Symposium P
Embodying Intelligence in Structures and Integrated Systems

ABSTRACTS

Session P-1 - Smart Materials/Sensors/Actuators/MEMS/NEMS

P-1:IL01  CNT Transduction for Measuring Composite Shear and Air Flow: Triggering of Autonomous Response
K. SLINKER1,2, C. KONDASH1,2, G. REICH3, J. BAUR1, 1Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH, USA; 2Universal Technology Corporation, Beavercreek, OH, USA; 3Aerospace Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH, USA

The change in electrical resistivity with compression of carbon nanotubes (CNTs) arrays can be used as a transduction element in a micro-scale sensor. When properly integrated with micro-scale mechanical elements and autonomous materials, these can be used to create compact and biologically inspired sensors that can be used to trigger an autonomous response. This presentation will discuss the design, fabrication, and structure-property relationships of sensors consisting of CNTs grown on individual structural fibers within electroded capillaries to create small, inexpensive, and highly sensitive sensors. The integration of these sensors with bonded composite structures under shear loading has shown the ability to internally detect early failure initiation events. Their integration with aerodynamic element as “hair-like” sensors under flow has shown their ability to measure boundary layer flow velocity. Due to their low-cost and small size, these sensors are easily integrated into arrays to provide spatial mapping of shear and air flow. We will highlight our current efforts to fabricate and characterize sensor arrays and project their potential use as triggers to initiate autonomous materials and structural responses such as self-healing, load redistribution, and shape morphing.


P-1:IL02  Piezoceramic MFC Thin Films Experimental Shear Sensing Response Simulation
A. BENJEDDOU, Institut Supérieur de Mécanique de Paris, Saint Ouen, France

Piezoceramic Macro Fibre Composite (MFC) thin films are nowadays widely used as sensors. They consist of rectangular cross-section fibres, separated with epoxy and forming an active core that is sandwiched between electrode and protective layers However, their use is still limited to longitudinal and transverse response modes; nevertheless, MFC thin films responding in the transverse shear response mode have been also realized. The objective of this invited lecture is, first, to present the challenging numerical characterization of multilayer shear piezoceramic MFC thin films using representative volume element-based finite element homogenization procedures. It is found that the latter provides the three-dimensional (3D) full set of electromechanical material constants while the former is able to provide, beside elastic constants, only shear-response piezoelectric and dielectric ones. Then, using resulting 3D full set of electromechanical material constants, static FE simulations are conducted and corresponding results are presented and discussed regarding the test-model correlation accuracy and influence of the glue type. The present work main output that it allowed validating the numerical characterization through the obtained excellent test-model correlation accuracy.


P-1:IL03  Shape control by PZT
H. IRSCHIK, Johannes Kepler University of Linz, Linz, Austria; M. KROMMER, Vienna University of Technology, Vienna, Austria; C. ZEHETNER, Linc Center of Mechatronics, Linz, Austria

We present an overview on recent work of our group on shape control, particularly on displacement tracking, of smart structures that are equipped with piezoelectric actuators and sensors made of various PZT materials. In the actuation version, one seeks for a distributed piezoelectric actuation, which produces a desired (prescribed) displacement field in the presence of given imposed transient forces. In the complementary sensing version, piezoelectric sensor distributions are sought, the combined output of which represents structural entities such as displacements or slopes due to arbitrary imposed force loadings. We start with theoretical derivations that are performed in the framework of the theory of small incremental dynamic deformations superimposed about a statically pre-deformed configuration of a hyper-elastic structure. In the latter context we derive classes of exact solutions for the required actuator and sensor distributions, assuming that the piezoelectric effects can be tailored freely and applied everywhere within the structure. From these solutions, discrete networks of PZT sensors and actuators are derived, which approximately satisfy the goals of shape control and displacement tracking, where the special behavior of the various PZT materials are utilized.


P-1:IL04  Shape Memory Alloys Wires for Engineering Applications. Particular Characteristics of NiTi SMA: From Small to Medium Diameter
S. CASCIATI, DICA Dept., University of Catania, Siracusa, Italy; M. VECE, Structural Mechanics Dept., Pavia University, Italy; V. TORRA, Applied Physics Dept. Polytechnic University of Catalonia, Barcelona, Spain

The use of Shape Memory Alloys as dampers was suggested in the literature. An analysis realized in standard cables of facilities shows the reliable efficiency of the SMA wire. This work focuses on the temperature analysis of the SMA wires. The study aims to assess the influence of the wire diameter when the macroscopic behavior of the alloy and the external temperature actions are considered. Damping requires the absorption of the mechanical energy and its conversion to heat via the action of the hysteresis cycle. The study was realized on wires of diameters 0.5 and in 2.46 mm. The flat cycles characteristic of the thinner wires (i.e., in 0.5 mm) and the non-classical S-shaped cycles observed in the 2.46 mm wires show clear differences under external summer-winter temperature actions. A complete flat transformation in thinner wires requires stresses, up to 300 MPa. For a S-shaped cycle 600 MPa were required. The analyzes of the behavior (i.e., 30 to -10 °C are carried out by using Clausius-Clapeyron coefficient: the thinner wires loses their pseudo-elastic state in winter. The S-shaped wire is particularly adequate for working under external temperatures as required in bridges. The S-shaped behavior can be improved by strain aging and created by an anomaly in specific heat.


P-1:L06  Carbon Nanotube Nanocomposites with Enhanced Strength and Damping Capabilities
G. LANZARA, S. CHAKRABARTI, G. FORMICA, University of Rome, RomaTre, Italy; M. TALÒ, W. LACARBONARA, Sapienza University of Rome, Italy

The realization of novel lightweight materials characterized by enhanced strength and dissipation, are highly desirable in the aerospace industry. Carbon nanotubes (CNT) are considered to be the ideal filler to individually achieve strength or dissipation. However, these two properties are usually considered to be conflicting and not simultaneously exploitable in the same material. This is because dissipation typically relies on the interfacial sliding motion of CNTs within a polymeric hosting matrix, while reinforcement relies on strong interactions between the two constitutive materials. Here novel designs, modeling and manufacturing methods that overcome the above limitation, are presented. The experimental work focuses on the design, realization and testing of novel CNT-matrix interfaces (e.g. with the help of proteins) to exploit specific interfacial shear strengths, while novel meso-mechanical nonlinear inelastic models are adopted to predict the effective damping capacity of CNT nanocomposites.


P-1:IL07  Vibroacoustic Behaviour of Periodic Smart Structures
M. ICHCHOU, C. ZHOU, J.P. LAINE, A. ZINE, Ecole Central de Lyon, Ecully, France

Structural dynamics can be described in terms of structural modes as well as elastic wave motions. The mode-based methods are widely applied in mechanical engineering and numerous model order reduction (MOR) techniques have been developed. When it comes to the study of periodic structures, wave description is mostly adopted where periodicity is fully exploited based on the Bloch theory. For complex periodic structures, several MOR techniques conducted on wave basis have been proposed in the literature. In this work, a wave and modal coupled approach is developed to study the wave propagation in periodic structures. The approach begins with the modal description of a unit cell (mesoscopic scale) using Component Mode Synthesis (CMS). Subsequently, the wave-based method –Wave Finite Element Method (WFEM) is applied to the structure (macroscopic scale). The method is referred as “CWFEM” for Condensed Wave Finite Element Method. It combines the advantages of CMS and WFEM. CMS enables to analyse the local behaviour of the unit cell using a reduced modal basis. On the other hand, WFEM exploits fully the periodic propriety of the structure and extracts directly the propagation parameters. Thus the analysis of the wave propagation in the macroscopic scale waveguides can be carried out considering the mesoscopic scale behaviour. The effectiveness of CWFEM is illustrated via several one-dimensional (1D) periodic structures and two-dimensional (2D) periodic structures. The criterion of the optimal reduction to ensure the convergence is discussed. Typical wave propagation characteristics in periodic structures are identified, such as pass bands, stop bands, wave beaming effects, dispersion relation, band structure and slowness surfaces...Their proprieties can be applied as vibroacoustics barriers, wave filters. CWFEM is subsequently applied to study wave propagation characteristics in perforated plates and stiffened plate. A homogenization method to find the equivalent model of perforated plate is proposed. The high frequency behaviours such as wave beaming effect are also predicted by CWFEM. Three plate models with different perforations are studied. Experimental validation is conducted on two plates. For the stiffened plate, the influence of internal modes on propagation is discussed. The modal density in the mid- and high- frequency range is estimated for a finite stiffened plate, where good correlation is obtained compared to the mode count from modal analysis.


P-1:IL08  Perspectives of TiNi-based and Fe-based SMA in Vibration Protection of Structures
A. VOLKOV, F.S. BELYAEV, M.E. EVARD, N.A. VOLKOVA, Saint Petersburg State University, Saint Petersburg, Russia

The developed microstructural approach provides a physically based description of the deformation processes on the micro level including the phase transformation, martensite reorientation and plastic slip. Thus, it is applicable to a wide class of the regimes of thermomechanical loading. This talk presents results of modeling of the specific mechanical behavior of SMA of the TiNi-type compared to the Fe-Mn-based alloys with fcc-hcp phase transformation. Examples of simulation of such phenomena as pseudoelasticity, shape memory, ferroelasticity (pseudoplasticity), irreversible strain accumulation under thermocycling are given. Microstructural modeling is used for simulation of the performance of the vibration protection devices including simulation of the base isolation of structures subjected to earthquake vibrations. Simulation shows that a semi-active vibration control can mitigate or avoid the resonance.


P-1:L09  In Situ Monitoring of CFRP’s Fatigue Damage due to Manufacturing Flaws using Carbon Nanotube-embedded Spatial Strain Sensor
YINGJUN ZHAO, S. HOERRMANN, M. SCHAGERL, Institute of Constructional Lightweight Design, Johannes Kepler University Linz, Linz, Austria; C. DOPPLER, Laboratory for Structural Strength Control of Lightweight Constructions, Linz, Austria

Carbon fiber-reinforced polymer (CFRP) composites are lightweight, durable, and corrosion-resistive materials that are being widely adopted for constructing automotive body structures and aircraft fuselages. However, they are less maneuverable than metals due to their heterogeneous composition and anisotropic behavior. To investigate CFRPs’ damage-to-failure mechanisms, a health monitoring system that can identify multiple damage attributes may significantly contribute to CFRP’s failure analysis. In this study a carbon nanotube (CNT)-embedded nanocomposite thin film is applied upon a defect-induced CFRP coupon to monitor its damage growth during a fatigue test. Unlike conventional strain gages which only track local strain values, this spatial damage sensor interrogates the entire damage-prone region in situ for nearly real-time measurement of spatial strains at or near the cracks. Images of the spatial damages can be reconstructed by electrical impedance tomography (EIT) to visualize a crack’s location and size. Coupled with EIT, this CNT-based composite thin film aims to provide cheap and reliable solutions to accommodate CFRP’s in situ health monitoring, contributing direct damage data toward its life cycle analysis.


P-1:L10  FBG-Galfenol Integrated Magnetic Field Sensors for Harsh Environments
D. DAVINO, C. VISONE, University of Sannio, Benevento, Italy; M.A. CAPONERO, C. CIANFARANI, A. POLIMADEI, ENEA C.R. Frascati, Frascati, RM, Italy

Design of magnetic field sensors in harsh environments is a challenging task. The paper aims to develop a simple, robust sensor to be exploited in harsh conditions, such as the the Tokamak vessel for nuclear fusion experiments where the presence of a high neutron flux makes standard sensors unusable. The proposed idea is to provide an indirect measurement of the magnetic field through the strain response of a magnetostrictive (galfenol) bar. The strain can be indirectly detected by integrating a fiber Bragg grating (FBG) glued to the bar, then acting as strain sensor. The information travels through the fiber and this guarantees reliability and robustness to work in heavy conditions. But, galfenol is quite a magnetically “soft” material, implying a reduced field range detection (around 100kA/m) while applications, as for Tokamak vessels, may require higher fields, up to 1MA/m. On the other hand, the increase of the mechanical applied stress to the material reduces magnetostrictive coupling, so requiring higher magnetic fields to reach saturation. Then, by exploiting the smart features of galfenol, it is possible to widen the measurable field range or, even, to have a stress-controlled measurable range. The paper presents the design and performance of such a device.


P-1:IL12  Nonlinear Modeling and Analysis of Electro-active Plates: Stability, Post-buckling Behavior and Nonlinear Vibrations
M. KROMMER, E. STAUDIGL, Y. VETYUKOV, Institute of Mechanics and Mechatronics, Vienna University of Technology, Vienna, Austria

In the present paper we study the nonlinear behavior of electro-active plates. In the first part such plates are modeled as material surfaces with mechanical and electrical degrees of freedom. In the modeling part we include both, exact geometrical nonlinearity as well as physical nonlinearities. In particular, we consider two such materials; piezoelectric materials and electro-active polymers. In the second part the resulting plate equations are somewhat simplified by imposing the von Karman and Tsien kinematic hypothesis and using a Galerkin procedure for the discretization of the problem, which allows to discuss the behavior of solutions with respect to stability, post-buckling behavior and nonlinear vibrations. Finally, the third part of the paper is dedicated to numerical solutions for the exact geometrically nonlinear theory; here, Finite Elements are implemented and the results are used to verify the ones obtained from the simpler von Karman and Tsien theory.


P-1:IL13  Dynamics of Shallow Arched Microstructures
M.I. YOUNIS, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia

Micromachined shallow arches have been under increasing focus in recent years in the Microelectromechanical systems MEMS community because of their unique attractive features. One major advantage is their bi-stability nature, which makes them suitable for switching, sensing, and actuation applications. Particularly, these bi-stable structures do not require power to hold them in either stable state (the on or off positions as switches); they need power only during the transition between the two states. Another advantage in actuation applications is that they can be displaced in large strokes compared to straight and mono-stable structures. Hence, they are also desirable for energy harvesting. Micromachined shallow arches can also be unintentionally produced due to fabrication imperfections, such as stress gradient, residual stresses, and flexible anchors. This phenomenon is also common at the Nano scale. Particularly, fabricating perfectly straight Carbon Nano Tubes CNTs with controlled geometry and orientation is very difficult. Whether it is intentional or not, the curvature of arched structures can have pronounced impact on their static and dynamic behavior, and hence on their practical performance. In this talk, we will discuss some of the recent research advances relevant to micromachined shallow arched structures. Several case studies will be presented demonstrating the interesting nonlinear behavior of these structures. Both intentionally fabricated in-plane arches and unintentionally fabricated out-of-plane arches (imperfect beams) will be discussed. The potential exploitation of these structures for logic, memory, and sensing applications will be illustrated.


Session P-2 - Integration Technologies

P-2:IL01  Development and Application of Some Hybrid Nonlinear Dissipative Devices
Z. LU, D. ZHANG, Tongji University, China; S.F. MASRI, University of Southern California, Los Angeles, CA, USA; X. LU, Tongji University, China

A comprehensive study, involving analytical, computational, and experimental approaches, is presented of the development and application of a class of highly nonlinear vibration mitigation devices for controlling the oscillation of multi-degree-of-freedom systems under the action of transient dynamic environments such as earthquake and wind loads. The subject devices combine features from conventional tuned mass dampers as well as impact dampers, by capitalizing on the strength of different damping approaches. In order to confirm the validity of the simulation studies, a series of shaking table tests of a five story steel frame with the particle tuned mass damper system were carried out to evaluate the performance and to verify the analysis method. It is shown that particle tuned mass dampers have good performance in reducing the response of structures under dynamic loads, especially under random excitation cases.


P-2:IL02  Model Order Reduction in Nonlinear Systems
L. FARAVELLI, University of Pavia, Pavia, Italy

Different techniques of model order reduction (MOR) for nonlinear systems are reviewed in order to identify the most suitable in view of integration in linear structural systems of nonlinear components. The selected method is applied to a soil structure interaction case study.


P-2:IL04  Advances in Ultrasonic Defect Detection and Imaging in Structures
T. NGUYEN, S. STERNINI, F. LANZA DI SCALEA, Department of Structural Engineering, University of California San Diego, La Jolla, CA, USA

In the field of non-destructive testing of structures, 3D imaging of internal flaws is a critical task. Defect imaging allows to make informed follow-up decisions based on the morphology of the flaw. This paper will present advances in ultrasonic tomography for the 3D visualization of internal flaws. In particular, improvements to the conventional tomographic imaging algorithms have been made by utilizing a mode-selective image reconstruction scheme that exploits the specific displacement field, respectively, of the longitudinal wave modes and the shear wave modes, both propagating simultaneously in the test volume. The specific mode structure is exploited by an adaptive weight assignment to the ultrasonic tomographic array. Such adaptive weighting forces the imaging array to look at a specific scan direction and better focus the imaging onto the actual flaw (ultrasound reflector). It will be shown that additional array gains can also be obtained by compounding, coherently or incoherently, images from up to four mode combinations in a solid. Finally, the use of matched filters applied to specific features of the received RF waveforms will be demonstrated to dramatically improve the spatial resolution of the array.


P-2:L05  A Magnetostrictive Energy Harvesting System for Bridge Structural Health Monitoring
C.S. CLEMENTE, D. DAVINO, A. IELARDI, M.R. PECCE, C. VISONE, University of Sannio, Benevento, Italy

Utilization of the inverse magnetostriction effect (Villari effect) for energy harvesting purposes has been recently on the rise. Within this context, numerous efforts have been dedicated towards the design, modeling and development of magnetostrictive energy harvesting devices. In this paper we present the design and experimental evaluation of the performance of such a device aimed to be employed together with a wireless sensor for structural health monitoring of bridges, leading to a self-powered sensor. Magnetostrictive materials offer higher energy densities with respect to piezoelectrics, i.e. smaller devices with higher converted energy. The presented energy harvester is designed to be placed under the asphalt of a road bridge and makes profit of mechanical solicitation induced by the ongoing traffic. It integrates galfenol rods, magnets and power coils within a mechanical structure, designed with the double aim to convert energy and to respect road safety rules. The paper includes the criteria behind the choice of several parameters crucial to the energy conversion performances of these devices, such as electrical load as well as longitudinal bias magnetic field and mechanical stress values.


Session P-3 - Smart Structures and Integrated Systems

P-3:IL01  Multifunctional Design of Materials & Structures: Critical Issues
B.-L. ("LES") LEE, U.S. Air Force Office of Scientific Research, Arlington, VA, USA

The concept of multifunctional design has become prominent in the last several years with a number of definitions and concepts being put forth. The most popular definition is the design of a material, structure or system that has the ability to perform multiple functions through judicious combinations of structural properties and at least one functional capability as dictated by the system requirements. It is hoped that individual material elements are concurrently participating in distinct, beneficial physical processes thereby delivering truly dramatic improvements in system-level efficiency instead of incremental improvements. Among various visionary contexts for developing such systems, most notable are: (a) “autonomic” structures that can sense, diagnose and respond to external stimuli with minimal external intervention, (b) “adaptive” structures allowing reconfiguration or readjustment of functionality, shape and mechanical properties on demand, and (c) “self-sustaining” systems with structurally integrated power harvest/storage/transmission capabilities. Dramatic improvement in system-level performance and efficiency can be achieved not only by designing multifunctional structures with integrated functional properties but also by developing complex materials that inherently possess the capacity to simultaneously meet the requirements for specific functionality as well as mechanical load carrying capability. This overview presentation will address key scientific issues underpinning the advancement of multifunctional materials and structures.


P-3:IL02  Monitoring of Building for Safety, Security and Soundness
AKIRA MITA, Department of System Design Engineering, Keio University, Yokohama, Japan

Monitoring of building is becoming more and more popular for many reasons. Among others the structural health monitoring system has evolved mainly to detect damage location and damage extent in the structural system due to earthquakes and winds. However, using the sensors solely for this purpose is only persuasive for large and/or tall buildings. Thus this type of systems is rarely installed into small buildings and individual houses. The author is the principal investigator the project to install MEMS-based and cloud supported structural health monitoring system into six tall buildings in the vicinity of Shinjuku Station that is the busiest station in Japan. In this paper, our project outline and our experience will be presented and the future direction of this type of system for safety, security and soundness is shown. Monitoring using robots is also briefly introduced.


P-3:IL03  Smart Monitoring System Based on Electromechanical Impedance and Guided Ultrasonic Waves
A. NASROLLAHI1, V. GULIZZI2, P. RIZZO1, 1University of Pittsburgh, Department of Civil & Environmental, Pittsburgh, PA, USA; 2Department of Civil, Environmental, Aerospace, and Materials Engineering, University of Palermo, Palermo, Italy  

In this paper we present a structural health monitoring (SHM) paradigm based on the simultaneous use of ultrasounds and electromechanical impedance (EMI) to monitor waveguides. The paradigm uses guided ultrasonic waves (GUWs) in pulse-echo and pitch-catch mode, and EMI simultaneously. The three methodologies are driven by the same sensing/hardware/software unit. To assess the feasibility of this unified system an aluminum plate was monitored and its repeatability under varying environmental conditions was evaluated. Damage was simulated by adding small masses to the plate. The results associated with pulse-echo and pitch-catch GUW testing and with EMI monitoring show that the proposed system is robust and can be developed further to address the challenges associated with the SHM of complex structures.


P-3:IL05  Verification of the Rotation Algorithm with Data from a Three Story Stee Frame Test  
K. BALAFAS, A. KIREMIDJIAN, YIZHANG LIAO, R. RAJAGOPAL, Stanford University, Stanford, CA, USA; C.H. LOH, National Taiwan University, Taipei, Taiwan  

An algorithm that utilizes acceleration measurements was previously developed by the authors to estimate the slope due to permanent deformation of structures subjected to strong earthquake motions. The initial demonstration was on a single reinforced concrete column tested at the University of Nevada, Reno where the column was tested to failure. The rotation estimates were used to obtain displacements at the top of the column and these were compared to displacements measured with LVDTs. A numerical simulation experiment was then developed to demonstrate that the rotation measurements could be also used for multi-story structures to estimates of the deformed shape due to permanent deformations from large earthquakes. Most recently the research team participated in a test of a three story steel frame structure and the acceleration measurements were used to further verify the rotation algorithm. The test results show excellent agreement between the estimated and measured displacements. Independent rotation measurements were also collected during the test using 3-dimensional gyroscope. Again, good agreement is found between the acceleration based rotations and the gyroscope measurements. The algorithm can be used for a rapid damage assessment shortly a major earthquake.


P-3:IL06  Structural Control for Large Civil Infrastructure
S. CASCIATI, University of Catania, Siracusa, Italy; L. Elia, University of Pavia, Italy

A large data set of recorded monitoring data is available for the TKB bridge in Hong Kong. The data set is used together with a numerical model of the bridge to reconstruct a relationship with the tension forces in the main cables. Part of the data are used to build the relation. The remaining data are used for validation.


P-3:IL07  Mobile Wireless Sensor Networks for the Assessment of Civil Infrastructure System Performance: Truck and UAV-based Sensing Systems
J.P. LYNCH, Department of Civil and Environmental Engineering, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA  

Tremendous excitement surrounds the use of wireless telemetry in modern monitoring and control systems. In the domain of civil infrastructure, wireless interfaces come with many benefits centered on the eradication of wiring including allowing sensors to be mobile. This presentation focuses on recent work in mobile wireless sensor networks that are designed to have seamless interaction with stationary wireless monitoring and control systems. Two application of mobile wireless sensor networks are presented. In the first, a wireless monitoring system is installed in heavy trucks that are used to load bridges in a highway system. The truck-based monitoring system is capable of direct communication with stationary wireless sensor networks installed in bridges for structural health monitoring. The coupling of the two networks allow for acquisition of vehicular loads on the bridge. In the second application, a wireless sensor network is deployed using an unmanned aerial vehicle (UAV). The UAV is capable of collecting data from wireless sensors, processing the data, and reconfiguring the wireless sensor network for improved field measurements. The concept is validated in the use of shear wave ground measurements for sub-surface characterization.


P-3:IL08  Sparse Solution Techniques in Load and Damage Monitoring Systems
C.-P. FRITZEN, D. GINSBERG, Dept. of Mechanical Engineering, University of Siegen, Siegen, Germany  

Load monitoring and damage identification are important tasks in the field of Structural Health Monitoring and are necessary for assessing the structural integrity and prediction the remaining useful life time. Reconstructing unknown force inputs or system parameters usually involves the solution of an inverse problem which is mostly ill-posed and therefore needs regularization.  Using prior information about the desired values is advisable for obtaining meaningful solutions. Damages like for example cracks can often be interpreted as spatial singularities, which cause local stiffness reductions of the observed structures. Damage identification is the task of localizing and quantifying these stiffness reductions. On the other hand, unknown structure excitation usually has also some special characteristics with can be assumed as known a priori, e.g. spatial concentration for singular forces, short time duration for impact loads or narrow frequency bands for harmonic loads. In this case force reconstruction becomes also a localization and magnitude estimation problem. This characteristic information is used to transform the inverse problem into a sparse recovery task. In the last years sparsity constrained regularization of inverse problem has attracted a lot of attention in applied mathematics, especially in the context of compressive sensing. In this contribution it is shown how sparse solution techniques can be applied in monitoring systems and how this will improve the reconstruction results and additionally reduce the number of required sensors.

P-3:L09  Wind Turbine Fault Detection through Principal Component Analysis and Statistical Hypothesis Testing
F. POZO, Y. VIDAL, CoDAlab, Departament de Matemàtiques, Escola Universitària d'Enginyeria Tècnica Industrial de Barcelona (EUETIB), Universitat Politècnica de Catalunya (UPC), Barcelona, Spain  

This work addresses the problem of online fault detection (FD) of an advanced wind turbine benchmark under actuators (pitch and torque) and sensors (pitch angle measurement) faults of different type: fixed value, gain factor, offset and changed dynamics. The fault detection scheme starts by computing the baseline principal component analysis (PCA) model from the healthy or undamaged wind turbine. Subsequently, when the structure is inspected or supervised, new measurements are obtained are projected into the baseline PCA model. When both sets of data --the baseline and the data from the current wind turbine-- are compared, a statistical hypothesis testing is used to make a decision on whether or not the wind turbine presents some damage, fault or misbehavior. The effectiveness of the proposed fault-detection scheme is illustrated by numerical simulations on a well-known large offshore wind turbine in the presence of wind turbulence and realistic fault scenarios. The obtained results demonstrate that the proposed strategy provides and early fault identification, thereby giving the operators sufficient time to make more informed decisions regarding the maintenance of their machines.


P-3:IL11  On-line Monitoring of High Speed Rail Systems
YI-QING NI, Hong Kong Branch of National Rail Transit Electrification and Automation Engineering Technology Research Center, Hong Kong;  Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong  

The rail industry of the future will rely on smart transportation systems that leverage a combination of technology, planning and intelligence to meet burgeoning demands for increasing running speed and traffic density, and large volumes of passengers. To keep safe and efficient operations of HSR, a great endeavor is being devoted to developing smarter railways by integrating sensors, information technology, data fusion and predictive modeling tools. Such a smart railway technology is anticipated to empower rail operators to sense and respond quickly to irregular operations and to act appropriately once a breakdown is forecasted. Through conducting online and on-board monitoring for mission critical train components, track system and wayside objects, the smart rail system embedded with appropriate analytic and predictive modelling tools not only provides real-time insight into the operational status of HSR systems and early-stage diagnosis of damage in its incipiency, but also enables the trend prediction and timely prognosis of failure before it happens. This paper outlines the development of the sensor-enabled smart rail technology for online defect/fault diagnosis and health monitoring of HSR tracks, bogies and vehicles, and showcases a number of application paradigms in HSR.


P-3:IL12  Adapting Fault-tolerant Control to Integration
J. RODELLAR, Ch. TUTIVEN, Y. VIDAL, L. ACHO, Universitat Politècnica de Catalunya, Department of Mathematics, Barcelona College of Industrial Engineering, Control Dynamics and Applications Research Group (CoDAlab), Barcelona, Spain  

Growing interest for improving reliability of safety-critical structures (such as wind turbines) has led to the advancement of structural health monitoring (SHM) and fault-tolerant control (FTC). FTC techniques that are capable of retaining acceptable performance in the presence of faults are being developed and researchers are exploring new paradigms and approaches for integrating SHM with realized controllers. In this regard, the main contribution of this work is to propose new control techniques, which not only provide fault tolerance capabilities to the wind turbine (WT), but also improve the overall performance of the system, in both fault free and faulty conditions, with respect to the standard industrial controllers. In this work, coupled non-linear aero-hydro-servo-elastic simulations of an offshore WT with jacket platform is carried out for different (realistic) faulty conditions using the FAST WT simulator. The proposed controllers are based on the super-twisting algorithm by using feedback of the generator shaft speed as well as the fore-aft and side-to-side acceleration signals of the WT tower. When designed, the controllers structure is adapted, with respect to a standard super-twisting, to mitigate vibrations and thus improving its capability for fault tolerance.


P-3:IL14  Piezoelectrically Actuated Bimorph Deformable Mirrors for Adaptive Optics
A. PREUMONT, D. ALALUF, Université Libre de Bruxelles, ULB, Brussels, Belgium  

For the past few years, the Active Structures Laboratory of ULB has been developing deformable mirrors based on Silicon wafers actuated by a bimorph PZT layer acting in d31 mode. These mirrors are intended for adaptive optics (AO), for terrestrial as well as for space applications. The paper summarizes recent technological developments: (i) The increase of the electrode density by laser ablation. (ii) Bonding the PZT active layer with a uniform voltage applied during curing, resulting in a concave initial shape, and allowing to recover a flat mirror with a bias voltage, in such a way that negative as well as positive voltages can be used in the normal operation of the AO mirror. (iii) Using a numerically predicted voltage distribution during the bonding of the PZT layer, to achieve a "free form" initial shape (without rotational symmetry) which would be impossible to obtain without a sophisticated manufacturing process. The paper also discusses the high frequency spatial waviness (dimples) introduced by the bimorph actuation and the parameters controlling this phenomenon.


P-3:IL15  Composite Structures with Nerves of Glass Fibers
A. GUEMES, Dept. Aeronautics, Universidad Politécnica de Madrid, Madrid, Spain  

About 25 years ago it was published the first article on the concept of embedding or attaching  an array of fiber optic sensors to aircraft structures, with the goal of implementing a sensorial capability. A much faster development was foreseen at that time, but there are still some issues to be solved before wide industrial applications. It is worthy to review the advances and dificulties found during this 25 years period. Among the main achievements, it has been the discovery of practical FBG sensor (1989) and distributed sensing by  OFDR (1999). Among the difficulties, the connectability and repairability of the optical sensor network, and the exploitation of strain data, or how to translate these strain data into information about damage ocurrence, shape sensing or external loads for control purposes. Early warning damage detection systems may have a huge impact of the maintenance procedures and costs, the big advantage of SHM concept is that sensors are permanently attached to the structure, thus minimizing the labour work for inspection, which can be fully automated. Fiber optic sensors are probably the preferred one, because its low size and non electrical nature. The development of algoritms to exploit these strain data is currently attracting most of the research, like in the SARISTU project. Some of the recent results will be presented.


P-3:L16  Data Evaluation in Smart Sensor Networks using Inverse Methods and Artificial Intelligence (AI): Towards Real-time Capability and Enhanced Flexibility
S. BOSSE, Department of Mathematics and Computer Science, University of Bremen, Bremen, Germany; A. LECHLEITER, Center for Industrial Mathematics (ZeTeM), University of Bremen, Bremen, Germany; D. LEHMHUS, ISIS Sensorial Materials Scientific Centre, University of Bremen, Bremen, Germany

Data evaluation is crucial for gaining information from sensor networks. Main challenges include processing speed and adaptivity to system change, both prerequisites for SHM-based weight reduction via relaxed safety factors. Our study looks at soft real time solutions providing feedback within defined but flexible, application-controlled intervals. These can rely on minimizing computation/communication latencies e.g. by parallel computation. Strategies towards this aim can be model-based, including inverse FEM, or model-free, including machine learning, which in practice bases training on a defined system state, too, hence also facing challenges at state changes. We thus introduce hybrid data evaluation combining multi-agent based systems (MAS) with inverse FEM, mainly relying on matrix operations that can be partially distributed: The MAS perform sensor data acquisition, aggregation, pre-computation, and finally application (the LM/SHM itself and higher information processing and visualization layers, i.e., WEB interfaces). System capabilities are evaluated against a virtual test case, demonstrating enhanced stability and reliability. Besides, we analyse system performance under conditions of in-service change and discuss system layouts suited to improve coverage of this issue.


P-3:L17  Integrated Sensing, Monitoring and Healing of Composite Systems
O.S. KUPONU, V. KADIRKAMANATHAN, The University of Sheffield, Sheffield, UK; B. BHATTACHARYA, Indian Institute of Technology Kanpur, Kanpur, India; S.A. Pope, The University of Sheffield, Sheffield, UK  

The ability of a material to recover its nominal properties through self-healing is gaining interest in the research community. However, current approaches remain predominantly passive in counteracting the effect of damage. As a result, healing only begins when damage has occurred in the material and this typically leads to a mismatch between the healing and damage rate. For applications such as aircraft structures, where there is a thin line between functionality and non-functionality, these limitations maybe inherently restrictive. A self-healing system that combines a prognosis unit to predict and estimate the failure rate and an active self-healing system that matches the healing rate to the estimated failure rate using a feedback loop, has the potential to overcome these limitations. In this paper we propose such a system and present results for its application to a ceramic composite material.


P-3:L18  Controllable Truss-frame Nodes in Semi-active Damping of Vibrations
B. POPLAWSKI, C. GRACZYKOWSKI, L. JANKOWSKI, Institute of Fundamental Technological Research (IPPT PAN), Warsaw, Poland

During the last few years, vibration damping strategies based on semi-active management of strain energy have attracted a considerable interest and have been proven to be highly effective. However, all published researches are significantly restricted in that they all study effectively the same very basic example (the fundamental vibration mode of a cantilever beam composed of two detachable layers) with the same general control strategy (energy transfer from the fundamental mode to the high-frequency highly-damped longitudinal mode), and differ only in the control techniques (controllable delamination, jammed granular material, magnetorheological elastomers, truss-frame nodes with controllable moment-bearing ability, etc.). This contribution studies the problem using controllable truss-frame nodes, and compared to the literature, extends it to more complex structures and more complex vibration patterns, where the optimum control strategy is no longer intuitively obvious. We discuss the general concept, define formal models of controllable truss-frame nodes, specify control performance measures, yield formally basic characteristics of the optimum control, propose control algorithms and verify them in numerical examples involving comparison to optimum passive control.


Session P-4 - Ongoing and Perspective Applications

P-4:IL01  Structural Monitoring and Assessment of Composite Structure
W. OSTACHOWICZ, Polish Academy of Sciences (IMP PAN) and Warsaw University of Technology, Poland

The paper presents methods and techniques oriented towards structural health monitoring (SHM) and extended non–destructive testing (ENDT) dedicated to composite structures. Particularly the paper presents the vibration–based methods, elastic waves propagation phenomenon, fibre optic sensors, laser sensing, electromechanical impedance, acoustic emission, and terahertz method. Investigated damage is in the form of mechanical failures as cracks, delaminations, debonding, bridging, voids. Also methods dedicated to thermal degradation, moisture and chemical contamination are shown. Presented methods are also suitable for performance of bonded joints assessment. Separate part of the paper is dedicated to influence of external factor (temperature, load) on investigated methods. The characteristic of each method is summarized by a critical look giving advantages and disadvantages that need to be addressed in future research. The paper presents multidisciplinary technologies devoted to development and implementation of of methods and systems that realize inspection and damage detection by non–destructive methods. It addresses the problem of optimisation of excitation signal parameters and sensor placement, as well as analysis of signals reflected from damage.


P-4:IL04  New Directions of Health Monitoring for Building Structures
AKIRA NISHITANI, PING XIANG, SHOHEI MARUTANI, Waseda University, Tokyo, Japan; TOMOHIKO HATADA, RYUUTA KATAMURA, Kajima Corporation, Japan

The concept of structural health monitoring (SHM) has appealed the attentions of structural engineers. However, most of the proposed schemes for SHM do not seem "friendly" for practicing engineers. In conducting SHM, the knowledge of system identification techniques or sensing technologies appears to be necessary. Among many seismic response data, inter-story drift displacement information during a seismic event could be "kind" for all structural engineers to recognize the state of a building structure. Even only the peak values of drift displacements would give the engineers certain valuable information. In such a situation, the authors' research group has invented a non-contact type of direct sensing devices of inter-story drift displacements. These devices do not need to occupy a large space and can be compactly set. The data obtained by those sensors would open the door to new SHM schemes. Those data are not only based on the construction of structural engineers-friendly SHM schemes but are used to establish a drift displacement-based response control schemes. In this regard, with these sensors, an innovation would be brought to the field of smart structures technology.


P-4:IL06  Adaptive Self-protection against Shock and Vibrations
L. JANKOWSKI, C. GRACZYKOWSKI, P. PAWLOWSKI, G. MIKUĊOWSKI, B. POPLAWSKI, R. FARAJ, J. HOLNICKI-SZULC, Institute of Fundamental Technological Research (IPPT PAN), Warsaw, Poland

This contribution provides a review of the field and challenges in adaptive self-protection of structures and presents selected examples to prove that, by employing a proper semi-active control strategy, structures can dramatically increase their ability to absorb impact-type loads and damp the resulting vibrations. Discussed systems constitute a new class of smart semi-actively controlled structures able of a real-time identification of impact-type loads and vibration patterns, followed by a low-cost optimum absorption of the energy by means of structural adaptation (adaptive impact absorption, AIA). Given the always surging quest for safety, such systems have a great potential for practical applications (adaptive landing gears, road barriers, flexible lightweight space structures, etc.). Compared to passive systems, their significantly better performance can be attributed to the paradigm of self-adaptivity, which is ubiquitous in nature, but still sparsely applied in structural engineering. Being in the early stages of development, their ultimate success depends on a concerted effort in facing a number of challenges. This contribution discusses some of the important problems, including these of a conceptual, methodological, technological and software engineering nature.


Session P-7 - Security Devices

P-7:L01  SPARTACUS: Enabling Space Technologies in Security Research
C. FUGGINI, I. TESFAI, D'Apollonia, Milan, Italy

GALILEO together with EGNOS will provide more robust positioning capability enhancing the adoption of satellite technologies in services where signal continuity and integrity are required, such as those related to Public Regulated Service (PRS) and Safety of Life (SOL) applications. This will have an impact on various sectors and applications, including emergency and disaster management, Search and Rescue Service (SAR) tasks and location-based services (LBS) supporting responders in mission critical operations. In this scenario, in November 2013, the SPARTACUS project started to design, realize and test in simulated and real world scenarios GALILEO-ready tracking solutions that can be deployed in operative missions for enhancing Location Awareness in emergency management and crisis operations. SPARTACUS developed new EU-specific services to ensure precise positioning and timing capabilities to three application areas: 1) tracking, tracing and localizing critical transport assets (railway containers) in case of major failure of existing networks (communications and power); 2) tracking the flow of relief support goods from the sending side to the receiving/end place; 3) supporting coordination of first responders in disaster management operations, ensuring their safety. By its Consortium, SPARTACUS innovations include hardware adaptations, algorithms for precision improvement, dead reckoning functionalities, location awareness, and ad-hoc independent communication networks.


P-7:L02  SPARTACUS: Positioning Units for Critical Asset Tracking and Emergency Management
L. VITTUARI, B. PAVKOVIC, A. GUINAMARD, F. CASCIATI, M. ZANZI, A. GHETTI, L. BERBAKOV, M. VECE, University of Bologna, Bologna, Italy

Motivated by the opportunity to develop industry pull applications and services for the European EGNOS and GALILEO satellite systems, within SPARTACUS are being tested satellite based positioning units aided by small inertial navigation platforms. In particular were designed and realized three different types of trackingunits for freight train, relief goods distribution, tracking and coordination of first responders. In order to improve the positioning accuracy in presence of several unitsinstalled on the same convoy, were developed software solutions based on two steps (low and high level) in order to allow the integration of information collected by the individual tracking unit and by the whole array of sensors.


P-7:L03  Satellite and Inertial Navigation Solution in Crises Management Operation for First Responders Applications
A. GHETTI, L. VITTUARI, M. ZANZI, University of Bologna, Bologna, Italy 

This work describes the activities and the results achieved within the SPARTACUS project with regards to the development of a pedestrian positioning system for first responders based on inertial sensors and GNSS data integration. In particular three steps have been dealt with. At first the analysis of a typical human motion profile, highlighting the Zero Velocity Update constraints; secondly, the definition of a high accurate reference trajectory for test validation purposes, with both indoor and outdoor tracts. Finally, the tuning of Extended Kalman Filter parameters for the calibration of the best sensor data fusion algorithm mainly focused to dead reckoning positioning and field test result assessment.


P-7:L04  Satellite and Inertial Navigation Solution in Crises Management Operation for Transport and Relief Goods Applications
F. CASCIATI, S. CASCIATI, L. FARAVELLI, M. VECE, University of Pavia, Pavia, Italy

SPARTACUS project lays its foundation on the implementation of a small size, low power consumption tracking unit integrating satellite receiver and antenna with terrestrial inertial sensors, enabling dead reckoning functionality. In case of a good GNSS signal coverage, precise positioning and timing capabilities of the system are respected, while the positioning accuracy for dead reckoning should be checked. In this paper, the results of field tests simulations are presented in order to validate positioning performance in GNSS signal outside conditions and to secure tracking, tracing and functionalities, customized for critical transport assets in case of failure of existing networks and the flow of relief support goods from the sending side to the receiving place.
 

Cimtec 2016

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