NoCoPilot
Posts : 20356
Join date : 2013-01-16
Age : 70
Location : Seattle
 | | Subject: Wave Propagation Speed Tue Oct 02, 2018 5:48 pm | |
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NoCoPilot
Posts : 20356
Join date : 2013-01-16
Age : 70
Location : Seattle
| | Subject: Re: Wave Propagation Speed Tue Oct 02, 2018 6:04 pm | |
| Okay, this seems backward. - Hyperphysics wrote:
- The wave speed depends upon wavelength and the depth of the water for tsunamis at sea. Characteristic data is shown in the table at right. As they enter shallower water, their wavelength and wave speed diminishes, causing their amplitudes to greatly increase. The speeds in the table follow from the wavespeed relationship for ideal waves, given the wavelength of 282 km at 7000 ft depth. That initial wavelength at depth is presumbly determined by the nature and size of the disturbance that produces the tsunami.
That makes sense. This does not. - Hyperphysics wrote:
- The Unimak tsunami of April 1, 1946 is a famous historical case which for which we have a considerable amount of data. "This tsunami was composed of a succession of crests 2 feet high and 122 miles apart in mid-ocean, moving at better than 400 knots so that the crests arrived at intervals of about 15 minutes.
How can crests be 122 miles apart? Does this mean the waves were 61 miles DEEP as well (circular motions), meaning a tsunami wave causes as much destruction on the ocean floor as the coastline when it lands? |
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NoCoPilot
Posts : 20356
Join date : 2013-01-16
Age : 70
Location : Seattle
| | Subject: Re: Wave Propagation Speed Tue Oct 02, 2018 6:10 pm | |
| The waves a ship throws off can be big or small, depending on the displacement (right?) but it seems, in my experience, that they all move at the same speed, regardless of the speed of the vessel. |
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NoCoPilot
Posts : 20356
Join date : 2013-01-16
Age : 70
Location : Seattle
| | Subject: Re: Wave Propagation Speed Tue Oct 02, 2018 6:17 pm | |
| - Warbird wrote:
- It is simple really, but I don't know the exact math. The peak to peak distance of the waves in the wake tells the speed. A boat hull speed is limited by the eqation (sqare root hull x 1.3?) which really defines the distance between the bow wave and the stern wave. I am pretty sure that this is a physical constant of wave action in water. So, waves 25 feet crest to crest are traveling approx 6.5kts. Estimate the crest to crest distance of waves you observe and do the math backwards.
- Estarzinger wrote:
- actually the physics formula is wave speed (m/s) = (g x wave length/ 2 x pi) ^ .5
Where g is the gravity constant 9.8066 m/s/s. |
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richard09
Posts : 4263
Join date : 2013-01-16
| | Subject: Re: Wave Propagation Speed Wed Oct 03, 2018 6:23 am | |
| - NoCoPilot wrote:
- How can crests be 122 miles apart? Does this mean the waves were 61 miles DEEP as well (circular motions), meaning a tsunami wave causes as much destruction on the ocean floor as the coastline when it lands?
No. A tsunami is caused by water displacement - I don't think it involves circular motion. Very long wavelength is the characteristic of these waves that does the damage. As they approach the shore and the depth decreases, the speed slows down and the water "piles up" (wave shoaling). So a wave that is only 1 foot high but travelling at 400-500 mph in mid-ocean hits the shore going much slower but much higher, and since the wavelength is so long (and the wave doesn't usually break), you get the result you see on the videos. It looks as if the sea has just decided to move inland, because the water just keeps coming - it's all part of the one very long wave.. |
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NoCoPilot
Posts : 20356
Join date : 2013-01-16
Age : 70
Location : Seattle
| | Subject: Re: Wave Propagation Speed Fri Oct 19, 2018 7:30 pm | |
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