Journal Bearing Stiffness and Damping Coefficients Using Nanomagnetorheological Fluids and Stability Analysis

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.