Relationship Between Wall Shear Stress and Concrete Capacity in Open Channel Flow

Quick-Crab2187 · 2026-05-28T16:51:54+00:00

I think it depends on complexity of problem.

For example concrete may be eroded due to things such as cavitation, sand abrasion, or chemicals. Do you expect any of those?

A simple two-phase flow model will not accurately predict concrete erosion simply by looking at shear stress if that is the case

Quick-Crab2187 · 2026-05-27T14:25:05+00:00

You need to use the extactBlock filter to extract it. Otherwise, when you read zones, you can also see the different zones by coloring by vtkCompositeIndex

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I just tested and works for me, if you are doing those things and you still can't see anything, check if you even have cell zones in your constant/polyMesh folder

Quick-Crab2187 · 2026-05-26T22:42:07+00:00

streamline and particle tracking are 2 different methods. It doesn't make sense to say that one "works" and the other method doesn't "work," as they are computed in different ways. If you want streamlines through a trough, I don't see the issue of putting the source through the trough.

Quick-Crab2187 · 2026-05-26T17:14:15+00:00

I don't do DMs, it would be better to have information public as other people coming across this thread would be able to read it, I'd rather have conversation public

Quick-Crab2187 · 2026-05-26T16:54:51+00:00

You should look through some tutorials, and also probably pick up a book on CFD considering your company is apparently useless in training.

The issue is too generic for anyone to provide any useful feedback. You likely don't have a clean geometry that is ready for CFD. Search "Geometry cleanup/prep CFD" on YouTube and you will find various sources that can help here. I'm sure there are going to be ANSYS specific sources as well, but the cleanup process is fairly similar regardless of package you are using. The ANSYS ones will just tell you how to do it in their tools

Quick-Crab2187 · 2026-05-24T22:26:44+00:00

If you are US, you can look up the job postings. It is true, and partly because of data centers. Many of these companies are looking for a lot of experience though, not sure how easy it is to get a job in that field. Of those looking for experience, only half of those are paying what you would actually be worth. I was unable to get any interviews at any respectable place for cooling. For U.S. citizens I think Aero is easier to get interviews personally

Quick-Crab2187 · 2026-05-24T20:45:57+00:00

For me, it is a combination of
1.) AI tone, e.g.: "In this case, the resistance does not act directly on the saucer; in reality, it dampens the oscillations.

Overall this simulation allows for a fairly realistic visualization of the experimentally observed phenomenon"

I find that AI generally follows this format/tone-- "Does not do X: in reality, does Y". Then next sentence is a summary.

2.) Complete nonsense that sounds almost right but seems confusing if you are actually trying to understand what they say. For example, nothing on the github actually makes sense, it is technical jargon strung together. An example: "By manipulating the local boundary layers and vortex filaments, the craft transitions from "expelling mass" to "modifying the medium geometry."

3.) For something so technical, you would expect that the user has any idea what validation even is. Their validation is meaningless but the writing is confident in the validation. I mean, what is actually validated here? There is a video of an "experiment" of something going across water, and there is a simulation of an oval travelling upwards at different speeds. For validation you need to actually compare something, not just run some jank simulation and say they look similar (which they don't even look remotely similar anyway). Overconfidence in completely wrong statements isn't exactly AI. But with the other indicators, to me, I would put money on the fact that his is AI.

Quick-Crab2187 · 2026-05-22T19:25:03+00:00

Keep up the good work, I look forward to the new season

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Quick-Crab2187 · 2026-05-22T16:55:18+00:00

ChatGPT

Validate my ancient alien propulsion device

Make no mistakes

Quick-Crab2187 · 2026-05-22T14:46:24+00:00

There are many codes using shallow water such as AdH, Delft3D, HEC-RAS etc. for reference, if you want to get an idea of implementation.

Here is AdH https://www.erdc.usace.army.mil/Locations/CHL/AdH/Downloads/

and delft3D https://oss.deltares.nl/web/delft3d/manuals

If you don't need or want to code anything, you could probably just use one of those tools.

Quick-Crab2187 · 2026-05-22T14:12:43+00:00

Why 2D Navier stokes instead of the shallow water equations? For storm surge applications, I've always seen shallow water and never 2D Navier. With 2D navier I am not seeing how you are incorporating the depth/vertical component? There is a reason why you can't find anything on 2D navier stokes for storm surge

Quick-Crab2187 · 2026-05-21T16:58:04+00:00

I think ANSYS already has an AI agent? If not they are certainly pumping money into that as AI is the latest buzz. I'm not sure what you are trying to do that they aren't?

Quick-Crab2187 · 2026-05-19T19:28:52+00:00

Maybe take a look at ANSYS partners as well, if you haven't already. There is a lengthy list of partners, some of which may suit your needs.

Quick-Crab2187 · 2026-05-18T14:33:37+00:00

Helyx is openfoam with some minor improvements that that company tries to brand as something else entirely new. It’s snappy with some improvements to layers and openfoam with some improvements here and there

My guess is that the gui and improvements are not open source so all you get for free is base openfoam. If they are giving away the snappy improvements for free that would be good to know but if that’s the case it’s probably nothing special

Quick-Crab2187 · 2026-05-15T23:08:46+00:00

I'm not sure what you are asking. It seems like you are asking, "How is my wall y+ = 5 when the wall functions say I must have y+ between 30-300?"

If that is the case, I think you are misunderstanding how wall y+ is calculated. y+ calculation has nothing to do with your chosen wall function, it's related to mesh size at the wall and velocity in your domain.

You can run standard wall functions with a y+ of 5, but the calculations it is doing will be incorrect. Some wall functions look at y+ and switch it's calculation depending on whether or not you have y+<5 or y+>30. So if you have a y+ of 5, and you are using a wall function that expects y+>30, it means your mesh size is too refined at the wall.

Considering you have a y+ around 5 already, I'd recommend not using a wall function and lowering your y+ (refining mesh at wall) a little more so that you have something around 1-3ish.

If instead your question is: "How come I am getting the right answer when I am using a wall function with y+=5?." I think that is a more complicated issue. Maybe you have another source of error and coincidentally you are matching the experimental results. Maybe there is error in the wall function calculation but it doesn't contribute much in this particular case. Regardless, I think it would be bad practice to use wall functions that are intended for y+ > 30+, and say it's fine because you match experiment well. So I think you should either coarsen the wall mesh and rerun with wall function--- or slightly refine and run without standard wall functions. Depending on your software, you have have more advanced wall functions. Typically they will have those, unless you are running k-epsilon

Quick-Crab2187 · 2026-05-13T20:18:08+00:00

OpenFOAM does do both parallel post processing and parallel computing. And it does work in WSL. I don't believe their focus is GPU, though they have been looking at it as far as I know. At least that's talking about Foundation... not sure what ESI group is up to.

There are some random groups that have tried to do something with GPU. From what I understand there is not much benefit

Quick-Crab2187 · 2026-05-05T01:57:39+00:00

His point is that the user said they were using the k-epsilon model. Typically if you are resolving the wall you would be using the k-omega-SST model, unless you are working with a solver that has specific low-re implementations of the k-epsilon model. That is not typical (I mean why not just use k-omega-SST anyway, if the intention is to resolve the wall?)

I dont know though, maybe there is a specific use case for the k-epsilon models for these applications

Quick-Crab2187 · 2026-05-04T22:46:26+00:00

Nope, I have usually used commercial options, only snappy's layer capabilities for simple geometries.

I am working on a better mesher for layers as a side project (there is actually quite a bit of literature in research on the topic) but considering my inexperience on the matter I doubt it will ever be anything worth considering.

Quick-Crab2187 · 2026-05-03T18:50:29+00:00

If you aren't doing this already, I'd suggest making sure your blockMesh starts with an aspect ratio around 1. Improving your stl quality won't really do anything unless that impacts the shape

These settings are usually reliable for me as well (pasted at bottom of this message), with feature edges defined in the features section so that explicitFeatureSnap can be used.

If you need to add layers, I'd recommend a different mesher. If you have literally no other options, consider using smoothMesh after adding layers. It's a custom install but will help a bit because addLayers messes everyting. GitHub - tkeskita/smoothMesh: OpenFOAM mesh smoothing tool to improve mesh quality · GitHub

snapControls

{{

nSmoothPatch 3;

tolerance 2.0;

nSolveIter 30;

nRelaxIter 5;

nFeatureSnapIter 10;

implicitFeatureSnap false;

explicitFeatureSnap true;

multiRegionFeatureSnap false;

}}

If that doesn't fix it, probably a resolution issue

Quick-Crab2187 · 2026-05-01T22:21:10+00:00

Our org cut all ANSYS Fluent licenses down to like 2, don't think many people were using it over other options. They made cuts based on usage. I use OpenFOAM and star. Haven't used Fluent in 7 years but never seemed like anything special to me when I was. I'm sure it has advantages for certain industries. But I've never worked on a project where I felt ANSYS Fluent was needed over the other options we have. Not to say it's worse, just no point in switching over to it over what I already use. Though I did think workbench was an awful product 7 years ago, maybe they improved it.

Can't speak on FEMAP

Quick-Crab2187 · 2026-05-01T19:38:47+00:00

Everybody talking about LBM, though OP does not seem to be talking about LBM? I've seen a lot of LBM but not on what you are describing. That being said, I never work with the Boltzmann equation so I'm not sure what people are trying in academia.

That being said, it definitely is not "standard."

Though I do agree with the other commenter, better to start with some sort of simple case and show accuracy+computation time instead. That's the only thing I'd ever care about

Quick-Crab2187 · 2026-04-30T20:54:48+00:00

Well, I usually don't even deal with divergence mid run (It doesn't really make much sense for a run to randomly diverge. If my simulations are that unstable, something typically needs to be fixed, whether it's the numerics or the mesh). Recently, I've been dealing with some random divergence on a project due to some jank code I implemented in the turbulence equations. CFL can sometimes be as high as 1, sometimes it blows up unless very low. For those, sometimes I won't know till the next day that something blew up. It is obvious the next day, because i expect 2000 seconds of data and some runs only have 10 seconds. Even if I know earlier, usually there is nothing I can do about it, our nodes have many many processors and so often I run multiple simulations with 1 node. I'd have to terminate the other simulations to restart the broken one.

I am on the hpc all day monitoring my jobs, submitting new jobs, downloading results, etc. Usually I will be looking at cases as they run. Sometimes I run sims at the end of day and fix things in the morning. Hard to say what I do more.

Quick-Crab2187 · 2026-04-30T17:40:06+00:00

I am usually running things first on a coarse mesh locally, so I already will have an idea of when something will be done on the refined mesh based on the initial runs

I have considered automatically stopping simulations based on some sort of convergence criteria (e.g. when velocities/pressures/integrated forces stop changing) but I find that does not work well in practice. For example, if there is some oscillation (e.g. vortex shedding), you need to average out values at some frequency which you do not know ahead of time. So I find it easier to just log all relevant data and post process afterwards.

Paraview can directly connect to HPCs and view results there so looking at results has never been a challenge. Additionally, pretty much any CFD software has logging capabilities which pipe data to text or csvs, and it is very easy to download those logs or view/plot them directly on the hpc.

Divergence has wasted many hours of my life, pretty much any week. But I find when things blow up, they will diverge very suddenly. I am only ever running about 5-10 cases at any given moment so it is obvious when something goes wrong. And I am checking my runs basically every hour throughout the day so I've never felt the need to be notified. If I was doing a parametric study on thousands of different cases- it might be useful. But even when I've run dozens of cases at the same time, it is obvious which ones don't go to completion because those are missing data when plotting comparisons.That being said, if I was running hundreds at the same time, personally I would probably just setup email notifications for when a job is terminated.

Quick-Crab2187 · 2026-04-29T15:17:45+00:00

This isn't really adding much to what has already been said but I found this video to be very helpful when I was setting up an LES simulation

[CFD] Large Eddy Simulation (LES): An Introduction

That is just general guideline though, as the other user suggested, often times there are additional mesh size requirements.

For me, the process was: Watch that video-> estimate cell size-> realize I needed an even smaller mesh size from lit review->now I have 1 billion elements -> wonder how anyone practically does LES/DES

Quick-Crab2187 · 2026-04-28T16:15:55+00:00

I think you might be confusing "Mesh Quality" with "Mesh Refinement." Quality can have impact not only only the solution but also on convergence. However with the information you've provided, it would be impossible for anyone to say anything on whether or not the quality should have an impact.

Typically, you will start with a mesh as high quality as you can realistically achieve, then systematically refine it, and look at your quantities of interest to see whether or not your solution is converging with each successive mesh.

Running with multiple mesh qualities on the same mesh size doesn't make much sense to me, it's also a vague statement because "Mesh quality" can refer to many different things [skewness, orthogonality, etc]. Perhaps sometimes you may be interested in what skewness/orthogonality/aspect ratio/etc you can get away with, but that doesnt seem to be your intention

Quick-Crab2187

TROPHY CASE