L. Godinho

On the use of a small-sized acoustic chamber for the analysis of impact sound reduction by floor coverings

The use of new technical solutions to minimize the impact noise generated in dwellings is progressively becoming more frequent and in some countries mandatory due to current regulations. EN ISO 140-8 proposes an objective methodology for characterization of impact noise reduction, but it requires that adequate large scale laboratory facilities are available, fulfilling the requirements of the EN ISO 140 standards. However, in the development of new solutions in the research stage or for direct comparison among technical solutions, alternative evaluation methods may be used, avoiding the full cost of large-scale tests in traditional acoustic chambers. In this work, the authors address the use of a reduced size acoustic chamber to study the impact noise reduction provided by different types of floor treatments, assessing its limitations and applicability. With this aim, a small concrete chamber has been built, characterized and used to test a number of floor treatments. Final results provided by the proposed system are compared with in-situ measurements obtained for the same types of treatments, indicating a very similar behavior for both the test facilities.

Analytical Evaluation of the Acoustic Behavior of Multilayer Walls When Subjected to Three-Dimensional and Moving 2.5-Dimensional Loads

This paper focuses on the analytical evaluation of the acoustic behavior of multilayer walls when subjected to 3D and moving 2.5D loads. The computations are performed in the frequency domain for a wall system composed of multiple solid and fluid layers. The pressure generated by the 3D load is computed as Bessel integrals, following the transformations proposed by Sommerfeld. The integrals are discretized by assuming the existence of a set of virtual loads equally spaced in a direction perpendicular to the plane of the wall. The expressions presented here allow the pressure field to be computed without discretizing the interfaces between layers. The full interaction between the fluid (air) and the solid layers is taken into account. As the 3D pressure field can also be computed as a summation of spatially sinusoidal harmonic line loads, which can be seen as a moving 2.5D load, this paper studies the contribution made to the global 3D response by the insulation provided by the wall when subjected to each of these loads. To illustrate the main findings, simulated responses are computed in the frequency domains for single and double walls that are subjected to 3D and moving 2.5D loads. Additionally, time responses have been synthesized using inverse Fourier transformations.

The acoustic behavior of concrete resonators incorporating absorbing materials

Acoustic resonators are a common engineering solution providing sound absorption in intermediate frequencies. They are used in many acoustic applications where noise absorption is required, such as outdoor barriers. Outdoor noise barriers face aggressive weather conditions and so their design has to reconcile durability and absorption. This compromise may be achieved by making use of materials such as standard and lightweight concrete. The work described in this paper analyzes the acoustic behavior of concrete resonator shapes using an experimental approach. The resonant frequency of resonators of different dimensions and the sound absorption they provide are determined. In addition, lightweight concrete resonator-like structures are analyzed, and their acoustic absorption is characterized. Mixed devices that incorporate both standard concrete, lightweight concrete (with expanded clay) and porous materials, arranged in different configurations, are also analyzed so as to define higher performance solutions.

2.5D Acoustic Wave Propagation in Shallow Water Over an Irregular Seabed Using the Boundary Element Method

In this paper a Boundary Element formulation, in the frequency domain, is used to investigate the 2.5D acoustic wave propagation in shallow water over an irregular seabed that is assumed to have a rigid bottom and a free surface.

Using A Dual-BEM Formulation To Model TheSound Pressure Wavefield Provided ByAbsorbing Thin Screens Attached To The Walls OfA Duct

The modelling of the 2D sound pressure wavefield in the presence of thin absorbing screens attached to the walls of a duct, assumed to be infinitely long, is described in this paper. The simulation uses a frequency-domain Dual-BEM (BEM/TBEM) formulation, which overcomes the thin-body difficulty that arises with the classical BEM formulation. The sound absorption is simulated by imposing impedance boundary conditions, which are applied in conjunction with a Dual-BEM approach. The fundamental solutions used in the formulation allow the solution to be obtained without discretizing the duct’s walls. Thus, only the boundary of each absorbing screen attached to the duct’s walls is modelled, which makes the proposed formulation efficient even at high excitation frequencies. The hypersingular integrals that result from the implementation of the TBEM are computed analytically. The formulation is used to compare results obtained with absorbing screens with those obtained with rigid screens and with those obtained in a duct without screens. Results in the time domain are obtained by applying an inverse Fourier transform to the frequency results.

Comparison Of Acoustic Insulation Provided By Infmite Plane Versus CircularClosed Walls

In this paper, analytical solutions are used to compute the acoustic insulation provided by plane and circular closed walls when subjected to sinusoidal harmonic line pressure loads. In the first case the panel is assumed to have infinite extent and the pressure wave field is computed using 2.5D Greens functions established in Cartesian co-ordinates for an infinite solid layer bounded by fluid media. The threedimensional problem is formulated as a summation of two-dimensional problems for different wave numbers along the z direction. Each two-dimensional problem in turn is written as a superposition of plane waves for varying wave numbers along the X direction. The curved wall is modelled as a cylindrical solid annulus bounded by fluid media, and the pressure wave field is computed using analytical expressions expressed in cylindrical co-ordinates. The threedimensional problem is likewise broken down into a set of two-dimensional problems, with different wave numbers along the z direction. The influence of the curvature of the wall on the results is studied by comparing the responses of both models where the thickness is the same, but the radius of the annulus varies. The assumption of a circular closed wall allows the vibration modes of the enclosure to be found, and makes it possible to assess the influence of this phenomenon on the sound insulation.

Stress analysis in pipelines submerged in a fluid medium subjected to a point pressure load

This work analyses the stresses in an infinite fluid-filled circular pipeline submerged in a homogeneous fluid medium when subjected to the incidence of waves generated by a point pressure load, The wall of the pipeline is modeled with constant thickness and assumed to behave elastically. This model leads to the resolution of what is commonly called a 2-l/2-D problem which allows the 3D solution to be obtained as a discrete summation of 2D problems with different spatial wavenurnbers. This procedure is defined by means of Fourier transformation in the direction in which the geometry does not vary, and considering an infinite number of virtuaI point sources equally spaced along the pipeline axis. The solution for each 2D problem is solved using analytical solutions. Calculations are first performed in the frequency domain and time solutions are then obtained using inverse Fourier transforms.