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
一
x。十a
8 x2y+a
+al0 Y +aII x3y+a
。
(a3+a5 x+2a6 y+a8 x +2暑
一~
q
xy (2a)
l2x),3
L9 xy
+3a1。Y +al1 x +3a1
一
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”.
I
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
气
J L
-
/ \
1
8
—
1
J L 2
8
C
1 『 ’
J
+ L二I 6 3
4
墨
1
I L
I
l
L。 I.暂
'’d
墨
1 .
S
一 _
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
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