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82 points by tosh 2 days ago | 17 comments

If you don't know Tom Scott, he has done a great video 4mn vide on the model where you can see it in action: https://www.youtube.com/watch?v=i70wkxmumAw

MontagFTB 51 minutes ago

Yes, that’s a great video. The Mythbusters used the same model to understand Bay Area current flows during their Alcatraz escape attempt episode.

rbanffy 11 minutes ago

Someone should do a follow up episode with a person dressed up as Godzilla.

mattlong 2 hours ago

I highly recommend a visit. It’s only a beautiful ferry ride and nice walk along the waterfront away from San Francisco. A refreshingly retro and analog experience.

carderne 2 hours ago

John McPhee talks about a similar model for the Mississippi River in “The Control of Nature” Well worth a read. Fun stories about Hawaii and Los Angeles too, iirc.

WillAdams 4 hours ago

It's a shame that there isn't a series of articles on such models --- saw the Chesapeake Bay model (mentioned in a footnote) on a field trip when I was much younger (and it was still in active use for research I believe, yes, as my kids constantly tell me, I'm old).

Simulation used to be essentially impossible, something one dreamed of, or had to pay for time on a Cray or similar supercomputer/cluster.

Apparently, the Chesapeake Bay model was built just as that was becoming feasible:

https://easternshorebrent.com/2017/11/30/doomed-progress-the...

and has since been dismantled and a business park built on the site.

Robdel12 2 hours ago

This is neat to see. US army crops of engineers is a negative “word” to me after growing up in FL and they destroyed so many ecosystems. And the entire Everglades. They’re still at it now. My family has basically spent the past 30 years fighting a ware they put in on our natural creek. It killed the creek, it shrunk the flow to the size of the culvert.

So, It’s neat to see something competent! Imagine if they modeled what cutting off the natural draining to the Everglades would do :p

eezing 31 minutes ago

This is a hidden gem in the Bay Area. Go check it out if you live near by.

nkrisc 4 hours ago

The distortion is interesting and something I didn’t realize the model included. I assume that it’s necessary because the effects of surface tension and the viscosity of water (and other effects?) change its behavior at this scale relative to the features of the model?

lorenzohess 2 hours ago

If I recall correctly, at an undistorted scale, the water would be so shallow that surface tension and viscosity would dominate, so the depths are exaggerated to keep the flow realistic.

More specifically, tidal flow obeys Froude similarity, not Reynolds. Matching the model's Froude number to the real Bay's requires enough depth for gravity waves and tides to scale correctly, which the vertical exaggeration provides.

But the distortion makes the flow too efficient, so copper strips are added throughout to achieve the right frictional resistance.

WillAdams 3 hours ago

Yes. Another technique was to use alcohol rather than water since it has lower surface tension, but that was only workable for smaller models (which were usually enclosed).

nkrisc 3 hours ago

I think a model this size full of alcohol would also be quite hazardous for several reasons.

btrettel 60 minutes ago

Even if it wasn't a large size, it likely wouldn't be great. During my PhD on sprays, I did some (unpublished) experiments using isopropyl alcohol to reduce the surface tension. The nozzles I used were around 1 mm in diameter as I recall. I did not anticipate that the room would fill up with isopropyl alcohol vapor and (probably) tiny droplets. I wore a mask and maybe left the room while each trial was running. Breathing that likely wasn't great for my lungs.

redm 4 hours ago

These are the kinds of interesting engineering challenges that were solved with human ingenuity and grit; I wish we were talking more about them to our youth to inspire imagination about what's possible.

contingencies 4 hours ago

The fellow who lived next door to me told me of a similar model system used to model Sydney Harbour which he worked on in the 1970s. IIRC it was instrumented with electronics and linked to a VAX or similar early machine.

emmelaich 2 hours ago

The Aus Navy had a computer simulation of Sydney Harbour, dating from the 70s or maybe 80s. One particular feature of the system was a disk drive about 1m in diameter with about 12 heads. Cost a bomb, but I guess it was worth it.

When I saw a demo, they had an easter egg of a Loch-Ness type monster in it.

There's also a topographical map of the harbour at St Ives showground but it's purely non-hydrographical. But it's almost disappeared now through neglect.

obvioustourist 2 hours ago

[dead]

supertroop 2 hours ago

Don’t show something good the government has done or the POTUS will cancel it!!!