Finding non-linearity is a common application of modal testing but in this way, there is a need to control the input signal. Nowadays, commercial data acquisition software is not enough flexible in controlling the applied signals, whereas MATLAB as general software which supports National Instrument makes it possible to run modal test and control input signal via closed-loop controlling. In this work, using MATLAB commands, a modal test is run with a stepped-sine excitation and the input is controlled to achieve desired pure sinusoidal excitation which commonly is used in finding the non-linearity.

Made available in DSpace on 2015-05-08T15:00:07Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3072301 bytes, checksum: cfa4169565d19880f430b4e2c197f55c (MD5) Previous issue date: 2010-03-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Oil wells may be as deep as 5000 m and consist of several types of casing. As these casings are cast in place, there is an annular space that needs to be filled to support the whole system and protect the metallic tubes against substances present in the environment of the well. This process is accomplished through cementing, by pumping a paste composed mainly of water, cement and additives. Various events such as variations in pressure and temperature, vibrations caused by explosive charges applied in the well and migration of undesirable substances in the interface casing/sheath of cement paste can impair the quality of the bond between the metallic coating and the sheath of cement paste.Specifically substances such as NaCl and oil can seep into this interface and interfere with the bond. This reflects in the operation of the well. This work aimed investigating the behavior of the condition of bond of the interface casing/sheath of cement paste, through modal tests. For this investigation modal tests were carried out on samples molded with metal pipes coated partially by a cylinder of cement paste and three contact conditions were simulated: no treatment on the surface of the pipes, treatment with NaCl and with oil. It was observed that the presence of these substances affects the modal parameters natural frequency and damping ratio and consequently affect the condition of bond, identified by the value of an elastic spring constant (K), inserted at the interface from a numerical model developed to investigate the phenomenon. It was also observed that the employed technique is sensitive to changes in adhesion at the interface metal tube / sheath of cement paste. / Poços de petróleo são constituídos de diversos tipos de revestimentos metálicos, podendo atingir profundidades de até 5000 m. À medida que são lançados esses revestimentos, surge um espaço anular que necessita ser preenchido para dar sustentação ao sistema completo e proteger o revestimento de substâncias inerentes ao ambiente do poço. Esse preenchimento é realizado por meio de processo de cimentação, com bombeamento de uma pasta composta essencialmente de água, cimento e aditivos, constituindo uma bainha ao redor do revestimento. Diversos acontecimentos como, variações de pressão e temperatura, vibrações provocadas por cargas explosivas aplicadas dentro do poço e migração de substâncias indesejáveis na interface revestimento metálico/bainha de pasta de cimento podem prejudicar a qualidade da ligação entre o revestimento metálico e a bainha de pasta de cimento. Especificamente, substâncias como cloreto de sódio (NaCl) e óleo podem se infiltrar nessa interface, interferir na aderência refletindo no funcionamento do poço. Desta forma este trabalho teve como objetivo principal investigar o comportamento da condição de aderência da interface revestimento metálico/bainha de pasta de cimento, através de testes modais. Para esta investigação foram aplicados testes modais em amostras moldadas com tubos metálicos revestidos parcialmente por uma pasta de cimento No experimento foram adotadas três condições de contato: sem substância na superfície nos tubos, com a substância NaCl na superfície dos tubos e com a substância óleo na superfície dos tubos. Foi observado que a presença dessas substâncias afetou os parâmetros modais freqüência natural e razão de amortecimento e, por conseqüência, afetou a condição de aderência. Esta última foi avaliada através do valor de constante elástica de mola (K), inserida na interface, nos modelos numéricos desenvolvidos para representar o fenômeno. Concluiu-se também que o uso desta técnica é viável para avaliação de aderência neste tipo de sistema.

Modal parameter identification of a structure is done through modal testing and modal analysis using various system identification methods. These methods employ linear input-output relationships to extract the modes of a structure. There are cases where laboratory testing of a structure is not possible or information about the structure under operating conditions is seeked. A set of techniques called Operational Modal Analysis have been developed for modal parameter identification in operating conditions of a structure. These techniques use only response measurements to extract the modes. The aim of this study is to investigate the applicability and use of three selected time-domain methods adapted to operational modal analysis. The algorithms are programmed in Matlab&copy / environment, and various cases are evaluated using computer simulations for each method. Two of the selected methods are evaluated on a laboratory scale test setup.