Chapter51 Field and Numerical Testing of the BWE SchRs4600.50 Dynamic Behavior Damian Pietrusiak, Przemysław Moczko, and Jerzy Czmochowski Abstract Surface mining machines are the largest mechanical engineering structures. Bucket wheel excavators operating in lignite mines are continually exposed to dynamic loads. Moreover, nearly all structures are over 10 years old. The methods used in design and construction did not cover the dynamic behavior of machines, which resulted in problems in their operation and decreased durability. The tendency to optimize and increase the operational time of machines is currently also visible in the field of surface mining. As a result the machines which have been operating for many years are subject to investigation. The SchRs (Schaufelradbagger auf Raupenschwenkbar) 4600.50 excavator, which is over 120 m long, 64 m high and weighs approximately 5,000 tons (excluding the dumping bridge), was investigated with regard to vibrations. Operational modal analysis was performed with 15 measurement points in different directions. This approach allowed to determine the variability of the dynamic characteristics of the machine in terms of operational conditions. Simultaneously a numerical model was prepared. Eventually, it was possible to compare and correlate both the numerical and experimental models and to establish the differences based on the operational load acting on the structure. Keywords Bucket wheel excavator • Numerical simulations • Experimental techniques • Modal analysis 51.1 Introduction The SchRs 4600.50 bucket wheel excavator (Fig. 51.1) is the largest lignite mining excavator in Poland. It is over 120 m long and 64 m high and its mass without the discharge bridge exceeds 5,000 tons. It is designed to excavate coal overburden and deposits. The 17.5 m diameter bucket wheel, powered by three 530 kW electric motors, achieves a nominal efficiency of 9;350m3=h. This particular machine has been operating for over 18 years. It is a result of the German engineering thought and was designed for the geological conditions in Germany. In Poland it was introduced in the lignite mine in Bełchato´w. The Bełchato´w power plant supplies 20 % of Poland’s electricity needs. Therefore the deposits which are excavated often require the removal of hard overburden layers, stone insertions and interlayer of cohesive rock. In consequence, the bucket wheel excavators operating in the pit are subject to dynamic loads which significantly exceed the limits allowed by the design. As a result a need arose to precisely determine the dynamic characteristics of the machine, which would help to establish its resonance range or to plan its modernization [1, 9]. Due to the fact that the machine is subject to heavy excavating and mass forces during operation, it was decided to perform experimental tests using operational modal analysis [8,10]. This approach makes it possible to establish the real dynamics of the machine, which are different while operation and in the unloaded state. Additionally a numerical model of the body was built. Based on the experimental tests the correlation between the two models was assessed depending on the operating conditions in which the modal model was identified experimentally. As a result it was possible to establish the usefulness of the numerical model [2] in calculating each particular case of loading. D. Pietrusiak ( ) • P. Moczko • J. Czmochowski Research Assistant, Institute of Machine Design and Operation, Wroclaw University of Technology, Lukasiewicza 7/9, 50-371 Wroclaw, Poland e-mail: damian.pietrusiak@pwr.wroc.pl; przemyslaw.moczko@pwr.wroc.pl; jerzy.czmochowski@pwr.wroc.pl R. Allemang et al. (eds.), Topics in Modal Analysis, Volume 7: Proceedings of the 31st IMAC, A Conference on Structural Dynamics, 2013, Conference Proceedings of the Society for Experimental Mechanics Series 45, DOI 10.1007/978-1-4614-6585-0 51, © The Society for Experimental Mechanics 2014 525
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