Dynamic response of a double-deck circular tunnel embedded in a full-space

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A three-dimensional dynamic model for calculating the ground-borne vibrations generated by harmonic loads applied on the interior floor of a double-deck circular tunnel is developed. The response of the system is obtained coupling the interior floor subsystem and the tunnel-soil subsystem in the wavenumber-frequency domain. The interior floor is modeled as a thin plate of infinite length in the train circulation direction and the tunnel-soil system is described using the Pipe in Pipe model. Some numerical instabilities of the resulting expressions are overcome by using analytic approximations. The results show that the dynamic behavior of the interior floor clearly influences the magnitude of the coupling loads acting on the tunnel structure. The soil response to a harmonic load acting on the double-deck tunnel is compared to the one obtained for the case of a simple tunnel finding significant differences between them for the whole range of frequencies studied. The proposed model extends the prediction of train-induced vibrations using computationally efficient models to this type of tunnel structure.Peer ReviewedPostprint (author's final draft

Using genetic algorithms to optimize the location of transducers for an active noise barrier

The effectiveness of an active noise barrier is heavily dependent on the positioning of secondary sources and error sensors. Typically, these components are located at the edge of the barrier; however, research suggests that alternative distributions may improve the performance of the active barrier. This paper utilizes a genetic optimizer to determine optimal transducer locations based on specific criteria. Two approaches are employed: the Two-step approach which, first identifies optimal control source positions and then seeks the best error microphone locations, and the Multi-parameter approach, which optimizes all active noise control parameters simultaneously. The acoustic fields of primary and secondary sources are analyzed for various numbers of control sources progressively increasing from 2 to 10 units. Results indicate that the Multi-parameter approach achieves higher outcomes and requires less computational effort. This approach is more desirable than the Two-step approach. The best configuration for the active noise barrier is determined to be control sources and error microphones placed at a height below the barrier’s edge and are distributed with an interval between a half and a full wavelength. The number of error sensors should be close to the number of secondary sources and both transducers should be placed at the farthest distance from the barrier surface, but oppositely. Furthermore, the study shows that when the primary noise source is close to the barrier adjacent transducers should not be spaced uniformlyThe author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Agència de Gestió d’Ajuts Universitaris i de Recerca (2020 FI_B2 00073)Postprint (published version

Evaluation of the effectiveness of control sources’ interval on active noise control performance

Amongst many important factors that affect the performance of active noise barrier, namely, the location of error microphones, and secondary sources, the intervals of adjacent error microphones and secondary sources, etc. this study focused on investigate the effect of secondary sources’ interval when they minimized the squared pressure at a set of 15 receivers located in the shadow zone of an infinite barrier. Three different positions around the top edge of barrier considered for secondary sources and best position which achieve the most reduction is selected. Also, the effect of ground reflections on the optimal secondary sources’ interval is investigated.Peer ReviewedPostprint (published version

Proper location of the transducers for an active noise barrier

The main intention of this study is to propose general criteria for the locations of the control sources and error microphones that improve the performance of the active noise barrier. Based on the proposed criteria of this study, the greater reduction is attained when the diffracted field of the noise source is canceled with the diffracted field of the control sources, that is, it is suggested to locate the control sources on the incident side and below the path that connects the furthest point in the shadow zone to the edge of the barrier. Furthermore, it is suggested that the error microphones are most suitably placed on the shadow side of the barrier where they are under the diffracted field of both the primary and control sources. The results also show that with these general criteria, the active noise control achieves an extra reduction that varies from 14.9 to 3.9 dB (for the third-octave band from 63 Hz to 1 kHz) and 9.3 dB for the broadband noisesPostprint (author's final draft

Low-cost device for fault diagnosis in bearings based on the Hilbert-Huang transform

In order to monitor the condition of machinery complex industrial environments, high-cost equipment is required for signal acquisition and processing. However, low-cost sensor nodes with high processing capability are a potential solution to improve diagnostic systems. This paper presents a low-cost device for fault diagnosis based on the vibration response in rotating machines with the implementation of the Hilbert-Huang transform (HHT) analysis to extract the main characteristics of the signal. HHT, used to analyze non-linear and non-stationary signals, incorporates an Empirical Mode Decomposition (EMD) process. Processing is carried out in an embedded system to acquire vibration response data and extract signal characteristics that allow condition monitoring. As a result of local processing in the vibratory measurement device in an embedded system, the signal decomposition is performed, enabling the detection of the characteristic failure in the bearing ring and transmitting the alarm to a hub. This eliminates the need for a central diagnostic system and reduces the total cost of the system.This work has been carried out within the framework of the Looming Factory project, reference 001-P-001643, of the RIS3CAT program of the Generalitat de Catalunya. This research has been made possible thanks to the support of the MCIA Electronic Drives and Industrial Applications Research Group of the Universitat Politècnica de Catalunya and its collaborators.Peer ReviewedPostprint (published version

Agglomeration noise strategic maps in Catalonia

The Directive 2002/49 on evaluation and management of the environmental noise demands in case of agglomerations, a series of information that one must communicate to the Commission, between which there is the number of people whose housings are exposed to every range of values of Lden and Lnight in dBA. In this work they present the criteria contemplated in the delimiting of the agglomerations inside Catalonia's territory, as well as the methodologies used in the estimation of the audible levels and the population exposed to the different indicators of noise with the results obtained.Peer ReviewedPostprint (published version

2.5D singular boundary method for exterior acoustic radiation and scattering problems

In this paper, a numerical methodology based on a two-and-a-half-dimensional (2.5D) singular boundary method (SBM) to deal with acoustic radiation and scattering problems in the context of longitudinally invariant structures is proposed and studied. In the proposed 2.5D SBM, the desingularisation provided by the subtracting and adding-back technique is used to determine the origin intensity factors (OIFs). These OIFs are derived by means of the OIFs of the Laplace equation. The feasibility, validity and accuracy of the proposed method are demonstrated for three acoustic benchmark problems, in which detailed comparisons with analytical solutions, the 2.5D boundary element method (BEM) and the 2.5D method of fundamental solutions (MFS) are performed. As a novelty of the present study, it is found that the 2.5D SBM provides a higher numerical accuracy than the 2.5D linear-element BEM and lower than the 2.5D quadratic-element BEM. Although the results obtained depict that a nodal approximation of the boundary geometry leads to a significant reduction in the accuracy of the 2.5D SBM, the delivered errors are still acceptable. For complex geometries, the 2.5D SBM is found to be simpler and more robust than the 2.5D MFS, since no optimization procedure is required.Peer ReviewedPostprint (published version

Modelo de control activo de transmisión de ruido a través de una apertura en pared delgada

La reducción activa de ruido transmitido a través de una apertura se investiga mediante un modelo teórico. El campo primario se compone de una onda plana que incide sobre una apertura rectangular situada en una pared infinita de grosor despreciable. El sonido radiado por la apertura se calcula a partir de la ecuación de radiación de Rayleigh una vez se han aplicado las condiciones de continuidad de presión y velocidad de partícula en la apertura. El modelo propuesto se compara con un modelo BEM del mismo problema con objeto de su validación. Una vez validado, la aplicación del control activo se realiza mediante la inclusión de una fuente secundaria cercana a la apertura que por superposición de campos acústicos minimiza el sonido transmitido en la región de radiación. Se presentan resultados de atenuación respecto a la frecuencia y dimensión de la apertura.Peer ReviewedPostprint (published version

Numerical study of the aerodynamics of sound sources in a bass-reflex port

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The aim of this paper is to study the aerodynamics phenomena of a bass-reflex port that causes noise in the audible frequency range. After discarding structural and mechanical vibration issues, the hypothesis considered is that vortex shedding is the source of the noise. Experimental and numerical evidences of the vortex, an analysis of its noise and the similarities between real and simulated performance are presented. The numerically simulated cases with the original geometry are excited at different frequencies and with modifications of the port geometry. Likewise, the internal performance of an enclosure with a closed port was simulated. The simulations have been performed with axisymmetrical geometries using the open-source OpenFOAM® toolbox. Moreover, experimental measurements were carried out. First, acoustic signal experiments were done to analyse the response of the bass-reflex ports. Secondly, a structure vibration measurement was conducted in order to exclude the cabinet structure vibration as a source of the noise in question. A good agreement was found between numerical and experimental results, especially in the frequency band of the detected noise, i.e. the 1000–1500 Hz range. Despite no remarkable improvement being made with the geometry changes explored, the presented CFD approach has proved a useful and cost-effective tool to address this kind of phenomenon.Peer ReviewedPostprint (published version

Experimental and numerical assessment of local resonance phenomena in 3D-printed acoustic metamaterials

The so called Locally Resonant Acoustic Metamaterials (LRAM) are a new kind of artificially engineered materials capable of attenuating acoustic waves. As the name suggests, this phenomenon occurs in the vicinity of internal frequencies of the material structure, and can give rise to acoustic bandgaps. One possible way to achieve this is by considering periodic arrangements of a certain topology (unit cell), smaller in size than the characteristic wavelength. In this context, a computational model based on a homogenization framework has been developed from which one can obtain the aforementioned resonance frequencies for a given LRAM unit cell design in the sub-wavelength regime, which is suitable for low-frequency applications. Aiming at validating both the proposed numerical model and the local resonance phenomena responsible for the attenuation capabilities of such materials, a 3D-printed prototype consisting of a plate with a well selected LRAM unit cell design has been built and its acoustic response to normal incident waves in the range between 500 and 2000 Hz has been tested in an impedance tube. The results demonstrate the attenuating capabilities of the proposed design in the targeted frequency range for normal incident sound pressure waves and also establish the proposed formulation as the fundamental base for the computational design of 3D-printed LRAM-based structures.Peer ReviewedPostprint (author's final draft