Buckling, vibration, and energy solutions for underwater composite cylinders

This study presents closed-form solutions for the critical buckling pressures and characteristic frequencies of underwater composite cylinders. The analytical solutions were derived using the full stiffness definitions from composite laminate theory, making them suitable for symmetric, asymmetric, hybrid, and/or double-shell (sandwich) cylindrical composite structures. These closed-form solutions were developed for critical buckling pressures in a hydrostatic environment as well as for critical buckling energy in a dynamic environment with combined hydrostatic and transient loads. Also, the characteristic frequencies were derived for a submerged and pressurized environment to account for added fluid mass and hydrostatic pressures. Computational and experimental data were used to validate the derived analytical work. The resulting solutions for critical buckling pressures agreed with numerical and experimental results for single-shell cylindrical structures. Moreover, for double-shell cylindrical structures with foam cores (sandwich structures), the collapse pressure is shown to be proportional to the core's transverse shear modulus. The solutions were suitable for predicting the collapse pressure for sandwich structures with relatively low-density cores. Lastly, solutions for estimating the energy emitted during an implosion event and the energy required for buckling in sub-critical pressure environments were also derived and validated with the experimental data.