Structure Optimization On Integral Forge Reinforcement For Nozzle Of Large Spherical Tank

Integral forge reinforcement is often used for nozzle of spherical tank. However, when it is designed by analysis, the reasonable structural dimensions are usually decided by trial and error. This paper proposed a quasi-equal strength criterion based on the code of "design by analysis" for d iscontinuous z one of p ressure v essel, w hich s tates t hat s tress 1 evel c oefficients b ased o n stress e valuation o f d esign b y a nalysis for d iscontinuous z one m ust be e qual o r 1 ess t han t he general membrane stress level coefficient. With the aid of APDL(ANSYS Parametric Design language) in ANSYS, parametric FEA model for connecting zone of nozzle on large spherical tank was set up. Taking advantage of the OPT(optimization tool) in ANSYS, integral forge reinforcement was optimized with the quasi-equal strength criterion. After optimization, the section has been decreased to a certain extent which results in the reduction of material consumption.A series of couple taper integral forge reinforcements for nozzles with various diameters of spherical shells with various diameters at various internal pressures have been calculated. The results were analyzed and fit. Both formulae and curves were given.With the ANSYS software and the isotropic hardening model, elastic-plastic finite element analysis was performed for the optimized structure. With the load-strain curve of high-stress zone, limit load was obtained by the couple tangent means. After modification by experience, it can be found that the modified limit load is about 60 percent larger than design pressure, which indicates that the optimized integral reinforcement satisfies the reinforced requirement from the viewpoint of limit load.The calculating precision of eight node's quadrangle element was also analyzed in the paper. Taking a s pherical s hell a s e xample, t he i nfluence o f gridding d ensity, 1 ength r atio o f b order, mesh layers on the calculating precision of the FEM was analyzed. The relationship of the gridding density, CPU time and account precision and applicability of eight node's quadrangle element in complicated zone was discussed. It was found that the precision can be satisfied when the gridding density is 20000-50000 elements per square meter and the length ratio of border is 0.1~10. Furthermore, when the gridding satisfies the requirement of equal parameter changing, the finite element calculating precision may be assured for irregular zone.