water resonance in a sphere

[TinselKoala]

and if f = v / (2 x pi x r) and the sphere is 20 cm diameter, r = 10 cm and in water v = 150000 cm/sec
then
f = (150000)/(20 x 3.14)
f = 2389 Hz

And to find the sphere size for 42 kHz, you work backwards (ASSUMING the formula is correct for the resonance you wish to excite):

f = (v / wavelength) generally, and if your resonance equation is f = v / (2 x pi x r) then the resonant wavelength is of course (2 x pi x r) and we are interested in finding r.

So rearranging we have

r = v / (2 x pi x f)

substituting knowns, we have

r = (150000) / (42000 x 2 x pi)

SO

r = a little over half a centimeter.

Which actually doesn't seem unreasonable for an ultrasonic resonator sphere filled with water.

[Hydro-Cell]

Theoretical Resonant Frequency Of A Sphere Filled With Water...

F = V / (2*PI*R)

5 cm Diameter = 95 khz
9 cm Diameter = 53 khz
12cm Diameter = 39.8 khz
15cm Diameter = 31.8 khz
20cm Diameter = 23.9 khz    1st harmonic = 47.8khz   Most appropriate size/frequency for testing cavitation
32cm Diameter = 14.9 khz    1st harmonic = 29.8khz
48cm Diameter = 10 khz      1st harmonic = 20 khz

The idea i have is to focus the frequency to the centre of the sphere. if i then place a steel ball bearing in the centre of the sphere cavitation will take place on the all bearing surface. the bearing and surrounding water will then heat up.

well thats the theory anyway.

any ideas / comments welcome

[TinselKoala]

Hmmm-one of us is making a math error.
It's probably me.
What value are you using for v ?

EDIT: well, I've checked my math and I'm still coming up with numbers a tenth of yours. Damn those decimals anyway.

[Cap-Z-ro]

I have a feeling its all about resonance of the water, from possibly 2 directions inside the sphere...itself serving to conduct and reflect the waves created be the 2 sources, so that the resonant waves clash.

I am no expert in this field...this is just my take...hopefully it may lead to something.

Regards...

[Yucca]

Maybe if you lightly strike the whole unit when full of water and record it with a good mic on your PC then you could use a WAV editor with a spectrum analyser function (like goldwave) to give an idea about the systems mechanical freq. response. Only good up to 22kHz though.

edit: idea is similar to sonoluminescense experiments aka star in a jar.

edit2: wow this forum´s getting shakey, just clicked on "modify" in cap-z-ros post by mistake and was taken to the editor

Yucca.