Uncertainty quantification and global sensitivity analysis of a thermally coupled hydrodynamic journal bearing

A deterministic bearing calculation gives one value per performance measure, although its inputs are uncertain. This paper attributes that uncertainty for one bearing class: a plain journal bearing with L / D  = 0.5 and ISO VG 46 oil, at two reference duty points and across a twelve-point duty sweep. The finite-width Reynolds equation with the Guembel condition is coupled to a Walther viscosity–temperature law and a global energy balance, and a similarity-based operator solves it in about 30 μs. Against published experiments, the predicted eccentricity agrees within 0.012 between 4 and 10 kN at 2000 rpm, whereas the maximum temperature is underpredicted. Eight documented uncertain inputs are propagated by Monte Carlo and Latin hypercube sampling and decomposed with Sobol indices. At heavy duty the supply temperature explains 67% of the variance of the minimum film thickness and 73% of that of the friction power loss; the load explains 80% of that of the peak pressure. Interactions are weak. The roughness share of the film-parameter variance (65%) is largely definitional. The local clearance elasticity of the film thickness changes sign at a nominal eccentricity ratio of 0.64, and the clearance index falls from 0.51 to a minimum of 0.002. From 10 ⁷ runs, a nominal film parameter of 6.0, twice the full-film limit, still leaves a mixed-lubrication probability of 2.51 × 10 ⁻³ . The leading input changes only if the supply-temperature standard deviation falls below about 3 K, whereas absolute probabilities depend on the input model and thermal closure.