Design of hydrodynamic bearings and sliders.

 1. Which statement is untrue? With full film lubrication, friction is limited to viscous shearing in the film. The coefficient of friction in the HL-regime is generally about 100 times less than in the BL-regime. The full film obtained by hydrodynamic lubrication is maintained by the surface motion. Hydrodynamic lubrication can be obtained by injecting pressurizing fluid between the surfaces.

 2. Which statement is untrue? Full film lubrication excludes mechanical friction and wear, resulting in a much more reliable bearing function. With full film lubrication the film thickness, friction by viscous shearing and the load capability can accurately be calculated resulting in a much more predictable and reliable bearing function then the case with boundary lubrication. The principle of hydrodynamic lubrication was discovered in England by Osborne Reynolds (1883). Osborne Reynolds (1886) presented a partial differential equation that describes the hydrodynamic pressure build up in a thin film between two surfaces in relative motion.

 3. Assumptions made in deriving the standard Reynolds equation are laminar flow, Newtonian fluid, constant viscosity and pressure over the film thickness, zero slip condition. Couette flow, Newtonian fluid, isoviscous, constant pressure over the film thickness, zero slip condition. Couette flow, Newtonian fluid, isoviscous, constant pressure over the film thickness, zero slip condition, incompressible fluid. laminar flow, Newtonian fluid, isoviscous, constant pressure over the film thickness, zero slip condition, incompressible fluid.

 1. Which statement is untrue? The self adjusting plane tilting pad is also referred as the Michell bearing. The stepped pad is also known as the Rayleigh step bearing. The maximum load capability of the Rayleigh step bearing is higher than that of the Michell bearing. The tapered land pad geometry has higher maximum load capability than that of the Rayleigh step bearing.

 2. Which statement is untrue? Hydrodynamic journal bearings do not have free play as in dry sliding bearings but exhibit stiffness. Cavitation in journal bearings is essential to obtain a stable bearing function. Dynamic instability (half omega whirl) can be arrested by making the journal bearing less stiff, for example by increasing the bearing clearance. For a small eccentricity ratio the attitude angle is approximately 0 degrees.

 3. Calculate the load capability of a journal bearing with Sommerfeld number S=10. Given: dR/R=0.001, η=0.04 Pa.s, D=0.04m, L/D=1, ω=30/s. F = 5 kN. F = 10 kN. F = 20 kN. F = 40 kN.