Impact of high strength steels over large ships fore peak structure

The fore area of the ships in extreme conditions is commonly subjected to external impact pressures such as bottom slamming and bow impact. The phenomenon combined with a poor design can lead to local structural damage (cracks, dents, buckling of plate panels) and malfunction to the installations on-board of the ship. In the present article, a comparison study between different steel material grades is performed for a VLCC fore peak structure subjected to external and internal dynamic pressures under the Harmonized Common Structural Rules for Bulk Carriers and Oil Tankers (H-CSR). Three steel grades generally used in the shipbuilding industry, one normal strength and two higher strength, are subjected for the assessment. The hull structure is built based on the benchmark crude oil carrier KVLCC2 surface developed by KRISO (Korea Research Institute for Ships and Ocean Engineering, and modelled with plate finite elements in FEMAP software. The study targets an optimization process to minimize the steel weight of the structural members by plate elements thickness reduction.

Weight and Cost Optimization of Midship Section Using Common Structural Rules

Cost and weight optimization in ship construction are usually investigated in the form of a multiobjective optimization problem. So far, many studies have been carried out to achieve various types of existing optimization objectives and different tools have been developed. Most of the studies in the field of structural optimization have focused on comparing the available optimization algorithms. In this study, a rule-based tool is developed based on the Common Structural Rules (CSRs), which despite its simplicity in application, provides high capabilities in producing an optimal solution. In the developed tool, structural analysis of serviceability limit state is performed by using the relationships of CSRs. The computational tool is created by MATLAB software (Mathworks, Natick, Massachusetts), and the optimization technique is a genetic algorithm. The performance of the computational tool is evaluated by analyzing the midship section of a chemical tanker. In the optimization procedure, weight and cost are assumed to have the same importance. From the results of the developed tool, all components of the weight and cost of ship construction decreased in the optimal solution relative to the initial design.

Methodical fundamantals and algorithms of software module for verification of fatigue life calculations in Atlas automated system

This paper discusses main assumptions and methodical foundations of verification calculations for fatigue life of hull structures in accordance with the requirements of Common Structural Rules (CSR) of IACS as per simplified procedure. The paper characterizes fatigue life assessment algorithm implemented in the development of Atlas automated system for verification calculations as per CSR.

RS experience in application of Atlas Hull 3D special software for FE-calculations as per IACS CSR

This paper analyzes Common Structural Rules (CSR) of IACS for finite-element calculations of hull structures and discusses the examples of Atlas Hull 3D application for corresponding calculations.

Structural Reliability Analysis Applied on Steel Ships for Rule Partial Safety Factors Calibration

Ultimate strength assessments in current IACS Common Structural Rules (CSR) are determined by a limited number of constant partial safety factors (PSF). These coefficients are inherited from the previous Common Structural Rules for Oil Tankers, and were determined using a structural reliability analysis (SRA) based on a limited number ship. The authors decided to lead a more comprehensive structural reliability analysis to propose and discuss a new set of rule formulations. A literature review is carried out in order to determine an extensive database of virtual ships covering the whole range of existing ships with a few representative parameters. SRA is applied for ultimate strength assessment on this database. Uncertainties are modeled by a set of probability distributions applied to each characteristic quantity (still water bending moment, wave bending moment and capacity) and a Second Order Reliability Method (SORM) is used to target the ultimate capacity corresponding to a given failure probability for each ship. A set of several PSF formulations are then derived from these results using both Working Stress Design (WSD) and Load and Resistance Factor Design (LRFD) approaches. These formulations are then discussed to get an optimum between simplicity and accuracy of the results.

Idealized Structural Unit Method: A Review of the Current Formulation

The evaluation of the maximum load-carrying capacity of structures is an essential issue in determining their safety. Only if the prediction of the ultimate strength is ensured, their probability of survival in extreme load conditions can be estimated. Particularly for safe dimensioning of ship structures, the determination of structural strength against buckling and yielding is required by Common Structural Rules (CSR). For ultimate strength calculations of ship structures, including ultimate hull girder capacity and ultimate strength of plates and stiffeners, the Finite Element Method (FEM) is a feasible tool. Despite the enormous development in computer technology, nonlinear finite element analyses (FEA) are still very time consuming and not easily to perform as well. Therefore the Idealized Structural Unit Method (ISUM) can be applied for collapse analysis of large structures.

Research on Some Issues related to Fatigue Assessment based on Latest IACS Harmonized CSR Amendments

The IACS Harmonized Common Structural Rules (CSR-H) for Bulk Carriers and Oil Tankers has been issued on 1st Jan 2014, and will enter into force on 1st July 2015 to supersede the current CSR version (CSR-BC or CSR-OT). The latest amendments to 01 Jan 2014 version of CSR-H give lots of significant modifications on fatigue assessment. The purpose of this study is to introduce the main changes for fatigue requirement in such amendments, and evaluate their rationality based on some detailed FE analysis for some key issues. Meanwhile, the impact on the structural design, especially on the scantlings, will be discussed as well as some proposal. Some typical bulk carriers and oil tankers are investigated.