Uncertainty of the density of moist air: Gum x Monte Carlo

Canaves, Moacyr; Pompeia, P. J.

doi:10.1590/s1516-89132006000200014

Cited by 5 publications

(5 citation statements)

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“…[4,117,120,175,181,191,192,246,292,297,300,303]. 31 For the case of water coupled NDT ultrasound see Refs. [78,133,171,223,224,290,304].…”

Section: Air-coupled Systemsmentioning

confidence: 99%

“…This is mainly because of the different approaches used during implementation of the attenuation process. For the Field II & DREAM cases a linear model was used (α = 2.628f −1.006) near the central frequency (f 0 ∼ = 0.8 MHz) in the bandwidth, while for the LAMB toolbox the model of equation (2.34) was employed 31 .…”

Section: Simulations and Experimental Comparisonsmentioning

confidence: 99%

“…30 The rectangular radiator is located in all the cases at: O = (0, 0, 0). 31 This is the final attenuation model used in the toolbox for all the simulations. 32 For an example of this process please see figures 5.3 and F.4 .…”

Section: Simulations and Experimental Comparisonsmentioning

confidence: 99%

“…However finding the roots of such an equation for an n-layer system is not an easy task 31 . This is especially true when material damping is used and/or when roots are in close proximity e.g.…”

Section: The Searching Algorithmmentioning

confidence: 99%

“…The calculation of the air density ρ[kg/m 3 ] was based on Refs. [31,53,79], with t [ o C] and T [K] being the ambient and absolute temperatures respectively 3 . Then:…”

Section: Appendix Amentioning

confidence: 99%

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Lamb: a simulation tool for air-coupled lamb wave based ultrasonic NDE systems

Prego Borges

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La técnica de las ondas de Lamb acopladas por aire representa un importante avance en el área de los Ensayos No Destructivos (END) de materiales laminares. Sin embargo la compleja naturaleza de las vibraciones mecánicas encontradas en acústica, hacen que el análisis y el estudio de esta área del conocimiento sea un tema muy complejo. De allí que la posibilidad de contar con una herramienta de simulación de software que permita la evaluación y prueba de diferentes configuraciones de excitación y recepción acústica utilizando la flexibilidad de un modelo de computadora sea de una gran utilidad y ayuda. El objetivo de la presente tesis es proveer al área de los END con un software de simulación gratuito: The LAMB Matlab® toolbox basado en el modelo del software libre de la GNU. El software es capaz de simular el comportamiento de sistemas de END basados en ondas de Lamb acopladas por aire en láminas isótropas simples utilizando transductores tipo array. El programa se basa en un arreglo tipo C-scan de un sistema de END y está compuesto por tres bloques principales: 1) Excitación, 2) Propagación y 3) Recepción. La verificación individual del funcionamiento de dichos módulos se presenta a lo largo de la tesis mediante una serie de comparaciones entre simulaciones y datos experimentales provenientes de diferentes pruebas. Por otro lado, la validación del programa completo se llevo a cabo por medio de experimentos en láminas de cobre y aluminio; utilizando un sistema real de END por ondas de Lamb acopladas en aire mediante arrays cóncavos. La influencia negativa en el desempeño general de dicho sistema de END real basado en este tipo de transductores se comprobó efectivamente mediante el simulador desarrollado. Esto se debió fundamentalmente al efecto de directividad de los sensores individuales en los transductores y a la simetría cóncava de los arrays. Para emular este comportamiento la tesis presenta un modelo geométrico bidimensional simple de un filtro espacial, junto a las simulaciones de un nuevo tipo de array plano propuesto. El programa desarrollado comprobó así mismo la naturaleza coherente de los campos acústicos emitidos en aire por las láminas sujetas a vibraciones de Lamb. Esto se realizó mediante la implementación de un conformador de haz simple de suma y demora; constituyéndose así la etapa inicial de procesamiento de señal del bloque de recepción del programa. El objetivo principal del presente trabajo fue contribuir con un modelo operativo de simulación y prueba de nuevos diseños de arrays e implementación de estrategias de procesado de señal útiles en sistemas de END basados en ondas de Lamb acopladas por aire. Finalmente, si bien el objetivo de la calibración del programa no se pudo conseguir; si se logró efectivamente un notable grado de similitud con un sistema de END real. Air-coupled ultrasonic Lamb waves represent an important advance in Non- Destructive Testing and Evaluation (NDT & NDE) techniques of plate materials and structures. Examples of these advances are the characterization and quality assessment of laminate materials in manufacturing processes, the location of damaged parts in aircrafts and structure monitoring in the aerospace industry. However the rich and complex nature of mechanical vibrations encountered in acoustics make the subject of analysis and study of these systems a very complex task. Therefore a simulation tool that permits the evaluation and testing of different configuration scenarios using the flexibility of a computer model is an invaluable aid and advantage. The objective of this thesis is to provide the field of NDT with free open source software i.e. the LAMB Matlabrtoolbox. The toolbox is capable of simulating the behaviour of Lamb wave based NDE systems for single ideal isotropic laminates using air-coupled ultrasonic arrays. The programme usesa pitch-catch type of a Cscan NDE arrangement and is composed of three integrated sections each individually modelling a feature in the system: 1) Excitation, 2) Propagation, and 3) Reception. For assessment of the individual modules of the toolbox the thesis presents comparisons between each section simulations and the data obtained from different acoustic experiments. The validation of the complete simulator was carried out by evaluation tests on the copper and aluminium plates by use of a real hardware prototype of a Lamb wave based NDE system with aircoupled concave arrays. The negative impact on the performance of the real air-coupled NDE systembased on concave arrays was effectively confirmed by the programme. This was produced by the inherent directivity of the individual sensors as well as their concave arrangement. To emulate this behaviour the thesis introduces a simple two-dimensional geometric model for the inclusion of the spatial filtering effect of the sensors plus a group of simulations for a new proposed air-coupled plane array transducer. The software also verified the spatial coherent nature of the Lamb wave fields emitted by a plate in air. This was demonstrated by the implementation of a delay and sum beamformer to constitute an initial signal processing stage in the reception section.

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“…[4,117,120,175,181,191,192,246,292,297,300,303]. 31 For the case of water coupled NDT ultrasound see Refs. [78,133,171,223,224,290,304].…”

Section: Air-coupled Systemsmentioning

confidence: 99%

Section: Simulations and Experimental Comparisonsmentioning

confidence: 99%

Section: Simulations and Experimental Comparisonsmentioning

confidence: 99%

Section: The Searching Algorithmmentioning

confidence: 99%

“…The calculation of the air density ρ[kg/m 3 ] was based on Refs. [31,53,79], with t [ o C] and T [K] being the ambient and absolute temperatures respectively 3 . Then:…”

Section: Appendix Amentioning

confidence: 99%

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