Progressive Collapse Analysis of an FPSO Vessel Hull Girder Under Vertical Bending Considering Different Corrosion Model
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RESEARCH ARTICLE
Progressive Collapse Analysis of an FPSO Vessel Hull Girder Under Vertical Bending Considering Different Corrosion Models Zorareh Nouri 1 & Mohammad Reza Khedmati 1 Received: 22 March 2020 / Accepted: 1 August 2020 # The Author(s) 2020
Abstract Nowadays, with the increasing operational life of ships, the aging effects on their structural behavior need to be investigated precisely. With the corrosive marine environment taken into consideration, one of the important effects of aging that must be studied is thickness degradation. In this paper, with the use of previously proposed equivalent thickness formulations for corroded plates, the progressive collapse analysis software HULLST is enhanced, and then, the effects of different corrosion models of uniform, random, pitting, and tanker pattern types on the ultimate and residual strengths of a floating production, storage, and offloading vessel hull girder are evaluated for the ages of 0 to 25 years. Results reveal that the uniform corrosion and random corrosion models have close outcomes. The value of relative reduction in the ultimate strength of ship hull girder (compared with the intact condition) ranges roughly from 6% for the age of 5 years to 17% for the age of 25 years in the hogging mode. The relative reduction in the ultimate strength ranges from 4% to 16% in the sagging mode. Pitting corrosion and tanker pattern (random) corrosion models lead to higher relative reductions in ultimate strength. The pitting corrosion model leads to a 16%– 32% relative reduction in the ultimate strength for the ages of 5–25 years of the ship in either hogging or sagging. The tanker pattern (random) corrosion model leads to a 6%–37% relative reduction in the ultimate strength in the hogging mode and 3%– 31% in the sagging mode at ship ages of 5 to 25 years. Keywords Uniform corrosion . Random corrosion . Pitting corrosion . Tanker pattern corrosion . Progressive collapse analysis . Vertical bending . Ultimate strength . Residual strength
1 Introduction A ship hull girder is a thin-walled structure formed by plates and stiffeners, which is mainly influenced by vertical bending as a result of the action of various forces, including the ship’s own weight, cargo weight, buoyancy, and wave loads. Typically, the strength of a ship structure is evaluated and controlled in three levels, namely, longitudinal strength, transverse strength, and Article Highlights • Progressive collapse analysis of an FPSO vessel hull girder under vertical bending is performed by using an in-home computer code. • The effects of different types of corrosion models on the ultimate strength and collapse behavior of the hull girder are assessed. • Both hogging and sagging conditions are considered. * Mohammad Reza Khedmati [email protected] 1
Department of Maritime Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran 15916-34311, Iran
local strength. Assessment of the longitudinal strength, or in other words, the strength of the main hull girder, is the most import
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