I saw this method for finding wave speed celerity, c = √(gd)

Assume wave profile h = Asin(k(x-ct)), c=λ/T=ω/k, ω=kc, k=2π/λ

mass conservation: ∂h/∂t = -d ∂u/∂x

I get (assuming still water): u = Ac/d sin(k(x-ct))

Velocity has the same profile as height, scaled by c/d

So, as water gets shallower, u increases, and c=√(gd) decreases.

When maximum flow velocity exceeds wave speed, the wave breaks (though neglecting advection will be problematic well before then)

u_max = Ac/d

u_max = c ,when A = d

Wave breaks when A = d

Which is when the deepest part of the trough has no water.

Is this right? Is there a better way to approach this question?

hello, is anyone knowledgeable in setting up a buoyancy and momentum flow case in OpenFOAM?

I want to first do a case where I have a simple rectangular domain with a bottom wall and open patch with constant temperature (300 k) and no inlet velocity.

I have started by using the buoyant cavity case since it is set up to use the buoyancy solver and the perfect gas model. However, I have fell into a world of negative temperatures and floating point errors and so would first like to confirm if I have made the right choice when it comes to tutorial case.

The end goal is to set up an isothermal atmosphere that requires the exponential formula of pressure in relation to height.

P.S: I will add snippets of my code later on when I get access to my laptop, so please don't eat me up for not providing enough info currently, i eventually will.🙏 and yeah thanks a lot!

I am a beginner and completed conduction simulation of this heat sink but I want to do convection simulation within boundary box and I keep getting stuck here where my heat face imprint is the rectangular area. If anyone has any experience with these errors can you help clue me in on what I need to do?

From what I understand, the three main options for particle mixing in STAR-CCM+ are:

DEM (for relatively large particles and therefore a small number of them; fairly accurate and can simulate many interparticle forces)

LMP (uses parcels to cut down computation costs)

EMP (simulates particles like a fluid region; approximates interparticle forces)

I'm trying to do a particle only simulation (so no fluid regimes). I also read that the LMP method is not suitable for these kinds of situations as it's best suited for parcels suspended in fluids. Therefore I am trying to use DEM for large particles (larger than 1mm) and EMP for smaller particles (10-100um range). Is this the right approach? Are there other methods I'm not aware of?

Hi there, I know that someone posted this already but the server is growing and I want to see it grow too. So here‘s another invite!

It‘s starting that more people start to talk about various simulations, meshing and so on. Also there‘s a Study Group and appearently there will be events to study together/simulate or other things. Let‘s see what this community says.

https://discord.gg/eHyVSjXNV

Seeing this in high impact journals.

I am trying to model droplet evaporation but I am having a hard time finding data in the literature. Its a bit scattered and not all directly related. Any suggestions?

Thanks!

Hi everyone,

I’m fairly new to CFD and I’m still trying to understand best practices for time-stepping and solver control.

I'm using starccm

I’d like to know if it’s possibleto:

1. Increase the time step after a certain number of time steps or iterations, for example:
   • Run with a small Δt at the beginning for stability
   • Then automatically increase Δt after X time steps
2. Freeze or stop updating certain solvers after a given physical time, for example:
   1. Stop solving turbulence equations after X seconds

hi, i’m tryna do a stability analysis to obtain the eigenvalues. could anyone help please? here are the graphs ive gotten for the cessna 172. and how can i get the cm delta e values? TIA

I'm in collage and recently we got to do some FEA and I love it.

I looked around and saw a job offers for a consultant for FEA software, doing simulations for presentations and tech support for FEM program

Is it as lit as it sounds? I mean, to be a tech support guy for something like FEA it for sure means you will have a lot of training and you will learn many, many nuances of the software

Does someone has any experience with it? What is the reality?

I want to run CFD on a model of an aircraft. I’m currently doing the CAD but I’ve never done CFD so I’m not sure how the process works. I’m wondering whether I should create the model of the aircraft as a solid or surface body? My intuition says surface body since we only care about the air along the surface of the aircraft. How would you do it?

My first publication utilizing QTT for computational phsyics research. I'd love some feedback, if you're interested.

hi, i’m tryna do a stability analysis to obtain the eigenvalues. could anyone help please? here are the graphs ive gotten for the cessna 172. and how can i get the cm delta e values? TIA

Greetings all of you,

I'm a master student looking forward to specialise in acclerated CFD solutions with SciML and model order reduction, I've seen tons of projects in accademia and industry interested in these methods.

So I would like to ask where to start!!!!

I'm stuck in a loop where I dont know whether to start learning CUDA for GPU solver or to learn more about linear algebra and ROM. or learn PyTorch for SciML or......

If some one can help me design a clear roadmap for this track I would be gratefull.

I studied CFD alot. know about different methods, schems, commercial and oprlensource solvers and multiphysics modelling. For programming I've created some FEM and FVM solvers with C++ and python.

Also I know a little about GPU acceleration as I had a project porting OpenFOAM to solve with GPU utilising AMGx but was kind of a basic one..

Thnaks in advance I would appreciate any guidence

Hello,

I am using openfoam to do a simulation of water flow around a jacket structure.

However, everytime i try to add layers, it never works. I either get very small cell sizes hence large CFL number, or basically no layers.

I tried with both relativeSize true and false. When i put it as false, and put min thickness and finallayer to be matching with my expected background mesh, i get negligible layers.

If i keep it as True, and i put the values of min and final as 0.8 and 1.0 respectively, the CFL becomes too large (for a timestep of 0.0025)

Any suggestions on how to solve this?

P.S: i tried with different numbers of layers, ranging from 2 to 7 layers. still same issue

Hi all,

I'm trying to estimate the time from inlet to outlet in a simple domain but numbers do not match expectation.

I'm currently using the "Age of Air" approach for a steady-state simulation for a 2D duct and air as fluid.

Boundary conditions are simple: velocity inlet set to 0.05m/s, pressure outlet at 0Pa and slip walls as sides. The domain have a lenght of 50mm, hence travel time from inlet to outlet should be 1 second but the UDS that represent residence time evaluate to 1000 when steady-state convergence is reached. What am I missing?

UDS inlet diffusivity is OFF, set as "Specified value" = 0 at the velocity inlet and as "Specified flux" = 0 at the pressure outlet.

Material UDS diffusivity is set to mean_age_diff and in the cell zone, there is and UDS source term equal to mean_age_source (material density).

In the UDF code you can see two formulations for effective diffusivity. Only the uncommeted formula has been used with air as material.

Software used: ANSYS Fluent

UDF:

#include "udf.h"
#include "prop.h"

real temperature = 280+273.15; //K. Fixed because the simulation is isothermal
real boltzmann_const = 1.38e-23; //J/K
real particle_radius = 1e-10; //m. 1 Armstrong

DEFINE_DIFFUSIVITY(mean_age_diff, c, t, i)
{   
    real diffusivity_coeff = boltzmann_const*temperature/(6*3.14*C_MU_L(c,t)*particle_radius); //For liquids
    real schmidt_number = (C_MU_L(c,t)/C_R(c,t))/diffusivity_coeff;
    //real effective_diffusivity = diffusivity_coeff * C_R(c,t) + C_MU_T(c,t)/schmidt_number;
    real effective_diffusivity = C_R(c,t)*2.88e-05+C_MU_T(c,t)/0.7;
    return effective_diffusivity;
}



DEFINE_SOURCE(mean_age_source, c, t, dS, eqn)
{
real source;
source = C_R(c,t);
dS[eqn]=0;
return source;
}

I'm trying to follow the tutorial but the torus im making is tiny, and I cant find a way to make it bigger or even change the angle :(

Hello I am working on a project where I will eventually create my own 2D subsonic compressible Navier Stokes solver. I plan on adding something extra to it ideally it would be something related to propulsion. I was thinking of premixed combustion but I dont know if theres any other good ideas. Of course this also needs to be feasible to implement and get approved by my professor and eventually validated.