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ANALYSIS ON ROTOR DYNAMICS 1 2 3 Shaft Model The most common and also most relevant dynamic analysis of turbomachinery deals with lateral shaft deflections. FE model of Centrifugal Compressor Shaft. A finite element model of the shaft is based on drawings or measurements. Ideally, the model is verified by comparing calculated free-free natural frequencies with impact test results. ODS deals with complex structural issues, such as: • Multi-layered shafts with internal degrees of freedom • Internal friction in shrink fits and material hysteresis • Arbitrary flexible elements (impellers, thrust disk, blades, etc.) Bearings and Seals The dynamic properties of bearings and other interaction forces between rotor and stator are equally important to predict critical speeds, damped natural frequencies and rotor dynamic stability margin (logarithmic decrement) correctly. ODS’s expertise therefore includes: • Journal bearings (sleeve, tilting pad, rolling element, magnetic, active lubrication, etc.) • Squeeze film damper bearings • Thrust bearings • Seals (labyrinth, honeycomb, wet, etc.) and other narrow internal clearances • Impeller/diffuser interaction • Pedestal and foundation flexibility Finite element model used to predict taper of division wall and centre honeycomb seal in back-to-back centrifugal compressor. Rotordynamic stability margin of centrifugal compressor as function of honeycomb seal taper A machine could have a critical speed in the operating speed range and run successfully for years before trouble is encountered. A rotor dynamic study that considers the entire range of possible values for bearing and seal parameters, shaft unbalance, process conditions, etc. will usually show the cause and remedy of the problem.