Decay time of waves in a swimming pool

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Discussion Overview

The discussion revolves around the decay time and amplitude of standing waves in an ideal cylindrical swimming pool, focusing on the effects of viscosity and surface tension. Participants explore theoretical expressions and relationships related to wave behavior in this specific fluid dynamics context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the setup of an ideal cylindrical pool and the generation of standing waves using a plunger, seeking expressions for wave decay time and amplitude.
  • Another participant suggests a paper that may provide insights into the decay of standing surface waves due to viscosity.
  • A participant questions the relationship between wave height and water volume, suggesting that nonlinearities may complicate this relationship, especially near resonance.
  • Another participant expresses uncertainty regarding the definition of shear rate in the context of the discussion and indicates a need for further investigation.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between wave amplitude and water volume, with some suggesting nonlinear effects may complicate this relationship. There is no consensus on the expressions for wave decay time or amplitude, and the discussion remains unresolved.

Contextual Notes

Participants acknowledge the complexity introduced by viscosity and surface tension, as well as the potential influence of nonlinear effects near resonance. The discussion includes references to specific mathematical models and assumptions that have not been fully explored or agreed upon.

avenged*7
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Hello,
Let's say I have an ideal cylindrical pool (rigid, vertical walls) of diameter d, with water of depth h. Take the ratio of d:h to be around 5:1 - 10:1. If I press down on the surface with a plunger of width w, I cause a standing wave resembling a single-node Bessel function, like a vibrating membrane with non-fixed edges. Taking into account the viscosity and surface tension, what are the expressions for (and how are they obtained)
  1. wave decay time
  2. wave amplitude
I've searched all over, but mostly get expressions for the surface heights obtained via slosh analysis and nothing for the decay time of the wave. Thanks!
 
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avenged*7 said:
Hello,
Let's say I have an ideal cylindrical pool (rigid, vertical walls) of diameter d, with water of depth h. Take the ratio of d:h to be around 5:1 - 10:1. If I press down on the surface with a plunger of width w, I cause a standing wave resembling a single-node Bessel function, like a vibrating membrane with non-fixed edges. Taking into account the viscosity and surface tension, what are the expressions for (and how are they obtained)
  1. wave decay time
  2. wave amplitude
I've searched all over, but mostly get expressions for the surface heights obtained via slosh analysis and nothing for the decay time of the wave. Thanks!
Maybe the following paper will be useful in finding the decay of the standing surface waves caused by viscosity:-
http://sites.apam.columbia.edu/courses/apph4200x/Behroozi_Viscous Gravity Waves.pdf
As for the height of the wave, I presume the volume of water in a half wave will equal the displacement of the plunger.
 
avenged*7 said:
Taking into account the viscosity and surface tension
Can you write shear rate as a function of (r,w)?
 
Thanks for responding! Sorry it took so long to respond as I have had to set the project aside for a short time. I'll be working on it here and there as my time permits.

tech99: I haven't had a chance to read the paper in depth, but it looks promising. As for the wave height, I believe that nonlinearities will not permit such a simple relationship between the displacement and water volume, especially near resonance. I say this also because the wave amplitude visibly grows to its maximum after some time of being constantly driven at the resonant frequency. That is, the wave heights differ at the beginning and at resonance while having the same displacement (or so it appears).

Bystander: I am not sure about that. My expertise is not in fluids, so I need to look into exactly how the shear rate is defined. When I figure that out, I will let you know.

Thanks again!
 

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