Manuel Recuero

Modelling seismic oceanography experiments by using first- and second-order Complex Frequency Shifted Perfectly Matched Layers

This work investigates the ability of modelling seismic oceanography experiments by using underwater acoustic propagation equations. Seismic oceanography tries to retrieve the fine structure of the ocean water masses by processing the acoustic waves reflected in the low-contrast interfaces of fronts, eddies, internal waves or thermohaline intrusions. Since the reflectivity of such interfaces is of order 10 ―3 ―10 ―4 , the absorption capability of the numerical boundaries becomes crucial. Complex Frequency Shifted offers a better alternative to classical Perfectly Matched Layer formulation, but has not yet been extended to acoustic equations. Here, first- and second-order Complex Frequency Shifted Perfectly Matched Layers equations are proposed which can provide reflection coefficients of order 10 ―5 . Therefore, a numerical Finite-Difference Time-Domain (FDTD) scheme combined with the proposed CFS-PML equations is able to model such experiments.

Synthetic modelling of acoustical propagation applied to seismic oceanography experiments

Recent work shows that multichannel seismic (MCS) systems provide detailed information on the oceans finestructure. The aim of this paper is to analyze if high order numerical algorithms are suitable to accurately model the extremely weak wavefield scattered by the oceans finestructures. For this purpose, we generate synthetic shot records along a coincident seismic and oceanographic profile acquired across a Mediterranean salt lens in the Gulf of Cadiz. We apply a 2D finite-difference time-domain propagation model, together with second-order Complex Frequency Shifted Perfectly Matched Layers at the numerical boundaries, using as reference a realistic sound speed map with the lateral resolution of the seismic data. We show that our numerical propagator creates an acoustical image of the ocean finestructures including the salt lens that reproduces with outstanding detail the real acquired one

Airport noise insulation programs: The Spanish case

Noise pollution around airports is one of the most important problems in environmental acoustics. The incessant development of modern societies is continuously increasing the demand for air transport, and airports have to grow to adapt their operational capacity to the new requirements. On the other hand, the economic activity related to airports is closely linked to the expansion of built-up areas around them. Consequently, two completely incompatible land uses are forced to coexist, causing airport capacity to remain limited while the inhabitants do not cease to be annoyed by aircraft noise. Although there are several international initiatives setting the focus on the reduction of noise at the source, people living in residential areas around airports need urgent solutions. Among others, the implementation of sound insulation programs is one of the most widely-adopted solutions worldwide, as it allows a reduction of sound levels in the interior of dwellings, while the operational capacity of the airport remains unaffected. The definition and application of a sound insulation program is a very complex process that needs to manage several opposing factors: health, annoyance, airport capacity, economic costs of insulation measures… In this paper we describe the case of Spanish airport insulation programs. We set the focus on a concise description of the full process, from the creation of noise maps, to the checking of installed soundproofing measures, as carried out by the Spanish administration. As a result of this process, thousands of dwellings and houses have been acoustically insulated to meet indoor noise comfort criteria in Madrid, Mallorca and Malaga airports, among others.

Uncertainty in Noise Maps Isolines: The Effect of the Sampling Grid

Noise maps results are usually presented as contour graphs or isoline curves, which describe the sound levels as functions of spatial location. These maps are added to Geographic Information Systems (GIS), allowing sound level evaluation as a function of the continuous coordinates x and y, for a given height above ground. Although the outcome of the system is a continuous variable, the calculations that allow its evaluation are obtained from discrete points structured in a calculation grid. This grid is created by the application of spatial sampling techniques. Using spatial interpolation tools (IDW, krigging... ), values are assigned to the locations in which acoustic calculations have not been performed. The application of sampling and interpolation techniques (the type of grid, its density, the interpolation algorithms... ) contributes to the uncertainty of the results. This paper describes a calculation method to quantify the uncertainty associated to the spatial sampling and interpolation processes. Despite most of the previous literature refers to the uncertainty in a noise map as the uncertainty of the receivers results (output of the noise model), in this approach we propose also including the contributions derived by the interpolation and classification processes, so that the uncertainty must be estimated only for the locations on the contour lines.

A new 3D finite element model of the IEC 60318-1 artificial ear

The artificial ear specified in IEC 60318-1 is used for the measurement of headphones and has been designed to present an acoustic load equivalent to that of normal human ears. In this respect it is specified in terms of an acoustical impedance, and modelled by a lumped parameter approach. However, this has some inherent frequency limitations and becomes less valid as the acoustic wavelength approaches the characteristic dimensions within the device. In addition, when sound propagates through structures such as narrow tubes, annular slits or over sharp corners, noticeable thermal and viscous effects take place causing further departure from the lumped parameter model. A new numerical model has therefore been developed, which gives proper consideration to the aforementioned effects. Both kinds of losses can be simulated by means of the LMS Virtual Lab acoustic software which facilitates finite and boundary element modelling of the whole artificial ear. A full 3D model of the artificial ear has therefore been developed based on key dimensional data found in IEC 60318-1. The model has been used to calculate the acoustical impedance, and the results compared with the corresponding data determined from the lumped parameter model. The numerical simulation of the artificial ear has been shown to provide realistic results, and is a powerful tool for developing a detailed understanding of the device. It is also proving valuable in the revision of IEC 60318-1 that is currently in progress.

Data Base Design for Acoustics: The Case of Churches

This paper reports on an example of a data base for church acoustics. The initial scheme of data base fields is presented, including relationships to store the minimum information possible, to derive the required acoustic parameters automatically. It is demonstrated that if cross-data tools are added to the data base, it may also serve as an investigation platform from which results can be obtained which will allow acoustic patterns to be set depending on the volume and the internal architectural style. This hypothesis has been tested with Baroque churches, and a formula is proposed to predict the reverberation time, depending on the total volume of the room.

Prediction equations of isolating systems: Gypsum panels

Several prediction equations of acoustic noise isolation are presented and applied to gypsum structures of one, two, and three plates, with different thickness. On the other hand, acoustic noise isolation for simple, double, and triple gypsum panels is measured in transmission loss chambers officially recognized. The experimental results obtained are compared with the values obtained with the prediction equations in order to evaluate the error. The measurements are done in 1/3‐octave bands as the ISO 140‐3 proposes, using B&K equipment. It has also measured the panel vibrations with accelerometers with acoustic intensity techniques in order to explain several panel behaviors. Taking into account the former results, some prediction equations have been obtained versus mass and frequency, for values below 50u2009kg/m2 so the measuring process can be done easily.

Implementation of a virtual laboratory for training on sound insulation testing and uncertainty calculations in acoustic tests

This paper describes a methodology and case study for the implementation of educational virtual laboratories for practice training on acoustic tests according to international standards. The objectives of this activity are (a) to help the students understand and apply the procedures described in the standards and (b) to familiarize the students with the uncertainty in measurement and its estimation in acoustics. The virtual laboratory will not focus on the handling and set-up of real acoustic equipment but rather on procedures and uncertainty. The case study focuses on the application of the virtual laboratory for facade sound insulation tests according to ISO 140-5:1998 (International Organization for Standardization, Geneva, Switzerland, 1998), and the paper describes the causal and stochastic models and the constraints applied in the virtual environment under consideration. With a simple user interface, the laboratory will provide measurement data that the students will have to process to report the insulation results that must converge with the virtual true values in the laboratory. The main advantage of the virtual laboratory is derived from the customization of factors in which the student will be instructed or examined (for instance, background noise correction, the detection of sporadic corrupted observations, and the effect of instrument precision).

Acoustic displacement triangle based on the individual element test

A three node -displacement based- acoustic element is developed. In order to avoid spurious rotational modes, a higher order stiffness is introduced. This higher order stiffness is developed from an incompatible strain field which computes element volume changes under nodal rotational displacements fields. The higher order strain resulting from the incompatible strain field satisfies the Individual Element Test (IET) requirements without affecting convergence. The higher order stiffness is modulated, element by element, with a factor. As a result, the displacement based formulation presented on this paper is capable of placing the spurious rotational modes above the range of the physical compressional modes that can be accurately calculated by the mesh.

Assessment of Noise Exposure During Commuting in the Madrid Subway

Because noise-induced hearing impairment is the result not only of occupational noise exposure but also of total daily noise exposure, it is important to take the non-occupational exposure of individuals (during commuting to and from their jobs, at home, and during recreational activities) into account. Mass transit is one of the main contributors to non-occupational noise exposure. We developed a new methodology to estimate a representative commuting noise exposure. The methodology was put into practice for the Madrid subway because of all Spanish subway systems it covers the highest percentage of worker journeys (22.6%). The results of the application highlight that, for Madrid subway passengers, noise exposure level normalized to a nominal 8 hr (LEx,8h-cj ) depends strongly on the type of train, the presence of squealing noise, and the public address audio system, ranging from 68.6 dBA to 72.8 dBA. These values play an important role in a more complete evaluation of a relationship between noise dose and worker health response.