Field Deployment of Sensing Skin on a Steel Bridge for Fatigue Crack Localization and Assessment

A sensor network constituted from novel soft elastomeric capacitors acting as large-area strain gauges has been deployed on a steel bridge near Kansas City, KS. The objective of the field deployment is to validate the capability of the sensing skin to localize and assess fatigue cracks

Dynamic Load and Response Prediction of HAWT Blades for Health Monitoring Application

Wind turbine blades of a Horizontal Axis Wind Turbine (HAWT) are prone to damage; some insurance agencies report that as much as 40% of all claims are from blade damage. While most claims are not very expensive in comparison to other HAWT component repairs, for example, repairing of the gel coat, others, like replacing the entire blade can be one of the most expensive tasks. As the world moves toward larger and longer blades to capture more wind energy this problem will continue to grow. Inspecting wind turbine blades presents a challenge with most techniques requiring a technician to repel down the blade for inspection using nondestructive evaluation techniques such as ultrasound or X-ray. While some US companies like General Electric propose to use robots to perform blade inspections, there is an alternate solution to this problem which requires continuous monitoring of the blades. There is an ongoing study at Iowa State University to explore a real-time monitoring and analysis of blade response using a new type of skin-mounted strain-gauge sensor onto the inside surface of the blade. This technique would allow for damage to be detected sooner in order to reduce the overall operations and maintenance cost of wind turbines

Algorithm for decomposition of additive strain from dense network of thin film sensors

The authors have developed a capacitive-based thin film sensor for monitoring strain on mesosurfaces. Arranged in a network configuration, the sensing system is analogous to a biological skin, where local strain can be monitored over a global area. The measurement principle is based on a measurable change in capacitance provoked by strain. In the case of bi-directional in-plane strain, the sensor output contains the additive measurement of both principal strain components. In this paper, we present an algorithm for retrieving the directional strain from measurements. The algorithm leverages the dense network application of the thin film sensor to reconstruct the surface strain map. A bi-directional shape function is assumed, and it is differentiated to obtain expressions for planar strain. A least square estimator (LSE) is used to reconstruct the planar strain map from the sensors measurement’s, after the system’s boundary conditions have been enforced in the model. The coefficients obtained by the LSE can be used to reconstruct the estimated strain map or the deflection shape directly. Results from numerical simulations and experimental investigations show good performance of the algorithm, in particular for monitoring surface strain on cantilever plates

Experimental wind tunnel study of a smart sensing skin for condition evaluation of a wind turbine blade

Condition evaluation of wind turbine blades is difficult due to their large size, complex geometry and lack of economic and scalable sensing technologies capable of detecting, localizing, and quantifying faults over a blade\u27s global area. A solution is to deploy inexpensive large area electronics over strategic areas of the monitored component, analogous to sensing skin. The authors have previously proposed a large area electronic consisting of a soft elastomeric capacitor (SEC). The SEC is highly scalable due to its low cost and ease of fabrication, and can, therefore, be used for monitoring large-scale components. A single SEC is a strain sensor that measures the additive strain over a surface. Recently, its application in a hybrid dense sensor network (HDSN) configuration has been studied, where a network of SECs is augmented with a few off-the-shelf strain gauges to measure boundary conditions and decompose the additive strain to obtain unidirectional surface strain maps. These maps can be analyzed to detect, localize, and quantify faults. In this work, we study the performance of the proposed sensing skin at conducting condition evaluation of a wind turbine blade model in an operational environment. Damage in the form of changing boundary conditions and cuts in the monitored substrate are induced into the blade. An HDSN is deployed onto the interior surface of the substrate, and the blade excited in a wind tunnel. Results demonstrate the capability of the HDSN and associated algorithms to detect, localize, and quantify damage. These results show promise for the future deployment of fully integrated sensing skins deployed inside wind turbine blades for condition evaluation

La complexité comme sagesse, lucidité et liberté : Entrevue avec Jacques Zylberberg, Université Laval, Québec

Dans cet entretien, Jacques Zylberberg s’exprime sur la manière dont le concept de complexité est intervenu dans son oeuvre. Le lecteur apprend que Zylberberg en est venu à la complexité en découvrant qu’elle est davantage savoir fuyant qu’accumulation de données ; qu’elle constitue une façon particulière de décrire le monde ou, mieux, une façon de l’interroger, car le savoir est limité et que la connaissance doit constamment être remise en question, être reconstruite. Associée à l’obligation d’un questionnement continu, la complexité est éthique, position non pas simplement analytique, mais aussi morale, dont les maîtres-mots sont sagesse, lucidité et liberté.In this interview, Jacques Zylberberg expresses himself on the role the concept of complexity has played in his research. The reader finds out that Zylberberg came to complexity in discovering that it is more vanishing knowledge than data accumulation; that it constitutes a particular way for describing the world or, furthermore, a way for questioning it; since knowledge is limited, it must continuously be challenged, reconstructed. Associated with the obligation of a continuous questioning, com-plexity is ethics, a position not only analytical, but moral, whose main terms are wisdom, lucidity, and liberty

Sciences sociales et approche relationnelle

La sociologie, comme l’économie dont elle est issue, et comme la plupart des sciences sociales, oscille entre deux approches : l’une qui veut que les phénomènes sociaux soient interprétables en fonction d’un acteur rationnel, l’autre d’après laquelle l’explication des phénomènes sociaux résulte de la possibilité d’en saisir les relations. Ces deux perspectives cohabitent souvent, même au sein d’une même théorie; mais elles sont contradictoires : le social ne peut être le strict produit d’actions individuelles en même temps que celui des interactions humaines ou des relations entre les phénomènes sociaux. C’est pourquoi l’interactionnisme s’impose aux théories individualistes et pourquoi aussi l’idéologie d’un acteur rationnel, libre, intéressé, intentionnel et stratégique n’annule pas toutes les démarches relationnelles. Les approches relationnelles sont essentielles aux sciences sociales bien simplement parce qu’il n’y a pas d’individu en dehors d’interactions humaines et qu’il n’y a pas non plus de phénomène social qui ne soit pas ou bien un composé de relations ou bien lui-même en relation avec d’autres phénomènes.Sociology, as well as most social sciences, alternates between two approaches: in one case, social phenomena should be understood through a rational actor, in the other, social phenomena is the result of the possibility to understand relations. These two perspectives, although contradictory, often cohabit, even within the same theory; sociality cannot be simultaneously the pure product of individual actions and of human interactions or of relations between social phenomena. This is why interactionism imposes itself upon individualist theories and why the ideology of a rational, free, interested, intentional, and strategic actor does not impend all relational research undertakings. Relational approaches are essential to social sciences simply because there is no individual without human interactions and because there is no social phenomena which is not either a combination of relations or itself in relation with other phenomena

Terrestrial Laser Scanning-Based Bridge Structural Condition Assessment

Objective, accurate, and fast assessment of a bridge’s structural condition is critical to the timely assessment of safety risks. Current practices for bridge condition assessment rely on visual observations and manual interpretation of reports and sketches prepared by inspectors in the field. Visual observation, manual reporting, and interpretation have several drawbacks, such as being labor intensive, subject to personal judgment and experience, and prone to error. Terrestrial laser scanners (TLS) are promising sensors for automatically identifying structural condition indicators, such as cracks, displacements, and deflected shapes, because they are able to provide high coverage and accuracy at long ranges. However, limited research has been conducted on employing laser scanners to detect cracks for bridge condition assessment, and the research has mainly focused on manual detection and measurement of cracks, displacements, or shape deflections from the laser scan point clouds. This research project proposed to measure the performance of TLS for the automatic detection of cracks for bridge structural condition assessment. Laser scanning is an advanced imaging technology that is used to rapidly measure the three-dimensional (3D) coordinates of densely scanned points within a scene. The data gathered by a laser scanner are provided in the form of point clouds, with color and intensity data often associated with each point within the cloud. Point cloud data can be analyzed using computer vision algorithms to detect cracks for the condition assessment of reinforced concrete structures. In this research project, adaptive wavelet neural network (WNN) algorithms for detecting cracks from laser scan point clouds were developed based on the state-of-the-art condition assessment codes and standards. Using the proposed method for crack detection would enable automatic and remote assessment of a bridge’s condition. This would, in turn, result in reducing the costs associated with infrastructure management and improving the overall quality of our infrastructure by enhancing maintenance operations

Data-Driven Risk-Based Assessment of Wind-excited Tall Buildings using Surrogate Models

The damage reported from structural and non-structural elements during severe windstorms promoted the extension of the performance-based design (PBD) philosophy to wind-excited tall buildings. A critical part of PBD is the risk assessment of the facility. Risk assessment allows the estimation of the probability of failure of the structure considering the uncertainties arising from the external hazard and the material properties. This probability is typically estimated using a nonlinear model, which permits for the evaluation of the building performance beyond the elastic regime. In wind-excited tall buildings, the use of sophisticated computational models and the long duration of typical wind events make risk-based assessment impractical and time-demanding. As a solution, this paper presents a framework for the risk-based assessment of wind-excited tall buildings using surrogate models. In the proposed framework, the surrogate models are leveraged to reduce the computational burden of time-consuming wind time history analyses. The risk of the building is quantified using the concept of fragility and hazard functions. The surrogate model is constructed using a data-driven approach, where the training data set is derived from a high-fidelity computational model. Then, the surrogate function is used as a representation of the original computational model for risk assessment and future predictions. The proposed procedure is applied to a 39-story building. The building is equipped with motion control devices for wind-induced vibrations mitigation. The wind load is simulated in the time domain as a multivariate stochastic process and numerically applied to the structure. To create the training dataset, the structural response of the building in terms of peak acceleration and inter-story drift is estimated under different wind time histories. Two cases are considered. In the first case, the mean hourly wind speed and the terrain roughness are considered as random variables, while in the second instance the capacity of the damping devices is considered as uncertain. In both cases, the surrogate model parameters are optimized using the maximum likelihood estimation method. Results show that the proposed approach can be used for improving structural resilience under extreme wind events, where the use of surrogate model represents a viable data-driven solution for uncertainty-based risk evaluation

Distributed thin film sensor array for damage detection and localization

The authors have developed a capacitive-based thin film sensor for monitoring strain on mesosurfaces. Arranged in a network configuration, the sensing system is analogous to a biological skin, where local strain can be monitored over a global area. The measurement principle is based on a measurable change in capacitance provoked by strain. In the case of bidirectional in-plane strain, the sensor output contains the additive measurement of both principal strain components. In this paper, we present an algorithm for retrieving unidirectional strain from the bidirectional measurements of the capacitive-based thin film sensor when place in a hybrid dense sensor network with state-of-the-art unidirectional strain sensors. The algorithm leverages the advantages of a hybrid dense network for application of the thin film sensor to reconstruct the surface strain maps. A bidirectional shape function is assumed, and it is differentiated to obtain expressions for planar strain. A least squares estimator (LSE) is used to reconstruct the planar strain map from the networks measurements, after the system’s boundary conditions have been enforced in the model. The coefficients obtained by the LSE can be used to reconstruct the estimated strain map. Results from numerical simulations and experimental investigations show good performance of the algorithm

Analyses qualitatives et quantitatives : deux visions, une même science

Cet article suggère que, malgré bon nombre de plaidoiries qui affirment que les méthodes qualitatives et quantitatives sont antinomiques, ces deux types de méthode ont beaucoup en partage et ils sont tous les deux soumis aux mêmes exigences de scientificité. Non seulement jouent-ils des rôles complémentaires dans les sciences humaines, mais, en plus, 1) leurs analyses doivent toujours avoir quelque représentativité, 2) leurs résultats doivent pouvoir caractériser un ensemble étudié, 3) les caractérisations doivent être modulées par les variations individuelles, 4) leurs analyses doivent établir des liens entre les objets/sujets étudiés, et 5) ces analyses sont soumises à la tension qui s’impose entre l’obligation de regrouper les données et celle d’en respecter les particularités.Qualitative and quantitative methods are often presented as opposed or contradictory. The present article suggests that these two types of methods have, in fact, much in common and are bound by the same scientific criteria. Not only are their roles, in human sciences, complementary, but also 1) both their analyses are defined by their representative character, 2) their results must characterize a specific group, 3) their characterizations must be adapted according to individual variations, 4) their analyses must establish links between the studied objects/subjects and 5) their analyses are subject to the necessary tension which stems from the obligation of grouping the results without disregarding the distinctive features of the data