Some sad individual has senselessly plagarised a review from the excellent Dans Data. If you have any spare bile or venom to donate, please send it in this direction. Why do I mention this? Well, I'm a longtime reader of Dan, and the comments are curtly summarised by Anonymous:
"Ahhhh - the eloquence of all these comments is enough to bring a tear to mine eye...and you know what? I agree with every word. Scumbag..."
Five minutes with google seems to indicate not a single thing on this crappy blog is original or attributed content, and is merely a large collection of (poorly done) cut-and-paste jobs. The entire site clearly is in violation of its advertisers content policy:
"Kontera does not work with web publishers that promote, contain or link directly to the following content.. ..Material that violates intellectual property rights of third parties."
Remember folks, the internet is full of stupid people.
6 August 2006
26 July 2006
Linear vs. Nonlinear FEM in biomechanics
The situation goes like this: in a biomechanical FE (Finite Element) simulation, the actual mechanical parameters of tissue are difficult to accurately determine. You can't just go poking tissue inside a live human being to get parameters because, well, they're alive. Dead tissue in cadavers responds differently, and the use of data from animal tissue is debatable - as well as having its own ethical problems.
So, given the issue of modeling tissue using near-real- or real-time FEM, is it worth using a more accurate mechanical model - say, nonlinear elasticity - over a simpler model, such as linear elasticity, which is easier to simulate?
Unless the deformations are really small, my own take on it is to use nonlinear FE (such as Neohookean elasticity) if at all possible. This is not because of precision, but because of better behavior under large strains. Let's look at an example.
Here I've meshed the infamous Stanford bunny using my own octree-based meshing technique into about 22,000 tetrahedra. I've fixed anchor points at the top of the left ear and near the lower rear of the bunny. Gravity is applied to the object, and we observe what happens as the FE-solver (in this case, a modified version of salmon by Nienhuys) converges to a rest-state (which is never completely reached, for the sake of brevity). The visualisation is done in VTK and computed on a 3.2Ghz Intel PC running kubuntu.
Linear Elasticity:
Initially, the solution is great, but eventually, the volume blows up. Not much practical use.
Neohookean (nonlinear) Elasticity:
Much better. The right ear makes a concerted effort to flop about a bit, and we see the mass of the object roughly rotating around the axis formed by the left ear and the anchor points in the bunny's rear end.
So, given the issue of modeling tissue using near-real- or real-time FEM, is it worth using a more accurate mechanical model - say, nonlinear elasticity - over a simpler model, such as linear elasticity, which is easier to simulate?
Unless the deformations are really small, my own take on it is to use nonlinear FE (such as Neohookean elasticity) if at all possible. This is not because of precision, but because of better behavior under large strains. Let's look at an example.
Here I've meshed the infamous Stanford bunny using my own octree-based meshing technique into about 22,000 tetrahedra. I've fixed anchor points at the top of the left ear and near the lower rear of the bunny. Gravity is applied to the object, and we observe what happens as the FE-solver (in this case, a modified version of salmon by Nienhuys) converges to a rest-state (which is never completely reached, for the sake of brevity). The visualisation is done in VTK and computed on a 3.2Ghz Intel PC running kubuntu.
Linear Elasticity:
Initially, the solution is great, but eventually, the volume blows up. Not much practical use.
Neohookean (nonlinear) Elasticity:
Much better. The right ear makes a concerted effort to flop about a bit, and we see the mass of the object roughly rotating around the axis formed by the left ear and the anchor points in the bunny's rear end.
Oh noes! The press!
It certainly looks like the papercraft work has taken a life of its own, and word of it has moved out of the blog domain and reached real publications (*gasp*)!
There's an article about the papercraft (and me!) on the excellent, Melbourne-based online Jumpbutton magazine.
There's also another article (mirrored on flickr) with a copy of page 24 from the August 2006 edition of Computer Gaming World :)
w00t :)
There's an article about the papercraft (and me!) on the excellent, Melbourne-based online Jumpbutton magazine.
There's also another article (mirrored on flickr) with a copy of page 24 from the August 2006 edition of Computer Gaming World :)
w00t :)
17 July 2006
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