Vibrations in Rotating Machinery Arising from Minor Imperfections in Component Geometries

Vibrations in machines can cause noise, decrease the performance, or even damage the machine. Vibrations appear if there is a source of vibration that excites the system. In the worst case scenario, the excitation frequency coincides with the natural frequency of the machine causing resonance. Rotating machines are a machine type, where the excitation arises from the machine itself. The excitation originates from the mass imbalance in the rotating shaft, which always exists in machines that are manufactured using conventional methods. The excitation has a frequency that is dependent on the rotational speed of the machine. The rotating machines in industrial use are usually designed to rotate at a constant rotational speed, the case where the resonances can be easily avoided. However, the machines that have a varying operational speed are more problematic due to a wider range of frequencies that have to be avoided. Vibrations, which frequencies equal to rotational speed frequency of the machine are widely studied and considered in the typical machine design process. This study concentrates on vibrations, which arise from the excitations having frequencies that are multiples of the rotational speed frequency. These vibrations take place when there are two or more excitation components in a revolution of a rotating shaft. The dissertation introduces four studies where three kinds of machines are experiencing vibrations caused by different excitations. The first studied case is a directly driven permanent magnet generator used in a wind power plant. The electromagnetic properties of the generator cause harmonic excitations in the system. The dynamic responses of the generator are studied using the multibody dynamics formulation. In another study, the finite element method is used to study the vibrations of a magnetic gear due to excitations, which frequencies equal to the rotational speed frequency. The objective is to study the effects of manufacturing and assembling inaccuracies. Particularly, the eccentricity of the rotating part with respect to non-rotating part is studied since the eccentric operation causes a force component in the direction of the shortest air gap. The third machine type is a tube roll of a paper machine, which is studied while the tube roll is supported using two different structures. These cases are studied using different formulations. In the first case, the tube roll is supported by spherical roller bearings, which have some wavinesses on the rolling surfaces. Wavinesses cause excitations to the tube roll, which starts to resonate at the frequency that is a half of the first natural frequency. The frequency is in the range where the machine normally operates. The tube roll is modeled using the finite element method and the bearings are modeled as nonlinear forces between the tube roll and the pedestals. In the second case studied, the tube roll is supported by freely rotating discs, which wavinesses are also measured. The above described phenomenon is captured as well in this case, but the simulation methodology is based on the flexible multibody dynamics formulation. The simulation models that are used in both of the last two cases studied are verified by measuring the actual devices and comparing the simulated and measured results. The results show good agreement.

Radio-frequency-based measurement methods for bearing current analysis in induction motors

The most common reason for a low-voltage induction motor breakdown is a bearing failure. Along with the increasing popularity of modern frequency converters, bearing failures have become the most important motor fault type. Conditions in which bearing currents are likely to occur are generated as a side effect of fast du/dt switching transients. Once present, different types of bearing currents can accelerate the mechanical wear of bearings by causing deformation of metal parts in the bearing and degradation of the lubricating oil properties.The bearing current phenomena are well known, and several bearing current measurement and mitigation methods have been proposed. Nevertheless, in order to develop more feasible methods to measure and mitigate bearing currents, better knowledge of the phenomena is required. When mechanical wear is caused by bearing currents, the resulting aging impact has to be monitored and dealt with. Moreover, because of the stepwise aging mechanism, periodically executed condition monitoring measurements have been found ineffective. Thus, there is a need for feasible bearing current measurement methods that can be applied in parallel with the normal operation of series production drive systems. In order to reach the objectives of feasibility and applicability, nonintrusive measurement methods are preferred. In this doctoral dissertation, the characteristics and conditions of bearings that are related to the occurrence of different kinds of bearing currents are studied. Further, the study introduces some nonintrusive radio-frequency-signal-based approaches to detect and measure parameters that are associated with the accelerated bearing wear caused by bearing currents.

Vibration analysis of a power take-off line

Gear rattle is a phenomenon that occurs when idling or lightly loaded gears collide due to engine’s torque fluctuations. This behaviour is related to vibration behaviour of the transmission system. Aim of this master’s thesis is to evaluate Adams and Adams/Machinery as a simulation tools for modelling the rattle e ect in a transmission system. A case study of tractor’s power take-o driveline, suspected to be prone to rattle, is performed in this work. Modelling methods used by Adams in this type of study are presented in the theory section while simulation model build with the software during this work is presented in the results. The Machinery toolbox is used to create gears and bearings while other model components are created with standard Adams tool set. Geometries and excitations are exported from other softwares. Results were obtained from multiple variations of a base model. These result sets and literature review suggest that Adams/Machinery may not be the most suitable tool for rattle analysis. While the system behaviour was partially captured, for accurate modelling user-written routines must be used which may be more easily performed with other tools. Further research about this topic is required.

Active Magnetic Bearing System Identification Methods and Rotor Model Updating

Active magnetic bearing is a type of bearing which uses magnetic field to levitate the rotor. These bearings require continuous control of the currents in electromagnets and data from position of the rotor and the measured current from electromagnets. Because of this different identification methods can be implemented with no additional hardware. In this thesis the focus was to implement and test identification methods for active magnetic bearing system and to update the rotor model. Magnetic center calibration is a method used to locate the magnetic center of the rotor. Rotor model identification is an identification method used to identify the rotor model. Rotor model update is a method used to update the rotor model based on identification data. These methods were implemented and tested with a real machine where rotor was levitated with active magnetic bearings and the functionality of the methods was ensured. Methods were developed with further extension in mind and also with the possibility to apply them for different machines with ease.

Bearing-spesific complications of total hip arthroplasty: characterization and treatment

Hip resurfacing arthroplasty (HRA) and large head metal-on-metal total arthroplasty (LDH MoM THA) gained popularity during the last decade. Adverse reaction to metal debris (ARMD) is a unique complication of metal bearings. ARMD is a complex reaction caused by metal debris from metal-on- metal bearing surfaces and from trunnion corrosion of modular junctions. We analyzed survivorship of 8059 LDH MoM THAs based on data of the Finnish Arthroplasty Register. We found relatively high short-term survivorship for some LDH MoM THAs, but there were remarkable differences between the devices studied. After some alarming reports of failing MoM THAs, we studied the first 80 patients who had received a ReCap-M2a-Magnum implant at our institution and evaluated the prevalence of ARMD. We found a high prevalence of pseudotumors, and, because of this, we discontinued the use of MoM bearings and followed up all patients with a MoM THA. Bone loss due infection, osteolysis or fracture poses a great challenge for reconstructive and fracture surgery. Onlay allografting for both revision and fracture surgery provides mechanical stability and increases bone stock. Bone loss and implant stability must be assessed preoperatively and adequately classified; this provides guidelines for the operative treatment of periprosthetic fractures and revision THA. In our studies on structural allografts union rates were high, although the rates of infections and dislocations were marked. In summary, early results of the use of LDH MoM devices were encouraging. However, the survival of the LDH MoMs varied. The prevalence of adverse reaction to metal debris was high after application of the ReCap-Magnum THA. New implants should be introduced carefully and under close surveillance by University clinics and arthroplasty registers.

Design and Simulation of High-Speed Rotating Electrical Machinery

Global energy consumption has been increasing yearly and a big portion of it is used in rotating electrical machineries. It is clear that in these machines energy should be used efficiently. In this dissertation the aim is to improve the design process of high-speed electrical machines especially from the mechanical engineering perspective in order to achieve more reliable and efficient machines. The design process of high-speed machines is challenging due to high demands and several interactions between different engineering disciplines such as mechanical, electrical and energy engineering. A multidisciplinary design flow chart for a specific type of high-speed machine in which computer simulation is utilized is proposed. In addition to utilizing simulation parallel with the design process, two simulation studies are presented. The first is used to find the limits of two ball bearing models. The second is used to study the improvement of machine load capacity in a compressor application to exceed the limits of current machinery. The proposed flow chart and simulation studies show clearly that improvements in the high-speed machinery design process can be achieved. Engineers designing in high-speed machines can utilize the flow chart and simulation results as a guideline during the design phase to achieve more reliable and efficient machines that use energy efficiently in required different operation conditions.

Minkä nuorena hallitsee sen aikuisena taitaa? Liikehallinnan pysyvyys kouluiästä aikuisikään – 24 vuoden seurantatutkimus

Tässä 24 vuoden pitkittäistutkimuksessa tutkitaan liikehallinnan kehitystä ja pysyvyyttä kouluiästä aikuisikään. Lisäksi ennustetaan ja selitetään aikuisiän liikehallintaa kouluiän liikehallinnan perusteella. Tutkimukseen osallistui 44 miestä ja 44 naista eri puolilta Suomea, joiden liikehallintaa mitattiin kouluiässä 1985 ja 1988 (9–16-vuotiaina) sekä aikuisiässä 2009 (33−39-vuotiaina). Liikehallintaa mitattiin kuudella liiketehtävämittarilla (flamingoseisonta, tarkkuusheittokiinniotto, kahdeksikkokuljetus, edestakaisinhyppely, vauhditon 5-loikka ja kärrynpyörä) sekä niistä lasketulla summamuuttujalla. Miesten ja naisten liikehallintaa vertailtiin varianssianalyysilla. Kouluiässä pojat menestyivät välineenkäsittelytehtävissä ja tytöt tasapaino- ja voimistelutehtävissä, mutta kokonaisuutena sukupuolten välillä ei ollut eroa. Aikuisena miehet olivat naisia parempia lähes kaikissa tehtävissä. Kovarianssianalyysissä havaittiin, että kehonrakenteeltaan (BMI) erilaisten ryhmien liikehallinnassa oli vain yksittäisiä eroja koulu- ja aikuisiässä. Toistettujen mittausten varianssianalyysissa ilmeni, että kouluiässä molempien sukupuolten liikehallinnan kehitys oli samanlaista. Kouluiän jälkeen kevyiden ja keskipainoisten poikien liikehallinta parani, mutta painavien tulokset eivät muuttuneet. Kevyiden tyttöjen tuloksissa ei tapahtunut muutosta, mutta keskipainoisten ja painavien tulokset heikkenivät. Koululiikunnan tehostus- ja vertailuryhmien välille kouluiässä muodostuneet erot kaventuivat tai katosivat aikuisena. Kouluiän liikehallinnaltaan eritasoisten ryhmien väliset erot kaventuivat, mutta eivät poistuneet kouluiän jälkeen. Klusterianalyysissa tutkittavat jakaantuivat kouluiässä neljään liikehallintatyyppiin (yleishyvät, tasapainoiset, pallotaitajat ja yleisheikot), jotka säilyivät myös aikuisiässä, mutta niiden väliset erot kaventuivat. Ristiintaulukointi ja khiin neliö -testi osoittivat, että tasoryhmän ja liikehallinnan monipuolisuuden pysyvyys oli vahvaa kouluiästä aikuisikään. Koulu- ja aikuisiän liikehallintatulosten välinen korrelaatio oli naisilla (0.69) vahvempaa kuin miehillä (0.48). Yksittäiset mittaustulokset kouluiässä selittivät keskimäärin 33 % aikuisiän tuloksista (korrelaation neliö). Regressioanalyysissa miesten aikuisiän liikehallintaa selittivät kouluiän muuttujista parhaiten liikehallinnan monipuolisuus sekä liikkuvuus (61 %), mutta naisilla vain liikehallinnan monipuolisuus (37 %). Miesten ja naisten erot liikehallinnassa syntyivät kouluiän jälkeen, mikä johtunee erilaisista liikuntatavoista ja -harrastuksista. Kouluiän liikehallinta määritti vahvasti varsinkin tytöillä aikuisiän liikehallintaa sekä yksilö- että ryhmätasolla, mikä korostaa monipuolisen koululiikunnan merkitystä. Yksilölliset muutokset olivat mahdollisia. Kouluiän jälkeen erityisesti naiset ja kehonrakenteeltaan painavat tarvitsisivat hermolihasjärjestelmää monipuolisesti kuormittavaa ja liikesuunniltaan moniulotteista liikuntaa liikehallinnan kehittämiseksi ja ylläpitämiseksi. Naisten liikehallinnan taantuminen varsinkin tasapainotehtävissä voi altistaa kaatumistapaturmille ja rajoittaa fyysistä toimintakykyä.

Sähkömekaanisen turvalaakerirakenteen suunnittelu

Turvalaakereita käytetään suojaamaan aktiivisia magneettilaakereita vikatilanteiden tapahtuessa. Tässä kandidaatintyössä suunniteltiin erilaisia ratkaisuja toteuttaa turvalaakerin toiminta sähkömekaanisella toimilaitteella. Työn tarkoituksena oli löytää uusia tapoja toteuttaa turvalaakerin rakenne. Uusilla ratkaisuilla poistettiin turvalaakereille ominaisia ongelmia. Suunnittelussa käytettiin perinteisiä koneensuunnittelun menetelmiä. Menetelmien tarkoitus oli mahdollistaa järjestelmällinen suunnittelu. Tässä työssä myös kirjallisuuskatsaus toimi yhtenä suunnittelun vaiheena. Tuloksiksi saatiin hahmotelmia ja 3D-malleja. Tulokset poikkesivat tavanomaisista turvalaakereiden rakenteista. Tuloksissa huomioitiin, että tässä työssä ei suunnitella valmista tuotetta. Suunniteltujen turvalaakereiden toiminta perustui mekanismeihin, jotka toivat mukanaan uusia ominaisuuksia. Sähkömekaanisen toimilaitteen sijoittaminen mekanismeihin oli kuitenkin vaikeaa. Työn tulokset avasivat uusia näkökulmia turvalaakerirakenteiden jatkokehittämiseen.

Multibody models for examination of touchdown bearing systems

Increased rotational speed brings many advantages to an electric motor. One of the benefits is that when the desired power is generated at increased rotational speed, the torque demanded from the rotor decreases linearly, and as a consequence, a motor of smaller size can be used. Using a rotor with high rotational speed in a system with mechanical bearings can, however, create undesirable vibrations, and therefore active magnetic bearings (AMBs) are often considered a good option for the main bearings, as the rotor then has no mechanical contact with other parts of the system but levitates on the magnetic forces. On the other hand, such systems can experience overloading or a sudden shutdown of the electrical system, whereupon the magnetic field becomes extinct, and as a result of rotor delevitation, mechanical contact occurs. To manage such nonstandard operations, AMB-systems require mechanical touchdown bearings with an oversized bore diameter. The need for touchdown bearings seems to be one of the barriers preventing greater adoption of AMB technology, because in the event of an uncontrolled touchdown, failure may occur, for example, in the bearing’s cage or balls, or in the rotor. This dissertation consists of two parts: First, touchdown bearing misalignment in the contact event is studied. It is found that misalignment increases the likelihood of a potentially damaging whirling motion of the rotor. A model for analysis of the stresses occurring in the rotor is proposed. In the studies of misalignment and stresses, a flexible rotor using a finite element approach is applied. Simplified models of cageless and caged bearings are used for the description of touchdown bearings. The results indicate that an increase in misalignment can have a direct influence on the bending and shear stresses occurring in the rotor during the contact event. Thus, it was concluded that analysis of stresses arising in the contact event is essential to guarantee appropriate system dimensioning for possible contact events with misaligned touchdown bearings. One of the conclusions drawn from the first part of the study is that knowledge of the forces affecting the balls and cage of the touchdown bearings can enable a more reliable estimation of the service life of the bearing. Therefore, the second part of the dissertation investigates the forces occurring in the cage and balls of touchdown bearings and introduces two detailed models of touchdown bearings in which all bearing parts are modelled as independent bodies. Two multibody-based two-dimensional models of touchdown bearings are introduced for dynamic analysis of the contact event. All parts of the bearings are modelled with geometrical surfaces, and the bodies interact with each other through elastic contact forces. To assist in identification of the forces affecting the balls and cage in the contact event, the first model describes a touchdown bearing without a cage, and the second model describes a touchdown bearing with a cage. The introduced models are compared with the simplified models used in the first part of the dissertation through parametric study. Damages to the rotor, cage and balls are some of the main reasons for failures of AMB-systems. The stresses in the rotor in the contact event are defined in this work. Furthermore, the forces affecting key bodies of the bearings, cage and balls can be studied using the models of touchdown bearings introduced in this dissertation. Knowledge obtained from the introduced models is valuable since it can enable an optimum structure for a rotor and touchdown bearings to be designed.

Brock University Coat of Arms

The armorial bearings for Brock University, or more simply the University Coat of Arms, or crest, was designed in a large part by Presdent Gibson, assisted by other members of the Board of Governors (A preliminary design can be seen here). The Coat of Arms was granted to Brock University on March 17th, 1965. The Coat of Arms consist of an eagle, taken from General Brock’s own arms, displayed against a scarlet background - one of the official colours of Brock University. Immediately above it on a chief argent is displayed a maple-leaf (for Canada), a scallop shell (from the Lincoln and Welland regiment), and a trillium (for the province of Ontario). An open book fronts the eagle representing learning and knowledge. The crest itself is made up of a torch symbolizing learning, surrounded by a serpent for wisdom, with two calumet or North American pipes of peace, to symbolize Canada, friendship and agreement. The supporters consist of a beaver on the dexter side, emblematic of Canada and representing work and industry in learning. On the sinister side, a brock or badger (also in commemoration of General Brock) represents tenacity of purpose. The motto 'Surgite' is visible just below the arms.

Post Scrum

The opposing team has the ball.

The Attack

A Brock player hits the ball over in this match suspected to be from 87/88 or 88/89.

The effect of literacy training on the self-concept of moderately mentally handicapped adults

In this single group, pretest/posttest design study the literacy level and self-concept of nine moderately mentally handicapped adults was assessed. The participants in the study were involved in reading lessons using the Ball-Stick-Bird reading system, a brainbased program. No significant differences were found in either literacy level or reading level after intervention. However, there were changes in reading behaviour. These changes occurred in the subskills ofdirectionality, letter-sound correspondence, wordreading, and use of reading materials.