Wednesday, June 16th, 2021. Time: 12 noon
Blending learning - Link for online session: meet.google.com/qjo-sttx-dgo
Acoustic black holes (ABHs) in mechanics have borrowed their name from their counterpart in astrophysics. Everyone has a more or less precise idea of what an astrophysical black hole is. A so massive object that nothing can escape from it, even light, once crossed the so-called horizon event. In mechanics, a peculiar phenomenon was discovered in the eighties, which somewhat reminded of black holes. If the end of a beam is tailored following a power law profile, such that its thickness ideally decreases to zero, it would take an infinite amount of time for an incident travelling wave to reach the tip of the ABH. Therefore, no reflection could occur, as if the wave had entered a black hole. In practice, however, the ABH wedge has to be truncated at some point resulting in a residual thickness which totally undermines the ABH effect. Consequently, the latter remained unexploited until the beginning of this century, when it was shown that the simple inclusion of some local damping turned ABHs into an effective passive vibration control technique. In recent years, ABH indentations have been designed for beams, plates and cylindrical shells. They slow down and trap waves, showing big potential for vibration and noise reduction, as well as for enhancing mechanical-based energy harvesting devices. In addittion, arrays of ABHs exhibit typical properties of phononic crystals and metamaterials like band gap formation, negative refraction and wave lensing. The ABH effect can also be used to design anechoic terminations in ducts and we will show that, in some cases, the correspondence between acoustic and astrophysical black holes is closer than one could may expect. In this talk, we will review all such amazing properties of ABHs in mechanics.
Dr. Oriol Guasch is Full Professor at the Department of Engineering, La Salle, Universitat Ramon Llull (URL) in Barcelona, where he heads the research in acoustics within the GTM group. He holds a five-year degree in Physics from the Universitat de Barcelona (UB) and a PhD in Computational Mechanics and Applied Mathematics from the Universitat Politècnica de Catalunya (UPC). His current research lines involve computational acoustics and aeroacoustics with application to voice production, graph theory and numerical modelling of mid and high frequency vibroacoustics, theoretical and experimental transmission path analysis, parametric array technology to generate audible sound from ultrasonic collimated beams, and acoustic black holes in mechanics. Dr. Guasch has authored or coauthored a significant number of papers in first rank international scientific journals and conferences and owns two patents. He has organized and chaired many sessions at international congresses and was the general chair of the NOVEM 2018 congress. He currently serves as Subject Editor for the Journal of Sound and Vibration. Dr. Guasch has led and participated in many international and national research projects.