Dynamic characteristics of magnetorheological fluid lubricated journal bearing and its application to rotor vibration control

Application of smart lubricants like magnetorheological (MR) fluids is always considered to be a promising field of realizing smart bearings with semi-active controllable capability. For bearings lubricated with MR fluid, the dynamic characteristics i.e. the stiffness and damping coefficients are important, while few studies have focused on this field. The present work adopts the Herschel-Bulkley model to describe the rheological behavior of MR fluid. The shearing-thinning effect incorporated in this model leads to different result compared to that from the Bingham model. Stiffness and damping coefficients of bearings lubricated with Newtonian fluid, Bingham fluid are calculated. Calculations show that shear-thinning effect has great influences on both static and dynamic characteristics of the journal bearing. Simulations of rotordynamics of a turbo-expander rotor with different bearing properties are performed to investigate the possibility of MR fluid as lubricants to control the behavior of rotor. Results show that MR fluids are applicable to change performances of the rotor system. Vibration amplitude suppression and critical speed alteration can be achieved by MR fluids

Vibration control of a hydrostatic bearing using magnetorheological elastomer shell bearing

In rotating machines, random movements or sliding movements of the rotor in its housing can produce undesirable phenomena for some parts. To solve this problem, a new hydrostatic bearing with an intelligent magnetorheological elastomer sell bearing has been designed to control the undesirable vibrations of rigid rotors. The different effects of the influence parameters on the vibratory behavior of the sell bearing are calculated numerically using Abaqus software, and the results found are encouraging

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

Guiados lubricados activos para máquinas herramienta de precisión basados en fluidos magnéticos y válvulas adaptativas

212 p.El trabajo de investigación que se presenta en esta memoria ha tenido como objetivo avanzar en el conocimiento de guiados lubricados presurizados, tanto hidrostáticos, hidrodinámicos como en régimen híbrido. Se ha trabajado con fluidos convencionales y con fluidos magnéticos, lográndose en ambos casos prestaciones mejoradas con respecto a soluciones pasivas convencionales, y una respuesta activa avanzada.En el desarrollo de lubricación basada aceites minerales convencionales, fluidos Newtonianos, se ha realizado una herramienta de cálculo con la que predecir el comportamiento de cojinetes radiales, axiales y guiados lineales; todo ello orientado a su uso durante la fase de diseño de máquinas herramienta. Los modelos se han validado mediante un nuevo banco de ensayos donde analizar los prototipos de cojinetes radiales. El nuevo banco de ensayos ha servido para aislar el comportamiento del cojinete radial a analizar con respecto al resto del sistema, efecto que en los bancos de ensayos clásicos limita su caracterización. Para finalizar con las soluciones de lubricación mediante fluidos convencionales se ha desarrollado una válvula adaptativa en base a diafragmas flexibles; y por otro lado, una solución de lubricación autocompensada basada en conductos internos en el propio guiado. Estos desarrollos han sido tanto teóricos, en base a modelos de fluidodinámica, como experimentales, con sendos bancos de ensayos.El siguiente gran bloque de la investigación presentada en esta memoria se orienta al uso de fluidos magnéticos para la obtención de lubricación activa. Se ha trabajado con fluidos magnetoreológicos y ferrofluidos, donde tras realizar una actividad de síntesis para adquirir un conocimiento básico sobre su composición, se ha realizado una caracterización experimental en profundidad de dos fluidos comerciales; los dos fluidos que se han utilizado durante la investigación. Se ha desarrollado un modelo teórico apoyado con su respectivo banco de ensayos para el estudio de cojinetes radiales, tanto hidrodinámicos como hidrostáticos. Para estos últimos se han desarrollado también válvulas magnetoreológicas con las que controlar el caudal de alimentación. En esta investigación se ha comprobado la mejora de la linealidad en la lubricación hidrodinámica, así como la rigidez infinita con las válvulas magnetoreológicas controladas en lazo cerrado. Finalmente se ha desarrollado una junta de estanqueidad basada en fluidos magnéticos, donde los ferrofluidos han demostrado un comportamiento compatible con los requerimientos de cabezales de máquinas herramienta de precisión

Guiados lubricados activos para máquinas herramienta de precisión basados en fluidos magnéticos y válvulas adaptativas

212 p.El trabajo de investigación que se presenta en esta memoria ha tenido como objetivo avanzar en el conocimiento de guiados lubricados presurizados, tanto hidrostáticos, hidrodinámicos como en régimen híbrido. Se ha trabajado con fluidos convencionales y con fluidos magnéticos, lográndose en ambos casos prestaciones mejoradas con respecto a soluciones pasivas convencionales, y una respuesta activa avanzada.En el desarrollo de lubricación basada aceites minerales convencionales, fluidos Newtonianos, se ha realizado una herramienta de cálculo con la que predecir el comportamiento de cojinetes radiales, axiales y guiados lineales; todo ello orientado a su uso durante la fase de diseño de máquinas herramienta. Los modelos se han validado mediante un nuevo banco de ensayos donde analizar los prototipos de cojinetes radiales. El nuevo banco de ensayos ha servido para aislar el comportamiento del cojinete radial a analizar con respecto al resto del sistema, efecto que en los bancos de ensayos clásicos limita su caracterización. Para finalizar con las soluciones de lubricación mediante fluidos convencionales se ha desarrollado una válvula adaptativa en base a diafragmas flexibles; y por otro lado, una solución de lubricación autocompensada basada en conductos internos en el propio guiado. Estos desarrollos han sido tanto teóricos, en base a modelos de fluidodinámica, como experimentales, con sendos bancos de ensayos.El siguiente gran bloque de la investigación presentada en esta memoria se orienta al uso de fluidos magnéticos para la obtención de lubricación activa. Se ha trabajado con fluidos magnetoreológicos y ferrofluidos, donde tras realizar una actividad de síntesis para adquirir un conocimiento básico sobre su composición, se ha realizado una caracterización experimental en profundidad de dos fluidos comerciales; los dos fluidos que se han utilizado durante la investigación. Se ha desarrollado un modelo teórico apoyado con su respectivo banco de ensayos para el estudio de cojinetes radiales, tanto hidrodinámicos como hidrostáticos. Para estos últimos se han desarrollado también válvulas magnetoreológicas con las que controlar el caudal de alimentación. En esta investigación se ha comprobado la mejora de la linealidad en la lubricación hidrodinámica, así como la rigidez infinita con las válvulas magnetoreológicas controladas en lazo cerrado. Finalmente se ha desarrollado una junta de estanqueidad basada en fluidos magnéticos, donde los ferrofluidos han demostrado un comportamiento compatible con los requerimientos de cabezales de máquinas herramienta de precisión

Tribological characteristics of smart fluids

Diplomová práca sa zaoberá experimentálnym štúdiom tribologických charakteristík smart kvapalín. Smart kvapaliny sú látky v kvapalnom skupenstve reagujúce na prítomnosť magnetického alebo elektrického poľa zmenou reologických vlastností. Pre možnosť aplikácie v zariadeniach využívajúcich konvenčné mazivá je potrebné zvoliť vhodnú smart kvapalinu a študovať vplyv budenia na utváranie mazacej vrstvy, trenie a opotrebenie. Komplexný popis vplyvu budenia je realizovaný použitím troch experimentálnych zariadení a teoretického modelu pre stanovenie parametrov meraní. Hodnotená je hrúbka mazacej vrstvy, priebeh súčiniteľa trenia a opotrebenie počas aktivácie smart kvapaliny v nekonformnom kontakte. Výsledky ukazujú výrazný pozorovateľný vplyv budenia na všetky hodnotené aspekty. Pochopenie mechanizmov budenia smart kvapalín môže byť kľúčovým krokom pri vývoji inteligentných zariadení s aktívnym externým riadením správania a povahy maziva, ktoré by napomohli k zníženiu nákladov na údržbu a k zlepšeniu efektivity.The master's thesis deals with experimental study of tribological characteristics of smart fluids. Smart fluids are substances in liquid state reacting to the presence of magnetic or electric field by change in rheological properties. For possible application in devices using conventional lubricants is necessary to choose suitable smart fluid and study the influence of excitation on formation of lubricating layer, friction and wear. Comprehensive description of excitation influence is executed using three experimental devices and theoretical model for measurements parameters specification. Assessed are lubricant film thickness, friction coefficient and wear under smart fluid activation in non-conformal contact. Results show significant observable influence of smart fluids excitation on all assessed aspects. Understanding the mechanisms of smart fluids excitation can be a key step in development of intelligent devices with active external control of lubricant behaviour and character, that could lead to maintenance cost reduction and effectivity improvement.

Study of nonlinear MHD tribological squeeze film at generalized magnetic reynolds numbers using DTM.

In the current article, a combination of the differential transform method (DTM) and Padé approximation method are implemented to solve a system of nonlinear differential equations modelling the flow of a Newtonian magnetic lubricant squeeze film with magnetic induction effects incorporated. Solutions for the transformed radial and tangential momentum as well as solutions for the radial and tangential induced magnetic field conservation equations are determined. The DTM-Padé combined method is observed to demonstrate excellent convergence, stability and versatility in simulating the magnetic squeeze film problem. The effects of involved parameters, i.e. squeeze Reynolds number (N1), dimensionless axial magnetic force strength parameter (N2), dimensionless tangential magnetic force strength parameter (N3), and magnetic Reynolds number (Rem) are illustrated graphically and discussed in detail. Applications of the study include automotive magneto-rheological shock absorbers, novel aircraft landing gear systems and biological prosthetics

DEVELOPING NEW ANALYTICAL AND NUMERICAL MODELS FOR MR FLUID DAMPERS AND THEIR APPLICATION TO SEISMIC DESIGN OF BUILDINGS

Magnetorheological (MR) and Electrorheological (ER) fluid dampers provide a fail-safe semi-active control mechanism for suppressing vibration response of structures as these smart fluids can change their apparent viscosity immediately under the influence of magnetic and electrical fields, respectively. MR based damping devices have recently received appropriate attention as they have less power demand, provide better dynamic range and are less sensitive to the temperature and external contaminants as compared to their ER counterparts. This thesis studies physics-based modeling of MR fluid dampers and their application in seismic design of buildings. In the first part of thesis, MR damper modeling and its related subject are studied, while in the second part of the thesis, application of MR dampers in tuned mass damper and bracing system is investigated. The existing models, namely the phenomenological models for simulating the behavior of MR and ER dampers rely on various parameters determined experimentally by the manufacturers for each damper configuration. It is of interest to develop mechanistic models of these dampers which can be applied to various configurations so that their fundamental characteristics can be studied to develop flexible design solutions for smart structures. This research presents a formulation for dynamics analysis of ER and MR fluid dampers in flow and mix mode configurations under harmonic and random excitations. The procedure employs the vorticity transport equation and the regularization function to deal with the unsteady flow and nonlinear behaviour of ER/MR fluid in general motion. Using the developed approach, the damping force of ER/MR damper can be evaluated under any type of excitations. While tuned mass dampers are found to be effective in suppressing vibration in a tall building, integrating them with semi-active MR based control system enables them to perform more efficiently under varying external excitations. To study the application of MR damper in tuned mass damper, a forty-storey tall steel-frame building assumed to be located in the Pacific Coast region of Canada (Vancouver), designed according to the relevant Canadian code and standard, has been studied with and without semi-active and passive tuned mass dampers. The response of the structure has been studied under a variety of ground motions with low, medium and high frequency contents to investigate the performance of the optimally designed semi-active MR based tuned mass damper in comparison to that of a passive tuned mass damper. It has been shown that the semi-active MR based system modifies structural response more effectively than the conventional passive tuned mass damper in both mitigation of the maximum displacement and reduction of the settling time of the building. Finally, the effectiveness of MR damper in structural bracing has been examined. Two steel building structures, five and twenty-storey building designed according to Canadian national building code, have been modeled using the finite element method. These building structures have been equipped with MR dampers in different floors appropriately based on the seismic floor-shear distribution. The governing equations of motion of the structures integrated with MR dampers have been cast into the state space representation for the implementation of the full state LQR combined with clipped optimal control strategies. The response of building structures under passive on and active controlled modes have been obtained for low, medium and high frequency content seismic records and compared

Study of failure symptoms of a single-tube MR damper using an FEA-CFD approach

From SAGE Publishing via Jisc Publications RouterHistory: epub 2020-11-03Publication status: PublishedA new magnetorheological (MR) damper has been designed, manufactured, modelled and tested under cyclic loads. A faulty behaviour of the damper was accidentally detected during the experiments. It was deduced that the presence of air bubbles within the MR fluid is the main reason for that failure mode of the damper. The AMT-Smartec+ MR fluid used in the current study, a new MR fluid whose characteristics are not available in the literature, exhibits good magnetic properties. However, the fluid has a very high viscosity in the absence of magnetic field. It is assumed that this high viscosity enables the retention of air bubbles in the damper and causes the faulty behaviour. To prove this assumption, a coupled numerical approach has been developed. The approach incorporates a Finite Element Analysis (FEA) of the magnetic circuit and a Computational Fluid Dynamics (CFD) analysis of the fluid flow. A similar approach was presented in a previous publication in which an ideal behaviour of an MR damper (no effect of air bubbles) was investigated. The model has been modified in the current study to include the effect of air bubbles. The results were found to support the assumptions for the reasons of the failure symptoms of the current MR damper. The results are shown in a comparative way between the former and current studies to show the differences in flow parameters, namely: pressure, velocity and viscosity, in the faultless and faulty modes. The results indicate that the presence of air bubbles in MR dampers reduces the damper force considerably. Therefore, the effect of the high yield stress of MR fluids due to the magnetic field is reduced