Non-linear dynamics of cylindrical shells containing fluid under blast loading Hamid Reza Moghaddasi h.moghaddasi@cv.iut.ac.ir Date of Submission: 2021/03/07 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: Ph.D. Language: Farsi Supervisors: Mojtaba Azhari, mojtaba@iut.ac.ir Mohammad Mehdi Saadatpour, mmehdi@iut.ac.ir Nonlinear modeling of shells has always involved simplifying assumptions on some computational parameters. In the latest nonlinear model based on eight parameters, that considers the displacement field as third-order polynomials in all three directions of curvilinear system, rotational inertia and shear deformations are also included; however, nonlinear terms are eliminated from some dependent variables, in addition, curvature and torsion variations of the shell are also assumed linear. In the modeling chapter, using a different approach, a new model for thick shells with any desired shape is presented, during which, the nonlinear effects are preserved in all kinematic dependent parameters as well as in the shell curvature and torsion changes, therefore a complete and accurate model for thick shells of any shape was presented. Then governing equations of motion of the system are derived through Lagrange relations and method of solving the mentioned equations and construction of bifurcation diagrams are explained in a separate chapter. In the results section, the circular cylindrical shell with simply supported boundary conditions is studied under circumferential static pressure and concentrated dynamic loads. Regarding static loading, it is observed that with increasing shell thickness, the nonlinear effects of curvature and torsion variations are limited. In addition, major changes in the post-buckling behavior of the shell in large deformations are achieved. It is also observed that the new nonlinear effects on the change of shell behavior in dynamic loading are more than static case, as it increases the frequency content and amplitude of the shell vibration, in addition to changing the style of the dynamic bifurcation curve. Finally, based on the results of dynamic analysis, a number of common phenomena in the behavior of circular cylindrical shells will be described. In the case of cylindrical shells containing fluid, it is observed that the presence of fluid reduces the system frequency and the number of peripheral waves of the fundamental mode and attenuates both nonlinear behaviors of the shell, including hardening and softening type, while increasing shell thickness increases the fundamental frequency. The presence of fluid also slightly reduces the deformation of the system against explosion. Keywords: Modeling, Shell, Nonlinear, Dynamics, Bifurcation, Harmonic, Fluid.