## Flutter and Tumble: The Physics of Falling Paper

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abaraba
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### Flutter and Tumble: The Physics of Falling Paper

hi,

isn't it amazing that such everyday thing is still a mystery for today's physics, but better than trying to explain let me just point this interesting article:
http://www.aip.org/png/html/paper.htm

http://www.weizmann.ac.il/complex/EMose ... index.html

- is anyone working on anything related to this?
- is this something that could be part of Bullet Physics library?

"How paper falls to the ground is a process impossible to describe exactly with the laws of physics"
- are you kidding me?! ...i refuse that!

flutter/tumble motion actually looks pretty regular to me,
why in a world would it be so difficult to approximate and somehow simplify this? if you asked me a few hours ago i would say - that's easy, and go on to assume its similar to calculating a lift with *simplified formula* for airfoil, where you calculate lifting force by taking into account horizontal speed, mass, air density, angle and surface area of the wing... pretty simple, only in the case of the falling paper there would also be some *rotational motion* as a result beside 'slide' (lift) ...then feed new angle with the rest of the changes back to calculate new frame and so on... or so it would seem

really, how hard could it be?
...to plug in some coefficients and 'magic numbers' to simulate this, and so my last question is: how accurate or how visually convincing simulation of this should be in order to be considered to be included in Bullet physics?

cheers
Last edited by abaraba on Fri Jun 27, 2008 12:45 pm, edited 6 times in total.

DannyChapman
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### Re: Flutter and Tumble: The Physics of Falling Paper

One of the soft body demos in Bullet already simulates this, and it's pretty cool.

abaraba
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### Re: Flutter and Tumble: The Physics of Falling Paper

sheesh, i think i went on to read probably 50% of this forum without getting a hint this, or anything like it was implemented in Bullet

anyhow, that's great! ...cloth demo?
- can you point out some links that say how it all works?
- how close would that be to simulate real parachute if soft body was that shape?
- could that simulate *gliding* of a 'paper plane' shaped mesh?

does anyone know any demos or any other reference that talk about simulating kite, paper plane, hang glider or something... maybe fish swimming mechanic or propeller/blades physics, wind tunnel simulator... anything, but where calculation is based on a mesh polygon data?

for example,
there is NASA kite simulator, but im not sure if that would really work in 'free fall' mode, also id preffer much more simple approximation... on the other hand there are simulators like X-plane that calculate some physics depending on aircraft triangle mesh, or maybe not? ...alternatively, for more pressure/density related approach to fluid dynamic - "Real-Time Fluid Dynamics for Games" i hear is a good start:
http://www.dgp.toronto.edu/people/stam/ ... h/pub.html

apparently, there is complete C++/OpenGL implementation included in the PDF, but would leaf flutter and tumble in such system or is that only good to render a smoke?

any thoughts, references or suggestions on the subject of *geometry based free fall physics model* are most welcome

thank you

Nathanael
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Joined: Mon Nov 13, 2006 1:44 am

### Re: Flutter and Tumble: The Physics of Falling Paper

abaraba wrote:can you point out some links that say how it all works?
Just applying (over)simplified lift and drag on a deformable model do the tricks, of course in the real world the paper is not that deformable, and its motion is mainly driven by the turbulence in the fluid, but it work well enough (run the demo).
abaraba wrote:how close would that be to simulate real parachute if soft body was that shape?
For that we need to find another trick, because parachutes trap air, so that the pressure build up inside, we can't do that with the current lift/drag approximation.

May be a limited fluid simulation in the body local frame could do the tricks, physic is the same if the body is moving in the fluid, or if fluid is moving around the body (Galilean invariance), so a low-res grid based solver (ie: http://www.dgp.toronto.edu/people/stam/ ... /GDC03.pdf) may be enough.
Here's a paper about it: http://jcohen.name/papers/Shah_Extended_2004.pdf
abaraba wrote:could that simulate *gliding* of a 'paper plane' shaped mesh?
I think so, but its going to be a pain to find the right parameters and shape (like in reality ).

Nathanael.

abaraba
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### Re: Flutter and Tumble: The Physics of Falling Paper

thanks,
that sounds promising!

...meanwhile, i found this:
http://aa.nps.edu/~jones/research/gui/v ... nd_tunnel/

so, apparently VIRTUAL WIND TUNELS exist, they even seem to work:- "flow may be visualized by releasing discreet particles.." and if you look at the 3rd picture you can actually see FLUTTERING of that airfoil ...all with vorticity and stuff just like in the 'falling paper' photos..

let me share this idea - "Darwinism simulator"
- simulation of the virtual world where inhabitants are composed of mechanical constructs that obey physical laws giving the creatures means to move and accomplish ultimate goals in their life - Eat, Multiply and Die

and the twist is,
with each new generation, species will evolve or try to change eg. offspring would be born with slightly different field of vision or modification to other 'sensors' and would slightly change in size or shape, maybe grow new limbs or get rid of some, maybe grow a few more eyes or ears around the body, maybe just change limb constraints or grow new or stronger motor for some limbs... how will that mutation affect its movement, will it survive, will it manage to pass its genes?

- world,
composed of different mediums with different physical properties eg. land, snow, ice, mud, salt sea, lake, river, atmosphere, ocean bottom...

- inhabitants,
"THE FIRST ONES", would be collection of "mechanical constructs" eg. limbs+constraints+motors+sensors that can mimic motion of earth creatures or whatever other design that can get creature move in some of the mediums, possibly *towards* the "FOOD" and "MATE" signal received from its sensor(s) and as fast as possible *away* from "DANGER".

- graphics,
i imagine this in simple flat-shaded graphics, each polygon would be exactly that in "Physics/Bullet" world and creatures would be made of simple polygons probably resembling stick figures or skeletons

- AI,
simple - chase food, chase mate, run from danger... its basically a *racing* type of game for them, where faster design not only wins the race, but means more food, more sex and a longer life

my main goal is to monitor 'evolution of motion mechanics', but i guess you could include attack/defense evolvable properties/limbs as well.. then have the creatures fight on the internet and let people place wagers

clearly Bullet can handle 90% of this stuff, but with some nice fluid dynamics, there could be swimming, flying, floating, gliding, drifting, Flutter&Tumble... and possibly other interesting creatures that could evolve into even more amazing creatures... actually, i would change the whole virtual planet with legged "stick figures" for one dirty pond where fins matter more and fluid dynamics could catalyze development of some very interesting ways for creatures to propel themselves...

how's that for the next generation game?
say, you can take control of any of the creature or speed up evolution, change temperature, gravity, density... and see how that affects the world, design your own creatures, maybe a fish with a propeller or really huge turtle-frog kind of animal, maybe a bird-shark ...how about human-spider?

- who would win: bear-snake or cat-whale? ...wanna bet?
- would you buy this game? is there anything like it?

cheers

p.s.
spider-man there gave me an idea,
similar to fish with a propeller animals could have "grappling hooks" to swing around, or even "extending limbs" like frog extends sticky tongue... or WHATEVER, the idea is to have really, really fantastic world, but based on real physics, so that in effect if you construct any of the creatures it should move similarly in a real life... maybe i should call them "robots" better... they are, after all, kind of - TRANSFORMERS - type of thing, aren't they? so, Toys would probably sell well with the game too ...and then the movie, there would be war, battle for survival, exotic places, strange creatures, lots of food and mating afterwards... maybe even a love story, true summer blockbuster!

feel free to share any of your crazy ideas and, even better, some practical examples how to simulate all that

abaraba
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### Re: Flutter and Tumble: The Physics of Falling Paper

"3D Grid Based Fluid Simulation for Hewlett-Packard Scalabe Visualization Array"
Virtual Wind Tunnel,
unfortunately these shader dont work on my hardware, but there it is including Linux & Windows source code and binaries: http://amon.ik.bme.hu/gridfluid/

... and there is this one:
http://web.engr.oregonstate.edu/~moorch ... FluidTest/

--------------------------------------
"Darwinism simulator" similar games:

- Spore
http://en.wikipedia.org/wiki/Spore_(computer_game)

- Cubivore
http://en.wikipedia.org/wiki/Cubivore

abaraba
Posts: 56
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### Re: Flutter and Tumble: The Physics of Falling Paper

oh, man!!!

.. it exists, they've made it... already

not quite a game, but still pretty close to what i imagined:

- Simulation of Evolution by Natural Selection