CERES :: Browsing by Author "Zanotti Fragonara, Luca"

Browsing by Author "Zanotti Fragonara, Luca"

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Open Access
The accuracy and computational efficiency of the Loewner framework for the system identification of mechanical systems
(MDPI, 2023-06-20) Dessena, Gabriele; Civera, Marco; Ignatyev, Dmitry; Whidborne, James F.; Zanotti Fragonara, Luca; Chiaia, Bernardino
The Loewner framework has recently been proposed for the system identification of mechanical systems, mitigating the limitations of current frequency domain fitting processes for the extraction of modal parameters. In this work, the Loewner framework computational performance, in terms of the elapsed time till identification, is assessed. This is investigated on a hybrid, numerical and experimental dataset against two well-established system identification methods (least-squares complex exponential, LSCE, and subspace state space system identification, N4SID). Good results are achieved, in terms of better accuracy than LSCE and better computational performance than N4SID.
Open Access
Adaptive detection tracking system for autonomous UAV maritime patrolling
(IEEE, 2020-08-06) Panico, Alessandro; Zanotti Fragonara, Luca; Al-Rubaye, Saba
Nowadays, Unmanned Aerial Vehicles (UAVs) are considered reliable systems, suitable for several autonomous applications, especially for target detection and tracking. Although significant developments were achieved in object detection systems over the last decades using the deep learning technique known as Convolutional Neural Networks (CNN), there are still research gaps in this area. In this paper, we present a new object detection-tracking algorithm that can be used on low power consuming processing boards. In particular, we analysed a specific application scenario in which a UAV patrols coastlines and autonomously classifies different kind of marine objects. Current state of the art solutions propose centralised architectures or flying systems with human in the loop, making the whole system poorly efficient and not scalable. On the contrary, applying a Deep Learning detection system that runs on commercial Graphics Processing Units (GPUs) makes UAVs potentially more efficient than humans (especially for dull tasks like coastline patrolling) and the whole system becomes easily scalable because each UAV can fly independently and the Ground Control Station does not represent a bottleneck. To deal with this task, a database consisting of more than 115000 images was created to train and test several CNN architectures. Furthermore, an adaptive detection-tracking algorithm was introduced to make the whole system faster by optimizing the balancing between detecting new objects and tracking existing targets. The proposed solution is based on the measure of the tracking confidence and the frame similarity, by means of the Structural SIMilarity (SSIM) index, computed both globally and locally. Finally, the developed algorithms were tested on a realistic scenario by means of a UAV test-bed.
Open Access
Application of fibre optic sensing systems to measure rotor blade structural dynamics - underlying data
(Cranfield University, 2021-03-12 09:17) James, Stephen; Kissinger, Thomas; Tatam, Ralph; Barrington, James; Chehura, Edmon; Weber, Simone; Mullaney, Kevin; Zanotti Fragonara, Luca; Petrunin, Ivan; Staines, Stephen
Refer to the paper for full details. Fig9a.csv: Comparison of the Power Spectral Density (PSD) of data recorded by the direct optical fibre shape sensing system, an optical fibre Bragg grating strain sensor and a 1D accelerometer with finite element modeling predictions, measured on the top surface of an Airbus Helicopters H135 bearingless main rotor blade on the quarter chord line at approximately 40% rotor radius. Fig9b.csv: Comparison of the Power Spectral Density (PSD) of data recorded by the direct optical fibre shape sensing system, an optical fibre Bragg grating strain sensor and a 1D accelerometer with finite element modeling predictions, measured on the top surface of an Airbus Helicopters H135 bearingless main rotor blade on the quarter chord line at approximately 60% rotor radius. Fig10_FBG_top.csv: Power Spectral Density (PSD) of the 7th fibre Bragg grating strain (FBG) sensor (FBG7) in the three FBG arrays bonded to the top surface of the Airbus Helicopters H135 bearingless main rotor blade, located at approximately 60% rotor radius. Fig10_FBG_bottom.csv: Power Spectral Density (PSD) of the 7th fibre Bragg grating strain sensor (FBG7) in the three FBG arrays bonded to the bottom surface of the Airbus Helicopters H135 bearingless main rotor blade, located at approximately 60% rotor radius. Fig11.csv: Time series of raw data of 3F frequency input collected at approximately 60% rotor radius for the accelerometer, fibre Bragg grating strain sensor and direct optical fibre shape sensor (vertical direction). Fig12.csv: Comparison of Power Spectral Density (PSD) for the 3F mode measured at approximately 60% rotor radius by the accelerometer, fibre Bragg grating strain sensor and direct optical fibre shape sensor (vertical direction). Fig14.csv: Mode shapes measured using the direct optical fibre shape sensor Fig15.cvs: Comparison of normalised displacement mode shapes measured using a 1D accelerometer, the direct optical fibre shape sensor with the finite element model prediction Fig16.csv: Normalised angle measurements performed by the direct optical fibre shape sensor with the ouput from the FE model for Mode 5F Fig17.csv:Comparison of normalised strain mode shapes determined by the FBG strain sensors and the output from the FE model.
Open Access
Autonomous inspection and repair of aircraft composite structures
(Elsevier, 2018-11-23) Kostopoulos, Vassilis; Psarras, Spyridon; Loutas, Theodoros; Sotiriadis, George; Gray, Iain; Padiyar M, Janardhan; Petrunin, Ivan; Raposo Gaudencio Campos, Joao; Zanotti Fragonara, Luca; Tzitzilonis, Vasileios; Dassios, Konstantinos; Exarchos, Dimitrios; Andrikopoulos, George; Nikolakopoulos, George
This paper deals with the development of an innovative approach for inspection and repair of damage in aeronautical composites that took place in the first two years of the H2020 CompInnova project which. The aim is a newly designed robotic platform for autonomous inspection using combined infrared thermography (IRT) and phased array (PA) non-destructive investigation for damage detection and characterization, while integrated with laser repair capabilities. This will affect the increasing societal need for safer aircraft in the lowest possible cost, while new and effective techniques of inspection are needed because of the rapidly expanding use of composites in the aerospace industry.
Open Access
A comparative analysis of optimization algorithms for finite element model updating on numerical and experimental benchmarks
(MDPI, 2023-12-01) Raviolo, Davide; Civera, Marco; Zanotti Fragonara, Luca
Finite Element Model Updating (FEMU) is a common approach to model-based Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) of civil structures and infrastructures. Its application can be further utilized to produce effective digital twins of a permanently monitored structure. The FEMU concept, simple yet effective, involves calibrating and/or updating a numerical model based on the recorded dynamic response of the target system. This enables to indirectly estimate its material parameters, thus providing insight into its mass and stiffness distribution. In turn, this can be used to localize structural changes that may be induced by damage occurrence. However, several algorithms exist in the scientific literature for FEMU purposes. This study benchmarks three well-established global optimization techniques—namely, Generalized Pattern Search, Simulated Annealing, and a Genetic Algorithm application—against a proposed Bayesian sampling optimization algorithm. Although Bayesian optimization is a powerful yet efficient global optimization technique, especially suitable for expensive functions, it is seldom applied to model updating problems. The comparison is performed on numerical and experimental datasets based on one metallic truss structure built in the facilities of Cranfield University. The Bayesian sampling procedure showed high computational accuracy and efficiency, with a runtime of approximately half that of the alternative optimization strategies.
Open Access
Comparison of semi-active control strategies for rocking objects under pulse and harmonic excitations
(Elsevier, 2016-12-28) Ceravolo, Rosario; Pecorelli, Marica Leonarda; Zanotti Fragonara, Luca
Recently, a considerable literature has grown up around the theme of seismic protection of rigid blocks, with a special focus on strategies to reduce the overturning vulnerability due to rocking motion. The present paper investigates a semi-active control method for rocking blocks and compares different strategies for its implementation. In more detail, a feedback control algorithm was developed to adjust the stiffness of the restraints placed at the two lower corners of the block. The utility of the proposed control was quantified through “ad hoc” indices derived from overturning spectra. The performance of a feedback strategy was numerically investigated and specific simulations were performed to quantify the control method degradation when implemented for a real-world application. Finally, the stability of the block controlled with the proposed strategy is compared with the stability of the block whose anchorage is set according to different control strategies.
Open Access
A computational methodology for assessing the time-dependent structural performance of electric road infrastructures
(Wiley, 2016-04-05) Ceravolo, Rosario; Miraglia, Gaetano; Surace, Cecilia; Zanotti Fragonara, Luca
An infrastructure adapted to dynamic wireless recharging of electric vehicles is often referred to generically as Electric Road (“e-road”). E-roads are deemed to become essential components of future grid environments and smart city strategies. Several technologies already exist that propose different ways to integrate dynamic inductive charging systems within the infrastructure. One e-road solution uses a very thin rail with box-section made of fibre-reinforced polymer, inside which an electric current flows producing a magnetic field. In spite of the great interest and research generated by recharging technologies, the structural problems of e-roads, including vibrations and structural integrity in the short and/or long period, have received relatively little attention to date. This article presents a novel computational methodology for assessing the time-dependent structural performance of e-roads, including a recursive strategy for the estimation of the lifetime of surface layers. The article also reports some numerical findings about e-roads that will drive further numerical analyses and experimental studies on this novel type of infrastructure. Finally, numerical simulations have been conducted to compare an e-road with a traditional road (“t-road”), in terms of static, dynamic and fatigue behavior.
Open Access
Diagnosis of composite materials in aircraft applications: towards a UAV active thermography inspection approach
(Society of Photo-Optical Instrumentation Engineers (SPIE), 2021-04-12) Alhammad, Muflih; Avdelidis, Nicolas Peter; Deane, Shakeb; Ibarra-Castanedo, Clemente; Pant, Shashank; Nooralishahi, Parham; Ahmadi, Mohammad; Genest, Marc; Zolotas, Argyrios; Zanotti Fragonara, Luca; Valdes, Julio J.; Maldague, Xavier P. V.
Diagnosis and prognosis of failures for aircrafts’ integrity are some of the most important regular functionalities in complex and safety-critical aircraft structures. Further, development of failure diagnostic tools such as Non-Destructive Testing (NDT) techniques, in particular, for aircraft composite materials, has been seen as a subject of intensive research over the last decades. The need for diagnostic and prognostic tools for composite materials in aircraft applications rises and draws increasing attention. Yet, there is still an ongoing need for developing new failure diagnostic tools to respond to the rapid industrial development and complex machine design. Such tools will ease the early detection and isolation of developing defects and the prediction of damages propagation; thus allowing for early implementation of preventive maintenance and serve as a countermeasure to the potential of catastrophic failure. This paper provides a brief literature review of recent research on failure diagnosis of composite materials with an emphasis on the use of active thermography techniques in the aerospace industry. Furthermore, as the use of unmanned aerial vehicles (UAVs) for the remote inspection of large and/or difficult access areas has significantly grown in the last few years thanks to their flexibility of flight and to the possibility to carry one or several measuring sensors, the aim to use a UAV active thermography system for the inspection of large composite aeronautical structures in a continuous dynamic mode is proposed.
Open Access
Dynamic investigation on the Mirandola bell tower in post-earthquake scenarios
(Springer Verlag (Germany), 2016-07-19) Zanotti Fragonara, Luca; Boscato, Giosue; Ceravolo, Rosario; Lentile, Silvia; Russo, Salvatore; Pecorelli, Marica Leonarda; Quattrone, Antonino
After the seismic events of the 20th and 29th of May 2012 in Emilia (Italy), most of the monumental and historic buildings of the area were severely damaged. In a few structures, partial collapse mechanisms were observed (e.g. façade tilting, out-of-plane overturning of panels…). This paper presents the case-study of the bell tower of the Santa Maria Maggiore cathedral, located in Mirandola (Italy). The dynamic response of the structure was evaluated through operational modal analysis using ambient vibrations, a consolidated non-destructive procedure that estimates the dynamic parameters of the bell-tower. The dynamic tests were carried out in pre-intervention and post-intervention conditions in order to understand the sensitivity of dynamic measurements to safety interventions. Furthermore, a comparative study is made with similar cases of undamaged masonry towers up to the 6th mode. Finally, an investigation on the state of connections and of the building itself is carried out via FE model updating.
Open Access
Experimental modal analysis of structural systems by using the fast relaxed vector fitting method
(Wiley, 2021-01-06) Civera, Marco; Calamai, Giulia; Zanotti Fragonara, Luca
System identification (SI) techniques can be used to identify the dynamic parameters of mechanical systems and civil infrastructures. The aim is to rapidly and consistently model the object of interest, in a quantitative and principled manner. This is also useful in establishing the capacity of a structure to serve its purpose, thus as a tool for structural health monitoring (SHM). In this context, input–output SI techniques allow precise and robust identification regardless of the actual input. However, one of the most popular and widely used approaches, the Rational Fraction Polynomial (RFP) method, has several drawbacks. The fitting problem is nonlinear and generally non‐convex, with many local minima; even if linearised via weighting, it can become severely ill‐conditioned. Here, a novel proposal for the broadband macro‐modelling of structures in the frequency domain with several output and/or input channels is presented. A variant of the vector fitting approach, the Fast Relaxed Vector Fitting (FRVF), applied so far in the literature only for the identification of electrical circuits, is translated and adapted to serve as a technique for structural SI and compared with other traditional techniques. A study about the robustness of the FRVF method with respect to noise is carried out on a numerical system. Finally, the method is applied to two experimental case studies: a scaled model of a high‐aspect‐ratio (HAR) wing and the well known benchmark problem of the three‐storey frame of Los Alamos laboratories. Promising results were achieved in terms of accuracy and computational performance.
Open Access
An experimental study of the feasibility of phase‐based video magnification for damage detection and localisation in operational deflection shapes
(Wiley, 2019-01-08) Civera, Marco; Zanotti Fragonara, Luca; Surace, Cecilia
Optical measurements from high‐speed, high‐definition video recordings can be used to define the full‐field dynamics of a structure. By comparing the dynamic responses resulting from both damaged and undamaged elements, structural health monitoring can be carried out, similarly as with mounted transducers. Unlike the physical sensors, which provide point‐wise measurements and a limited number of output channels, high‐quality video recording allows very spatially dense information. Moreover, video acquisition is a noncontact technique. This guarantees that any anomaly in the dynamic behaviour can be more easily correlated to damage and not to added mass or stiffness due to the installed sensors. However, in real‐life scenarios, the vibrations due to environmental input are often so small that they are indistinguishable from measurement noise if conventional image‐based techniques are applied. In order to improve the signal‐to‐noise ratio in low‐amplitude measurements, phase‐based motion magnification has been recently proposed. This study intends to show that model‐based structural health monitoring can be performed on modal data and time histories processed with phase‐based motion magnification, whereas unamplified vibrations would be too small for being successfully exploited. All the experiments were performed on a multidamaged box beam with different damage sizes and angles.
Open Access
Experimental testing of a masonry arch bridge model subject to increasing level of damage
(European Commission, 2011-01-31) Degiovanni, L.; Quattrone, Antonino; Zanotti Fragonara, Luca; Ceravolo, Rosario; De Stefano, Alessandro
Masonry arch bridges are particularly sensitive to the bearings loss produced by scour of the streambed soil at the piers foundations. A 1:2 scaled experimental model of a masonry arch bridge was built to study the evolution of the damage mechanism related to the application of foundation movements. The model was built with handmade clay bricks and a mortar with poor mechanical properties in order to reproduce typical materials of historical constructions, and an extensive characterization of the materials has been carried out. The mid-span pier is placed on a settlement application system, expressly designed to simulate the scour effect, quantified through hydraulic flume tests performed on a further scaled down model. Damage levels of increasing intensity have been simulated through the application of pier settlements and rotations. Experimental vibration tests were performed on the undamaged structure and after each settlement step. Both the environmental noise and the impacts of a sledge hammer were used as excitation sources. A complete dynamic identification was carried out and the variation of modal parameters at different levels of damage monitored. Moreover, the use of a testing shaker allowed investigating the non - linear behaviour of the damaged model.
Open Access
A generalised power-law formulation for the modelling of damping and stiffness nonlinearities
(Elsevier, 2020-12-26) Civera, Marco; Grivet-Talocia, Stefano; Surace, Cecilia; Zanotti Fragonara, Luca
In this paper, a single-degree-of-freedom dynamic model is described, with displacement- and velocity-dependent nonlinearities represented by power laws. The model is intended to support the dynamic identification of structural components subjected to harmonic excitation. In comparison to other analytical expressions, the data-driven estimation of the nonlinear exponents provides a large versatility, making the generalised model adaptable for a wide number of different nonlinearities in both stiffness and damping. For instance, the proposed damping formulation can naturally accommodate air drag (quadratic) damping as well as dry friction. Differently to purely data-driven methods (e.g. black boxes), the obtained model is fully inspectable. The proposed formulation is here applied to the large oscillations of a prototype highly flexible wing and fitted on its steady state response in the frequency domain. These large-amplitude flap-wise bending oscillations are known to be affected by nonlinearities in both the stiffness (nonlinear hardening) and the velocity-dependent damping terms. The model is validated against experiments for different structural configurations and input amplitudes, as both these nonlinearities are energy-dependent.
Open Access
A global-local meta-modelling technique for model updating
(Elsevier, 2023-10-09) Dessena, Gabriele; Ignatyev, Dmitry I.; Whidborne, James F.; Zanotti Fragonara, Luca
The finite element model updating procedure of large or complex structures is challenging for engineering practitioners and researchers. Iterative methods, such as genetic algorithms and response surface models, have a high computational burden for these problems. This work introduces an enhanced version of the well-known Efficient Global Optimisation technique to address this issue. The enhanced method, refined Efficient Global Optimisation or rEGO, exploits a two-step refinement and selection technique to expand the global search capability of the original method to a global–local, or hybrid, search capability. rEGO is tested and validated on four optimisation test functions against the original methods and genetic algorithms with different settings. Good results in terms of precision and computational performance are achieved, so an application for model updating is sought. A penalty function for the finite element model updating is identified in residuals of the modified total modal assurance criterion. Finally, rEGO for finite element model updating is implemented on a hybrid, numerical and experimental, case study based on a well-known experimental dataset and on a higher dimension finite element model of a wing spar. Satisfactory results in terms of precision and computational performance are achieved when compared to the original methods and genetic algorithms, needing two orders of magnitude fewer evaluations and achieving comparable results in terms of precision.
Open Access
Ground vibration testing of a flexible wing: a benchmark and case study
(MDPI, 2022-08-10) Dessena, Gabriele; Ignatyev, Dmitry I.; Whidborne, James F.; Pontillo, Alessandro; Zanotti Fragonara, Luca
Beam-like flexible structures are of interest in many fields of engineering, particularly aeronautics, where wings are frequently modelled and represented as such. Experimental modal analysis is commonly used to characterise the wing’s dynamical response. However, unlike other flexible structure applications, no benchmark problems involving high-aspect-ratio flexible wings have appeared in the open literature. To address this, this paper reports on ground vibration testing results for a flexible wing and its sub-assembly and parts. The experimental data can be used as a benchmark and are available to the aeronautical and structural dynamics community. Furthermore, non-linearities in the structure, where present, were detected. Tests were performed on the whole wing as well as parts and sub-assembly, providing four specimens. These were excited with random vibration at three different amplitudes from a shaker table. The modal properties of a very flexible high-aspect-ratio wing model, its sub-assembly and parts, were extracted, non-linear behaviour was detected and the experimental data are shared in an open repository.
Open Access
Ground Vibration Testing of a High Aspect Ratio Wing with Revolving Clamp
(Cranfield University, 2022-12-01 09:17) Dessena, Gabriele; Ignatev, Dmitrii; Whidborne, James; Pontillo, Alessandro; Zanotti Fragonara, Luca
33rd Congress of the International Council of the Aeronautical Sciences (ICAS). Abstract: The advancements in the aeronautical industry and research on materials and manufacturing methods in the last 70 years have been shifting the paradigm of wing design to high aspect ratio flexible wings. These wings can show a varying behaviour in different operating conditions, as per the nature of their geometry and materials. This work proposes a case study of a high aspect ratio flexible wing in order to study the effect of operating conditions on its structural properties. To test different operating conditions on the ground, a revolving clamp is designed to attach the specimen to a clamp-on shaker. A clear relationship between the wing’s modal properties, and so structural properties, and the angle the clamp sets is found.
Open Access
Ground vibration testing of a high aspect ratio wing with revolving clamp
(ICAS, 2022-11-28) Dessena, Gabriele; Ignatyev, Dmitry I.; Whidborne, James F.; Pontillo, Alessandro; Zanotti Fragonara, Luca
The advancements in the aeronautical industry and research on materials and manufacturing methods in the last 70 years have been shifting the paradigm of wing design to high aspect ratio flexible wings. These wings can show a varying behaviour in different operating conditions, as per the nature of their geometry and materials. This work proposes a case study of a high aspect ratio flexible wing in order to study the effect of operating conditions on its structural properties. To test different operating conditions on the ground, a revolving clamp is designed to attach the specimen to a clamp-on shaker. A clear relationship between the wing’s modal properties, and so structural properties, and the angle the clamp sets is found.
Open Access
Identification of flexible structures dynamics.
(Cranfield University, 2023-04) Dessena, Gabriele; Ignatyev, Dmitry I.; Whidborne, James F.; Zanotti Fragonara, Luca
The pursuit of aerodynamic efficiency and the advances in materials technology, particularly in composite material, has contributed to shifting the paradigm of wing design to high aspect ratio wings. Increasing the span, for decreasing drag, and using composite lightweight materials make the new wing very flexible and prone to nonlinear dynamic behaviour. With nonlinearities, increasing challenges arise for the identification and modelling of the wing. These challenges cannot be overlooked for flexible structures as these models are critical for the prediction of aeroelastic phenomena. Hence, it is fundamental to expand the knowledge of the behaviour of these structures through the identification and modelling of sample flexible wing models. In this work, a series of methods and approaches are proposed and employed for the identification and modelling of a flexible wing. First, a system identification technique in the frequency domain, the Loewner Framework, is applied for modal parameters extraction in mechanical systems for structural health monitoring. This new technique, with a linear reduced order model, is used to characterise the flutter behaviour of a flexible wing. The results are compared to similar techniques. A thorough experimental campaign is run on a flexible wing model to characterise its nonlinear behaviour and the underlying linear system. In particular, nonlinearities are detected, identified and quantified. Then, a meta-model technique based on Kriging, the refined Efficient Global Optimisation, is proposed for finite element model updating. First, the technique is used for damage detection in benchmark structures, then, it is employed for the validation of component-based strategies for model updating of a flexible wing.
Open Access
Inspection of aircraft wing panels using unmanned aerial vehicles
(IEEE, 2018-09-03) Malandrakis, Konstantinos; Savvaris, Al; Gonzalez Domingo, Jose Angel; Avdelidis, Nicolas Peter; Tsilivis, Panagiotis; Plumacker, Florence; Zanotti Fragonara, Luca; Tsourdos, Antonios
In large civil aircraft manufacturing a time-consuming post-production process is the non-destructive inspection of wing panels. This work aims to address this challenge and improve the defects' detection by performing automated aerial inspection using a small off-the-shelf multirotor. The UAV is equipped with a wide field-of-view camera and an ultraviolet torch for implementing non-invasive imaging inspection. In particular, the UAV is programmed to perform the complete mission and stream video, in real-time, to the ground control station where the defects' detection algorithm is executed. The proposed platform was mathematically modelled in MATLAB/SIMULINK in order to assess the behaviour of the system using a path following method during the aircraft wing inspection. The UAV was tested in the lab where a six-meter-long wing panel was one-side inspected. Initial results indicate that this inspection method could reduce significantly the inspection time, cost, and workload, whilst potentially increasing the probability of detection.
Open Access
Inspection of aircraft wing panels using unmanned aerial vehicles
(MDPI, 2019-04-17) Tzitzilonis, Vasileios; Malandrakis, Konstantinos; Zanotti Fragonara, Luca; Gonzalez Domingo, Jose Angel; Avdelidis, Nicolas Peter; Tsourdos, Antonios; Forster, Kevin
In large civil aircraft manufacturing, a time-consuming post-production process is the non-destructive inspection of wing panels. This work aims to address this challenge and improve the defects’ detection by performing automated aerial inspection using a small off-the-shelf multirotor. The UAV is equipped with a wide field-of-view camera and an ultraviolet torch for implementing non-invasive imaging inspection. In particular, the UAV is programmed to perform the complete mission and stream video, in real-time, to the ground control station where the defects’ detection algorithm is executed. The proposed platform was mathematically modelled in MATLAB/SIMULINK in order to assess the behaviour of the system using a path following method during the aircraft wing inspection. In addition, two defect detection algorithms were implemented and tested on a dataset containing images obtained during inspection at Airbus facilities. The results show that for the current dataset the proposed methods can identify all the images containing defects.

Browsing by Author "Zanotti Fragonara, Luca"

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