“…Among the few methods existing in the literature, we cite the following approaches with some representative works: the finite element method (Kapur, 1966;Hoa, 1979;Kolberg 1987), the Galerkin method (Wang and Chou, 1998;Dadfarnia et al, 2005), the Rayleigh-Ritz method (Oguamanam and Heppler, 1996), the Laplace transform method resulting in an integral form solution (Boley & Chao, 1955;Wang & Guan, 1994;Ortner & Wagner, 1996), and the eigenfunction expansion method, also referred to as the series or modal expansion method (Anderson, 1953;Dolph, 1954;Huang, 1961;Ekwaro-Osire et al, 2001;Loudini et al 2006;Loudini et al 2007a;Loudini et al 2007b). …”