Séminaire n°57

Intervenant : José Antunes, Instituto Superior Técnico, Université de Lisbonne, Portugal

Contact : jantunes (at) ctn.ist.utl.pt

Date : 5/12/2016

Abstract :
Tibetan bowls have been traditionally used for ceremonial or meditation purposes, but also in contemporary music-making. They are handcrafted and produce different tones depending on their shape, size, mass and their alloy composition. Most important is the sound producing technique by impacting and/or rubbing, as well as the excitation location, the hardness and friction characteristics of the excitation stick.
In this work, we develop a physically-based method for nonlinear time-domain simulation of Tibetan bowls. Our computational approach, based on a compact modal formulation, produces realistic dynamical responses, both for impacted and rubbed bowls. Of particular interest is the radiation pattern of rubbed bowls, which spins with the stick, as a result of the combined motions of the two near-degenerate unstable shell modes.
Moreover, we focus on an interesting feature of Tibetan bowls: in order to produce self-excited responses, the stick must rub the bowl against the external side of the rim, e.g. radially pressing outwards the bowl center. Indeed, experimenting with many bowls show that they do not sing when rubbed internally. We exploit our computational model in order to reproduce the observed behavior, which can be understood from an energy balance of the system. Our results are in good agreement with experiments, thereby demonstrating that internally excited bowls are dissipative and hence unable to sing.