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A sandwich wall-panel solution based on Cross-Laminated Timber (CLT) has been recently developed aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. Such panel, named Cross-Insulated Timber (CIT), was previously optimized to fulfil structural and thermal requirements with a minimum production cost. The layout of the new panel is similar to the one of a five-layer CLT panel, but the inner layer is made of polyurethane rigid foam instead of timber. Besides its technical and economical benefit, it is also of interest to assess its environmental impact. This paper presents a study about the environmental impact assessment through Life-Cycle Analysis (LCA) of this new type of wood-based sandwich wall panel. A cradle-to-gate LCA with consideration of different end-of-life scenarios is performed in order to identify the processes that contribute the most to the environmental impact of the CIT panel solution proposed during its life cycle, namely during manufacturing. The LCA includes also the comparative assessment of: (i) varying the thickness of the wood layers, with respect to the optimized CIT panel; (ii) using an alternative core material, namely insulation cork board (ICB), and (iii) applying structurally equivalent three-layered CLT solutions, with alternative core materials. The results obtained show that the manufacturing process of the CIT panel, namely the polyurethane foam production and the press and curing processes during the panels assembly are the ones that produce the highest impacts. It was also found out that varying the thickness of the wood layers compared to the optimized solution leads, in general, to an increase in all impact categories. This means that the optimized solution in terms of economic costs is also the one which presents the lowest environmental impacts. Compared to equivalent CIT panels with ICB core and CLT solutions, the environmental performance of the panel proposed was better for some impact categories, while it was worse in others.

A novel experimental/numerical hybrid methodology for the assessment of railway-induced ground-borne vibration in buildings based on experimental measurements in the soil surface is proposed in this paper. This methodology has been specifically designed for the prediction of railway-induced vibration in buildings to be constructed close to an operative railway infrastructure, although it can be applied for other types of vibration sources. The model of the incident wave field induced by the railway infrastructure consists of a set of virtual forces applied in the soil, which would be obtained from vibration experimental measurements in the surface of the ground where the building will be constructed. These virtual forces can be subsequently applied to a model of the building-soil system to obtain a prediction of the vibration levels that will be induced by the existing railway infrastructure to the studied building. In the present work, this methodology is theoretically defined and it is numerically validated for two-dimensional and two-and-a-half-dimensional cases. To numerically test the methodology, the measured ground surface responses are replaced by simulated ones obtained in a set of points called collocation points. In this context, a parametric study has been developed with the aim of finding out a robust criterion for the application of the present methodology with respect to the amount and location of the collocation points (representing vibration sensors) and virtual forces. It is found that the distance between virtual sources should be smaller than the S-wave wavelength of the upper soil layer corresponding to the highest frequency of the frequency range of interest to ensure the reliability of the methodology. Moreover, the proposed method is found to be insignificantly affected by the building-tunnel dynamic coupling for building-tunnel distances above 20 m. The proposed hybrid model would simplify the usual numerical prediction approach commonly adopted for dealing in detail with these problems, since a model of the railway infrastructure is no longer required. Moreover, it would reduce the uncertainty of the prediction due to the use of experimental measurements of the particular site to be studied. In addition, it would provide a higher accuracy and flexibility than empirical models based on experimental transmissibility functions between the soil surface and the building This work was financially supported by: • Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT - Instituto de I&D em Estruturas e Construç˜oes - funded by national funds through the FCT/MCTES (PIDDAC) and by “Institute for sustainability and innovation in structural engineering” - ISISE (UIDP/04029/2020), funded by the Fundaç˜ao para a Ciˆencia e a Tecnologia (FCT), I.P., and Regional Operational Programme CENTRO2020 within the scope of project CENTRO-01- 0145-FEDER-000006. • The project NVTRail: Noise and Vibrations induced by railway traffic in tunnels: an integrated approach, funded by FEDER funds through COMPETE2020 and by national funds (PIDDAC) through FCT/ MCTES, with grant reference POCI-01-0145-FEDER-029577. • The project VIBWAY: Fast computational tool for railway-induced vibrations and re-radiated noise assessment, with reference RTI2018- 096819-B-I00, supported by the Ministerio de Ciencia e Innovación, Retos de Investigación 2018. This work was partially carried out under the framework of In2Track2, a research project of Shift2Rail (H2020). The financial support provided by University of Leeds Cheney Award Scheme is also appreciated

• Ministerio de Economia y Competitividad y Fondos FEDER. Proyecto RA2015-70487-R, para David Montes Gonzalez, Juan Miguel Barrigon Morillas • Fundacao para a Ciencia e a Tecnologia. P proyecto POCI-01-0145-FEDER-007633, para Luis Manuel Cortecao Godinho, Paulo Jorge Amado Mendes

[EN] We propose the application of a numerical model based on the Method of Fundamental Solutions to the estimation of the target strength (TS) of single fish, a crucial parameter for evaluating fish abundance when using active acoustical techniques. We consider a realistic beam and the influence of the evolution of the scattered field with distance maintaining the target in the far field of the ultrasonic transducer. The cases of a fluid sphere and a prolate spheroid model for the swimbladder are used to verify the application of MFS against other analytical and numerical methods. Additionally, a model considering only the swimbladder and the fishbone is presented to evaluate the differences between dorsal and ventral aspect measurements, and to understand previous experimental works performed with Atlantic salmon (Salmo salar) in floating cages., I. Perez-Arjona and V. Espinosa acknowledge funding of ACUSTUNA project ref. CTM2015-70446-R (MINECO/FEDER, UE), and UPV grants of PAID-00-15 and GVA BEST/2015/270. L. Godinho acknowledges the funding by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633. The authors would like to thank Dr. Manuel Bou and Carlos Albino for the technical assistance with work-station procedures.

This paper presents an experimental study about the acoustic and thermal behaviour of a novel type of sandwich panel solution based on Cross-Laminated Timber (CLT). The layout of the new panel, named Cross-Insulated Timber (CIT), is similar to the one of a five-layer (CLT) panel, but the inner layer is made of polyurethane (PUR) rigid foam instead of timber, aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. For the acoustic behaviour, the study included the assessment of (i) the airborne and impact sound insulations of the developed panel, as well as of equivalent-thickness CLT solutions, and of (ii) the suitability of analytical models to describe such sound insulation. In general, the airborne and impact sound insulation of the CIT panels were found to be lower than that of CLT panels with equivalent thickness, namely due to their mass differences. Analytical models available in the literature to describe the airborne sound insulation of typical sandwich panels failed to describe the behaviour of the CIT panels. The Sharp model for homogeneous isotropic elements was able to provide a good description of the airborne sound insulation behaviour of the thicker CIT panels; however, it also failed to describe the behaviour of the thinner CIT panels. An adaptation of such model, by replacing the typical critical frequency due to bending by the dilatational frequency, enhanced the accuracy of predictions. An empirical model to estimate the impact sound insulation of both CIT and CLT panels was also proposed and fitted quite well the results. Regarding the thermal behaviour, some variability was found in the thermal resistance of the CLT and CIT panels, which was attributed to the intrinsic scatter in their material properties, namely for wood. Despite such variability on the coefficient of thermal conductivity of wood, its overall influence on the thermal resistance of the CIT panel solutions was actually marginal due to the considerably lower thermal conductivity of PUR. As expected, the analytical model (conventional heat conduction) was able to predict the thermal resistance of the CIT panels, with good accuracy.

In this work, ground-borne vibrations due to pile driving impact are analyzed. A comparison between numerical results and experimental responses obtained in a low strain test measurement is presented. The experimental campaign is held at a construction site next to the Faculty of Engineering of the University of Porto (Portugal). The low strain test is carried out with 13 accelerometers equally distanced in a straight line and the ground vibrations are measured at the ground surface for several blows induced by an impact hammer. Soil properties and stratification are determined through non-intrusive geophysical tests - seismic refraction tests and SASW (Spectral Analysis of Surface Waves) tests. The numerical model is developed in time domain with the same characteristics of the construction site, considering a finite element axisymmetric formulation and an effective semi-explicit/explicit time marching procedure. The numerical results present good agreement with the in situ measured response, which indicates the effectiveness of the developed numerical model. In the sequence, a parametric study is developed and the results compared to previous numerical and experimental studies available in the literature.

This paper presents an experimental and numerical study about the flexural and compressive behaviour of a novel type of sandwich panel solution based on Cross-Laminated Timber (CLT). The layout of the new panel, named Cross-Insulated Timber (CIT), is similar to the one of a five-layer (CLT) panel, but the inner layer is made of polyurethane rigid foam instead of timber as in Structural Insulated Panels (SIP), aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. The study about the mechanical behaviour of CIT included the variation of the layers' thicknesses, in order to assess their influence in the mechanical behaviour and also the suitability of the numerical models to describe such behaviour. The experimental campaign included bending tests and axial compression tests in full-scale CIT beams (only one lamella at the external layers) and panels (multiple lamellas at the external layers) and SIP beams, which allowed assessing their global stiffness, resistance, buckling behaviour and failure modes. In bending, both CIT and SIP presented non-linear behaviour, due to the polymeric foam core, and their load capacity was governed by the shear failure of the core, which was the dominant failure mechanism. For the bending tests, the Timoshenko and Kreuzinger analytical models described quite well the deflection observed in the linear range, while for the non-linear branch of the load-displacement curves, the developed finite element model provided good accuracy. The Euler’s buckling load formula adapted for sandwich panels predicted quite well the buckling load measured in the compression tests. The results showed the potential of the CIT solution for structural applications and of the analytical and numerical models for design purposes.

The dynamic changes in a traditional layout of a short-span timber floor due to deterioration on supports were investigated experimentally and numerically. The floor was evaluated for its normal si...

This paper deals with the acoustic performance of timber and timber-concrete floor solutions assessed through an experimental campaign. In the case of the composite solutions, two types of concrete were adopted: a normal and a lightweight composition, the last one incorporating expanded cork aggregates. The acoustic tests were performed under controlled conditions in laboratory, to determine the airborne and impact sound insulations. The basic solutions were also evaluated including the presence of a ceiling composed of gypsum plasterboard and mineral wool. The results reveal a promising behavior of the tested solutions, particularly the composite solutions.

Vibrations induced by underground railway traffic have been receiving special attention from the technical and scientific communities, and different models for their prediction can be found in the literature. Since the tunnel can be seen as a longitudinally invariant structure, a 2.5D approach can be applied, minimizing the computational requirements without losing the 3D character of the problem. A global numerical strategy that allows simulating the vehicle–track–tunnel–soil interaction is proposed here. Tunnel–soil interaction is accounted by coupling the Finite Element Method and the Method of Fundamental Solutions. This model is then linked with a train–track interaction model, allowing to simulate the complete process of vibration propagation from the vehicle to the soil. The model is verified against reference solutions, and its application is illustrated for a practical engineering problem. The presented results indicate that the method can be quite accurate and competitive, when compared with other currently available models.

The growing of railway infrastructures in urban environments demands accurate methods to predict and mitigate potential annoyance of the inhabitants of the surrounding buildings. The present paper aims to contribute to the goal by proposing a numerical model to predict vibrations and reradiated noise due to railway traffic. The model is based on a substructuring approach, where the whole propagation media are considered, from the vibration source (the vehicle–track interaction) to the receiver (the building and its interior acoustic environment). The system track–ground–building is simulated by a 2.5D finite element method–perfectly matched layers (FEM–PML) model, formulated in the frequency-wavenumber domain. The reradiated noise assessment is based on a 2.5D FEM–method of fundamental solutions (MFS) model, where the FEM is used to obtain the structural dynamic response. The structural displacements computed are used as the vibration input for the MFS model in order to assess the acoustic response inside the building's compartments. An application example is presented to assess vibrations and reradiated noise levels inside the building due to railway traffic. This is then followed by a discussion about the potential benefits of the introduction of floating-slab-track systems.

Grooved acoustic panels are rigid plates consisting of an interconnected network of periodically arranged slits and circular holes. These devices are traditionally used as resonant absorbers in building acoustics. This paper presents a model to predict the acoustic properties of such absorbers. For this purpose, the classical Johnson-Champoux-Allard (JCA) model and the Transfer Matrix Method (TMM) are used together to describe the acoustic wave propagation through these systems. The proposed model was validated against Finite Element (FE) simulations in terms of sound absorption coefficient under normal incidence, for different configurations with good agreement. Additionally, a parametric study was found very useful to investigate the influence of the geometrical characteristics of the panel on the absorption performance of the absorber and in understanding its acoustic behaviour. As expected, the performance of the absorber varies with the size of the pores and thickness of the panel. The limits of the proposed approach are also discussed. The model is proven to be a useful tool to estimate the acoustic properties of grooved acoustic panel absorbers in a simple manner. This work is partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633.

In the last decades, the number of railway projects in urban environment has continuously increased. This rising requires a significant level of knowledge from the scientific and technical communities about the phenomena of generation and propagation of vibrations with emphasis on its interference in nearby buildings and the consequent nuisance of their occupants. In this context, a numerical model to predict vibrations and re-radiated noise in buildings induced by railway traffic is presented. The model is based in a sub-structuring approach, where the whole propagation media is considered, from the vibration source (vehicle-track interaction) to the receiver (building and interior acoustic media). The track-ground-building system is simulated by a 2.5D FEM-PML model, formulated in the frequency - wavenumber domain. The re-radiated noise evaluation is based on a 2.5D FEM-MFS model, where the FEM is used to obtain the structural response. The computed structural displacements are then used as vibration input to the Method of Fundamental Solutions (MFS) model in order to assess the acoustic response in the building’s enclosures. Finally, a parametric-study focused in the evaluation of the influence of a mitigation measure in the reduction of the vibrations and re-radiated noise levels is presented.

The impact noise reduction provided by floor coverings is usually obtained in laboratory, using the methodology described in the standard EN ISO 140-8, which requires the use of standard acoustic chambers. The construction of such chambers, following the requirements described in the EN ISO 140-1, implies a significant investment, and therefore only a limited number exists in each country. Alternatives to these standard methodologies, that allow a sufficiently accurate evaluation and require lower resources, have been interesting many researchers and manufacturers. In this paper, one such strategy is discussed, where a reduced sized slab is used to determine the noise reduction provided by floor coverings, following the procedure described in the ISO/CD 16251-1 technical document. Several resilient coverings, floating floors and floating slabs are tested and the results are compared with those obtained using the procedures described in the standards EN ISO 140-8 and EN ISO 717-2.

In this paper, the authors present a frequency domain coupled model making use of the Finite Element Method (FEM) and of the Method of Fundamental Solutions (MFS) in order to address soil-structure interaction problems. In this model, the MFS is used to account for the presence of an infinite soil surrounding an elastic structure, which is modeled using the FEM. Application examples concerning the vibration introduced in an infinite soil by a dynamic load acting within a tunnel are presented, in order to illustrate the usefulness and practical applicability of the method.

Most recent European acoustic design codes and regulations establish a maximum value for impact sound insulation on pavement slabs. These requirements demand the implementation of technical solutions such as floating floors, with the introduction of a resilient layer under the finishing pavement layer. Technical solutions such as floating concrete slabs (placed over synthetic foam or natural fibers layers), or floating pavements (like wooden floors built over synthetic foam layers) became quite common on recently built constructions. A possible alternative solution to floating pavements is the use of lightweight soft layers, applied over the structural concrete slab. These lightweight materials may present high quality results on the reduction of impact sound transmission. In the present work, lightweight mortar slabs were tested, and the impact sound insulation for different materials was quantified. Different types of cement mortar containing expanded polystyrene, expanded cork and expanded clay granulates were compared. The acoustical performance of these solutions was evaluated through laboratory tests, using an acoustic chamber with small dimensions, which allows comparing several solutions, on similar test conditions, in an expedite way. The influence of the type floor covering used over the lightweight mortar layer was also analysed. Different types of materials were tested.

The cost of rehabilitation works increases exponentially with time. Therefore, the development of on-site non-destructive tests (NDTs) for early detection of damage in concrete structures is an extremely important goal. However, in spite of the recent new technological developments, current assessment techniques are still based on visual inspections and are therefore only suitable for mapping major damages. An ultrasound-based procedure aiming to detect cracking at an early stage using propagation of ultrasonic waves is herein analysed. Two advanced numerical models were applied to simulate, first, the process of crack propagation and, next, the propagation of ultrasonic waves in a progressively damaged structure. Results are promising and enforce the feasibility of developing ultrasonic equipment for on-site application. Thus, future developments include an experimental validation of the present study.

The reinforcement of a timber floor with a concrete layer properly connected to produce a composite system represents not only an improvement in the stiffness but also a foreseeable change in the modal frequencies of the floor. In order to assess that change, a typical timber floor, which was subsequently reinforced with a concrete layer to produce a composite, was tested at both stages in the research reported in this paper. Additionally, composite beams taken from the original floor were also tested. The results showed a significant decrease (44%) in the fundamental frequency after the reinforcement. In order to obtain the mode shapes and frequencies of the floor, finite-element (FE) models of the floors and beams were created. The FE models accurately matched the experimental results. Having validated the model, a parametric study was carried out to compare the results provided by the proposed FE model with a numerical model from the bibliography and to understand the influence of the most rele...

In this paper, numerical frequency domain formulations are developed to simulate the 2D acoustic wave propagation in the vicinity of an underwater configuration which combines two sub-regions: the first one consists of a wedge with rigid seabed and free surface, and the second one is assumed to have a rigid flat bottom and a free flat surface. The problem is solved using two different numerical methods: the Boundary Element Method (BEM) and the Method of Fundamental Solutions (MFS). Two models are developed by using a sub-region technique, where only the vertical interface between sub-regions of different geometries has to be discretized. These formulations incorporate Green's functions that take into account the presence of flat rigid and free surfaces and of a wedge. Green's functions are defined using two approaches: the image source method is used to model the rigid flat bottom and free flat interface, whereas the response provided by the wedge sub-region is based on a normal mode solution. Additionally, a MFS and a BEM model are also implemented which require the discretization of the sloping rigid seabed of the wedge, therefore making use of Green's functions for a rigid flat bottom and a free surface (using the image source method). A detailed discussion on the performance of these formulations is performed, with the aim of finding an efficient formulation to solve the problem. It is found that the model based on the MFS and on the sub-region technique has a significantly lower computational cost and is stable, therefore being the most suitable for the analysis of acoustic wave propagation in the studied configurations.

This paper computes the sound pressure attenuation provided by thin rigid screens placed on the walls of a tall building to protect the building from the direct sound incidence produced by sound pressure sources placed in its vicinity. The problem is formulated in the frequency domain via the Traction Boundary Element Method (TBEM), which overcomes the thin-body difficulty arising with the classical Boundary Element Method (BEM) formulation. The building, the screens and the ground are assumed to be infinitely long and rigid. The Green's functions used in the TBEM formulation allow the solution to be obtained without discretizing the flat solid ground and vertical solid façade. Thus, only the boundary of each rigid screen is modelled, which allows the TBEM to be efficient even at high excitation frequencies. The hypersingular integrals that result from the implementation of the TBEM are computed analytically. The algorithm is verified using a BEM model, which incorporates the Green's functions for a full space, thus requiring the full discretization of the domain. The model developed is then used to simulate wave propagation in the vicinity of thin rigid screens with different dimensions and geometries. The two-dimensional (2D) and three-dimensional (3D) time and frequency responses and sound pressure attenuation results are both computed over grids of receivers placed perpendicular and parallel to the building wall. http://www.sciencedirect.com/science/article/B6WM3-4NMCV71-5/1/05fa9e0f203c93cbdb578430fe4544a8

Most of the analytical models devoted to determine the acoustic properties of a rigid perforated panel consider the acoustic impedance of a single hole and then use the porosity to determine the impedance for the whole panel. However, in the case of not homogeneous hole distribution or more complex configurations this approach is no longer valid. This work explores some of these limitations and proposes a finite element methodology that implements the linearized Navier Stokes equations in the frequency domain to analyse the acoustic performance under normal incidence of perforated panel absorbers. Some preliminary results for a homogenous perforated panel show that the sound absorption coefficient derived from the Maa analytical model does not match those from the simulations. These differences are mainly attributed to the finite geometry effect and to the spatial distribution of the perforations for the numerical case. In order to confirm these statements, the acoustic field in the vicinities of the perforations is analysed for a more complex configuration of perforated panel. Additionally, experimental studies are carried out in an impedance tube for the same configuration and then compared to previous methods. The proposed methodology is shown to be in better agreement with the laboratorial measurements than the analytical approach. (C) 2014 Elsevier Ltd. All rights reserved.

This paper focuses on the propagation of sound waves in the presence of acoustic barriers placed close to very tall buildings. The boundary element method (BEM) is used to model the acoustic barrier, while the presence of the tall buildings is taken into account by using the image source method. Different geometries are analyzed, representing the cases of a single building, two buildings forming a corner and three buildings defining a laterally confined space. The acoustic barrier is assumed to be non-absorbing, and all the buildings and the ground are modeled as infinite rigid plane surfaces. Calculations are performed in the frequency domain and time signals are then obtained by means of Inverse Fourier Transforms. The sound pressure loss provided by the acoustic barrier is computed, illustrating the importance of the lateral confinements. http://www.sciencedirect.com/science/article/B6V1S-458WC1V-2/1/e22100c682ff34b162d71d73339e5beb

Sonic crystals are a relatively recent concept that is being explored for different applications. Several types of models exist in literature for their analysis, although in many cases they consider their elements to be rigid. In this work, the authors propose a hybrid numerical-analytical model based on the Method of Fundamental Solutions (MFS) to address the problem of sound scattering by a sonic crystal composed of non-rigid scatterers. This model would account for the full interaction between the acoustic medium and an array of elastic shell structures, which are assumed to be circular and filled with fluid. For that purpose, each scatterer is accounted for by means of a closed form solution, and the full set of scatterers is then coupled by means of the MFS. This strategy allows a compact description of the propagation medium while being very accurate and efficient from the computational point of view. Application examples are presented considering structures embedded in different acoustic media (air or water), and using the sonic crystal either as a waveguide or as a sound barrier.

[EN] In the present paper, a methodology is proposed for obtaining empirical equations describing the sound absorption characteristics of an absorbing material obtained from natural fibers, specifically from coconut. The method, which was previously applied to other materials, requires performing measurements of airflow resistivity and of acoustic impedance for samples of the material under study. The equations that govern the acoustic behavior of the material are then derived by means of a least-squares fit of the acoustic impedance and of the propagation constant. These results can be useful since they allow the empirically obtained analytical equations to be easily incorporated in prediction and simulation models of acoustic systems for noise control that incorporate the studied materials., [ES] En este trabajo se describe el proceso seguido para obtener ecuaciones empíricas del comportamiento acústico de un material absorbente obtenido a partir de fibras naturales, concretamente el coco. El procedimiento, que ha sido ensayado con éxito en otros materiales, implica la realización de medidas de impedancia y resistencia al flujo de muestras del material bajo estudio. Las ecuaciones que gobiernan el comportamiento desde el punto de vista acústico del material se obtienen a partir del ajuste de ecuaciones de comportamiento de la impedancia acústica y la constante de propagación del material. Los resultados son útiles ya que, al disponer de ecuaciones analíticas obtenidas empíricamente, facilitan la incorporación de estos materiales en predicciones mediante métodos numéricos del comportamiento cuando son instalados formando parte de dispositivos para el control del ruido.

This work focuses on the way the pressure field generated by a dilatational load changes inside a channel waveguide filled with a homogeneous fluid, in the presence of an irregular floor. The problem is solved in the frequency domain using the boundary element method. The Green's functions used are obtained by superposing virtual acoustic sources defined so as to generate the free or rigid surfaces of the fluid channel. The responses in the time domain are obtained by means of Fourier transforms, using complex frequencies. Irregular floors of varying sizes are modeled. The main features and spectral representation of the signals scattered by these inclusions are described. They are used to elucidate the most important aspect of wave acoustics, which can be used as the basis for the development of nondestructive testing and imaging methods.

1 Structural Engineering Department, Federal University of Juiz de Fora, Juiz de Fora, MG 36036-330, Brazil 2 Institute of Modeling and Computation, Hamburg University of Technology, 21073 Hamburg, Germany 3 Department of Mechanics, Slovak Academy of Sciences, 845 03 Bratislava, Slovakia 4 CICC—Research Center in Construction Sciences, Department of Civil Engineering, University of Coimbra, 3030-788 Coimbra, Portugal

This paper describes the use of a boundary element formulation in the frequency domain to investigate the 2.5D acoustic wave propagation in an underwater configuration with a bottom irregularity, simulating the effect of a possible slippage between two flat parts of a waveguide. Each part is delimited by a free surface and a flat bottom, which may be built as multilayered fluid structure. The problem is solved using a model which incorporates Green's functions that take into account the presence of flat layers of different thicknesses, computed using the definition of pressure potentials at each flat interface. With this procedure only the bottom irregularity and the slippage interface need to be discretized. The mathematical formulation is presented for the general case in which two multilayered structures are connected via an interface, and then verified and applied to the computation of 3D frequency and time domain pressure responses for the benchmark problem of a rigid bottom with step or slope irregularities. These simulations are used to identify wave propagation features that may help to assess the presence and shape of the bottom irregularities.

In this work, the authors use analytical solutions to assess the airborne sound and impact insulation provided by homogeneous partitions that are infinite along their plane. The algorithm uses Green’s functions, derived on the basis of previous work by the authors on the prediction of airborne sound insulation provided by single and double panels. The model is now extended to handle multilayer systems, allowing the simulation of three-dimensional loads applied in both the acoustic and solid media. The model is validated against experimental results and compared with simplified expressions for single, double and triple panels. The results provided by the analytical model were found to provide a good agreement with the experimental results, except in the vicinity of the coincidence effect in the presence of thicker panels. The applicability of the proposed tool is then illustrated by analyzing the acoustic behavior provided by single layers and by a suspended ceiling. Different variables are studied, such as the mass, the stiffness of the layers, the position and direction of the load within the elastic medium and the presence of porous material in the fluid layers. It was found that the model is able to simulate the acoustic phenomena involved in single and multilayer systems. � 2006 Elsevier Ltd. All rights reserved.

The transmission of sound energy is a complex phenomenon on account of the number and the interdependence of variables involved. In this context the mathematical modelling of this phenomenon becomes difficult. Of the models that have been developed, some of them only take a limited number of variables into account, leading to simplified models such as the Mass Law. Among the simplified methods for evaluating the sound insulation provided by a single panel are those described by Sewell [1], Sharp [2], Cremer [3] and Callister et al. [4]. Novikov [5] used the mass law with the addition of a correction coefficient to study the sound insulation of finite plates, at low frequencies. Osipov et al. [6] studied the sound transmission through a single panel using an infinite plate model and a room–plate–room model. They noticed that at low frequencies the results are strongly influenced by the geometry and the dimensions of the room–wall–room system, in addition to the properties of the panel material. Most of the articles published that take the full coupling between the fluid and the solid structure into account are restricted to low frequencies, because of the computational cost entailed, particularly when modelling closed spaces. This kind of analysis is simpler in the case of circular enclosures, for which analytical solutions can be derived. Other authors in a different context have tackled the study of circular cylindrical shells. Veksler et al. [7] studied the modal resonances of submerged elastic circular cylindrical shells filled with air, when struck by plane harmonic acoustic waves. Their work used a standard resonance scattering theory, and paid special attention to the generation of bending waves. Bao et al. [8] analyzed the various circumferential waves generated when a circular cylindrical shell submerged in a fluid and filled with another fluid is disturbed by a normally incident plane wave. Maze et al. [9], in a related work, analyzed the existence of various guided acoustic circumferential modes in a water-filled tube. ARTICLE IN PRESS

The acoustic insulation provided by infinite double panel walls, when subjected to spatially sinusoidal line pressure loads, is computed analytically. The methodology used extends earlier work by the authors on the definition of the acoustic insulation conferred by a single panel wall. It does not entail any simplification other than the assumption that the panels are of infinite extent. The full interaction between the fluid (air) and the solid layers is thus taken into account and the calculation does not involve limiting the thickness of any layer, as the Kirchhoff or Mindlin theories require. The problem is first formulated in the frequency domain. Time domain solutions are then obtained by means of inverse Fourier transforms using complex frequencies. The model is first used to compute the sound reduction provided by a double homogeneous brick wall, with identical panels, when illuminated by plane sound waves. The results are then compared with those provided by the simplified method proposed by London, which was later extended by Beranek (London–Beranek method). The limitations of the simplified London–Beranek model, namely, its applicability only to double walls with identical mass, subjected to plane waves, and its failure to account for the coincidence effect, are overcome by the method proposed. Time signatures are produced to illustrate the different sound transmission mechanisms. Several types of body and guided waves are originated, giving rise to a complex dynamic system with multiple reflections within the solid and fluid layers and the global resonance of the system. The effect of the cavity absorption is considered by attributing a complex density to the air filling the space between the two wall panels. Absorption attenuates the dips of insulation controlled by the cavity resonances. Several simulations are then performed for different combinations of wall and air layer thickness to assess the influence of this variable on the final acoustic insulation. The influence of the air cavity on sound reduction was found to be dependent on the frequency. At low frequencies a better performance was achieved for thicker air layers, while at higher frequencies a thinner air layer is preferable. The use of wall panels with different mass resulted in the wall performing better, particularly for high frequencies.

The acoustic scattering of a three-dimensional (3D) sound source by an infinitely long rigid barrier in the vicinity of a tall building is analyzed using the boundary element method (BEM). The acoustic barrier is modeled using boundary elements, and is assumed to be nonabsorbing, while the image source method is used to model the tall building as an infinite vertical barrier. A frequency domain BEM formulation is used, and time domain responses are then obtained by applying an inverse Fourier transformation. Since the geometry of the problem does not vary along one direction, the 3D solution can be calculated as the summation of a sequence of 2D problems, each solved for a different spatial wavenumber, kz: To obtain the 3D solution, a discrete form wavenumber transform is performed by considering an infinite number of virtual point sources equally spaced along the z axis. Complex frequencies are used to minimize the influence of these neighboring fictitious sources. Numerical simulations are performed using barriers of varying sizes, evaluating the attenuation of the sound pressure level in the vicinity

The boundary element method (BEM) is used to fully simulate the propagation of waves between two fluid-filled boreholes. The sources are placed in one of the boreholes while the receivers are placed in the other. This model is frequently used in cross-hole seismic prospecting techniques to assess the characteristics of the elastic medium between the two boreholes. This work studies the dependence of the wave propagation patterns on the distance between the source and the receiver, their location and orientation relative to the axis of a circular borehole and type of elastic formation (fast and slow formations). In addition, this BEM model is used to compute the influence of the deformed boreholes whose cross-section is not circular. Both the spectra responses and the time-domain responses are computed to elucidate the main physical features of the problem solved. http://www.sciencedirect.com/science/article/B6V2N-44VDYFD-1/1/694be0b9fc1ef415b7449ec2defd9d08

The BEM is used to calculate the variation in the pressure field generated by a dilatational point load inside a channel filled with a homogeneous fluid, in the presence of an irregular floor. The Green's functions are defined in the frequency domain and obtained by superposing virtual acoustic sources combined so as to generate the boundary conditions of the free or rigid surfaces of the channel. The responses in the time domain are obtained by means of Fourier transforms, making use of complex frequencies. The main features and spectral representation of the signals scattered by irregular floors are then described and used to elucidate the most important aspect of wave acoustics, which can provide the basis for the development of non-destructive testing and imaging methods. http://www.sciencedirect.com/science/article/B6V2N-435KHF7-5/1/b30ece947f68667901f14d7ad8005aac

This paper presents a set of analytical solutions (Green functions) for the steady state response of a homogenous acoustic three-dimensional space subjected to a point harmonic load or a spatially sinusoidal harmonic line load. The propagation medium is modelled with plane surfaces placed so as to reproduce spaces that vary from a simple half-space to a rectangular parallelepiped closed space. The final expressions are implemented to evaluate first the pressure field inside a rectangular parallelepiped room, whose walls allow different absorption coefficients. Then, the acoustic scattering of a three-dimensional sound source by an infinitely long rigid barrier in the vicinity of a tall building is evaluated using the boundary-element method (BEM), making use of the analytical solution for a spatially sinusoidal line source. The use of these Green functions allows the required BEM discretization to be limited to the surface of the barrier, avoiding the discretization of the tall building and ground. The calculations are performed in the frequency domain and time signatures are obtained by means of inverse Fourier transforms. Complex frequencies are used to attenuate the response at the end of the time frame, which is taken into account by rescaling the time response. http://www.sciencedirect.com/science/article/B6WM3-457CSW7-4M/1/1de64d56f8cb502849f24b9c9943633d