| 1. |
- Dolcetti, Giulio, et al.
(författare)
-
Identification of localised water surface patterns using unsupervised learning
- 2021
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Water surface deformations in rivers can have very different shapes and dynamics depending on which mechanism drives them: turbulence, wind, and/or bed morphology. While some surface patterns can be treated as effective tracers for image-based velocimetry, others, such as gravity waves, affect the accuracy of the measurements. Emerging analysis techniques attempt to filter out the contribution of waves, or conversely to enhance them in order to infer the flow properties based on their dynamics. These approaches are typically based on Fourier analysis, which decomposes the images in a homogeneous distribution of sinusoidal waves. In contrast, water surface patterns such as vortices, scars, wakes, or even groups of ripples, are localised in space and in time. Identifying them, or distinguishing them from other types of waves, requires a more targeted approach. This work proposes the use of unsupervised machine learning to identify a collection of wave patterns that can represent the water deformations. Unlike Fourier bases, the wave patterns learned are able to capture more sophisticated dynamics with increased efficiency. Provided enough training data, it is in principle possible to distinguish different types of surface deformations, and to determine their scale and speed with a higher resolution than is currently allowed by Fourier analysis. This work shows preliminary results including learned components from two video recordings of the river Sheaf (Sheffield, UK) obtained with a fixed camera at different flow conditions. The learned components resemble a combination of wave-groups localised in space-time, confirming the importance of moving beyond the assumption of stationarity.
|
|
| 2. |
- Kraxberger, Florian, et al.
(författare)
-
On the Alignment of Acoustic and Coupled Mechanic-Acoustic Eigenmodes in Phonation by Supraglottal Duct Variations
- 2023
-
Ingår i: Bioengineering. - : MDPI AG. - 2306-5354. ; 10:12
-
Tidskriftsartikel (refereegranskat)abstract
- Sound generation in human phonation and the underlying fluid–structure–acoustic interaction that describes the sound production mechanism are not fully understood. A previous experimental study, with a silicone made vocal fold model connected to a straight vocal tract pipe of fixed length, showed that vibroacoustic coupling can cause a deviation in the vocal fold vibration frequency. This occurred when the fundamental frequency of the vocal fold motion was close to the lowest acoustic resonance frequency of the pipe. What is not fully understood is how the vibroacoustic coupling is influenced by a varying vocal tract length. Presuming that this effect is a pure coupling of the acoustical effects, a numerical simulation model is established based on the computation of the mechanical-acoustic eigenvalue. With varying pipe lengths, the lowest acoustic resonance frequency was adjusted in the experiments and so in the simulation setup. In doing so, the evolution of the vocal folds’ coupled eigenvalues and eigenmodes is investigated, which confirms the experimental findings. Finally, it was shown that for normal phonation conditions, the mechanical mode is the most efficient vibration pattern whenever the acoustic resonance of the pipe (lowest formant) is far away from the vocal folds’ vibration frequency. Whenever the lowest formant is slightly lower than the mechanical vocal fold eigenfrequency, the coupled vocal fold motion pattern at the formant frequency dominates.
|
|
| 3. |
- Laudato, Marco, et al.
(författare)
-
Analysis of the contact critical pressure of collapsible tubes for biomedical applications
- 2023
-
Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Nature. - 0935-1175 .- 1432-0959. ; 36:1, s. 217-228
-
Tidskriftsartikel (refereegranskat)abstract
- The onset of self-excited oscillations in airways and blood vessels is a common phenomenon in the human body, connected to both normal and pathological conditions. A recent experimental investigation has shown that the onset of self-excited oscillations happens for values of the intramural pressure close to the contact critical pressure. The goal of this work is to analyse the dependence of the contact critical pressure on the vessel’s geometric parameters. The methodology is based on the implementation of an experimentally validated computational model of a collapsible tube. The results confirm the correlation between the contact critical pressure and the onset of self-excited oscillations in collapsible tubes. Moreover, a set of general equations to compute the contact critical pressure and the corresponding areas of collapsible tubes with arbitrary geometries has been derived.
|
|
| 4. |
- Laudato, Marco, et al.
(författare)
-
Buckling critical pressures in collapsible tubes relevant for biomedical flows
- 2023
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- The behaviour of collapsed or stenotic vessels in the human body can be studied by means of simplified geometries like a collapsible tube. The objective of this work is to determine the value of the buckling critical pressure of a collapsible tube by employing Landau’s theory of phase transition. The methodology is based on the implementation of an experimentally validated 3D numerical model of a collapsible tube. The buckling critical pressure is estimated for different values of geometric parameters of the system by treating the relation between the intramural pressure and the area of the central cross-section as the order parameter function of the system. The results show the dependence of the buckling critical pressures on the geometric parameters of a collapsible tube. General non-dimensional equations for the buckling critical pressures are derived. The advantage of this method is that it does not require any geometric assumption, but it is solely based on the observation that the buckling of a collapsible tube can be treated as a second-order phase transition. The investigated geometric and elastic parameters are sensible for biomedical application, with particular interest to the study of the bronchial tree under pathophysiological conditions like asthma.
|
|
| 5. |
- Laudato, Marco, et al.
(författare)
-
Computational aeroacoustics in flexible conduits with application to biomedical fluid dynamics
- 2023
-
Ingår i: 184th Meeting of the Acoustical Society of America. - Chicago, USA : Acoustical Society of America (ASA). ; , s. A194-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Flexible tubes are simple yet powerful tools for the modeling of respiratory and circulatory systems [1, 2]. In the last decade, access to high-performance computational resources has allowed the implementation of realistic numerical models of human vessels based on Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) simulations. Interestingly, the recently proven correlation [3] between CFD observables (like the pharyngeal airway's resistance) and clinical data (such as the Apnoea Hypopnea Index in Obstructive Sleep Apnoea patients) suggests a possible development of diagnostic methods based on numerical simulations. This work aims to investigate the extension of these correlations to the aeroacoustics characteristics of flexible conduits by means of a fully coupled FSI numerical model based on the Large Eddy Simulation method. These results have relevant applications to studying diseases of the human upper vocal tract, voice production, obstructive sleep apnoea, and adventitious lung sounds, such as wheezing and crackling.[1] Grotberg, J. B., & Jensen, O. E. (2004). Annu. Rev. Fluid Mech., 36, 121–147.[2] Schwartz, A. R., & Smith, P. L. (2013). The Journal of Physiology, 591(Pt 9), 2229.[3] Schickhofer L., Malinen J., Mihaescu M., J. Acoust. Soc. Am. - JASA, 145 (4): 2049–2061, 2019. https://doi.org/10.1121/1.5095250
|
|
| 6. |
- Laudato, Marco, et al.
(författare)
-
Dynamical Vector Fields on Pantographic Sheet: Experimental Observations.
- 2019
-
Ingår i: New Achievements in Continuum Mechanics and Thermodynamics. - Cham : Springer International Publishing. ; , s. 257-269
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this work, we will present and discuss some experimental observations of the dynamical displacement vector field on a pantographic sheet. We will sketch the experimental setup and we will qualitatively describe the observed behavior for a set of relevant frequencies.
|
|
| 7. |
- Laudato, Marco, et al.
(författare)
-
Experimental analysis on metamaterials boundary layers by means of a pantographic structure under large deformations
- 2022
-
Ingår i: Mechanics research communications. - : Elsevier BV. - 0093-6413 .- 1873-3972. ; 125, s. 103990-
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the dynamical behavior of a pantographic structure undergoing large deformations is analyzed. A harmonic force is applied on the structure, while its motion in time is recorded by means of a high-speed camera system. The resulting displacement field is obtained via the digital image correlation (DIC) method for the whole domain. A parametric study with respect to the amplitude of the imposed force exhibits the appearance of non-linear effects in the system response as well as the presence of a so-called boundary layer region. Such geometric nonlinearities are of paramount interest for studying the accuracy of a potential computational model. Boundary layers are known to be effected by the microstructure, but their roles in the system response are yet to be comprehended. The experimental results obtained in this work may be used as a benchmark case in modeling metamaterials.
|
|
| 8. |
- Laudato, Marco, et al.
(författare)
-
First experimental observation of the dynamical behavior of a pantographic metamaterial
- 2018
-
Ingår i: Mechanics research communications. - : Elsevier. - 0093-6413 .- 1873-3972. ; 94, s. 125-127
-
Tidskriftsartikel (refereegranskat)abstract
- The first experimental observation of the dynamical behavior of a pantographic sheet is presented. The experimental setup and the measurement procedures are accurately described. Finally, a qualitative description of the displacement vector field in time for a set of relevant frequencies is presented.
|
|
| 9. |
- Laudato, Marco, 1990-, et al.
(författare)
-
Linear dynamics of 2D pantographic metamaterial: numerical and experimental study
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, the results of numerical and experimental studies on the linear time-invariant dynamics of a 2D pantographic material are presented. The outcomes of a linear second gradient model enforcing the same symmetry of the microstructure is compared to experimental observations obtained via Digital Image Correlation.
|
|
| 10. |
- Laudato, Marco, et al.
(författare)
-
Sound generation mechanisms in a collapsible tube
- 2024
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 155:5, s. 3345-3356
-
Tidskriftsartikel (refereegranskat)abstract
- Collapsible tubes can be employed to study the sound generation mechanism in the human respiratory system. The goals of this work are (a) to determine the airflow characteristics connected to three different collapse states of a physiological tube and (b) to find a relation between the sound power radiated by the tube and its collapse state. The methodology is based on the implementation of computational fluid dynamics simulation on experimentally validated geometries. The flow is characterized by a radical change of behavior before and after the contact of the lumen. The maximum of the sound power radiated corresponds to the post-buckling configuration. The idea of an acoustic tube law is proposed. The presented results are relevant to the study of self-excited oscillations and wheezing sounds in the lungs.
|
|
