Inspired by this question... If you're told that the Eulerian $(\vec{x},t)$ and Lagrangian $(\vec{X},t)$ descriptions are related by the system of equations $$\vec{x} = \vec{f} (\vec{X},t)$$ where $\vec{f}=(f_1, f_2, f_3)$, must all $f_i$ be invertible? I assume so? https://cdn.discordapp.com/attachments/400697259819270145/1364657029301538877/Screenshot_2025-04-23_at_18.37.56.png?ex=680a7765&is=680925e5&hm=94123e9518591c5c43a41a0acf28826b4bbc7190074c5f3f2cdadd4b87211165&

learning introductory fluid mech https://cdn.discordapp.com/attachments/400697259819270145/1364657043939524750/711934347934040125.png?ex=680a7769&is=680925e9&hm=527814c2d623d8c8d699b80f151df25793a67e19541d9b5255e300a6a2120921&

actually it probably makes more sense to think of it as x=f(X) and f might be a matrix with t dependence, rather than f acting on (X,t)

anyone familiar with the usage of the EDC combustion model version 2016? I am having an issue with simulating ammonia combustion in MILD regime using JHC burner. In addition, there seems to be some bugs in the 2016 model.

Is there some kind of switch that allows me to stop writing of ALL fields at writeTime, except those that I specifically list for writing? Basically I'm looking for a quick way to write a small set of fields at a high frequency, but the overall framework has many fields which are written out so turning them off one by one is a bad idea for the long term health of the solver.

Don't save things at all, and use a ``writeObject`` FO to save only the variables you want at the interval you want?

Yeah but what's the one runtime setting to do "don't save anything at all"

Use a ``writeInterval`` bigger than your ``endTime`` in ``controlDict``?

Crazy hack

Until you regret not saving it because you wanted to restart your case!

Still possible to play it safe and still fully write only the last timestep

I'm currently simulating a gas-liquid stirred tank with two different impellers. I'm having trouble implementing a tracer for mixing time and calculating hold-up. Unfortunately, I'm using STAR-CCM+ and can't switch software. Does anyone here have expertise with STAR-CCM+, or know of another forum or server where I could get help?

Sir, this is a OpenFOAM server

If you paid for a STAR license, you can ask them for help

license? whats that?

Whats your point here?

Well, In Elementary FluidMech they will explain you that the general state of stress on a control volume at rest is one in which the pressure (the component of stress normal to a CVs surface) is a constant at equal heights and points towards the volume, by convention.

That's why your two forces act "against the surface"

when you are in thermodynamics and/or intermediate fluid mechanics they will explain you that perfect fluids cannot be in a state of tension

Man, download White's Solution Manual and stop spamming this channel

The whole chatgroup is called "OpenFOAM", not "White's Fluid Mechanics Solution Manual Group"

this isn't really a homework help server though

your classmates are probably a better resource

just go talk to them

Ok, well please could you tell me a better server to get help from? I'm a maths student, but the module is taught by bioengineering, which is on a completely different campus to the maths department (i.e. on the other side of London). Because of this, I don't have any classmates to ask so the internet is the best resource I have

You have teachers, TA's, 1000's of books, Solution Manuals, etc... If you rely on random chat servers for your education, I have some news for you: stack exchange

Hi, I am solving an equation with OpenFoam, however when i use lower values for 'k' which represents the thermal conductivity, it starts either not converging, or when k is even lower it immediatly crashes with a floating point error... any ideas for making this convection dominated problem converge? Either via changing my formulation of the equation or by tweaking the solvers/preconditioners?

const volVectorField& U = primalVars_.UInst();
surfaceScalarField phiBeta("phibeta", fvc::flux(U*(1-beta)));

// Adjoint energy equation
fvScalarMatrix TaEqn
(
     rho_fluid * c_p_fluid * fvm::div(-phiBeta, Ta)
      - fvm::laplacian(k, Ta) 
);

Current solvers:

"Ta.*"
    {
        solver          PBiCGStab;
        preconditioner  DILU; 
        tolerance       1e-09;
        relTol          0;
    }

If i use upwind phi instead of linear interpolation it doesnt crash any more but the solution still diverges via some weird checkerboard thing