The method of fundamental solutions for the analysis of infinite 3D sonic crystals

[EN] The use of periodic structures in acoustic applications has interested the scientific community in the last two decades. Although in-depth research has been thoroughly performed, many issues have still not been solved. Computational analysis of sonic structures using realistic 3D models still poses significant problems, and most of the published results correspond to 2D problems. Analysing 3D problems of such structures using conventional methods demands large computational resources, which may be prohibitive. This paper proposes a new approach for such 3D problems making use of a highly efficient Method of Fundamental Solutions (MFS) approach to deal with sonic crystals made of 3D scatterers, infinitely repeated with constant spacing along one direction. The method makes use of a special form of the acoustic fundamental solutions which can be highly efficient in such analysis, while allowing just the cell that is repeated to be effectively modelled. Verification of the model is provided by first comparing its results with those from an ACA-MFS model. Results are compared with those from a FDTD algorithm, and a parametric study is presented revealing the 3D character of the computed responses, and evidencing the formation of acoustic band-gaps at specific frequency bands associated with the Bragg effect.The EU funding support in the scope of COST (European Cooperation in Science and Technology) through the COST ActionPlease check funding information and confirm its correctness. CA15125 - DENORMS: "Designs for Noise Reducing Materials and Structures" is here also acknowledged.Godinho, L.; Redondo, J.; Amado-Mendes, P. (2019). The method of fundamental solutions for the analysis of infinite 3D sonic crystals. Engineering Analysis with Boundary Elements. 98:172-183. https://doi.org/10.1016/j.enganabound.2018.09.015S1721839

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells