Just a few days ago, I found out about a MIT competition called The Art of Astrophysics. Naturally my interest was piqued. The only problem was the deadline… 24 hours!
As a back burner project I’ve been experimenting with creating jupiter cloud bands that are truly fluidic. Its very difficult to keep the multiple bands separate, so I’ve been testing the interaction between just two bands. The Kelvin–Helmholtz instability is a fascinating topic to focus on, but its heavy to simulate and difficult to predict.
Often when I begin these type of experiments, I’m on a grand impossible mission. Those make for the most interesting challenges right? And this time I was on a mission to create jupiter or a hot jupiter as a fluid dynamic system. In the past I’ve created a hot jupiter animated texture in After Effects, using the turbulence displacement and the twist effects. But I wanted a system that was self-reliant. And so, as always, I get stuck on the quest for that holy grail and need a jolt to remind me that often the steps along the way are quite interesting.
So I selected one particularly beautiful simulation in Maya, cached/rendered it, and then spent the rest of the evening tweaking in After Effects. It was fun trying to burn out and degrade the footage to make it appear as if it was raw data from a satellite or space telescope. A bit far fetched, I know, to see an extreme zoom of a hot jupiter, but hey I had a vision and had to run with it. So in homage to that fact, I appropriately named it ‘The (Fictitious) Formation of a Hot Jupiter Cloud Band’.
You might be wondering why I cropped the video in this strange boxed style with burnt edges and film grain… Well I was trying to mimic the the style raw data of a satellite. I actually used this jupiter image as a the source for the border and overall inspiration. I’m not sure if its simply a stitch of several images, the sensor blocking out specific light, or such. But I figured it would be a realistic addition instead of the all-too-perfect Maya render.
I’m not going to explain all the details of this Maya simulation, because honestly its just alot of trial and error. Lots of playblasts which need overnight to compute. But see below for the notes which can serve as an introduction for further experimentation.
maya scene – jupiter bands simulation
— The fluid box is wrapping left/right, with the top/bottom closed off.
— There are two volume emitters for the top and bottom half that are keyframed to emit density and velocity at the start frame then turn off quickly.
— There are also two “wind” emitters on the sides to keep the incoming velocity at a fixed rate. They use the replace method and have speed emission with a low rate. The target speed is determined by the directional speed attribute. The rate is the amount that changes the velocity on the fluid to that target speed. So the rate is low in order to keeps things going but not influence the simulation too much. But you can confine the shear region more by increasing the rate.
— There is a very small amount of negative density buoyancy to keep things from mixing too much over time. Increasing the strength of the buoyancy will tend to force the boundary closer to the center, providing the solver quality is high enough or else it will collapse to the bottom. Again tricky business.
— High detail solve and a high grid resolution is used to get more fluid detail. The higher the grid resolution of the fluid, then the more substeps and solver quality that are generally needed. Although substeps also determine how fast the fluid flow is. So its a tricky balance. If there is still too much diffusion, try yet higher grid resolution, substeps, and solver quality. Also a higher resolution, higher solver quality, and more substeps should create more small scale eddies.
— For a little extra detail you can play around with the Density noise, Density tension, Gradient force. Try tiny values between 0.01 to 0.05
I couldn’t have got this far without the help of Duncan Brinsmead, Principal Scientist at Autodesk. I contacted him because I was curious of his approach to this type of simulation and his response was insightful.
The song in the video is In the Hall of the Mountain King by Edvard Grieg. I am amazed at the beautiful diversity of classical music recordings that are public domain licensed on the MusOpen website. What a serendipitous boon finding this!
More about The Art of Astrophysics Competition:
Astrophysicists try to share the mysteries of the Universe around us in a clear and understandable fashion, but we don’t always succeed. It’s a hard challenge – the wonders of the Solar System, the Galaxy, and the ever expanding Cosmos demand more of our imaginations than can be captured by numbers in a table or terms in an equation. However, a work of art can uniquely inspire us to look closely, to dream freely, to understand openly – anything from the smallest curiosity to the biggest discovery.
So, we’re asking members of the MIT community to create works of art that help us visualize our Universe and how we observe it. Whether you’re a photographer or a poet, a crafter or a coder, a musician or a moviemaker, we want you to use your talents and creativity to illuminate the beauty of astrophysical results. Please consider participating in this year’s Art of Astrophysics competition during MIT’s 2014 Independent Activities Period (IAP), sponsored by the MIT Kavli Institute for Astrophysics and Space Research.