NOISE

Author: ARGÒELLES DÍAZ KATIA M..
Year: 2004.
University: OVIEDO [www.uniovi.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: E.P.S. DE INGENIERÍA DE GIJÓN.

Summary: Today turbomachinery are present in many industrial applications and social rights, there is a continuous demand to improve their benefits through more efficient designs. In addition, it is essential that the new design is intended to reduce noise emissions from turbomachinery because they have a strong impact on society. Thus, noise, seen until recently as a byproduct inherent in the turbomachinery, he has to go to become an essential and indispensable goal of the stages of designing the new prototypes. Most of the noise generated by turbomachinery is nature aeroacústica, so that only a thorough knowledge of the phenomena fluildodinámicos taking place within the same will be able to detect the basic mechanisms of generation and make noise such proceedings with a view to reducing the resulting noise. In addition, knowledge of the nature of the flow inside the turbomachinery will also improve benefits and performance of the same. That is why in this dissertation is a study of one of the mechanisms responsible for generating the most noise aeroacústico in turbomachinery: interaction stator-rotor. It then develops the thesis in a methodology based on a numerical approximation hybrid: decoupling mechanisms generating noise and the spread of it. This desacomplamiento allows aerodynamic phenomena are dealt with through traditional CFD techniques, while phenomena spread aeroacústicos addressed through an algorithm based on the full-resolution in the frequency domain and time-of the equation wave aeroacústica with corresponding source terms. The numerical method is applied to the particular case of an axial fan of a single stage with a stator thirteen guidelines located upstream of a rotor nine alábes for various configurations of operating the same: two axial gaps between stator and rotor, and three flow Operating different. Numerical models are validated with experimental results obtained from a series of tests carried out in the fan through techniques anemometría thermal transducers piezoeléctrios and microphones trained. It then provides a tool that allows users to reduce and, in the design stage, the noise levels generated by turbomáquina.

Author: Fernández Fernandez Alejandro.
Year: 2005.
University: PONTIFICIA COMILLAS [www.upcomillas.es].
Place of defense: E.T.S.I. del ICAI.
Place of preparation: E.T.S.I.

Summary: In this dissertation explores systems absorbent acoustic hybrids pasivos-activos and shows how, through proper design, it is possible to obtain small absorbent devices capable of providing very high performance. To do so, has developed an analytical model that permits hybrid systems and how the parameters of the passive part of the system affect the absorption active, both at normal incidence and at oblique incidence and random. It has been studied using absorbent materials and porous panels microperforados. Likewise, have studied the two most active control mechanisms used to obtain active absorption, releasing pressure and adjusting impedances, in addition to suggesting a third person, the reflection zero, which uses the model system for seek absorption regardless of the material used. The model has been shown that there are optimal parameters of passive system that can obtain maximum values in the active absorption. As a result, it is possible to use the mechanism easier to implement in practice, the release of the pressure, and get a close to the absorption unit in the entire frequency range. The results of experiments to validate the model have been excellent. For the passive system, the experiments carried out in a tube of waves (normal incidence) and camera anecoica (oblique incidence), as well as reverberant chamber (Random incidence) have yielded results that match in a very accurate with predicted by the model. Experiments of the hybrid system pasivo-activo have been made in the tube waves, using a system Assets Control of Noise with a control strategy feedforward adaptive. The results have allowed not only validate the model, but to show the feasibility of absorbents hybrids. To make these measures have been implemented and adapted different methods of measuring the absorption, in both tube waves in camera anecoica, which in themselves have resulted in improvements to the systems used conventionally. We have developed a number of virtual instruments that have led to all the experiences quickly and accurately. Likewise, both actuators have been developed, based on piezoelectric patches, while minimizing the size of absorbing devices. As a result, it has become a hybrid of acquiring only 8 cm in thickness including the actuator based on porous material, which is able to provide an average of 97% absorption between 100 Hz and 1600 Hz. Another system, based on a unit Microperforada Insertion or MIU, presents an absorption averaged 94% between 100 Hz and 1600 Hz, with a total thickness of 5 cm.

Author: PAVON GARCIA IGNACIO.
Year: 2006.
University: POLITÉCNICA DE MADRID [www.upm.es].
Place of defense: E.T.S. ING. INDUSTRIALES.
Place of preparation: E.T.S. ING. INDUSTRIALES.

Summary: Noise pollution is one of the greatest physical presence in the area of opencast mining industries as well as their assistants. Various international agencies have tried in one way or another the problem of noise at work, both from the policy and law, as is the case with the European Union, as from a descriptive and informative, if the World Organization for the Health. Currently known many negative effects caused by exposure to noise, especially with regard to the auditory system. Although there is evidence of the existence of many other effects, some of them are not yet defined in a precise manner. Because of the importance of these effects on the health and welfare of the people, it becomes necessary to develop mechanisms to study and raise preventive solutions on these issues. In the year 2003 the European Union adopted a new directive (2003/10/EC) regarding the exposure of workers to the risks arising from physical agents (noise). This directive was transposed into Spanish law by Royal Decree 286/2006. The particularities and difficulties presented by the mining and constructive, with respect to other industrial activities, makes complex application of the various regulations of noise at work. In this investigation have studied levels of noise to which workers are exposed in the mining and manufacture of cements de la Comunidad de Madrid, using different techniques and procedures for measuring and comparing the results with those values limit expressed in the various laws in force. Moreover, it has developed an algorithm to estimate the optimal time measure, which allows the assessment of the levels of noise exposure through the implementation of measures measuring personal noise exposure, and among other contributions, has analyzed the contribution of the different variables to the total uncertainty of the measures, which will be useful for the assessment of exposure to noise at work in the productive sector.