释义 |
Heat Conduction EquationA diffusion equation of the form
| (1) |
Physically, the equation commonly arises in situations where is the thermal diffusivity and the temperature.
The 1-D heat conduction equation is
| (2) |
This can be solved by Separation of Variables using
| (3) |
Then
| (4) |
Dividing both sides by gives
| (5) |
where each side must be equal to a constant. Anticipating the exponential solution in , we have picked a negativeseparation constant so that the solution remains finite at all times and has units of length. The solutionis
| (6) |
and the solution is
| (7) |
The general solution is then
If we are given the boundary conditions
| (9) |
and
| (10) |
then applying (9) to (8) gives
| (11) |
and applying (10) to (8) gives
| (12) |
so (8) becomes
| (13) |
Since the general solution can have any ,
| (14) |
Now, if we are given an initial condition , we have
| (15) |
Multiplying both sides by and integrating from 0 to gives
| (16) |
Using the Orthogonality of and , | | | (17) | so
| (18) |
If the boundary conditions are replaced by the requirement that the derivative of the temperature be zero at the edges,then (9) and (10) are replaced by
| (19) |
| (20) |
Following the same procedure as before, a similar answer is found, but with sine replaced by cosine:
| (21) |
where
| (22) |
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