Table of Links Abstract and 1 Introduction 2 Unit cell design and analysis 3 Unit cell experimental and numerical characterization 4 Rainbow AM labyrinthine panel 4.1 Panel design and fabrication 4.2 FE model of the AM panel 4.3 AM panel characterization 4.4 AM panel sound absorption results 5 Numerical evaluation of different labyrinthine sound absorption panel solutions 5.1 Macrocell with backing cavity 5.2 Results Conclusions, Acknowledgements, and References Appendix I 5.1 Macrocell with backing cavity Given the promising results for the design procedure outlined in the previous Sections, and the good agreement between numerical and experimental results, a further numerical study is performed to evaluate possible developments of the AM-based sound absorption panel. The objective is to assess its acoustic performance under different design configurations. More specifically, three additional configurations are assessed: a) the addition of a melamine foam inside the UCs of the panel; b) the addition of a rigid rear backing cavity applied in correspondence with the uneven bottom surface of the panel (in this case with open apertures), with/without melamine foam filling; c) a combination of a) + b). The acoustic performance of each of these features can be studied and compared to the original configuration (taken as a baseline), again performing FE simulations with COMSOL Multiphysics, focusing on a single marcocell, taken as representative of the panel behaviour. Again, thermoviscous effects need to be accounted for. In the second configuration, the AM panel is coupled to an additional acoustic domain of a depth equal to four times its side length (Fig.11a and b). Non-reflective Perfectly Matched Layer (PML) boundary conditions are applied to the back of the acoustic domain. Once again, structural domains are considered perfectly rigid, since results from fully vibro-acoustic and simple acoustic simulations give rise to negligible differences. The foam material is chosen as melanine, whose properties are summarized in Table 1. 5.2 Results Figure 12 shows the calculated absorption coefficient in the three considered cases. The baseline simulation, corresponding to the dashed curve in Fig. 10b, is shown in red. The effect of the presence of a backing cavity (5mm thick) filled with melamine foam (green dashedcurve in Fig.11) is to shift absorption peaks to lower frequencies (the lowest from 1 kHz to about 700 Hz), with a beneficial effect for the attenuation of low frequencies. The addition of a foam filling in the AM cavities, on the other hand, leads to a more uniform absorption coefficient over the whole frequency range, at the expense of a lower efficiency at the AM working frequencies. This solution can however be useful in the case where a more distributed attenuation effect is required over the whole frequency range, rather than at specific target frequencies. Other types of foams can also be considered to optimize the combined effect with the AM. This paper is available on arxiv under CC BY-NC-ND 4.0 DEED license. Authors:
(1) F. Nistri, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy and Politecnico di Milano, Milano, Italy;
(2) V. H. Kamrul, Politecnico di Milano, Milano, Italy;
(3) L. Bettini, Politecnico di Milano, Milano, Italy;
(4) E. Musso, Politecnico di Milano, Milano, Italy;
(5) D. Piciucco, Politecnico di Milano, Milano, Italy;
(6) M. Zemello, Politecnico di Milano, Milano, Italy;
(7) A.S. Gliozzi, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy;
(8) A.O. Krushynska, Faculty of Science and Engineering, University of Groningen, Groningen, The Netherlands;
(9) N. M. Pugno, Laboratory for Bioinspired, Bionic, Nano, Meta Materials & Mechanic, University of Trento, Trento, Italy and School of Engineering and Materials Science, Queen Mary University of London, United Kingdom;
(10) L. Sangiuliano, Phononic Vibes s.r.l., Milano, Italy;
(11) L. Shtrepi, Department of Energy "Galileo Ferraris", Politecnico di Torino, Torino, Italy;
(12) F. Bosia, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy and a Corresponding Author (federico.bosia@polito.it). Table of Links Abstract and 1 Introduction Abstract and 1 Introduction 2 Unit cell design and analysis 2 Unit cell design and analysis 3 Unit cell experimental and numerical characterization 3 Unit cell experimental and numerical characterization 4 Rainbow AM labyrinthine panel 4.1 Panel design and fabrication 4.1 Panel design and fabrication 4.2 FE model of the AM panel 4.2 FE model of the AM panel 4.3 AM panel characterization 4.3 AM panel characterization 4.4 AM panel sound absorption results 4.4 AM panel sound absorption results 5 Numerical evaluation of different labyrinthine sound absorption panel solutions 5.1 Macrocell with backing cavity 5.1 Macrocell with backing cavity 5.2 Results 5.2 Results Conclusions, Acknowledgements, and References Conclusions, Acknowledgements, and References Appendix I Appendix I 5.1 Macrocell with backing cavity Given the promising results for the design procedure outlined in the previous Sections, and the good agreement between numerical and experimental results, a further numerical study is performed to evaluate possible developments of the AM-based sound absorption panel. The objective is to assess its acoustic performance under different design configurations. More specifically, three additional configurations are assessed: a) the addition of a melamine foam inside the UCs of the panel; b) the addition of a rigid rear backing cavity applied in correspondence with the uneven bottom surface of the panel (in this case with open apertures), with/without melamine foam filling; c) a combination of a) + b). The acoustic performance of each of these features can be studied and compared to the original configuration (taken as a baseline), again performing FE simulations with COMSOL Multiphysics, focusing on a single marcocell, taken as representative of the panel behaviour. Again, thermoviscous effects need to be accounted for. In the second configuration, the AM panel is coupled to an additional acoustic domain of a depth equal to four times its side length (Fig.11a and b). Non-reflective Perfectly Matched Layer (PML) boundary conditions are applied to the back of the acoustic domain. Once again, structural domains are considered perfectly rigid, since results from fully vibro-acoustic and simple acoustic simulations give rise to negligible differences. The foam material is chosen as melanine, whose properties are summarized in Table 1. 5.2 Results Figure 12 shows the calculated absorption coefficient in the three considered cases. The baseline simulation, corresponding to the dashed curve in Fig. 10b, is shown in red. The effect of the presence of a backing cavity (5mm thick) filled with melamine foam (green dashedcurve in Fig.11) is to shift absorption peaks to lower frequencies (the lowest from 1 kHz to about 700 Hz), with a beneficial effect for the attenuation of low frequencies. The addition of a foam filling in the AM cavities, on the other hand, leads to a more uniform absorption coefficient over the whole frequency range, at the expense of a lower efficiency at the AM working frequencies. This solution can however be useful in the case where a more distributed attenuation effect is required over the whole frequency range, rather than at specific target frequencies. Other types of foams can also be considered to optimize the combined effect with the AM. This paper is available on arxiv under CC BY-NC-ND 4.0 DEED license. This paper is available on arxiv under CC BY-NC-ND 4.0 DEED license. available on arxiv Authors: (1) F. Nistri, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy and Politecnico di Milano, Milano, Italy; (2) V. H. Kamrul, Politecnico di Milano, Milano, Italy; (3) L. Bettini, Politecnico di Milano, Milano, Italy; (4) E. Musso, Politecnico di Milano, Milano, Italy; (5) D. Piciucco, Politecnico di Milano, Milano, Italy; (6) M. Zemello, Politecnico di Milano, Milano, Italy; (7) A.S. Gliozzi, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy; (8) A.O. Krushynska, Faculty of Science and Engineering, University of Groningen, Groningen, The Netherlands; (9) N. M. Pugno, Laboratory for Bioinspired, Bionic, Nano, Meta Materials & Mechanic, University of Trento, Trento, Italy and School of Engineering and Materials Science, Queen Mary University of London, United Kingdom; (10) L. Sangiuliano, Phononic Vibes s.r.l., Milano, Italy; (11) L. Shtrepi, Department of Energy "Galileo Ferraris", Politecnico di Torino, Torino, Italy; (12) F. Bosia, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy and a Corresponding Author (federico.bosia@polito.it). Authors: Authors: (1) F. Nistri, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy and Politecnico di Milano, Milano, Italy; (2) V. H. Kamrul, Politecnico di Milano, Milano, Italy; (3) L. Bettini, Politecnico di Milano, Milano, Italy; (4) E. Musso, Politecnico di Milano, Milano, Italy; (5) D. Piciucco, Politecnico di Milano, Milano, Italy; (6) M. Zemello, Politecnico di Milano, Milano, Italy; (7) A.S. Gliozzi, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy; (8) A.O. Krushynska, Faculty of Science and Engineering, University of Groningen, Groningen, The Netherlands; (9) N. M. Pugno, Laboratory for Bioinspired, Bionic, Nano, Meta Materials & Mechanic, University of Trento, Trento, Italy and School of Engineering and Materials Science, Queen Mary University of London, United Kingdom; (10) L. Sangiuliano, Phononic Vibes s.r.l., Milano, Italy; (11) L. Shtrepi, Department of Energy "Galileo Ferraris", Politecnico di Torino, Torino, Italy; (12) F. Bosia, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy and a Corresponding Author (federico.bosia@polito.it).

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