Solving a Difficult Math Problem

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Discussion Overview

The discussion revolves around a mathematical problem involving derivatives and vorticity in cylindrical coordinates. Participants are exploring the solution to the equation (1/r) ∂/∂r (r√(C/r)), with references to similar equations and their solutions.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant presents the equation (1/r) ∂/∂r (r√(C/r)) and seeks help in solving it.
  • Another participant notes that equations typically have something on both sides of the equal sign, implying a need for context.
  • A participant clarifies that the equation relates to vorticity, specifically ω_z in cylindrical coordinates.
  • There is a question about the dependence of vorticity on the cylindrical coordinates r, φ, and z.
  • One participant suggests that the vorticity is dependent on r and that the equation can be solved using the derivative rule for powers, proposing a potential solution.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the solution to the original equation, and multiple approaches and interpretations are being discussed.

Contextual Notes

There are unresolved assumptions regarding the nature of the variables involved and the conditions under which the equations apply. The discussion also reflects uncertainty about the correct method for solving the initial problem.

alexmarison
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Hi, I'm doing some research on my own, but my math is pretty bad and I am stuck trying to find the solution to this problem:
(1/r) ∂/∂r (r√(C/r))=

I've seen these solutions of similar-looking problems:
(1/r) ∂/∂r (r^2 (Ω))=2Ω
and
(1/r) ∂/∂r (r K/r)=0, except when r=0, in which case the solution is infinite.

Thank you very much!
 
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alexmarison said:
Hi, I'm doing some research on my own, but my math is pretty bad and I am stuck trying to find the solution to this problem:
(1/r) ∂/∂r (r√(C/r))=

Usually equations have something on both sides of the equal sign...:wink:
 
gabbagabbahey said:
Usually equations have something on both sides of the equal sign...:wink:

Hi, sorry, guess the thing on the other side would matter. It happens to be vorticity or, in cylindrical coordinates, ω_z.
 
alexmarison said:
Hi, sorry, guess the thing on the other side would matter. It happens to be vorticity or, in cylindrical coordinates, ω_z.

What coordinate variables does the vorticity depend on (i.e. does it depend on [itex]r[/itex],[itex]\phi[/itex] and/or[itex]z[/itex])?
 
gabbagabbahey said:
What coordinate variables does the vorticity depend on (i.e. does it depend on [itex]r[/itex],[itex]\phi[/itex] and/or[itex]z[/itex])?

Out of the 3 cylindrical coordinates, there is only vortical motion wrt z, which motion is dependent on r, as the equation shows, I think.
 
Last edited:
I've been still looking at the problem too, and I think I noticed that in the example solution I gave:
ωz = (1/r) ∂/∂r (ruφ ) = (1/r) ∂/∂r (r2Ω) = 2Ω

it seems as though it was solved like a regular differential equation using only the rule for the derivative of powers:
If f(x)=xn, then f'(x)=nxn-1

Can I just do that to solve mine, too, in which case, I would get f'(x)=(1/2)r-1/2 to give me:
ωz = C1/2/2rr1/2?
 
Last edited:

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