Sunday, August 21, 2011

Staggered mesh

Someone out there has encountered the zigzag garbage a numerical solution spits out when there is pressure-velocity decoupling. You can try to refine the mesh, smooth forcing functions or adjust the Peclet number, but in the end you are undone by a fundamental flaw in the advection terms and the central difference approximation of a first derivative. The problem is advection requires a first derivative, and the central difference may be very weakly coupled to its own node. The result is essentially two solutions, one for the odd nodes, and one for the even. This is why it is often called odd-even decoupling. But why not turn this apparent weakness into an advantage? Cut your degrees of freedom in half, and just use a staggered mesh. Solve for enthalpy (energy) at the odd  nodes, solve for momentum (pressure) at the even nodes, and solve both in the half nodes at the inlet and exit, where forward or backward difference approximations are used. Use linear averages everywhere else. This has worked very well for me. I also solve for all of the mass flow everywhere at once since it is explicit on boundary conditions and the time rate of change of mass in the system (i.e. continuity or mass balance). Given the enthalpy and pressure at every node, I can explicitly calculate the density using the IAPWS-IF97 steam tables, and given the mass flux from continuity, I can now calculate the velocity. No more zig-zags, I've reduced my degrees of freedom nearly in half, and I didn't have to add artificial diffusion or any other fudge factors. Yay!

Apple drama

I can't wait for Google to start making their own hardware. Or for Android machines to start taking over a larger market share. I get Android. I don't get Apple. For all the hype, so far not a single thing has worked hitch free. Ah, but the gadgets are sexy. The macbookpro is so sleek and cool, the iPad so convenient.

Sunday, August 14, 2011


I must be fun-challenged, because while everyone else is lapping up carny food and gawking over watercolored bears and jewelry made from scrap flatware, I'm completely miserable. I'm irritated that I've spent gobs of money on crap. To me the whole thing is a sham. The idea of carny food always sounds delicious, but the reality is usually grossly-overpriced over-glorified gut-busting greasy garbage. The bands are fine, I love music, so the free fairs have at least got that, but I haven't been wowed enough by carny music to justify paying. And pay dear. Movies at the Parkway (RIP) were cheaper! I guess the only thing I like is the people watching. And as a kid I remember liking the rides. Maybe I've got to just suck it up and pretend to have fun for the kids. But honestly I'd rather be outside, walking, not choking my arteries, relaxing, enjoying nature for free. Ah, that sounds nice.

Friday, August 12, 2011

new os

I'm sure linux or android already do this, but I'm tired of folders and directories. Isn't that idea a bit antiquated? I was thinking that in this day of objects and tags, can't files just have a tag attribute that can be set so that you can sort and cross reference your files anyway you want? to this user this could be transparent, so that it looks just like folders except it's so much better. Then you wouldn't have all of there ridiculous pathnames, everything would be in root/files.

corporate batman belt

I was thinking with 3G (and 4G lite) access, it wouldn't be too hard to develop a device, actually a system, that would be a corporate office away from the office. This device let's you receive and make calls of course, but also lets you access your laptop if you leave it in the office, even control the desktop, access the network. But most importantly, allows complete customization, for example, would allow an app to be installed that automatically detect when it was going into roaming and shut down all data transfer, and switch to something like Skype for calls.

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