To plot the average void fraction over a line, I need to use “Extract Timetesp” and “Temporal statistics” filters in paraview. The problem with .RES is that the res_dt is 0.05 in MFiX but in paraview I have only 10 timesteps in each second. What is the problem?
On the other hand, when I use the .VTU group files in paraview and apply the mentioned filters, I have a slightly different values including some NaN values in my plot which lead to discontinuities in plot line. Why do I have this NaN values in VTU and slightly different values in comparison with the results of the .RES?
res_dt controls how often the restart file is written. Although it looks like Paraview only reads this file, it is actually reading the .SP* files to loop through a time series of files. My guess is that spx_dt(1) is set to 0.1. Go to Output>SPx and change the write interval for the fluid volume fraction to 0.05 s.
If the VTU file frequency is different from the SP1 file frequency, then you can expect slight differences in temporal statistics. I don’t now why you would get NaNs though.
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You are right @jeff.dietiker . But the GUI does not let me to set a value smaller than 0.1 for SPx write intervals!?
About the NaN values in the average void fraction, when I plot the void fraction over the line for different timesteps, I can see the Nan values again. However, I do not face this issue when using the RES files(using .RES file directly in paraview or writing the data using the postmfix at that specific time that we have NaN values in paraview).
What do you think I should do to address this problem.
BTW, is there any difference between the precision of RES and VTU results?
@jeff.dietiker I found the reason for the NaN value in paraview in a forum and it seems correct:
The problem is that you are trying to plot right on the edge of your mesh, and numerical inaccuracies are causing points of the line to be outside of your mesh. (This is not a criticism of your data. Rather, this is just the nature of floating point numbers on a computer.)
I changed the line that I decided to plot on a bit and there were no NaN values but why dont we have such a problem with .RES results?
And how to save SPx files for time interval of 0.05?
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Can you please elaborate on:
What MFiX version, OS are you using? Do you get an error message, do you see the keyword value in the console?
The SPX and VTU files should have the same precision.
The GUI of MFiX 20.2.1 on Ubuntu 20.4 does not let to use value under 0.1 to save SPx. However, I changed the mfx file by text editor and it worked.
Error in GUI is: Value below allowed range:0.05<0.1
BACKGROUND_IC_0843.zip (701.0 KB)
@jeff.dietiker If you only plot the void fraction over line y=0.2, and save the plot data into file you can see the NaN values. Also, if you change the resolution of plot to 60, you can easily see the discontinuities in the plot
Regarding spx_dt: Set both res_dt and spx_dt to 0.05. Looks like there is a constrain that spx_dt cannot be smaller than res_dt.
Regarding the Nan: Apply the CleantoGrid filter before you extract the line, this got rid of the Nans for me
@jeff.dietiker Thanks for your response. First, the CleantoGrid filter does not work for me. So I have plotted the average void fraction on a line using .VTU and .RES as inputs with exactly the same filters. However, to eliminate the discontinuities I have plotted the void fraction on y=0.1999 instead of y=0.2. You can see the difference between the results. Spx-dt, Res_dt and Vtk_dt is 0.05.
Also, If I plot the .VTU results on y=0.2, the plots would not be the same! (Blue plot: .RES, Red plot: .VTU)
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Hi @mohsenclick and @jeff.dietiker ,
Hope you are doing well. I am graduate student in University of Houston and new to using MFiX DEM. I would be grateful if you could help me guide with some material for learning MiX DEM in addition to that given in website ‘4. Model Guide — MFiX 22.4 documentation’.
I have been following the tutorials and model guide for using MfiX from GUI. However, for our research, we want to run DEM models on cluster as well. So, I am trying to learn to use MFiX from command line on terminal. I am following building solver and running solver from ‘4. Model Guide — MFiX 22.4 documentation’.
I would be grateful to you if you could guide me with some materials for learning MFiX DEM.
Thank you very much.
Sincerely,
Bimal Chhushyabaga.
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