100 FUNDAMENTAL SOLUTIONS
This can be transformed to a simpler form by taking spherical polar
coordinates and integrating twice to give
VTj(x)
= A-& Ρ^(η)ά8
(4.58)
8πΓ
^|
=
ι
The integral is now taken round a unit circle which has centre at the
source point (the origin here) and lying in the plane perpendicular to
the line joining
3c
to the origin at a distance r.
For a general source point ξ (4.58) becomes
Ufj
(3c,
t)
=
-,,1
-?, <j>
FT,
l
(f) ds (4.59)
For an isotropic material (4.59) may be evaluated to give the Kelvin
solution:
„
sft
a__>
(iz*.^-· .<*-«<*-«
4πμ|χ-|1 4(l-v) " 4(1
—
v)
|3c —^|
χ-ξ
In the general case (4.59) must be evaluated numerically.
4.6 NUMERICAL SOLUTIONS (ANISOTROPIC BODIES)
We have seen that the determination of the fundamental solution
involves taking transforms of both sides of our original equation with
respect to the eigenfunctions φ
η
, and later inverting these trans-
forms.
These processes can only be performed in closed form for a very
limited number of special cases. When we have a governing equation
with different coefficients such as with anisotropic media, a numerical
approach for the evaluation of our solution becomes essential.
Suppose for simplicity we are working in rectangular Cartesian
coordinates, then the operator if may be represented as a polynomial
combination of the derivatives d/dx
i9
i = 1, . . ., n. We can write
ΞΡ
(
αι
έ
,α
°'
where a
0
, a
u
a
2
, . . . are constants independent of x. Then the
^
p
i
fl
'^
fl
»·^'-
'
(461)