The active magnetic bearing (AMB) is a relatively new technology which has many advantages compared with conventional bearing design. In an AMB system, the rolling-element back-up bearings are indispensable to protect the magnetic bearing rotor and stator, and other stationary seals along the rotor shaft. In this paper, a theoretical formulation is proposed and solved numerically to examine the transient response of the flexible rotor, from the time just previous to the AMB shuts down and including the rotor drop onto the back-up bearing. The backward whirl of the rotor, which may lead to the destructive damage of the machinery, has been analytically predicted at very light support damping and very high support damping. Also, the vibration due to the non-linearity of the contact point geometry has been included in the analysis. The influence of the support damping on the displacement of the disk and also the contact force between the journal and the inner-race of the back-up bearing have been computed for various rotor system parameters. By comparing these results with the optimum support damping for the simple flexible rotor model, it is shown that this support damping optimization can be applicable for specifying the required optimum range of support damping for the back-up bearings of AMB systems. / Master of Science

The need for better performance of turbomachinery with active magnetic bearings has necessitated a study of such systems for accurate prediction of their vibrational characteristics. This research presents a modification of existing transfer matrix methods for rotor analysis, to predict the response of rotor systems with active magnetic bearings. The position of the magnetic bearing sensors is taken into account and the effect of changing sensor position on the vibrational characteristics of rotor systems is studied. The modified algorithm is validated using a simpler modified Jeffcott model. The effect of changing from a rotating unbalance excitation to a constant excitation in a single plane is also studied. An eight-stage centrifugal compressor rotor is analyzed using the modified transfer matrix code. The results for a two-mass Jeffcott model are presented as plots of critical frequency vs. sensor position and amplitude at critical frequency vs. sensor position. Plots of amplitude vs. frequency and phase angle vs. frequency for different cases of sensor location are also presented. The results obtained by analyzing this two-mass model with the modified transfer matrix method have been compared with the results of the modified Jeffcott analysis for the purpose of verification. Also included are plots of amplitude vs. frequency and phase angle vs. frequency for the eight-stage centrifugal compressor rotor. These plots will demonstrate the significant influence that sensor location has on the critical frequencies and the amplitudes at the critical frequencies of the rotor system. / Master of Science

M. Tech. (Mechanical Engineering) Vaal University of Technology / Monitoring the condition of equipment in industry is very important to prevent unplanned breakdowns and to prolong their life. This is necessary, since it is not always economically viable to stop equipment at regular intervals to do maintenance. Failure on machines can lead to high repair costs and production losses. It is thus of paramount importance that early failure symptoms be identified by means of condition monitoring. This study in the field of condition monitoring is performed to determine if the mechanical shock values induced in defect bearings could be used to measure the condition of a bearing while operating under variable speed and variable load. Variable speed and variable load is becoming more popular in industry because variable speed drives applications ensure effective process control. Variable speed application, cause fault frequencies to fluctuate and therefore vibration applications for constant speed applications, which are speed-dependent, can no longer apply. Vibration-monitoring techniques that have applied for many years have now become obsolete in these variable speed applications. Methods such as Short Time Fourier Transformation (STFT), time scale like wavelet transform, and Order tracking has been applied in variable speed applications with some success. These methods analyses the vibration phases on the signal buy compensating for the speed changes. In this thesis, the Shock pulse method is selected as the analyses tool to measure the mechanical shock. Shock pulse monitoring does not focus on the vibration phases but measures in a small-time window when mechanical shocks are induced in the bearing material before the vibration phase. There is very little documented research in the field of mechanical shock pulse monitoring for conditions of variable speed and variable loads, and therefore this research focuses on recording these mechanical shock values by empirical tests. The tests were performed on a bearing with an induced defect on the outer race. The rolling element of the bearing strikes the defect and the mechanical shock value (dBsv) is measured. The mechanical shock is measured with the Shock pulse method in a small-time window before vibration occurs. In this time window, the dBsv is recorded over time to provide diagnostic information of the bearing during acceleration, deceleration and various loading conditions. These mechanical shocks are elastic waves that mirror the impact-contact-force's time function and the Shock pulse monitoring accelerometer, which is tuned to 32 kHz, will respond to the elastic wave fronts with transient amplitudes proportional to the square of the impact velocities. The mechanical shock values were analysed and reoccurring fault levels were identified on each empirical test. These recurring events from the empirical tests were used as primary data for analysis in this research. These tests were performed on a bearing with an induced failure and it was found that the dBsv measured over time could not be used to monitor the condition of the bearing under variable speed applications. This was because the dBsv changed as the speed increased. To overcome this problem Sohoel’s theory was applied and the initial mechanical shock value (dBi) was calculated for the bearing. The dbi value was subtracted from the dBsv and a value called the maximum mechanical shock value (dBm) was obtained. The dBm values stayed constant for the duration of the test and this allowed the condition of the bearing to be measured under variable speed and variable load conditions with some exception. The exception to the findings was that the dBm values stayed constant during acceleration phases, but during the deceleration phases the values were erratic and scattered. At speed below 200rpm the dBm values did not stay constant and therefore it was concluded that the dBm value recorded the best results only when thrust on the bearing was maximum. The other exception was under no-load conditions. The values were erratic and scattered, and therefore the results were not a true reflection of the bearing condition. The third exception was that the results on bearings with various loads remained constant during increased load changes unless the loading was erratic. During erratic load changes, the results were affected. The results also indicated that the larger the defect on the bearing raceway, the higher the dBm values were. Multipil defects on the bearing race ways were not part of this thesis and this gives an opertunity for futher research. The Shock pulse monitoring technique was 100% successful in monitoring the bearing condition only while the speed of the bearing was increasing. The results obtained in this work demonstrated that the condition of bearings can be monitored in applications of variable speed and variable load if the exception are eliminated and to obtain conclusive results the mechanical shock pulses should be measured over time and not be used as once-off value.

Cam follower systems are generally designed to operate at a fixed speed or a range of fixed speeds. However manufacturing defects, wear, or a change of design goals may require altering the camshaft speed to produce a follower trajectory which is not possible using a fixed speed. The follower trajectory may also be optimized for some performance criteria such as minimizing vibration and wear. Like most real world systems, the differential equations governing a cam follower system are nonlinear. A common approach for controlling a nonlinear system is to first linearize the system about a nominal operating point, then apply linear control laws. In many cases, such as the cam follower system, one can create a trajectory and numerically solve the nonlinear system for the inputs required to follow it. Linearizing about this solution creates a linear time varying system whose states are deviations from the desired solution. The speed trajectory in the cam follower system is periodic, which results in a linear system with periodic coefficients. Repetitive control creates control systems that aim to converge to zero tracking error following a periodic command, or aim to completely cancel the effects of a periodic disturbance. Using the inverse of the steady state frequency response as a compensator has been shown to be very effective for linear time invariant systems. That idea is applied here to linear time periodic systems. The periodic state matrices lend themselves well to frequency domain representations, which can be used to construct a matrix form of the steady state frequency response. The first law studied in this work analyzes a moving window implementation which monitors the output errors and previous commands to create an update to the change in the command for the current time step using the inverse of the steady state frequency response matrix. Asymptotic convergence conditions for zero tracking error are derived. When the number of samples in one period is not an integer number, the moving window method is not feasible without interpolation. Therefore a second method based on the projection algorithm from adaptive control is developed and analyzed. In linear constant coefficient systems, one generally needs to incorporate a frequency cutoff filter to robustify to high frequency model error. The additional intricacies of designing a cutoff filter for periodic systems is considered, aiming to handle the fact that for periodic coefficient systems, addressing error components below the intended cutoff can excite harmonics above the cutoff. The control laws developed in this work are applicable to any nonlinear system which may be linearized about a periodic trajectory. Development of these control laws is motivated by improving the performance of a cam follower system. Additional improvements in cam follower behavior can be done through parameter optimization. This includes optimizing a nonlinear follower spring such that it provides just sufficient force to maintain contact while reducing the load on the cam.

Vibration signals generated from spalled elements in rolling element bearings (REBs) are investigated in this thesis. A novel signal-processing algorithm to diagnose localized faults in rolling element bearings has been developed and tested on a variety of signals. The algorithm is based on Spectral Kurtosis (SK), which has special qualities for detecting REBs faults. The algorithm includes three steps. It starts by pre-whitening the signal's power spectral density using an autoregressive (AR) model. The impulses, which are contained in the residual of the AR model, are then enhanced using the minimum entropy deconvolution (MED) technique, which effectively deconvolves the effect of the transmission path and clarifies the impulses. Finally the output of the MED filter is decomposed using complex Morlet wavelets and the SK is calculated to select the best filter for the envelope analysis. Results show the superiority of the developed algorithm and its effectiveness in extracting fault features from the raw vibration signal. The problem of modelling the vibration signals from a spalled bearing in a gearbox environment is discussed. This problem has been addressed through the incorporation of a time varying, non-linear stiffness bearing model into a previously developed gear model. It has the new capacity of modeling localized faults and extended faults in the different components of the bearing. The simulated signals were found to have the same basic characteristics as measured signals, and moreover were found to have a characteristic seen in the measured signals, and also referred to in the literature, of double pulses corresponding to entry into and exit from a localized fault, which could be made more evident by the MED technique. The simulation model is useful for producing typical fault signals from gearboxes to test new diagnostic algorithms, and also prognostic algorithms. The thesis provides two main tools (SK algorithm and the gear bearing simulation model), which could be effectively employed to develop a successful prognostic model.

Vibration signals generated from spalled elements in rolling element bearings (REBs) are investigated in this thesis. A novel signal-processing algorithm to diagnose localized faults in rolling element bearings has been developed and tested on a variety of signals. The algorithm is based on Spectral Kurtosis (SK), which has special qualities for detecting REBs faults. The algorithm includes three steps. It starts by pre-whitening the signal's power spectral density using an autoregressive (AR) model. The impulses, which are contained in the residual of the AR model, are then enhanced using the minimum entropy deconvolution (MED) technique, which effectively deconvolves the effect of the transmission path and clarifies the impulses. Finally the output of the MED filter is decomposed using complex Morlet wavelets and the SK is calculated to select the best filter for the envelope analysis. Results show the superiority of the developed algorithm and its effectiveness in extracting fault features from the raw vibration signal. The problem of modelling the vibration signals from a spalled bearing in a gearbox environment is discussed. This problem has been addressed through the incorporation of a time varying, non-linear stiffness bearing model into a previously developed gear model. It has the new capacity of modeling localized faults and extended faults in the different components of the bearing. The simulated signals were found to have the same basic characteristics as measured signals, and moreover were found to have a characteristic seen in the measured signals, and also referred to in the literature, of double pulses corresponding to entry into and exit from a localized fault, which could be made more evident by the MED technique. The simulation model is useful for producing typical fault signals from gearboxes to test new diagnostic algorithms, and also prognostic algorithms. The thesis provides two main tools (SK algorithm and the gear bearing simulation model), which could be effectively employed to develop a successful prognostic model.

Submitted by Eduardo Murbach Junior null (emurbach@yahoo.com.br) on 2016-04-26T01:22:34Z No. of bitstreams: 1 Avaliação de Ciclo de Vida em Processo de Fabricação de Rolamento.pdf: 4713134 bytes, checksum: a227fc8fe662842ed31c722e2242c43e (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-28T12:20:12Z (GMT) No. of bitstreams: 1 murbachjunior_e_me_bauru.pdf: 4713134 bytes, checksum: a227fc8fe662842ed31c722e2242c43e (MD5) / Made available in DSpace on 2016-04-28T12:20:12Z (GMT). No. of bitstreams: 1 murbachjunior_e_me_bauru.pdf: 4713134 bytes, checksum: a227fc8fe662842ed31c722e2242c43e (MD5) Previous issue date: 2016-02-23 / Este trabalho se propôs a realizar Avaliação de Ciclo de Vida em Processo de Fabricação de Rolamento de Agulhas, com intuito de identificar impacto ambiental nas etapas do processo de fabricação para eventual direcionamento de ações de melhorias em ternos ambientais, produtivos, e a título informativo. Foram mapeados processos de fabricação dos componentes do rolamento: anel interno, gaiola plástica de agulhas, agulhas e montagem. Os processos de fabricação apresentaram impactos ambientais nas categorias de combustíveis fósseis, respiráveis inorgânicos, alterações no clima, uso da terra, carcinogênicos, acidificação, ecotoxicidade e minerais, utilizando-se software SimaPro® e o método Eco-Indicator 99. Houve a identificação dos impactos ambientais provenientes de cada etapa do processo de fabricação de forma individual e global. / This scientific research offered to perform Life Cycle Assessment in Needles Bearing Process Manufacturing, with focus to identify environmental impacts in process manufacturing steps to eventual guidance of environmentally improvements actions, productivity, and informative notice as well. Manufacturing process components’ were identified inner ring, plastic cage, needles. The manufacture process presents environmental impacts in categories of fossil fuels, inorganic respirable, climate change, land use, carcinogens, acidification, ecotoxicity, minerals, according to software SimaPro® and method Eco-Indicator 99. The environmental impacts were identified concern to each manufacture process steps as individual and global conception.

The current development in the field of electric machinery is focusing on high-speed electric machines. This opens also other fields related to high-speed machines. One of them are magnetic bearing systems. Tradition approach of using ball bearing brings a few problems in design dealing with friction at high speeds. Together with magnetic bearings, development is their control. Faster chips opened a new way of thinking of control and helped to evolve robust control loops. The biggest advantage of magnetic bearing is non-friction run and almost no maintenance. Compare to traditional ball bearing, a magnetic bearing system needs more space and in some applications could happen that the shaft will be twice as long. This problem can be solved designing complex system with motor and integrated magnetic bearing what leads to downsizing. In this master thesis, the design of magnetic bearing for 12kw, 45000rpm is discussed. It focuses on practical design and correlations between parameter selection. The analytical approach is used to sketch the design and optimization is done afterwards. Problem with an analytical design is that it doesn't cover all parasitic phenomenae and thus numerical modelling snd optimization are demanded. Also, the critical speed analyze is included in this thesis. The results of the work will be used for manufacturing prototype as an extension to the existing high-speed machine.

Thesis. (M. Tech. (Mechanical Engineering))--Vaal University of Technology / Bearing condition monitoring and fault diagnosis have been studied for many years. Popular techniques are applied through advanced signal processing and pattern recognition technologies. The subject of the research was vibration condition monitoring of incipient damage in rolling element bearings. The research was confined to deep-groove ball bearings because of their common applications in industry. The aim of the research was to apply neural networks to vibration condition monitoring of rolling element bearings. Kohonen's Self-Organising Feature Map is the neural network that was used to enable an automatic condition monitoring system. Bearing vibration is induced during bearing operation and the main cause is bearing friction, which ultimately causes wear and incipient spalling in a rolling element bearing. To obtain rolling element bearing vibrations a condition monitoring test rig for rolling element bearings had to be designed and built. A digital vibration measurement acquisition environment was created in Labview and Matlab. Data from the bearing test rig was recorded with a piezoelectric accelerometer, and an S-type load cell connected to dynamic signal analysis cards. The vibration measurement instrumentation was cost-effective and yielded accurate and repeatable measurements. Defects on rolling element bearings were artificially inflicted so that a pattern of bearing defects could be established. An input data format of vibration statistical parameters was created using the time and frequency domain signals. Kohonen's Self-Organising Feature Maps were trained in the input data, utilising an unsupervised, competitive learning algorithm and vector quantisation to cluster the bearing defects on a two-dimensional topographical map. A new practical dimension to condition monitoring of rolling element bearings was developed. The use of time domain and frequency domain analysis of bearing vibration has been combined with a visual and classification analysis of distinct bearing defects through the application of the Self-Organising Feature Map. This is a suitable technique for rolling element bearing defect detection, remaining bearing life estimation and to assist in planning maintenance schedules. / National Research Foundation; Council for Scientific and Industrial Research

The key focus of this research was to investigate the bearing options most suited to operation in a novel direct drive linear generator. This was done through bearing comparisons, modelling and testing. It is fundamental that the linear generator is designed to suit the marine environment. Key design constraints include reliability, survivability, maintenance intervals and cost. Resilient mechanical structural components, such as bearings, will prolong the time a device can operate without maintenance hence prolonging the operating period. Effective lifespan predictions for bearings will feed into the structural design of the generator which forms part of an overall objective to combine each generator design stage into one integrated design process. This promises to provide a cost effective, light weight generator design. This thesis covers the initial investigations into effective, long life and low-wear bearings to meet the operating demands of WEC. It includes an assessment of conventional bearing technology, designs of water-fed hydrostatic bearings and testing of novel polymer bearings. The development of an experimental test rig from a prototype linear generator is described. The rig was built in order to validate and fully explore the potential of self-lubricating, submersible polymer bearings with the ultimate aim of identifying wear constants and frictional properties of the bearings in the low-speed, mid to high-load, oscillating operation of a WEC in order to more accurately predict a bearing lifespan. The outcome of this research served to underpin the need for the design of application specific bearing systems to be based on empirically determined data and observations from test data taken from application specific tests. For inclusion in the design of these linear generators, sizing a bearing requires knowledge of the electrical loading in addition to the expected operating conditions of a WEC. Choosing bearing materials and hence lubricant regimes is dependant on the thermal operating characteristics. Then bearing knowledge in terms of size, load capacity and lifespan can be put directly into the structural model. This iterative process of design can then be merged into a fully integrated generator design tool hence this research was part of the development of an integrated design tool for direct drive generators.