Real-Time Physics Simulation Forum

Re: My explicit euler cloth code

2012-04-07T01:23:30+00:00

Thanks for sharing!

Statistics: Posted by youthlion — Sat Apr 07, 2012 1:23 am

Re: My explicit euler cloth code

2011-09-14T05:50:31+00:00

I have updated the codes. Initially, my semi-implicit integration (was doing IMEX) rather than the actual semi implicit integration. I have made these changes. Now the semi-implicit and IMEX are correctly contained in their own projects. So currently, the OpenCloth project (http://code.google.com/p/opencloth) contains the following,

Explicit Euler
Explicit Euler with Wind
Implicit (Baraff & Witkins Model)
Implicit Euler
IMEX
Position based Dynamics
Semi-Implicit
Verlet
Verlet CUDA/GLSL/OpenCL/CPU

Statistics: Posted by mobeen — Wed Sep 14, 2011 5:50 am

Re: My explicit euler cloth code

2011-08-25T07:18:47+00:00

Where can we find your Implicit-Explicit (IMEX) integration version?

The semi-implicit integration is doing this and it is based on the GI99 paper linked by Sagitta in the last reply. If this is not IMEX could u tell me the paper describing it?

Statistics: Posted by mobeen — Thu Aug 25, 2011 7:18 am

Re: My explicit euler cloth code

2011-08-24T22:19:30+00:00

Hi Mobeen,

Your OpenCloth is a fantastic job.

Where can we find your Implicit-Explicit (IMEX) integration version?
Thanks,
Erwin

Statistics: Posted by Erwin Coumans — Wed Aug 24, 2011 10:19 pm

Re: My explicit euler cloth code

2011-08-23T12:05:45+00:00

Hi Saggita,
Thanks for your input. I have already implemented the linked (IMEX) approach. Hope to have more feedback from you.

Thanks,
Mobeen

Statistics: Posted by mobeen — Tue Aug 23, 2011 12:05 pm

Re: My explicit euler cloth code

2011-08-16T19:04:23+00:00

Just my 2 cents about Explicit method..

1. The force between two points are not constant even during the discrete time step. We already know that the force is changing as a result of moving points. The good thing is that we can compute how much the force will change during the time step. Unfortunately it is a function of point velocity and we don't know this until we integrate! So those two information (force change rate and point velocities) are strongly coupled together. That is why we need to solve a linear equation in implicit method.

2. If one point is moving towards the other point, we know that the force change rate is a vector with the same direction of the two points. However, if the point is moving perpendicular to the line of two points, there is still change of force. In this case, the force change rate is dependent on the point velocity direction but not the same direction. So the force change rate is always vector and the relationship with point introduces some 3x3 matrix which is Jacobian matrix. For real-time simulation, we can ignore the perpendicular case, then the Jocobian matrix is no longer needed because the force change rate will be always the same direction as the line of two points. This makes it possible to implement implicit integration without solving linear equation. Below paper explains this concept.

http://www.multires.caltech.edu/pubs/GI99.pdf

Statistics: Posted by saggita — Tue Aug 16, 2011 7:04 pm

Re: My explicit euler cloth code

2011-07-28T01:51:44+00:00

WOW. Thanks Erwin for this. I would surely have a look through those resources.

Thanks,
Mobeen

Statistics: Posted by mobeen — Thu Jul 28, 2011 1:51 am

Re: My explicit euler cloth code

2011-07-27T21:21:55+00:00

Thanks for sharing these cloth implementations, it will be helpful.

For FEM, you can also buy the 'Game Physics Pearls' book, and check out chapter 10.

I recently extracted the corotational linear fem implementation from OpenTissue (removed BOOST and only use the necessary code) here:
https://github.com/erwincoumans/experiments (there is a Download button) and check out the dynamics/corotational_fem folder.
You can build it under Windows using Visual Studio 2008/2010 by clicking on the build/msvc2008.bat batchfile and open the new folder.

I plan to add some collision detection to it. You could use it to simulate cloth as well (thick cloth of a single layer of tetrahedra)
Cheers,
Erwin

Statistics: Posted by Erwin Coumans — Wed Jul 27, 2011 9:21 pm

Re: My explicit euler cloth code

2011-07-27T15:12:21+00:00

Can you elaborate a bit more about the KahanSum and where you added it to the PDB algorithm - maybe a simple example? I will look at the code after this, but it might be nice to discuss this in isolation. I looked at Wikipedia and it seems to deal with Cancelation problems. Good stuff DevO

Statistics: Posted by Dirk Gregorius — Wed Jul 27, 2011 3:12 pm

Re: My explicit euler cloth code

2011-07-27T04:15:52+00:00

WOW, using KahanSum the behaviour is more accurate as compared to not using the KahanSum.
DevO I am grateful to you for pointing this out. I didnt know about this and the errors numerical inprecision generates. Thanks man.

Statistics: Posted by mobeen — Wed Jul 27, 2011 4:15 am