Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
EXPERIMENTAL MODAL ANALYSIS APPLIED TO A FOUNDATION STRUCTURE
Submission Author:
Leonardo Gusmão , SP
Co-Authors:
Leonardo Gusmão, Tiago Machado
Presenter: Leonardo Gusmão
doi://10.26678/ABCM.COBEM2021.COB2021-0190
Abstract
This work details the procedure of experimental modal analysis of a metallic structure, used as foundation of a rotating system. The procedure was carried out with the structure arranged in different configurations, in order to define the reliability of the methodology used, as well as the influence of the addition of several attachments to the structure, such as bearing housing and metal beams. Regarding the extraction of modal parameters, it is necessary to emphasize the importance of some steps, such as, structure marking, positioning of accelerometers and definition of modal nodes. After marking the structure and fixing the accelerometers, all points on the structure were excited using an impact hammer. The later phase, or data pre-processing, grouped all the information about the structure geometry and the positioning of accelerometers, since the adopted spatial geometrical reference must be used in all steps of the process. As the used accelerometers are uniaxial, this step is also important to define the modal nodes by grouping information from three accelerometers fixed in different directions. The modal parameters were obtained using the Matlab® modalfit function. This function uses the system's frequency response functions, giving the possibility to choose the type of methodology for extracting the modal parameters. Finally, with the use of a Matlab® plugin software called EasyANIM, it was possible to visualize the respective modal shapes of the structure. This plugin, through information on the structure geometry and its modal parameters, is capable of graphically displaying the modal shapes of the analyzed modes by each accelerometer. The procedure employed in this study proved to be effective and reliable in obtaining the modal parameters of a metallic foundation structure. The study allowed to infer that the increase in the stiffness of a foundation structure impacts on the increase of its natural frequencies. The same happens when comparing the natural frequencies of a free and clamped structure. In relation to the modal shapes, when elements of complex geometry are added to the structure, combinations of the modal shapes of the foundation occur with such elements. The change in mass and stiffness, through the addition of metal beams to the foundation, promotes an increase in stiffness in the longitudinal direction of the structure, impacting both the modal shapes and the first natural frequency. Another significant contribution of this work is the documentation of experimental procedures.
Keywords
Rotordynamics, Modal Parameters, : Experimental modal analysis, support structures
