http://hdl.handle.net/2117/3363 Thu, 23 May 2013 03:06:22 GMT 2013-05-23T03:06:22Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/18640 Title: Micro-mechanical damage in tool steels analyzed by acoustic emission technique Authors: Picas Anfruns, Ingrid; Martínez González, Eva; Casellas, Daniel; Romeu Garbí, Jordi Abstract: The carbides in tool steels act as hard particles and dictate the wear resistance. The origin of failure of these steels is mostly related with the carbide cracking, as a nucleation site of final cracks. This paper shows the acoustic emission (AE) signals related with the nucleation (carbide cracking) and the crack growth (in the metallic matrix) during a monotonic bending test of a tool steel obtained by ingot metallurgy routes (DIN 1.2379). The paper presents a relationship between the frequency spectrum of AE signals obtained and the microscopic images during the test. Fri, 05 Apr 2013 11:01:05 GMT http://hdl.handle.net/2117/18640 2013-04-05T11:01:05Z Picas Anfruns, Ingrid; Martínez González, Eva; Casellas, Daniel; Romeu Garbí, Jordi no The carbides in tool steels act as hard particles and dictate the wear resistance. The origin of failure of these steels is mostly related with the carbide cracking, as a nucleation site of final cracks. This paper shows the acoustic emission (AE) signals related with the nucleation (carbide cracking) and the crack growth (in the metallic matrix) during a monotonic bending test of a tool steel obtained by ingot metallurgy routes (DIN 1.2379). The paper presents a relationship between the frequency spectrum of AE signals obtained and the microscopic images during the test. http://hdl.handle.net/2117/18181 Title: New siren tones optimised for increased detectability distances of emergency vehicles Authors: Balastegui Manso, Andreu; Romeu Garbí, Jordi; Clot Razquin, Arnau; Martín Román, Sara-Regina Abstract: Sirens from emergency vehicles are particularly annoying for people living in the vicinities of emergency centres. In order to reduce their discomfort, the present work computes the optimal output power and frequency content of the sirens by taking into account the car noise reduction, the background noise inside the car and the hearing threshold. The combination of these parameters gives rise to frequency windows where the sirens are more effective, hence new siren tones are proposed and their annoyance is assessed through a jury test procedure. The new tones can either increase the detectability distance by 40% without increasing their annoyance or reduce their sound pressure level by 3 dB while keeping their effectiveness in being detected. Mon, 11 Mar 2013 16:09:47 GMT http://hdl.handle.net/2117/18181 2013-03-11T16:09:47Z Balastegui Manso, Andreu; Romeu Garbí, Jordi; Clot Razquin, Arnau; Martín Román, Sara-Regina no Sirens from emergency vehicles are particularly annoying for people living in the vicinities of emergency centres. In order to reduce their discomfort, the present work computes the optimal output power and frequency content of the sirens by taking into account the car noise reduction, the background noise inside the car and the hearing threshold. The combination of these parameters gives rise to frequency windows where the sirens are more effective, hence new siren tones are proposed and their annoyance is assessed through a jury test procedure. The new tones can either increase the detectability distance by 40% without increasing their annoyance or reduce their sound pressure level by 3 dB while keeping their effectiveness in being detected. http://hdl.handle.net/2117/17598 Title: Some analytical aspects of viscoelastic Lamb’s problem for improving its numerical evaluation Authors: Arcos Villamarín, Robert; Romeu Garbí, Jordi; Clot Razquin, Arnau; Genesca Francitorra, Meritxell Abstract: Two analytical modifications of the original viscoelastic time-harmonic Lamb’s problem expressions are presented with the aim of improving their numerical integration efficiency. Firstly, a new change of variable in the Lamb’s problem integrands is proposed, which allows a standardization of the integration sampling vector and a complete spatialfrequency field solution after performing only one numerical integration/transformation. Secondly, the Lamb’s problem static integrands are modified and introduced into the original integrands to reduce their spectral content at high wavenumbers and, therefore, the sampling vector lengths needed to avoid aliasing. Thu, 07 Feb 2013 16:13:13 GMT http://hdl.handle.net/2117/17598 2013-02-07T16:13:13Z Arcos Villamarín, Robert; Romeu Garbí, Jordi; Clot Razquin, Arnau; Genesca Francitorra, Meritxell no Two analytical modifications of the original viscoelastic time-harmonic Lamb’s problem expressions are presented with the aim of improving their numerical integration efficiency. Firstly, a new change of variable in the Lamb’s problem integrands is proposed, which allows a standardization of the integration sampling vector and a complete spatialfrequency field solution after performing only one numerical integration/transformation. Secondly, the Lamb’s problem static integrands are modified and introduced into the original integrands to reduce their spectral content at high wavenumbers and, therefore, the sampling vector lengths needed to avoid aliasing. http://hdl.handle.net/2117/17597 Title: On the use of a linear microphone array to measure wind turbine aerodynamic noise Authors: Genesca Francitorra, Meritxell; Romeu Garbí, Jordi; Pàmies Gómez, Teresa; Solé, Jaume Abstract: A linear microphone array is shown to be a simple tool to locate aerodynamic sound sources on a horizontal axis wind turbine. This paper discusses the capabilities and limitations of a linear microphone array to locate sound sources and measure aerodynamic noise on the blades of a horizontal axis wind turbine rotor. Compared with a planar microphone array, a linear array requires fewer microphones to achieve the same resolution, a simpler structure to support it and a simpler signal processing algorithm. For a linear array, areas exist in the rotor plane where the sources cannot be located unambiguously. For certain applications, it is not necessary to map the whole rotor plane. This paper also shows the result of an experimental test aimed at locating and measuring aerodynamic sound sources on the three blades of a wind turbine. Each blade received a different surface treatment, with the goal of comparing their relative sound emission levels. The test was carried out with a 10.32 m linear microphone array, placed horizontally near the ground, extending parallel to the rotor plane. The results show that for all three blades, most of the noise is generated in the outer 25% of the blade span, with a maximum occurring just after the blade has passed the horizontal position going downwards. Results also show that tripped blade is the noisiest of the three, whereas the smoothest, polished blade is clearly the quietest. Copyright © 2012 John Wiley & Sons, Ltd. Thu, 07 Feb 2013 15:53:52 GMT http://hdl.handle.net/2117/17597 2013-02-07T15:53:52Z Genesca Francitorra, Meritxell; Romeu Garbí, Jordi; Pàmies Gómez, Teresa; Solé, Jaume no A linear microphone array is shown to be a simple tool to locate aerodynamic sound sources on a horizontal axis wind turbine. This paper discusses the capabilities and limitations of a linear microphone array to locate sound sources and measure aerodynamic noise on the blades of a horizontal axis wind turbine rotor. Compared with a planar microphone array, a linear array requires fewer microphones to achieve the same resolution, a simpler structure to support it and a simpler signal processing algorithm. For a linear array, areas exist in the rotor plane where the sources cannot be located unambiguously. For certain applications, it is not necessary to map the whole rotor plane. This paper also shows the result of an experimental test aimed at locating and measuring aerodynamic sound sources on the three blades of a wind turbine. Each blade received a different surface treatment, with the goal of comparing their relative sound emission levels. The test was carried out with a 10.32 m linear microphone array, placed horizontally near the ground, extending parallel to the rotor plane. The results show that for all three blades, most of the noise is generated in the outer 25% of the blade span, with a maximum occurring just after the blade has passed the horizontal position going downwards. Results also show that tripped blade is the noisiest of the three, whereas the smoothest, polished blade is clearly the quietest. Copyright © 2012 John Wiley & Sons, Ltd. http://hdl.handle.net/2117/14718 Title: Acelerómetros y sensores de vibración Authors: Romeu Garbí, Jordi; Genesca Francitorra, Meritxell Fri, 20 Jan 2012 16:40:00 GMT http://hdl.handle.net/2117/14718 2012-01-20T16:40:00Z Romeu Garbí, Jordi; Genesca Francitorra, Meritxell no http://hdl.handle.net/2117/14357 Title: Estimating the rate and luminosity function of all classes of GRBs Authors: Balastegui Manso, Andreu; Canal, Ramon; Ruiz-Lapuente, Pilar Abstract: The aim of the present work is to estimate the rate and luminosity functions of short, intermediate and long gamma-ray bursts (GRBs) by fitting their intensity distributions wih parameterized explosion rates and luminosity functions. The results show that the parameters of the rate and luminosity function for long GRBs can be calculated with an accuracy of 10-30%. However, some parameters of intermediate and short GRBs have large uncertainties. An important conclusion is that there was initially a large outburst in the frequency of long GRBs, and consequently a large outburst in the star-formation rate, if they come from collapsars. Finally, a simulated intensity distribution has been constructed to test the ability of the method to recover the simulated parameters. Thu, 29 Dec 2011 14:50:10 GMT http://hdl.handle.net/2117/14357 2011-12-29T14:50:10Z Balastegui Manso, Andreu; Canal, Ramon; Ruiz-Lapuente, Pilar no The aim of the present work is to estimate the rate and luminosity functions of short, intermediate and long gamma-ray bursts (GRBs) by fitting their intensity distributions wih parameterized explosion rates and luminosity functions. The results show that the parameters of the rate and luminosity function for long GRBs can be calculated with an accuracy of 10-30%. However, some parameters of intermediate and short GRBs have large uncertainties. An important conclusion is that there was initially a large outburst in the frequency of long GRBs, and consequently a large outburst in the star-formation rate, if they come from collapsars. Finally, a simulated intensity distribution has been constructed to test the ability of the method to recover the simulated parameters. http://hdl.handle.net/2117/12017 Title: Analysis of fracture resistance of tool steels by means of acoustic emission Authors: Martínez González, Eva; Picas Anfruns, Ingrid; Casellas Padró, Daniel; Romeu Garbí, Jordi Abstract: The automotive manufacturers currently use advanced high-strength steels (AHSS) to produce lightweight vehicles with increased safety performance. While showing excellent strengthto-weight ratios, AHSS have several limitations due to the high loads required in cold forming and cutting processes, which lead to accelerated wear and premature fracture of tools. Thus, new tool materials with improved mechanical behavior ought to be developed with regard to the tool failure mechanisms. The aim of this work is to shed light on the fracture mechanisms acting in tools (i.e. crack nucleation and propagation) applying the acoustic emission (AE) technique. Bending tests using two different tool steels were monitored in order to establish a relationship between AE signals and fracture events. Tue, 22 Mar 2011 13:06:33 GMT http://hdl.handle.net/2117/12017 2011-03-22T13:06:33Z Martínez González, Eva; Picas Anfruns, Ingrid; Casellas Padró, Daniel; Romeu Garbí, Jordi no The automotive manufacturers currently use advanced high-strength steels (AHSS) to produce lightweight vehicles with increased safety performance. While showing excellent strengthto-weight ratios, AHSS have several limitations due to the high loads required in cold forming and cutting processes, which lead to accelerated wear and premature fracture of tools. Thus, new tool materials with improved mechanical behavior ought to be developed with regard to the tool failure mechanisms. The aim of this work is to shed light on the fracture mechanisms acting in tools (i.e. crack nucleation and propagation) applying the acoustic emission (AE) technique. Bending tests using two different tool steels were monitored in order to establish a relationship between AE signals and fracture events. http://hdl.handle.net/2117/10176 Title: Two step optimization of transducer locations in single input single output tonal global active noise control in enclosures Authors: Palacios Higueras, José Ignacio; Romeu Garbí, Jordi; Balastegui Manso, Andreu Abstract: Global active control of sound can be achieved inside enclosures under low modal acoustic fields. However, the performance of the system depends largely on the localization of the elements of the control system. For a purely acoustic active control system in which secondary acoustic sources (loudspeakers) and pressure transducers (microphones) as error sensors are used, several optimization strategies have been proposed. These strategies usually rely on partial approximation to the problem, focusing on the study of number and localization of secondary sources without considering error transducers, or selecting the best positions of secondary sources and error transducers of an initial set of candidate locations for these elements. The strategy presented here for tonal global active noise control of steady states comprises two steps; the first is rather common for this sort of problem and its goal is to find the best locations for secondary sources and their strengths by minimizing the potential energy of the enclosure. The second step is the localization of the error transducer, which ensures the results of the first step. It is analytically demonstrated that for a single input single output system, the optimum location of error transducers is at a null pressure point of the optimally attenuated acoustic field. It is also shown that in a real case, the optimum position is that of a minimum of the optimally attenuated acoustic field. Finally, a numerical validation of this principle is carried out in a parallelipedic enclosure. Mon, 08 Nov 2010 14:25:47 GMT http://hdl.handle.net/2117/10176 2010-11-08T14:25:47Z Palacios Higueras, José Ignacio; Romeu Garbí, Jordi; Balastegui Manso, Andreu no Global active control of sound can be achieved inside enclosures under low modal acoustic fields. However, the performance of the system depends largely on the localization of the elements of the control system. For a purely acoustic active control system in which secondary acoustic sources (loudspeakers) and pressure transducers (microphones) as error sensors are used, several optimization strategies have been proposed. These strategies usually rely on partial approximation to the problem, focusing on the study of number and localization of secondary sources without considering error transducers, or selecting the best positions of secondary sources and error transducers of an initial set of candidate locations for these elements. The strategy presented here for tonal global active noise control of steady states comprises two steps; the first is rather common for this sort of problem and its goal is to find the best locations for secondary sources and their strengths by minimizing the potential energy of the enclosure. The second step is the localization of the error transducer, which ensures the results of the first step. It is analytically demonstrated that for a single input single output system, the optimum location of error transducers is at a null pressure point of the optimally attenuated acoustic field. It is also shown that in a real case, the optimum position is that of a minimum of the optimally attenuated acoustic field. Finally, a numerical validation of this principle is carried out in a parallelipedic enclosure.