In this paper, a modified cost function is proposed in order to achieve the maximum noise attenuation using a set of secondary sources for a harmonically excited sound field. The modified cost function drives the error signal to the optimally attenuated sound field instead of minimizing the squared pressure. Moreover, changing the value to which the error signals must be driven allows change of the control strategy from global to local. The modified cost function requires the knowledge of the attenuated sound field, which is a condition that is well suited to narrowband noises, as is the case of turboprops. A numerical example of the application of the cost function is carried out using a finite element model/boundary element model of a real turboprop, with the goal of minimizing the interior sound field in the cabin to about 17m(3). A maximum averaged attenuation of 7dB at blade-passage frequencies is achieved using six secondary sources and six error sensors. Besides, when the same control system is tuned to achieve local control around the head of a seated crew member, 11dB of attenuation is achieved.
The performance of an active control system in global control of enclosed sound fields depends largely on the localization of the error sensors, among other factors. In this paper a modified cost function is proposed in order to guarantee the maximum attenuation that can be produced by a set of secondary sources in the case of an harmonically excited sound field. The cost function is modified in order to drive the error signal to the value corresponding to the optimally attenuated sound field, instead of minimizing the squared pressure. To evaluate the performance of the proposed control system, its robustness against unstructured error is also investigated using a set of intensive calculations. Following this approach, the sensors can be located anywhere and the optimal attenuation is reached using an equal number of error sensors and secondary sources. The results also suggest that the greater the number of error sensors than secondary sources the more robust the control system is. This behavior holds for both the usual strategy of minimizing the squared pressure and the approach presented in this paper. However, the latter strategy is more robust than the traditional approach of minimizing the squared pressures and its robustness does not depend on the location of the error sensors. Thus, as a main conclusion, the use of the new cost function leads to a guaranteed efficiency and a more robust control system and gives absolute freedom in selecting the location of the error sensors.
In certain environments it is not possible to achieve compliance with the external noise levels. In such cases, however, normative stresses the compliance levels in the interior of the housing.
The communication presents a study of the possible actions in a recreation area consisting of a set of open doors music bars which gives as a result loud street levels. The first step is creating
a detailed sound map of the environment through simulation, in which the sources of noise are the openings in the façades of these bars. The second step is to determine the acoustic sound insulation of the receivers’ façades. Known the relationship between interior level of each activity, the level on the façade of the receptors and considering the acoustic insulation, the solution consists of reducing the level of noise emission of the activities and/or increase the isolation of the affected homes. Through the use of GIS, the level inside of the receivers and the affected population is also calculated. These variables along with the cost associated with the necessary increase insulation in facade, defines a mathematical model that allows to optimize the combination of acoustic insulation and reducing the noise emission of the activities.
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. (C) 2013 Elsevier Ltd. All rights reserved.
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.
The prediction of vibration levels near underground trains is of growing importance for newly constructed infrastructures in cities. Before construction, preliminary studies of vibration impact need to be undertaken in order to identify the buildings that may be affected based on vibration contamination laws and modify the railway line or the type of superstructure if necessary. These studies need fast and economic models due to the large areas they need to cover. The present study aims at predicting the vibration impact for the new Line 9 of Barcelona Underground which is 48 km long. The solution presented is a fast pre-calculated 2D FEM model which is run once for a set of different soil types and tunnel depths, obtaining sets of surface vibration levels. Interpolating between the depths and distances of the tabulated results can be used as a very fast model for prediction. The model is calibrated with measurements in the same conditions (rolling stock and superstructure) as those expected in Line 9 and offers an accuracy not far from current 2.5D and 3D models.
Sirens from emergency vehicles are particularly annoying for people living in the vicinities of hospitals. The power regulations for sirens vary for different countries as well as it does their frequency content. In order to reduce their annoyance the present work computes the optimal output power and frequencies of the siren by taking into account the car's sound insulation, the background noise inside the car and the masked threshold of hearing. The combination of these parameters gives rise to frequency windows where the sirens are more effective, so new tones are proposed and their annoyance is assessed through a jury test procedure.
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.
Palacios, J.; Romeu, J.; Balastegui, A. Journal of vibration and acoustics. Transactions of the ASME Vol. 132, num. December, p. 1-8 DOI: 10.1115/1.4002122 Data de publicació: 2010-12 Article en revista
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.
Due to the increasing number and kilometres of new railways lines, either high speed railway lines or commuter lines, as well as the increasing in human sensitivity versus ground-borne vibration generated for this mean of transport, a sustained growth in complaints due to the annoyance caused by railway vibrations has been detected.
In order to predict the field vibrations caused by new railway lines in the project stage, which will be useful to design appropriate countermeasures, in the present work a ground-borne vibration model for rail systems at-grade developed by the authors is validated with experimental measurements in an existing commuter railway line. It checked that this model is a very useful tool to predict the vibration field that will be caused by a railway infrastructure in the planning stage of the project.