Steffen Dünner

Just started watching this brand new MPM fundamentals video https://www.youtube.com/watch?v=fDmJo3zpb1g [www.youtube.com]

And right at the start it says "...capable of simulating small scale fluids...".

Now I'm excited and will watch this.

Hi there,

I'm currently simulating a piece of chocolate with a caramel filling. The chocolate breaks open and the caramel filling should ooze out while sticking to the chocolate pieces. The MPM solver sounds like a reasonable simulation method.

At first I tried building the scene at real life scale, the piece of chocolate is ~2cm wide. I built a fractured piece of chocolate, MPM colliders, a filling with a "honey" preset etc. The filling itself consists of around 500.000 particles, nothing to write home about.

The problem is that the sim is running extremely slow. Like 1 frame per minute (!!!) max.

I tried a few things but the only thing that helped was to scale up the scene by a factor of 100 so that the piece of chocolate now is more like 2m tall. The amount of particles is still at 500.000 but now the sim runs at 2-3 frames per second. What a difference!

Now the question: Is the MPM solver intended for large scale sims only or did I miss an advanced / hidden setting? I mean I can live with manually scaling up and exporting the downscaled results afterwards, but I would prefer working at the intended scale all the time.

Thanks a lot, it actually works!

I tried a lot of things but never to use a primitive attribute instead of a point attribute because of this in the documentation:



It clearly states "point attribute". :/
The attribute selection in the Surface Deform SOP also only offers to select the attribute if it's on points. So in the end it's not a bug but just a case of wrong documentation. I didn't use the Surface Deform before, maybe this behaviour (primitive instead of point attribute) changed some version of Houdini ago?