RE: [Algorithms] Simple Air Resistance Simulation for Shells
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From: Tom F. <to...@mu...> - 2002-09-18 12:18:09
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If this is just for things like particle systems (e.g. bits coming off something exploding), then damping the horizontal movement to zero over time, but leaving the vertical as a standard parabola looks perfectly good. Tom Forsyth - purely hypothetical Muckyfoot bloke. This email is the product of your deranged imagination, and does not in any way imply existence of the author. > -----Original Message----- > From: Andrew Jones [mailto:an...@em...] > Sent: 18 September 2002 13:01 > To: Hansen, Daniel; gda...@li... > Subject: Re: [Algorithms] Simple Air Resistance Simulation for Shells > > > You don't have any requirement for the ballistics of these shells > to be absolutely realistic with respect to air resistance, so as you > say a fudged solution is appropriate. If the analytical solution for > velocity-squared air resistance is too slow for you, then think > about a lesser model which will have a qualitatively similar effect, > but has a much simpler analytical solution. At the low end, try > having a constant accelleration in the opposite of the launch > direction > of the projectile. You could calculate the value of this accelleration > using v-squared from the launch velocity of the projectile. As the > projectile alters direction under gravity the 'air resistance' will be > acting in the wrong direction and as it slows the decelleration due > to air resistance will be too large, but why not just run the > 'correct' > reference fricition model against it and see what you get. Compare > the shapes of the ballistic arcs they give you, and see if > you can live > with a lesser version of reality. Of course, a constant accelleration > drag model may be quite poor, but you can try anything you want > provided it has a quick analytical solution. As a final > suggestion, you > may think that the correct analytical solution seems a bit > slow, but is this > really going to matter? If you're coding it up as a reference > you could > just leave it and see if it is ever too slow. Can you post a reference > with an analytical solution to ballistics with v-squared > drag? I'd like > to see one myself. How intensively is this being used? Bear > in mind that > your solver for this may not be a bottleneck anywhere at all if that > particular piece of code is memory bandwidth bound. > > Andrew Jones > Empire Interactive > > > > > Well an analytic solution is what I'm after. I've only seen > very nasty > > long (read slow) equations. I need somethinbg simpler (faster). > > > > -----Original Message----- > > From: Jamie Fowlston [mailto:ja...@qu...] > > Sent: den 18 september 2002 12:44 > > To: gda...@li... > > Subject: RE: [Algorithms] Simple Air Resistance Simulation > for Shells > > > > > > take your pick, really. just have some acceleration opposing your > velocity. > > you can have a factor of your velocity, or the square of > your velocity, or > > whatever. all are variously inaccurate, but may well give > you the effect > > you're after. > > > > then it's simple integration to get your velocity and > position. but you > may > > well not find an analytic solution, if that's what you're > after, as they > > don't always exist. > > > > jamie > > > > > > -----Original Message----- > > From: gda...@li... > > [mailto:gda...@li...]On Behalf Of > > Hansen, Daniel > > Sent: 18 September 2002 09:22 > > To: gda...@li... > > Subject: RE: [Algorithms] Simple Air Resistance Simulation > for Shells > > > > > > Has anyone parametricized the velocity and position taking > air-resistance > > into consideration. I.e > > > > v(t) = v0 + a * t > > p(t) = p0 + (v0 + 0.5 * a * t) * t > > > > ..could be used when there's no air-resistance. > > I'd like something similar with air-resistance. > > I've seen some formulas with alot of nasty exponents in > them, I'm looking > > for a simpler hack. Anyone? > > > > > > -----Original Message----- > > From: Charles Bloom [mailto:cb...@cb...] > > Sent: den 11 september 2002 07:58 > > To: gda...@li... > > Subject: RE: [Algorithms] Simple Air Resistance Simulation > for Shells > > > > > > > > This "midpoint method" is 2nd order Runge-Kutta. See, for example : > > > > http://www.sst.ph.ic.ac.uk/angus/Lectures/compphys/node11.html > > http://csep1.phy.ornl.gov/ode/node7.html > > > > The traditional so-called "Runge-Kutta method" is the 4th > order method. > > Anyway, all silliness, but some of the stuff on the web is > pretty good. > > > > At 12:19 AM 9/11/2002 -0400, ja...@jn... wrote: > > >Thanks to all. Using the midpoint method combined with a > small enough > time > > >step appears to provide a reasonable amount of accuracy > for my use. I'll > > > >keep Runge-Kutta in mind for future use if it proves necessary. > > > > > >Jack > > > > > >-----Original Message----- > > >From: Chris Butcher (BUNGIE) [mailto:cbu...@mi...] > > >Sent: Monday, September 09, 2002 2:52 PM > > >To: Jon Watte; ja...@jn...; > > gda...@li... > > >Subject: RE: [Algorithms] Simple Air Resistance Simulation > for Shells > > > > > > > > >Even using something as simple as the midpoint method (a > second-order > > >integrator) will give much better results for minimal > effort. Runge-Kutta > > >is probably overkill... ? > > > > > >v_intermediate= v - 0.5*k(v^2)t; > > >v_final= v - k(v_intermediate^2)t; > > > > > >-- > > >Chris Butcher > > >Rendering & Simulation Lead > > >Halo 2 | Bungie Studios > > >bu...@bu... > > > > > > > > >-----Original Message----- > > >From: Jon Watte [mailto:hp...@mi...] > > >Sent: Monday, September 09, 2002 12:43 > > >To: ja...@jn...; gda...@li... > > >Subject: RE: [Algorithms] Simple Air Resistance Simulation > for Shells > > > > > > > > >> I'm trying to do a simple ballistics model for shells. > The formula I'm > > >> using is: > > >> > > >> v' = v - k(v^2)t; > > > > > >This is a first-order Euler integrator (I believe). These are known > > >to be unstable at any time step -- as you notice :-) > > > > > >The typical answer when faced with numerical integration problems > > >is to turn to a fourth-order Runge-Kutta integrator. I'm > sure if you > > >plug that into Google, you'll get a massive number of > hits. It might > > >show up on MathWorld, too. > > > > > >Cheers, > > > > > > / h+ > > > > > > > > > > > > > > > >-------------------------------------------------------------------- > > >mail2web - Check your email from the web at > > >http://mail2web.com/ . > > > > > > > > > > > > > > >------------------------------------------------------- > > >In remembrance > > >www.osdn.com/911/ > > >_______________________________________________ > > >GDAlgorithms-list mailing list > > >GDA...@li... > > >https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > > >Archives: > > >http://sourceforge.net/mailarchive/forum.php?forum_ida88 > > > > > ------------------------------------------------------- > > Charles Bloom cb...@cb... http://www.cbloom.com > > > > > > > > ------------------------------------------------------- > > In remembrance > > www.osdn.com/911/ > > _______________________________________________ > > GDAlgorithms-list mailing list > > GDA...@li... > > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > > Archives: > > http://sourceforge.net/mailarchive/forum.php?forum_id=6188 > > > > > > ------------------------------------------------------- > > This SF.NET email is sponsored by: AMD - Your access to the experts > > on Hammer Technology! Open Source & Linux Developers, register now > > for the AMD Developer Symposium. Code: EX8664 > > http://www.developwithamd.com/developerlab > > _______________________________________________ > > GDAlgorithms-list mailing list > > GDA...@li... > > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > > Archives: > > http://sourceforge.net/mailarchive/forum.php?forum_id=6188 > > > > > > > > ------------------------------------------------------- > > This SF.NET email is sponsored by: AMD - Your access to the experts > > on Hammer Technology! Open Source & Linux Developers, register now > > for the AMD Developer Symposium. 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Code: EX8664 > > http://www.developwithamd.com/developerlab > > _______________________________________________ > > GDAlgorithms-list mailing list > > GDA...@li... > > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > > Archives: > > http://sourceforge.net/mailarchive/forum.php?forum_id=6188 > > > > > > > > ------------------------------------------------------- > This SF.NET email is sponsored by: AMD - Your access to the experts > on Hammer Technology! Open Source & Linux Developers, register now > for the AMD Developer Symposium. Code: EX8664 > http://www.developwithamd.com/developerlab > _______________________________________________ > GDAlgorithms-list mailing list > GDA...@li... > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_id=6188 > |