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Finite Element Analysis and Structure Optimum Design of Lifting Padeye

Zhong-chi Liu 1, a , Bo Zhou 2,b , Soon-Keat Tan 2,c 1Department of Mechanical Engineering, National ni!er"it# of Singapore, Singapore 11$%$&

2Maritime 'e"earch (entre an) School of (i!il an) En!ironmental Engineering, Nan#angTechnological ni!er"it#, Singapore &*+$+ , Singapore

aa $ % .nu"/e)u/"g, b0houbo.ntu/e)u/"g, c(T NSK.ntu/e)u/"g

Keywords: Lifting a)e#e3 4ptimum De"ign3 5inite Element nal#"i" 65E 73 4ff"hore Structure3Shipbuil)ing/

Abstract. The lifting padeyes are widely used in the offshore and shipbuilding industry. The designof lifting padeye requires extremely high safe reliability and economic rationality. Based on finiteelement analysis (FEA) the !ariations of stress and deformation with external force and hoist angleare analy"ed. For minimi"ing cost of steel optimum design models of lifting padeye were built andthe reliability of the optimum design scheme was pro!ed. The results show that the optimum designaccords with structure design principle and the cost of padeye steel reduce notably.

Introduction

#ifting operation is an integral part of any construction ship$building ship$repairing ormanufacturing process. %ith the de!elopment of modern shipbuilding industry the construction

bloc&s of offshore structures and ships are now in the region of hundreds to thousands of tons. 'ormally these hea!y bloc&s can be constructed only by cranes with the aid of slings and shac&leswhich are attached to a number of padeyes built on the structures. As many countries enhance theimportance of %or&place afety and ealth lifting acti!ities has been identified as a *high ris&+operation. #ifting padeyes play a !ery important role in #ifting operation. Therefore high safereliability of padeyes is required,$-.

Another important aspect to pay attention to is the steel consuming of lifting padeyes. n recentyears most of the new ships in large shipyards are ,/ ///$0// /// tons. 1eanwhile the si"e andweight of the hull bloc&s present the macro$scale de!elopment trend. #ifting operations are requiredin all the stages of the construction of macro$scale bloc&s which means the consuming of padeyesincreases notably. According an in!estigation in 2alian hipyard there are 0334 different padeyesused for 5 ships of 46 ///2%T oil tan&er and ,,- ///2%T bul& carrier. The total weight of these

padeye is ,03 tons. n order to reduce the shipbuilding cost optimum design of lifting padeye becomes a !ery important 7ob.

n this paper an attempt was made toward de!eloping a new optimum design scheme of lifting padeyes. 'umerical simulation of lifting padeyes was performed based on finite element analysis.

Simulation of FEA

FEA is an effecti!e tool and has successful application in a lot of scientific fields. n this study padeyes are analy"ed by the finite element code A' 8 . The forms of structural and specificationsof the padeyes 2 are pro!ided in Fig. , and Table ,. n the following study the type 4/ 3/t of

padeyes model 2 is ta&en as an example for the strength chec&. The material of padeye is A T1 A04steel 8oung9s modulus is 5./e,,:a poisson9 ratio is /.0 and yield stress is 5-/1:a.

Advanced Materials Research Vol. 658 (2013) pp 399-403Online available since 2013/Jan/25 at www.scientific.net © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.658.399

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net . (ID: 177.192.144.214-21/03/13,01:04:47)

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Fig., The structural forms and FE1 model of 2 padeye

Table , The specifications of 2 padeyes

ustainable loads ;tpecifications ;mm

T, B < a < F T 0 < b T5 h b

0/ =/ 0/ 5>/ 5>/ =/ ,=/ ,4/(,=/) ,/ ,=/ 54/=/ -/ 0/ 0- 0,/ 0,/ =- ,-- ,3-(,--) ,>$5- ,,/ ,> ,-- 56/

-/ 4/ 0/ 0- 0=/ 0=/ -/ ,3/ ,6/(,3/) ,>$5- ,5/ 55 ,3/ 05/

4/ 3/ 0/ 0- 03/ 03/ -- ,>- 5/-(,>-) 55$0/ ,0> 55 ,>- 0-/

The padeye bottom is constrained. The external force 4/t is applied on padeye model. The resultsare illustrated in Fig.5 and Table 5. All the results are shown in a cylindrical coordinate system theorigin of which is the center of pin hole and the !ertical direction is along the thic&ness of padeye.The maximum stress is in the internal surface of padeye pin hole. The radial stress is compressi!estress and the tangential stress is tensile stress.

2isplacement Equi!alent stress

<adial stress Tangential stress

Fig.5 <esults of FE1

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Table.5 2isplacement extremes and stress extremes

2isplacement;m

<adial stress;1:a

Tangential stress;1:a

?ertical stress;1:a

E@? stress;1:a

/.336E$/= $,,/ 4/ $05 ,/3 $,0 04 ,5-

Optimum Design of Lifting Padeye

n modern structural design optimum methods play an increasingly important role. tructuraloptimi"ation design is basically a decision procedure based on different design requirements. n thedesign process a set of decision criteria which are then used to e!aluate possible design results isimposed 4$>.

,) ?ariables of optimum design2esign !ariables2esign !ariables form the decision (design) space of an optimum design. Any set of !ariables

which defines the design of a structure represents a point in the decision space. The design !ariablesof this study are the specification of padeyes as shown in Table ,. The parameters T, T5 T0 <a <b

and B is ta&en as design !ariables where other parameters are set as B 5< 5F 5h.onstraints in optimum structural designonstraints are the restrictions placed on a design. Each constraint will be influenced by one or

more design !ariables. The onstraints of this study are the allowable stress of padeye. As the stressfactor is /.43 the allowable stress is ,4>1pa6.

Cb7ecti!e functionsCb7ecti!e (cost criterion) function is a function of design !ariables. t is the merit measurement

(criterion) of a design. To better utili"e materials and reduce costs of a structure structural weight can be chosen as the ob7ecti!e function. The ob7ecti!e functions of this study are structural weight.

5) Cptimum methodsTwo commonly used optimum methods are the ub$problem Approximation 1ethod ( A1) and

the First Crder 1ethod (FC1). The A1 can be described as an ad!anced "ero$order method in thatit requires only the !alues of the dependent !ariables and not their deri!ati!es. ompared to the

A1 the FC1 is seen to be more computationally demanding and more accurate. owe!er highaccuracy does not always guarantee the best solution. ere are some situations to watch out forD t is

possible for the FC1 to con!erge with an infeasible design. n this case it has probably found a localminimum or there is no feasible design space. f this occurs it may be useful to run a subproblemapproximation analysis which is a better measure of full design space. Also you may try generatingrandom designs to locate feasible design space (if any exists) then rerun the FC1 using a feasibledesign set as a starting point.

results of optimum design?ariables cur!es of A1 are shown in Fig.0. According to the new !ariables range of A1

padeyes are optimally designed with FC1 again and !ariables cur!es are shown in Fig.=. Among alle!aluated configurations the best designs of different methods are shown in table.0.

ur!es of !olume ur!es of T , T5 and T 0 ur!es of < a < b and B

Fig.0 ur!es of A1

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ur!es of !olume ur!es of T , T5 and T 0 ur!es of < a < b and B

Fig.= ur!es of secondary FC1

Table.0 The optimum designs of different methods

2esign B ; m < a ; m < ; m T , ; m T 5 ; m T 0 ; m ?olume;mnitial design 0.3/E$/, -.-/E$/5 ,.0>E$/, 0.-/E$/5 5.5/E$/5 0.//E$/5 >.6-E$/0

A1 0./>E$/, -./,E$/5 ,./0E$/, 5./=E$/5 ,.>6E$/5 0./0E$/5 =.55E$/0FC1 0.05E$/, -.-/E$/5 ,.,>E$/, 5.00E$/5 5./3E$/5 5.0/E$/5 -./3E$/0

econdary FC1 0./-E$/, -./>E$/5 ,./=E$/, 5.,5E$/5 ,.6/E$/5 5.30E$/5 =./6E$/0

0) The safe reliability of final designAccording to the result of optical analysis and real thic&ness situation of steel plate the final

design is built and shown in table.=. The safe reliability of final design is chec&ed with FE1 andresult is shown in Table.-. t can be seen that the stresses of final design is less than the allowablestress ,4>1pa. The results show that the optimum design scheme accords with structure design

principle.

Table.= The specifications of final design2esign B ; m < a ; m < ; m T, ; m T5 ; m T0 ; m ?olume;m

Cptimun design 0./-E$/, -./>E$/5 ,./=E$/, 5.,5E$/5 ,.6/E$/5 5.30E$/5 =./6E$/0Final design 0.//E$/, -./E$/5 ,./-E$/, 5.5E$/5 ,.6/E$/5 5.6E$/5 =.55E$/5

Table.- 2isplacement extremes and stress extremes of final design

2isplacement;m

<adial stress;1:a

Tangential stress;1:a

?ertical stress;1:a

E@? stress;1:a

,.,4E$/= $,03., ,4-./ 4/.3 ,4,.5

ConclusionsBased on external force analysis FEA models of padeyes are set up. The final optimi"ation designsa!es -/ of the cost of steel and the strength also accords with structure design principle. Based onsome conser!ati!e assumptions and formulae most of the traditional padeyes are o!er$designed andtherefore more costly for fabrication. %ith the de!elopment of new methods (such as FEA) thetraditional padeyes can be optimally designed. t should be noted that the security and economy forthe optimum design of padeyes can be promoted notably. The proposed method presents a !aluablereference for the analysis of similar structures.

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Materials and Manufacturing Research 10.4028/www.scientific.net/AMR.658

Finite Element Analysis and Structure Optimum Design of Lifting Padeye 10.4028/www.scientific.net/AMR.658.399