Identification Techniques in Rotordynamics
In order to find out the condition of a rotating machine during operation usually vibrations (output signals) are measured at specified machine locations. Indications can be determined from these signals, which allow a diagnosis of possible failures (faul
- PDF / 1,939,501 Bytes
- 24 Pages / 481.89 x 691.654 pts Page_size
- 89 Downloads / 220 Views
R. Nordmann University of Kaiserslautern, Kaiserslautern, Germany
In order to find out the condition of a rotating machine during operation usually vibrations (output signals) are measured at specified machine locations. Indications can be determined from these signals, which allow a diagnosis of possible failures (fault parameters) based on the support of expert knowledge and/or good rotordynamic models. However, the success of failure diagnostic would probably be much better, if in addition to the output signals more information would be available about rotor excitation forces. This leads to the idea of using Identification Techniques with measured input and output signals. Frequency response functions can than be calculated and an extraction of physical and/or modal parameters, expressing the actual system condition, is possible. This contribution describes the basic relations of Identification Techniques in rotordynamics, including rotordynamic models, measurement and excitation methods and parameter estimation procedures.
Some
applications of parameter identification are presented together with the corresponding test procedures and test apparatus
G. Diana (ed.), Diagnostics of Rotating Machines in Power Plants © Springer-Verlag Wien 1994
2
R. Nordmann
INTRODUCTION -DIAGNOSTICS BY MEANS OF MODELS Rotating machinery systems like turbines, pumps, compressors are used in different areas of modem technique. Users of such machines expect that they run safe and reliable and have good efficiency and high availability. In order to fulfill these requirements mechanical problems have to be considered very careful. Particularly the mechanical shaft-vibrations in connection with strains and stresses of rotating and nonrotating machine parts are of great importance for a machines life time. Bending vibrations for example are caused by unbalance, process forces or selfexcitation-mechanisms like oil-film bearings, seals, aerodynamic forces, internal friction etc. These undesired vibrations should be investigated in an early stage of the machine design. Well developed computer simulation tools are available today, in order to predict the machines dynamic behaviour and to avoid trouble after commissioning and start up. These tools are mostly based on the Finite Element Method and allow to include all important components (shaft, bearings, seals, pedestals foundations) with their corresponding mechanical effects. By simulation the following informations about the rotordynamic characteristics can be found (Fig. l ), e.g. for the case of bending vibrations: • Natural Frequencies, damping, mode shapes, stability • Unbalance Vibrations • Transient Vibrations Such results are not only important for the machine design. They can also be very helpful for an evaluation of the machines dynamic behaviour and correspondingly the machines mechanical condition during operation. Therefore it seems to be obvious to work also with a rotordynamic model as a diagnostic model in order to find out possible machine malfunctions with respect t
Data Loading...
