Axisymmetric Finite Element Analysis for Sloshing Response of Floating Roofs in Cylindrical Storage Tanks Shoichi YOSHIDA*3,Kazuyoshi SEKINE and Tsukasa MITSUTA *3 Center for Risk Management and Safety Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa, 240-8501 Japan The floating roofs are widely used to prevent evaporation of content in the large oil storage tanks. The 2003 Tokachi-Oki earthquake caused severe damage to the floating roofs due to liquid sloshing. The structural integrity of the floating roofs for the sloshing is urgent issue to establish for the petrochemical and oil refining industries. This paper presents the axisymmetric finite element analysis for the sloshing response of floating roofs in cylindrical storage tanks. The hydrodynamic coupling of fluid and floating roof under seismic excitation is taken into consideration in the analysis. It is assumed that the fluid is incompressible and inviscid, and the roof is linear elastic while the sidewall and the bottom are rigid. The theory for the finite element analysis in which the behavior of the fluid is formulated in terms of dynamic pressure as the Eulerian approach is developed. The basic vibration characteristics of the floating roof, such as natural frequencies and vibration modes, can be obtained from the analysis. These give engineers important information on the floating roof design. Key Words : Sloshing, Coupled Vibration, Seismic Motion, Finite Element Method, Structural Analysis, Floating Roof, Cylindrical Storage Tank E-mail : s-yoshi@ynu.ac.jp
Fig.1 Analytical model of floating roof tank Fig.2 Axisymmric fluid element
1294 Nodes. 74 Shell elements. 1200 Fluid elements Table1 Circular plate model Fig.5 Mesh division Table3 Numerical examples Table2 Natural period Fig.4 Analytical model of single deck floating roof
Fig.7 Dynamic pressure mode at z=h Table4 Natural period (a) 1st, 2nd and 3rd modes Fig.8 (b) 4th and 5th modes Dynamic pressure mode on roof surface Fig.6 Vibration mode
Fig.10 Input acceleration wave (a) 1st mode (b) 2nd mode Fig.11 Displacement response at r=40000mm Fig.9 (c) 3rd mode Bending stress mode of deck plate
Fig.13 Radial bending stress Fig.14 Pontoon cross section Fig.12 Displacement
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