CILAMCE 2016 - plenary lecture BONTEMPI

Piezoelectric Energy Harvesting under Airflow Excitation:

Numerical Modeling and Applications

Franco Bontempi*, Francesco Petrini, Konstantinos GkoumasPhD, PE, Professor of Structural Analysis and Design

School of Engineering

University of Rome La Sapienza

Rome - ITALY

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3

Design Complexity(Optimization)

Loosely – Tightly Couplings (Interactions)

No

nlin

ear

–Li

ne

arB

eh

avo

ur

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Index of words

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ABOUT

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• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGETHER

aboutflow induced vibrations

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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)

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Classification:after Naudascher / Rockwell

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10

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).

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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)

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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.

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2)

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IIE

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againstflow induced vibrations

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ABOUT

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WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGHETER

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2003

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27

2009

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30

2000

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Structural Scheme

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i non lin

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str

uttura

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Modello

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. (b

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b

c

d

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Argand’s diagram of the first Vibration Modes

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

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towardflow induced vibrations

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ABOUT

AGAINST

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WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGHETER

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.

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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 processesthat allow to capture the freely available energy in theenvironment and convert it in (electric) energy that can be usedor stored.

Harvesting ConversionUse

Storage

Energy harvesting - Overview

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2010

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MODEL

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MESH

43

LOADS & RESTRAINTS

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SHELL MODEL

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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.

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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.

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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.

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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.eu50

http://www.piezotsensor.eu/

why/whereextract energy

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ABOUT

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WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGHETER

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.

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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.

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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

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http://www.enocean-alliance.org/

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/s56

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

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Piezo energy harvesters drawback

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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 thatperiodically detach alternatively fromthe body .

For value of vortex shedding frequencynear to the natural oscillation objectfrequency fn, the frequency f of theexciting force is controlled completelyby the body vibration.

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The Scruton Number

The Scruton Number is adimensionless number thatrepresents how the mass anddamping affect the lock-inphenomenon:

By increasing the Scruton Number, it was found a reductions in maximum amplitude and width of the lock-in range.

2

2

D

mSC

Mei

er –

Win

dh

ors

t(1

93

9)

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

mSC

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)

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how to extract energy

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ABOUT

AGAINST

TOWARD

WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGETHER

Mechanism of piezoelectricity

63

Piezoelectric effect:coupling between

structural domain & electrical domain

൯𝝈

:𝐬𝐭𝐫

𝐞𝐬𝐬

𝐭𝐞𝐧

𝐬𝐨𝐫

(Τ

𝑵𝒎

𝟐

S: matrix of compliance coefficients (m2ΤN)

ε: s

trai

n t

enso

r (-

)

)𝑬

:𝐞𝐥𝐞

𝐜𝐭𝐫𝐢

𝐜𝐟𝐢

𝐞𝐥𝐝

𝐬𝐭𝐫𝐞

𝐧𝐠

𝐭𝐡(

Τ𝑽

𝒎

d: matrix for the direct piezoelectric effect(mΤV)

dT: matrix for the converse piezoelectric effect(mΤV)

e: permittivity (FΤm)D: e

lect

ric

char

ge d

ensi

ty

dis

pla

cem

ent

(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

൯𝝈

:𝐬𝐭𝐫

𝐞𝐬𝐬

𝐭𝐞𝐧

𝐬𝐨𝐫

(Τ

𝑵𝒎

𝟐

S: matrix of compliance coefficients (m2ΤN)

ε: s

trai

n t

enso

r (-

)

)𝑬

:𝐞𝐥𝐞

𝐜𝐭𝐫𝐢

𝐜𝐟𝐢

𝐞𝐥𝐝

𝐬𝐭𝐫𝐞

𝐧𝐠

𝐭𝐡(

Τ𝑽

𝒎

d: matrix for the direct piezoelectric effect(mΤV)

dT: matrix for the converse piezoelectric effect(mΤV)

e: permittivity (FΤm)

D: e

lect

ric

char

ge d

ensi

ty

dis

pla

cem

ent

(C /

m2)

൯𝝈

:𝐬𝐭𝐫

𝐞𝐬𝐬

𝐭𝐞𝐧

𝐬𝐨𝐫

(Τ

𝑵𝒎

𝟐

)𝑬

:𝐞𝐥𝐞

𝐜𝐭𝐫𝐢

𝐜𝐟𝐢

𝐞𝐥𝐝

𝐬𝐭𝐫𝐞

𝐧𝐠

𝐭𝐡(

Τ𝑽

𝒎

=

=

+

+

66

3 - 3

1 - 1

3 - 167

68

Design Complexity(Optimization)

Loosely – Tightly Couplings (Interactions)

No

nlin

ear

–Li

ne

arB

eh

avo

ur

69

Fluid domain

Structural domain

Electricaldomain

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.

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1 - Optimal electric load for the piezo component

Range of body displacement: +/- 3 mm

Range of electrical resistance Ω

Po

we

r (g

en

era

ted

) μW

Co

mp

on

en

t o

scill

atio

n

fre

qu

en

cy71

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

mSC

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)

tutICC

C

ut

tiP

prect

rect ,)sin(

0,0

0

PP

prect

rectprect II

CC

CCC

PrectP CVI

ti22

0

PrectPrect CVI

VtP

2

P

Prect

C

IV

2The 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

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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.


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3 - Power harvesting and shunt damping (d)


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optimizationof the design

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ABOUT

AGAINST

TOWARD

WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGHETER

Technical Development

2

2

D

mSC

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)

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2

2

D

mSC

Structural Set Up

Minimize Scruton

Mass (m)



Optimize shape

Define shape

Electrical Set Up




HVAC Integration


Numerical/Analyticaland Wind Tunnel

Manufacturing and Wind Tunnel

T.R.L.

Tech

no

logy R

ead

iness

Level

80

Optimization: modeling levels

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PiezoTSensor – basic arrangement

l

lb b

th1

d

d1

th

l1

d= 30 mmlb= 65 mml= 250 mmb= 30 mmth= 2 mmMassaPunta= 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 schemaNota 3: c’è un tappo alla fine del cilindro

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piezoTsensor – piezoelectric component

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Numerical modelling

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Circular shape section – CFD analysis

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Rectangular shape section – CFD analysis

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T- shape section- CFD analysis

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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


d1= l1= th1=

Vista laterale


= Massa di punta



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91

Alternative design #1

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Alternative design #2

confirmationsfrom the real world

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ABOUT

AGAINST

TOWARD

WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGETHER

CRIACIV - University Research Center for Building Aerodynamics and Wind Engineering)

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Note: effects of details on fluid wake (1)

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Note: effects of details on fluid wake (2)

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97


l

lb b

th1

d

d1

th

l1


d1= l1= th1=

Vista laterale


= Massa di punta



98

Circular prototype (a)

No scaling factor!

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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 prototypesC

ircu

lar

shap

eR

ect

angu

lar

sh

ape

T-se

ctio

n

shap

e

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 velocityNo

rmal

ize

d d

isp

lace

me

nt

(max

)

> beginning of lock-in

VORTEXSHEDDING

105




Mechanical response of the rectangular shape

reduced wind velocity

No

rmal

ize

d d

isp

lace

me

nt

(max

)


VORTEXSHEDDING

106




Mechanical response of the T shape

reduced wind velocity

No

rmal

ize

d d

isp

lace

me

nt

(max

)


VORTEXSHEDDING

+GALLOPING!

107

Mechanical response of the prototypes

Cir

cula

r sh

ape

Re

ctan

gul

ar s

hap

eT-

sect

ion

sh

ape VORTEX

SHEDDING+

GALLOPING!

108

109

Galloping

α=0Uflux≠0

Fy increases

the body velocity increase

α increases

The drag decrease much

less than lift

Non hydrostatic

pressure

Uy.

arctan

Galloping: instability cycle

110

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111

https://www.youtube.com/watch?v=G1w_MZSb3D0&feature=youtu.be

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

112

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

alltogether now!

113

ABOUT

AGAINST

TOWARD

WHY/WHERE

• HOW

• OPTIMIZATION

• CONFIRMATIONS

• ALL TOGETHER


2

2

D

mSC

Structural Set Up

Minimize Scruton

Mass (m)



Optimize shape

Define shape

Electrical Set Up




HVAC Integration


114

Preliminary electrical characterization of piezo-

115

Electronic circuit prototype 116

Electro-mechanical response of the prototypesC

ircu

lar

shap

e

T-se

ctio

n

(sin

gle

PZT

p

atch

)

T-se

ctio

n

(do

ub

le P

ZT

pat

ch)

117

Electro-mechanical response of the prototypes

LEFT: mechanical response of the

prototypes at different values of the

electrical resistance.

Cir

cula

r sh

ape

T-se

ctio

n

(do

ub

le P

ZT

pat

ch)

BELOW: power/flow velocity law for non

optimized circuit –T-section shape

prototype.

T-se

ctio

n

(sin

gle

PZT

p

atch

)

118

Electro-mechanical response of the prototypes

T-se

ctio

n

(sin

gle

PZT

p

atch

)

Cir

cula

r sh

ape

119


2

2

D

mSC

Structural Set Up

Minimize Scruton

Mass (m)



Optimize shape

Define shape

Electrical Set Up




HVAC Integration


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122

123

124

Sensibility of the response of the prototypes

Free flow Confined flow

125

closing credits

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129

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131

132

133

134

135

conclusion

136

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

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140

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Piezoelectric Energy Harvesting under Airflow Excitation:

Numerical Modeling and Applications

Franco Bontempi*, Francesco Petrini, Konstantinos GkoumasPhD, PE, Professor of Structural Analysis and Design

School of Engineering

University of Rome La Sapienza

Rome - ITALY

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