elliptical

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2023年4月13日发(作者:威斯康星大学麦迪逊分校)

Computer Technology and Application 2(20 1 1)324-328

N umerical and Experimen

l Investigation of an Elliptical

Paraboloid ShelI ModeI

Hamadi Dj amal,Mellas Mekki and Chebili Rachid

Civil Engineering and Hydraulics Department,Faculyt ofSciences and Technology,Biskra University,B.P 07000.A lgeria

Received:November 03,2010/Accepted:November 30,2010/Published:April 25,201 1

Abstract:For practical engineering purpose,a new fiat shell element baptized(ACM

Q4SBE1)is presented in this paper.The

_

formulated element can be used for the ana背景纯音乐 lysis of thin shell structures;no matter how the geometrical shape might beTests on

standard problems have been examined.Since,the nalaysis ofthin shell structures has generally been purely carried out on a theoretical

basis;it is of importance to present some experimental results ofan elliptical paraboloid under uniformly distributed load pressureThe

results obtained from both numerical and experimental work are presented.

Key words:Elliptical paraboloid,finite element,fiat shell element

1.Introduction

In recent years,the analysis of be啥意思 structures has been

element.The quadrilateral shell element used is

obtained by the superposition of the Q4SBE 1

considerably eased by t精字开头的成语 he use of computers programs,

especially those based on the finite element method.In

practice engineers prefer to deal with the structures

analysis by simple finite elements such as triangular

elements with 3 nodes,quadrilateral with 4 nodes or

solids with 8 nodes and with the same number of

degrees of freedom per node.The purpose is to avoid

mistakes which can be made when using complicated

data elements.The application of the finite element

method to the analysis of shells started in the early

1 960’s by replacing the actual curved surface of the

shell by an assembly of triangular or rectangular flat

(Quadrilateral Strain Based Element)membrane strain

based element[5]with the ACM standard plate

bending element【6—71). The performance of the

developed shell element is

evaluated on standard test

problems.

The analysis of thin shell structures has generally

been purely carried out on a theoretical basis and it is of

importance to try to establish the validity of the

theories pounded by comparing their correlation with

experimental results.It will be appreciated that the

numerical analysis exposed in this study has assumed

that the material from which the shell was constructed

is perfectly elastic.In attempting to verify this theory

by experimental test it would be natural to use such a

plate elements[1.4].Intuitively,as the size of the

subdivision decreases it would seem that convergence

perfectly elastic materia1.This would obviously

must occur,and indeed experience indicates such a

convergence.The stiffness matrix of the shell was

approximated by combining the two independent

provide the closest correlation between numericaI and

experimental results.

membranes and bending stiffness matrices of the plate

2.Numeri美国联邦参议员 cal Analysis

Corresponding author:Hamadi Djamal,Ph.D., senior

lecturer,research fields:numerical analysis,finite element

method,

shell

structures

analysis.

E・mail:

2.J,Construction of口New Flat Shell Element

ACM Q4SBE1

The quadrilateral shell element used is obtained by

dhamadiuk@yahoo.corn.

Numerical and Experimental Investigation of an Elliptical ParaboIOid Sh

ell MOdeI

325

the superposition of the Q4SBE 1 membrane strain

based element[5】with the ACM standard plate Y,V

bending element[6—7】.We have obtained a flat element

shell called ACM

_

Q4SBE 1[8】.

2.2 Description ofthe Q4SBE1 Element[51

Fig・1 shows the geometric properties of Q4SBE 1

element,the corresponding nodal displacements

.At

Fig・1 Coordinates and nodal points for the quadrilate

each node(i)the degrees of ̄eedom are Ui nad Vi.

The

displacement fields of the Q4SBE 1 element are given

by the following Eq.

(1):

U=aI。a3 y+a4 x+a5 xy.a

7 Y (R+1)/2+

a8 y/2+a9(x Hy )/2 (1a)

V=a2+a,x。a x。(R ) 2:a y+a xy+0b)

a 8 x/2+al0(Y Hx )/2

with H=2/(1一V),R=2 v/(1.v)

2.3RectangularPlateElement'ACM,

The displacement fields of the ACM element(see

Fig・2)are given by the following Eq.(2):

W(x )=al+a2 x+a3 y+a4 x +a5 xy

+a6 Y +a7

x。十a

8 x2y+a

+al0 Y +aII x3y+a

(a3+a5 x+2a6 y+a8 x +2暑

一~

xy (2a)

l2x),3

L9 xy

+3a1。Y +al1 x +3a1

2 xy)

(2b)

a2+2a4 x+a5 y+3a7

+2a

s xy

+a9 y +3all X2 y+al2 y’

The shell element ACM

_

Q4SBE 1 is composed by

assemblingthetwoelementsQ4SBE1 andACM(seeFig.

31.

The stiffness matrix of the shell element ACM

Q4SBE I is obtained by using the analytical integration

ofthe membrane and bending stiffness matrix

The evaluation of the element stiffness matrix is

summarized with the evaluation of the following weI1

known Eq.(3):

】= ‘‘】r[ [Q r[D】[Q】出 ] 一 】

(3a)

】= 】r 。 一-】

(3b)

With: 。】=IIDr[D][olax

(3c)

raI

element“Q4SBE1”.

Fig.2 Coordinates and nodal points for the rectangular

plate element“ACM”.

Fig・3 The shell element ACM

Q4SBE I.

3.Validation

The performance of the developed shell element is

evaluated on a standard test problems presented in this

section.

3.】Clamped Cylindrical Shell

The clamped cylindrical shell presented in Fig

4(a)

326 Numerical and Experimental Investigation of an Elliptical Paraboloid Shell Model

is selected as a test problem 智取威虎山观后感 in literature.The

geometrical dimensions,loading and elastic properties

are given in Fig.4.Due to symmetry of the cylinder

Table 1 Clamped cylindrical shell,convergence ofWc.

Meshes

ACM

旦!翌 竺! ! !苎

_

Q4SBE1 ACM-SBQ4【1 1】

only 1/8(ABCD)is considered in the finite element

idealizations Fig.4(b).

The results of this analysis are compared to the

analytical solution based on the thin shell structures

(R/h 1oo)given by Flugge[9]and Lindberg et a1.[10】

below:

Wc=一Wc Eh/P=164.24 deflection under load P in

poin怎么进入安全模式 t C only.

VD=一VD Eh/P=4.11 deflection in Y direction.

The results obtained for different meshes are given

inTables l and 2.

The results obtained for both deflections Wc and VD

for the refined mesh(20 x4)are very good compared to

the analytical solution.

3.2 Scordelis-Lo Roof

The next test to be considered which is frequently

Data:

L=6m E:3x1010

SylmH ̄a-y c0lIdi’dD№

Bounda ̄c0l_d出0lI《

W—OY—Ox一0 st ^B

V—Ox-0z一0 ll BC

U=W=0Y=0 atAD

U=OY Oz一0 CD

Fig.4 Clamped cylindrical shel1.

Table 2 Clamped cylindrical shell,convergence of VD. Meshes

Displacement Wc at point C

ACM

_

Q4SBE1 ACM-SBQ4【1 1】

used to test the performance of shell element is that of

Scordelis—Lo roof having the geometry as shown in Fig

5.

The straight edges are free,while the curved edges

are supported on rigid diaphragms along their plan.The

geometrical and mechanical characteristics are given in

Fig.5.

The results obtained by the new formulated element ACM

Q4SBE 1 are compared to the reference values

based on the deep shell theory.The analytical solution

based on the shallow shell theory is given by Scordelis

and Lo[1 2】,which is slightly different from the deep

shell theory.The results obtained for different meshes

are given in Table 3.

4.Experimental Test

Tests on ful1.scale shells are few because the loading

of such structures is difficult and costly.Experimental

investigation of shells therefore usually resorts to

small—scale tests.Hence.the experimental work

described in this study is of this tyDe.

The test model is made of an aluminum alloy in an

elliptical shape and has a constant thickness of 2 mm

with a plan rectangular projection of 880 mm by 400

mm Fig.6,the material properties have been assumed

to be:The modulus ofelasticity E=70.000 N/mm .鬼故事长篇 the

Numerical and Experimental Investigation of an Elliptical Paraboloid Shell ModeI

327

Table 3 Scordelis—Lo roof,convergence of Wc and W B.

Meshes Vertical displacement at point C and B

The mesh size used in numerical analysis

The model is free along the long edges

fixed at

certain points on wooden support along the short edges

Due to the double symmetry in geometry and loading

measuring points are located on one quarter of the area

Data:

of the model at eight points Fig

7.

L=6m;R=3m =0,03m; =400

E=3x10 。Pa;v=0;fz=.0,625x104Pa

5.Numerical and Experimental Results

The vertical deflections resulting from numerical

Bounda ̄conditions: S ̄anmeuy conditions

U=o1r=oz=0 forCD

V=e2c=。z=0 forCB

Reference value(Deep SheH Theory)

WB=-3,61 cm:Wc=0,541 cnl

U=W=8Y=0 forAD

analysis and experimental work for different loading

values are presented in Table 4

6.Conclusions

From the results obtained from the numerical

analysis the following conclusion can be drawn:

Fine relatively meshes lead to almost identical

results thus proving the eficiency of fthe strain based

element.

Analytical solution(ShaIlow SheⅡIheory):

w日=-3,703 cm

Wc=0,525 cm

VA=・0,1513 cnl

U日=-1,965 ClTt

Fig.5 Scordelis-Lo Roof.

Poisson ratio u 0.33.A uniform normal pressure is

applied by covering the shell top surface with a

Excellent agreement is shown between the shell

element ACM_Q4SBE 1 results and those from

pneumatic pressure bag in close contact with it[131. experimental work(in清朝太后 inside points).

Fig-6 The elliptical paraboloid shell undergoing the experimental test

328 Numerical and Experimental Investigation of an Elliptical Paraboloid Shell Model

J L

/ \

J L 2

1 『 ’

+ L二I 6 3

I L

L。 I.暂

'’d

1 .

一 _

,'0

~ 一一山

Fig.7 Dial gauge positions(distance in mm).

Table 4 Vertical displacements W(mm)under different applied Ioadings.

The presented shell element“ACM

Q4SBE 1’’has

_

【61

A.Adini,R.W.Clough,Analysis of plate bending by the

ifnite element method.Report to the Nat.Sci.Found.,

U.S.A..G 7337 1961.

been demonstrated to be robust.effective and usefulin

analyzing thin shell structures.

【7】

【8】

R.J.Melosh.Basis of derivation of matrices for the direct

References

B.E.Green,D.R.Strome,R.C Weikel,Application of the

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initfe elements,Ph.D.Thesis. Civil Engineering

Department,Biskra University,Algeria,2006.

【9】

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M.

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【l3】 D.Hamadi

an elliptical parboloid thin shell structures.Master Thesis.

[5】

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efncient quadrilateral membrane element for civil

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