In this interesting paper (1), a concentrated load was applied to the clamped-free annular plate. The problem domain was divided into two parts by the cylindrical section where a concentrated load was applied. The author used the Trefftz method (2) to construct the homogeneous solution
$u=∑m=0∞Rm(r)cosmθ$
1
in each part. By substituting Eq. 1 into the governing equation, the author could determine $Rm(r)$. Mathematically speaking, the series in Eq. 1 can be seen as the summation of Trefftz bases. To simulate the concentrated force, a circularly distributed force using the Fourier series is used. Then, the author utilized two boundary conditions (BCs) in each part, two continuity, and two equilibrium conditions on the interface to determine the eight unknown coefficients. Variation of deflection coefficients, radial moment...