Full Speed Ahead on Welding Analysis

Reprinted with permission from the

Winter 2008 edition of8

Conce

pt To

Realit

y Fa

ll 07 /

Wint

er 08

www.alta

ir.com

/c2r

for ex

ample

, SHI r

ecen

tly im

plemen

ted a

compu

ter-

aided

analy

sis sy

stem th

at en

ables

shipb

uildin

g engi-

neers

to quick

ly sim

ulate a

nd min

imize

weld

ing-

indu

ced d

istor

tion an

d shrin

kage

. Analy

sis re

sults

are us

ed to

contro

l hull

panel

weld di

storti

on in

the

desig

n and p

rodu

ction

plan

ning s

tages

so th

at SHI

can m

ake r

apid

decisi

ons for m

odifyin

g weld

ing

proce

dures

or fa

brica

tion m

ethod

s.

Weld

ing i

s a co

mplex t

hermo-m

echan

ical p

rocess

that

is diffi

cult t

o sim

ulate

analy

ticall

y. In

most

cases

,

the e

xperi

ence

of se

asoned

weld

ing engin

eers

is use

d

to co

ntrol t

he effe

cts of

the w

eldin

g pro

cess

so th

at

distor

tions a

nd shrin

kage

can be

man

aged

effec

tively

.

Even w

ith th

is ex

perie

nce, m

ost l

arge w

elded

stru

c-

C

FullS

peed

Ahe

ad on

Welding

Ana

lysis

FullS

peed

Ahe

ad on

Welding

Ana

lysis

Simulat

ion en

ables

shipbu

ilder

sto

auto

mate

welding

proc

edur

es –

savin

gtim

e an

dm

oney

.

Simulat

ion en

ables

shipbu

ilder

sto

auto

mate

welding

proc

edur

es –

savin

gtim

ean

dm

oney

.

Compe

tition

in th

e worl

dwide

shipb

uildin

g indu

s-

try is

fierce

. That

is why s

hipbuil

ders

are co

nstantly

search

ing f

or in

novati

ve w

ays t

o elim

inate

ineff

i-

ciencie

s, impro

ve qu

ality,

boost

prod

uctiv

ity an

d cut

costs

to st

ay af

loat.

Samsun

g Hea

vy In

dustr

ies (S

HI) Co.

Ltd., p

art of

the S

amsu

ng Gro

up, is a

Kore

an sh

ipbuild

er w

ell

aware

of gl

obal

busin

ess ch

allen

ges.

The com

pany’s

Shipbuil

ding &

Offs

hore D

ivisio

n spec

ialize

s in co

m-

mercial

and v

alue-a

dded

ships

, offs

hore v

essels

and

struc

tures,

and c

argo a

nd mate

rial-h

andli

ng fac

ilities

.

To kee

p its

posit

ion as

a lea

der i

n the i

ndustr

y,

SHI pro

activ

ely pu

rsues

cutti

ng-edg

e tec

hnology

in

prod

uct d

esign

and d

evelo

pmen

t. In

man

ufactu

ring,

by Heeyoung Heo

9

www.alta

ir.com

/c2r

Conce

pt To

Realit

y Fa

ll 07 /

Wint

er 08

PR

OC

ES

SA

UT

OM

AT

I ON

tures

rely o

n compli

cated

fixtur

es an

d jigs

and s

ignifi-

cant r

ework

to pro

duce a

struct

ure w

ith th

e righ

t

shap

e and s

trength

to m

eet t

he desi

gn re

quire

ments.

In Ship Shape

Super-la

rge c

ontain

ersh

ips,

liquid

nat

ural g

as

carri

ers,

Arc

tic sh

uttle t

anker

s and dril

l ship

s

are a

mong the v

esse

ls th

at S

HI build

s in K

orea.

The cutti

ng and w

eldin

g of t

hick plat

es (g

reat

er

than

10 mm) a

re par

amount t

o their

fabric

atio

n.

Howev

er, th

e pro

cess

inhere

ntly in

volve

s therm

al

defor

mation

and s

hrinka

ge.

Weld

disto

rtion

and s

hrinka

ge oc

cur d

ue to

the

large

therm

al gra

dients

indu

ced d

urin

g weld

ing.

In

the w

eld zo

ne, th

e meta

l is m

olten

, and a

s it c

ools,

it

shrin

ks. T

he sur

roun

ding m

etal i

s rigi

d and r

esists

this

shrin

kage

. As a

resul

t, man

y com

plex m

echan

i-

cal lo

ads a

re ge

nerated

in th

e stru

cture

to ba

lance

the

therm

al load

s, lea

ding t

o warp

age,

distorti

on and

shrin

kage o

f the s

truct

ure. I

f you w

ere t

o thro

w

a piec

e of a

lumin

um fo

il in

a ca

mpfire,

you w

ould

notice

that

it wou

ld dis

tort

and c

hange

shap

e as i

t

heats

up. T

his is

due t

o the s

ame p

rincip

le where

in

the

tem

perat

ure d

iffer

ence

s in th

e fo

il ca

use

mechan

ical lo

ads t

hat de

form th

e foil

.

In ge

neral, w

arpag

e, or

out-o

f-plan

e defo

rmati

on,

is ty

pically

fixed

during a

ssembly

using a

jig a

nd

afte

r asse

mbly

usin

g th

erm

al o

r mec

hanic

al

rewor

k. Therm

al rew

ork i

s usin

g a hea

t sou

rce, su

ch

as a

torc

h, to d

eform

the

overal

l stru

cture

to th

e pro

per s

hape.

Quality w

eldments

of thick plates

(greater than 10

mm)

are paramount to

fabricatin

g hull

structures t

o

withsta

nd the rig

ors

of oceanic sh

ipping.

10

Concept To Reality Fall 07 / Winter 08

www.altair.com

/c2r

Mechanical rework uses jigs or other mechanical

forces to deform the as-welded structure to the proper

shape. Both processes can be time-consum

ing

and usually require expert technicians with years of

experience. In-plane deformation, or shrinkage,

cannot be easily fixed during assembly and needs to

be corrected prior to assembly.

Traditional weld analysis methods, using the

finite-element method, are relatively easy to set up,

but the computer run time can take days or weeks.

This makes it difficult to make weld planning

decisions since a welding

engineer would need to

wait a long time

just to un-

derstand the effects

of different weld sequences, fixturing or the welding

process. As a result, weld engineers typically rely on

experience and engineering judgment.

Over the years, researchers have developed

some simplified analysis methods that can more

quickly predict weld-induced

shrinkage and distortion.

These methods make several

simplified assumptions but

are able to accurately predict

shrinkage and distortion

trends and can be used to

better plan welding processes.

These models run quickly

(in minutes vs. days) and can

provide rapid feedback to the

welding engineer that helps

him/her better understand

the effects of welding on the

overall structure.

The challenge with these

methods is that the setup

of the model can be tim

e-

consuming and subject to

mistakes if done manually.

SHI, working with Altair Engineering, developed a

semi-automated analysis setup system that can

generate and run models in a few hours. Weld analysis

can now be used to positively affect the business of

SHI. This pre-processor enables the company to

quickly predict the effect of the weld process and

fixturing on the final shape of the welded ship structure.

The system automatically creates the FEA model

from the geometry and property information imported

from the computer-aided design (CAD) model. This

FEA model, in turn, is used to predict the weld shrink-

age and distortion based on the type of weld joints,

welding process and plate thickness of the weld region.

This is all done with a user-friendly interface that

ensures consistency and flexibility.

Macro Power

The customized welding deformation analysis

pre-processor was built as a series of macros inside the

Altair HyperMesh pre-processor, a solver-neutral

environment with a rich feature set to build and edit

computer-aided engineering (CAE) models. The

tailored HyperMesh pre-processing system interfaces

directly to SHI’s specialized 3D CAD software and

FEA solvers.

With this solution, engineers extract 3D geometry

and property information as ACIS and text files,

respectively. Meshing and surface editing tools allow

From the3D CAD geometry

(above), SHI

engineers create

quality meshes

using Altair

HyperMesh (right).

8Concept To Reality Fall 07 / Winter 08 www.altair.com/c2r

for example, SHI recently implemented a computer-aided analysis system that enables shipbuilding engi-neers to quickly simulate and minimize welding-induced distortion and shrinkage. Analysis resultsare used to control hull panel weld distortion in thedesign and production planning stages so that SHIcan make rapid decisions for modifying weldingprocedures or fabrication methods.

Welding is a complex thermo-mechanical processthat is difficult to simulate analytically. In most cases,the experience of seasoned welding engineers is usedto control the effects of the welding process so thatdistortions and shrinkage can be managed effectively.Even with this experience, most large welded struc-

C

FullSpeedAhead onWelding AnalysisFullSpeedAhead onWelding Analysis

Simulation enables

shipbuilders to automatewelding procedures –saving time and money.

Simulation enables

shipbuilders to automatewelding procedures –saving time and money.

Competition in the worldwide shipbuilding indus-try is fierce. That is why shipbuilders are constantlysearching for innovative ways to eliminate ineffi-ciencies, improve quality, boost productivity and cutcosts to stay afloat.

Samsung Heavy Industries (SHI) Co. Ltd., part ofthe Samsung Group, is a Korean shipbuilder wellaware of global business challenges. The company’sShipbuilding & Offshore Division specializes in com-mercial and value-added ships, offshore vessels andstructures, and cargo and material-handling facilities.

To keep its position as a leader in the industry,SHI proactively pursues cutting-edge technology inproduct design and development. In manufacturing,

by Heeyoung Heo

Reprinted with permission from the

Winter 2008 edition of

9www.altair.com/c2r Concept To Reality Fall 07 / Winter 08

P R O C E S S A U T O M A T I O N

tures rely on complicated fixtures and jigs and signifi-cant rework to produce a structure with the rightshape and strength to meet the design requirements.

In Ship ShapeSuper-large containerships, liquid natural gas

carriers, Arctic shuttle tankers and drill shipsare among the vessels that SHI builds in Korea.The cutting and welding of thick plates (greaterthan 10 mm) are paramount to their fabrication.However, the process inherently involves thermaldeformation and shrinkage.

Weld distortion and shrinkage occur due to thelarge thermal gradients induced during welding. In

the weld zone, the metal is molten, and as it cools, itshrinks. The surrounding metal is rigid and resiststhis shrinkage. As a result, many complex mechani-cal loads are generated in the structure to balance thethermal loads, leading to warpage, distortion andshrinkage of the structure. If you were to throwa piece of aluminum foil in a campfire, you wouldnotice that it would distort and change shape as itheats up. This is due to the same principle whereinthe temperature differences in the foil causemechanical loads that deform the foil.

In general, warpage, or out-of-plane deformation,is typically fixed during assembly using a jig andafter assembly using thermal or mechanicalrework. Thermal rework is using a heat source, suchas a torch, to deform the overall structureto the proper shape.

Quality weldmentsof thick plates(greater than 10 mm)are paramount tofabricating hullstructures towithstand the rigorsof oceanic shipping.

10Concept To Reality Fall 07 / Winter 08 www.altair.com/c2r

Mechanical rework uses jigs or other mechanicalforces to deform the as-welded structure to the propershape. Both processes can be time-consumingand usually require expert technicians with years ofexperience. In-plane deformation, or shrinkage,cannot be easily fixed during assembly and needs tobe corrected prior to assembly.

Traditional weld analysis methods, using thefinite-element method, are relatively easy to set up,but the computer run time can take days or weeks.

This makes it difficult to make weld planningdecisions since a welding

engineer would need towait a long time

just to un-derstand the effects

of different weld sequences, fixturing or the weldingprocess. As a result, weld engineers typically rely onexperience and engineering judgment.

Over the years, researchers have developedsome simplified analysis methods that can morequickly predict weld-inducedshrinkage and distortion.These methods make severalsimplified assumptions butare able to accurately predictshrinkage and distortiontrends and can be used tobetter plan welding processes.These models run quickly(in minutes vs. days) and canprovide rapid feedback to thewelding engineer that helpshim/her better understandthe effects of welding on theoverall structure.

The challenge with thesemethods is that the setupof the model can be time-consuming and subject tomistakes if done manually.

SHI, working with Altair Engineering, developed asemi-automated analysis setup system that cangenerate and run models in a few hours. Weld analysiscan now be used to positively affect the business ofSHI. This pre-processor enables the company toquickly predict the effect of the weld process andfixturing on the final shape of the welded ship structure.

The system automatically creates the FEA modelfrom the geometry and property information importedfrom the computer-aided design (CAD) model. ThisFEA model, in turn, is used to predict the weld shrink-age and distortion based on the type of weld joints,welding process and plate thickness of the weld region.This is all done with a user-friendly interface thatensures consistency and flexibility.

Macro PowerThe customized welding deformation analysis

pre-processor was built as a series of macros inside theAltair HyperMesh pre-processor, a solver-neutralenvironment with a rich feature set to build and editcomputer-aided engineering (CAE) models. Thetailored HyperMesh pre-processing system interfacesdirectly to SHI’s specialized 3D CAD software andFEA solvers.

With this solution, engineers extract 3D geometryand property information as ACIS and text files,respectively. Meshing and surface editing tools allow

From the3D CAD geometry(above), SHIengineers createquality meshesusing AltairHyperMesh (right).

Reprinted with permission from the

Winter 2008 edition of

11www.altair.com/c2r Concept To Reality Fall 07 / Winter 08

P R O C E S S A U T O M A T I O N

engineers to easily cut and join geometric surfaces tocreate quality meshes critical for analysis. The thick-ness of the plates is extracted from the 3D geometryand property files.

The user can define the type of weld for eachregion (e.g., butt-weld, fillet weld, etc.), the weldprocess and sequence, and the weld dimensions.The system then generates the models with all of theappropriate boundary conditions and input for anaccurate, repeatable analysis. Given that the systemis hosted in HyperMesh, the user has the flexibilityto edit any regions that are not set up properly inunique situations.

Previously, SHI used another pre-processor.However, it lacked the capabilities to successfullyimport geometr ica l ly cor rect ACIS f i le s .HyperMesh’s open architecture allowed Altairengineers to develop custom integrations with theCAD and FE solvers used by SHI.

A Way with WeldingAltair engineers worked closely with SHI to

automate the weld distortion analysis process. Overseveral months, they developed a core program andgraphical user interface specific to SHI’s needs.

They also suggested proper 3D CAD import meth-ods and offered implementation details based on welddeformation analysis algorithms (see Algorithms forWeld Distortion Analysis) and other boundary condi-tions. In addition, they customized the solver analysistemplate to comply with SHI’s request.

With the solution completed, SHI engineerswere able to evaluate welds by followingthree easy steps: establishing the user profile,defining and selecting the process, andrunning the analysis.

The User Profile: Altair developed a newuser profile under the existing menu structure.A simple click of a radio button calls up theMacro Menu.

The Process: Upon clicking the SHI radiobutton, the Instance Manager window opensand shows three main function buttons: NewInstance, Open Instance and Use DefaultHyperMesh. In the case of the Open Instance,all data-like parameters applied during previoussessions remain. Information is recorded intothe metadata of the HyperMesh model files.

Algorithms for WeldDistortion Analysis

Currently, there are two simplified methodologies used for welddistortion analysis. The first is the Equivalent Load Method, or ELM, andthe second is the Strain as Direct Boundary (SDB) method.

The ELM technique adds equivalent mechanical loads on the finite-element nodes and elements in the analysis model to simulate thethermal loads induced after welding. For example, in-plane loads on theboundary edges of the element adjacent to the weld line are added tocapture thermal shrink behavior after butt-welding. Although this methodis well-known in weld distortion simulation, applying the loads on theproper domain with the proper value and direction is a relatively time-consuming process and subject to errors if not done in an automated,repeatable manner.

The SDB method describes weld distortion by thermal contractionthrough the equivalent thermal expansion coefficient and equivalenttemperature difference applied around the weld region. If the heatcoefficient is negative or the temperature difference is negative, then theshrink behavior at the weld line after welding is well-captured. The SDBmethod is relatively easy in that it adds temperature on the selected nodes,but the theory is slightly tricky. The SDB method allows weld sequence tobe modeled, which can be important in determining the final distortedshape of the structure. This also allows users to understand the effects ofdifferent weld sequences virtually.

In the analysis process, finite elements are generated on existing andnewly created surfaces. The ELM method requires one special layer ofperpendicular quad elements to add perpendicular theoretical loads, likeforces and moments, on the node. The SDB method requires two speciallayers near the weld line to add temperatures on the nodes betweenelements of the two layers.

12Concept To Reality Fall 07 / Winter 08 www.altair.com/c2r

P R O C E S S A U T O M A T I O N

The definition phase involves building theFE model by generating finite elements, creating theboundary and load conditions, and defining controlcards. Two files are used for generating the shape geom-etry. The first, Geometry Files, includes the surfaceentity of the initial plate and the line entity of theweld line. The second, Property Files, includes thethickness and material of the plate, type of weld line,shape and material information on structural stiffeners.

What makes the solution unique is that the twofiles are imported into HyperMesh simultaneously,and the proper properties of surfaces and lines areautomatically created. In addition, the geometry ofthe structural stiffeners from the lines is created,and geometry editing at the weld region for properwelding analysis is performed.

Next, welding boundary conditions are applied.Then, load cases are created and applied automati-cally, and the contact definition and the boundarycondition used during analysis are properly made.

Solver: The system generates an input deck forthe solver. It includes all options required forrunning the analysis and is exported without anyfurther debugging.

Being able to virtually simulate the weld deforma-tion analysis process has made a difference at SHI.

Prior to installation, it was impossible to qualita-tively predict the weld distortion of complex parts.

In addition, what used to take 40 hours of manuallabor for structural modeling has been reduced to twoto three hours for the entire process. And, humanerrors have been reduced, resulting in cost savings.What’s more, the system provides visualization of thehidden regions of the welded parts, which may nothave been considered if it were not for the simulation.

The developed weld analysis system is providingsignificant benefits to SHI. Engineers can nowquickly analyze the effects of different weld processes,fixturing, sequencing and postweld rework operationson the final structure. This is resulting in fewer“surprises” that affect rework and other downstreamprocesses and provides more efficient weldingprocesses and better quality ships. It also creates aconsistent framework for implementing weld distor-tion and shrinkage analysis processes throughout theenterprise, which means the tools are accessible tomore engineers and just not the FEA experts.

Heeyoung Heo is Senior Research Engineer, WeldingResearch, Institute of Industrial Technology, Samsung HeavyIndustries. Robert Yancey, Regional Managing Director,Altair Engineering, Inc., was a contributor to this article.

To receive more information about HyperMesh,visit www.altair.com/c2r

or check 02 on the reply card.

Innovation in ActionSamsung Heavy Industries (SHI), with eight worldwide branch offices and two manufacturing subsidiaries, is part of Korea’s SamsungGroup. In 2007, SHI received a record number of orders,surpassing the US$10 billion mark during the first half ofthe year – a milestone among Korean shipbuilders.SHI maintains the world’s No. 1 market share in highvalue-added vessels and has installed the world’slargest offshore facilities off Sakhalin.

In November 2007, SHI delivered to Stena, a Swedishship company, the world’s first drill ship designed to operatein polar regions. The ship is 228 meters long, 42 meters wideand 19 meters high. It can drill as deep as 11 kilometers andoperates in severe weather conditions, including waves of up to16 meters and wind speeds of up to 41 meters per second.

SHI also is a leader in building super-large liquid natural gas (LNG) tankers. It recently delivered the largest LNG ship in theworld, christened TEMBEK, to Qatar Gas. The ship is 217,000 m2

in volume, 303 meters long, 50 meters wide and 27 meters high. Unlike traditional LNG ships that use steam turbine engines, the TEMBEK runs on a low-speed diesel engine.

Reprinted with permission from the

Winter 2008 edition of

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