Keywords: rotordynamics, mass unbalance, force identification, time-domain, SWAT, ISF, DMISF.

The study of rotordynamics is essential to understand the behaviour of certain components in engineering such as pumps, compressors, turbines and generators. In the field of aeronautics, rotordynamics has a wide application in the context of aircraft engines. One of the challenges in this area is related to the identification of the forces acting in rotary systems, i.e. the ability to characterise the forces acting at a specific point of the rotating structure in what concerns its application point, amplitude and shape, using solely the measurements taken from its response. Efforts in the recent decades have been made in the sense of achieving a practical method capable of solving in a satisfactory way this type of inverse problem of dynamic systems [1,2]. Today there are various available methods in the literature that propose various force identification algorithms, showing good results for non-rotating structures.

In this paper, three time-domain force identification's methods, known by the acronyms SWAT, ISF and DMISF, are by the first time (to the authors' knowledge) applied to rotordynamics. These time-domain identifications have the advantage of allowing the determination of the amplitude and evolution of the forces acting on a given structure practically in real-time. Firstly, a short description of the dynamic behaviour of rotors is given, after which the above mentioned methods are briefly presented. These methods are then adapted to be numerically applied to a simple rotor configuration rotating at constant speed with a given mass unbalance. A comparison of the results from the three methods is presented and some conclusions are drawn. In the rotor application example the SWAT method presented some values of the force estimation curve higher than the measured ones while the opposite was demonstrated by the ISF and DMISF results.

The authors had found difficulties in the application of the DMISF method in this specific example in comparison with the ISF example. Stable results were obtained in every method applied to the rotor, making time-domain force reconstruction methods a valid option for constant spin speed rotors [3].

1

K. Stevens, "Force Identification Problems - An Overview", Proceedings of the 1987 SEM Spring Conference on Experimental Mechanics, 838-844, 1987.

2

M.S. Allen, T.G. Carne, "Delayed, multi-step inverse structural filter for robust force identification", Mechanical Systems and Signal Processing, 22, 1036-1054, 2008. doi:10.1016/j.ymssp.2007.11.022

3

P. Paulo, "A Time-Domain Methodology For Rotor Dynamics: Analysis and Force Identification", Instituto Superior Técnico, Lisbon, MSc thesis, October 2011.

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