DYNAMICS OF SHELL-LIKE LIFTING BODIES. PART I. THE ANALYTICAL INVESTIGATION.

Abstract : The vibration characteristics of typical shell-like lifting bodies, consisting of an outer skin covering and stiffened with both longitudinal stringers and transverse parallel flexible frames, were investigated using an approach based upon the matrix force method. Following an extensive literature survey, matrix equations were developed for structural flexibility characteristics of a stiffened shell with free-fixed boundary conditions and the equations of motion for free vibration were solved to determine natural frequencies and mode shapes. Equations of motion of a general stiffened shell configuration with free-free boundary conditions were developed and applied to the special case of a stiffened shell with a rigid root frame. A mode modifying matrix was determined which allows solution of the equations using structural flexibility parameters established for the shell with free-fixed boundary conditions. Analytical results for the case with free-fixed boundary conditions are compared with results obtained from an experimental investigation performed upon nine typical configurations and conclusions and recommendations are presented. (Author)