1,721,082 research outputs found
Nel nome di Bologna
No full textLa relazione verteva sulle istituzioni filantropiche nella storia moderna e contemporanea di Bologna, sulle ragioni del loro intenso fiorire e sull'atteggiamento della città in tema di assistenza ai cittadini disagiati
Impact detection on thin structures via machine learning approaches
No full textIn this study, machine learning algorithms are trained and compared to identify and characterise impacts effects on typical aerospace panels with different geometries. Experiments are conducted to create a suitable impact dataset. Polynomial regression algorithms and shallow neural networks are applied to panels without stringers and optimised to test their ability to identify the impacts. The algorithms are then applied to panels reinforced with stringers, which represents a significant increase in complexity in terms of the dynamic characteristics of the system under test. The focus is not only on the detection of the impact position, but also on the severity of the event. The aim of the work is to demonstrate the validity of the application of machine learning to impact localization on realistic structures and to demonstrate the simplicity and efficiency of the computations despite the complexity of the test specimens
Elastic waves interference for the analysis of disbonds in single lap joints
Full text linkIn the present paper a method for the Structural Health Monitoring (SHM) of bonded lap joints is presented. This method is based on the interference of elastic waves generated by piezo sensors and travelling along thin bonded plates through the adhesion area. Tone bursts of different extension were generated and, when they encountered the debonded area, the wave speed changed. This affected the wave reflection at the boundary of the disbond and the subsequent interference of the reflected wave with the main wave travelling along the joint. Destructive interference conditions were promoted when the adhesive was partially debonded and this was related to the length of the disbond. In the present study numerical simulations based on finite elements were performed and compared with a simplified analytical model describing the Lamb waves propagation through the joint. The simulation results were subsequently compared with the experimental data and a good agreement was found: the proposed method was simple, straightforward and its application on thin single lap joints provided reliable results
Impact characterization on thin structures using machine learning approaches
No full textMachine learning algorithms are trained and compared to identify and to characterise the impact on typical aerospace panels of different geometry. Experimental activities are conducted to build a proper impacts’ dataset. Polynomial regression algorithm and artificial neural network are applied and optimised to panels without stringer to test their capability to identify the impacts. Subsequently, the algorithms are applied to panels reinforced with stringers that represent a significant increase of complexity in terms of dynamic features of the system to test: the focus is not only on the impact position's detection but also on the event's severity. After the identification of the best algorithm, the corresponding machine learning model is deployed on an ARM processor mini-computer, implementing an impact detection system, able to be installed on board an aerial vehicle, making it a smart aircraft equipped with an artificial intelligence decision-making system
Subharmonics and beating: A new approach to Local Defect Resonance for bonded single lap joints
No full textThe present paper is focused on the analysis of the adhesion integrity of Single Lap Joints (SLJ). The technique adopted for the monitoring is based on the employment of vibration signals generated and received by piezo sensors attached on the specimens surfaces on the two opposite sides of the adhesive. Undamaged joints, when subjected to harmonic excitation, behave linearly exhibiting a spectral response including just the excitation frequency. As soon as the adhesive fails, harmonic excitation induces a rich variety of spectral components in the joints response, including subharmonics and superharmonics. A new approach is presented based on the beating resulting from the superposition of harmonic waves. The interpretation of the spectral content of the joint response is based on an analytical model of the single lap joint with different amounts of debondings associated with a nonlinear behaviour. Local Defect Resonance (LDR)conditions are promoted with the consequent superposition of defect with main structure vibration. Analytical results are compared with experiments and Finite Elements (FE)simulations demonstrating the consistence of the formulation. An efficient method for the Structural Health Monitoring (SHM)of the bonded single lap joints is provided, able to correlate the joint vibrational response to the debonding extension through the analysis of the response spectral content
Numerical evaluation and experimental comparison of airframe noise for the optimization of next generation aircraft design
No full textIn this paper the airframe noise of civil transport aircraft is numerically evaluated and compared with measurements taken in some european airports with the target of separating the airframe contribution from other noise contributions effective on a typical aircraft. The attention has been focused on airframe noise since it sets a lower limit below whichever reduction of noise generated by engine have no significant effect on the overall noise level perceived by an observer and due to the aircraft flyover. The intensity of airframe noise depends on the aircraft configuration: during the cruise the aircraft exhibit an aerodynamically 'clean' configuration that produces less noise than the configuration assumed by the aircraft during landing and take-off, that usually is referred as 'dirty' one. The configuration with slats extended, flaps down and undercarriage lowered is more noisy than the clean configuration. In this paper the results of numerical simulations performed on common operating aircraft are presented: these simulations allow the contribution breakdown and, therefore, the classification of the most noisy airframe components for the different approach and take-off configurations
Nonlinearities associated with impaired sensors in a typical SHM experimental set-up
Full text linkStructural Health Monitoring (SHM) gives a diagnosis of a structure assessing the structural integrity and predicting the residual life through appropriate data processing and interpretation. A structure must remain in the design domain, although it can be subjected to normal aging due to usage, action of the environment, and accidental events. SHM involves the integration of electronic devices in the inspected structure that sometimes are Piezoelectric Transducers (PZT). These are lightweight and small and can be produced in different geometries. They are used both in guided wave-based and electromechanical impedance-based methods. The PZT bonding requires essential steps such as preparation of the surfaces, application of the adhesive, and assembly that make the bonding process not so easy to be realised. Furthermore, adhesives are susceptible to environmental degradation. Transducer debonding or non-uniform distributed glue underneath the sensor causes the reduction of the performance and can affect the reliability of the SHM system. In this paper, a sensor diagnostic method for the monitoring of the PZT operational status is proposed in order to detect bonding defect/damage between a PZT patch and a host structure. The authors propose a method based on the nonlinear behaviour of the contact PZT/structure that allows the identification of the damaged PZT and the geometrical characterization of the debonding. The feasibility of the diagnostic procedure is demonstrated by numerical studies and experiments, where disbonds were created by inhibiting the adhesive action on a part of the interface through Teflon film. The proposed method can be used to evaluate the sensor functionality after an extreme loading event or over a long period of service time
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