The delayed brittle fracture of high-strength bolts in long-span steel bridges threatens the safety of the bridges and even lead to serious accidents. Currently, human periodic inspection, the most commonly applied detection method for this kind of high-strength bolts damage, is a dangerous process and consumes plenty of manpower and time. To detect the damage fast and automatically, a visual inspection approach based on deep learning is proposed. YOLOv3, an object detection algorithm based on convolution neural network (CNN), is introduced due to its good performance for the detection of small objects. First, a dataset including 500 images labeled for damage is developed. Then, the YOLOv3 neural network model is trained by using the dataset, and the capability of the trained model is verified by using 2 new damage images. The feasibility of the proposed detection method has been demonstrated by the experimental results.
Concrete piles are widely used in the construction of civil infrastructures and it is important to perform the health
monitoring of concrete piles for safety purposes. In this paper, a piezoceramic-based innovative approach is proposed for
the damage detection and health monitoring of concrete piles. A multi-functional piezoceramic-based transducer device,
the smart aggregate, is developed for health monitoring purposes. An active-sensing network is formed by embedding
the proposed smart aggregates at the pre-determined locations in the concrete piles before casting. In the proposed
approach, one smart aggregate is used as an actuator to excite the desired waves and the other distributed smart
aggregates are used as sensors to detect the wave responses. An energy distribution vector is formed based on the
wavelet-packet analysis results of sensor signals. A damage index is formed by comparing the difference between the
energy distribution vectors of the health concrete pile and that of the damaged concrete pile. To verify the effectiveness
of the proposed approach, two concrete piles instrumented with smart aggregates are used as testing objects. One
concrete pile is intact and the other has a man-made crack in the middle of the pile. Experimental results show that the
there are differences between the energy distribution vectors of the damaged pile and that of the intact pile due to the existence of the crack. The proposed method has the potential to be applied to perform automated integrity inspections for new piles and for the long-term health monitoring of piles in services.
KEYWORDS: Sensors, Structural health monitoring, Sensor networks, Microcontrollers, Data processing, Ferroelectric materials, Actuators, Signal processing, Control systems, Transducers
Piezoceramic based transducers are widely researched and used for structural health monitoring (SHM) systems due
to the piezoceramic material's inherent advantage of dual sensing and actuation. Wireless sensor network (WSN)
technology benefits from advances made in piezoceramic based structural health monitoring systems, allowing easy
and flexible installation, low system cost, and increased robustness over wired system. However, piezoceramic
wireless SHM systems still faces some drawbacks, one of these is that the piezoceramic based SHM systems require
relatively high computational capabilities to calculate damage information, however, battery powered WSN sensor
nodes have strict power consumption limitation and hence limited computational power. On the other hand,
commonly used centralized processing networks require wireless sensors to transmit all data back to the network
coordinator for analysis. This signal processing procedure can be problematic for piezoceramic based SHM
applications as it is neither energy efficient nor robust. In this paper, we aim to solve these problems with a
distributed wireless sensor network for piezoceramic base structural health monitoring systems. Three important
issues: power system, waking up from sleep impact detection, and local data processing, are addressed to reach
optimized energy efficiency. Instead of sweep sine excitation that was used in the early research, several sine
frequencies were used in sequence to excite the concrete structure. The wireless sensors record the sine excitations
and compute the time domain energy for each sine frequency locally to detect the energy change. By comparing the
data of the damaged concrete frame with the healthy data, we are able to find out the damage information of the
concrete frame. A relative powerful wireless microcontroller was used to carry out the sampling and distributed data
processing in real-time. The distributed wireless network dramatically reduced the data transmission between
wireless sensor and the wireless coordinator, which in turn reduced the power consumption of the overall system.
The dynamic behaviour of civil structures under strong earthquakes is usually nonlinear or inelastic. Conventional
control approach is almost based on linear theory, such as the linear quadratic regulator (LQR) design. One of the
common characteristics shared by seismically excited civil structures is a distinct subsystem property, which indicates
there are only several floors of civil structures with nonlinear or inelastic vibration and the other with linear vibration. In
this study, a robust control approach combining decentralized control with adaptive fuzzy control is proposed to treat the
nonlinear control for civil structures. The structural system is decomposed into several artificially subsystems, while the
different subsystem is adopted the corresponding control algorithm. The input-to-state stability of the entire system can
be guaranteed by the proposed control method, and an H infinity performance is achieved through a subsystem with the
proposed controller. Numerical examples are presented to demonstrate the effectiveness and robustness of the proposed
controller.
Smart precast concrete frame connection based on unbonded shape memory alloy (SMAPCFC) was proposed as a
possible seismic resistance measure for reinforced concrete frame buildings. To investigate the restoring force
characteristics of SMA wire, cyclic tensile tests on superelastic NiTi SMA wires with three diameters were carried out.
The effects of the different loading conditions, namely: cyclic loading-unloading number, strain amplitude, loading
frequency and ambient temperature, on the mechanical behavior described by some fundamental quantities, such as
energy dissipation per cycle, secant stiffness, equivalent damping, residual strain, were examined. The temperature
changes of the SMA wires due to the latent heat under different loading conditions were also discussed.
The problem of optimizing an absorber system for three-dimensional seismic structures is addressed. The objective is to
determine the number and position of absorbers to minimize the coupling effects of translation-torsion of structures at
minimum cost. A procedure for a multi-objective optimization problem is developed by integrating a dominance-based
selection operator and a dominance-based penalty function method. Based on the two-branch tournament genetic
algorithm, the selection operator is constructed by evaluating individuals according to their dominance in one run. The
technique guarantees the better performing individual winning its competition, provides a slight selection pressure
toward individuals and maintains diversity in the population. Moreover, due to the evaluation for individuals in each
generation being finished in one run, less computational effort is taken. Penalty function methods are generally used to
transform a constrained optimization problem into an unconstrained one. The dominance-based penalty function contains
necessary information on non-dominated character and infeasible position of an individual, essential for success in
seeking a Pareto optimal set. The proposed approach is used to obtain a set of non-dominated designs for a six-storey
three-dimensional building with shape memory alloy dampers subjected to earthquake.
A fuzzy logic control (FLC) algorithm optimized by the genetic algorithm (GA) is developed in the paper for the
benchmark problem application regarding the vibration control of tall buildings under along wind excitation. The
adopted control scheme consists of an MR damper which the control action is achieved by a Fuzzy Controller. The fuzzy
rules for the controller are optimized by the genetic algorithm to enhance the efficiency of the control system. A fuzzy
strategy of two-input and single-output variables is adopted in the control system. The fuzzy subset and rules base for the
controller are optimized by the genetic algorithm to further decrease the responses of the controlled structure. The
robustness of the controller has been demonstrated through the uncertainty in stiffness (15% and -15% variations from
initial stiffness) of the building. The results of the simulation show a good performance by the fuzzy controller for all
tested cases.
Fiber Bragg grating (FBG) sensors demonstrate great potentials for structural health monitoring of civil structures to
ensure their structural integrity, durability and reliability. The advantages of applying fiber optic sensors to a tall building
include their immunity of electromagnetic interference and multiplexing ability to transfer optical signals over a long
distance. In the work, FBG sensors, including strain and temperature sensors, are applied to the construction monitoring
of an 18-floor tall building starting from its construction date. The main purposes of the project are: 1) monitoring the
temperature evolution history within the concrete during the pouring process; 2) measuring the variations of the main
column strains on the underground floor while upper 18 floors were subsequently added on; and 3) monitoring the
relative displacements between two foundation blocks. The FBG sensors have been installed and interrogated
continuously for more than five months. Monitoring results of temperature and strains during the period are presented in
the paper. Furthermore, the lag behavior between the concrete temperature and its surrounding air temperature is
investigated.
To investigate the influence of shape memory alloys (SMAs) on the dynamic properties (mainly refers to the frequency
and the damping ratio) of concrete columns, the vibration curves of the concrete column reinforced with steel wire and
SMA wires with different phase were measured through initial displacement method. In this study, the experiment
included two parts. One is the free vibration test, which utilized the active property tuning (APT) principle, i.e. the
passive damping, of SMAs to change the vibration performance of the concrete columns. The results show that SMAs
can increase the damping ratio of the concrete column due to its high damping and decrease the frequency owing to its
lower stiffness. The other is the vibration test with electrical current activation, the active strain energy tuning (ASET)
principle, i.e. the active damping, was applied to alternate the vibration performance of the concrete columns. In this test,
martensitic SMA wires were strained up to 4% and were heated with a current of 40A. The test results show that with
increasing of the temperature, the frequency of the concrete column decreases, while its damping ratio increases.
Comparing the results of these two tests, the influence of two tuning principles, APT principle and ASET principle, on
the damping ratio of concrete columns is almost the same. However, for the frequency of the concrete columns, the
influence of ASET principle is larger than that of APT principle.
Energy dissipation technique, relying on the absorption and dissipation of big amount of energy by devices, provides
a very effective passive method of protecting structures from the hazard of earthquakes. An innovative hybrid
damper combining friction device with superelastic shape memory alloy (SMA) wires was proposed. The most
important property of the damper is the integration with stable energy dissipation capacity mostly provided by the
friction device and re-centring feature profited from the superelastic pre-tensioned SMA wires. To investigate the
mechanical behaviors of the damper as a function of pre-displacement, displacement amplitude and loading
frequency, cyclic tensile tests on a scale model under various loading conditions were conducted. The effectiveness
of the damper to reduce the seismic vulnerability of structures is assessed through nonlinear time history analysis on
a steel frame with the innovative dampers subjected to representative earthquake ground motions. The experimental
and analytical results show that the hybrid SMA damper has both the stable energy dissipating and recentring
features with the hysteretic loop under cyclic loading-unloading, and it is effective in reducing the seismic response
of structures.
Superelastic shape memory alloy (SMA) is a potential candidate for use in structural damping devices due to its unique
mechanical properties. An innovative re-centering SMA damper is presented. Being configurated simply, the device
comprises two functional groups of SMA strands, such as the un-pre-tensioned wires and the pre-tensioned wires,
resulting in a perfect energy dissipation compatible with a negligible residual displacement. Based on the cyclic loading
tests of the superelastic SMA wires, the Lagoudas simplified model is determined. Extensive experiments are carried out
to investigate the influence of cycles, frequency and displacement amplitude on the mechanical behaviors of the damper,
such as the secant stiffness, the dissipated energy per cycle and the equivalent viscous damping. By analyzing the
working mechanism, a model is set up to simulate the hysteretic curve of the damper, its feasible predictions being
validated by the experimental results. Furthermore, nonlinear time history analyses of a SDOF system are performed,
and the results show that the re-centering damper not only can decrease the vibration of the system under excitations, but
also can mitigate residual displacement after excitations.
A neural networks-based structural identification method using absolute acceleration without mode shapes and frequency
extraction is proposed and validated with vibration absolute acceleration measurements from shaking table test of a
two-storey frame structure. An acceleration-based neural network modeling for acceleration forecasting and a parametric
evaluation neural network for parametric identification are constructed to facilitate the whole identification process.
Based on the two neural networks and by the direct use of absolute acceleration measurement time histories of the object
frame structure under base excitation, the inter-storey stiffness and damping coefficients of the frame structure are
identified. The identified results by the proposed methodology are compared with them by solving eigenvalues equation.
Results show that the structural stiffness and damping coefficients identification accuracy is acceptable and the proposed
strategy can be a practical tool for model updating and damage detection of engineering structures.
In this work, we propose an Adaptive Neuro Fuzzy Inference System (ANFIS) based hysteresis modeling and
control strategy for a thin Shape Memory Alloy (SMA) wire. Controlling the SMA wire is a challenging problem
because of its dynamic hysteretic behavior. By using a hybrid learning procedure ANFIS architectures are
powerful tools for many applications, such as identifying nonlinear parameters in a controlled system, predicting
chaotic time series and modeling nonlinear functions. We tested our ANFIS model by making it predict major
and minor hysteresis loops in different driving frequencies and compared them with the experimental data. To
compensate the hysteretic effect, we used an inverse ANFIS model and used it directly as a controller. After
dramatically reducing the hysteretic effect, we implemented a PI control to fine tune the response.
Shape memory alloys (SMAs) are a relatively new class of functional materials, exhibiting special thermo-mechanical behaviors, such as shape memory effect and superelasticity, which enables their applications in seismic engineering as energy dissipation devices. This paper investigates the properties of superelastic shape memory alloys and highlights the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests on NiTi SMA wires. A novel constitutive equation is proposed to describe the strain-rate dependent hysterestic behavior of superelastic SMAs at different strain levels. This development is based on the Graesser and Cozzarelli's model, which has the advantage of simplicity. To verify the effectiveness of the proposed constitutive equation, experiments on a superelastic NiTi wire with different strain rates and strain levels are conducted. Experimental results and the numerical simulation based on the proposal constitutive equation are in close agreement. The results in this paper are useful for future design of superelatic SMA-based energy dissipation devices for seismic protection of structures.
Superelastic shape memory alloy (SMA) is a potential candidate for use in structure damping devices due to its unique
mechanical properties. In order to mitigate the vibration of a structure subjected to earthquake tremors from different
directions, an innovative, multi-directional SMA-based damper is advanced. The damper, with two movable cylinders
attached to four groups of SMA strands arranged in a radial symmetry, can not only function in a plane, but also can
work vertically and rotationally. Based on experimentation, the Graesser model of superelastic SMA is determined. By
analyzing the damper's mechanism working in different directions, the corresponding theoretical models are developed.
Numerical simulations are conducted to attain the damper's hysteresis. Working in a plane, the damper, with a 3%
initial strain, provides a rectangular hysteresis with the maximum amount of damping. A rectangular flag hysteresis can
be supplied in the absence of a pre-stress in the wires, going through the origin with a moderate amount of energy
dissipation and higher force capacity. Moreover, the damper has better working capacities (i.e. force, stroke and energy
dissipation) if the deflection is parallel to the internal bisectors of the tension axes. Working vertically or rotationally,
similar triangular flag hysteresis is generated with small energy dissipation and a self-centering capacity. For a given
deflection, the initial strain (3%) increases the force of the damper, but decreases its stroke.
An improved two-dimensional constitutive model for Shape memory alloys (SMAs), which can describe both the shape
memory effect (SME) and super elasticity effect (SE) of the SMAs, is developed based on the previous work of Boyd
and Lagoudas, who used the thermodynamics theories of free energy and dissipation energy to derive the constitutive
law of SMAs. The improved model, which will combine the ideas of Brinsion's one-dimensional constitutive law and
the concepts of Boyd and Lagoudas' two-dimensional one, has a simple but accurate expression. The results of the
simulations show that the developed constitutive model can qualitatively describe the thermo-mechanical behaviors of
two-dimensional SMAs and can be used in the analysis of structures actuated by SMAs.
This paper presents studies of seismic response control of a frame structure braced with SMA (Shape Memory Alloy)
tendons through both numerical and experimental approaches. Based on the Brinson one-dimensional constitutive law
for SMAs, a two-story frame structure braced diagonally with SMA tendons is used as an example to simulate
numerically the vibration control process. By considering the temperature, different initial states and thermal properties
of the SMA tendon, and the variable intensity and frequency of earthquake input, the parameters of the system were
analyzed during the numerically simulation. The time histories of the displacement and hysteretic loops of the SMA
tendons were simulated under earthquake ground motion by using finite element method (FEM). To validate the
efficiency of the simulation, a shaking table test for the frame structure was conducted. Both numerical simulation and
experimental results show that the actively controlled martensite SMA tendons can effectively suppress the vibration of
the multi-story frame structure during an earthquake.
KEYWORDS: Actuators, Ferroelectric materials, System identification, Control systems, Sensors, Linear filtering, Control systems design, Filtering (signal processing), Matrices, Electronic filtering
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.
Biomechanical studies often involve measurements of the strains developed in tendons or ligaments in posture or
locomotion. Fiber optic sensors present an attractive option for measurement of strains in tendons and ligaments due to
their low cost, ease of implementation, and increased accuracy compared to other implantable transducers. A new
displacement sensor based on fiber Bragg grating and shape memory alloy technology is proposed for the monitoring of
tendon and ligament strains in different postures and in locomotion. After sensor calibration in the laboratory, a
comparison test between the fiber sensors and traditional camera displacement sensors was carried out to evaluate the
performance of the fiber sensor during application of tension to the Achilles tendon. Additional experiments were
performed in cadaver knees to assess the suitability of these fiber sensors for measuring ligament deformation in a
variety of simulated postures. The results demonstrate that the proposed fiber Bragg grating sensor is a high-accuracy,
easily implantable, and minimally invasive method of measuring tendon and ligament displacement.
KEYWORDS: Vibration control, Systems modeling, Signal processing, Digital signal processing, Control systems, Bridges, Power supplies, Feedback control, Process control, System identification
In this paper, a simple non-model based control strategy is developed to control stay cable vibration using MR dampers. The strategy
is an integral plus double integral control based on the collocated accelerometer feedback. To experimentally study this control
method, a model stay cable equipped with an Magneto-Rheological(MR) damper is used in this study. To demonstrate the
effectiveness of the proposed controller, comparisons of the unimpeded stay cable, passive off, passive on and the proposed integral plus double integral control are conducted. For each case, the damping ratio of the stay cable vibration is calculated. Comparisons of the experimental results show that non-model based vibration control of the stay cable using the MR damper is most effective in reducing the stay cable vibration.
Past RC panel tests performed at the University of Houston show that reinforced concrete membrane elements under reversed cyclic loading have much greater ductility when steel bars are provided in the direction of principal tensile stress. In order to improve the ductility of low-rise shear walls under earthquake loading, high seismic performance shear walls have been proposed to have steel bars in the same direction as the tensile principal direction of applied stresses in the critical region of shear walls. This paper presents the results of reversed cyclic tests on three low-rise shear walls with SMA bars. The height, width, and thickness of the designed shear walls are 1.0 m, 2.0 m, and 0.12 m, respectively. SMA bars are provided in the directions of 27 degrees to the horizontal that are in the diagonal direction. The reinforcing bars of the shear walls are in vertical and horizontal directions. The ratios of both SMA and reinforcing bars are 0.24%. The main parameter used in the study is the type of SMA bar, namely Superelastic and Martensite SMA bars. The test results from the walls with SMA bars are also compared to a conventional wall without SMA bars. Test results also show that the maximum shear strengths of the tested walls are affected by the SMA bars. It was found that the shear wall with Martensite SMA bars has greater residual displacement. In contrast, the shear wall with superelastic SMA bars has less residual displacement. At the ultimate state, one of the four superelastic SMA bars buckled, resulting in less energy dissipation capacity than the expected value. Preventing buckling of SMA bars is the research focus in the near future.
Vacuum-Assisted Resin Transfer Molding (VARTM) process was used to fabricate the nanocomposites through integrating carbon nanofiber paper into traditional glass fiber reinforced composites. The carbon nanofiber paper had a porous structure with highly entangled carbon nanofibers and short glass fibers. In this study, the carbon nanofiber paper was employed as an inter-layer and surface layer of composite laminates to enhance the damping properties. Experiments conducted using the nanocomposite beam indicated up to 200-700% increase of the damping ratios at higher frequencies. The scanning electron microscopy (SEM) characterization of the carbon nanofiber paper and the nanocomposites was also conducted to investigate the impregnation of carbon nanofiber paper by the resin during the VARTM process and the mechanics of damping augmentation. The study showed a complete penetration of the resin through the carbon nanofiber paper. The connectivities between carbon nanofibers and short glass fibers within the carbon nanofiber paper were responsible for the significant energy dissipation in the nanocomposites during the damping tests.
KEYWORDS: Actuators, Shape memory alloys, Finite element methods, Sensors, Manufacturing, Data acquisition, Mechanical engineering, Control systems, Power supplies, Electromechanical design
Compliant mechanisms have a wide range of application in microassembly, micromanipulation and microsurgery. This article presents a low cost Flexure-Stage actuated by two SMA-wires that produces displacement in one direction in a range from 0 to 10 μm. The Flexure-Stage acts as a mechanical transform by reducing and changing the direction of the SMA actuator output displacement. The Flexure-Stage system has its application in microassembly operation and was built at cost of US$ 35 cost. The design methodology of a flexure-stage from concept design through FEA modeling and finally to construction and characterization is presented in this paper.
An optimal placement of MR dampers using genetic algorithm (GA) is put forward in this paper in order to reduce the vibration responses of high-rise building under wind load. The shear dynamic model and equation of motion of the structural system are set up and some parameters of the system are determined based on the model considering the torsion effects of the building. Moreover, an optimal installation model for MR dampers based on genetic algorithm is set up. To simulate the vibration procedures under wind load, a 12-story reinforced concrete eccentric frame structure is used as an example to show the optimal steps and response control effect. The results of the simulation show that genetic algorithm can be used effectively and economically in the optimal installation design of MR dampers in high-rise eccentric buildings to decrease the structural vibration responses induced by wind load.
The superelastic shape memory alloys (SMAs) have received increasing interest attributed to their unique mechanical properties. Modeling of SMAs' thermomechanical behavior has been an active area of research; however the existing models are generally valid only for quasi-static loading conditions and extremely complex for practical use. In this research, one-dimensional cyclic loading tests of superelastic shape memory alloy wires are first performed to determine their hysteresis properties. The effects of the strain amplitude and the loading rate on the mechanical properties are studied and formulized by least-square method. Based on the Graesser's model, an improved model is developed. The improved model divides the full loop into three parts: the loading branch, the unloading branch before the completion of the reverse transformation and the elastic unloading branch after the completion of reverse transformation, each part adopts its respective parameters. The improved model not only has the same advantages as the Graesser's model, such as relative simple formulation with parameters that can be easily acquired and being valid for dynamic loading conditions, but also overcomes the deficiency of the Graesser's model, i.e. ignoring the effects of loading path on the model parameters. Numerical simulations are conducted. Comparisons indicate that the improved Graesser's model accurately reflects all the hysteresis characteristics and provides a better prediction of the SMA's actual hyteresis behavior than the Graesser's model at varying levels of strain and loading rate.
It is important to conduct early age strength monitoring of concrete structures because it will help speed up construction.
Piezoelectric-based strength monitoring method provides an innovative experimental approach to conduct concrete
strength monitoring at early ages. In the presented paper, piezoelectric transducers were embedded into the concrete
specimen during casting. The development of strength of concrete structures was monitored by observing the
development of harmonic amplitude from the embedded piezoelectric sensor at early ages. From the experimental
results, the amplitude of the harmonic response decreased with the increment of the concrete strength. The amplitude of
the harmonic response from piezoelectric sensor dropped rapidly for the first week and continued to drop slowly as
hydration proceeded which matches the development of the concrete strength at early ages. Concrete is heterogeneous
and anisotropic which makes it difficult to be mathematically analyzed. Fuzzy logic has the advantage to conduct
analysis without requiring a mathematical model. In this paper, a fuzzy logic system was trained to correlate the
harmonic amplitude with the concrete strength based on the experimental data. The concrete strength estimated by the
trained fuzzy correlation system matches the experimental strength data. The proposed piezoelectric-based monitoring
method has the potential to be applied to strength monitoring of concrete structures at early ages.
We develop an analytical model for the relationship between the strain measured by a fiber Bragg grating sensor and the actual structural strain. The values of the average strain transfer rates calculated from the analytical model agree well with available experiment data. Based on the analytical model, the critical adherence length of an optical fiber sensor can be calculated and is determined by a strain lag parameter, which contains both the effects of the geometry and the relative stiffness of the structural components. The analysis shows that the critical adherence length of a fiber sensing segment is the minimum length with which the fiber must be tightly bonded to a structure for adequate sensing. The strain transfer rate of an optical fiber sensor embedded in a multilayered structure is developed in a similar way, and the factors that influence the efficiency of optical fiber sensor strain transferring are discussed. It is concluded that the strain sensed by a fiber Bragg grating must be magnified by a factor (strain transfer rate) to be equal to the actual structural strain. This is of interest for the application of fiber Bragg grating sensors.
This paper presents a new approach to numerical implementation of a classical Preisach model to hystersis modeling of Shape Memory Alloys (SMA). Classical Preisach hysteresis model is a phenomenological model and it offers various advantages over other models. After reviewing the basic properties of the classical Preisach model, this paper reveals one difficulty to numerically implement a classical Preisach model. Numerical simulations have to be done in two different cases: 1) when input ascends and 2) when input descends. Based on the geometrical interpretation, this paper proposed a unified approach to numerical implementation of a Preisach model and there is no need to consider the different cases. To demonstrate the effectiveness of the proposed numerical method, an experiment setup with an SMA wire with severe hysteresis is utilized. Experimental results convincingly demonstrate that the proposed method accurately captures the features of the hysteresis. Using the forward Preisach model, an approach to find the inverse model is presented for compensation purpose.
KEYWORDS: Sensors, Actuators, Data modeling, Feedback control, Signal attenuation, Ferroelectric materials, Control systems, Systems modeling, Vibration control, Electromechanical design
This paper reports multimodal vibration control of a flexible beam structure with piezoceramic actuators and sensors using the loop shaping method. These piezoceramic patch actuators and sensors are surface-bonded on the flexible beam. The non-parametric identification of the flexible beam structure is carried out using the Schroeder wave. The identified open loop model is then used for loop shaping based on the extended sensitivity charts. A loop shaping compensator is designed to achieve multimodal vibration suppression. Numerical results showed a reduction of 8 decibels for first mode, 12-14 decibels for second and third mode, respectively. Experimental results closely match the simulation results. Furthermore, the results of loop shaping method are compared with those of the methods of LQR (Linear Quadratic Regulator) and pole-placement control, which are designed using state space models. Comparisons show that the loop shaping method requires less control effort while maintaining the effectiveness in vibration suppression.
This paper presents a new design of piezoelectric friction damper, which consists of tube piezoceramic stack actuators, load cells, preload bolts, brass sheets, spring washers and slotted bolted connection. A semi-active control strategy for variable friction dampers based on an improved suboptimal Bang-Bang control algorithm presented in this paper is also developed. By using genetic algorithm, the amplitudes of the control and preloading friction forces in the control system are obtained for enhancing the seismic performance of the controlled structures. The proposed approach is applied to a three-story building with a variable friction damper installed in the first story. The numerical results indicate that more reduction of the peak accelerations under seismic excitations and a better adaptability can be achieved than those of the unmodified controller.
It is well known that both martensite and austenite (superelastic) Nitinol Shape Memory Alloys (SMAs) have damping capacities, benefiting from their hysteretic stress-strain relationships. In general, for SMA devices for passive vibration control, martensite SMA has a larger damping capacity; however, it requires external heat to cause a phase transformation to restore its original shape. On the other hand, superelastic SMA has less damping capacity, but it has a strong re-centering force to restore its initial shape and there is little residual strain of the superelastic SMAs. This paper researches the damping capacity of Nitinol in martensite and austenite co-existence phase. Nitinol with the co-existence of both martensite and austenite phases combines advantages of martensite SMAs and superelastic SMAs and has a large damping capacity with self-shape restoring ability. To quantitatively study the damping effect of Nitinol in martensite and austenite co-existence phase, a setup is designed and fabricated. This setup involves a cantilevered steel beam with pre-stressed SMA wires attached to each surface at the remote end of the beam. The SMA wires function as a damper to the cantilevered beam. A piezoceramic patch sensor attached to the beam near its cantilevered end is used to record the data of the vibration of beam and the data is then used to estimate the damping ratio of the system. The percentage of the martensite phase in the Nitinol SMA wires is controlled by electrically heating the wires via a closed-loop control system. Experimental results verify that the Nitinol wires with the co-existence of the both martensite and austenite have the best damping property for vibration suppression. For practical implementation, the transformation temperate of the SMA wire damper can be chosen as the room temperature so that both martensite and austenite co-exist.
Simulation of piezoelectrically actuated valveless microupump (PVAM) indicates that both the pumping rate and membrane deflection amplitude will increase with the increase of the actuating frequency at a low frequency range (<7.5 kHz). However, because of the electro-mechanical-fluid coupling, the membrane deflects in an undesirable way at high frequencies. This will lower the pumping rate at high frequencies (>7.5 kHz). At even higher frequencies (>50 kHz), the
pumping rate will decrease further because the deflection amplitude decreases. This agrees with reported experimental results. The changing membrane deflection shape at various frequencies clearly plays an important role in the performance of the pump.
We report on the use of a high-speed wavelength division multiplexing (WDM) technique for multiplexing Fiber Bragg Grating (FBG) sensors applied to structural Vibration Control for the measurement of strain, permitting many sensing devices along a single optical fiber at different locations collecting samples at 5000 Hz with microstrain resolution. In this demonstration, a cantilevered flexible aluminum beam is used as the object for vibration control. A piezoceramic patch surface-bonded to the cantilevered end of the beam is used as an actuator to suppress the beam vibration. Various active vibration controllers such as positive position feedback (PPF), strain rate feedback (SRF), proportional plus derivative (PD), pole placement, and sliding mode based robust control are tested by using the fiber optical sensor for feedback purpose. Experiments successfully demonstrate that the signals from the fiber optic sensor can be used for active feedback control of the beam vibration.
In this paper, an approach based on "energy-damage" theory for structural damage diagnosis is presented by use of wavelet packet analysis and improved BP neural network. The damage characteristics of the time domain response signals are more obvious after being transformed by the wavelet. Using the node energy in different frequency bands as the sample of tbe ANN can quite well reflect the damage features. As a numerical example, the benchmark structure given by the ASCE is used for describing the process of the damage detection presented here.
KEYWORDS: Shape memory alloys, Actuators, Feedback control, Control systems, Fluctuations and noise, Position sensors, Temperature metrology, Data acquisition, Data modeling, Control systems design
There is no reported research of using shape memory alloy (SMA) actuators for variable area exhaust nozzle for a jet engine in the literature, to the authors' best knowledge. SMA actuators have the advantages of high power-to-weight ratio and can result in dramatic weight reduction as compared to hydraulic systems. However, the difficulty of using SMA actuators for controlling variable area exhaust nozzle lies in the fact that the temperature near exhaust nozzle is far higher than the transformation temperature of an SMA actuator. Due to the flexibility and small volume of SMA wire actuators, they can be remotely replaced in a region where temperature is lower than that of its transformation temperature. By exploiting this fact, this paper presents a novel design of a proof-of-concept variable area exhaust nozzle using shape memory alloy wire actuators. The SMA actuators are remotely placed away from the exhaust nozzle area so that the environmental temperature is below their transformation temperature. By electrically heating the SMA actuators, the exhaust nozzle will experience an area reduction of up to 40%. Bias springs will apply forces to return the fan nozzle to the open-up configuration. A feedback controller based sliding mode method is used to regulate the SMA actuators' position. Experimental results demonstrate that the proposed design meets the desired area variation specifications and show the promise of a lightweight and simple exhaust nozzle design by using shape memory alloy actuators.
This paper investigates the feasibility of direct model reference adaptive control (MRAC) scheme for the vibration suppression of a smart flexible beam. Direct model reference adaptive controller whose parameters are updated directly from the Lyapunov-based adaptive laws is developed. The adaptive laws for updating the controller parameters are derived and the stability for the closed loop system is proved. The developed MRAC design is numerically verified on a flexible beam model, showing that it has better performance and robustness in vibration suppression with respect to the system parameter variations. Compared with classical active vibration control such as positive position feedback (PPF) control, MRAC can produce more efficient and faster control than PPF control. The satisfactory simulation results show that the MRAC scheme is an effective approach for vibration suppression.
Composite materials are widely applied in aerospace, mechanical and civil structures. Delamination of composite material happens due to aging, chemical corruption and mechanical vibration, among other factors. It is important to detect the delamination in the incipient stage before the delamination reaches a notable level. Piezoelectric material can act as both actuators and sensors. In this research, two composite plates are fabricated as test specimen, of which one has a small delamination and the other is healthy. Four PZT patches are bonded at four corners of each composite plate, and one PZT patch is bonded in the middle of the composite plate. Wavelet packet analysis is applied as the signal-processing tool to analyze the sensor data. A damage index is formed based on the wavelet packet analysis to show the existence and the severity of damage. The experiment results show the proposed method can detect the delamination. This sensitive method is suited for delamination detection of inaccessible composite structures without using additional excitation facility.
Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in recent years, and the applications have promoted interest in health monitoring of structural composites. Although primary layouts of these composite structures are similar, the FRP composites used in civil engineering structures are usually relatively thicker and larger in size. Hence, more power authority is needed in the experimental procedure for health monitoring purposes. In this study, health monitoring of thick composite structures using smart piezoelectric materials is presented. Monitoring technique based on wave propagation is evaluated for possible damage detection in civil composite structures. For comparison purposes, the composite laminated beams with two different thickness are made of E-glass fiber and epoxy resins by vacuum bagging process, and the damage in the form of delamination is created by inserting Teflon sheet between the lamina at certain location. Smart piezoelectric materials are used as both the emitter and receiver of the wave. The exploratory experimental program developed in this study can be used for better understanding of the possibility of wave propagation based technique in health monitoring and damage detection of large civil FRP composite structures.
KEYWORDS: Shape memory alloys, Actuators, Control systems, Resistance, Neural networks, Feedback control, Position sensors, Control systems design, Signal processing, Crystals
This paper presents the development of a position control system for a shape memory alloy (SMA) wire actuator using the electrical resistance feedback. It is commonly known that an SMA actuator is highly nonlinear and a position sensor is often required to achieve a stable and accurate positioning. And this position sensor often contributes a large portion of the system cost. To eliminate the position sensor in an SMA actuator system, a novel control theme is proposed by utilizing the actuator’s electrical resistance feedback. With an SMA wire test setup, the relationship between the electrical resistance and the displacement is experimentally investigated. However, this relationship is highly nonlinear, and a neural network is employed to model this relationship and predicts the position of the actuator using only its electrical resistance information. To enable feedback control of the SMA wire actuator using only its electrical resistance, a Proportional-Integral-derivative (PID) controller is used. Feedback control experiments are performed and the results demonstrate that the proposed position control system achieves a good control performance without using a position sensor.
KEYWORDS: Actuators, Control systems, Feedback control, Mathematical modeling, Sensors, MATLAB, Simulink, Data modeling, Control systems design, Smart materials
This paper presents the classical Preisach modeling of the hysteresis and tracking control of a Thunder actuator system. The numerical expressions of the classical Preisach model were presented in details for different input variations. It was found that the saturation output values in these numerical expressions could be cancelled out. A series of tests were conducted to study the hysteresis properties of the Thunder actuator system. The classical Preisach model was then applied to simulate the static hysteresis behavior of the system. Higher-order hysteresis reversal curves predicted by the classical Preisach model were verified experimentally. The good agreement found between the measured and predicted curves showed that the classical Preisach model is an effective mean for modeling the hysteresis of the Thunder actuator system. Subsequently, the inverse classical Preisach model was established and applied to the real time microposition tracking control of the Thunder actuator system. Real time tracking control was achieved by combining a lead-lag feedback controller and the inverse model. On a moving range of 0-0.1mm, the tracking error with hysteresis compensation was less than 2.5%, compared to an error of up to 10% without hysteresis compensation. Experimental results showed that control accuracy with hysteresis compensation is greatly improved compared to that without hysteresis compensation.
This paper presents the design, testing, and application of a thin-film Magnetorheological (or simply MR) fluids damper/lock. This MR damper/lock is designed for the use in a model adaptive fan nozzle system actuated by shape memory alloy wires. The MR damper/lock (a total of 8 in the fan nozzle system) will lock the opening size of the fan nozzle and provides damping when the system vibrates. For this purpose, the MR damper/lock has to have the following characteristics: 1) The device is in lock position when power is off. 2) The device has a small static friction force (less than 1 lbf) when power is on. 3) The device generates a small kinetic friction force when it slides during power-on period. 4) Its damping coefficient can be adjusted. 5) Being compact. To meet these requirements, a new design of a damper/lock using thin MR fluid film is employed. The device consists of five major components: two soft steel bars, two stacks of permanent magnets, two groups of magnetic wires, a soft steel slider, and MR fluid. Utilizing the permanent magnets, the MR fluid is trapped and the device is always in lock position. When the device is powered on, the flux of the electrical magnets partially cancels and re-directs the rest of the flux from the permanent magnets, and then the slider is free to move. In this design, MR fluid reduces the air gap and increases locking force when it is powered off. On the other hand, it also functions as a lubricant to reduce the kinetic friction forces when it is powered on. Extensive tests of the MR damper/lock are conducted to reveal its force-displacement curves and force-velocity curves under different applied voltages. Utilizing these testing results, the MR damper/lock is applied to the model adaptive fan nozzle system to perform both locking and damping tasks with a feedback control. Experimental results show that these tasks are successfully achieved.
Maintaining surface shape of precision structures such as spacecraft antenna reflectors has been a challenging task. The surface errors are often introduced by thermal distortions due to temperature differences. This paper presents numerical and experimental results of active compensation of thermal deformation of a composite beam using piezoelectric ceramic actuators. To generate thermal distortion to the composite beam, two film heaters are bonded to only one-side of the beam using thermally conductive materials. To correct thermal deformation caused by the film heaters, PZT (Lead Zirconate Titanate), a type of a piezoelectric ceramic material, is used in the form of patches as actuators. These PZT patches are bonded on the other side of the beam. First, finite element analyses are conducted with the consideration of the coupled effects of structural, electric, and thermal fields on the composite beam. These analyses include static coupled field modeling of the beam deformation with PZT actuation, transient modeling of the beam under thermal loading, and static coupled field modeling of the composite beam with thermal distortion and simultaneous PZT actuation to correct this distortion. Then, experiments are conducted to study thermal effect, PZT actuation effect and active thermal distortion compensation using PZT actuators with a Proportional, Integral, and Derivative (PID) feedback controller. FEM and experimental results agree well and demonstrate the proposed method can actively perform structural shape control in the presence of thermal distortion.
In this paper, structural health monitoring based on wavelet analysis is investigated to detect damages in thin aluminum plates. Conventional methods in health monitoring mainly focus on differences in the modal parameters such as natural frequency, but they require the existence of a large damage in order to detect the damage efficiently. In this paper the damage feature is extracted from the distribution energy metric by means of wavelet packet algorithms, which can demonstrate the large difference even when the damage is very small. Experimental research is carried out to validate the method used in our approach. Piezoceramic actuators and sensors are used to excite the plate and sense the induced vibrations. Wavelet analysis is then conducted using the recorded data to obtain the distribution energy metric for each plate. As a result, it is shown that the health status of thin aluminum plates with small holes can be effectively identified through the distribution energy metric.
Theoretical analysis of active control of vibration in a cylindrical shell is presented in this paper. The forced vibration wave in a circular cylindrical shell is studied and the propagation of the vibration wave is controlled actively. The structural model considered is an infinite elastic circular cylindrical shell and excited harmonically by a primary force arranged in a line around its circumference. Active control is achieved by applying another line circumferential distributed force apart form the primary force. The input vibration power flow is theoretically studied and used to evaluate the performance of the active control method. Numerical simulation results demonstrate that it is possible to achieve a vibration reduction of 15 dB for only one control force. To realize this active control force, smart actuators such as the piezoceramic material can be used. It is hoped that the investigation will shed some light on the control of vibration propagation in such structures by using smart materials.
KEYWORDS: Shape memory alloys, Actuators, Modulation, Modulators, Control systems, Energy efficiency, Resistance, Control systems design, Smart materials, Power supplies
Shape memory alloy (SMA)s, in particular the nickel-titanium alloy (or Nitinol), have been used as actuators in some astronautic, aeronautic and industrial applications. Future will see more SMA application if less energy is required for actuation. This paper presents the design and experimental results of control of an SMA actuator using Pulse Width (PW) Modulation to reduce the energy consumption by the SMA actuator. An SMA wire test stand is used in this research. Open-loop testing of the SMA wire actuator is conducted to study the effect of the PWM parameters. Based on results of testing results and parameter analysis of the PW modulator, a PW modulator is designed to modulate a Proportional plus Derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PW modulation effectively save actuation energy whiling maintaining same control accuracy as compared to continuous PD control. PW modulator also demonstrates robustness to external disturbances. A comparison with pulse width pulse frequency (PWPF) modulator is also presented.
Advanced and innovative materials and structures are increasingly used in civil infrastructure applications. By combining the advantages of composites and smart sensors and actuators, active or smart composite structures can be created and be efficiently adopted in practical structural applications. This paper presents results of active vibration control of a pultruded fiber-reinforced polymer (FRP) composites thin-walled I-beams using smart sensors and actuators. The FRP I-beams are made of E-glass fibers and polyester resins. The FRP I-beam is in a cantilevered configuration. PZT (Lead zirconate titanate) type of piezoelectric ceramic patches are used as smart sensors and actuators. These patches are surface-bonded near the cantilevered end of the I-beam. Utilizing results from modal analyses and experimental modal testing, several active vibration control methods, such as position feedback control, strain rate feedback control and lead compensator, are investigated. Experimental results demonstrate that the proposed methods achieve effective vibration control of FRP I-beams. For instance, the modal damping ratio of the strong direction first bending mode increases by more than 1000 percent with a positive position feedback control.
This paper presents the design and experiment results of active position control of a shape memory alloy (SMA) wires actuated composite beam. The composite beam is honeycomb structured with shape memory alloy wires embedded in one of its phase sheet for active actuation. The potential applications of this experiment include thermo-distortion compensation for precession space structure, stern shape control for submarines, and flap shape control for aeronautical applications. Shape memory alloy wires are chosen as actuating elements due to their high recovery stress (maybe greater than 700 MPa) and tolerance to high strain (up to 8%). However, shape memory alloy wires are inherently nonlinear and pose a challenge for control design. A robust controller is designed and implemented to active control the tip position of the composite beam. The experiment setup consists of the composite beam with embedded SMA wires, programmable current/voltage amplifier to actuate the SMA wires, an infrared laser range sensor to detect the beam tip displacement, and a real-time data acquisition and control system. Experiments demonstrated the effectiveness of the robust control.
The application of the acoustic emission (AE) technique has been severely limited during the past several decades due to the difficulties of source location on general shell structures. Two major obstacles are the lack of search algorithms on shell structures, where wave paths are guided by structure shapes, and the lack of the ability to process AE data for meaningful source location. This paper discusses a systematical approach for precise source location on shell structures. The approach not only provides the satisfactory answers to these two problems but also addresses the issue how a precise source location techniques can be used on a daily and routine basis. The approach has been applied to two important studies: analysis of AE data from a rocket motor case and AE monitoring of a railroad tank car. The success in both applications is remarkable. In the case of the railroad tank car where 12 sensors were used, the typical error margin is only 50-150 mm with the best accuracy of 10 mm for a set of data. In viewing of the consistently of the high performance of this approach as demonstrated in both cases as well as the fact that these studies were carried out under the normal industrial monitoring conditions, including structure size, sensor array arrangement and data gathering procedure, we believe that the approach is reliable, technically and economically feasible and ready for general industrial applications.
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