Help understanding BASIC fluid dynamics behind faraday waves

In summary: This leads to the sudden onset of Faraday waves and the long decay period as the fluid tries to regain stability. This phenomenon can be explained by the primary Faraday instability, which is a result of a nonlinear interaction between the driving force and the fluid surface.In summary, the experiment with Faraday waves involves vertically shaking water with a speaker-like device to observe the growth and decay of Faraday waves. The difference in behavior between the two can be explained by the primary Faraday instability, which is a result of a nonlinear interaction between the driving force and the fluid surface. The sudden onset of Faraday waves is caused by a diffusion of viscous forces, while the long decay period is a result of the fluid trying to regain stability.
  • #1
piareround
79
0
Dear Sir and Mam,



So recently, I have been doing an experiment with Faraday waves. I feel like there are some critical things I don't understand about fluid dynamics (they don't offer it as a course where I go to school), so I was wondering if anyone on pf was good with fluid dynamics and help me understand the qualitative side of Faraday Waves.

In the experiment we vertically shake water with speaker-like device. At certain critical amplitude and frequency, we observe Faraday waves like in Fig. 1 below.

On of the things that really mystify's me is difference the growth of Faraday waves vs. the decay of Faraday waves. For example, let say I introduce a constant sinusodial variation to the speaker. If I plot the acceleration of the speaker vs. the magnitude out put of the Faraday wave, I get something like Fig. 2. Here it easy to see how the onset of the Faraday is quiet sudden vs. the long decrease in Faraday waves.


Can anyone explain qualitatively how or why an oscillation grow differently than its decay?
I have heard some paper use the word "primary Faraday instability". Could it have anything to do with an instability?



https://www.youtube.com/watch?v=<iframe width="420" height="315" src="http://www.youtube.com/embed/v-XEhY4OThs" frameborder="0" allowfullscreen></iframe>
Fig. 1: The following youtube video is


BifRamp60.png

Fig 2: A picture of the Amplitude vs. acceleration graph. It shows how the growth and decay behavior of a Faraday Wave are different.
 
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  • #2
Well the whole thing has to do with an instability. The whole mechanism is nonlinear, so without going and doing the math behind it, I would say you are most likely dealing with a hysteresis effect.
 
  • #3
If I had to give you a qualitative explanation without any prior experience with Faraday waves, I would say that during the growth that viscous forces keep the fluid stable, but then upon the sudden growth in amplitude the viscous forces are diffused and this leads to the hysteresis.

Essentially, fluid stays stable as long as it can, but then it becomes unstable and these instabilities "feed themselves."
 

Related to Help understanding BASIC fluid dynamics behind faraday waves

1. What are faraday waves and how do they form?

Faraday waves are standing wave patterns that form on the surface of a fluid when it is subjected to vertical oscillations. When a fluid is vibrated at a particular frequency, the surface tension and gravity forces interact to form these distinct wave patterns.

2. What is the role of surface tension in faraday waves?

Surface tension is a force that is caused by the imbalance of cohesive forces between molecules at the surface of a liquid. In faraday waves, the surface tension of the fluid plays a critical role in the formation and stability of the wave patterns.

3. How does the frequency of the vibrations affect faraday waves?

The frequency of vibrations directly affects the wavelength and amplitude of faraday waves. At certain frequencies, the waves will amplify and become more pronounced, while at other frequencies, they may cancel each other out and disappear.

4. Are there any real-world applications of understanding faraday waves?

Faraday waves have been studied extensively in various fields, including fluid dynamics, materials science, and engineering. Understanding the principles behind faraday waves can lead to advancements in areas such as surface patterning, mixing and separation processes, and even drug delivery systems.

5. Is there any ongoing research on faraday waves?

Yes, there is ongoing research on faraday waves in various fields, including the study of nonlinear dynamics, pattern formation, and surface tension effects. Researchers are also exploring how faraday waves can be controlled and manipulated for practical applications.

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