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Description of the Finite Element Code DYNAZ

DYNAZ is a two/three dimensional computer model capable of performing simulation of the complex dynamic behavior of various types of liquid storage tanks subjected to a strong seismic base excitation. The model takes into consideration large amplitude liquid sloshing and the geometric, material and contact nonlinearities of the tank shell and base plate. The computer simulation included the following features:

• A variational principle that forms the basis for the numerical discretization of fully-coupled nonlinear liquid-structure interaction problems with free surface sloshing. The program uses an updated Eulerian-Lagrangian description of the liquid-structure interface in order to enforce compatibility between structure and liquid elements.
• An up-to-date finite element technology in the analysis of structures and curved shells using the degeneration concept, and considering both material plasticity and geometric nonlinearity.
• Free surface sloshing modeling that utilizes the nonlinear wave theory formulation. The updated Lagrangian description of the liquid domain boundaries is utilized to keep track of the free surface position at any time.
• The foundation is modeled using tensionless springs. This approach was found to be efficient in representing the nonlinear uplift problem.
• An efficient handling of the contact/uplift analysis of unanchored tanks. A Lagrange multiplier technique was employed to enforce both displacement compatibility and force transmissibility constraints along the unknown contact surface.
• The nonlinear governing equations are solved using an efficient time integration technique that has been developed specifically to solve liquid-structure interaction problems.

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