Re: [sparta-users] Surface and flow mesh resolutions

[Zuheyr A. <zuh...@vk...>]

Dear Steve,

Thank you for your kind reply. What I showed was for single time steps.
Just to help fellow colleagues, I have solved the problem also taking a smaller time step, please see the attached screenshot.
Apparently one has a compromise between Ntouch (I do not know the significance) and Nscheck.

Kindest regards,

Zuheyr


Dr. Zuheyr Alsalihi
Senior Research Eng.
von Karman Institute
72, Chee. de Waterloo
1640 Rhode-St-Genese, Belgium.
+32 359 98 65
+32 473 69 32 27
________________________________
From: Steve Plimpton <sj...@gm...>
Sent: Friday, March 24, 2023 12:28 AM
To: Zuheyr Alsalihi <zuh...@vk...>
Cc: spa...@li... <spa...@li...>
Subject: Re: [sparta-users] Surface and flow mesh resolutions

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Hi - not sure what your question is.  Are the outputs you are showing for a single timestep,
or cumulative Nscoll Nscheck for a long run?  You could also post your input files.
How many procs are you running on?  When you say "slow", is that a Q or comment or what?

Nscheck of 44M with only Nscoll of 400K means you probably have grid cells with lots of surface
elements in them.  That can indicate you need a finer resolution grid.

Steve

On Thu, Mar 16, 2023 at 6:56 AM Zuheyr Alsalihi <zuh...@vk...<mailto:zuh...@vk...>> wrote:
Dear Colleagues,

I am not new to Sparta but I am mostly moving in the dark due to lack of time, despite the very valuable community help I get here.

I have a small model of 5mm x 4mm x 0.5mm at high Kn flow but still with collisions, density about 1.4e+16 /m^3.

I normally choose the flow mesh resolution from the principles of at least around 15 particles in a cell, and particle travel time in the cell, usually time step is 1/3rd of the particle travel time. The surface mesh usually coarsest mesh with well surface definition.

My question is the meaning of the  Nscoll Nscheck variables and their reasonable orders.

With 100 x 50 x 30 flow mesh and  31000 element surface mesh:
Nscoll=401,414, Nscheck=289,249,273, Natt=0, Ncoll=0, 11k particles.

Same flow mesh with a surface mesh of 3500 elements, and same number of particles:
Nscoll=398264  and Nscheck=44803563.

Slow... Can you please share your ideas? This is a very basic question.

Many thanks for reading.

Zuheyr






Dr. Zuheyr Alsalihi
Senior Research Eng.
von Karman Institute
72, Chee. de Waterloo
1640 Rhode-St-Genese, Belgium.
+32 359 98 65
+32 473 69 32 27
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