Machine Dynamics - Acoustics

Head of Department: Dr.techn. Andreas Marn

General machine dynamics and acoustics

Machine dynamics deals with the external and internal forces that work in machines as well as the vibration processes in the entire field of mechanical engineering. Computation of vibration modes, journal bearing damping and amplitude calculations are the main means for secure vibration tuning to avoid resonances and overstrain in machine elements.

Non-linear elements like the oil film in journal bearings represent the greatest computational difficulty. But currently, it is possible to predetermine the entire oscillation behavior and the sound radiation of a diesel engine with numerical methods. The same applies to the quietness and the vibration safety of the rotors and turbine blades, and for short-circuit resistance of the turbo sets.

However, appropriate experiments are necessary in the case of complicated forms of vibration behavior as well as damping parameters. The research works of the institute deal with short-circuit states in turbo sets, rotor dynamics and internal shaft cooling of high frequency motors, vibrations and functional behavior of string stranding machines, calculations of vibrating foundations, functional behavior and vibration behavior of rock milling, study of the sound radiation from power plant components and sound attenuation by active sound control as well as the reduction of sound radiation of vibrating surfaces.

The institute has a test rig (STTF) where the flow phenomenon and vibration behavior of rotor and blades may be tested under appropriate conditions. With rotor dynamic monitoring devices these processes can be analyzed and so, comparison of the measurements with computational solutions are possible. In this way, required improvements in the analytical models for vibration monitoring in rotating machines and diagnostic methods is made possible. As a result vibration reduction can be achieved and therefore service life and safety can be increased. Additionally, possibilities for an effective noise control can be found.

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Rotor dynamics in steam and gas turbines, turbo compressors and other turbomachinery

Rotor dynamic investigations to predict the behavior of large and fast running rotors that provide an exact description of the properties of the bearings are inevitable. They help to ensure low shaft vibration amplitudes and to secure the safe operation of blading with very narrow clearances, as generally is the case.

Stability issues arise due to oil film instability or fluid flow clearance instability. Also proper running of rotors has to be ensured with special designs such as squeeze film damped roller bearings, which are applied to jet engines and modern power plants. Computer programs for the simulation of these rotor dynamic effects have been developed and successfully applied by the institute and also investigations regarding disc vibrations have been conducted in cooperation with the industry.

Another part of this work area is concerned with the torsional vibrations which may happen when synchronizing large power shafts and especially during short circuit which result in large exciting electrical moments causing torsional vibrations being transmitted through the shafts of steam and gas turbine plants. Especially fast running steam and gas turbines with gears in the shaft train pose a difficult problem since non-linearity due to the clearances in gears and couplings have to be properly accounted for. By automatic synchronization, the action of governing systems causes quick actions and response of shafts which have to be investigated and simulated in the course of torsional vibrations. The institute has an intensive cooperation not only with machine building industry but also with owners of power stations especially regarding the question of resistance to short circuits, which requires intensive calculations in order to supply the safety and security of operation.

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Contact
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Institute of Thermal Turbomachinery and Machine Dynamics

Graz University of Technology
Inffeldgasse 25/A
A-8010 Graz

Tel: +43 (0)316 873 - 7226
Fax: +43 (0)316 873 - 7239
ttmnoSpam@tugraz.at