And of course if possible you want to let the user choose arbitrary inter-particle spacings, possibly at runtime. This is e.g. the reason why #GPUSPH has a built-in simple #CSG (#ConstructiveSolidGeometry) system: it's not needed for #SPH, but it allows user to set up test cases even with relatively complex geometries without resorting to external preprocessing stages that wouldn't give the same flexibility in term of resolution choices.

And here's the thing: the CSG in GPUSPH has a *lot* of room for improvement, but it's not really the “core” of GPUSPH: how much developer time should be dedicated to it, especially considering that the number of developers is small, and most have more competences in the mathematical and physical aspects of SPH rather than in CSG?

The end result is that things get implemented “as needed”, which brings me back to the gamedev thread I was mentioning earlier:

3/

Point 1. (non-trivial geometries) is one of the reasons why most CFD systems have a separate, heavy-duty preprocessing stage dedicated to help users design said geometries and make them “accessible” to the method. The problem for us is that the vast majority of the “tools of the trade” are dedicated to mesh-based methods (especially the finite elements method, FEM) and are thus not useful for particle methods such as #SPH.

There's still a lot of ongoing research on how to “optimally” fill arbtirary geometries with particles for these applications (see for example a recent work by the #SPHinXsys team on the topic <https://doi.org/10.1016/j.cpc.2023.108744>): although superficially one could think that this is a simple extension of what is used for the standard meshes (which is almost true as long as one sticks to a single layer of boundary particles) things devolve pretty quickly when multiple layers are needed (which is the case for many solid boundary models in #SmoothedParticleHydrodynamics) or a complete fill to be achieved in a way that respect a number of equilibrium conditions that should be satisfied at the beginning of the simulation. (And remember: you might need to do both an “outer” and an “inner” fill for the same geometry, putting fluid particles on one side, and boundary particles on the other).

2/

There's something to be said about #Fediverse weirdness, that we all see different things. I discovered the Page42 hashtag game on my "unprofessional" profile, but since I'm at work now and taking a break, I participated by grabbing the closest book I have on hand, which is unsurprising a (somewhat dated, but still valid) reference on #SPH #SmoothedParticleHydrodynamics —and that seems to actually be quite characteristic of _this_ corner of the Fediverse

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@skykiss
He can only talk about what he doesn't have at this point. A dictatorship and a big penis.

@DemocracyMattersALot

He talks about things he wants but doesn't have. Dictatorships and a big penis.

@AaronDavid
The #SPH hitting hard here.