Analysis of Ship Structural Plate Panels During Service by the Method of Finite Elements

Abstract

The structure of a ship, submarine or an offshore structure is made from steel plates [1, 2] and stiffened with rolled sections or fabricated sections. The marine structures are usually designed for a service life of 25 years. The scantlings are determined considering the strength and the corrosion allowance required for the designed service life as per classification rules (rules and regulations for the construction and classification of steel ships, Indian Register of Shipping, Mumbai, India, January 2016; Rules for conditions of classification 2016, American Bureau of Shipping, Houston, TX, USA, August 2016). However, the actual life of the structure will depend upon the upkeep of the structure, periodical survey and in-service repairs and also the condition of water where it is operating. The loss of surface material due to corrosion and erosion may cause stress concentration which may lead to some sort of catastrophic failure of the structure. It is necessary to periodically assess the strength in-service, employing some mathematical/numerical techniques such as finite element method (FEM). This paper discusses a method based on FEM by which an attempt can be made to assess the strength of such deterioration of the structures in-service. The method utilizes the concept of negative stiffness introduced by Satsangi (in: Proceedings of INCHOE, Pune, pp B43–B55, 1994). A quadratic plate bending element is selected for the analysis. Further, another plate element of thickness equivalent to the loss due to corrosion/erosion is selected fully contained within the parent element. The assumptions are detailed by Satsangi [3], Mukhopadhyay and Satsangi (Trans. RINA 141–151, 1983). For the strength assessment, a computer code is developed in FORTRAN and plate problems analyzed to validate the formulation. Results obtained are in good agreement with those published in the literature.