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Differential equation resembling to cycloid 
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#1
Nov1512, 10:58 AM

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What is the function corresponding to this ODE:
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 


#2
Nov1512, 09:30 PM

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P: 9,792

If you divide through by the surd and subtract the 1st eqn from the second, I believe you get something integrable. 


#3
Nov1612, 06:30 AM

P: 2

Thank you for your comment. I tried to devide 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 


#4
Nov1612, 02:07 PM

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P: 9,792

Differential equation resembling to cycloid
Sorry, I overlooked what happens to the RHS. My original suggestion was nonsense.



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