“…Such problems cannot be solved exactly for general function of variable cross section but in special cases, only when the equation is reduced to Euler's equation, special Bessel functions can be used to find the solution (ZORYJ 1982). The approach proposed by the author of this paper to apply the characteristic series method to the analysis of multi-parameter continuous systems seems warranted (JAROSZEWICZ, ZORYJ 1985, 1994. The literature reports analyses of this issue carried out using numerical and analytical methods including the MES, transfer matrix method and approximate methods based on energy principle such as those of Rayleigh-Ritz, Galerkin--Bubnow and Treffz (SOLECKI, SZYMKIEWICZ 1964).…”