Abstract
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.
Highlights
Received: July 26, 2017In Revised Form: June 29, 2018 Accepted: July 03, 2018 Available online: July 10, 2018Floating, production, storage and offloading units FPSOs are employed to receive oil and gas through the riser system, process it and store on board the vessel tanks, remaining on position by means of a mooring system or dynamic positioning system as described by Moan et al 2003
Ultimate strength formulations for FPSO stiffened panels under combined compression and shear with initial imperfections and damage using FE analysis followed by Alinia and Dastfan 2006 who studied the effect of surrounding members i.e. beams and columns on the overall behavior of thin steel plate shear walls
Each of the following analyses steps are presented in Section 2.3: i buckling analysis for initial imperfection estimation based on the first response mode, ii quasi-static analysis of the rigid body indentation to simulate the damage and the spring back response, iii quasi-static analyses subjected to shear loading taking into account the initial imperfections and the residual stresses from indentation followed by iv the modified Riks method Crisfield 1981 analyses applying compression to estimate the ultimate strength under combined loading
Summary
In Revised Form: June 29, 2018 Accepted: July 03, 2018 Available online: July 10, 2018. Ultimate strength formulations for FPSO stiffened panels under combined compression and shear with initial imperfections and damage using FE analysis followed by Alinia and Dastfan 2006 who studied the effect of surrounding members i.e. beams and columns on the overall behavior of thin steel plate shear walls. From the literature review performed, one can observe that none of the previous researchers considered the combined action of shear and compression in a limit state assessment of a stiffened panel structure with residual plastic strain caused by indentation. A very good correlation is observed for the case study presented where one can observe that the ultimate strength is more sensitive to compression than to shear and that higher levels of damage lead to lower values of limit state strength, as expected
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