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Water Wavemaker calculation need. fluid dynamics help.?

by opmeetsprep
Tags: calculation, dynamics, fluid, water, wavemaker
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opmeetsprep
#1
Mar6-13, 10:31 AM
P: 2
Hi guys,

I haven't taken any physics classes or any of the sort to figure out the problem that Im faced with.

basically what where creating is a wave maker like this

http://www.youtube.com/watch?v=_Lpvv-J1y0k
(sorry this is the only video i found)

basically the "float" that you see is shaped like a quarter of a circle. It goes down on the water slowly and lift back up relative fast. Thus creating a wave.

After analyzing it with my little background. It looks as if the wave is created after the "float" is removed-through the force the water gains as it tries to fill up the displaced area of the float. Once it does it bounces off to the other side since one side is a solid wall.
^^ does that make sense?

Is that how the wave is formed?


The problem:
The issues I'm having is calculating the size of that float that is submerged under the water.

I figured it will be dependent on how big the wave will be right?

if this is correct how does the wave size it create (above the regular water level) related to the "float" size?

The only thing I could think of is buoyancy but came up unsuccessful on researching how that can be used.


if anyone can give me a topic to research that will help that would be great.
or how to proceed.

thanks
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mfb
#2
Mar6-13, 10:43 AM
Mentor
P: 11,589
I don't see how the waves are made. In general, those systems need numerical simulations, there is no general, easy relation between your movable object and the wave amplitude. All motion in the water will contribute to the shape of the wave.
olivermsun
#3
Mar6-13, 12:12 PM
P: 617
Quote Quote by opmeetsprep View Post
After analyzing it with my little background. It looks as if the wave is created after the "float" is removed-through the force the water gains as it tries to fill up the displaced area of the float. Once it does it bounces off to the other side since one side is a solid wall.
^^ does that make sense?

Is that how the wave is formed?
Yes.


The issues I'm having is calculating the size of that float that is submerged under the water.

I figured it will be dependent on how big the wave will be right?

if this is correct how does the wave size it create (above the regular water level) related to the "float" size?
What you could imagine is that the float creates a disturbance which is a "depression" that propagates in both directions when the float is suddenly removed. One half of the wave reflects off the back wall, as you noticed, with a phase reversal (the "depression" becomes an "elevation"). After the wave propagated away from the wave maker for a bit, you'd probably notice the surface wave dispersing, but the shape of the float was probably chosen to reduce this effect (relative to a squared-cross-section float, for instance)..

opmeetsprep
#4
Mar7-13, 12:35 PM
P: 2
Water Wavemaker calculation need. fluid dynamics help.?

Quote Quote by olivermsun View Post
Yes.



What you could imagine is that the float creates a disturbance which is a "depression" that propagates in both directions when the float is suddenly removed. One half of the wave reflects off the back wall, as you noticed, with a phase reversal (the "depression" becomes an "elevation"). After the wave propagated away from the wave maker for a bit, you'd probably notice the surface wave dispersing, but the shape of the float was probably chosen to reduce this effect (relative to a squared-cross-section float, for instance)..
Is there any way to calculate how the water acts in that scenario?

I saw mfb's post and while there may not be an easy way to calculate. I want to have atleast something to have calculated support the size selection. even if its very rough calculation its better than nothing.

perhaps calculate the buoyancy and calculate that overall energy it creates and somehow tie that potential speed/force of the wave created?
I do not fully understand these concept and still reading up on them so sorry if that sounds idiotic.
olivermsun
#5
Mar7-13, 12:41 PM
P: 617
Buoyancy is exactly what I am thinking. The entire energy of the wave (before it starts moving) is contained in the potential energy associated with the displaced water. If the wave propagates away symmetrically, then a bump with half the energy propagates into the tank right away, and half reflects of the wall and comes back. It seems like it would be at least close. (I would imagine that the designer chose the wave maker to have at least approximately the same shape as the propagating bump, but I can't know without a better digram).

If you know the shape (mostly the approximate length) of the wave maker then you can even try to roughly predict the speed of the bump as it travels (see the Wikipedia entry on Wind Wave for starters).

I don't think you need a full-on numerical simulation to get at least an approximate answer in this example.
Bobbywhy
#6
Mar8-13, 03:18 AM
PF Gold
P: 1,881
opmeetsprep, Wave makers vary in size from miniscule to gigantic, and they are designed to produce specific kinds of waves. I don’t know how to calculate what you’re asking for. If you want to make a “Ripple” tank then you may just duplicate the mechanism that others already use. Wave energy, that is height, size, and speed of the wave, will be proportional the energy applied to the wave maker used to create the waves and other variables such as depth and tank shape. Here is a variety of types and sizes that give you examples of how others generate waves, starting with the smallest waves.

http://en.wikipedia.org/wiki/Ripple_tank

http://en.wikipedia.org/wiki/Wave_tank

http://wiki.seasteading.org/index.ph...Cost_Wave_Tank

“The below wave maker module comprises a stainless steel hinged paddle with rolling gusset seal actuated by a precise electric linear actuator with force feedback control, running on real-time computer control hardware able to reproduce scientifically accurate panchromatic wave climates.”
http://www.omeylabs.com/#!products

Cheers, Bobbywhy


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