Cracking assessment in concrete structures by distributed optical fiber

In this paper, a method to obtain crack initiation, location and width in concrete structures subjected to bending and instrumented with an optical backscattered reflectometer (OBR) system is proposed. Continuous strain data with high spatial resolution and accuracy are the main advantages of the OBR system. These characteristics make this structural health monitoring technique a useful tool in early damage detection in important structural problems. In the specific case of reinforced concrete structures, which exhibit cracks even in-service loading, the possibility to obtain strain data with high spatial resolution is a main issue. In this way, this information is of paramount importance concerning the durability and long performance and management of concrete structures. The proposed method is based on the results of a test up to failure carried out on a reinforced concrete slab. Using test data and different crack modeling criteria in concrete structures, simple nonlinear finite element models were elaborated to validate its use in the localization and appraisal of the crack width in the testing slab.Peer ReviewedPostprint (author’s final draft

Interactive real-time physics: an intuitive approach to form-finding and structural analysis for design and education

Real-time physics simulation has been extensively used in computer games, but its potential has yet to be fully realised in design and education. We present an interactive 3D physics engine with a wide variety of applications. In common with traditional FEM, the use of a local element stiffness matrix is retained. However, unlike typical non-linear FEM routines, elements forces, moments and inertia are appropriately lumped at nodes following the Dynamic Relaxation Method. A semi-implicit time integration scheme updates linear and angular momentum, and subsequently the local coordinate frames of the nodes. The Co-Rotational formulation is used to compute the resultant field of displacements in global coordinates including large deformations. The results obtained compare well against established commercial software. We demonstrate that the method presented allows the making of interactive structural models that can be used in teaching to develop an intuitive understanding of structural behaviour. We also show that the same interactive physics framework allows real-time optimization that can be used for geometric and structural design application

Reconstruction and Simulation of Cellular Traction Forces

Biological cells are able to sense the stiffness, geometry and topography of their environment and sensitively respond to it. For this purpose, they actively apply contractile forces to the extracellular space, which can be determined by traction force microscopy. Thereby cells are cultured on elastically deformable substrates and cellular traction patterns are quanti- tatively reconstructed from measured substrate deformations, by solving the inverse elastic problem. In this thesis we investigate the influence of environmental topography to cellular force generation and the distribution of intracellular tension. For this purpose, we reconstruct traction forces on wavy elastic substrates, using a novel technique based on finite element methods. In order to relate forces to single cell-matrix contacts and different structures of the cytoskeleton, we then introduce another novel variant of traction force microscopy, which introduces cell contraction modeling into the process of cellular traction reconstruction. This approach is robust against experimental noise and does not need regularisation. We apply this method to experimental data to demonstrate that different types of actin fibers in the cell statistically show different contractilities. We complete our investigation by simulation studies considering cell colonies and single cells as thermoelastically contracting continuum coupled to an elastic substrate. In particular we examined the effect of geometry on cellular behavior in collective cell migration and tissue invasion during tumor metastasis

3D Simulation of Partial Discharge in High Voltage Power Networks

Open accessPartial discharge (PD) events arise inside power cables due to defects of cable’s insulation material, characterized by a lower electrical breakdown strength than the surrounding dielectric material. These electrical discharges cause signals to propagate along the cable, manifesting as noise phenomena. More significantly, they contribute to insulation degradation and can produce a disruptive effect with a consequent interruption of power network operation. PD events are, therefore, one of the best ‘early warning’ indicators of insulation degradation and, for this reason, the modeling and studying of such phenomena, together with the development of on-line PDs location methods, are important topics for network integrity assessment, and to define methods to improve the power networks’ Electricity Security. This paper presents a 3D model of PD events inside a void in epoxy-resin insulation cables for High Voltage (HV) power networks. The 3D model has been developed using the High Frequency (HF) Solver of CST Studio Suite® software. PD events of a few µs duration have been modelled and analyzed. The PD behavior has been investigated using varying electrical stress. A first study of the PD signal propagation in a power network is described

A REAL TIME DECISION SUPPORT SYSTEM FOR THE ADJUSTMENT OF SAILBOAT RIGGING

The operational complexity and performance requirements of modern racing yachts demand the use of advanced applications, such as a decision support system (DSS) able to assist crew members during navigation. In this article, the authors describe a near-time computational solver as the main piece of a DSS which analyses and monitors the behaviour of sails and rigging. The solver is made up of two different interconnected tools: an iterative Fluid-Structure Interaction algorithm and an advanced Wireless Sensor Network to monitor rigging. The real-time DSS quantifies crew manoeuvres in physical terms, which are reproduced by a simulation program. It can be used in the design phase of sailing yachts and as an aid for real-time boat performance optimisation and accident prevention. This novel DSS is a useful tool for navigation, especially in races

A real-time decision support system for the adjustment of sailboat rigging

The operational complexity and performance requirements of modern racing yachts demand the use of advanced applications, such as a decision support system (DSS) able to assist crew members during navigation. In this article, the authors describe a near-time computational solver as the main piece of a DSS which analyses and monitors the behaviour of sails and rigging. The solver is made up of two different interconnected tools: an iterative FluidStructure Interaction algorithm and an advanced Wireless Sensor Network to monitor rigging. The real-time DSS quantifies crew manoeuvres in physical terms, which are reproduced by a simulation program. It can be used in the design phase of sailing yachts and as an aid for realtime boat performance optimisation and accident prevention. This novel DSS is a useful tool for navigation, especially in races

Seismic response trends evaluation and finite element model calibration of an instrumented RC building considering soil-structure interaction and non-structural components

Peer reviewedPostprin

Development of a decision support system for the design and adjustment of sailboat rigging

The two main objective of this work are: - To develop a simulation program of the behaviour of upwind sails and rigging, to help the crew to optimize the performance of the sailing yacht in real time. For this purpose, it will be necessary to formulate a fluid-structure interaction algorithm to compute the performance of a particular sail/rigging configuration. Since the crew dynamically trims the rigging and sails, in order to evaluate the performance of the actual configuration, a tool to monitor the rigging and sails will be necessary, too. - To adjust a monitoring element to quantify in physic values the manoeuvre of the crew. This will be our monitoring tool. - To reproduce the crew manoeuvre in the simulation program with the data obtained with the monitoring tool. Once the sail/rigging configuration has been adapted ‘in real time’ to the actual one, the performance of this new configuration can be computed. For this purpose the simulation program and the monitoring tool must communicate among them

Numerical and experimental investigation of spectral domain vibration based indicators for structural health monitoring

Structural health monitoring has been defined as the acquisition, validation and analysis of technical data to facilitate life- cycle management decisions. It is the result of a convergent path from many previous existing disciplines the two most influential being condition monitoring for rotary machinery and non-destructive testing. Vibration based testing presents the greatest stage of maturity of all non-destructive techniques applied to structural health monitoring. Although modal domain use is convention, spectral domain data is by nature more complete in information and requires less manipulation. The use of spectral-domain measurements brings the need to develop new damage detection indicators, as much of the literature existing is focused on modal derived damage indicators. In this work, an integrated methodology for the evaluation of some spectral domain vibration based indicators for structural health monitoring is proposed. These indicators, namely the CFDAC and SCIs, are based on the correlation between covariance matrices of frequency response functions obtained from experimental modal analysis. An extensive numerical campaign is performed on a simple structure (consisting on a 1-edge clamped square aluminium plate) over multiple structural alteration scenarios to assess the sensibility and stability of the proposed indexes in front of common acquisition parameters. The ability of the proposed indicators to assess structural alteration progression is also evaluated. This numerical analysis is used as well to observe the relationship between proposed indicators and the residual stiffness of the simple structure evaluated in terms of relative shift from the pristine condition. Finally, the numerical methodology proposed is applied to a different and more complex typology of structure, a 3d latticed and downscaled power transmission tower to investigate the validity of the methodology for other structural configurations. Some of the cases studied in the numeric campaign are later reproduced in experimental scenarios using two specimens of aluminium plates and a downscaled prototype of a power transmission tower. Stability analysis on the indicators are reproduced and confirmed. For the aluminium plates, the relationship between indicators and residual stiffness is also obtained, showing close agreement with numerical data. Sensibility of the indicators to detect different damage typologies is found to be very similar to the one obtained in the initial numerical analysis. Results for the downscaled prototype model tower shown more dispersion than the results observed in the numerical investigation due to the influence of the boundary conditions in the model. The research finally applies the structural damage alteration indexes studied to the detection of degradation in a real scale structure in an operational environment. An installation consisting of 3 full-scale medium-voltage power transmission towers is constructed. An experimental modal analysis campaign is performed on the central tower of the installation by introducing a series of intentionally made structural alterations on the structure. Spectral indicators developed are applied to the detection of those structural modifications with noticeable success. Cases involving changes in the structural components of the tower are successfully detected. Changes in the interface between power lines and their supports of the tower are hardly noticeable using this methodology. Results of this investigation show that spectral domain damage indicators present some advantages over modal domain and temporal domain based indicators such as convenient condensing procedures without loss of information through the Fourier transform, added post-process simplicity and enhanced sensitivity to degradation that state of the art indexes.Es coneix com monitorització de la salut estructural a l'adquisició, validació i anàlisis de dades tècniques que faciliten la presa de decisions al llarg del cicle de vida d'un sistema. Aquesta tecnologia és resultat de la convergència tecnològica d'altres disciplines, com la monitorització operacional per màquines rotatòries i les tècniques d'assaig no destructiu. Els mètodes d'assaig basats en vibracions presenten el major grau de maduresa d'entre totes elles. Malgrat que la pràctica industrial sovint usa informació condensada en el domini modal, les dades en domini espectral son per naturalesa més completes i requereixen de menys post-procés. La utilització del domini espectral requereix desenvolupar nous indicadors d'alteració ja que la major part de la literatura existent se centra en indicadors basats en el domini modal. Es proposa una metodologia integrada per a la avaluació d'alguns indicadors d'alteració estructural en domini modal basats en vibració i aplicats a la monitorització de la salut estructural. Aquests indicadors, referits com a CFDAC i SCIs, estan basats en la correlació entre les matrius de covariància generades a partir de les funcions de resposta en freqüència obtingudes mitjançant anàlisi modal experimental. Es realitza una extensa campanya numèrica en una estructura senzilla (una placa d'alumini quadrada i encastada) a través d'una multitud d'estats estructuralment alterats per avaluar la sensibilitat i l'estabilitat dels indicadors enfront els paràmetres d?adquisició més comuns. En segon lloc, també s?avalua la capacitat dels indicadors per avaluar l'alteració estructural introduïda en cada cas. L'anàlisi numèrica s'utilitza a continuació per observar una possible relació entre els indicadors proposats i la rigidesa residual avaluada com a variació relativa respecte el seu valor intacte. Finalment, la metodologia numèric proposada s'aplica a una tipologia estructural diferent i més complexa, una estructura reticulada 3d que reprodueix una torre de transmissió d'energia elèctrica a escala per investigar la validesa de la metodologia en altres configuracions estructurals. Alguns dels casos estudiats a la campanya numèrica es reprodueixen experimentalment en un parell d?espècimens de placa d'alumini i en un prototip a escala de torre de transmissió elèctrica. Els anàlisis d'estabilitat numèrics sobre els indicadors es reprodueixen experimentalment, tot confirmant els resultats obtinguts. Per les plaques d'alumini, s'estudia la relació entre els indicadors i la rigidesa residual mostrant una correlació molt propera amb els resultats numèrics. La sensibilitat dels indicadors en la detecció de diferents tipologies de dany també s'observa molt similar als casos numèrics. Pere altra banda, els resultats experimentals sobre el prototip de torre a escala presenten més dispersió respecte a la corresponent campanya numèrica degut a la variabilitat en les condicions de contorn. Els indicadors proposats s'apliquen finalment en la detecció d'alteracions estructurals en una torre a escala real en condicions operacionals. Es construeix una línia que consisteix en tres torres de mitja tensió i s'executen anàlisis modals experimentals en la torre central de la mencionada instal·lació tot introduint una sèrie d'alteracions estructurals intencionals. Els indicadors espectrals presentats s'apliquen a la detecció de dites alteracions amb un èxit apreciable. Els casos que incorporen canvis en els membres de l'estructura son detectats amb èxit, mentre que la detecció en els casos que incorporen modificacions sobre les interfícies cable-estructura son més difusament detectables. Els resultats de la investigació mostren que els indicadors estructurals espectrals estudiats presenten algunes avantatges sobre els indicadors basats en domini com ara un procés de condensació més senzill sense pèrdua d'informació vibratòria (...

Numerical and experimental investigation of spectral domain vibration based indicators for structural health monitoring

Structural health monitoring has been defined as the acquisition, validation and analysis of technical data to facilitate life- cycle management decisions. It is the result of a convergent path from many previous existing disciplines the two most influential being condition monitoring for rotary machinery and non-destructive testing. Vibration based testing presents the greatest stage of maturity of all non-destructive techniques applied to structural health monitoring. Although modal domain use is convention, spectral domain data is by nature more complete in information and requires less manipulation. The use of spectral-domain measurements brings the need to develop new damage detection indicators, as much of the literature existing is focused on modal derived damage indicators. In this work, an integrated methodology for the evaluation of some spectral domain vibration based indicators for structural health monitoring is proposed. These indicators, namely the CFDAC and SCIs, are based on the correlation between covariance matrices of frequency response functions obtained from experimental modal analysis. An extensive numerical campaign is performed on a simple structure (consisting on a 1-edge clamped square aluminium plate) over multiple structural alteration scenarios to assess the sensibility and stability of the proposed indexes in front of common acquisition parameters. The ability of the proposed indicators to assess structural alteration progression is also evaluated. This numerical analysis is used as well to observe the relationship between proposed indicators and the residual stiffness of the simple structure evaluated in terms of relative shift from the pristine condition. Finally, the numerical methodology proposed is applied to a different and more complex typology of structure, a 3d latticed and downscaled power transmission tower to investigate the validity of the methodology for other structural configurations. Some of the cases studied in the numeric campaign are later reproduced in experimental scenarios using two specimens of aluminium plates and a downscaled prototype of a power transmission tower. Stability analysis on the indicators are reproduced and confirmed. For the aluminium plates, the relationship between indicators and residual stiffness is also obtained, showing close agreement with numerical data. Sensibility of the indicators to detect different damage typologies is found to be very similar to the one obtained in the initial numerical analysis. Results for the downscaled prototype model tower shown more dispersion than the results observed in the numerical investigation due to the influence of the boundary conditions in the model. The research finally applies the structural damage alteration indexes studied to the detection of degradation in a real scale structure in an operational environment. An installation consisting of 3 full-scale medium-voltage power transmission towers is constructed. An experimental modal analysis campaign is performed on the central tower of the installation by introducing a series of intentionally made structural alterations on the structure. Spectral indicators developed are applied to the detection of those structural modifications with noticeable success. Cases involving changes in the structural components of the tower are successfully detected. Changes in the interface between power lines and their supports of the tower are hardly noticeable using this methodology. Results of this investigation show that spectral domain damage indicators present some advantages over modal domain and temporal domain based indicators such as convenient condensing procedures without loss of information through the Fourier transform, added post-process simplicity and enhanced sensitivity to degradation that state of the art indexes.Es coneix com monitorització de la salut estructural a l'adquisició, validació i anàlisis de dades tècniques que faciliten la presa de decisions al llarg del cicle de vida d'un sistema. Aquesta tecnologia és resultat de la convergència tecnològica d'altres disciplines, com la monitorització operacional per màquines rotatòries i les tècniques d'assaig no destructiu. Els mètodes d'assaig basats en vibracions presenten el major grau de maduresa d'entre totes elles. Malgrat que la pràctica industrial sovint usa informació condensada en el domini modal, les dades en domini espectral son per naturalesa més completes i requereixen de menys post-procés. La utilització del domini espectral requereix desenvolupar nous indicadors d'alteració ja que la major part de la literatura existent se centra en indicadors basats en el domini modal. Es proposa una metodologia integrada per a la avaluació d'alguns indicadors d'alteració estructural en domini modal basats en vibració i aplicats a la monitorització de la salut estructural. Aquests indicadors, referits com a CFDAC i SCIs, estan basats en la correlació entre les matrius de covariància generades a partir de les funcions de resposta en freqüència obtingudes mitjançant anàlisi modal experimental. Es realitza una extensa campanya numèrica en una estructura senzilla (una placa d'alumini quadrada i encastada) a través d'una multitud d'estats estructuralment alterats per avaluar la sensibilitat i l'estabilitat dels indicadors enfront els paràmetres d?adquisició més comuns. En segon lloc, també s?avalua la capacitat dels indicadors per avaluar l'alteració estructural introduïda en cada cas. L'anàlisi numèrica s'utilitza a continuació per observar una possible relació entre els indicadors proposats i la rigidesa residual avaluada com a variació relativa respecte el seu valor intacte. Finalment, la metodologia numèric proposada s'aplica a una tipologia estructural diferent i més complexa, una estructura reticulada 3d que reprodueix una torre de transmissió d'energia elèctrica a escala per investigar la validesa de la metodologia en altres configuracions estructurals. Alguns dels casos estudiats a la campanya numèrica es reprodueixen experimentalment en un parell d?espècimens de placa d'alumini i en un prototip a escala de torre de transmissió elèctrica. Els anàlisis d'estabilitat numèrics sobre els indicadors es reprodueixen experimentalment, tot confirmant els resultats obtinguts. Per les plaques d'alumini, s'estudia la relació entre els indicadors i la rigidesa residual mostrant una correlació molt propera amb els resultats numèrics. La sensibilitat dels indicadors en la detecció de diferents tipologies de dany també s'observa molt similar als casos numèrics. Pere altra banda, els resultats experimentals sobre el prototip de torre a escala presenten més dispersió respecte a la corresponent campanya numèrica degut a la variabilitat en les condicions de contorn. Els indicadors proposats s'apliquen finalment en la detecció d'alteracions estructurals en una torre a escala real en condicions operacionals. Es construeix una línia que consisteix en tres torres de mitja tensió i s'executen anàlisis modals experimentals en la torre central de la mencionada instal·lació tot introduint una sèrie d'alteracions estructurals intencionals. Els indicadors espectrals presentats s'apliquen a la detecció de dites alteracions amb un èxit apreciable. Els casos que incorporen canvis en els membres de l'estructura son detectats amb èxit, mentre que la detecció en els casos que incorporen modificacions sobre les interfícies cable-estructura son més difusament detectables. Els resultats de la investigació mostren que els indicadors estructurals espectrals estudiats presenten algunes avantatges sobre els indicadors basats en domini com ara un procés de condensació més senzill sense pèrdua d'informació vibratòria (...)Postprint (published version