U.S. Army Corps of Engineers Bay Model

Post by Gibbon1 » Fri, Jun 05, 2026, 6:18 AM UTC

lorenzohess wrote: post #12

nkrisc wrote: post #5

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?

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.…

Post by emmelaich » Sat, Jun 06, 2026, 7:50 AM UTC

contingencies wrote: post #49

emmelaich wrote: post #11

Earlier quoted context omitted.

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'…

Interesting about the St Ives showground map. Where is it exactly? They have a nice orchid show. Usually it seems to be mostly a bunch of HK dudes playing with RC cars.

Post by [deleted] » Sun, Jun 07, 2026, 1:21 AM UTC

Gibbon1 wrote: post #61

lorenzohess wrote: post #12

Earlier quoted context omitted.

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.…

Triggered a memory. As I understand wind tunnel models often has bits of sand paper placed to generate turbulence at the right spots.

Post by emmelaich » Sun, Jun 07, 2026, 10:13 AM UTC

contingencies wrote: post #64

emmelaich wrote: post #63

Earlier quoted context omitted.

I think it is under heritage order now. I looked for it last time I was there; maybe it's covered up ready for restoration? It's actually a topographical map of the whole Sydney basin. This article has a pic: https://www.neighbourhoodmedia.com.au/post/st-ives-showgroun... [edit: Seems to be where the RC cars race!]

Awesome local history, thanks. I vaguely recall seeing it myself. Another page on that site mentions Eben Gowrie Waterhouse OBE CMG (1881–1977) ... while he is known for Camellia cultivation my research suggests he met with Mussolini and the Japanese government around war time and was a bit of a fascist. They don't mention that bit.