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In this focused RnD, I implemented a small-scale fluid simulation algorithm within Flip to accurately resolve adhesion forces. The core algorithm is relatively straightforward: the fluid's surface field is extrapolated into the collider volume, factoring in the contact angle, and is subsequently adjusted and smoothed. Furthermore, a localized viscosity is introduced at the fluid-collider interface to approximate boundary friction.

The simulation operates at a physically accurate real-world scale, utilizing empirical physical constants where the baseline water viscosity is 0.001 and surface tension is 0.072. APIC was chosen as the underlying solver.

While this technique requires a high substep count and is computationally expensive to evaluate, it successfully produces highly nuanced and realistic fluid dynamics.

Hey everyone!

Working on a custom local upresing pipeline for FLIP sims to optimize hardware resources while running everything on a MacBook Pro. Since simulating the entire continuous body of water in high resolution rapidly runs out of RAM, this approach is essential for making high-detail simulations actually feasible on a single machine, while also drastically cutting down simulation times and cache sizes. SideFX has solid native tools for this, but they mostly push you into SOPs, and I wanted a flexible setup that runs directly inside DOPs.

How it evolved:

Boundary Layers only: Started with standard boundary layers driven by the low-res base sim. It was fast and looked okay at first, but completely broke down during complex collisions and splashing.

Gas Guiding + Boundary Layers: Switched to combining Gas Guiding Volumes with Boundary Layers. Dialing in the velocity transfer and pressure stability took a lot of tweaking, but the setup is now rock-solid and predictable.

Also, I built a few custom HDAs along the way:

FLIP Cache: Isolates volumetric and particle data into separate caches (huge credit to Igor Zanic for the workflow inspiration). Tracks sim times and disk usage, then feeds those stats directly into the flipbook UI.

FLIP Vis: Basic utility for quick attribute visualization.

FLIP Limit Band Width: Extracted the logic from SideFX's Fluid Compress node and rewrote it into a lightweight standalone tool to avoid the heavy node wrapper.

PDG Flipbook Generator: An automated review pipeline paired with a Python script that overlays custom stats onto playblasts. Saves a ton of time during iterations.

Still tweaking the full river setup, will drop the final project once it's finished.

Popping boxes effect created using Houdini RBD and Octane Standalone

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In this project, I figured out how to dynamically create and delete RBD objects with constraints; I also finalized my RBD instance workflow. Essentially, everything in the render is instances of RBD object variants that inherit the correct transformations from Bullet's proxy geometry. These aren't packages within SOPs, not are they implemented via Transform Pieces, but rather instance points with a variant attribute. This solution is very useful for situations where, for example, you need to reference instances to RS Proxy or files from disk to maximize scene optimization; or, as in the case of the final render, to correctly transfer the instancing setup to other rendering software without losing optimization