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- Front Matter: Volume 6523
- Smart Devices I
- Aircraft Wing Design and Control
- Smart Devices II
- Control of Systems with Hystersis
- Robust Control
- Control Theory
- Identification of Complex Structures
- Wavelets
- Algorithms for Damage Detection
- Material Modeling
Front Matter: Volume 6523
Front Matter: Volume 6523
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This PDF file contains the front matter associated with SPIE
Proceedings Volume 6523, including the Title Page, Copyright
information, Table of Contents, Introduction (if any), and the
Conference Committee listing.
Smart Devices I
Dynamic analysis of a biology-inspired miniature directional microphone
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In this paper, recent efforts conducted to analyze the dynamic behavior of a biology-inspired miniature directional
microphone are presented. Inspired by the tiny ears of the fly Ormia, the proposed directional microphone consists of two
circular diaphragms coupled by a beam. The numerical study has shown that the biology-inspired directional microphone
enables the amplification of the time delay between the sound pressure induced displacement responses of the two
diaphragms. Factors such as the beam stiffness and the air backed cavity, which influence the performance of the
directional microphone, are investigated. These analyses and results are expected to be valuable for the development of
biology-inspired miniature directional microphones for various applications.
Jitter control for an initially stablized tactical rifle
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While good marksmanship is the key to the effectiveness of the infantry mission, all soldiers experience a decrease in
accuracy due to combat stress that generates detrimental physiological effects. INSTAR is a tactical rifle designed to
address these effects by decoupling unwanted shooter-induced disturbances from the barrel via an active suspension
system. Previous papers have addressed the design of the active suspension system: the actuation, driving electronics
and power supply. In this paper we consider the development of the jitter control system. Beginning with an analytical
model of the gun that includes the shooter, we develop the appropriate model for the design of the control system. We
investigate two designs. The first design is based on lead compensation. The second design is based on LQG. Both
designs show that the control system can effectively reduce the jitter to acceptable levels. The classical compensator
demonstrates better transient performance.
Design and quasi-static characterization of SMASH SMA (Stabilizing Handgrip)
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Due to physiologically induced body tremors, there is a need for active stabilization in many hand-held devices such as
surgical tools, optical equipment (cameras), manufacturing tools, and small arms weapons. While active stabilization has
been achieved with electromagnetic and piezoceramics actuators for cameras and surgical equipment, the hostile
environment along with larger loads introduced by manufacturing and battlefield environments make these approaches
unsuitable. Shape Memory Alloy (SMA) actuators are capable of alleviating these limitations with their large
force/stroke generation, smaller size, lower weight, and increased ruggedness. This paper presents the actuator design
and quasi-static characterization of a SMA Stabilizing Handgrip (SMASH). SMASH is an antagonistically SMA
actuated two degree-of-freedom stabilizer for disturbances in the elevation and azimuth directions. The design of the
SMASH for a given application is challenging because of the difficulty in accurately modeling systems loads such as
friction and unknown shakedown SMA material behavior (which is dependent upon the system loads). Thus, an iterative
empirical design process is introduced that provides a method to estimate system loads, a SMA shakedown procedure
using the system loads to reduce material creep, and a final selection and prediction for the full SMASH system
performance. As means to demonstrate this process, a SMASH was designed, built and experimentally characterized for
the extreme case study of small arms stabilization for a US Army M16 rifle. This study successfully demonstrated the
new SMASH technology along with the unique design procedure that can be applied to small arms along with a variety
of other hand-held devices.
Modeling and sensitivity study of the dual-chamber SMART (SMA ReseTtable) lift device
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Morphing structures for applications such as impact mitigation is a challenging problem due to the speed and
repeatability requirements that limit the viable actuation approaches. This paper examines a promising stored-energy,
active-release approach that can be deployed quickly (~40 ms), is reusable/resetable and can be tuned in the field for
changing conditions such as additional mass, temperature compensation or platform changes. The Dual-Chamber
SMART (SMA ReseTtable) Lift is a pneumatic air spring controlled via an ultra-fast SMA actuated valve. This paper
presents the modeling, sensitivity analysis and experimental validation of this new technology. A control-volume based
analytical model was derived that employs compressible, sonic flow and thermodynamic relations to provide a set of
differential equations that relate the design parameters (cylinder and valve geometry), application parameters (deployed
mass), and operational parameters (pressure, temperature and SMA valve actuation profile), to the deployment
performance (deploy time, profile, position, etc.). The model was exercised to explore the sensitivity of the performance
with regards to these parameters and explore the off-line and on-line adjustability of the device's performance to
compensate for cross platform applications and uncontrolled environmental effects such as temperature and added mass.
As proof-of-concept, a full-scale prototype was designed via the model, built and experimentally characterized across
several of the parameters for the real case-study of automotive pedestrian protection. The prototype performance agreed
closely with model predictions and met the rigorous specifications of the case study with in-situ tailoring which is
applicable to a wide range of morphing applications beyond this case study.
Model identification and controller design of a fish-like robot
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Robotic fish is an interesting and prospective subject to develop. The simplest fish swimming mode to be mimicked for
fish robots is the ostraciiform mode which only requires caudal fin flapping. An almost submerged ostraciiform fish
robot was constructed to study its swimming characteristics. The swimming direction can be controlled by changing the
mean angle of caudal fin oscillation. Experiments were conducted to study the behavior of the fish robot and in particular,
the transfer function between swimming path angular rate and mean angle of the caudal fin oscillation were identified.
Error to signal ratio quantity was used to determine how well the model fits with the experimental data. This
identification model was used to design a 2-degree-of-freedom PID controller that meets some specific requirements to
improve the steering performance.
Aircraft Wing Design and Control
Tendon actuated cellular mechanisms for morphing aircraft wing
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Morphing aircraft wings offer great potential benefits of achieving multi mission capability as well as high
maneuverability under different flight conditions. However, they present many design challenges in the form of
conflicting design requirements. The current research aims to develop design methodologies for the design of a
morphing aircraft wing. Focus of this work is on developing an internal mechanism of the wing that can produce the
desired wing shape change.
This paper presents a design methodology that employs planar unit cells of pre-determined shape and layout as the
internal wing structure for achieving the desired wing shape change. This method is particularly useful in cases where
the desired morphing is two-dimensional in nature. In such cases, intuitive cell designs such as diamond or hexagonal
shaped cells may be used in layouts that achieve desired wing morphing. The shape change depends on the cell shape as
well as cell arrangement in the design domain.
In this paper, a design based on the TSCh wing (NextGen Aeronautics Inc.) using cellular mechanisms to achieve a two-dimensional
wing shape change is discussed. Additionally, a reeling mechanism for achieving cable actuation is presented
Energy-based aeroelastic analysis of a morphing wing
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Aircraft are often confronted with distinct circumstances during different parts of their mission. Ideally the
aircraft should fly optimally in terms of aerodynamic performance and other criteria in each one of these mission
requirements. This requires in principle as many different aircraft configurations as there are flight conditions, so
therefore a morphing aircraft would be the ideal solution. A morphing aircraft is a flying vehicle that i) changes
its state substantially, ii) provides superior system capability and iii) uses a design that integrates innovative
technologies. It is important for such aircraft that the gains due to the adaptability to the flight condition are not
nullified by the energy consumption to carry out the morphing manoeuvre. Therefore an aeroelastic numerical
tool that takes into account the morphing energy is needed to analyse the net gain of the morphing. The code
couples three-dimensional beam finite elements model in a co-rotational framework to a lifting-line aerodynamic
code. The morphing energy is calculated by summing actuation moments, applied at the beam nodes, multiplied
by the required angular rotations of the beam elements. The code is validated with NASTRAN Aeroelasticity
Module and found to be in agreement. Finally the applicability of the code is tested for a sweep morphing
manoeuvre and it has been demonstrated that sweep morphing can improve the aerodynamic performance of an
aircraft and that the inclusion of aeroelastic effects is important.
Active aeroelastic control aspects of an aircraft wing by using synthetic jet actuators: modeling, simulations, experiments
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This paper discusses modeling, simulations and experimental aspects of active aeroelastic control on aircraft wings by
using Synthetic Jet Actuators (SJAs). SJAs, a particular class of zero-net mass-flux actuators, have shown very
promising results in numerous aeronautical applications, such as boundary layer control and delay of flow separation. A
less recognized effect resulting from the SJAs is a momentum exchange that occurs with the flow, leading to a
rearrangement of the streamlines around the airfoil modifying the aerodynamic loads. Discussions pertinent to the use of
SJAs for flow and aeroelastic control and how these devices can be exploited for flutter suppression and for aerodynamic
performances improvement are presented and conclusions are outlined.
Comparison of active flow control devices on bluff body shapes
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Results from experimental studies on the performance of plasma and synthetic jet actuators for active control
of flow over a circular cylinder in subcritical flow conditions ranging from a Reynolds Number of 2.5 x 104 to
7.3x104 are presented. The experiments were conducted at the NASA Langley Research Center in the 20" x 28"
Shear Flow Wind Tunnel and the results provide an indication of the effectiveness of, as well as the similarities
and differences between these two active flow control (AFC) methods for reducing pressure drag on a bluff body
shape. Flows over a cylinder are well understood and in particular flow separation characteristics for cylinders
are well documented both experimentally and theoretically. The effect of the flow control devices is quantified by
measuring the pressure distribution around the bluff bodies using a multi-port piezoelectric pressure scanner and
integrating the distribution for drag analysis. This comparison consists of operating the two types of actuators in
the same range of Reynolds Numbers (Re) over the cylinder and for the same actuator angular positions on the
cylinder. The applied voltages and frequencies to the actuators varies based on the individual actuator operating
conditions. At low Re, the plasma actuators have a strong effect on the pressure distribution reducing the drag
up to 32% relative to the drag with no actuators on the surface. The synthetic jet reduces drag up to 25% but
with lower voltage and frequency. For both actuator cases, the actuator is the most effective 5° to 10° upstream
of the baseline separation point.
Smart Devices II
Lyapunov stability of periodically modulated cosine drivers for resonance tuning of harmonic oscillators
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Resonance tracking control of harmonic oscillators whose natural frequency is unknown is investigated from a Lyapunov
stability perspective. In particular, a periodically-modulated cosine driver (PMCD) is investigated for this purpose. The
proposed resonance tuner is time-synchronized with periodic sampling of the harmonic oscillator's output to ensure that an
analytical relationship exists between the drive frequency and the tracking error. This relation defines a class of discrete time
nonlinear systems whose origin, is shown to be asymptotically stable.
Piezoactuator design considering the optimum placement of FGM piezoelectric material
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Functionally Graded Materials (FGMs) possess continuous variation of material properties and are characterized
by spatially varying microstructures. Recently, the FGM concept has been explored in piezoelectric materials
to improve properties and to increase the lifetime of piezoelectric actuators. Elastic, piezoelectric, and dielectric
properties are graded along the thickness of a piezoceramic FGM. Thus, the gradation of piezoceramic properties
can influence the performance of piezoactuators, and an optimum gradation can be sought through optimization
techniques. However, the design of these FGM piezoceramics are usually limited to simple shapes. An interesting
approach to be investigated is the design of FGM piezoelectric mechanisms which essentially can be defined as a
FGM structure with complex topology made of piezoelectric and non-piezoelectric material that must generate
output displacement and force at a certain specified point of the domain and direction. This can be achieved by
using topology optimization method. Thus, in this work, a topology optimization formulation that allows the
simultaneous distribution of void and FGM piezoelectric material (made of piezoelectric and non-piezoelectric
material) in the design domain, to achieve certain specified actuation movements, will be presented. The method
is implemented based on the SIMP material model where fictitious densities are interpolated in each finite element,
providing a continuum material distribution in the domain. The optimization algorithm employed is based on
sequential linear programming (SLP) and the finite element method is based on the graded finite element concept
where the properties change smoothly inside the element. This approach provides a continuum approximation
of material distribution, which is appropriate to model FGMs. Some FGM piezoelectric mechanisms were
designed to demonstrate the usefulness of the proposed method. Examples are limited to two-dimensional models,
due to FGM manufacturing constraints and the fact that most of the applications for such FGM piezoelectric
mechanisms are planar devices. An one-dimensional constraint of the material gradation is imposed to provide
more realistic designs.
Control modeling of LIPCA using miniaturized piezoelectric actuator driver
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A smart material is known to be able to generate large force in broad bandwidth in a compact size. However it needs
relatively large voltage to drive it and this makes the system bulky. In this paper, first, we introduce an improved version
of miniaturized piezo actuator driver and modeling of the dynamics of the piezo actuator, LIPCA. ARX model was used
to model the dynamics of the LIPCA. We applied rectangular waves to the LIPCA and measured its responses with a
strain gauge and a signal processing circuit. A 5th order model was obtained from the input/output data and applying
identification algorithm. Secondly, we designed a simple PID controller based on the obtained model to improve the
characteristics of the LIPCA actuator.
Estimation of control capacity for squeeze mode MR damper with electro-magnetic system
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This paper is focused on developing a Squeeze Mode MR damper with large control capacity for effective vibration
mitigation in infrastructures such as long span bridges and skyscrapers, etc. In order to maximize the magnetic field
required for control of MR fluid, this device is designed by separating electromagnet system from the main cylinder for
large capability of control force without changing its total length. This developed MR damper is tested to estimate its
maximum control capacity and dynamic range(defined as the ratio of the maximum force to the minimum force that MR
devices provide), inputting various strength magnet fields. These experimental results make it possible to estimate its
maximum control force by drawing a curve showing the relationship between generated forces and applied magnetic
fields. In order to verify its performance as a semi-active control device, its dynamic range is calculated. Through all
tests, the developed MR is proved to be an effective device for the response control of infrastructures.
Control of Systems with Hystersis
Passivity-based control of magnetostrictive materials
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In this article, velocity and position controllers for magnetostrictive materials are designed and discussed.
Magnetostrictive materials are a competitive choice for micro-positioning actuation tasks because of the large force and
strain they provide. Unfortunately, they are highly nonlinear and hysteretic, which makes them difficult to control. In
this article, the passivity approach is used to establish stability for velocity control. Using a physical argument, passivity
of the system under discussion is proved. No model for magnetostrictive material is used in this proof and the result can
be used in any hysteresis model for the material. This result is used to develop a stabilizing velocity controller. For
position control, it is shown that a PI controller can provide stability and tracking if the hysteretic plant satisfies certain
conditions. It is shown that these conditions are satisfied for the Preisach model under mild assumptions. Using this
result, a class of stabilizing position controllers is identified. The velocity and position controllers are evaluated
experimentally and their performances discussed.
Modeling and identification of the hysteretic dynamics of an MR actuator for its application to semiactive control of flexible structures
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This paper presents the results of modeling a shear-mode MR damper. The prototype damper consists of two steel parallel plates and in the middle, there is a paddle covered by foam saturated with MR fluid. The force is produced when the paddle is in motion and the magnetic field generated by a coil in one end of the device
reaches the fluid. Several response forces were captured at different displacement excitations and magnetic field levels. The goal is to find a relationship between the velocity, the control voltage (inputs of the system) and the force generated by the device. The results of predicting the force using the Bingham, Bouc-Wen and Hyperbolic
Tangent based models are compared and the suitability of these models is discussed.
Robust Control
Active fault tolerant control of a flexible beam
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This paper presents the development and application of an H∞ fault detection and isolation (FDI) filter and
fault tolerant controller (FTC) for smart structures. A linear matrix inequality (LMI) formulation is obtained
to design the full order robust H∞ filter to estimate the faulty input signals. A fault tolerant H∞ controller
is designed for the combined system of plant and filter which minimizes the control objective selected in the
presence of disturbances and faults. A cantilevered flexible beam bonded with piezoceramic smart materials,
in particular the PZT (Lead Zirconate Titanate), in the form of a patch is used in the validation of the FDI
filter and FTC controller design. These PZT patches are surface-bonded on the beam and perform as actuators
and sensors. A real-time data acquisition and control system is used to record the experimental data and
to implement the designed FDI filter and FTC. To assist the control system design, system identification is
conducted for the first mode of the smart structural system. The state space model from system identification
is used for the H∞ FDI filter design. The controller was designed based on minimization of the control effort
and displacement of the beam. The residuals obtained from the filter through experiments clearly identify the
fault signals. The experimental results of the proposed FTC controller show its e effectiveness for the vibration
suppression of the beam for the faulty system when the piezoceramic actuator has a partial failure.
Energy-to-peak induced norm upper bound control approach for collocated structural systems
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The current paper presents an explicit expression for an upper bound on the induced energy-to-peak norm
for structural systems with collocated sensors and actuators. Using a linear matrix inequality (LMI)-based
representation of the L2 - L∞ norm of a collocated structural system, we determine an analytical upper bound
on the L2 - L∞ norm of such a system. The paper also addresses the problem of static output feedback
controller design for such systems. By employing simple algebraic tools, we derive an explicit parametrization of
feedback controller gains which guarantee a prescribed level of L2 - L∞ performance for the closed-loop system.
Finally, numerical examples are provided to validate the effciency and benefits of the proposed techniques. The
effectiveness of the obtained bound and control design methodology is evident, in problems involving very large
scale structural systems where solving Lyapunov equation or LMIs with large number of decision variables is
time-consuming or intractable.
Control and integrated design of smart material systems using analytical upper bound method
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This paper presents an explicit expression for an upper bound on H2 norm for structural systems with collocated
sensors and actuators. Using a linear matrix inequality (LMI)-based representation of the H2 norm of a collocated
structural system, we determine an explicit upper bound on H2 norm of such a system. The present paper also
addresses the problem of output H2 feedback controller design for collocated systems. Employing some simple
algebraic tools, we derive an explicit parametrization of H2 feedback controller gain which guarantees a prescribed
level of H2 performance for the closed-loop system. Numerical examples will be finally provided to validate the
efficiency and benefits of the proposed method.
Utilizing spatial robustness measures for the optimization of a PZT-actuated flexible beam
Show abstract
In this work, we revisit the problem of actuator placement within the context of spatial robustness. When one
optimizes location-parameterized H2 or H∞ closed loop measures, arrives at actuator locations that provide
performance optimality. However, these measures assume an a priori given distribution of disturbances. When
the above measures include an additional optimization stage whereby one searches for the worst distribution of
disturbances, then the resulting actuator location will result in both an improved performance and enhanced
spatial robustness. Using an analytical bound approach that provides an explicit expression for an upper bound
on the H∞ norm of the system transfer function, the worst distribution of disturbances can be found that
maximizes the open loop H bound. Subsequently, an optimal actuator location is found that minimizes the
H∞ bound of the closed loop transfer function. This method minimizes the optimization complexity and provides
great computational advantages in large scale flexible systems where the solution to H∞ optimization problems
using standard tools becomes computationally prohibitive.
Control Theory
Exact controllability of a multilayer Rao-Nakra beam with minimal number of boundary controls
Show abstract
We consider a multilayer Rao-Nakra sandwich beam with shear damping included in alternate layers. In the case
that the wave speeds of the layers are distinct, we show that by "tuning" the damping in each layer appropriately,
it is possible to construct a scalar boundary control that exactly controls the entire layered system in a control
time related to the sum of the control times of each separate layer. In the case where some waves speeds coincide,
one can reduce the number of controls needed, but not to a single scalar control.
Adaptive control of vibration transmission in a strut system
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In this article, theoretical and the experimental studies are reported on the adaptive control of vibration transmission in a
strut system subjected to a longitudinal pulse train excitation. In the control scheme, a magneto-strictive actuator is
employed at the downstream transmission point in the secondary path. The actuator dynamics is taken into account.
The system boundary parameters are first estimated off-line, and later employed to simulate the system dynamics. A
Delayed-X Filtered-E spectral algorithm is proposed and implemented in real time. The underlying mechanics based
filter construction allows for the time varying system dynamics to be taken into account. This work should be of interest
for active control of vibration and noise transmission in helicopter gearbox support struts and other systems.
Identification of Complex Structures
High-speed parameter estimation algorithms for nonlinear smart materials
Show abstract
A fundamental step in the model construction for ferroelectric, ferromagnetic, and ferroelastic materials is
the estimation or identification of material parameters given measurements of the material response. Moreover,
actuator and/or material properties may be a function of operating conditions which can necessitate the re-estimation of parameters if conditions change significantly. In this paper, we focus on the development of highly robust and efficient identification algorithms for use in industrial, aeronautic and aerospace applications.
Following a discussion of present and future applications, we summarize the homogenized energy model used to characterize hysteresis and constitutive nonlinearities in these compounds. We next discuss the parameter estimation problem and detail algorithms used to speed implementation. The validity of the framework is illustrated through comparison with experimental data.
Tracking of transient displacements of plates with support excitations
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The present paper is concerned with dynamic shape control of linear elastic plates under the action of transient forces,
with prescribed time-dependent boundary conditions, and with given initial conditions. We consider anisotropic linear
elastic plates. The following displacement tracking problem is treated: We ask for an additional distribution of actuation
stresses such that the resulting displacements of the plates under consideration follow exactly some desired trajectories in
every point and at every time instant. We present relations that must be satisfied for the actuation stresses in order that
this goal of transient displacement tracking is reached. The actuation stresses we have in mind for enforcing tracking of
transient displacements are induced by eigenstrains, such as thermal expansion strains or, more technologically
important, piezoelectric parts of strain. Transient vibrations of circular plates in axi-symmetric bending are studied as an
exemplary case. The vibrations are excited by support excitations. Actuation stresses are superimposed, which enforce
the plate to track prescribed transient deflections. We present analytical solutions for the tracking of prescribed plate
deflections with time-dependent support excitation. Coupling between electric and mechanical field is taken into account
already at the level of plate theory. The analytical plate solutions are validated by Finite Element computations.
Electromechanically coupled three-dimensional piezoelectric elements are used in these numerical calculations.
Excellent coincidence between the analytical and the Finite Element computations is observed.
On the identification of modal couplings and inherent capacitances of piezoelectric structures
Show abstract
We propose two identification techniques for estimating the piezoelectric couplings and the piezoelectric capacitances
of reduced order modal models of linear piezoelectric structures. The two methods are easily implementable
and demand few input data, which can be obtained both with experimental testing and numerical
models (e.g. finite elements). We apply these methods to a sample structure hosting multiple transducers.
We discuss in details the proper definition and identification of the inherent piezoelectric capacitances, whose
meaning is often misunderstood.
Parameter estimation in active laminated plate structures
Show abstract
An inverse method for material parameter estimation of elastic, piezoelectric and viscoelastic laminated plate
structures is presented. The method uses a gradient based optimization technique in order to solve the inverse
problem, through minimisation of an error functional which expresses the difference between experimental free
vibration data and corresponding numerical data produced by a finite element model. Applications are presented
using a simulated test case for an adaptive plate.
Wavelets
Wavelet-based signal processing applied to deformable mirror PZT actuators for wavefront control
Show abstract
The objective of this paper is to address one of the more difficult problems in astronomical Adaptive Optics (AO): on future Extremely Large Telescopes (ELT), the computing power required for the requisite number of actuators will exceed the computing power presently available. The PZT actuators for Deformable Mirrors (MD) have three axes: tilt, tip and piston. It is envisioned that these three axes can be controlled by adaptive wavelet filter banks. Adaptive echo cancellation will be applied to achieve wavefront correction in a manner analogous to that used to cancel telephone echoes. This approach will provide a viable alternative to those presently available and reduce the number of computations.
Damage assessment of a two-span RC slab using wavelet analysis
Show abstract
A two-span RC slab that measures 6400mm×800mm×100mm with 3000mm spans and 200mm overhang on each end was tested to failure in the laboratory. UB sections were used as supports. The slab was designed according to the moment redistribution method with 11 N6 bars at 75mm centres for both positive and negative reinforcement. The slab was incrementally loaded at the middle of each span to different load levels to create crack damage using four-point loading. Twelve loading stages were performed with increasing maximum load level. Two load cells are used to record the static loads on left and right spans. The crack locations and lengths were monitored in addition to the displacement measurements. Four displacement transducers are located at two sides of the middle of each span to measure the deflection under the static load. Three sets of accelerometers with nine of them in each set are evenly distributed along the slab to measure the dynamic responses. The measured responses from the RC slab in different cracked damage states are analyzed using the wavelet transform (WT). The damping ratios and instantaneous frequency are extracted. The results show that the damping ratio and instantaneous frequency changes could be two good indicators of damage in the reinforced concrete structure.
Numerical modelling and simulations for optimal sensor location in damage detection with Lamb waves
Show abstract
This paper applies wave propagation modelling for the analysis of sensor positions in Lamb wave based damage
detection. The problem is investigated using the local interaction simulation approach for Lamb wave propagation
modelling in an aluminum plate with a rectangular damage slot and a fatigue crack. The study demonstrates the great
potential for optimal sensor location in damage detection techniques based on Lamb waves.
Algorithms for Damage Detection
Non-invasive methodology for diagnostics of bearing impacts
Show abstract
Various events in reciprocating machinery, such as connecting rod or piston movement, and diesel combustion produce a
series of highly transient forces within the machine. These events generate force transients of short duration and broad
frequency content. Even though these events may be part of a machine cycle and therefore periodic, it is often more
appropriate to treat them on an individual basis because more diagnostics information is available from a single
waveform during a cycle than from averages over several cycles. However, it is very rare for one to have direct access
to source waveforms because of the expense and reliability problems associated with the required instrumentation, and
non-invasive techniques will have to be used. This paper explores the use of cepstral smoothing and minimum phase
extraction technique for non-invasive diagnostics of bearing impacts in reciprocating machinery. The methodology is
based on extracting diagnostic signals from vibration measurements taken at a "convenient" location such as the
crankshaft casing or bearing end-cap, and consists of source identification, diagnostic signature recovery, and diagnostic
system decision-making. A dynamic simulation with lumped mass model is developed to analyze bearing impacts for
the big end bearings, experimental measurements from accelerometers, transfer functions of vibration, and the structural
response are presented.
Hidden Markov model based classification of structural damage
Show abstract
The ability to detect and classify damages in complex materials and structures is an important problem from
both safety and economical perspectives. This paper develops a novel approach based on Hidden Markov Models
(HMMs) for the classification of structural damage. Our approach here is based on using HMMs for modeling
the time-frequency features extracted from time-varying structural data. Unlike conventional deterministic
methods, the HMM is a stochastic approach which better accounts for the uncertainties encountered in the
structural problem and leads to a more robust health monitoring system. The utility of the proposed approach
is demonstrated via example results for the classification of fastener damage in an aluminum plate.
Cable 3D nonlinear model and damping systems on stayed bridges
Show abstract
The dynamic analysis using computational models is an important tool to simulate the dynamic of structures that have
specific uncertain behavior like the cable stayed bridges which nowadays is an alternative to solve long span bridges
with a slim structure. In this work we developed a 3D non linear model of a cable in order to evaluate the wind effect on
the Papaloapan cable stayed bridge located on Veracruz Mexico, under different scenarios. The health of the structure is
an important factor to analyze and there are many different fail causes, one of them is the fatigue fall that is relevant in
the anchorage elements of the cable stayed bridges. It is possible to modify the behavior of the structure using dampers
to minimize that effect. The geometry and all the forces and stress on the structures are a challenge also for the
specialists of the structures, in this work the developed methodology resulted very successful to analyze the behavior of a
cable on a cable stayed bridge using damping.
Material Modeling
Monte Carlo simulation of ion transport of the high strain ionomer with conducting powder electrodes
Show abstract
The transport of charge due to electric stimulus is the primary mechanism of actuation for a class of
polymeric active materials known as ionomeric polymer transducers (IPT). At low frequency, strain
response is strongly related to charge accumulation at the electrodes. Experimental results demonstrated
using conducting powder, such as single-walled carbon nanotubes (SWNT), polyaniline (PANI) powders,
high surface area RuO2, carbon black electrodes etc. as an electrode increases the mechanical deformation
of the IPT by increasing the capacitance of the material. In this paper, Monte Carlo simulation of a two-dimensional
ion hopping model has been built to describe ion transport in the IPT. The shape of the conducting powder is assumed to be a sphere. A step voltage is applied between the electrodes of the IPT,
causing the thermally-activated hopping between multiwell energy structures. Energy barrier height includes three parts: the energy height due to the external electric potential, intrinsic energy, and the energy height due to ion interactions. Finite element method software-ANSYS is employed to calculate the static
electric potential distribution inside the material with the powder sphere in varied locations. The interaction between ions and the electrodes including powder electrodes is determined by using the method of images. At each simulation step, the energy of each cation is updated to compute ion hopping rate which directly
relates to the probability of an ion moving to its neighboring site. Simulation ends when the current drops
to constant zero. Periodic boundary conditions are applied when ions hop in the direction perpendicular to
the external electric field. When an ion is moved out of the simulation region, its corresponding periodic
replica enters from the opposite side. In the direction of the external electric field, parallel programming is
achieved in C augmented with functions that perform message-passing between processors using Message Passing Interface (MPI) standard. The effects of conducting powder size, locations and amount are discussed by studying the stationary charge density plots and ion distribution plots.
An investigation into the electrical breakdown characteristics of cellulose based electro-active paper
Show abstract
Cellulose Electro-Active Paper (EAPap) has been reported as a new smart material that can be used as sensors and
actuators. This material is attractive due to its advantages of biodegradable, lightweight, dryness, large displacement
output, low actuation voltage and low power consumption. Its actuation principle has been known as a combination of
ion migration and piezoelectric effects. Although extensive investigations have been made on mechanical properties,
chemical and physical characteristics, the electrical properties have not been studied. This paper presents an
investigation into the electrical breakdown strength of EAPap, which is important for determining the electric field limit
for EAPap actuator. AC dielectric breakdown strength is measured with different humidity levels, according to ASTM
standard. The measured data are statistically analyzed and it was found that failures associated with the formative stages
of a breakdown mechanism might result in Weibull Statistics. As the humidity of the sample increases, the stress levels
on cellulosic portions of the sample are enhanced, leading lower breakdown strength. This investigation will give an
insight in understanding EAPap material.
Load-dependent hysteresis of magnetostrictive materials
Show abstract
A load-dependent hysteresis model for magnetostrictive materials is studied. Magnetostrictive materials are a class
of smart materials which react with a magnetic field and are suitable for many micro-positioning actuation tasks.
Unfortunately, these materials are difficult to use because of their highly nonlinear and hysteretic response. Unlike the
hysteresis seen in magnetic materials, the shape of the hysteresis curve changes significantly if the load is changed.
Because of this complex hysteresis, magnetostrictive actuators are difficult to control. To achieve sub-micron accuracy
for micropositioning, an accurate hysteresis model is needed. The model studied in this paper is similar to the Preisach
model. By modeling the Gibbs energy for each dipole and the equilibrium states, hysteresis in magnetostrictive
materials is modeled. The model is implemented in a way that different hysteresis curves are generated if the load is
changed. Using experimental data, optimum model parameters are obtained. The model results and experimental data
were compared at different loads. A modification is proposed for more accuracy and the modified model is compared to
the original model.