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1.4 Softwares for Rotor Dynamics Analysis: World War II can be considered as the demarcation between the early stages of rotor dynamics and what might be called modern rotor dynamics. In the 1960s there was a coalescence of numerical methods applied to structural dynamics and of digital computer capacity that fostered the development of a series of general purpose computer codes. The initial application of these codes to rotor dynamics was based on the TMM method but in the 1970s another underlying algorithm, the FEM, became available for the solution of the prevailing beam-based models.
Now, in the beginning of the 21st century, rotor dynamicists are combining the FEM and solid modeling techniques to generate simulations that accommodate the coupled behavior of flexible disks, flexible shafts and flexible support structures into a single, massive, multidimensional model. Crandall (1992) gave an overview of the rotor dynamic computer codes (e.g. ANSYS, ARMD, CADENSE, ComboRotor, DYNAMICS R4, DyRoBeS, iSTRDYN, MADYN, NASTRAN ROTORDYNAMICS, RAPPID-RDA, RODYN, ROMAC, ROTECH, RSR, SAMCEF, TURBINE-PAK, VT-FAST, XLRotor, XLTRC4, etc.).
He also concluded that with regards to quality and quantity of software the specialised area of rotor dynamics still lags behind the broader field of non-rotating structural dynamics. Modern computer models have been commented on in a quote attributed to Dara Childs, 'the quality of predictions from a computer code has more to do with the soundness of the basic model and the physical insight of the analyst. Superior algorithms or computer codes will not cure bad models or a lack of engineering judgment.' 1.5 Dynamic Balancing of Rotors: The most important and fundamental procedure to reduce unfavourable vibrations is to eliminate geometric unbalance in the rotor. The balancing procedure for a rigid rotor was established relatively early. The arrival of high-speed rotating machines made it necessary to develop a balancing technique for flexible rotors.
Two representative theories were proposed for flexible rotors. One was the modal balancing method proposed in the 1950s by Federn (1957), and Bishop and Gladwell (1959). The other is the influence coefficient method proposed in late 1930s by Rathbone (1929), and later by Thearle (1932) and developed mainly in the Unites States along with the progress of computers and instruments for vibration measurements (Wowk, 1995; Darlow, 1989). Modern methods based on FEM requires good model of the rotor-bearing-foundation systems along with startup/rundown data, and hence the trend is to couple the estimation of unbalnce along with the bearing and foundation dynamic parameters (in which the modelling error is large) subject to minimum number of rundowns (Edwards, et al., 1998; Tiwari et al., 2004). 1.6 Condition Monitoring of Rotating Machineries: Another area in which lot of development took place is on assessment of turbomachinery condition monitoring and failure prognosis technology (Mitchell, 1993). High-performance turbomachines are now extremely important elements of worldwide industry.
The electric power, petrochemical, mining, marine, and aircraft industries are prime examples for which turbomachinery is crucial to business success (Fig. Condition monitoring involves the continuous or periodic assessment of the condition of a plant or a machinery component. Basically condition monitoring is the process of monitoring some parameters from the machinery, such that a significant change in the parameter can give information about the health of the machinery. Noise and vibration signal from machine can contain vital information about the internal process and can provide valuable information about a machine running condition. Noise signal are measured in a reason proximity to the external surface of the machine while vibration signals are measured on the surface of the machine. Most noise and vibration analysis instruments utilize a Fast Fourier Transform (FFT) which is a special case of the generalized Discrete Fourier Transform (DFT).
According to Eshleman (1990), over the past several years, instrumentation and monitoring capabilities have increased dramatically, but techniques for fault diagnosis have evolved slowly. The tools are therefore still more advanced than the techniques. Edward et al.
(1998) provided a broad review of the state of the art in fault diagnosis techniques, with particular regard to rotating machinery. Special treatment was given to the areas of mass unbalance, bowed shafts, misalignments, and cracked shafts, these being amongst the most common rotor-dynamic faults. Vibration response measurements yield a great deal of information concerning any faults within a rotating machine. Cracks in shafts have long been identified as factors limiting the safe and reliable operation of turbomachines. They can sometimes result in catastrophic failure of equipment (rotor bursts) and, more often, in costly process upsets, repairs and premature scrapping and replacement of equipment.
In the past two decades, much research and many resources have gone into developing various on-line (Fig. 1.11) and off-line (Fig. 1.12) diagnostic techniques (expert systems) to effectively detect faults before they cause serious damage (e.g., Bently Nevada, ozWatch, SV3X). The expert system uses the probability table such as compiled by Sohre (1991).
SERVICES. Technical consulting in rotor dynamics. Design of rotor-bearing structures. Dynamical analysis of rotor-bearing structures. Design of the non-standard and unique experimental equipment for rotor-bearing structures. Development of vibration diagnostic and condition monitoring systems for gas turbine engines.
Special software in rotor dynamics of turbomachinery - programming and development. Engineers training in rotor dynamics. Students training in rotor dynamics. Training in rotor dynamics field.