In this work, we introduce an open-source implementation of a time-domain wave-based room acoustic modeling software package, named DG_RoomAcoustics. In this software, the linear acoustic equations are spatially discretized by the nodal discontinuous Galerkin method, and are integrated in time by either the explicit Runge-Kutta or the arbitrary high-order derivatives (ADER) integration schemes. Following the principles of object-oriented programming paradigm, the software is structured to ensure generic applicability and to facilitate future extensions with additional functionalities (e.g., different time integration schemes, boundary conditions). A comprehensive presentation of the physical and numerical aspects of the problem is provided. A detailed exposition of the code structure and components is presented, all of which are released under an open-source license, fostering community feedback and collaborative contributions for ongoing improvements. A brief overview of the current capabilities of the software is introduced. Future work regarding possible functionality extensions and performance optimizing are discussed.@en

The in situ characterization of materials is a crucial challenge in room acoustics, as laboratories measurement cannot always be applied in consultancy practices. In particular, there is a lack of method to characterize in situ systems with perforated facings, which are commonly encountered systems in room acoustics. In this paper, the in situ characterization of a rigidly-backed porous material behind a rigid perforated facing by means of pressure–velocity measurements is presented. The method includes an inverse impedance model fitting based on measurement in a limited frequency range. The applicability of this method was studied by measuring a variety of perforated facings, whether in front of an air cavity or backed by a porous layer, and comparing the obtained impedance model parameters to reference values. Good agreement was observed between the retrieved parameters and the references, with the errors in all retrieved parameters moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.

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This study presents numerical solutions for two vibroacoustic problems using the time-domain nodal discontinuous Galerkin (DG) method. The first problem is the impact sound radiation from a rectangular slab into a cuboid room, and the second is the sound transmission between two cuboid rooms with direct and flanking contributions. The structures are modelled as a three-dimensional solid governed by the linear elasticity equations, and sound propagation in the rooms is governed by the linear acoustic equations. In the impact sound radiation case, the normalised sound pressure is evaluated and compared to the one obtained by the modal expansion method. In the sound transmission case, pressure transfer functions between different positions are calculated and compared to those obtained by the finite element method (FEM). The upwind numerical fluxes in DG for both governing equations, as well as the coupling conditions, are presented. There is excellent agreement between the solutions obtained by the nodal DG and those obtained by the modal expansion method/FEM. Although minor discrepancies exist in the resonance frequencies and magnitude, the overall trend shows good agreement.@en

In this work, the vibrations of a structure excited by an impact source are modelled using the time domain nodal discontinuous Galerkin (DG) method, which solves linear elasticity equations. A scaled lightweight wooden floor (LWF) structure which consists of components that differ in their mechanical properties is taken as a case study. The Rankine-Hugoniot jump conditions for piece-wise constant material properties are used to obtain accurate numerical fluxes in the DG method, and their detailed derivation is the main contribution of this work. Free boundary conditions are applied on the surface of the structures, and constant viscous damping force is added to the model to have vibrational energy losses. To validate the numerical results, the mobility of the structure is calculated and compared with experimental data. The agreement is good regarding the natural frequencies, with a maximum absolute difference of less than 11 Hz in the frequency range below 200 Hz. The adopted damping approach is shown to be insufficient to represent a broad frequency range.@en

Triply periodic minimal surfaces (TPMS), a class of periodic implicit surface with zero mean curvature, are emerging as an excellent solution to create graded porous structures. The grading of a porous layer can enhance and broaden the acoustic absorption in a target frequency range. The porosity gradient within the TPMS structure can be precisely controlled by a mathematical function, straightforwardly allowing for optimization towards the desired absorption. As the first step of the optimization procedure, we present a computational approach to determine acoustic absorption properties of functionally graded TPMS porous structures: the transport parameters of a rigid-frame homogeneous TPMS porous absorber are found by the finite element simulations of three static problems, then the absorption coefficient of the TPMS porous structure with graded porosity along the thickness is calculated with the transfer matrix method. The presented approach is validated by direct numerical simula- tions of the same porous structure.@en

Reliable data on acoustical properties of materials are crucial for the design of a desired acoustic environment as well as to obtain accurate results from acoustic simulations. Although the acoustical properties of materials can be obtained via laboratory measurements, situations where in situ measurements are needed are often encountered. However, in situ measurement methods presented so far are limited by their poor portability or inaccuracies in the low-frequency range. In this work, we propose a characterization method that combines an in situ pressure-velocity (PU) measurement with a model fitting procedure using the Delany-Bazley-Miki impedance model for porous materials. The method uses an optimization routine to find the best match of measured and modelled reflection coefficient values within a given frequency range for the optimization parameters: flow resistivity, panel thickness, and probe-sample distance. The optimal parameter values allow, in turn, calculating the porous panel’s reflection coefficients for a broad frequency range including frequencies below the lower bounds of the optimization frequency range. The sensitivity of the method to panel width, lower bound of fitting frequency range, and to excluding parasitic reflections by time windowing is studied. The study shows that the proposed method provides characterization results in good agreement with reference data for panels of dimensions larger than 1800 mm and that the method is robust for reduction of one dimension of the panel down to 300 mm. It also shows that the model fitting accuracy is best when the frequency range of analysis is restricted to 1000–5000 Hz.@en

The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials.@en

Accurate modeling of boundary conditions is of critical importance for acoustic simulations. Recently, the time-domain nodal discontinuous Galerkin (TD-DG) method has emerged as a potential wave-based method for acoustic modeling. Although the acoustic reflection behavior of various time-domain impedance boundaries has been studied extensively, the modeling of the sound transmission across a locally-reacting layer of impedance discontinuity is far less developed. This paper presents a formulation of broadband time-domain transmission boundary conditions for locally-reacting surfaces in the framework of the TD-DG method. The formulation simulates the acoustic wave behavior at each of the boundary nodes using the plane-wave theory. Through the multi-pole model representation of the transmission coefficient, various types of transmission layers can be simulated. One-dimensional numerical examples demonstrate the capability of the proposed formulation to accurately simulate the reflection and transmission characteristics of the limp wall and the porous layer, where quantitative error behavior against analytical results is presented. Furthermore, to demonstrate the applicability, two scenarios of two-dimensional acoustic environment are considered. One is the sound transmission between two rooms partitioned by a limp panel and the other is the sound propagation through a transmissive noise barrier. Comparison of the predicted results from the proposed method against the results from the frequency-domain finite element simulations further verifies the formulation.@en