Finite Element Analysis of Von-Mises Stress Distribution in a Spherical Shell of Liquified Natural Gas (Lng) Pressure Vessels
This research work investigated the modeling of Von Mises stress in LNG Spherical Carbon Steel Storage tank using assumed displacement Finite Element analysis based on shallow shell triangular elements. Using equations of elasticity, constant thickness carbon steel spherical storage tanks were subjected to different loading conditions. This paper stresses the need for proper definition of shallow element using sector angles to obtain the shallowness. The shallow spherical triangular element has five degrees of freedom at each of its corner node, which are the essential external degrees of freedom. The assumed displacement fields of these shallow triangular elements satisfied the exact requirement of rigid body modes of motion. The FORTRAN 90 programming language was used for the programme coding to solve finite element equations resulting from the model while Von Mises stresses distribution within the spherical storage tank shell subjected to different internal pressures were determined. The results showed that the use of non-shallow elements due to improper sector angles resulted in unreliable results while real shallow elements produced results that tallied with ASME Section VIII Div 1, Part UG values.
Structural and Vibrational Analysis of Liquid Storage Tanks
The finite element method (FEM) is used to conduct an analysis of two sets of liquid storage tanks. The first set comprises of ten broad tanks with height-to-radius ratio generally less than 1.5. These tanks are representatives of a typical oil storage tank farm. The second set of tanks comprises of ten tall tanks, with height-to-radius ratio generally greater than 1.5. These tanks are representative of tanks which buckled or collapsed during past earthquakes. In the present study the tanks are analyzed as ideal shells, not considering possible geometric imperfections. The FEM is used to carry out a free vibration analysis, and a nonlinear collapse analysis for simulated seismic loadings. Step changes in thickness are accounted for in the first set of tanks, and the presence of a plate or conical roof or stiffening girder are considered for the second set of tanks. The procedures of the study are extensively validated by making comparisons with available results in the literature. The current report provides results for the frequencies of the tanks in empty state conditions, and for the collapse loads for geometries without imperfections. In a further study it is planned to provide results for frequencies of full tanks, and for the collapse loads of tanks with imperfections.
Nonlinear Analysis of Anchored Tanks Subject to Equivalent Seismic Loading
The finite element method is applied to the problem of the nonlinear behavior of anchored cylindrical liquid-storage tanks subject to horizontal seismic loading. The tank alone is modelled with assumptions of fixed conditions at the base and free conditions at the top. Geometric nonlinearity is considered and the material behavior is taken as elastic-perfectly plastic. The loading consists of a constant hydrostatic pressure to which is added an equivalent static pressure representing hydrodynamic effects arising from seismic action. The latter loading is increased until failure occurs. As an indication of the validity of the approach a comparison with a test result is given. A parametric study is then conducted. Nonlinear failure loads are calculated in each case, and these are compared with previously determined elastic buckling loads.© 2002 ASME