Operational modal analysis application to support structure identification under rotating machinery unbalance

Author(s)

Saint Martin, Leonardo B. ^[1] ; Gusmao, Leonardo L. ^[1] ; Machado, Tiago H. ^[1] ; Okabe, Eduardo P. ^[2] ; Cavalca, Katia L. ^[1]

Affiliation

^[1] Univ Estadual Campinas, Lab Rotating Machinery, Sch Mech Engn, 200 Mendeleyev St, BR-13083860 Campinas, SP - Brazil

^[2] Univ Estadual Campinas, Sch Appl Sci, 1300 Pedro Zaccaria St, BR-13484350 Limeira, SP - Brazil

• Document type: Journal article
• Source: ENGINEERING STRUCTURES; v. 249, DEC 15 2021.
• Web of Science Citations: 0

Abstract

Rotating machines are an essential part of the majority of the power plants. They have to be extremely reliable to avoid power outages, therefore, it is important to predict and monitor their behavior. It is known that these machines are affected by their support structure, thus it is essential to identify its dynamic behavior. The modal analysis is essential in this task being able to identify modal parameters such as natural frequencies, vibrating modes, natural damping, modal stiffness and modal mass. One of the main challenges is to perform this analysis in the rotating machines during their operation. To do this a technique called Operational Modal Analysis (OMA) can be adopted. This technique is performed with the response of the structure subjected to the inherent excitation of the machine operation and is commonly applied to structures and equipment that cannot be turned off due to the high operating costs involved in such process. Contrary to the Experimental Modal Analysis (EMA), where the excitation has to be measured to obtain the frequency response functions (FRFs), in the OMA techniques only outputs are taken into account. OMA usually demand a long time to acquire all the data, which sometimes takes days or weeks. One way to render it faster, it is using the machine start (ramp-up) as an excitation source. Thus, the main objective here is to apply an OMA approach to a rotating system using the ramp-up excitation aiming to extract the modal parameters of the support structure. In order to ensure the validation of the applied OMA methodology, a comparison with a traditional EMA technique is also carried-out. Accelerometers, mounted on the bearings' housings and on the supporting structure of a test rig, are used to perform the analysis. It is shown that is possible to obtain a good estimative of the modal parameters of the analyzed structure using OMA techniques near the excitation operation range, even when using a reduced set of sensors. (AU)

• FAPESP's process: 15/20363-6 - Fault tolerant identification and control of rotating systems
• Grantee: Katia Lucchesi Cavalca Dedini
• Support Opportunities: Research Projects - Thematic Grants