Discussion of Induction Motor Effect on Rotordynamics

In this dissertation, the influence of using induction motor in machinery train on rotordynamics is discussed. Two areas are considered – the use of variable frequency drives (VFDs), which control and drive the induction motor; and the unstable forces due motor eccentricity, which is resulted from motor rotor lateral motion. VFDs – The dissertation documents fatigue related mechanical failures in VFD motor machinery due to mechanical vibrations excited by drive torque harmonics which are created by PWM switching. Present effort models the coupled system with full electrical system including DC bus, inverter, motor, and an industrial mechanical system including flexible couplings, gearboxes and multiple inertias. The approach extends failure prediction beyond simple occurrence of resonance, to fatigue life evaluation based on Rain-flow algorithm, which is suitable for both steady state and transient startup mechanical response. The use of multilevel inverters is demonstrated having the possibility actually exacerbate resonance and fatigue failure. The model is also compared to an industrial test case, which provides good agreement. Motor eccentricity – In this dissertation, a MEC modeling method is proposed to calculate both the radial and tangential motor eccentric force. The proposed model is also coupled with the motor electric circuit model to provide capability of transient simulation. FEM (Ansys Maxwell) is used to verify the proposed model. Parametric study is performed on the motor radial and tangential eccentric forces. Also a Jeffcott rotor model is used to study the influence of the motor eccentric force on mechanical stability. A stability criteria of the bearing damping is calculated. The motor radial and tangential eccentric forces are all curved fitted to catch their nonlinearity, which are used in time domain simulation. Nonlinear motions are observed, including limit cycle and jumping phenomena. The results of this dissertation show that both the use of VFDs and the motor lateral motion (motor eccentricity) can cause severe mechanical vibration problem in a rotating machinery train. Both of these two problems need to be carefully concerned in design stage

SIRM 2017

This volume contains selected papers presented at the 12th International Conference on vibrations in rotating machines, SIRM, which took place February 15-17, 2017 at the campus of the Graz University of Technology. By all meaningful measures, SIRM was a great success, attracting about 120 participants (ranging from senior colleagues to graduate students) from 14 countries. Latest trends in theoretical research, development, design and machine maintenance have been discussed between machine manufacturers, machine operators and scientific representatives in the field of rotor dynamics. SIRM 2017 included thematic sessions on the following topics: Rotordynamics, Stability, Friction, Monitoring, Electrical Machines, Torsional Vibrations, Blade Vibrations, Balancing, Parametric Excitation, and Bearings. The papers struck an admirable balance between theory, analysis, computation and experiment, thus contributing a richly diverse set of perspectives and methods to the audience of the conference

"Analysis of dynamic responses and instabilities in rotating machinery\u201d

The first task of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., micro Gas Turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed, and the performance of its bearings were investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial Rotor Kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for ThermoElasto-HydroDynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this work, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RK, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results. The second main task of the present work is the development and the implementation of a suitable analytical model to correctly capture rolling bearing radial stiffness, particularly nearby the critical speeds of the investigated rotor-bearings system. In this work, such bearing non-linear stiffness lumped parameter model is firstly validated on the commercial RK and then it is applied to both air bladeless turbines (or Tesla turbines) and to an innovative microturbine, in order to assess their global rotodynamic behavior when they are mounted on ball bearings. In order to properly investigate all the issues related to critical speeds and stiffness, an adequate number of experimental tests was performed by exploiting an experimental air Tesla turbine prototype located at TPG experimental facility of the University of Genoa. The correlation between measured flexural critical speeds and their numerical predictions is markedly conditioned by the correct identification of ball bearings dynamic characteristics; in particular, bearings stiffness effect may play a significant role in terms of rotor-bearings system natural frequencies and therefore it must be properly assessed. Indeed, Tesla turbine rotor FE model previously employed for numerical modal analysis relies on rigid bearings assumption and therefore it does not account for bearings stiffness overall contribution, which may become crucial in case of \u201chard mounting\u201d of rotor-bearings systems. Subsequently, high-speed air Tesla rotor is investigated by means of an enhanced FE model for numerical modal analysis within Ansys\uae environment, where ball bearings are modelled as non-linear springs whose stiffness is expressed according to the analytic model implemented in Matlab\uae. Two different numerical FE models are devised for microturbine rotor modelling which respectively rely on beam elements and on three-dimensional solid elements for mechanical system spatial discretization. The obtained results in terms of rotor-bearings system modal analysis exhibit an improvement in experimental-numerical results correlation by relying on such ball bearing stiffness model; moreover, beam-based FE model critical speeds predictions are coherent with experimental evidence and with respect to solid elements model it is characterized by lower computational time and it is more easily interpretable. Thus, such experimentally validated numerical model represents a reliable and easily adaptable tool for highspeed rotating machinery critical speeds prediction in practical industrial application cases. Finally In this work, several signal processing techniques performed on vibro-acoustic signals acquired from a T100 Turbec microturbine (which is furnished with a centrifugal compressor) are illustrated. Research activity goal focuses on the investigation different kinds of system response starting from non-intrusive probes signals like accelerometers and microphones; this is made by means of techniques such as HOSA and Wavelet Transform, developed in Matlab\uae environment, for early detection of the onset of unstable phenomena in centrifugal compressors. These new and different methods have been applied to the same set of data to get sufficiently independent information useful to synergistically improve knowledge in the diagnostic system. Data were acquired by means of an experimental facility based on a T100 turbine developed by the Thermochemical Power Group (TPG) at the University of Genoa. Sampling rate and sensor placement were carefully taken into account, basing both on the physical phenomena to be observed and on the sensor dynamic characteristics. In this context, it is meant to study microphones and accelerometers signals not from an isolated centrifugal turbomachine installed in a dedicated line, but from a whole compressor placed in a mGT system for energy generation. Indeed, the investigated machine is not operating in standalone mode, but its working point and angular velocity depend on the coupling with several elements. In particular, compressor working point and then its vibro-acoustic signals are expected to convey vibration and sound contributions coming from all the plant components; thus, they are more representative of machine realistic behavior in the energy system

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction

Rotordynamic Instability Problems in High-Performance Turbomachinery

Diagnostic and remedial methods concerning rotordynamic instability problems in high performance turbomachinery are discussed. Instabilities due to seal forces and work-fluid forces are identified along with those induced by rotor bearing systems. Several methods of rotordynamic control are described including active feedback methods, the use of elastometric elements, and the use of hydrodynamic journal bearings and supports

Vibration exciting mechanisms induced by flow in turbomachine stages

The quasisteady computer analysis of the perturbated centrifugal impeller passage flow was reviewed. A total of 115 stage calculations were used to define the fluid damping coefficient, delta sub fluid. Results indicate that the average total damping coefficient per stage needed for stability is delta sub total 1.85

Stability evaluation of rotor/bearing system

A stability study of rotor/bearing systems is presented. Even though it was limited to study of a fully lubricated bearing subject to oil whirl, and further limited to low eccentricity region for linearity and with only one type of lubricant, it can be seen that the perturbation methodology, together with the sorting of the impedance terms into direct and quadrature with respect to input force can be very useful to the general study of stability. Further, the concept of active feedback should assist to increase knowledge in rotor system stability. While there remains a large amount of study to be accomplished, perhaps some more tools are available to assist this field of analysis

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction