CILAMCE 2016 - plenary lecture BONTEMPI

Piezoelectric Energy Harvesting
under Airflow Excitation:
Numerical Modeling and Applications
Franco Bontempi*, Francesco Petrini, Konstantinos Gkoumas
PhD, PE, Professor of Structural Analysis and Design
School of Engineering
University of Rome La Sapienza
Rome - ITALY
1

Design Complexity
(Optimization)
Loosely – Tightly Couplings (Interactions)
Nonlinear–Linear
Behavour
4

Index of words
5
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about
flow induced vibrations
6
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Collar’s Triangle of Forces (1)
Aerodynamic
(Fluid)
Elastic
(Structure)
Inertia
(Dynamic)
7

Aeroelastic
Problems
Stability
Response
Aeroelastic
static
stability
Aeroelastic
dinamic
stability
Static
aeroelastic
response
Dynamic
aeroelastic
response
0 EA
0 EFA
0 EIA
0 FEIA
Torsional
Divergence
Galloping
Flutter
Buffeting
Vortex
Shedding
Collar’s Triangle of Forces (2)
8

Classification:
after Naudascher / Rockwell
9

Sources of excitation:
from where energy is coming
• The following material distinguishes three
types:
1. Extraneously-Induced Excitation (EIE)
(externally from fluid);
1. Instability-Induced Excitation (IIE)
(from instability);
1. Movement-Induced Excitation (MIE)
(from movement of object).
11

Extraneously-Induced Excitation (EIE)
• Extraneously induced excitation (EIE) is caused by
fluctuations in flow velocities or pressures that are
independent of any flow instability originating from the
structure considered and independent of structural
movements except for added-mass and fluid-damping
effects.
• Examples are the bluff body being ‘buffeted’ by turbulence of
the approach flow (buffeting).
• The exciting force is mostly random in this category of
excitation, but it may also be periodic. A case in point is a
structure excited by vortices shed periodically from an
upstream cylindrical structure. In either case, the vibration is
sustained by an extraneous energy source. 12

• Instability-induced excitation (IIE) is brought about by a
flow instability. As a rule, this instability is intrinsic to the
flow system: in other words, the flow instability is inherent
to the flow created by the structure considered.
• Examples of this situation are the alternating vortex
shedding from a cylindrical structure.
• The exciting force is produced through a flow process (or
flow instability) that takes the form of local flow oscillations
even in cases where body or fluid oscillators are absent. The
excitation mechanism can therefore be described in terms of
a self-excited ‘flow oscillator’.
(Note that the flow rather than the body or fluid oscillator is
self-excited in this instance in contrast to cases of MIE)
Instability-Induced Excitation (IIE)
13

Movement-Induced Excitation (MIE)
• Movement-induced excitation (MIE) is due to fluctuating
forces that arise from movements of the vibrating body or
fluid oscillator.
• Vibrations of the latter are thus self-excited (flutter /
galloping).
• If the air- or hydrofoil is given an appropriate disturbance in
both the transverse and torsional mode, the flow will induce
a pressure field that tends to increase that disturbance.
• This situation can be described in terms of a dynamic
instability of the body oscillator which gives rise to energy
transfer from the main flow to the oscillator.
14

16
<-Energyisintroduced
inthesystem

Vortexsheddingregimes(Blevins,1992)
18
IIE

against
22
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Analisinonlineareevolutivadelpontestrallato(strutturanominale)per
unaassegnatacondizionedicarico.
(a)Modellodelponte.(b)Evoluzionedellaconfigurazionedeformata.
Distribuzionedellafessurazionealcollasso(arearetinata):(c)
impalcatoe(d)antenne.(e)Decompressionedeiconci
dell’impalcato.(f)Perditaditrazioneneglistralli.
a
b
c
d
e
f
34

Argand’s diagram of the first Vibration Modes
35

Critical Mode for flutter U = Ucr = 155 m/s
36

toward
37
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Energy Harvesting
• This term means the process of extracting energy from
the surrounding environment and converting it in
consumable electrical energy.
• This process, which originated from windmill and water
wheel, is currently having a great development as an
autonomous energy source for a wide variety of
applications.
• There are a various forms of energy that can be
scavenged: thermal; electromagnetic; mechanical: from
motion or vibrations; solar and light energy; energy from
wind or wave; acoustic; energy from pressure gradients.
38

Extraction systems
Magnetic Induction
Electrostatic
Piezoelectric
Photovoltaic
Thermal Energy
Radiofrequency
Radiant Energy
Resources
Sun
Water
Wind
Temperature differential
Mechanical vibrations
Acoustic waves
Magnetic fields
…
Energy Harvesting (EH) can be defined as all those processes
that allow to capture the freely available energy in the
environment and convert it in (electric) energy that can be used
or stored.
Harvesting Conversion
Use
Storage
Energy harvesting - Overview
39

Macro-scale Energy Harvesting
• MACRO-SCALE: generally with macro-scale energy
harvesting is intended the energy production for
supplying the electrical grid.
• The produced energy is commonly known as
renewable energy (the current exploitation of the
energy sources does not affect their availability in
the future).
• Geothermal, hydroelectric, solar thermal, marine
and wind energy are examples of renewable types
of energy.
• Currently the produced energy is in the range of
MWs.
47

Meso-scale Energy Harvesting
• MESO-SCALE: it is possible to define as EH on
meso-scale all those applications that have as an
objective the supply of power to systems
otherwise powered by the electrical grid.
• The energy produced in excess could supply the
electrical grid.
• The energy sustainability of houses, structures and
infrastructures provides an example of meso-scale
EH implementation.
• Currently, the produced energy is in the range of
W/kWs.
48

Micro-scale Energy Harvesting
• MICRO-SCALE: micro-scale EH aims to the
powering of sensors or other small electronic
devices, including those based on MEMS (Micro
Electronic Mechanical Systems) that require small
amounts of energy.
• The objective is the elimination of traditional wire
connections (in the case of sensors) and to provide
an alternative to traditional limited energy
sources (e.g. batteries).
• Currently the produced energy is in the range of
µW/mW.
49

an advanced autonomous sensor for the
temperature sensing in building HVAC (Heating,
Ventilation and Air Condition) systems
Dynamic responsive website based on the bootstrap framework:
www.piezotsensor.eu
50

why/where
extract energy
51
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Smart Building
• This term has been introduced in the last two decades to express
the concept of using networking devices and equipment in
buildings, also towards their energy efficiency.
• In the second half of the 1970s it was used to indicate a building
that was built using a concept of energy efficiency, while in
1980s, the term evolved to indicate a building that could be
controlled from a house PC.
• Currently, smart buildings build on these concepts are integrating
them with additional subsystems for managing and controlling
renewable energy sources, house appliances and minimize
energy consumption using most of the times a wireless
communication technology.
52

Component of Smart Building
• Sensors: used for monitoring and submitting messages
in case of changes;
• Actuators: used for performing a physical action;
• Controllers: for controlling units and devices based on
programmed rules set by the user;
• Central unit: for enabling the programming of different
units in the system;
• Interface: used for the user communication with the
system;
• Network: used for the communication between units;
• Smart meter: devices that provide a two-way
communication and remote reading.
53

Applications for the energy sustainability:
energy harvesting in smart buildings
• EH devices are used for powering remote monitoring sensors (e.g. temperature
sensors, air quality sensors), also those placed inside heating, ventilation, and air
conditioning (HVAC) ducts. These sensors are very important for the minimization of
energy consumption in large buildings
Imagecourtesyofenocean-alliance
http://www.enocean-alliance.org
54

an advanced autonomous sensor for the temperature sensing in
building HVAC (Heating,Ventilation and Air Condition) systems55

Proposal of space technology transfer for the design, testing, production and
commercialization of a self-powered piezoelectric temperature and humidity sensor
(PiezoTSensor), for the optimum energy management in building HVAC (Heating, Ventilation and
Air Condition) systems.
PiezoTSensor©
Operating flow velocity range 2-6 m/s
56

Essentially, piezoTsensor consists in an Energy Harvesting
(EH) device that uses a piezoelectric bender and an
appropriate customizable aerodynamic fin that takes
advantage of specific air flow effects (principally Galloping
and Vortex Shedding) for producing energy. The sensor is
completed with a temperature probe.
piezoTsensor – overview
piezoTsensor scheme
a. Steel plate (support)
b. Sensor transmitter module
c. Piezoelectric bender
d. Fin
e. Temperature probe
57

Piezo energy harvesters drawback
58

AVOID THE DRAWNBACK: by setting the aerodynamic fin to undergo in VS regime
one can obtain the maximum efficiency in terms of energy extraction
Advantages from the vortex shedding effect
A body, immersed in a current flow,
produces a wake made of vortices that
periodically detach alternatively from
the body .
For value of vortex shedding frequency
near to the natural oscillation object
frequency fn, the frequency f of the
exciting force is controlled completely
by the body vibration.
59

The Scruton Number
The Scruton Number is a
dimensionless number that
represents how the mass and
damping affect the lock-in
phenomenon:
By increasing the Scruton Number, it
was found a reductions in maximum
amplitude and width of the lock-in
range.
2
2
D
m
SC



Meier–Windhorst(1939)
AVOID THE DRAWNBACK: to maximize the vibration energy transformed
by the kinetic fluid energy we minimize the device’s Scruton number 60

2
2
D
m
SC



The Scruton Number
It is proportional to the structural damping and to the
ratio between the vibrating mass and the mass of the air
displaced by the structure, and it is defined as:
air density
(kg/m3)
structural damping by the
logarithmic decrement
mass per unit length (kg/m)
Body diameter (m)
61

how
to extract energy
62
ABOUT
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WHY/WHERE
• HOW
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• ALL TOGETHER

Mechanism of piezoelectricity
63
Piezoelectric effect:
coupling between
structural domain & electrical domain

൯𝝈:𝐬𝐭𝐫𝐞𝐬𝐬𝐭𝐞𝐧𝐬𝐨𝐫(Τ𝑵𝒎𝟐
S: matrix of compliance coefficients (m2ΤN)
ε:straintensor(-)
)𝑬:𝐞𝐥𝐞𝐜𝐭𝐫𝐢𝐜𝐟𝐢𝐞𝐥𝐝𝐬𝐭𝐫𝐞𝐧𝐠𝐭𝐡(Τ𝑽𝒎
d: matrix for the direct piezoelectric effect(mΤV)
dT: matrix for the converse
piezoelectric effect(mΤV)
e: permittivity (FΤm)
D:electricchargedensity
displacement(C/m2)
64

Equation for the converse piezoelectric effect
Equation for the direct piezoelectric effect
permittivity
matrix of compliance coefficients
matrix for the converse
piezoelectric effectmatrix for the direct piezoelectric effect
65

S: matrix of compliance coefficients (m2ΤN)
ε:straintensor(-)
d: matrix for the direct piezoelectric effect
(mΤV)
dT: matrix for the converse
piezoelectric effect(mΤV)
e: permittivity (FΤm)
D:electricchargedensity
displacement(C/m2)
=
=
+
+
66

Design Complexity
(Optimization)
Loosely – Tightly Couplings (Interactions)
Nonlinear–Linear
Behavour
69
Fluid
domain
Structural
domain
Electrical
domain

Electro-mechanical problems
1. Coupling between body oscillations
characteristics and power generation.
2. The extraction of energy from movement
introduce an equivalent decay on the dynamics of
the body: the extracted energy is stolen t the
kinetic energy of the body ( -> retroaction with
Scruton Number: more energy extracted, higher
the Scruton Number, farer from lock-in region).
3. Adaptive power extraction: only in peak regions.
70

1 - Optimal electric load for the piezo component
Range of body displacement: +/- 3 mm
Range of electrical resistance Ω
Power(generated)μW
Componentoscillation
frequency 71

2 - Power harvesting and shunt damping
The effect of power harvesting on the dynamics of a structure
It is apparent that as more energy is removed from the system, faster
the impulse dies out until a critical level is reached, after which the
resistive load of the circuit exceeds the impedance of the PZT
network causing lower efficiency power generation and lower energy
dissipation to the beam.
Estimation of Electric Charge Output for Piezoelectric Energy Harvesting - H. A. Sodano, G. Park, D. J. Inman
72

2
2
D
m
SC



The Scruton Number
It is proportional to the structural damping and to the
ratio between the vibrating mass and the mass of the air
displaced by the structure, and it is defined as:
air density
(kg/m3)
structural damping by the
logarithmic decrement
mass per unit length (kg/m)
Body diameter (m)
73

3 - Power harvesting and shunt damping (a)
 







 

tutI
CC
C
ut
ti
P
prect
rect
,)sin(
0,0
0
PP
prect
rect
prect II
CC
C
CC 


 



PrectP CVI
ti
22
0 
   PrectP
rect
CVI
V
tP 


2
P
P
rect
C
I
V
2
The peak output power occurs when
Adaptive piezoelectric energy harvesting circuit for wireless remote power supply - Geffrey K. Ottman, Heath F.
Hofmann, Archin C. Bhatt, and George A. Lesieutre
74

3 - Power harvesting and shunt damping (b)
The magnitude of the polarization current
generated by the piezoelectric transducer,
and hence the optimal rectifier voltage, may
not be constant as it depends upon the
vibration level exciting the piezoelectric
element.
This creates the need for flexibility in the
circuit, i.e., the ability to adjust the output
voltage of the rectifier to achieve maximum
power transfer.
Optimized piezoelectric energy harvesting circuit using step-down converter in discontinuous conduction mode -
Geffrey K. Ottman, Heath F. Hofmann, and George A. Lesieutre
75

3 - Power harvesting and shunt damping (c)
The magnitude of the polarization current
generated by the piezoelectric transducer,
and hence the optimal rectifier voltage, may
not be constant as it depends upon the
vibration level exciting the piezoelectric
element.
This creates the need for flexibility in the
circuit, i.e., the ability to adjust the output
voltage of the rectifier to achieve maximum
power transfer.
76

3 - Power harvesting and shunt damping (d)
77

optimization
of the design
78
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AGAINST
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WHY/WHERE
• HOW
• OPTIMIZATION
• CONFIRMATIONS
• ALL TOGHETER

Technical Development
2
2
D
m
SC



Structural Set Up
Minimize Scruton
Mass (m)
Structural damping (ζs)
Characteristic dimension (D)
Optimize shape
Define shape
Electrical Set Up
Optimal electrical load R and frequency f to
maximize the extracted power and maintain
an acceptable damping (ζe). Optimization of
the energy extraction algorithm
Operating
conditions
HVAC Integration
Fluid-Structure Interaction (FSI)
79

2
2
D
m
SC



Structural Set Up
Minimize Scruton
Mass (m)
Optimize shape
Define shape
Electrical Set Up
Operating
conditions
HVAC Integration
Numerical/Analytical
and Wind Tunnel
Manufacturing and Wind Tunnel
T
.
R
.
L
.
TechnologyReadiness
Level
80

Optimization: modeling levels
81

PiezoTSensor – basic arrangement
l
lb b
th1
d
d1
th
l1
d= 30 mm
lb= 65 mm
l= 250 mm
b= 30 mm
th= 2 mm
MassaPunta= 0
d1=
l1=
th1=
Vista laterale
Componente già
acquistato e da
incollare alla balsa,
Vedi disegno a parte
= Massa di punta
Materiale costitutivo: Balsa
Nota 1: La parte in rosso è un
elemento piezoelettrico già in
nostro possesso da incollare sulla
balsa. I dettagli alla slide successiva
Nota 2: La parte del fissaggio in
alluminio NON è rappresentata nel
presente schema
Nota 3: c’è un tappo alla fine del
cilindro
82

piezoTsensor – piezoelectric component
83

Circular shape section – CFD analysis
85

Rectangular shape section – CFD analysis
86

T- shape section- CFD analysis
87

Rectangular shape section – electromech analysis
88Basic analytical modeling to assess range of displacements

Rectangular shape section – electromech analysis
89Basic analytical modeling to assess range of production of power

l
lb b
th1
d
d1
th
l1
d= 30 mm
lb= 65 mm
l= 250 mm
b= 30 mm
th= 2 mm
MassaPunta= 0
d1=
l1=
th1=
Vista laterale
Componente già
acquistato e da
= Massa di punta
presente schema
cilindro
90

confirmations
from the real world
93
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CRIACIV - University Research Center for Building
Aerodynamics and Wind Engineering)
94

Note: effects of details on fluid wake (1)
95

Note: effects of details on fluid wake (2)
96

l
lb b
th1
d
d1
th
l1
d= 30 mm
lb= 65 mm
l= 250 mm
b= 30 mm
th= 2 mm
MassaPunta= 0
d1=
l1=
th1=
Vista laterale
Componente già
acquistato e da
= Massa di punta
presente schema
cilindro
98

Circular prototype (a)
No scaling factor!
99

Circular prototype (b)
Laser measurements
100

Circular prototype (c)
Only fluid-structure domain 101

Circular prototype
Sensibility
to tip mass
Tip mass = 5 g Tip mass = 10 g
102

Alternatives: T-shape and rectangular prototypes
103

Normalized dynamic response of
the model, varying the reduced
wind velocity.
• Circles: first testing series
(increasing values with wind speed)
• Crosses: second testing series
(decreasing values with wind speed)
• Dotted red line: reduced speed equal
to 1/St, assuming a value of St = 0.2
for the Strouhal number.
Mechanical response of the prototypesCircular
shape
Rectangul
arshape
T-section
shape
104

• Circles: first testing series (increasing values with wind speed)
• Crosses: second testing series (decreasing values with wind speed)
• Dotted red line: reduced speed equal to 1/St, assuming a value of St = 0.2 for the Strouhal number.
Mechanical response of the circular shape
reduced wind velocity
Normalizeddisplacement(max)
> beginning of lock-in
VORTEX
SHEDDING
105

Mechanical response of the rectangular shape
VORTEX
SHEDDING
106

Mechanical response of the T shape
VORTEX
SHEDDING
+
GALLOPING!
107

Mechanical response of the prototypes
Circular
shape
Rectangul
arshape
T-section
shape
VORTEX
SHEDDING
+
GALLOPING!
108

α=0
Uflux≠0
Fy increases
the body
velocity
increase
α increases
The drag
decrease much
less than lift
Non
hydrostatic
pressure









U
y
.
arctan
Galloping: instability cycle
110

https://www.youtube.com/watch?v=G1
w_MZSb3D0&feature=youtu.be
111

https://www.youtube.com/watch
?v=Nf3SmO03w6U
112

all
together now!
113
ABOUT
AGAINST
TOWARD
WHY/WHERE
• HOW
• OPTIMIZATION
• CONFIRMATIONS
• ALL TOGETHER

2
2
D
m
SC



Structural Set Up
Minimize Scruton
Mass (m)
Optimize shape
Define shape
Electrical Set Up
Operating
conditions
HVAC Integration
114

Preliminary electrical characterization of piezo-
115

Electronic circuit prototype 116

Electro-mechanical response of the prototypes
Circular
shape
T-section
(singlePZT
patch)
T-section
(doublePZT
patch)
117

LEFT: mechanical response of the
prototypes at different values of the
electrical resistance.
Circular
shape
T-section
(doublePZT
patch)
BELOW: power/flow velocity law for non
optimized circuit –T-section shape
prototype.
T-section
(singlePZT
patch)
118

T-section
(singlePZT
patch)
Circular
shape
119

2
2
D
m
SC



Structural Set Up
Minimize Scruton
Mass (m)
Optimize shape
Define shape
Electrical Set Up
Operating
conditions
HVAC Integration
120

Sensibility of the response of the prototypes
Free flow Confined flow
125

At the end of my experience
• Computational methods (numerics) produce
flexibility to face different problems with the
same tools or to face the same problem at
different scale.
• It is important not to fall in love with
computational tools: there are limits.
• Computational methods are extremely important
(together with knowledge!) for the screening of
the problem,
• but, experimental confirmations are necessary.
137

At the beginning of my experience

Piezoelectric Energy Harvesting
under Airflow Excitation:
Numerical Modeling and Applications
Franco Bontempi*, Francesco Petrini, Konstantinos Gkoumas
PhD, PE, Professor of Structural Analysis and Design
School of Engineering
University of Rome La Sapienza
Rome - ITALY
143

CILAMCE 2016 - plenary lecture BONTEMPI

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