Differential equation resembling to cycloid

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Discussion Overview

The discussion revolves around a specific ordinary differential equation (ODE) that exhibits characteristics similar to those of a cycloid. Participants explore the function corresponding to this ODE, its representation in complex notation, and the implications of certain terms within the equation. The scope includes theoretical exploration and mathematical reasoning related to the ODE's solutions.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Tom presents an ODE in complex notation and notes that its numerical solution resembles a cycloid.
  • Another participant questions the connection between the ODE and the cycloid, suggesting that manipulating the equations might yield something integrable.
  • Tom responds that attempts to manipulate the equations have not simplified the problem, particularly due to a complex term involving derivatives.
  • Tom further investigates the cycloid ODE in complex notation, indicating that the presence of the term |z'| alters the equation's characteristics and relates it to a phugoid, which he believes may not have an analytic solution.
  • A later reply acknowledges a misunderstanding regarding the right-hand side of the equation and retracts an earlier suggestion, indicating a recognition of the complexity involved.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the ODE and cycloid behavior, with some uncertainty about the implications of specific terms in the equations. The discussion remains unresolved regarding the existence of an analytic solution for the phugoid.

Contextual Notes

Limitations include the complexity of the terms involved in the ODE, the dependence on specific conditions for the cycloid representation, and the unresolved nature of the mathematical manipulations attempted by participants.

tom-73
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What is the function corresponding to this ODE:
http://home.arcor.de/luag/math/dgl.jpg

In complex notation it obviously shows up like this:

a * z''(t) + b * |z'(t)| * z'(t) + c = 0;

The numerical solution shows a graph resembling to a cycloid.

Thanks for any help!
Tom
 
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tom-73 said:
What is the function corresponding to this ODE:
http://home.arcor.de/luag/math/dgl.jpg

In complex notation it obviously shows up like this:

a * z''(t) + b * |z'(t)| * z'(t) + c = 0;
It does? I don't see how.
If you divide through by the surd and subtract the 1st eqn from the second, I believe you get something integrable.
 
Thank you for your comment. I tried to divide and subtract. The problem is the term in the middle: (y' - eps*x') vs. (x' + eps*y')
It makes the situation even worse - I did not succeed in finding a simplified pattern.

The complex notation in my first post has been derived by simply multiplying the 2nd equation by i and adding the result to the first equation.

What I investigated in the meanwhile:

The cycloid ODE in complex notation should be

a * z''(t) + b * z'(t) + c = 0;

The only difference is the multiplication with |z'| in the middle which in fact produces a value near 1 for curtate cycloids with r1 << r0 (the point tracing out the curve is inside the circle, which rolls on a line AND it is close to the center).

The ODEs in my first posts describe a phugoid, a more general form of the cycloid I suppose.

It seems that the phugoid has no analytic solution. Any suggestions?

Tom
 
Sorry, I overlooked what happens to the RHS. My original suggestion was nonsense.
The complex notation in my first post has been derived by simply multiplying the 2nd equation by i and adding the result to the first equation.
Ah yes, I see it now. Sorry for the noise.
 

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