Table of contents

PROCEEDINGS OF THE XXVIII A.I.VE.LA. ANNUAL NATIONAL MEETING

17-18 December 2020, ONLINE EVENT

http://www.aivela.org/XXVIII_Meeting/index.html

A.I.VE.LA. – the Italian Association of Laser Velocimetry and non-invasive diagnostics is a non-profit cultural association whose objective is to promote and support research in the field of non-contact or minimally invasive measurement techniques, particularly of electromagnetic-based and optical techniques.

Through its Annual Meeting, AIVELA aims at creating an active and stimulating forum where current research results and technical advances can be exchanged and the development of new systems for laboratory use, field testing and industrial application can be promoted. The techniques addressed include Laser Doppler Anemometry – LDA, Phase Doppler Anemometry – PDA, Image Velocimetry – PIV, Flow visualization techniques, Spectroscopic measurement techniques (LIF, Raman, etc.), Laser Doppler Vibrometry – LDV, Speckle Pattern Interferometry – ESPI, Holographic techniques, Shearography, Digital Image Correlation – DIC, Moiré techniques, Structured light techniques, Infrared imaging, Photoelasticity, Image based measurement techniques, Ultrasonic sensing, Acoustic and Aeroacoustic measurements, etc.

The first Annual Meeting was held back in October 1992 and, since then, the event has met large consensus among the research and scientific communities worldwide for the high scientific interest of the papers presented.

The XXVIII AIVELA Annual National Meeting was organised in collaboration with the Department of Industrial Engineering and Mathematical Sciences of Università Politecnica delle Marche and was held online, due to the Covid-19 pandemic and related restrictions.

The Meeting was held live on the Microsoft 365/Teams platform and featured 3 Invited lectures, 2 of which delivered by instrumentation manufacturers, 15 papers organised into 4 Technical Sessions, and a session entirely dedicated to manufacturers.

All presentations were plenary. The Invited lectures had 1 hour each to deliver their talks, including possible discussion and Q&As at the end of their presentations, whereas the speakers had 15 mins each followed by 5 mins for possible discussion and Q&As.

32 participants attended the event. Most of them were from Italy, since it was the Association's National event, but there were also three attendees from Germany.

The official language of the Meeting was English.

No particular technical difficulty was encountered, and although the atmosphere of an online event is not the same as for a face-to-face event, the Meeting still gave participants the opportunity to share their research activities and results, in the full spirit of the Association.

This volume contains a selection of the papers presented at the event.

The full Programme of the Meeting can be found at:

http://www.aivela.org/XXVII_Meeting/final-programme.html.

Trusting our Association and its initiatives will meet your interest, I wish to thank you in advance for your kind attention and hope to meet you soon at one of our events.

EDITOR, SCIENTIFIC COMMITTEE, INVITED LECTURERS are available in the pdf

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

• Type of peer review: Single-blind

• Conference submission management system: //

• Number of submissions received: 11

• Number of submissions sent for review: 11

• Number of submissions accepted: 11

• Acceptance Rate (Number of Submissions Accepted / Number of Submissions Received X 100): 100%

• Average number of reviews per paper: 1

• Total number of reviewers involved: 2

• Any additional info on review process: //

• Contact person for queries:

Name : Enrico Primo Tomasini

Affiliation: A.I.VE.LA., Università Politecnica delle Marche

Email : aivela@univpm.it

Metasurfaces are, at the actual state-of-the-art, a constant topic for scientific community as they find widespread applications in several fields, including acoustics and aeroacoustics. In this paper, the potential of recurrence analysis was evaluated by applying it to some metasurfaces. These devices effectiveness has been previously demonstrated with a reflection coefficients analysis in the Fourier and Wavelet domains. A novel strategy based on the Recurrence Analysis, which is a no man's land applied on the metasurfaces, was performed. The evaluation of the recurrence plot and phase space attractors led to interesting results. The results show an introduction of non linearities after the forcing wave interacts with the metasurfaces. In light of that, there is the evidence that the chaotic analysis principles may be a powerful tool to characterize the performance of metasurfaces in particular through the calculation of the chaotic indexes. This method could be integrated with previous ones for the evaluation of more complex and multiscale geometries that nowadays show huge potential in too many fields of application.

The dynamics of rising bubbles in still water can be influenced by the wake characteristics of the neighbouring bubbles. An experimental study was conducted on individual rising bubbles rising in still water by means of volumetric shadowgraphy technique. Results highlighted a phase opposition relationship between the volumes and rising velocities and between the minor semi-axis and the two semi-axes median and major of the three air bubbles. The cross-correlation function applied on the eccentricities of the three bubbles highlighted similar positive peaks but also a negative peak between eccentricities of the second and third bubbles. Frequency spectra of the three bubbles eccentricities exhibited some common features, with peaks around 10 Hz for the first and third bubbles and around 5 Hz for the second and third bubbles. In addition, cross-correlation applied on the rising velocities showed negative correlations between the three bubbles, with each bubble that reduces its rising velocity while another accelerates. The application of the volumetric shadowgraphy allowed a simultaneous measurement of the geometry and rising velocities of the in-line bubbles, leading to identify common and different features among them.

Surface science and engineering gained an increasing importance in recent years, due to the potential benefit they can offer in many applications. An important parameter in this field is the surface wettability, that is in general evaluated by the contact angle. One of the most accurate techniques to measure this quantity is the axisymmetric drop shape analysis, based on the fitting of the theoretical Laplace-Young profile to the contour of experimental drops. In this paper the performance of a simple, low-cost setup – that can be built "at home" – to apply this technique is assessed, also including a detailed analysis about the influence of the most important parameters to set in the procedure. The latter aspect was evaluated by using computer-generated drop profiles and pictures, to have "realistic" images, but for drops of known properties. The experimental setup was built using a desk, a table lamp, a medical syringe, a support for the samples and a "bridge" camera. Measurements were performed on smooth and rough textile surfaces and the results were compared with previous measurements taken with a professional setup. From the comparison it can be affirmed that the performance of the home-made setup is very satisfactory.

High-performance imaging techniques represent the present of academic and industrial research. The use of these technologies in the maritime sector sees different applications in different phases of the life of a ship: photogrammetry in the design phase and the use of Lidar sensors to measure emissions are just a few examples. The novelty of this study is the application of these acquisition techniques to ship ballast systems. The new ballast water management regulations aimed at limiting the alteration of the marine ecosystem has overturned the canonical use of the ballast systems. In recent years, studies have shown how the spillage of ballast water has generated the proliferation of invasive species in seas all over the world. For this reason, the IMO has tried to regulate these operations. In this work, transportation phenomena of sediments through the duct, suctioned by a pump have been analysed. The inspected duct has been exposed to a CMOS MINI FASTCAM AX100. This camera was used to acquire images that allow studying the behaviour of the particles. With the use of a Matlab toolbox, a post processing of the images has been realized in order to estimate the speed and accelerations of the particles.

In this paper a methodology is discussed concerning the measurement of yarn's angle of a reinforced polypropylene matrix used in the production of automotive components. The measurement method is based on a vision system and advanced processing of images in order to evaluate the geometrical parameters of interest; the accuracy of measurement is a mandatory requirement, in order to assess the simulation approach for thermoplastic process optimization. Many aspects influencing the whole accuracy of the method have been identified and their effect evaluated, of both geometrical and optical type, allowing to perform angle measurements of the fiber angle with a whole accuracy in the order of a few degrees. By this way both local and extended defects can be identified in a reliable way also with reference to components of complex geometry. According to these results, accurate measurements of angle allows us to both validate the simulation of the thermoplastic process and to give suggestions for process improvement of fiber glass components of complex geometry.

Non-contact ultrasonic techniques are fundamental to devise online monitoring systems for moving or difficult to access structures. Gas-Coupled Laser Acoustic Detection (GCLAD) is an unestablished, non-contact detection technology which relies on measuring the deviation affecting a laser beam when travelling across an ultrasonic wavefront propagating in a fluid. The aim of the work is to provide in-depth highlights on the principles on which the technique leverages, with a view towards how several laser beam and ultrasonic wave features reflects on the signal acquired by the GCLAD device. By numerical and experimental approaches, parameters needing to be specifically addressed and suitably set during the investigation phase are highlighted, which enable amplitude maximization of the acquired signal. Specifically, effect of the probe laser beam spot size is thoroughly analyzed, as well as the mutual orientation between the beam and the ultrasonic propagation directions. Three test configurations are lastly proposed, providing different results in terms of GCLAD sensitivity to the acoustic waves; such differences are highlighted by applying the technique to a railway axle on which an artificial crack has been machined, providing a first assessment of the GCLAD capabilities in the non-destructive testing field.

The present study reports an experimental investigation regarding one of the most effective and most studied passive control technique in literature to mitigate the noise pollution radiating by a small drone: the Serrated Trailing Edge (STE). 23 quiet propellers have been designed and manufactured in order to identify the most silent configuration. An aeroacoustic pre-qualification of the designed propellers has been performed by means of microphone measurements within the anechoic chamber of Niccolò Cusano University. Then, an aeroacoustic and fluid dynamic characterization of the most performing configuration has been carried out by means of load cell, microphone and PIV measurements in the anechoic wind tunnel facility of TUDelft University of Technology in order to investigate the mechanism that stands behind the noise mitigation. With this purpose, the aerodynamic and aeroacoustic performance and even the velocity and vorticity field along the blade of STE propellers have been characterized. Particular attention is devoted to the fluid-dynamic aspects related to the low Reynolds number flow regime. Results show that serrations seems to modify the wake velocity and the tip voretx intensity resulting in a lower acoustic emission.

An experimental investigation of the noise emissions of a twin-rotor together with the evolution and spatial organization of the flow structures wakes has been carried out by means of aeroacoustics and time-resolved PIV (TR-PIV) measurements. Each rotor is characterized by three bladed propellers with diameter D = 393.7 mm running at four different rotational speeds (2620, 3500, 4360, 5200 RPM). Intricate flow patterns characterized by periodic vortical structures are formed in the wake of the rotors in twin configuration at the rotor-to-rotor distance of 1.02D. Their interaction determines a strong impact on the aerodynamic performances as well as on the noise generation. Hence, the need for TR-PIV measurements relies on what is the role of these instantaneous flow patterns to unveil the spatial organization and the dynamic behaviour inspected by imaging the region between the rotors. It is found that the flow organization and the interaction between evolution of vorticity intensity of tip vortices characterize the twin-rotors wakes.

Niobium superconductive radio frequency cavities (SRF cavities) are commonly employed in linear accelerator; very pure, clean, and smooth internal walls are required to make the cavity working properly and with a high Q factor. Typically, to achieve a suitable surface quality the SRF cavities are subjected to a surface treatment called Buffered Chemical Polish (BCP), the latter uses a strong concentrated acids mixture flowing through the cavity to chemically etch a thin niobium layer (∼250 μm). A viable way to understand and optimize the BCP process is by using computational fluid dynamic (CFD); however, the experimental validation of the numerical and physical models is required to confidently use CFD results. The aim of our work is to investigate the fluid dynamics of the BCP process by using the Particle Image Velocimetry (PIV) and the refractive index matching (RIM) techniques, and to provide data to validate CFD simulations. The paper describes and briefly analyse the experimental setup and the preliminary results achieved so far.

In this preliminary work, the feasibility of the combination of a volumetric velocimetry technique such as Defocusing Particle Image Velocimetry and a particle phase-discrimination methodology based on ridge detection algorithm for the analysis of turbulent multiphase flows with non-spherical fiber-like particles is discussed. Experimental results of a dilute suspension of fibers in an open-channel apparatus are provided.

In recent years, optical-based sensors have sparked interest for the many advantages over traditional, electrical-based sensors, such as EMI insensitivity, ease of multiplexing on a single line, resilience to hostile environment and very compact size and global weight saving due to signal cables reduction. Considering said properties, optical sensors offer a compelling alternative to traditional sensing elements. One type of optical sensor is the Fiber Braggs Gratings sensors (FBG), which is a type of sensor that reflects a very narrow band of wavelengths, called Bragg wavelength, while being transparent for others; this behavior is achieved by local variations of the core refractive index. The Bragg wavelength can be easily correlated with physical changes in the sensor itself, due to either physical strain or temperature variation. It should be noted that the achievable measurement accuracy is thus comparable to the Bragg wavelength. However, for any practical application, FBGs need to be bonded to a support or surface; in this case, there is a lack of understanding of the effects of temperature and humidity variations on the combined sensor-glue system. In this work, a setup, intended to characterize the sensitivity of the fiber-glue combination to humidity and temperature will be presented.