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© CADFEM 2016

FEA within Ship and Submarine Design James Underwood

Principal Naval Architect & Structures Group Manager,

BMT Defence Services Ltd

1st CADFEM ANSYS Simulation Conference, United Kingdom

2nd & 3rd November 2016 – Oxford Spires Hotel, Oxford

BMT Group Overview

A network of knowledge and resources

ENERGY & ENVIRONMENT

TRANSPORT DEFENCE3 sectors

• BMT Designers &

Planners

• BMT Defence

Services

• BMT Design &

Technology

• BMT Fleet

Technology

• BMT Hi-Q Sigma

• BMT Isis

• BMT Reliability

Consultants

• BMT Asia Pacific

(Indonesia)

• BMT Cordah

• BMT Oceanica

• BMT WBM

• BMT ARGOSS

• BMT Scientific

Marine Services

• BMT Fluid

Mechanics

• BMT Asia Pacific

(Malaysia)

• BMT Navcon

Defence EnergyEnvironment

• BMT Asia Pacific

(Hong Kong)

• BMT Asia Pacific

(Singapore)

• BMT Consultants

India

• BMT JFA

• BMT Ship &

Coastal Dynamics

• BMT WBM

(Machinery Group)

Ports,

Infrastructure

and Resources

Ship Design,

Surveys and

Vessel

Performance

• BMT Nigel Gee

• BMT SMART

• BMT Surveys

• Verweij & Hoebee

BMT Group

Structure - sector

BMT Defence Services

A subsidiary of BMT Group

• Established in 1988 in

Bath, UK,

• Two offices in Bath, with

a further three offices in

Fareham, Weymouth,

and Barrow-In-Furness.

Locations

285 people based

in Bath, UK

55 people based

in Fareham,

Weymouth and

Barrow, UK

BMT Defence Services

Services

NAVAL DESIGN & ENGINEERING

SYSTEMS ENGINEERING

ACQUISITION SUPPORT

COMBAT SYSTEMS

IN-SERVICE SUPPORT

HYDRODYNAMICS

TECHNICAL ASSURANCE

STRUCTURAL DESIGN & ANALYSIS

TECHNOLOGY MANAGEMENT

SOFTWARE DEVELOPMENT

HUMAN FACTORS

Whole Ship Stress Analysis

Global Stress Analysis

• Focus on stress analysis in relation to Classification

Society rules and prescribed reserve factors to ensure ship

safety at sea under varying loading conditions.

• Fatigue analysis of ship at sea under varying loading

conditions.

• FEA:

− Linear Elastic analysis of the whole ship under wave induced bending

moment;

− Load applied through application of forces to transverse frames along

the keel of the vessel or as surface pressure loads;

− Shell and Beam element modelling.

− Stress and buckling analysis of structure.

− Fatigue assessment of design details using sub-modelling with loading

derived from global model.

Images:

Flight Deck: http://www.public.navy.mil/surfor/ddg86/Pages/News-Archive.aspx

Bow Slamming: https://uk.pinterest.com/pin/484840716108123118/

Whole Ship Stress Analysis

Whole Ship Ultimate Strength Assessment

Ultimate Bending Strength Assessment

• Focus on ultimate limit state analysis for vessel under

wave induce bending moment in both the intact and

damage condition.

• FEA

− Non-linear collapse analysis of the hull structure under global

bending moment;

− Shell element model;

− Load applied by applying pure bending moment to longitudinal

section of vessel;

− Model includes weld induced manufacturing imperfections and

residual stresses.

− Structure will progressively fail from region in compression

around side shell until complete failure occurs.

Images: MOL Comfort: http://dev.twentytwowords.com/large-cargo-ship-snaps-in-two-in-rough-

seas-both-pieces-remain-afloat-5-pics/

Frigate FEA: Benson S. Progressive Collapse Analysis of Lightweight Ship Structures.

Doctoral Thesis; November 2011.

Destroyer FEA: Downes J, Ham WL, Dow RS. Assessment of the residual strength of a

lightweight naval vessel. Proceedings of Practical Design of ships and Offshore Structures

2013 (PRADS 2013).

Whole Ship Ultimate Strength Assessment

Whole Ship Ultimate Strength Assessment

Structural Integration

• Replenishment at Sea (RAS) of liquid and solid stores to re-

store front line warships from auxiliaries within a hostile

area.

• Auxiliary lines run from bespoke RAS Mast to RAS

connection points on receiving ship.

• Loading required to contend with line loads whose tension

is maintained by series of active winches.

• Structural capability to comply with Classification Society

rules based on an allowable stress approach in relation to

prescribed reserve factors.

• FEA:

− Linear elastic analysis for peak stress in structure of mast and its

integration up to two decks below weather deck.

− Shell and beam element modelling.

− Buckling assessment of mast structure.

− Fatigue analysis of mast structure.

− Model built using ANSYS Mechanical APDL, though subsequent study

showed significant modelling time savings by using ANSYS SpaceClaim

and Workbench.

RAS Mast

Structural Integration

RAS Mast

Structural Integration

RAS Mast

Submarine Pressure Hull Design

• Pressure hull design undertaken to required dive depth

multiplied by required safety factors.

• Focus on ultimate collapse strength of the pressure hull

and end closure structures.

• Failure due to instability of the pressure hull or end

closure dome.

Concept end closure studies:

• Current end closures of large diameter submarines are

either hemispherical or torospherical in form,

manufactured through the welding of segments of very

thick plate into which double curvature has been cold

pressed.

• Current process is therefore very complex and

expensive.

• BMT investigated concepts surrounding alternative end

closures including flat sandwich bulkhead and faceted

dome form.

End Closure Analysis

Submarine Pressure Hull Design

End Closure Analysis

Submarine Pressure Hull Design

End Closure Analysis

Submarine Pressure Hull Design

End Closure Analysis

Submarine Pressure Hull Design

End Closure Analysis

Copyright Statement

Copyright © 2016 by BMT Defence Services

All rights reserved. No part of this publication may be reproduced,

distributed, or transmitted in any form or by any means, including

photocopying, recording, or other electronic or mechanical methods,

without the prior written permission of BMT Defence Services.

Where content has not been produced by BMT Defence Services, we

have sought the appropriate authorisation for its use and does not

constitute an infringement of copyright.

Thank You.