Uploaded February 2020 | Updated September 2026, 2 weeks ago
Simulating raindrop impacts is particularly challenging for CFD software, because the Reynolds number Re=d*u/nu is very high and for such turbulent flow many solvers become unstable. With D3Q19 and the SRT collision operator, the LBM solver FluidX3D is still stable at Re=51k despite the free surface extension, enabling proper raindrop impact simulations without cheating on the viscosity.
References for simulation parameters:
[1] researchgate.net/publication/256687896_Effects_of_Altitude_on_Maximum_Raindrop_Size_and_Fall_Velocity_as_Limited_by_Collisional_Breakup
[2] engineersedge.com/physics/water__density_viscosity_specific_weight_13146.htm
FluidX3D is a real time 3D fluid simulation based on the lattice Boltzmann method. It is written in OpenCL C (GPU code) and optimized to the physical limit (video memory bandwith, ~520GB/s).
All demonstrations are simulated and visualized on a Nvidia Titan Xp. Compute time of all simulations combined was about 15 minutes. Graphics are done with the OpenCL C version of Line3D, the fastest graphics engine ever written for primitive shapes like lines, dots and circles. It can handle up to 2 billion lines per second.
The free surface is done with the volume-of-fluid (VoF) extension to LBM. It allows simulating free surfaces with a sharp interface layer.
The volume force (gavity) is implemented with the Gou forcing scheme.
Visualization of the surface is done with the marching cubes algorithm (implemented in OpenCL C).
paulbourke.net/geometry/polygonise
Hardware Setup:
CPU: Intel Core i7-8700K @ 4.5GHz all core
GPU: Nvidia Titan Xp
RAM: 2x8GB Corsair Vengeance LPX DDR4 3200MHz CL16
Mainboard: ASUS ROG STRIX Z370-I GAMING
SSD 1: Samsung 970 PRO 512GB
SSD 2: Samsung 860 EVO 1TB
CPU Cooler: Cooltek LP53
PSU: Corsair SF600
Housing: Fractal Design Node 202
Timestamps:
0:00 - Intro
0:06 - 1 mm drop size
0:13 - 2 mm drop size
0:21 - 3 mm drop size
0:28 - 4 mm drop size
0:36 - 5 mm drop size
0:43 - 6 mm drop size
0:51 - 7 mm drop size
More information at projectphysx.de
Simulating raindrop impacts is particularly challenging for CFD software, because the Reynolds number Re=d*u/nu is very high and for such turbulent flow many solvers become unstable. With D3Q19 and the SRT collision operator, the LBM solver FluidX3D is still stable at Re=51k despite the free surface extension, enabling proper raindrop impact simulations without cheating on the viscosity.
References for simulation parameters:
[1] researchgate.net/publication/256687896_Effects_of_Altitude_on_Maximum_Raindrop_Size_and_Fall_Velocity_as_Limited_by_Collisional_Breakup
[2] engineersedge.com/physics/water__density_viscosity_specific_weight_13146.htm
FluidX3D is a real time 3D fluid simulation based on the lattice Boltzmann method. It is written in OpenCL C (GPU code) and optimized to the physical limit (video memory bandwith, ~520GB/s).
All demonstrations are simulated and visualized on a Nvidia Titan Xp. Compute time of all simulations combined was about 15 minutes. Graphics are done with the OpenCL C version of Line3D, the fastest graphics engine ever written for primitive shapes like lines, dots and circles. It can handle up to 2 billion lines per second.
The free surface is done with the volume-of-fluid (VoF) extension to LBM. It allows simulating free surfaces with a sharp interface layer.
The volume force (gavity) is implemented with the Gou forcing scheme.
Visualization of the surface is done with the marching cubes algorithm (implemented in OpenCL C).
paulbourke.net/geometry/polygonise
Hardware Setup:
CPU: Intel Core i7-8700K @ 4.5GHz all core
GPU: Nvidia Titan Xp
RAM: 2x8GB Corsair Vengeance LPX DDR4 3200MHz CL16
Mainboard: ASUS ROG STRIX Z370-I GAMING
SSD 1: Samsung 970 PRO 512GB
SSD 2: Samsung 860 EVO 1TB
CPU Cooler: Cooltek LP53
PSU: Corsair SF600
Housing: Fractal Design Node 202
Timestamps:
0:00 - Intro
0:06 - 1 mm drop size
0:13 - 2 mm drop size
0:21 - 3 mm drop size
0:28 - 4 mm drop size
0:36 - 5 mm drop size
0:43 - 6 mm drop size
0:51 - 7 mm drop size
More information at projectphysx.de
![Line3D [GRAPHICS ENGINE] Dynamische Beleuchtung](https://i.ytimg.com/vi/_9i8RSxTkjA/mqdefault.jpg "Line3D [GRAPHICS ENGINE] Dynamische Beleuchtung
Ich hab noch ein bisschen an der Java-Grafikausgabe aus meinem Projekt PhysX3D weiter geschrieben. Aus einfachen Linien sind Polygone geworden, die dynamisch von einer (oder auch mehreren) frei beweglichen Lichtquellen beleuchtet werden. In diesem Beispiel berechnet die CPU auf einem Kern 25.600 Dreiecke pro Frame, und das etwa 30 Mal in der Sekunde.
Ich verwende dazu nur die elementarsten Java-Bibliotheken wie das JFrame, ein Fenster, in dem ich Linien, Text und Vielecke zeichnen kann.
Wie funktioniert die Berechnung?
Für jedes Dreieck wird der Normalenvektor berechnet. Das ist sozusagen eine Linie, die immer senkrecht auf der Fläche des Dreiecks steht. Dann wird der Normalenvektor skalar mit dem Vektor vom Mittelpunkt des Dreiecks zur Lichtquelle multipliziert. Einfach ausgedrückt vergleicht man dabei, ob der Normalenvektor zur Lichtquelle zeigt. Wenn er das tut, ist die Fläche heller, sonst dunkler. Mit dem Ergebnis der skalaren Multiplikation wird die Helligkeit des Dreiecks skaliert.
Die Lichtquelle muss nicht immer am selben Punkt sein, sie kann sich auch bewegen, wie hier im Video demonstriert.
Was ist der praktische Nutzen davon?
Das Prinzip der dynamischen Beleuchtung ist heutzutage in jedem Computerspiel und in jeder Rendering-Software zu finden, bloß werden dort die Dreiecke noch viel kleiner gemacht, damit zum Beispiel ein animiertes Gesicht nicht eckig aussieht.")
![FluidX3D [FLUID SIMULATION] - Real Time Free Surface LBM with Volume-of-Fluid](https://i.ytimg.com/vi/a1u2g9ahIDk/mqdefault.jpg "FluidX3D [FLUID SIMULATION] - Real Time Free Surface LBM with Volume-of-Fluid
FluidX3D is a real time 3D fluid simulation based on the lattice Boltzmann method. It is written in OpenCL C (GPU code) and optimized to the physical limit (video memory bandwith, ~520GB/s).
All demonstrations in the video are simulated and visualized in real time on a Nvidia Titan Xp. Graphics are done with the OpenCL C version of Line3D, the fastest graphics engine ever written for primitive shapes like lines, dots and circles. It can handle up to 2 billion lines per second.
The free surface is done with the volume-of-fluid (VoF) extension to LBM. It allows simulating free surfaces with a sharp interface layer. Having to avoid race conditions makes an efficient GPU implementation of VoF is quite challenging. Currently there is no surface tension yet; the curvature estimation algorithm is still under construction.
The volume force (gavity) is implemented with the Gou forcing scheme.
Hardware Setup:
CPU: Intel Core i7-8700K @ 4,5GHz all core
GPU: Nvidia Titan Xp
RAM: 2x8GB Corsair Vengeance LPX DDR4 3200MHz CL16
Mainboard: ASUS ROG STRIX Z370-I GAMING
SSD 1: Samsung 970 PRO 512GB
SSD 2: Samsung 860 EVO 1TB
CPU Cooler: Cooltek LP53
PSU: Corsair SF600
Housing: Fractal Design Node 202
Timestamps:
0:00 - Intro
0:02 - honey coiling
0:34 - large drop impact
0:45 - drop splashing in flowing water
0:55 - throwing drop sideways in resting water
1:00 - eternal periodic water tap
1:07 - dam break without obstacles
1:18 - asymmetric dam break with two connected chambers
1:29 - droplet impact
1:39 - eternal periodic fountain
1:50 - dam break with cuboid obstacle
2:06 - more honey coiling (just because it is so cool)
More information at http://www.projectphysx.de
Music: Notaker - Fatal System Error")
![FluidX3D [FLUID SIMULATION] - Smashing the Memory Wall with FP16 | 100 Subscriber Special](https://i.ytimg.com/vi/aWFi__zMUkk/mqdefault.jpg "FluidX3D [FLUID SIMULATION] - Smashing the Memory Wall with FP16 | 100 Subscriber Special
FluidX3D is a real time 3D fluid simulation based on the lattice Boltzmann method. It is written in OpenCL C (GPU code) and optimized to the physical limit (video memory bandwith, ~520GB/s).
All demonstrations in the video are simulated and visualized in real time on a Nvidia Titan Xp. Graphics are done with the OpenCL C version of Line3D, the fastest graphics engine ever written for primitive shapes like lines, dots and circles. It can handle up to 2 billion lines per second.
LBM performance is only limited by video memory bandwidth - the so-called memory wall. Storing the LBM distribution functions in memory as FP16 instead of FP32 cuts the memory bandwidth requirements in half, doubling the simulation speed at the cost of a bit of accuracy. My implementation has a hardware efficiency of up to 95%, meaning that 520 GB/s of the total 548 GB/s of video memory bandwidth are used. This results in a peak performance of 5.2 GLUPs (giga lattice updates per second, how many LBM lattice points are processed in 1 second) for the D3Q19 velocity set.
More information at http://www.projectphysx.de
Music: Notaker - Fatal System Error")
