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Transcript of 1 PSSC 1998. 10. 13. Mode Localization in Multispan Beams with Massive and Stiff Couplers on...
1
PSSC 1998. 10. 13.
Mode Localization in Multispan Beams with Massive and Stiff Couplers on Supports
Dong-Ok Kim and In-Won Lee
Department of Civil Engineering in
Korea Advance Institute of Science and Technology
2
CONTENTS
Introduction Definition of mode localization Literature Survey Objectives
Theoretical Background Multispan Beams Simple Structure Occurrence of Mode Localization Conditions of Significant Mode Localization
Numerical Examples Mode Localization in Two-Span Beam
Conclusions
3
INTRODUCTION
Definition of Mode Localization– Under conditions of weak internal coupling, the mode
shapes undergo dramatic changes to become strongly localized when small disorder is introduced into periodic structures. (C. Pierre, 1988, JSV)
• Trouble by Mode Localization– When mode localization occurs, the modal amplitude o
f a global mode becomes confined to a local region of the structure, with serious implication for the control problem. (O. O. Bendiksen, 1987, AIAA)
4
Introduction
• Example : Mode Localization of Two-Span Beam
Figure 1. Weakly Coupled Simply Supported Two-Span Beam
Figure 2. Non-Localized First Two Mode Shapes
Figure 3. Localized First Two Mode Shapes
5
Introduction
• Example : Mode Localization of Parabola Antenna
Figure 4. Simple Model of Space Parabola Antenna
6
Introduction Mode Localization of Parabola Antenna
Figure 5. Non-Localized Mode Shape
Figure 6. Localized Mode Shape
7
Introduction
Literature Survey
• Localization of electron eigenstates in a disordered solid
– P. W. Anderson (1958)
• Mode localization in the disordered periodic structures
– C. H. Hodges (1982)
• Localized vibration of disordered multispan beams
– C. Pierre (1987)
• Influences of various effects on mode localization
– S. D. Lust (1993)
• Mode localization up to high frequencies
– R. S. Langley (1995)
8
Introduction
Objective:To study influences of the stiffness and mass of coupler on mode localization
• Scope• Theoretical Background:
Qualitative analysis using simple model
• Numerical Examples:Verifications of results of the theoretical background using multispan beams
• Conclusions
9
THEORETICAL BAGROUND
Multispan Beams
Figure 7. Simply supported multispan beam with couplers.
- Periodically rib-stiffened plates or
- Rahmen bridges
• Two-span beam : Two substructures and one coupler
Figure 8. Simply supported two-span beam with a coupler.
10
Theoretical Background
Simple Structure Analysis
Figure 9. Simple model with two-substructures and a coupler.
• Subject : Qualitative analysis of influences of stiffness and mass of coupler on mode localization using simple model
11
Theoretical Background
• Eigenvalue Problem
0
0
0
0
0
3
2
1
354343
4242
3131
y
y
y
mkkkkk
kmkk
kmkk
• Equation for ratio of and , and
2
1
21
2
143
2
24
1
23
3543
11)(
y
y
my
y
mkk
m
k
m
kmkkk d
1
31)1(
m
kk
2
42)2(
m
kk
2y1y )2()1( d
where
The ratio represents degree of mode localization corresponding mode.
(1)
(2)
12
Theoretical Background
Occurrence of Mode Localization
where
rsrsr 21
4
31 k
ks
2
1
3
42 m
m
k
ks
dmkkkkk
m )( 354343
1
1
2
y
yr • Equation for Degree of Mode Localization
and
(3)
• In Equation (3)Left-hand side : Parabolic curve
Right-hand side : Line passing origin with slop
(4)
13
Theoretical Background
• Graphical Representation
Figure 10. Two curves.
f
r
))(( 21 srsrf p
rfl
1s 2s1r
2r
– Steep line
Significant mode localization
1
1,0 21 rr
– Identical substructures: )2()1(
No mode localization
0
1,1 21 rr
14
• Delocalization condition
or
• Classical condition ( ) :
• Becoming and , under the condition of
results in significant mode localization, .
Theoretical Background
Conditions for Significant Mode Localization
1||
43
35
kk
mk
143
5 kk
k
)2()1()2()1(
1||
03 m
3
5433543 0
m
kkkmkkk
(6)
(5)
(7)
15
NUMERICAL EXAMPLES
Mode Localization in Two-Span Beam
• Assumptions– All spans have identical span lengths initially.
– Length disturbances are introduced into the first span only.
Figure 11. Simply Supported Two-Span Beam with a Coupler
• Subjects to Discuss– Influences of length disturbance of a span
– Influences of the stiffness and the mass of coupler
16
Mode Localization in Multispan Beams
%41 L
0.20K 0.0J
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
0.0K 02.0J 0.20K 02.0J
Figure 12. First ten mode shapes:
• Selected Mode Shapes of Two-Span Beam
17
Mode Localization in Multispan Beams
• Measure of Degree of Mode Localization
Classical Measure– Span response ratio
b
aba y
yr ,
ay
by
a
b
: Maximum amplitude of span
where
Note !
Classical measure is good for analysis but not for practice.
: Maximum amplitude of span
(8)
18
Mode Localization in Multispan Beams
: Total number of spans
1
T
CTL N
NND
TN
CN
jy j: Maximum amplitude of span
Note !
Proposed measure is good for practice but not for analysis.
where
: Number of spans in which vibration is confined1
1
2
2
1
TT N
jj
N
jjC yyN
(9)
(10)
Proposed Measure– Normalized number of spans having no vibration
19
Mode Localization in Multispan Beams
Figure 13. Influence of the stiffness
0 2 4 6 8 10
M ode N um ber
0.0
0.2
0.4
0.6
0.8
1.0
Deg
ree
of M
ode
Loca
lizat
ion
%5.0,100 1 LKC
%0.1,100 1 LKC
%0.1,1000 1 LKC
%5.0,1000 1 LKC
• Coupler with Stiffness
• Stiffness makes the system sensitive to mode localization
20
0 2 4 6 8 10
M ode N um ber
0.0
0.2
0.4
0.6
0.8
1.0
Deg
ree
of M
ode
Loca
lizat
ion
Mode Localization in Multispan Beams
Figure 14. Influence of the mass
%5.0,1.0 1 LJC
%0.1,1.0 1 LJC
%0.1,0.1 1 LJC
%5.0,0.1 1 LJC
• Coupler with Mass
• Mass makes the system sensitive to mode localization in higher modes.
21
0 2 4 6 8 10
M ode N um ber
0.0
0.2
0.4
0.6
0.8
1.0
Deg
ree
of M
ode
Loca
lizat
ion
Mode Localization in Multispan Beams
Figure 15. Influences of stiffness and mass
%5.0,1.0,100 1 LJK CC
%0.1,1.0,100 1 LJK CC
%0.1,0.1,1000 1 LJK CC
%5.0,0.1,1000 1 LJK CC
• Coupler with Stiffness and Mass
• Stiffness governs sensitivities of lower modes.
• Mass governs sensitivities of higher modes.
• Delocalized modes can be observed.
22
CONCLUSIONS
Influences of the Coupler are Discovered.– The stiffness of coupler makes the structures sensitive
to mode localization.
– The mass of coupler makes the structures sensitive to mode localization in higher modes.
– The coupler with stiffness and mass is a cause of delocalization* in some modes.
* Delocalization is that mode localization does not occur or is very weak in certain modes although structural disturbances are severe.
• The mass as well as the stiffness of coupler give significant influences on mode localization especially in higher modes.