An energy flow study of a double-deck tunnel under quasi-static and harmonic excitations

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This paper presents a comparison between the vibration energy flow radiated by a double-deck tunnel and the one radiated by a simple tunnel when both are excited by constant or by harmonic moving loads. For both cases, the radiated energy is computed using a three-dimensional semi-analytical model of the system. The total energy radiated upwards is presented for a wide range of load speeds, when a constant moving load is considered, and for a wide range of excitation frequencies, when the excitation is a harmonic moving load. Significant differences have been obtained, first, for constant loads moving at very high speeds and, second, for harmonic loads moving at typical speeds for underground trains.Peer ReviewedPostprint (author's final draft

Annual traffic noise levels estimation based on temporal stratification

© 2017. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This paper proposes a temporal sampling strategy that increases the accuracy of long-term noise level estimation and allows to establish the estimation error according to the number of sampled days. Days of the week are stratified into working days and weekend days. This research shows how to use measurements of Leq on working days to estimate the corresponding values for weekend days. This is possible because working days have higher noise levels and less variability than weekend days. The improvement in accuracy allows for a reduction in the number of required sampled days compared to taking samples randomly, which would help to reduce the uncertainty in environmental noise assessment. As a reference, to obtain a 90% confidence interval of ±1 dB for Lday, the proposed sampling strategy reduces the required measurement days by more than 38%. For LDEN, the reduction is close to 18% of the total number of days. The proposed strategy could be adapted to different environments by simply changing a few parameters.Peer ReviewedPostprint (author's final draft

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

Temporal and spatial stratification for the estimation of nocturnal long-term noise levels

Noise pollution in cities is mainly caused by the vehicular traffic but, depending on the place under assessment, it could be affected by the land use. For noise assessment and strategic noise mapping, the night period equivalent level (), which evaluates sleep disturbance, is one of the requirements of the European Directive 2002/49/EC to be presented for the equivalent time of one year. This research aims to find the influence of the land use in the weekdays stratification to improve the accuracy of the long-term noise level estimation for the night period. It is found that depending on the land use of the place under assessment, the weekdays temporal and spatial stratification could be affected by leisure activities. From a statistical analysis based on a clustering procedure of samples in 19 points, it is observed that both, temporal and spatial stratification depend on the intensity of the surrounding leisure activity, and not on traffic. Following these stratification criteria, a sampling method is presented that reduces by 47% the number of days needed to estimate the annual levels with respect to random samplingPostprint (author's final draft

Stick-slip phenomena and acoustic emission in the Hertzian linear contact

AE detection and analysis usually requires a specific, costly platform due to its particular burst nature and high-frequency content. This experimental study investigates the relationship between low-demand acoustic emission parameters (AE) and the occurrence of stick–slip (SS) at the Hertzian linear contact. Hence, the correlation of basic AE characteristics (amplitude, energy, and evolution in time) with stick–slip characteristics (static and kinetic friction coefficients, amplitude, energy, and evolution in time) is pursued. Tribological tests were conducted on cylinder–plane specimens under dry friction conditions with different loads at different low driving speeds and Hertzian contact pressures at a constant stiffness. The AE, normal, and friction forces were recorded simultaneously on the experimental stand. At the cylinder–plane interface, the jumps specific to the stick–slip phenomenon (friction coefficient—COF) were followed after a few milliseconds by AE jump peaks. The results of the experiments show that the amplitude and energy generated by AE were sensitive to the occurrence of the stick–slip phenomenon, while the AE and COF energies in the stick and slip phases had the same law of variation based on the driving velocities. The results show that the amplitude and energy of the sampled low-frequency AE signals were enough to detect the friction in SS and demonstrate the potential of AE as a tool for detecting and monitoring the tribological behaviour of SS at the linear Hertzian contact.Peer ReviewedPostprint (published version

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

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

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

Acoustic emission at the wheel-rail contact with micro-slip and stick-slip

The paper aimsto analyse the occurrence of acoustic emission at the wheel-rail contact during microslip. The experimental model allows the different loads and the low sliding speeds specific to the wheel-rail contact. It is determined experimentally the appearance of the stick-slip phenomenon at the Hertzian contact of cylinder type (fixed-wheel specimen) - plane (mobile with very low speed - rail specimen). The experimental stand simultaneously measures the normal force, the friction force and the acoustic emission at different normal forces, sliding speeds and rigidities of the wheel specimen fixing system. The specimens are made of UIC standard materials used in the driving wheels and rails. The stick-slip phenomenon occurs at low micro-slip speeds and normal bending stiffness. Experimentally, it is found that the jumps specific to the stick-slip phenomenon (friction coefficientCOF) are accompanied by the acoustic emission (AE) at the cylinder-plane interface. The energy emitted by AE (WAE) is correlated with the energy consumed by friction during the stick-slip period (WCOF).Postprint (published version

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