The integrity and reliability of a rotor depend significantly on the dynamic characteristics of its bearings. Bearing design has evolved in many ways in order to achieve higher damping and stiffness. A promising field in terms of vibrations control and overall performance improvement for the journal bearings is the use of smart lubricants. Smart lubricants are fluids with controllable properties. A suitable excitation, such as an electric or a magnetic field, is applied to the lubricant volume and changes its properties. Magnetorheological (MR) fluids consist one category of lubricants with controllable properties. Magnetic particles inside the MR fluid volume are coerced by a magnetic field. These particles form chains which hinder the flow of the base fluid and alter its apparent viscosity. According to the magnetic particle size, there are two subcategories of magnetorheological fluids: the regular MR fluids with particles sizing some tens of micrometers and the nanomagnetorheological (NMR) fluids with a particle size of a few nanometers. The change of magnetorheological fluid's viscosity is an efficient way of control of the dynamic characteristics of the journal bearing system. In this work, the magnetic field intensity inside the volume of lubricant is calculated through finite element analysis. The calculated value of the magnetic field intensity is used to define the apparent viscosity of both the MR and the NMR fluids. Using computational fluid dynamics (CFD) method, the pressure developed inside the journal bearing is found. Through this simulation with the use of a suitable algorithm, the stiffness and damping coefficients are calculated and stability charts of Newtonian, MR, and NMR fluid are presented and discussed.
The environmental impact of many industrial and naval applications is becoming increasingly important. Journal bearings are crucial components related with the reliable, safe and environmentally friendly operation of rotating machinery in many applications, e.g., in hydroplants, ships, power generation stations. The maintenance activities in certain cases also have considerable environmental impact. Fortunately, it is relatively easy to reduce the impact by changing the way lubricants are being used. Selecting the proper lubricant is important to sharply reduce long-term costs. The best-fit product selection can mean longer lubricant life, reduced machine wear, reduced incipient power losses and improved safety. Suitable basestocks and additives reduce environmental impact. In this paper, three types of lubricants are used in order to examine their effects on the tribological behavior of journal bearings. A mineral oil, a synthetic oil and a bio-based lubricant are experimentally and analytically examined for several configurations of load and journal rotational velocity. The friction forces and the hydrodynamic friction coefficients are calculated and compared. This investigation can assist the correct choice of lubricant in journal bearings with minimized environmental footprint.
The rotordynamic behavior of a system supported by journal bearings is critical to its reliability.A suitable method of control of the orbital motion of a shaft in a journal bearing is the use of smart lubricants, in effect fluids with controllable physical properties. There are various categories of smart lubricants. One class of smart lubricants, the magnetorheological fluids, are produced as a dispersion of magnetic particles in a carrier fluid which is usually a conventional lubricant. These particles form chains under the influence of a magnetic field, which hinder the lubricant flow, thus changing its apparent viscosity. Magnetorheological (MR) fluids exhibit high yield stress, low delay of response and relatively low friction while not in their active state.A subcategory of MRF's, the nanomagnetorheological (NMR) fluids with particle size in the nanometer scale, exhibit lower yield stress than the MRF's but, on the other hand, display high viscosity. The effect of the MRF's and NMRF's on the rotordynamic behavior of a shaft is calculated through a combined finite element and computational fluid dynamics analysis. While the MR fluid with the specific geometrical configuration of the bearing is not sufficiently activated and therefore does not improve the performance of the magnetorheological journal Downloaded by [New York University] at 19:53 15 June 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 bearing, the NMR fluid has the ability of limiting up to 82% the amplitude of the vibrations of the shaft.
The integrity and reliability of a rotor depend significantly on the dynamic characteristics of its bearings. Bearing design has been altered in many ways in order to achieve improvement in terms of damping and stiffness. A promising field in terms of vibration control and overall performance improvement for the journal bearings is the use of smart lubricants. Smart lubricants are fluids with controllable properties. A suitable excitation, such as an electric or a magnetic field, is used as a means of smart fluid properties control. Magnetorheological (MR) fluids consist one category of lubricants with controllable properties, thanks to magnetic particles inside the fluid volume. In this case of material, a magnetostatic field affects the apparent viscosity of the fluid by aligning the magnetic particles into chains. In this work, an MR fluid is produced. An MR fluid film bearing was constructed, which is capable of exciting the MR fluid. These bearing performances are examined experimentally and its dynamic properties are evaluated using an impact excitation method for an SAE-10 W lubricant as well as with the produced MR fluid both in its active and in its inactive state.
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