Modelling of thin and imperfect interfaces : Tools and preliminary study

Sammanfattning: For quite some time, the strive for more efficient acoustic absorbers keepsincreasing, driven by a number of psycho-physiological studies on health re-lated dangers of noise exposure. As the global wealth increases and with itthe global expectation of quieter living and working environments, manifestedin both politics and research, an important market for sound absorbing andnoise control systems develops in all industrialised countries. In the acousticcommunity, the main endeavours of the two last decades have been orientedtowards a better understanding of the dissipation phenomena in absorbers(and especially in poroelastic media) as well as proposing new topologies andstructures for these elements. These efforts have resulted in an abundant lit-erature and numerous improvements of the characterisation, modelling anddesign methodologies for a wide range of media and many different systems.The chosen research direction for the present thesis slightly deviates fromthis usual path of modelling absorbing materials as bulk media. Here theaim is to investigate the interfaces between the different components of typ-ical absorbers. Indeed, these interface regions are known to be difficult tocharacterise and controlling their properties is challenging for a number ofreasons. Interfaces in sound packages for instance are inherently by-productsof the assembly process and, even if they surely have an important impact onthe acoustic performance, they remain mostly overlooked in the establishedmodelling practices. Therefore, the overall objective of the current doctoralproject is to identify strategies and methods to simulate the effect(s) of un-certainties on the interface physical or geometrical parameters.The present licentiate thesis compiles three works which together form adiscussion about techniques and tools designed in an attempt to efficientlymodel thin layers and small details in rather large systems. As part of thework a section of physical model simplifications is discussed which will laythe ground for the next stages of the research. Two publications on the firsttopic are included, presenting Finite-Element-based hybrid methods that al-low for coating elements in meta-poroelastic systems to be taken into accountand reduce the computational cost of modelling small geometric features em-bedded in large domains. The third included contribution is an anticipation,to a certain extent, of the remainder of the doctoral project, discussing theuse of physical heuristics to simplify porous thin film models. Here a steptowards the modelling of interface zones is taken, departing from numericalsimulations and reflecting instead on the physical description and modellingof thin poroelastic layers.