Systematic approach for active control of acoustic radiation modes
- Autores: Gabriel Alarcon Rovira
- Directores de la Tesis: J. Romeu (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2008
- Idioma: español
- Tribunal Calificador de la Tesis: Ramón Capdevila Pagès (presid.), Jordi Ramón Martínez Miralles (secret.), Francisco Javier Fuenmayor Fernández (voc.), Pedro Cobo Parra (voc.), Joel Bordeneuve Guibé (voc.)
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- Resumen
For noise and vibration problems related to complex structures, active control system research and development are often characterized by using a large number of control system inputs and outputs, processors in the controller, actuators and sensors, power amplifiers, etc. This fact makes the technology inaccessible in a practical setting for the majority of uses. Accordingly, the main objective of the work presented in this thesis is the investigation of active control systems that reduce the noise radiated from panels using distributed structural sensors and actuators. An innovative active structural-acoustic control (ASAC) approach tries to be obtained taking advantage of the concept of radiation modes. The radiator elements are focused on transport vehicles, where the users awareness regarding noise and comfort is the highest: interior trimming panels in trains, aircrafts and automotives.
An initial analysis of the theoretical basis and performance of several already-known active structural-acoustic control strategies is carried out and a set-up to test a flat rectangular plate chosen as reference is designed and built. Some basic AVC and ASAC tests at several frequencies are described to demonstrate the effectiveness of the set-up. Once it is validated, a systematic test campaign including each one of the already-known ASAC strategies described is performed. The assessment of these results confirms as the strategy of the structural modes minimization does not work well enough, except for the first mode at very low frequencies, and the same works for the minimization of the net volume velocity. The tests show as well that the strategy of the minimization of the first four radiation modes, by means of a simple algebraic combination of the four accelerometers signals, needs to be improved or that the noise reduction does not depend directly on the plate's kinetic energy reduction.
Overcoming the main drawbacks found in the already-known methods, the first radiation modes are approximated to the named conceptual volume displacements. On the other hand, an optimization process to the best description of radiation modes in terms of structural modes is implemented. Making use of this last advance, shaped PVDF strips for the first six radiation modes of the reference plate are designed. Nevertheless, it does not reveal to be a simple enough system to monitor the noise radiation behaviour of plates.
A practical approach to describe radiation modes over a frequency range using mathematical expressions is developed and their accuracy is demonstrated. Then, the radiation modes radiation efficiency is analytically computed. First, PVDF strips are designed to the sensoring of these radiation modes, concluding that it is theoretically possible to reduce drastically the number of strips with respect to the strategy based on the structural modes description. Secondly, the strategy based on accelerometers is extensively evolved even optimizing the position of them making use of the aforementioned mathematical descriptions of the radiation modes and their radiation efficiencies. In similar terms, a strategy based on rectangular PVDF strips is successfully developed. These advances are then applied to two specially designed and created non-rectangular flat plates and to a non-planar plate example (this last, using boundary element analysis) in order to shown the feasibility of the new approach under these more complex conditions.
Experimental work on the proposed new ASAC approach under the same physical and control conditions than the previously mentioned tests is conducted. The utility of the new approach is revealed: results in the rectangular plate are significantly better. Moreover, the noise radiated decreased in most of the tests using the new ASAC approach, both in rectangular and non-rectangular flat plates. When this is not true because the actuators placement makes it non-possible, it did not increase at all, showing its robustness.
