[matejmuller]

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:

scalar maxUx_water=0
forAll(U,celli)
{
    if (alpha1[celli]>0.5)
        {
	      if (U[celli].x() > maxUx_water)
           {
              maxUx_water = U[celli].x();
           }
        }
}
Info<< "maxUx_water= "<< maxUx_water << endl;

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

Thanks!

Matej

[demichie]

I think you need the absolute value here:

maxUx_water = U[celli].x()



Mattia

[akidess]

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

or, if you want just a component:

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

(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?

[matejmuller]

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

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

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

[akidess]

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

[matejmuller]

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

Although, the line above gives:

maxU: max((pos((alpha.water-0.5))*U.component(0))) [0 1 -1 0 0 0 0] 0.549513

and I need only the values like:

maxU: 0.549513

Any ideas?

Matej

[akidess]

Yes, what you want is the value. Hence

max((pos((alpha.water-0.5))*U.component(0))).value()

should do the trick.

[JM27]

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?

[matejmuller]

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

for max Ux:

max(pos(alpha1-0.5)*U.component(0)).value()

best regards, Matej

[JM27]

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:

maxU: Fatal error in MPI_Recv: Message truncated, error stack:
MPI_Recv(224).....................: MPI_Recv(buf=0x7ffd14e0b6b0, count=8, MPI_BYTE, src=1, tag=1, MPI_COMM_WORLD, status=0x7ffd14e0b620) failed
MPIDI_CH3U_Receive_data_found(131): Message from rank 1 and tag 1 truncated; 5816 bytes received but buffer size is 8

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

[matejmuller]

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

[JM27]

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:

coded function object in parallel

Thanks again Matej for your input

[JM27]

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:

min(pos(alpha1-0.5)*U.component(1)).value()

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.