To calculate the effective radii of two conductive elements in series in wo
od specimens by using the gas permeability measurement, the four parameters
from the curvilinear relationship of superficial specific permeability aga
inst reciprocal mean pressure as illustrated in Perry's model must be evalu
ated. This paper describes a detailed procedure for obtaining such paramete
rs by using the least-squares fit calculated from a statistical analysis sy
stem (SAS) program. Three different iterative optimization algorithms and s
tarting points were used separately to fit the Petty's nonlinear model base
d on the same experimental data from one specimen of birch. The estimate of
the parameters: A = 35.38 darcy, B = 80.51 darcy, 1 = 0.19 darcy atm, m =
6.34 darcy atm was recommended for the fitted model. Compared to the result
s on the estimate of parameters obtained in the previous papers, this estim
ate for the parameters was a global minimum, thus it was a refinement and m
ore accurate. Since the Gauss-Newton method resulted in almost the same con
vergence results for all the three sets of starting values with the least i
terations in the evaluation, it was the preferred optimization algorithm bo
th for simplicity and accuracy in solving the Petty's model. Because the sa
me solutions for all three iterative optimization algorithms were obtained
by using two different sets of starting points produced from the grid searc
h, a grid search seemed to be very helpful for finding reasonable starting
values for various iterative optimization techniques.