Methods for ultimate limit state assessment of ships and ship-shaped offshore structures: Part II stiffened panels

doi:10.1016/j.oceaneng.2007.08.007

Ocean Engineering

Volume 35, Issue 2, February 2008, Pages 271-280

https://doi.org/10.1016/j.oceaneng.2007.08.007 Get rights and content

Abstract

The present paper is Part II of a series of three papers on methods useful for the ultimate limit state assessment of ships and ship-shaped offshore structures. In contrast to Part I [Paik et al., 2007a. Methods for ultimate limit state assessment of ships and ship-shaped offshore structures: Part I unstiffened plates, Ocean Engineering, doi:10.1016/j.oceaneng.2007.08.004] that deals with unstiffened plates, the present paper (Part II) is focused on methods for the ultimate limit state assessment of stiffened plate structures under combined biaxial compression and lateral pressure actions. The object structure is the bottom part of an AFRAMAX-class hypothetical double-hull oil tanker structure designed by IACS common structural rules (CSR) method, that is the same ship studied in Part I. Three candidate methods, namely ANSYS nonlinear finite element method, DNV PULS method, and ALPS/ULSAP method, are employed for the present study. The results and insights developed from the present study are summarized in terms of ultimate strength characteristics of bottom-stiffened plate structures.

Introduction

Today in maritime industry, it is a mandatory task to compute the ultimate strength of structural components and their system for structural design and strength assessment based on ultimate limit states (ISO, 2007, ISO, 2006; IMO, 2006; IACS, 2006a, IACS, 2006b). This is because it is not possible to determine the true margin of structural safety as long as the ultimate strength remains unknown.

It was concluded in Part I (Paik et al., 2007a) that there are methods useful for computing ultimate strength of unstiffened plates, and it is mature enough to employ them in day-by-day design and strength assessment practice. In the present series of study, a benchmark study is carried out on ultimate limit state assessment of ship structures, using some candidate methods such as ANSYS nonlinear finite element analysis (FEA) (ANSYS, 2006), DNV PULS (DNV PULS, 2006), ALPS/ULSAP (2006), ALPS/HULL (2006), and IACS common structural rules (CSR) (IACS, 2006a).

The present paper (Part II) is focused on methods for ultimate limit state assessment of stiffened plate structures, while Part I deals with methods for ultimate limit state assessment of unstiffened plates (Paik et al., 2007a), and Part III treats methods for progressive collapse analysis of hull girders (Paik et al., 2007b).

As an illustrative example, bottom-stiffened plate structures of an AFRAMAX-class hypothetical double-hull oil tanker designed by the IACS CSR method are considered. The stiffened panels are subjected to combined biaxial compression and lateral pressure loads. For the present study, ANSYS FEA, DNV PULS, and ALPS/ULSAP methods are employed.

Section snippets

Candidate methods

For the present benchmark study in terms of ultimate limit state assessment of stiffened plate structures, the following three methods are employed, namely

•
ANSYS nonlinear FEA (ANSYS, 2006);
•
DNV PULS (DNV PULS, 2006);
•
ALPS/ULSAP (2006).

Although the ANSYS nonlinear FEA may be the most refined method among the candidate methods, and believed to give the most accurate solutions, it is important to realize that the modeling technique applied must be adequate enough in terms of representing actual

The object ship and its structural characteristics

Although some details of the object ship structure are described in Part I (Paik et al., 2007a), a brief summary of the object structure is given for convenience. For the present study purpose, an AFRAMAX-class hypothetical double-hull oil tanker designed by CSR methods is adopted. Table 1 indicates the principal particulars of the object ship.

Fig. 1, Fig. 2 show the stiffened plate structures of the object ship at the deck and the outer bottom, respectively. The entire ship structure is made

Ultimate limit state assessment of stiffened panels

For the present benchmark study, the bottom-stiffened plate structure of the object ship, surrounded by bottom girders and transverse floors as shown in Fig. 4, is considered. The ultimate strength of the bottom-stiffened panel with T-type longitudinal stiffeners is then analyzed under biaxial compression and lateral pressure loads (p=0.16 MPa). The lateral pressure load of p=0.16 MPa acting on the bottom plate structure has been determined from the design condition of the object ship. Table 2

Concluding remarks

The aim of the present study has been to identify the accuracy and applicability of some candidate methods, which are considered to be useful for ultimate limit state assessment of ships and offshore structures.

Based on the limited amount of the present benchmark study results obtained for stiffened plate structures, it is concluded that DNV PULS and ALPS/ULSAP are useful for the ultimate limit state assessment of stiffened plate structures in terms of the computational effort and the resulting

Acknowledgments

The present study was undertaken at the Ship and Offshore Structural Mechanics Laboratory (http://alps.ac), Pusan National University, Korea, which is a National Research Laboratory funded by the Korea Science and Engineering Foundation (Grant no. ROA-2006-000-10239-0). The authors are pleased to acknowledge the support of Samsung Heavy Industries.

References (13)

User's Manual (Version 10.0)
(2006)
A Computer Program for Progressive Collapse Analysis of Ship Hulls (Version 2006.3)
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A Computer Program for Ultimate Limit State Assessment for Stiffened Panels (Version 2006.3)
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DNV PULS, 2006. User's Manual (Version 2.05). Technical Report No. 2004-0406, Det Norske Veritas,...
IACS, 2006a. Common structural rules for double hull oil tankers. International Association of Classification...
Common Structural Rules for Bulk Carriers
(2006)

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Methods for ultimate limit state assessment of ships and ship-shaped offshore structures: Part II stiffened panels

Abstract

Introduction

Section snippets

Candidate methods

The object ship and its structural characteristics

Ultimate limit state assessment of stiffened panels

Concluding remarks

Acknowledgments

User's Manual (Version 10.0)

A Computer Program for Progressive Collapse Analysis of Ship Hulls (Version 2006.3)

A Computer Program for Ultimate Limit State Assessment for Stiffened Panels (Version 2006.3)

Common Structural Rules for Bulk Carriers