释义 |
Helmholtz Differential Equation--Circular Cylindrical CoordinatesIn Cylindrical Coordinates, the Scale Factors are , , and the separation functions are , , , so the Stäckel Determinant is 1. Attempt Separation of Variables by writing
| (1) |
then the Helmholtz Differential Equation becomes
| (2) |
Now divide by ,
| (3) |
so the equation has been separated. Since the solution must be periodic in from the definition of the circularcylindrical coordinate system, the solution to the second part of (3) must have a Negative separation constant
| (4) |
which has a solution
| (5) |
Plugging (5) back into (3) gives
| (6) |
| (7) |
The solution to the second part of (7) must not be sinusoidal at for a physical solution, so thedifferential equation has a Positive separation constant
| (8) |
and the solution is
| (9) |
Plugging (9) back into (7) and multiplying through by yields
| (10) |
| (11) |
| (12) |
This is the Bessel Differential Equation, which has a solution
| (13) |
where and are Bessel Functions of the First andSecond Kinds, respectively. The general solution is therefore | | | (14) |
Actually, the Helmholtz Differential Equation is separable for general of the form
| (15) |
See also Cylindrical Coordinates, Helmholtz Differential Equation References
Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 514 and 656-657, 1953. |