  In outdoor acoustics, the calculations of sound propagating in air can be
computationally heavy if the domain is chosen large enough to fulfil the
Sommerfeld radiation condition. By strategically truncating the computational
domain with a efficient boundary treatment, the computational cost is lowered.
One commonly used boundary treatment is the perfectly matched layer (PML) that
dampens outgoing waves without polluting the computed solution in the inner
domain. The purpose of this study is to propose and assess a new perfectly
matched layer formulation for the 3D acoustic wave equation, using the nodal
discontinuous Galerkin finite element method. The formulation is based on an
efficient PML formulation that can be decoupled to further increase the
computational efficiency and guarantee stability without sacrificing accuracy.
This decoupled PML formulation is demonstrated to be long-time stable and an
optimization procedure of the damping functions is proposed to enhance the
performance of the formulation.
