Niall Horn's FX Blog: Explosive Jet-Ski'n - RealFlow 2015 Alpha Test Shot

Hi Guys,

Here is an updated version of my Explosive Jet-Ski'n Shot as I once again got the change to Alpha & Beta test RealFlow 2015, this is my First test shot, using the RealFlow 2015 alpha. The Overall production time of this shot was around 1.5 weeks, the main purpose was testing the new Collision Volumes in RealFlow 2015 aswell as the faster sim times. The Original version from 4 days ago I was not happy with, the Ocean surface I used was mainly based on fractal noise displacement and looked really bad, this time I am using HOT (Houdini Ocean Toolkit in Max) with some additional noise to get rid of Tiling and also to add the smaller waves/ripples on the surface. I also added in the Rock the Jet Ski collides with, aswell as including side water explosions as if the Jet-Ski's are riding through a minefield! I also added more spray and mist and some rainbowing (caused by rays travelling at different lengths/Refractions through water spray, Physics Knowledge!) and also Water on the Lens which I love doing as it adds a lot of Realism. Here is the making of the shot-

Max Scene WIP

The Jet Ski models were quite lowres and had bad topo however the new collision volumes in RealFlow created an accurate isosurface without any problems! The Jet Skis were then Keyframed and the Red Ski that gets thrown in the air, was a simple RBD RayFire Sim. This was then sent to RealFlow as SD (Scaled Down to RealFlows Scale).

I used Hybrido (FLIP) for the shot, The Jet Skis have small cylinders on the back of them, these emit fluid with inital velocity to mimic the Jets on the Jet Ski, without this the velocity in the fluid would come from the collisions only which is not realistic. Also having that extra velocity in the water creates nicer Foam Patterns and Secondary Simulations.

RealFlow Jet Ski, Jet Emitters

The Core Fluid sim had around 45 Million particles, Originally the camera was in from of the Skis and showed the full length of the fluid, so I didn't go for a Moving Domain method, I used a Full Static Tank approach, However I changed the camera before rendering for a better shot, in the end I could of used a Moving Fluid Emitter/Domain but it was too late! The sim took only 10-11 Hours, thats a lot quicker than RF2014, compared to how long my Space Pyramid Rise Project took to sim. One thing I found with doing a Jet Ski sim is, usually the worry is that the scale will look to small, well I was using a proper scaled scene very close to Real World Scale, however the Jet Ski Jets loved to shoot fluid really high, so I ended up using higher gravity and then cutting the top of the Fluid Mesh off at Render time.

Nice Foam Wakes from the Jet Emitters and Using HyFLIP Splash & Foam

The Secondary Sims were done using Dumb and HyFLIP for the Splash and Foam, I encountered a problem I have now named, "The Radial Spray Problem"! Its due to really fast moving objects and not using enough sub steps (I think). I solved it by using Bounded Noise Fields parented to each Jet Ski to mess up the initial emission and give more natural swirls to the splash emission. I went for Splash and Foam rather than separate Splash and Foam sims because I knew I wanted direct emission of Foam from the Splash sim. And Splash & Foam is a lot more improved than having to do Splash as a septate sim that then drives a Foam sim.

The Water Explosion was done in a Separate scene, a very simple Sphere colliding with a Low Res Hybrido sim, using Noise and attractors to get the fluid to Explode like a small depth charge, the WhiteWater Splash and Foam sim was using Dumb Particles, these were then used without the core fluid sim. I orgianlly planted to use the Ocean Force Field Daemon, however this method give me more control without having to go back and re-animate texture Sequences. The side water Explosions were using PFlow, Its quite hard to get a nice water explosion at this scale, as inreality Depth Chrage explosions are very huge and traily, where as I wanted more of a smaller scale blast explosions.

Water Explosion Sims

PFlow Side Water Explosions Setup WIP

The Hybrido PRT's were meshed through Frost, Using Krakatoa to extract the velocities and drive a V-Ray Extra Tex map (With Refraction) to create the Bubbles Refraction Velocity Effect. The Mesh was cut off as I said to stop the fluid looking out of scale from the Jet emitters at the rear of the Jet Skis. I used a Texture map under the Fluid Mesh with a Seabed map on for a more realstic ocean look.

The Fluid Mesh with Velocity Shading

The Splash and Foam was rendred also through PRT using Krakatoa, The other passes were the Water Explosion sim again through Krakatoa, the Extended Ocean Pass took the longest, the Skydome was tracked in, in comp. I added some green/bluey tint to the refraction/Velocity pass to create a nicer refraction in the whitewater. The main Splash and Foam passes were using Krakatoa Isotropic Particle rendering (With Specular based on the Normals) the Explosion passes were the same but I also rendered the same PRT's from there sims through Krakatoa Voxels and comp'd them on top to create a mist/fine spray element.

Just Some Of The Render Passes

Comp WIP (AE)

Comping the WhiteWater

Comping The Main Water Blast Passes

Adding Rainbowing and Water Droplets on the Lens

The Comp was done as the render passes were finishing, the majority of comp time as always was blending the Fluid Mesh to the Extended Ocean. The Extra Tex Vertex Colour and Refraction pass were then comp'd with the main Fluid mesh, aswell as the Secondary sim renders. I added a flares in a frame before the blast to show its an underwater explosion, I used a still image to break the extended ocean pass up to the sky using an Ocean Horizon and used RefineMatter and more masking to blend these together. Most of the motion blur is faked in comp using RSMB, the Depth of Field was rendered as Z-Depth passes and added in Comp also.

Dailies/Comp WIP

FINAL SHOT AND BREAKDOWN

So as I mentioned, Version one of the shot I was not happy with, so I deicded to make these comparions and hopefully you'll agree with me that for another 4 days of work, Re Renders and a Full Re-Comp, The shot has now turned out better?!