1 Limitations
Analytical solution methods are limited to highly simplified problems in simple
geometries (Fig. 5–2). The geometry must be such that its entire surface
can be described mathematically in a coordinate system by setting the variables
equal to constants. That is, it must fit into a coordinate system perfectly
with nothing sticking out or in. In the case of one-dimensional heat conduction
in a solid sphere of radius r0, for example, the entire outer surface can be
described by r r0. Likewise, the surfaces of a finite solid cylinder of radius
r0 and height H can be described by r r0 for the side surface and z 0 and
z H for the bottom and top surfaces, respectively. Even minor complications
in geometry can make an analytical solution impossible. For example, a
spherical object with an extrusion like a handle at some location is impossible
to handle analytically since the boundary conditions in this case cannot be expressed
in any familiar coordinate system.