[pt] A Dissertação aqui apresentada descreve um acidente em um rotor de máquina de grande porte (compressor de ar) de uma fábrica de fertilizante cujas conseqüências foram perdas financeiras de alta monta tanto para a empresa quanto para o Estado, pela importância econômica onde a fábrica é situada. O objetivo da Dissertação foi simular matematicamente o acidente ocorrido e esclarecer o mesmo. Para se chegar ao diagnóstico do problema se modelou o rotor e o discretizou pelo Método de Elementos Finitos. As técnicas de investigação do problema e a sua seqüência de investigação podem ser tomadas como base em investigação de eventuais acidentes envolvendo rotores futuramente. O capítulo relativo a Análise Modal será extraído como base de apostila para curso envolvendo pessoal da área de Manutenção Mecânica. / [en] A problem related with an air compressor gave birth to the MSc Thesis. Problems related with rotative machines are usual in the industrial field. Difficulties come from the data gathering in order to analyze, and propose a theory of failure in order to explain and avoid the recurrence of such problem. Modelling a rotor with a Timoshenko beam element and the discretization by finite element method permit the dynamical analysis and the modal analysis of the rotor considering its interaction with the radial and thrust bearings (assuming stiffness and rigidity). The work is divided in seven chapters: chapter one introduces the work and gives the overview of it; chapter two describes the industrial problem; chapter three is a brief explanation of bearing types and the fundamental principle of lubrication; chapter four introduces vibration theory and modal analysis; chapter five introduces the finite element method; chapter six is the simulation of the problem, using tailor-made MATLABr programs to reconstruct the problem and to compare the test field results with the here mentioned formulation; chapter seven discusses the results and proposes future works. Appendix shows the kinetic theory and the beam deformation model used in the program and the Laval simple rotor as a limited description of the dynamic of a rotor with distributed mass, rigidity and stiffness. The aim of this work is to help understand and avoid the recurrence of the failure described and to easy the understanding of modal analysis for new engineers and technicians which will deal with rotor dynamics.