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Non-invasive Ultrasonic Inspection Through Steel Pipes Using the SURF Method
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Electronics and Telecommunications.
2014 (English)MasteroppgaveStudent thesis
Abstract [en]

The main objective of this thesis has been to study the possibility to establish a simulation tool for Second Order Ultrasonic Field (SURF) based on finite element modeling implemented in COMSOL Multiphysics. The SURF method is a dual-frequency ultrasonic imaging technique where two waves are trans- mitted in the same direction with a large separation in frequency of about 1:10. This causes interaction between the waves, which give rise to non-linear sound propagation. The method can be used for enhanced ultrasonic imaging ca- pabilities. The COMSOL implementation has been documented and through studies of normal incident waves and oblique incident waves at a steel interface, the advantages and disadvantages of the implementation has been highlighted. The SURF method has been implemented in the built-in physical interfaces of Pressure Acoustics and Acoustic-Solid Interaction in COMSOL. Simple 2D normal incident plane wave simulations have been compared to theoretically calculated values of non-linear speed of sound, with matching results. The study of the plane wave model has been extended to include water and steel modeled as both linear and non-linear materials. Studies on the possibility of analyzing non-linear materials behind steel have shown possible ways to ensure transmission through steel, despite high impedance ratios between water and steel. The most promising methods proved to be based on impedance match- ing and standing waves which coincides with other studies on the topic. Simulations with the Acoustic-Solid Interaction interface on large models, which include structural waves and deformations, have been bounded to a low frequency study in a SURF scheme. This is because of a rapidly increas- ing computational time, as a function of degrees of freedom to solve for in the model. Estimations predict solution time of in terms of weeks on large scale models, when the fundamental convergence criteria of elements per wavelength and number time steps in a time dependent finite element analysis are fulfilled. Possible measures to overcome this are performing the simulations on a more powerful computer, modifying the implemented solution process or using a different solver than the direct solver used in this thesis.

Place, publisher, year, edition, pages
Institutt for elektronikk og telekommunikasjon , 2014. , 75 p.
URN: urn:nbn:no:ntnu:diva-26490Local ID: ntnudaim:11058OAI: diva2:747991
Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2014-09-17Bibliographically approved

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