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Shape-optimal design of graded index sonic crystal noise barriers with line defects

Bart Van der Aa (Institutionen för bygg- och miljöteknik, Teknisk akustik, Vibroakustik) ; Jens Forssén (Institutionen för bygg- och miljöteknik, Teknisk akustik, Vibroakustik)
42nd International Congress and Exposition on Noise Control Engineering 2013: Noise Control for Quality of Life, INTER-NOISE 2013; Innsbruck; Austria; 15 September 2013 through 18 September 2013 Vol. 3 (2013), p. 2325-2334.
[Konferensbidrag, refereegranskat]

A graded index sonic crystal gives rise to upward refraction due to a negative sound speed gradient, which progresses with height. However, in addition to upward refraction, these cylinder formations can simultaneously benefit from band-gap phenomena. This paper presents a method to optimise graded index sonic crystals for broadband traffic noise by: (1) organising cylinders in complex formations using natural cubic splines and (2) introducing line defects. All variables were optimised with a multi-objective genetic algorithm, for structures based on horizontally oriented acoustically hard cylinders, located above a perfectly reflecting ground plane. A four-lane outdoor situation, with a traffic scenario consisting of 95 % light and 5 % heavy vehicles driving at 70 km/h has been studied. For such a configuration we obtained a spatially averaged mean reduction of 3.7, 4.3 and 5.4 dBA, with optimised structures covering an effective cross-sectional area of 0.69, 1.25 and 1.45 m2, respectively. It is found that the focussing performance of the studied structures is enhanced by increasing the number of scatterers as a function of height, which effectively represents a negative sound speed gradient. In addition, it is found that the effect of line defects is significant, and that the insertion loss among the studied traffic lanes is reasonably constant.

Nyckelord: Graded index sonic crystal; Optimisation; Outdoor sound propagation; Sonic crystal



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Denna post skapades 2013-10-18. Senast ändrad 2015-05-06.
CPL Pubid: 185370