Noise absorption of gap graded mixtures with rubberized asphalt

Sound absorption is a material property which contributes to reduce noise levels when sound propagates from the source to the receiver. Porous materials have particularly good absorption characteristics, not only because of the high percentage of air voids, but also due to their flow resistance and tortuosity. Road surface layers made of gap graded mixtures are among those absorptive materials. Because these mixtures have a void content that may be considered of medium level, this study aims to characterise their absorption capacity, particularly of those with rubberized asphalt binder. For this purpose, absorption measurements in a Kundt’s tube were performed on cores extracted from slabs with different gap graded asphalt. In order to study the effect of the rubberized asphalt, the mixtures were produced in laboratory with two types of rubberized asphalt and with unmodified asphalt. The effect of the binder was pondered with this procedure. Furthermore, the effect of porosity was considered bycomparing the results of mixtures which have considerably high and low void contents.(undefined

Avaliação do desempenho acústico de dispositivos de redução do ruído de tráfego

O desenvolvimento urbano que se verificou em Portugal nas últimas décadas do século 20 foi acompanhado por um rápido e elevado crescimento do tráfego e, consequentemente, pela construção de vias rodoviárias quer urbanas quer rurais. A partir do ano 1980, as políticas de controlo do ruído levaram as administrações rodoviárias e os construtores a aplicarem medidas de mitigação do ruído que passaram sobretudo pela construção de barreiras acústicas e, em menor grau, pela aplicação de pavimentos com características que produzem menos ruído. Em ambos os casos, a avaliação do desempenho acústico permite a comparação das especificações de projecto com dados de desempenho reais e a verificação do mesmo a longo prazo para a devida validação das soluções adoptadas. Neste trabalho apresentam-se os métodos essenciais para uma gestão eficaz do ruído rodoviário, que permitem avaliar o ruído de contato pneu-pavimento e o desempenho acústico de dispositivos de redução de ruído do tipo barreiras acústicas. Apresenta-se ainda um método complementar para a determinação da absorção sonora em pavimentos rodoviários.The urban development that has occurred in Portugal in the last decades of the 20th century was accompanied by a fast growth of road traffic and, consequently, by the construction of rural and urban roadways. After 1980, the noise control policies lead the road administrations and constructors to apply noise mitigation measures, like barriers but also pavements with noise reduction characteristics. In both cases, the evaluation of the acoustic performance allows a comparison of the design specifications with real performance data and its verification at the long run for an adequate validation of the adopted solutions. In this work the essential methods for an effective road noise management that allow the evaluation of road/tyre noise and of the acoustic performance of noise reduction devices, such as noise barriers. A method for the determination of the sound absorption in road pavements is also presented.Fundação para a Ciência e a Tecnologia (FCT

In situ assessment of the normal incidence sound absorption coefficient of asphalt mixtures with a new impedance tube

Normal incidence sound absorption coefficient of materials is usually calculated with the use of an impedance tube following the ISO 10534-2 international standard. The same is applied in the evaluation of the sound absorption characteristics of pavement mixtures. In this research an impedance tube which was specifically designed to be used in field conditions has been developed. In order test the tube six asphalt slabs were constructed in laboratory and its sound absorption coefficient measured with the new impedance tube. Then, several road sections, with different types of surface, among dense asphalt layers and thin layers, namely with rubberized asphalt were tested. In this paper, some considerations are made regarding the performance of the new impedance tube and the sound absorption coefficient of each asphalt mixtures.(undefined

Sound levels and risk perceptions of music students during classes

It is well recognized that professional musicians are at risk of hearing damage due to the exposure to high sound pressure levels during music playing. However, it is important to recognize that the musicians’ exposure may start early in the course of their training as students in the classroom and at home. Studies regarding sound exposure of music students and their hearing disorders are scarce and do not take into account important influencing variables. Therefore, this study aimed to describe sound level exposures of music students at different music styles, classes, and according to the instrument played. Further, this investigation attempted to analyze the perceptions of students in relation to exposure to loud music and consequent health risks, as well as to characterize preventive behaviors. The results showed that music students are exposed to high sound levels in the course of their academic activity. This exposure is potentiated by practice outside the school and other external activities. Differences were found between music style, instruments, and classes. Tinnitus, hyperacusis, diplacusis, and sound distortion were reported by the students. However, students were not entirely aware of the health risks related to exposure to high sound pressure levels. These findings reflect the importance of starting intervention in relation to noise risk reduction at an early stage, when musicians are commencing their activity as students

A modal method for the simulation of nonlinear dynamical systems with application to bowed musical intruments

Bowed instruments are among the most exciting sound sources in the musical world, mostly because of the expressivity they allow to a musician or the variety of sounds they can generate. From the physical point of view, the complex nature of the nonlinear sound generating mechanism – the friction between two surfaces – is no less stimulating. In this thesis, a physical modelling computational method based on a modal approach is developed to perform simulations of nonlinear dynamical systems with particular application to friction-excited musical instruments. This computational method is applied here to three types of systems: bowed strings as the violin or cello, bowed bars, such as the vibraphone or marimba, and bowed shells as the Tibetan bowl or the glass harmonica. The successful implementation of the method in these instruments is shown by comparison with measured results and with other simulation methods. This approach is extended from systems with simple modal basis to more complex structures consisting of different sub-structures, which can also be described by their own modal set. The extensive nonlinear numerical simulations described in this thesis, enabled some important contributions concerning the dynamics of these instruments: for the bowed string an effective simulation of a realistic wolf-note on a cello was obtained, using complex identified body modal data, showing the beating dependence of the wolfnote with bowing velocity and applied bow force, with good qualitative agreement with experimental results; for bowed bars the simulated vibratory regimes emerging from different playing conditions is mapped; for bowed Tibetan bowls, the essential introduction of orthogonal mode pairs of the same family with radial and tangential components characteristic of axi-symmetrical structures is performed, enabling an important clarification on the beating phenomena arising from the rotating behaviour of oscillating modes. Furthermore, a linearized approach to the nonlinear problem is implemented and the results compared with the nonlinear numerical simulations. Animations and sounds have been produced which enable a good interpretation of the results obtained and understanding of the physical phenomena occurring in these system

A case study

UID/EAT/00472/2013 EAT/00472/2013Excessive vibrations in the work environment not only harm exposed workers but can also affect the integrity of building structures. This problem was detected in a wine cellar in Alijo ́, Portugal, where a concrete slab is driven to resonance by two vibrating hoppers. In order to address the problem, a strategy combining physical modelling techniques and in-situ vibratory measurements have been developed. The general objective was first to reproduce the qualitative trends observed and then to assess the effectiveness of the proposed solution. The strategy developed here allowed to study how to decrease the vibration amplitude without making structural modifications on the slab, nor serious changes to the vibrating equipment.publishersversionpublishe

A case study

UID/EAT/00472/2013 EAT/00472/2013Excessive vibrations in the work environment not only harm exposed workers but can also affect the integrity of building structures. This problem was detected in a wine cellar in Alijo ́, Portugal, where a concrete slab is driven to resonance by two vibrating hoppers. In order to address the problem, a strategy combining physical modelling techniques and in-situ vibratory measurements have been developed. The general objective was first to reproduce the qualitative trends observed and then to assess the effectiveness of the proposed solution. The strategy developed here allowed to study how to decrease the vibration amplitude without making structural modifications on the slab, nor serious changes to the vibrating equipment.publishersversionpublishe

The physics of Tibetan singing bowls

Tibetan bowls have been traditionally used for ceremonial and meditation purposes, but are also increasingly being used in contemporary music-making. They are handcrafted using alloys of several metals and produce different tones, depending on the alloy composition, their shape, size and weight. Most important is the sound producing technique used - either impacting or rubbing, or both simultaneously - as well as the excitation location, the hardness and friction characteristics of the exciting stick (called puja). In this paper, we extend to axi-symmetrical shells - subjected to impact and friction-induced excitations - our modal techniques of physical modelling, which were already used in previous papers concerning plucked and bowed strings as well as impacted and bowed bars. Our simulation results highlight the existence of several motion regimes, both steady and unsteady, with either permanent or intermittent bowl/puja contact. Furthermore, the unstable modes spin at the angular velocity of the puja. As a consequence, for the listener, singing bowls behave as rotating quadropoles. The sound will always be perceived as beating phenomena, even if using perfectly symmetrical bowls

The dynamics of Tibetan singing bowls

Tibetan bowls have been traditionally used for ceremonial and meditation purposes, but are also increasingly being used in contemporary music-making. They are handcrafted using alloys of several metals and produce different tones, depending on the alloy composition, their shape, size and weight. Most important is the sound-producing technique used - either impacting or rubbing, or both simultaneously - as well as the excitation location, the hardness and friction characteristics of the exciting stick (called puja). Recently, researchers became interested in the physical modelling of singing bowls, using waveguide synthesis techniques for performing numerical simulations. Their efforts aimed particularly at achieving real-time synthesis and, as a consequence, several aspects of the physics of these instruments do not appear to be clarified in the published numerical formulations and results. In the present paper, we extend to axi-symmetrical shells - subjected to impact and friction-induced excitations - our modal techniques of physical modelling, which were already used in previous papers concerning plucked and bowed strings as well as impacted and bowed bars. We start by an experimental modal identification of three different Tibetan bowls, and then develop a modelling approach for these systems. Extensive nonlinear numerical simulations were performed, for both impacted and rubbed bowls, which in particular highlight important aspects concerning the spatial patterns of the friction-induced bowl vibrations. Our results are in good agreement with preliminary qualitative experiments