Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2006. / Includes bibliographical references (p. 67-69).

Aquesta tesi presenta treball original i aplicat en l'àrea del control i la col·locació de sensors/actuadors (S/A) en sistemes de Control Actiu de Soroll (ANC). Primer, s'han aplicat tècniques de control i identificació robustes per a aconseguir ANC. La fase d'identificació està basada en una proposta d'identificació robusta orientada al control, considerant descripcions del sistema tant paramètriques com no-paramètriques, així com quantificant la incertesa. El disseny del controlador compara les estructures de control feedback (FB), feedforward (FF) i híbrida (FB/FF). El controlador feedback és sintetitzat i avaluat en el marc del control robust, i s'ha dissenyat utilitzant control òptim H∞ plantejat com un problema de sensibilitats mixtes. El controlador FF és un identificador adaptatiu, basat en l'algorisme σ robustament normalitzat. S'han desenvolupat dues propostes per a decidir quina de les estructures de control és més eficient, aplicades a un conducte de 4 metres amb soroll de banda ampla. A més a més, s'han mostrat de manera explícita els compromisos entre identificació i control, les limitacions inherents a un llaç de control feedback, així com qüestions relatives a la implementació de sistemes ANC. També s'han tractat altres qüestions com la relació entre acompliment, ordre del controlador, models paramètrics/no-paramètrics i implementació en processadors digitals de senyal (DSP), així com s'han comparat resultats teòrics i experimentals en el conducte. Les llacunes que encara resten entre teoria i pràctica en aquest tipus d'aplicacions també s'han resumit. D'altra banda, en aquest treball també es tracta el problema de com quantificar la col·locació de sensors i actuadors, amb la finalitat de controlar un sistema físic determinat. La mesura per a determinar la millor localització de S/A es basa en un criteri de llaç tancat orientat al control, el qual optimitza tant acompliment com qüestions pràctiques d'implementació. Aquesta mesura hauria de calcular-se abans del disseny, implementació i prova del controlador. La utilització d'aquesta mesura minimitza la prova combinatòria de controladors en totes les possibles combinacions de S/A. Per a aconseguir-ho, s'han definit diferents mesures que pesen l'acompliment potencial en llaç tancat, la robustesa, el número de condició de la planta (guanys relatius entrada/sortida (I/O)) així com altres qüestions d'implementació, com l'ordre del controlador. Aquestes poden calcular-se utilitzant software estàndard, tant per a models d'una-entrada-una-sortida (SISO) com per a models de múltiples-entrades-múltiples-sortides (MIMO) i poden aplicar-se a múltiples problemes d'enginyeria, ja siguin mecànics, acústics, aeroespacials, etc. En aquest treball, aquests resultats també s'han il·lustrat amb l'aplicació ANC presentada i validat amb dades experimentals. Com a resultat d'aplicar aquestes mesures, s'obté la localització de S/A que aconsegueix la millor atenuació del soroll en llaç tancat amb el menor ordre possible del controlador. / Esta tesis presenta trabajo original y aplicado en el área del control y la colocación de sensores/actuadores (S/A) en sistemas de Control Activo de Ruido (ANC). Primero, se han aplicado técnicas de control e identificación robustas para conseguir ANC. La fase de identificación está basada en una propuesta de identificación robusta orientada al control, considerando descripciones del sistema tanto paramétricas como no-paramétricas, así como cuantificando la incertidumbre. El diseño del controlador compara las estructuras de control feedback (FB), feedforward (FF) e híbrida (FB/FF). El controlador feedback es sintetizado y evaluado en el marco del control robusto, y se ha diseñado utilizando control óptimo H∞ planteado como un problema de sensibilidades mixtas. El controlador FF es un identificador adaptativo, basado en el algoritmo σ robustamente normalizado. Se han desarrollado dos propuestas para decidir cual de las estructuras de control es más eficiente, aplicadas a un conducto de 4 metros con ruido de banda ancha. Además, se han mostrado de manera explícita los compromisos entre identificación y control, las limitaciones inherentes a un lazo feedback, así como cuestiones relativas a la implementación de sistemas ANC. También se han tratado otras cuestiones como la relación entre desempeño, orden del controlador, modelos paramétricos/no-paramétricos e implementación en procesadores digitales de señal (DSP), así como se han comparado resultados teóricos y experimentales en el conducto. Las lagunas que aún quedan entre teoría y práctica en este tipo de aplicaciones también se han resumido. Por otra parte, en este trabajo se trata también el problema de como cuantificar la colocación de sensores y actuadores, con la finalidad de controlar un sistema físico determinado. La medida para determinar la mejor localización de S/A se basa en un criterio de lazo cerrado orientado al control, el cual optimiza tanto desempeño como cuestiones prácticas de implementación. Esta medida debería calcularse antes del diseño, implementación y prueba del controlador. La utilización de esta medida minimiza la prueba combinatoria de controladores en todas las posibles combinaciones de S/A. Para conseguirlo, se han definido distintas medidas que pesan el desempeño potencial en lazo cerrado, la robustez, el número de condición de la planta (ganancias relativas entrada/salida (I/O)) y otras cuestiones de implementación, como el orden del controlador. Éstas pueden calcularse utilizando software estándar, tanto para modelos de una-entrada-una-salida (SISO) como para modelos de múltiples-entradas-múltiples-salidas (MIMO) y pueden aplicarse a múltiples problemas ingenieriles, ya sean mecánicos, acústicos, aeroespaciales, etc. En este trabajo, estos resultados también son ilustrados con la aplicación ANC presentada y validados con datos experimentales. Como resultado de aplicar estas medidas, se obtiene la localización de S/A que consigue la mejor atenuación de ruido en lazo cerrado con el menor orden posible del controlador. / This thesis presents novel and applied work in the area of control and sensor/actuator (S/A) allocation in Active Noise Control (ANC) systems. First, robust identification and control techniques to perform ANC have been applied. The identification phase is based on a control-oriented robust identification approach that considers both parametric and nonparametric descriptions of the system, and quantifies the uncertainty. The controller design compares the feedback (FB), feedforward (FF) and hybrid (FB/FF) control structures. The feedback control is synthesized and evaluated in the robust control framework, and it is designed using H∞ optimal control as a mixed-sensitivity problem. The FF controller is an adaptive identifier, based on the robustly normalized σ-algorithm. Two approaches are developed to decide which control structure is more efficient on a 4-m duct example with broadband noise. In addition, the compromises between identification and control, the inherent limitations of feedback and implementation issues in ANC are explicitly pointed out. Relations between performance, controller order, parametric/nonparametric models and digital signal processor (DSP) implementation are discussed. Theoretical and experimental results on the duct are compared. The gaps that still remain between theory and practice in this type of applications, are also outlined. Furthermore, this work considers the problem of quantifying the location of sensors and actuators in order to control a certain physical system. The measure to determine the best S/A location is based on a closed loop control-oriented criteria, which optimizes overall performance and practical implementation issues. In addition, it should be computed before the actual controller is designed, implemented and tested. The use of this measure minimizes the combinatorial controller testing over all possible S/A combinations. To this end, several measures have been defined which weight the potential closed-loop performance, robustness, plant condition number (input/output (I/O) relative gains) and implementation issues, such as the controller order. These may be computed with standard software, either for Single Input Single Output (SISO) models or Multiple Input Multiple Output (MIMO) models, and may be applied to many engineering problems: mechanics, acoustics, aerospace, etc. Here, these results are also illustrated with the prior ANC example and validated against experimental data. The outcome of applying these measures is the selection of the S/A location which achieves the best closed loop noise attenuation with the lowest possible controller order.

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Low disturbance wind tunnels, such as the Klebanoff–Saric Wind Tunnel (KSWT), offer an ideal environment to study boundary layer transition. In particular, the leading-edge receptivity of sound can be measured by creating acoustic disturbances that interact with the leading edge of a model to create Tollmien–Schlichting Waves. The magnitude and composition (sound, turbulence) of the background disturbances can affect these experiments, so the background disturbances should be minimized and documented thoroughly. The purpose of this thesis is to document the background acoustic signature of the KSWT and describe infrastructure upgrades for acoustic receptivity experiments. The measurements presented in this thesis will support future receptivity measurements in the KSWT. Microphone measurements revealed several important acoustic features in the tunnel. Cross correlations showed that two sources of low-frequency unsteadiness (the extended diffuser and corner two) create large pressure fluctuations that dominate the pressure spectrum. Directional separation of waves in the test section revealed that motor and blade passing noise travels primarily upstream into the test section. Finally, the acoustic treatments in the plenum are effective at removing sound from the tunnel. A wall of speakers was installed in the plenum to enable acoustic receptivity experiments. The speakers create both the primary downstream traveling waves and reflected upstream traveling waves in the test section. An adaptive closed loop control system was installed to reduce the amplitude of the reflected waves during acoustic forcing. Although the performance of the control system is frequency dependent, the technique was implemented successfully. The reduction in the diffuser reflection will increase the quality of future acoustic receptivity experiments in the KSWT.

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2004. / Includes bibliographical references (p. 65-69).

Thesis (Ph. D.)--School of Industrial and Systems Engineering, Georgia Institute of Technology, 2004. Directed by Paul H. Kvam. / Vita. Includes bibliographical references (leaves 108-113).

Hospital sound environments are complex and hard to understand. One of the most important factors in these environments is the effective communication between staff members in regards to patient care and successful communication depends in part on the hospital’s sound environment. In this study, objective sound measurements as well as occupant perceptive data were collected at three hospitals. Sound pressure levels; including maximum, peak, minimum and equivalent levels were recorded in these hospitals, in addition to active impulse response measurements. Acoustic descriptors of the sound environment such as spectral content, level distributions, energy decay and temporal patterns were examined. The perception of the hospital soundscape (sound environment) was evaluated through surveys of the staff, patients and visitors to units. It was found that noise levels in all patient rooms and work areas were significantly higher than guidelines laid out in previous literature and by professional organizations. This work contributes to the field by broadening the metrics used to quantify hospital acoustic environments. In addition, this work added to the field by providing the most rigorous acoustic field measurement set published to date. This was done to create an accurate portrayal of the hospital soundscape environment.

A study of methods for reducing the acoustic noise in magnetic resonance imaging (MRI) scanners is presented in this thesis. The structural-acoustic coupling mechanism of MRI scanners was investigated using a method of structural-acoustic modal analysis. Mathematical expressions of generalized radiation impedances of gradient coil ducts with perforated panel inserts were developed and the effects of the perforated panel inserts on the acoustic noise in the duct were discussed. The possibility of using micro-perforated panel (MPP) absorbers in MRI scanners to reduce the acoustic noise was then investigated through analytical and computational modeling. A comprehensive experimental study was conducted after the analytical and computational investigation. Finally, design methods and procedures were developed specifically for the MPP absorbers in MRI scanners. Design considerations and recommendations were given as well. Several major conclusions can be made from this research. Firstly, the method of structural-acoustic modal analysis is effective for finding the structural-acoustic coupling modes which should be avoided in the design of MRI scanners. Secondly, a perforated panel insert produces significant effects on the radiation impedance of gradient coil ducts and MRI scanner bores. This attribute partly contributes to its capability of reducing the acoustic noise in a duct. Thirdly, the effectiveness of MPP absorbers in MRI scanners can be accurately predicted using a combination of theoretical analysis and computational modeling. Moreover, it has been proved that well designed MPP absorbers are effective in reducing the acoustic noise in MRI scanners. Lastly, the presented design methods and recommendations for the MPP absorbers can be relatively easily used by MRI designers or engineers to tackle the acoustic noise problem in MRI scanners. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2010-07-13 11:46:03.585

No description available.

No description available.