Where to access formulas?

How would I go about accessing values/formulars of constants like Smagorinsky and Blin constants?

I find these constants in the Run file:

And also in the "JSph.h" source file, but can't figure out how to find how DualSPHysics calculates it.

Kind regards


  • Hey @Alex !

    Thanks for your time, but unfortunately this confuses me a bit, since when I run the floating test case I get different values depending on dp (initial particle spacing). Here are the screenshots from run file with dp = 0,025 m:

    If I then do a simulation with dp = 0,0125:

    None of these values correspond with the GitHub page:


    Have I misunderstood something - I thought they were treated as constant in DualSPHysics?

    Kind regards, Ahmed
  • Exactly, some values are computed using the particle spacing.
    You can read that in the theory and the link I sent before.
    Note that SPS means sub-particle scale model, so that, some ctes are computed depending on the scale!


  • Hey again

    I am sorry but I am still confused. When I read the wiki page this is what I see:

    According to the wiki page the constants are set as Cs=0.12, CI=0.0066 and when I look through the code (JSph.h):

    So here I would expect to get the values as in the wiki, but I do not as seen in my previous answer.

    I understand that turbulent eddy viscosity variates with particle spacing and therefore the stress tensor also variates, but I expect the Smagorinsky and Blinn constants to be the same as in the wiki, which they are not.

    Of course it could be I am still misunderstanding something and that is why I hoped it would be possible to see the exact calculation of the constants in the DualSPHysics code - I've been trying to look through the source files in the DualSPHysics folder but I can't find the place where the constants are defined or calculated - I hope you could guide me to the right place.

    Thanks for taking time to answer.

    Kind regards, Ahmed

    1.png 88.6K
    2.png 6.4K
  • Thanks Ahmed
    Let us take a look
  • No problem - looking forward to your reply.
  • I can't edit my comment for some reason so I will post an update here to correct some, what I assume, mistakes in the wiki chapter 3.2.

    By looking through Dalrymple 2006 and 2004 I will note that they describe C_I = 0.00066 and not C_I = 0.0066 as in the DualSPHysics wiki.

    The way the magnitude, |bar(S)| is calculated in the wiki is also wrong according to Dalrymple 2006 it should be done as:

    Maybe some kind of formatting went wrong since "0.5" is infront in the wiki.

    In the calculation of the sub-particle stress tensor, at the end |S|^2 is added which doesn't correspond with the formula given in Dalrymple 2006 (equation 10).

    This could be my mistake if I am misunderstanding something in the tensor notation, so sorry for that if it is.

    I am just trying to understand the SPH method and how it is implemented in DualSPHysics, so that is why I am spending so much time on these issues.

    Kind regards, Ahmed

    a.PNG 8.5K
    b.PNG 16.5K
  • Dear Ahmed,

    The correct value of C_l is 0.0066. The paper Dalrymple and Rogers (2006, Coastal Engineering) contains a typographical error. The value of C_l = 0.0066 comes from Wang et al. (2001, reference is given below):

    SpsBlin = Blin_const = twoThirds*0.0066*dp*dp

    Shanwu Wang, Shih-Yang Hsieh, Vigor Yang, "Numerical Simulation of Gas Turbine Swirl-Stabilized Injector Dynamics", AIAA 2001-0334.

    You are also correct the equation for |S| on the wiki is not correct. it should be

    The bars are dropped for convenience.

    For the value of Cs, this is always a tricky one and you are right to be careful. The
    confusion arises because many people use a dynamic value of Cs that varies throughout a simulation - they then tend to replace Cs^2 by another symbol confusingly also C or Cs. So, in the papers I sent you, they use Cs, but as an example you can see that in the following
    text on google books by Herring & Williams "Lecture Notes on Turbulence", they use Cs^2 with a value of Cs~=0.1-0.2.

    I hope this helps,
  • Thank you very much Ben!

    It cleared up some confusion for me, since the constants in the DualSPHysics wiki are stated as just constants and not formulaes.

    1. SpsBlin = (2/3)*C_I*dp*dp, where C_I is 0.0066

    Which I understand, but I am having trouble with Smagorinsky still. According to wikipedia I find that:

    And as you state Cs should be between 0.1-0.2. But in DualSPHysics simulation SpsSmag is different according to particle size. So do you happen to know where I can find the formulation for SpsSmag?

    I hope my question makes sense.

    Kind regards
    gs.PNG 11.4K
Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!