Computationally Intractable (or maybe not?)

26 03 2011

In Bussard’s 2006 Google tech talk  Should Google Go Nuclear? he talks about computer modeling of his reactor. He concludes that computer modeling is unfeasible. Beyond a handful of particles in the model, the computation slows down to the point of useless.

Now there may be a new approach to this type of problem.

Professor Charbel Farhat, chair of the Aeronautics and Astronautics Department at Stanford’s School of Engineering, and David Amsallem, an engineering research associate who worked on his PhD thesis with Farhat, have been studying and trying to solve aeroelastic flutter for years. Computers help, but only to a point.

Essentially it’s a story of the unfeasible made feasible by mathematical inovation:

How have Farhat and Amsallem succeeded where others have come up short? The answer sounds suitably complex: interpolation on manifolds. What it means, in essence, is approximating unknowns based on known information. The two engineers devised a system of mathematical approximations that break down complex, computationally demanding equations into smaller, more manageable parts. In mathematics, this is known as “reducing.” Reducing allows them to make some very educated guesses, very quickly.

I wonder if this technique could be applied to computer modeling of the Bussard reactor?

I suppose in our case we would be looking FOR the flutter, not trying to avoid it.



Another good article:

New Job

20 03 2011

I’m almost out of money… so back to work.

I start a new development contract in SOHO Monday.

I expect it will be quiet on the blog for a few weeks.

Once I’m in the new rhythm, I hope to make it to the lab a few times a week.


8 03 2011

I am very excited to learn of an effort to build an open source EBM 3D metal printer :

This technology is currently offered commercially by Arcam AB.

EBM fabrication is rather amazing. It can make fully melted metal parts from STL files.

I am planning to build the superconducting polywell in titanium using Arcam’s process. It would be amazing to eventually have a Makerbot for metal.

Additionally the EBM device itself has much in common with a fusion reactor. Both use high vacuum, electron beams, high voltage.

I’d be happy to help this project with any vacuum, high voltage questions.

Vacuum Fixed!

4 03 2011

All photos.

I had a real leak, and possibly a virtual leak.

The leak:

See the break in the groove? My knife edge has a small ding.

But it’s no problem as long as you tighten the conflat enough.

There are 20 bolts on these conflats, it’s easy to accidentally skip one or more.

To improve the process I made this paper insert:

Pretty proud of this one actually.

In addition to an actual leak, I may have had a virtual leak, which is just air trapped behind a screw. To eliminate a virtual leak, the bolts inside the vacuum need a channel to let trapped air escape:

I’ll cut those channels on the bolts today.

As a control I put the coil former and supports in the chamber unassembled:

It’s looking good!!

And dropping.


Outgassing Check

2 03 2011

All photos.

Last week I mentioned I would start taking smaller steps. Turns out to be a good strategy.

My small step is investigating the coil former’s outgassing.

I put the coil former into the chamber:

At first I had to troubleshoot a gross leak. By listening I traced the problem to the connection from pump to chamber:

The pump had shifted under the chamber and unseated the gasket:

I fixed this leak with a fresh gasket. Now I don’t hear any leaks.

The turbo pump spins up almost all the way:

Either I have a small quiet leak or the coil formers are outgassing like crazy.

I’m going to let the pump run overnight. If outgassing is the culprit it will abate with time.

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