Numerical analysis of single pad of thrust bearing with the energy equation solved by the characteristic-based split method

The solution of the energy equation of thermo-elasto-hydrodynamic analysis for bearings by the finite element method usually leads to convergence difficulties due to the presence of convection terms inherited from the Navier–Stokes equations. In this work, the numerical analysis is performed with finite element method universally by adopting the characteristic-based split method to solve the energy equation. Five case studies of fixed pad thrust bearings have been set up with different geometries, loads, and lubricants. The two-dimensional film pressure is obtained by solving the Reynolds equation with pre-defined axial load on the pad. The energy equation of the lubricant film and the heat transfer equation of the bearing pad are handled by characteristic-based split method and conventional finite element method in three-dimensional space, respectively. Hot oil carry-over effect and variable lubricant viscosity are considered in the simulations. The results of the temperature distributions in the lubricant film and the bearing pad are presented. The possible usability of characteristic-based split method for future thermo-elasto-hydrodynamic analysis is discussed

A Nonlinear k-ε Turbulence Model Applicable to High Pressure Gradient and Large Curvature Flow

Most of the RANS turbulence models solve the Reynolds stress by linear hypothesis with isotropic model. They can not capture all kinds of vortexes in the turbomachineries. In this paper, an improved nonlinear k-ε turbulence model is proposed, which is modified from the RNG k-ε turbulence model and Wilcox's k-ω turbulence model. The Reynolds stresses are solved by nonlinear methods. The nonlinear k-ε turbulence model can calculate the near wall region without the use of wall functions. The improved nonlinear k-ε turbulence model is used to simulate the flow field in a curved rectangular duct. The results based on the improved nonlinear k-ε turbulence model agree well with the experimental results. The calculation results prove that the nonlinear k-ε turbulence model is available for high pressure gradient flows and large curvature flows, and it can be used to capture complex vortexes in a turbomachinery

Microbial Community Diversities and Taxa Abundances in Soils along a Seven-Year Gradient of Potato Monoculture Using High Throughput Pyrosequencing Approach

<div><p>Background</p><p>Previous studies have focused on linking soil community structure, diversity, or specific taxa to disturbances. Relatively little attention has been directed to crop monoculture soils, particularly potato monoculture. Information about microbial community changes over time between monoculture and non-monoculture treatments is lacking. Furthermore, few studies have examined microbial communities in potato monoculture soils using a high throughput pyrosequencing approach.</p><p>Methodology/Principal Findings</p><p>Soils along a seven-year gradient of potato monoculture were collected and microbial communities were characterized using high throughput pyrosequencing approach. Principal findings are as follows. First, diversity (<i>H</i>_Shannon) and richness (<i>S</i>_Chao1) indices of bacterial community, but not of fungal community, were linearly decreased over time and corresponded to a decline of soil sustainability represented by yield decline and disease incidence increase. Second, <i>Fusarium</i>, the only soilborne pathogen-associated fungal genus substantially detected, was linearly increased over time in abundance and was closely associated with yield decline. Third, <i>Fusarium</i> abundance was negatively correlated with soil organic matter (OM) and total nitrogen (TN) but positively with electrical conductivity (EC). Fourth, <i>Fusarium</i> was correlated in abundances with 6 bacterial taxa over time.</p><p>Conclusions</p><p>Soil bacterial and fungal communities exhibited differential responses to the potato monoculture. The overall soil bacterial communities were shaped by potato monoculture. <i>Fusarium</i> was the only soilborne pathogen-associated genus associated with disease incidence increase and yield decline. The changes of soil OM, TN and EC were responsible for <i>Fusarium</i> enrichment, in addition to selections by the monoculture crop. <i>Acidobacteria</i> and <i>Nitrospirae</i> were linearly decreased over time in abundance, corresponding to the decrease of OM, suggesting their similar ecophysiologial trait. Correlations between abundance of <i>Fusarium</i> with several other bacterial taxa suggested their similar behaviors in responses to potato monoculture and/or soil variables, providing insights into the ecological behaviors of these taxa in the environment.</p></div

Regressions between relative abundance of <i>Fusarium</i> and bacterial taxa.

<p>Regressions with <i>p</i> values >0.05 are not shown.</p

Regressions between bacterial taxa abundances and the year of potato monoculture.

<p>Regressions between bacterial taxa abundances and the year of potato monoculture.</p

Overall fungal (A) and bacterial (B) communities in the soil samples along a year-gradient of potato monoculture.

<p>Pie charts show the average relative abundance over 18 samples. OTUs were assigned at the 97% identity level, based on which the <i>H</i>_Shannon and <i>S</i>_Chao1 indices were calculated, which are shown by graphs. Phylogenetic lineages of bacteria were assigned by phylum/subphylum and of fungi by order or higher levels. ARA stands for average relative abundance. The “unidentified fungus” is a taxon able to be assigned to kingdom Fungi but unable to any lower taxon.</p

Correlation coefficient between abundance of microbial taxa and the year of monoculture^a.

a<p>RA is relative abundances. * and ** represent significance level at <0.05 and <0.01 respectively. The taxa with average relative abundance over 18 samples <0.5% and with significance level >0.05 were not shown.</p

The correlations between <i>Fusarium</i> abundances and soil variables.

<p>The correlations between <i>Fusarium</i> abundances and soil variables.</p