1,720,979 research outputs found
Computer aided detection of clustered microcalcifications in digitized mammograms using Gabor functions
No full textThis paper presents a multiresolution approach to the computer aided detection of clustered microcalcifications in digitized mammograms based on Gabor elementary functions. A bank of Gabor functions with varying spatial extent and tuned to different spatial frequencies is used for the extraction of microcalcifications characteristics. Classification is performed by an Artificial Neural Network with supervised learning.First results show that most microcalcifications, isolated or clustered, are detected by our algorithm with a 95\% value both for sensibility and specificity as measured on a test data set
Feasibility study for a tonal vibration control system of a mounting bracket for automotive gearboxes
No full textA conceptual design of an active device able to attenuate the tonal vibrations of a mounting bracket for automotive gearboxes is addressed in this paper. A preloaded piezo stack actuator is used to counteract the unbalanced vibrations of the component by monitoring its operational deformations. Firstly, a numerical modal analysis is carried out to characterize the normal modes in the frequency range of interest. The piezo stack is simulated by a rod element and its effect is numerically characterized. The upper and lower faces of the stack are mechanically coupled with the bracket structure, whereas the active control deals with the relative displacement of two points of the bracket. The primary disturbance was simulated by a shaker to control the vibrations in correspondence of the second bending mode (around 1.6 kHz). A 20 Hz narrow band was additionally selected as the control window. Then, this frequency range was enlarged around the resonance peak in order to optimize the control effect, till 80 Hz to investigate the resulting effects. Finally, focus is given to the structural damping by assessing its impact on the control forces and phases to cancel the deformation along the contact direction. The description of the experimental results concludes this work by generally confirming the numerical expectations
Fiber Optic Shape Sensor System for a Morphing Wing Trailing Edge
Full text linkThe objective of this work is to present a conceptual design and the modelling of a distributed sensor system based on fiber optic devices (Fiber Bragg Grating, FBG), aimed at measuring span-wise and chord-wise variations of an adaptive (morphing) trailing edge. The network is made of two different integrated solutions for revealing deformations of the reference morphing structure. Strains are confined to typical values along the span (length) but they are expected to overcome standard ranges along the chord (width), up to almost 10%. In this case, suitable architectures may introduce proper modulations to keep the measured deformation low while preserving the information content. In the current paper, the designed monitoring system combines the use of a span-wise fiber reinforced patch with a chord-wise sliding beam. The two elements make up a closed grid, allowing the reconstruction of the complete deformed shape under the acceptable assumption that the transformation refers to regular geometry variations. Herein, the design logic and some integration issues are reported. Preliminary experimental test results are finally presented
Computer-aided Detection of Clustered Microcalcifications in Digitized Mammograms using Gabor Functions
No full textThis paper presents a multiresolution approach to the computer aided detection of clustered microcalcifications in digitized mammograms based on Gabor elementary functions. A bank of Gabor functions with varying spatial extent and tuned to different spatial frequencies is used for the extraction of microcalcifications characteristics. Classification is performed by an Artificial Neural Network with supervised learning.First results show that most microcalcifications, isolated or clustered, are detected by our algorithm with a 95\% value both for sensibility and specificity as measured on a test data set
Active vibration control of a mounting bracket for automotive gearboxes
Full text linkThe aim of this paper is to investigate the use of active vibration control in automotive gearboxes mounting brackets to reduce tonal disturbances. A combination of piezoelectric accelerometers and an internally preloaded piezo stack actuator is used to counteract their unbalanced caused vibrations. Initially, a numerical modal analysis was carried out to identify the normal modes in the frequency range of interest. The piezo stack was simulated by a ROD element and its effect numerically characterized. The upper and lower faces of the stack were mechanically coupled with the bracket structure, whereas the active control strategy involved the relative displacement of two opposite points of the bracket. To this aim, dedicated interfaces were designed to integrate the stack into the mounting bracket. In order to control the vibrations in correspondence of the second bending mode (1599.4Hz), the primary disturbance, simulated by a shaker, was modelled in the frequency domain using a white noise signal. A narrow window of 20Hz was initially selected as the control system domain. Then, this frequency range has been made gradually wider around the resonance peak, in order to optimize the control effect, and then extended up to 80 Hz when undesired effects occurred. Primary and secondary control plants were firstly numerically fitted from the measured responses and excitations using system identification techniques, and then used for the active controller design and simulations
Multi-tone Switched Shunt Control by a PZT Network Embedded into a Fiberglass Panel: Design, Manufacture and Test
No full textResearch in noise and vibration control has partially focused on semi-active attenuation techniques such as switching shunt control (SSC) systems. Among the various methods, SSC architectures exhibit several interesting advantages such as low power absorption and intrinsic adaptive capabilities. This approach may represent an acceptable compromise between passive and active solutions. In previous work the authors implemented and validated 1D and 2D numerical models, addressed to describe continuous simple isotropic structures under tonal excitations controlled by single-element SSC system. Further efforts were then directed to extend the applicability of those models to non-isotropic structures and to multi-tone control devices. In this article, a 6-PZT network multi-tone SSC system is presented, and embedded into a balanced fiberglass laminate. The network geometry is defined according to an optimization process following modal information. The former 1-channel control circuit was extended to drive up to four independent channels. The complete system dynamics was simu- lated by assembling the structural matrices into a Matlab code, where both the electromecha- nical coupling and the control circuit behavior were taken into account. The structure was excited by broadband sweep signals in a selected range. Numerical and experimental results were compared and discussed
Feasibility study for a tonal vibration control system of a mounting bracket for automotive gearboxes
No full textA conceptual design of an active device able to attenuate the tonal vibrations of a mounting bracket for automotive gearboxes is addressed in this paper. A preloaded piezo stack actuator is used to counteract the unbalanced vibrations of the component by monitoring its operational deformations. Firstly, a numerical modal analysis is carried out to characterize the normal modes in the frequency range of interest. The piezo stack is simulated by a rod element and its effect is numerically characterized. The upper and lower faces of the stack are mechanically coupled with the bracket structure, whereas the active control deals with the relative displacement of two points of the bracket. The primary disturbance was simulated by a shaker to control the vibrations in correspondence of the second bending mode (around 1.6 kHz). A 20 Hz narrow band was additionally selected as the control window. Then, this frequency range was enlarged around the resonance peak in order to optimize the control effect, till 80 Hz to investigate the resulting effects. Finally, focus is given to the structural damping by assessing its impact on the control forces and phases to cancel the deformation along the contact direction. The description of the experimental results concludes this work by generally confirming the numerical expectations
Shape memory polymer composite actuator: Modeling approach for preliminary design and validation
No full textThe work at hand focuses on the modeling, prototyping, and experimental functionality test of a smart actuator based on shape memory polymer technology. Particular attention is paid to the specific modeling approach, here conceived as an effective predictive scheme, quick and, at the same time, able to face those nonlinearity aspects, strictly related to the large displacements shape memory polymers usually undergo. Shape memory polymer composites (SMPCs) may play a critical role for many applications, ranging from self-repairing systems to deployable structures (e.g., solar sails, antennas) and functional subcomponents (e.g., pliers, transporters of small objects). For all these applications, it is very important to have an effective tool that may drive the designers during the preliminary definition of the main parameters of the actuation system. For the present work, a SMPC plate sample has been conceived and realized in view of aerospace applications. An external fibre optic sensor has been then fixed with special adhesive. The temperatures needed for the activation of the Shape Memory Polymer (SMP) and strain storing have been provided by a thermo-gun and complete load-unload cycles, including strain storing, have been performed. Experimental displacements and strains have been used to validate a dedicated predictive theoretical approach, suited for laminates integrated with SMP layers
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