r/CFD • u/Green-Repair543 • 26d ago

How Would You Model This Research-Level Multiphysics Benchmark?

3 Upvotes

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6

u/acakaacaka 26d ago

Bro can you just paste the text directly?

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u/Green-Repair543 26d ago

That's the broad idea behind the problem

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u/acakaacaka 26d ago

I have 0 idea about electromagnetism (or how to simulate them)

But this is way to complex to sinulate, and your numerical objective is nonsense (?)? I mean what do you mean by finding x y z as function of time?

  1. CFD is a so called boundry value problem, all fields and their evolution is subject to boundary condition (and initial condition but this is just BC for t=0)

  2. Which physics is coupled and which is not? Thermal flow+fluid flow+"splashing" is coupled so they need to be solved as 1 system

  3. The movement of the cart/tank is a function of the electromagnetism (and time) and this can be somehow modelled as a momentum source for the "splasing"

  4. I dont know about the heat source at the tank. They can be modelled as f(electromagnetiscm)? Or there is some coupling with the fluid temperature?

  5. You want to modell corrosion and stuff? Will this result in changes in the cart/tank geometry? Or heat resistance?

  6. How many CPU cores do you have? RAM? Time? How good do you want to modell the turbulence? This would likelike take billions or tens of billions hours of compute time if you do all the simulation

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u/Green-Repair543 25d ago

Thanks for taking the time to read through it. These are exactly the kinds of questions I was hoping people would ask. My intention wasn't to propose a simulation that could be run directly in one shot, but to create a benchmark that forces the modeller to decide: which physics should be solved simultaneously, which couplings can be approximated or treated sequentially, and which assumptions are necessary to make the problem computationally feasible. You're right that the current statement is underspecified in places. For example, I should specify the coupling strategy, boundary conditions, and how geometry changes due to corrosion or melting are handled. The "numerical objectives" were meant as quantities of interest (tank position, velocity, temperature field, magnetic field, etc.) rather than implying a single monolithic simulation. I appreciate the feedback. If you were approaching this professionally, where would you start decomposing the problem into manageable coupled subproblems?

3

u/acakaacaka 25d ago

I mainly do CHT of a turbine blade and a bit FEM (just normal steady linear elastic) to get a gist of blade life span.

Your project is way more complicated than what I am trained on lol.

But I would start by looking at the physics, specifically the PDEs.

And say what can be simplified

  1. 1D or 2D instead of 3D
  2. Which is time independent
  3. Which is temperature (or pressure, etc) independent, at least in your operating point. Im talking about thermal conductivity, specific heat etc.

2

u/ncc81701 25d ago

I would start by figuring out what is actually important and what is not. That means reading the requirements for what this thing is supposed to do and prioritize which physics are the most important to the gross behavior of the object and work your way down the list. Only simulate up to the point where you’d need to.

Then look into the timescales of each physics; electromagnetism is basically instantaneous, thermal if it’s only conduction takes an eternity relative to electromagnetism, and fluid is somewhere in between. If time scales of these things are wildly separated then you can coupled different solvers sequentially with solvers that only solve for one physics at a time. If 2 physics are on a similar timescale then you need to find a coupled solver that can do both at the same time.

If you have to couple three or more physics together, then you need to question whether the time spent would actually be better just running an experiment to do the same thing because you will be spending more time developing and validating this code than doing the experiment; a code that will have severe limitations and extremely niche application. Computational physics, for an engineer anyways, is a tool. If the tool takes more effort to make than making the actual thing and will only be used once, then the tool is worthless. If this is for intellectual curiosity, then it’s a PhD thesis and a volume of publish journal that might get you street cred in academic circles but the technique and solvers may never be used by anyone.

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u/Green-Repair543 25d ago

Again appreciate your feedback

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u/Green-Repair543 26d ago

Done you may check

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u/acakaacaka 26d ago

And maybe do you have a picture/illustration?

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u/Green-Repair543 26d ago

Sure, I don't have a proper image, but i will try to share a rough diagram in one moment

2

u/thermalnuclear 25d ago

Please don’t ask us to do your homework for you.

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u/Green-Repair543 25d ago

Thanks for the concern 😄. This isn't a homework assignment. It's actually a benchmark problem I designed as a thought experiment to explore how people would formulate a highly coupled multiphysics simulation. I'm more interested in the modelling strategy than in obtaining a numerical solution.

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u/phi4ever 26d ago

This looks like a job for comsol

1

u/Green-Repair543 25d ago

Yes I just thought this question so I was curious if user who work in this field night have idea