Piezoelectric Shunt Damping
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Transcript of Piezoelectric Shunt Damping
Damping with Piezoelectric MaterialsMohammad Tawfik
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Damping with Piezoelectric Material
Mohammad Tawfik
Damping with Piezoelectric MaterialsMohammad Tawfik
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Objectives
• General Introduction to smart materials and structures
• Recognize the nature of piezoelectric material
• Understand the use of passive shunt circuits
• Dynamics of structures with shunt piezoelectric materials
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Smart Structures
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Smart Structures: What?
• Controlled change in properties– Change in mechanical properties– Change in geometry
• Energy Converters!
– Mechanical Electrical (Piezoelectric)
– Heat Mechanical (SMA)– Mechanical Heat (Viscoelastic)– Etc…
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Smart Structure: Why?
• Vibration Damping
• Shape Control
• Noise Reduction
• Vibration/Damage Sensing
• Heat Sensing
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Smart Structures: Classification
Wada, Fanson, and Crawly
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Piezoelectric Materials
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What is Piezoelectric Material?
• Piezoelectric Material is one that possesses the property of converting mechanical energy into electrical energy and vice versa.
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Piezoelectric Materials
• Mechanical Stresses Electrical Potential Field : Sensor (Direct Effect)
• Electric Field Mechanical Strain : Actuator (Converse Effect)
Clark, Sounders, Gibbs, 1998
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Conventional Setting
Conductive Pole
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Piezoelectric Sensor
• When mechanical stresses are applied on the surface, electric charges are generated (sensor, direct effect).
• If those charges are collected on a conductor that is connected to a circuit, current is generated
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Piezoelectric Actuator
• When electric potential (voltage) is applied to the surface of the piezoelectric material, mechanical strain is generated (actuator).
• If the piezoelectric material is bonded to a surface of a structure, it forces the structure to move with it.
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Other types of Piezo!
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1-3 Piezocomposites
T 3=cE
33S 3+e33E 3
D3=e33S 3+εS
33E3
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Active Fiber Composites (AFC)
ceff
11=c
E11
+v pe31
2
(vC ε 33+vp ε
S33)
eeff
31=ε33e31
vC ε33+vpε
S33
εeff
33=ε33 ε
S33
(vC ε33+vp ε
S33)
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Applications of Piezoelectric Materials in Vibration Control
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Collocated Sensor/Actuator
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Self-Sensing Actuator
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Hybrid Control
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Passive Damping / Shunted Piezoelectric Patches
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Passively Shunted Networks
Resonant
Capacitive Switched
Resistive
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Adaptive Structures
Wada, Fanson, and Crawly
Passive Networks
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How does it work?
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Shunted Piezoelectric Material (Physical)
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Shunted Piezoelectric Material (Physical)
•Mechanical energy is converted to electrical energy through piezoelectric effect•Electric charge is driven by potential difference through the circuit•Energy is dissipated in the resistance
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Shunted Piezoelectric Material (Electric)
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Shunted Piezoelectric Material (Energy)
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Mechanical Impedance / Viscoelastic Analogy
Z11RES
=1−k31
2
1+iρ3
Z11RSP=1−k 31
2 δ2
γ 2+δ 2rγ+δ2
Resistor Shunt
R-L Shunt
r=RC ωn (dissipation tuning parameter )
γ=sωn
( complex non-dimensional frequency )
δ=ωe
ωn
( resonant shunted piezoelectric frequency tuning parameter )
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Viscoelastic analogy
• The model of the shunted piezoelectric patches, in many researches, is reduced to an equivalent of a viscoelastic patch.
• But Piezoelectric patches are elements that respond to the total strain rather than the local strain!
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The Problem With Viscoelastic Analogy!
Base structure
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Modeling of Piezoelectric Structures
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Constitutive Relations
• The piezoelectric effect appears in the stress strain relations of the piezoelectric material in the form of an extra electric term
• Similarly, the mechanical effect appears in the electric relations
S=s11T +d 31E
D=d 31T 1+¿33E
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Constitutive Relations
• ‘S’ (capital s) is the strain• ‘T’ is the stress (N/m2)• ‘E’ is the electric field (Volt/m)• ‘s’ (small s) is the compliance; 1/stiffness
(m2/N)• ‘D’ is the electric displacement, charge per
unit area (Coulomb/m)• Electric permittivity (Farade/m)¿
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The Electromechanical Coupling
• d31 is called the electromechanical coupling factor (m/Volt)
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Manipulating the Equations
D=QA
D=1A∫ Idt=
IAs
• The electric displacement is the charge per unit area:
• The rate of change of the charge is the current:
• The electric field is the electric potential per unit length: E=
Vt
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Using those relations:
• Using the relations:
• Introducing the capacitance:
• Or the electrical admittance:
S=s11T +d 31
tV
I=Ad 31 sT 1+A∈33 s
tV
I=Ad 31 sT 1+CsV
I=Ad 31 sT 1+YV
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For open circuit (I=0)
• We get:
• Using that into the strain relation:
• Using the expression for the electric admittance:
V=−Ad 31 s
YT 1
S=s11T−Asd 31
2
tYT 1
S=s11(1−d 31
2
¿33 s11)T 1
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The electromechanical coupling factor
• Introducing the factor ‘k’:
• ‘k’ is called the electromechanical coupling factor (coefficient)
• ‘k’ presents the ratio between the mechanical energy and the electrical energy stored in the piezoelectric material.
• For the k13, the best conditions will give a value of 0.4
S=s11(1−k312 )T 1
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Different Conditions
• With open circuit conditions, the stiffness of the piezoelectric material appears to be higher (less compliance)
• While for short circuit conditions, the stiffness appears to be lower (more compliance)
S=s11(1−k312 )T 1 == sDT 1
S=s11T=sET
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Different Conditions
• Similar results could be obtained for the electric properties; electric properties are affected by the mechanical boundary conditions.
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Damping of Structural Vibration with Piezoelectric Materials and
Passive Electrical NetworksN. W. HAGOOD AND A. VON
FLOTOWJournal of Sound and Vibration (1991)
146(2), 243-268
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The Constitutive Relations for Piezoelectric Materials
• The constitutive relation is:
• Where:
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Constitutive relation (cont’d)
• The electric permiativity:
• Electromechanicalcoupling:
• Mechanicalcompliance:
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Electrical relation
• Into constitutive relations:
• Where the capacitance is:
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The Electric admittance
• Introducing the electric admittance:
• Generally; with a shunt circuit:
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The Electromechanical Model
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Remember
• The electric admittance is the reciprocal of the electric impedance.
• Also, you may have up to three circuits:
Z EL=1
Y EL
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From Constitutive Relations
• The voltage may be written as:
• Into the strain equation
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The Electromechanical Compliance
• The Electromechanical Compliance
• Or
• Where
• Generally:
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The Mi matrices
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Uniaxial Loading Cases
• The compliance:• Introducing the
electromechanical coupling coefficient:
• The compliance becomes:
• For open circuit conditions
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Uniaxial Loading Cases
• For open circuit, the compliance becomes:
• A similar expressions for capacitance in case of zero stress is:
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Uniaxial Loading Cases
• Introducing the mechanical impedance:(Which is the reciprocal of the compliance)
• We may write the non-dimensional mechanical impedance:
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The Complex Modulus
• Now, let’s reintroduce the complex modulus of the viscoelastic material:
• Where:
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Resistive Shunt Example
• For the case or resistive shunting, the resistance and the capacitance are in parallel 1
Z EL=
1
ZD+
1
Z SU=Cs+
1R
=RCs+1
R
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Resistive Shunt Example
• Recall:
• Using the previous results:
• Simplifying:
Z jjME
=Z jjRES
=1−k ij
2
1−k ij2( RCs
1+RCs )
Z jjRES
=1−k ij
2
1+(1−k ij2 )RCs
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Resistive Shunt Example
• Substituting s=iω and
• Introducing the non-dimensional parameter ρ=RCω, we get:
• Finally:
Z jjRES=1−
k ij2
1+(1−k ij2 ) ρi
=1−k ij
2
1+(1−k ij2 )
2ρ2
+k ij
2 (1−k ij2) ρi
1+(1−k ij2 )
2ρ2
Z jjRES
=(1−k ij
2
1+(1−k ij2)
2ρ2 )(1+
k ij2 ρ
1+(1−k ij2 ) ρ2
i)
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Resistive Shunt Example
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10
E Current
Eta Current
E von Flotto
Eta von Flotto
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Homework #11
1. Derive the equations for the RL shunt circuit.
2. Plot the frequency response of piezoelectric bar with a shunt circuit (R & RL)
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RL Shunt Example
• For the case or RL shunting, the resistance and the inductance are in series and are in parallel with the capacitance
1
Z EL=
1
ZD+
1
Z SU=Cs+
1Ls+R
=LCs2+RCs+1
Ls+R
Z EL=LCs2+RCs
LCs2+RCs+1
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RL Shunt Example
• Recall:
• Using the previous results:
• Simplifying:
Z jjME
=Z jjRSP
=1−k ij
2
1−k ij2( LCs2+RCs
LCs2+RCs+1)
Z jjRSP=
(1−k ij2 )(LCs2+RCs+1)
1+(1−k ij2 )(LCs2+RCs )
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RL Shunt Example
• Ignoring (1-k2) in the denominator:
Z jjRSP=1−k ij
2
ωe2
ωn2
s2
ωn2+ωe
2
ωn2RC ωn
sωn
+ωe
2
ωn2
Z jjRSP=1−k ij
2 δ 2
γ2+δ2 rγ+δ 2
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RL Shunt Example
Z jjRSP=
(1−k ij2 )( s
2
ωe2+RC
ωn
ωn
s+1)1+(1−k ij
2 )( s2
ωe2+RC
ωn
ωn
s)• Using the full
term:
Z jjRSP=
(1−k ij2 )( s
2
ωn2+ωe
2
ωn2RC
ωn
ωn
s+ωe
2
ωn2 )
ωe2
ωn2+(1−k ij
2)( s2
ωn2+ωe
2
ωn2RC
ωn
ωn
s)Z jjRSP=
(1−k ij2 )(γ 2+δ2rγ+δ2 )
δ2+(1−k ij
2 )(γ2+δ2 rγ )
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RL Shunt Example: Hagood results
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Comparing results
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Modulus of Elasticity
• Recall that:
• And:
• Where:
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Modulus of Elasticity
• Substituting:
• Getting the stiffness:
• Simplifying:
s jjSU=
A j
Z jjSU L j s
E jjSU
=Z jjSU L j s
A j
=Z jj
DZ jjME L j s
A j
E jjSU
=Z jj
ME
s jjD
=Z jj
ME
s jjE (1−k ij
2 )
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Finite Element Model
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Recall
• Recall the constitutive relations of Piezoelectric materials:
• Rearranging the terms:
S1=s11T 1+d 31 E3
D3=d 31T 1+¿33E3
T 1=1
s11
D S1−h31 D3
E3=−h31S 1+1
¿33SD3
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Where:
h31=d 31
s11 ∈33(1−k312 )
¿33s =¿33(1−k 31
2 )s11D=s11(1−k 31
2 )
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Potential Energy
• Writing the expression for the potential energy of the shunted piezoelectric material:
U=12∫0
l
S 1T 1 Adx+12∫0
l
D3E 3Adx
U=12∫0
l
S 1( S1
s11D−h31D3)Adx+ 1
2∫0
l
D3(−h31 D3+D3
¿33S )Adx
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The interpolation functions
u ( x )=(1− xl )u1+( xl )u2=⌊N ( x ) ⌋{ue}
d ( x)=(1−xl )d 1+( xl )d 2=⌊N (x) ⌋ {d e}
S1 (x )=du ( x)dx
=(−1l )u1+(1
l )u2=⌊N x ( x)⌋ {ue }
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The Stiffness Matrices
k e=1
s11D∫
0
l
{N x}⌊ N x ⌋ Adx
k D=1
¿33S ∫
0
l
{N }⌊N ⌋Adx
k eD=−h31∫0
l
{N x}⌊N ⌋Adx
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Kinetic Energy
T=12∫0
l
ρ u2Adx
me= ρA∫0
l
{N }⌊N ⌋dx
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External Work
W=∫0
l
VDbdx=∫0
l
(L I+RI )Dbdx=∫0
l
(LQ+RQ )Dbdx
¿∫0
l
A ( L D+R D )Dbdx
mD=AbL∫0
l
{N }⌊N ⌋dx cD=AbR∫0
l
{N }⌊N ⌋dx
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Element Equation
[me 0
0 mD ]{ueD e
}+[0 00 cD ]{
ueDe
}+[ k e k eDkDe kD ]{ueDe
}={ f0 }