Study on Roughness Parameters Screening and Characterizing Surface Contact Performance based on Sensitivity Analysis

As microtopography can influence the contact behavior of materials, it is of great significance to study the correlation between morphology characterization parameters and contact performance. In the light of complex relevance of parameters, a method for screening roughness parameters (RP) to characterize contact performance is constructed to get the maximum influence parameters on the contact stress (CS) and avoid the error of experiential selection. Firstly, Pearson's coefficient and BP neural network are utilized to elaborate on correlation level between RP and CS and to build the regression model. Then global sensitivity analysis (Sobol) and local sensitivity analysis (MIV and Garson) are introduced to demonstrate RP quantitative influences on CS and select main RP for characterizing contact performance. The research shows: 1) In the correlation analysis, RP with high correlation and non-collinearity on σmax are Sa, Sdq, S5p, Spk and Svk; With regard to Mpmax and τmax, Sa, S5p, Sdq and Vmp are on display. 2) RP importance sequence based on the results of correlation analysis is: Sa, Spk, Sdq, Svk, S5p for σmax, and Sa, Vmp, Sdq, S5p for Mpmax and τmax. 3) For the comprehensive main parameters model, RP for characterizing contact performance under the three contact stresses are Sa, Spk and Vmp, belonging to height parameter, function parameter and volume parameter, respectively. According to definition, all of them can significantly affect the stress concentration and distribution on contact surface of materials, which validates the rationality of the method.

Morris method with improved sampling strategy and Sobol’ Variance-based method, as validation tool on Numerical Model of Richard’s Equation

Richard’s equation was approximated by finite-difference numerical scheme to model water infiltration profile in variably unsaturated soil. The published data of Philip’s semi-analytical solution was used to validate the simulated results from the numerical scheme. A discrepancy was found between the simulated and the published semi-analytical results. Morris method as a global sensitivity tool was used as an alternative to local sensitivity analysis to assess the results discrepancy. Morris method with different sampling strategies were tested, of which Manhattan distance method have resulted a better sensitivity measures and also a better scan of input space than Euclidean method. Moreover, Morris method at and Manhattan distance sampling strategy, with only 2 extra simulation runs than local sensitivity analysis, was able to produce reliable sensitivity measures ( , ). The sensitivity analysis results were cross-validated by Sobol’ variance-based method with 150,000 simulation runs. The global sensitivity tool has identified three important parameters, of which spatial discretization size was the sole reason of the discrepancy observed. In addition, a high proportion of total output variance contributed by parameters and is suggesting a greater significant digits is required to reduce its input uncertainty range.

Local Sensitivity Analysis of Steady-State Response of Rotors with Rub-Impact to Parameters of Rubbing Interfaces

Local sensitivity analysis, which describes the relative importance of specific design parameters to the response of systems, is crucial for investigating dominant factors in optimal design. In this paper, local sensitivity analysis of the response of rotors with rub-impact to parameters of rubbing interfaces is carried out. The steady-state motion of the rotor is evaluated by a harmonic balance method and the sensitivity coefficients for every rotation speed over the speed range are derived analytically. Two classical models, including the Duffing oscillator and the gap model, are utilized to validate the accuracy and capability of the adopted methods and high accuracy is shown. Numerical investigations of sensitivities of steady-state response of rotors to parameters of rubbing interfaces are then carried out, based on a lumped Jeffcott rotor and a finite element model respectively. Conclusions are drawn that the response of rotors subjected to rubbing problems is more sensitive to initial clearance than other parameters of the applied friction model. With increase of initial gap, the response of rotors becomes more sensitive and the range of region subjected to rub-impact forces shrinks until the separation of rotor and stator.