Proceeding from the previous week, my goals for this one were to start the sand simulation, as it was the only one I haven’t tried before, and update my previs, as the camera moved frantically and lot in the previous version.
Looking for various tutorials, I haven’t managed to find a lot on the sand, so just to introduce myself to the nodes and what various physical aspects do, I used a tutorial on a tire in the wet sand.
This was my Houdini scene set-up and various graphs that I made. The only downside of it was that I hoped the sand graphs would be created from scratch and every single original node that was used would be explained. However, in the end, a shelf tool for “Wet Sand” was used, which automatically set up nodes inside “sandGeo”, created a node “AutoDopNetwork”, where it set up the required POP particles nodes for the simulation, as well as created the “grain_particles” node, where the DOP network was read into. One of the useful features of the shelf tool is that it automatically creates the necessary connected relationships between nodes.
Now that I had a better understanding of how it works, I imported a modeled hourglass as an alembic file to Houdini, to start simulating the movement of falling sand grains. Then the file had to be prepared and some reference model shapes were chosen to be used as the sand source. After that, I separated out the glass from the supporting case, such that I could apply a glass material to the cone-shaped part so that the sand could be seen inside of it in the viewport.
One of the problems I did come across, was that usually when importing files from Maya, Houdini and Maya’s software have different world scales. Typically, you would apply 0.01 scale to imported alembic files. However, when I did so, hence decreasing the clock drastically in size, after applying the sand simulation shelf tool the sand grains seemed to be so heavy that they wouldn’t hold the original lattice shape and just press onto each other to form a flat sheet at the bottom of the hourglass. After trying to solve it in various ways, given that my knowledge of sand tools is rough, I decided to skip the de-scaling part and work with the enlarged version of the sand clock. But that would mean that the physics of my simulation would be far away from truthful in this case.
Currently, there are a few problems and visual appearances that I am trying to solve (here using https://vimeo.com/481058293 as the video reference). Firstly, the way that the sand was falling from the top compartment was such that the grains were going to the center of the shape and fall down there, whilst keeping the overall shape of the top part intact with the glass and mostly not moving at all. Whereas compared with the hourglass in real life, the shape of the sandpile moves down altogether as the sand escapes through the hole.
The values also affect the sand pile at the bottom: the sand keeps falling and not forming the perfect small hill that we would typically observe. Instead, the grains level out but push the ones at the bottom to spread and thus making the grains that are in touch with the glass to move up.