interfoam - maximal velocity in water phase
 

Hi!

I want to get the maximal velocities for each velocity component in the water phase in each time step and get them in the log file. I've tried:

but something is not working correctly. The values are not right (they are too small). Any ideas how to solve this?

Thanks!

Matej

I think you need the absolute value here:

maxUx_water = U[celli].x()



Mattia

or, if you want just a component:
(as Mattia already pointed out you may want to also print the minimum or use absolute values)

How do you know your values are too small?

Hi!

Thanks for the responses.

Mattia, I need the minimal component values too, so I thought I'd use the
same code as for the maximal.

Anton, with my approach the given velocity values are smaller than obtained in postprocessing in paraView.

I don't know what the code pos(alpha1-0.5) does exactly, but the whole line

gives a list of velocities for all cells. Weirdly, the values are eather 0, or the same value as max(U.component(0)).

regards, matej

Are you looking at cell values or interpolated values in Paraview?

I made a mistake in my code - pos() will return 1 whenever the expression in the brackets is positive, otherwise negative. And it does so for every cell, which is why you got what you got. So how to fix this?


.
.
.

Info << "maxU: " << max(pos(alpha1-0.5)*U.component(0)) << endl;

Too bad I couldn't hide the answer behind a spoiler tag ;)

I'm looking the cell values in paraView, and now they are correct! Thank you.

Although, the line above gives:

and I need only the values like:

Any ideas?

Matej

Yes, what you want is the value. Hence
should do the trick.

does this work in parallel?
 

Hi,

Thanks for the interesting post. I have tested this code on the depthCharge tutorial and it works perfectly when running in serial. However it does not work in parallel, and crashes after the first time-step without writing the max velocity in the liquid. I am using scotch for decomposition.

Have you also tried this code in parallel and has it worked for you?

Hi, for me it works also in parallel (I also use scotch):

for max Ux:

best regards, Matej

Hi Matej,

Thanks for the response especially on a not so recent post. May I ask which OF version you are using?

I am using v5. Just trying to understand what could be causing the issue as I never had trouble with coded function objects in parallel until now.

This is the error I get when running in parallel:

I suspect max might be causing the issue in parallel, but still testing.

I actually didn't use this in the coded function object (i don't think that was an option back then). I've compiled a new solver and put the code somewhere at the end of interFoam.C

best regards, m

resolved
 

Hi Matej,

That must explain why you did not run into this issue when running in parallel.

As I suspected, the MPI error arises due to the max keyword inside Pstream (for those using coded function object). For others who might encounter this issue: I have resolved this by rewriting some of the code, similar to that described in this post:

https://www.cfd-online.com/Forums/op...tml#post719879

Thanks again Matej for your input :)

Hi,

I am now trying to use a similar code to calculate the largest negative value of Uy in the liquid phase. However, I have so far been unable to do this.

I have tried replacing max with min, but this will print the minimum positive/absolute value rather than the largest negative value of Uy:

using the above code, the minimum value is not the largest negative value I can see in paraview.

Any ideas of how to do this?

p.s. I've also tried changing pos with neg but I understand this would mean that the maximum being calculated is that of alpha2 and not alpha1.