t1 to 1. In configuration, I used the the first analysis as the initial condition for second analysis. However, when I checked the second analysis results, I realized that the initial geometry is the geometry at t=0 (non-constricted pipe) not t=t1. Do you have any idea where the poblem could be?

April 17, 2014, 04:21		#5
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Thanks Lance, it works.

April 17, 2014, 05:47		#6
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Dear Lance, I encountered with a strange problem. I defined two transient analyses, one from 0[s] to 0.25[s] (transient 1) and the other from 0.25[s] to 1.25[s] (transient 2). As suggested, I used the transient 1 mesh as initial condition for transient 2. However, I faced with a strange problem in transient 1 results. I attached here the wall deformation in transient 1 analysis at t=0.248[s] and t=0.25[s]. As seen, at 0.248[s], as instructed by the mesh displacement graph on the left, the middle section of pipe is narrowed. However, at t=0.25[s], the middle section of pipe is returned to its initial non-deformed state in contrast to its corresponding displacement graph shown on the left. I am confused with this, do you know why this happens? Thanks