Abstract
Dynamic analysis of a tank containing liquid is a complex problem involving fluid-structure interaction. The tank-liquid system is simplified by an equivalent model in which the total liquid mass is divided into two zones – impulsive and convective. The paper is primary focused on the behavior of the free liquid surface (the convective portion of liquid) subjected to the dynamic loading which may result in liquid spilling or tank wall damage. Therefore, the sufficient freeboard must be required to design. The paper deals with the seismic design of the open cylindrical liquid storage tank with the aim to determine convective dynamic properties (natural frequencies and modes of oscillation), maximum vertical displacements over tank radius and overall response of the liquid to an earthquake. The analysis is performed analytically by applying procedures for the determination of convective effects based on simplified equivalent spring-mass model, numerically response spectrum, and method of motion integrating equations utilizing ANSYS Multiphysics.
Highlights
Cylindrical tanks or pressure vessels are commonly used in the power and processing industries
In the simplified model (Fig. 1a) the total liquid is divided into two parts – the impulsive liquid, located near the tank base which moves with the tank walls, and the convective liquid which represents sloshing of the free surface and oscillates independently of the tank wall
The impulsive portion of the liquid is represented by a respective mass ݉୧ rigidly attached to the tank wall, whereas the convective part is described by an infinite number of masses ݉ୡ flexibly attached by a spring of appropriate stiffness ݇ୡ
Summary
Cylindrical tanks or pressure vessels are commonly used in the power and processing industries. They can be employed as storage vessels for various liquids (from non-flammable, nontoxic liquids to highly volatile, toxic chemicals with explosive nature). Time-dependent hydrodynamic forces, pressures and stresses are induced by the liquid on the tank walls and bottom. Knowledge of hydrodynamic effects is essential since they influence the response of the tank and must be considered in the design. One of the phenomena observed at the free liquid surface is a sloshing effect of the upper (convective) portion of the liquid. Oscillation of the convective liquid in the storage tanks may result in negative effects such as deformations and ruptures of the tank walls due to impact [1]. The sufficient freeboard (clearance) between the free surface and the top of the tank or the roof must be provided
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