Posted on 07/25/2004 12:36:29 AM PDT by Yosemitest
Seiching is the formation of standing waves in water body, due to wave formation and subsequent reflections from the ends. These waves may be incited by earthquake motions (similar to the motions caused by shaking a glass of water), impulsive winds over the surface, or due to wave motions entering the basin. The various modes of seiching correspond to the natural frequency reponse of the water body.
In this example, a rectangular basin (of infinite width) with given length and depth is seiching in accordance with the mode that you specified (greater than zero). The period of seiching (T) is determined by finding the correct length wave that will fit in the basin for the given water depth (based on linear water wave theory). The percent refers to the difference between the seiching period predicted by the dispersion relationship versus that usually used: shallow water theory.
(For shallow water theory, the seiching period is given by twice the basin length (l) divided by the modal number (n) and the speed of a shallow water wave (which depends on the water depth h)
As an example, try a basin of length 100 m, a depth of 20 m, and a mode number of two. Note that the water surface motion is out of phase with the velocities (shown with white lines). Also notice that the water motions do not have the elliptical orbits as progressive waves do (as in the Linear Kinematics applet). Under a node (no displacement of the water surface), the velocity is always horizontal, while under an antinode (max. displacement), the velocity is vertical. Further, this example (with quite a large water depth) gives quite a discrepancy between the linear theory result of the applet and the shallow water theory.
In the figure, you will notice that the number of modes corresponds to the number of nodal points (points of no motion of the water surface).
There are an infinite number of seiching modes possible, from the lowest (mode 1) to infinity. The period of oscillation decreases with mode number. Realistically, the lower modes probably occur in nature, as frictional damping affects the higher modes preferentially (higher frequency).
The seiching calculations for linear theory are given in Chapter 4 and 5 of Dean and Dalrymple, Water Wave Mechanics for Engineers and Scientists, World Scientific Press.)
But you would have to spell it:-Remonstorate.
wow
"Reporters, surfers, and normal people look and a wave and think of the height as being from the top to the bottom -- makes sense but that can turn a '29-metre' wave into a '58-metre' wave."
Missleading at it's best!
I brought nback a 38' sailboat from the Istmus of Catalina to San Pedro in a whole gale that had been blowing for 3 days and the trough to peak of the waves was 50-70' which in a storm isn't that unusual in the Catalina channel.
It was a pretty exciting trip, the 25 miles was covered in an hour and 46 minutes, almost power boat speed.
Shackleton survived such a massive wave on his small boat trip to S. Georgia. Damage from a 1400 foot splash, after a landslide in Alaska, was reported on the Mega-Tsunami TV show on (?) Discovery channel.
bump
"King" waves we call them... known to pluck fishermen off high cliffs on the west coast of Australia. They even have signs posted..."Beware of King Waves".
If Bush had supported the Kyoto Treaty, these waves would never happen. /sarcasm
If I owned one of those two ships I would just beach it and try to sell it for scrap. Every week? That has to be beyond annoying.
http://www.freerepublic.com/focus/f-news/1177972/posts
goon = gonna
How can they beware of them? By the time they see one coming, it's probably too late to run very far.
right- beware of standing too near the edge of the cliffs... just in case ya know!
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Note: this topic is from 7/22/2004.
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