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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.

by bumby2 hours ago|

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Have you ever watched a movie with a fire or explosion just didn't look right because it was a scale replica? At a subconscious level, you may have picked up on how the dynamics of the smoke or debris didn't fit right with the scale. It's because the fluids in the model lacked "similitude" at the adjusted scale.

When building scaled models, adjustments have to be made to create that similitude, usually done by comparing some dimensionless number at the real scale and model scale. If you're using water, maybe you can't adjust the viscosity, so you may you have to adjust the velocity to get the same dimensionless number. Everything doesn't just scale linearly; you tweak the variables to achieve the dimensionless value so the whole system dynamics remain faithful.

E.g.,

https://en.wikipedia.org/wiki/Froude_number

https://en.wikipedia.org/wiki/Rayleigh_number

by WillAdams6 hours ago|

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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).

by nkrisc6 hours ago|

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

by btrettel5 hours ago|

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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 During my PhD on sprays, I did some (unpublished) experiments using isopropyl alcohol to reduce the surface tension.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.

by lstodd2 hours ago|

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You just get drunk from the vapour way faster than it can have a measurable impact on the lungs.

(you can actually drink it if it's reasonably pure. it's even less toxic than ethanol, but the hangover is terrible)