The composite conical lattice structure in this paper made of helical ribs and thin outer skin. In this research, free vibrations of these structures with and without outer skin were investigated. A smeared method is employed to obtain the coefficients of stiffness of conical shell. Theoretical formulations are based on sander thin theory of shell. For verification of the analytically obtained results, using ANSYS software the 3D finite element model of composite lattice conical shell is built and analyzed. To verify the accuracy of this method, comparison of the results are made with numerical results from ANSYS Software and show a good agreement between them. Also, some special cases as influences of the semi vertex angle and thickness of the outer skin on the natural frequencies of the conical shell are studied. It is concluded that, the increasing of the semi vertex angle leads to increasing the natural frequencies of conical shell. Moreover for outer shell thicknesses greater than a specific value, the increment of the thickness of the outer skin leads to decreasing the natural frequencies. Because of few researchers investigated merely vibrational behavior of the composite lattice cylindrical shell, the obtained results of this paper have novelty and can be used for further and future researches.

Keywords: Conical lattice structure, Vibrations, rib, Composite, Smear stiffness method

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