Nonlinear Finite Element Results Research Articles

Ultimate strength formulations for FPSO stiffened panels under combined compression and shear with initial imperfections and damage

Abstract Accidental collision of striking objects, such as a supply vessel, into the side panel of a FPSO highly influences its ultimate strength assessment. An empirical formula for predicting the ultimate strength of damaged stiffened panels under combined loading of shear and longitudinal compression is empirically derived in this work based on curve fitting of quasi-static nonlinear finite element (FE) analyses. Initial imperfections are introduced by scaling the first buckling mode shape and the damage is caused by residual deformation from a rigid sphere indentation. A pure shear loading is applied at several levels followed by compression loading using the modified Riks method for a number of sphere indentation damages. The suggested formula for a typical FPSO stiffened side shell panel presented an excellent correlation with the nonlinear FE results and can be particularly useful in the preliminary design phase (no damage) and for a quick estimation of the panel residual strength with indentation damage.

Probabilistic ultimate buckling strength of stiffened plates, considering thick and high-performance steel

The probabilistic distribution of ultimate buckling strength for stiffened steel plates subjected to a distributed axial stress was obtained using Monte Carlo simulations in association with the response surface method. The plates of both normal and high-performance steel (SBHS) were taken into account, and their thickness was varied from 10 to 90mm. The ultimate buckling strength was determined by nonlinear elasto-plastic finite element (FE) analysis, considering geometric and material nonlinearity. The initial out-of-plane deflection and residual stress were considered as two independent random variables upon which the ultimate buckling strength depends. The response surface, showing the variation of ultimate strength due to the initial deflection and residual stress, was estimated using the nonlinear FE results. Based on the obtained statistical distribution, partial safety factors for the ultimate buckling strength were proposed.

In-Plane Nonlinear Buckling Analysis of Deep Circular Arches Incorporating Transverse Stresses

Large discrepancies exist among current classical theories for the in-plane buckling of arches that are subjected to a constant-directed radial load uniformly distributed around the arch axis. Discrepancies also exist between the classical solutions and nonlinear finite-element results. A new theory is developed in this paper for the nonlinear analysis of circular arches in which the nonlinear strain-displacement relationship is based on finite displacement theory. In the resulting variational equilibrium equation, the energy terms due to both nonlinear shear and transverse stresses are included. This paper also derives a set of linearized equations for the elastic in-plane buckling of arches, and presents a detailed analysis of the buckling of deep circular arches under constant-directed uniform radial loading including the effects of shear and transverse stresses, and of the prebuckling deformations. The solutions of the new theory agree very well with nonlinear finite-element results. Various assumptions often used by other researchers, in particular the assumption of inextensibility of the arch axis, are examined. The discrepancies among the current theories are clarified in the paper.