Chapter 19 Vibro-Acoustic Modal Model of a Traction Motor for Railway Applications Fredrik Botling, Hanna Amlinger, Ines Lopez Arteaga, and Siv Leth Abstract A vibro-acoustic modal model of a traction motor for railway applications is presented based on an experimental modal analysis of the system. Noise requirements for railway traction motors are getting more and more demanding as part of the overall levels of new rolling stock. It is therefore of great interest to understand and predict the vibro-acoustic behaviour of electromagnetic noise generated by traction motors. The modal parameters are derived from an experimental modal analysis. The primary source for the radiated sound of the tested traction motor is the radial deflections of the stator shield. The modal parameters for the radial deflections are implemented in a reduced order modal model in a state space format using Matlab/Simulink. Only the structural modes that have a match in both the frequency and the spatial domain with the excited electromagnetic force will cause important vibro-acoustic response. This makes it possible to create an accurate and efficient reduced order modal model with only a fraction of the total number of structural modes. The simulation results from the modal model are compared to measurements of operational deflection shapes and acoustic measurements of the motor. Keywords Modal analysis • Vibro-acoustics • Rotating machines • Electro-magnetic forces 19.1 Introduction Electrically driven trains are today often characterized by an annoying tonal noise which is generated during acceleration and deceleration from platforms [1, 2]. This noise is audible both for people on the platforms and passengers on the train. The focus on this issue has increased the last years, both regarding legalisation and contractual requirements but also because of expectations from citizens and travellers. The dominating acoustic noise at low train speeds (below 50 km/h) is in many cases coming from the traction motors. Three different type of noise sources can be found for electrical motors namely; aerodynamic, mechanical and electromagnetic noise. At low speed the electromagnetic noise from the electrical components on the train, especially the traction motor, can be clearly dominating since other sources on the train as the rolling noise is low at low speeds. The electromagnetic noise from traction motors are mainly generated by radial air-gap Maxwell forces that excite stator vibrations causing audible noise. To be able to design electrical and mechanical components that reduces the acoustic radiation without compromising other requirements as i.e. weight, size and efficiency requires full understanding of the process of electromagnetic noise generation. The cause of the electromagnetically generated audible noise is influenced by several different physical domains. See Fig. 19.1. • Acoustic domain • Structural domain • Electromagnetic domain F. Botling ( ) • H. Amlinger • S. Leth KTH Royal Institute of Technology, The Marcus Wallenberg Laboratory for Sound and Vibration Research (MWL), KTH Railway Group, 100 44 Stockholm, Sweden Bombardier Transportation Sweden AB, Centre of Competence Acoustics and Vibration, 722 14 Västerås, Sweden e-mail: botling@kth.se I.L. Arteaga KTH Royal Institute of Technology, The Marcus Wallenberg Laboratory for Sound and Vibration Research (MWL), KTH Railway Group, 100 44 Stockholm, Sweden © The Society for Experimental Mechanics, Inc. 2016 J. De Clerck, D.S. Epp (eds.), Rotating Machinery, Hybrid Test Methods, Vibro-Acoustics & Laser Vibrometry, Volume 8, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-30084-9_19 197
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