Strength Analysis for the Design of Local Ship Structures in Concept Stage

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Helsinki University of Technology | Diplomityö
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Date

2007

Department

Konetekniikan osasto

Major/Subject

Laivanrakennusoppi

Mcode

Kul-24

Degree programme

Language

en

Pages

80 s. + liitt.

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Abstract

Formation of the design space for a stiffened panel element in design of ship structures was investigated in the present work. Capabilities of the stiffened panel criteria to find primary constraints in structural design of a cruise ship in concept stage were analyzed with discrete design variables. Buckling, yielding and fatigue of the stiffened panels were included in the criteria. Cruise ships with complex structure and non-linear stress distribution are time-consuming to analyze using FEA, and therefore the development of analytic or semi-empiric methods are useful is seen as useful for the concept design stage. Majority of the steel weight of the ship structures consists of stiffened panels. Stiffened panel criteria were compiled into computer code that can be used to analyze a large number of stiffened panels in a short period of time. Enumeration was used to study how the design space of a stiffened panel is formed when the design variables are discrete. The design space, limited by the stiffened panel criteria, was studied in the form of sensitivity analysis. Sensitivities of the masses of the stiffened panels to four different variables; plate thickness, stiffener spacing, stiffener height and stiffener thickness were investigated in a case study. Realistic loading and structural dimensions for midships upper deck, and recess- and side shell of the maximum shear force area were implemented. Results include actual and critical stresses, usage factors, mass, and scantlings for the stiffened panels that pass the criteria. Global response has been assumed as statically determined. Based on the results it can be said that when the design space is limited by the developed set of strength criteria, the lightest design is not always equal to the design option with the smallest allowable stiffener spacing or smallest possible plate thickness. Fatigue seems to be critical constraint in upper deck panels of cruise ships whereas material yield strength and thickness of the plating determines the minimum attainable mass if shear force and external lateral pressure are primary loads on the structure. Further research can be recommended to include more refined fatigue analysis, secondary response model for the girder systems, buckling model of the stiffened panels under shear loading, and extending the area of applicability of the buckling interaction equation to more slender structures. Applying the rational design approach, as opposed to rule based approach, to shell structures of ships would require development of larger set of constraints to be included in the design criteria, including production constraints and global response.

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Supervisor

Varsta, Petri

Thesis advisor

Remes, Heikki

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https://urn.fi/URN:NBN:fi:aalto-2020120553344

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[dipl] Teknillinen korkeakoulu / TKK