CFD Online Discussion Forums

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   CFX (https://www.cfd-online.com/Forums/cfx/)
-   -   Question about Moving Mesh Modelling (https://www.cfd-online.com/Forums/cfx/133498-question-about-moving-mesh-modelling.html)

ashtonJ April 16, 2014 00:20

Question about Moving Mesh Modelling
 
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.
http://tinypic.com/r/25qzyi0/8
I created the model of narrowing to t1 and then tried to model it; however, Iíve 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 (Post 486454)
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?
http://tinypic.com/r/15nolyd/8

Thanks


All times are GMT -4. The time now is 10:20.