Next Article in Journal
Effect of Third-Particle Material and Contact Mode on Tribology Contact Characteristics at Interface
Previous Article in Journal
Mechanical and Tribological Behavior of Austempered Ductile Iron (ADI) under Dry Sliding Conditions
Previous Article in Special Issue
Sensitivity of TEHL Simulations to the Use of Different Models for the Constitutive Behaviour of Lubricants
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Impact of Ad Hoc Post-Processing Parameters on the Lubricant Viscosity Calculated with Equilibrium Molecular Dynamics Simulations

by
Gözdenur Toraman
1,
Toon Verstraelen
2 and
Dieter Fauconnier
1,3,*
1
Soete Laboratory, Ghent University, Technologiepark-Zwijnaarde 46, 9052 Ghent, Belgium
2
Center for Molecular Modeling (CMM), Ghent University, Technologiepark-Zwijnaarde 46, 9052 Ghent, Belgium
3
FlandersMake@UGent, Core Lab MIRO, 9000 Ghent, Belgium
*
Author to whom correspondence should be addressed.
Lubricants 2023, 11(4), 183; https://doi.org/10.3390/lubricants11040183
Submission received: 21 March 2023 / Revised: 13 April 2023 / Accepted: 17 April 2023 / Published: 19 April 2023

Abstract

Viscosity is a crucial property of liquid lubricants, and it is theoretically a well-defined quantity in molecular dynamics (MD) simulations. However, no standardized protocol has been defined for calculating this property from equilibrium MD simulations. While best practices do exist, the actual calculation depends on several ad hoc decisions during the post-processing of the raw MD data. A common protocol for calculating the viscosity with equilibrium MD simulations is called the time decomposition method (TDM). Although the TDM attempts to standardize the viscosity calculation using the Green–Kubo method, it still relies on certain empirical rules and subjective user observations, e.g., the plateau region of the Green–Kubo integral or the integration cut-off time. It is known that the TDM works reasonably well for low-viscosity fluids, e.g., at high temperatures. However, modified heuristics have been proposed at high pressures, indicating that no single set of rules works well for all circumstances. This study examines the effect of heuristics and ad hoc decisions on the predicted viscosity of a short, branched lubricant molecule, 2,2,4-trimethylhexane. Equilibrium molecular dynamics simulations were performed at various operating conditions (high pressures and temperatures), followed by post-processing with three levels of uncertainty quantification. A new approach, “Enhanced Bootstrapping”, is introduced to assess the effects of individual ad hoc parameters on the viscosity. The results show a strong linear correlation (with a Pearson correlation coefficient of up to 36%) between the calculated viscosity and an ad hoc TDM parameter, which determines the integration cut-off time, under realistic lubrication conditions, particularly at high pressures. This study reveals that ad hoc decisions can lead to potentially misleading conclusions when the post-processing is performed ambiguously.
Keywords: equilibrium molecular dynamics; thermo-elastohydrodynamic lubrication; viscosity; Green–Kubo; time decomposition method equilibrium molecular dynamics; thermo-elastohydrodynamic lubrication; viscosity; Green–Kubo; time decomposition method
Graphical Abstract

Share and Cite

MDPI and ACS Style

Toraman, G.; Verstraelen, T.; Fauconnier, D. Impact of Ad Hoc Post-Processing Parameters on the Lubricant Viscosity Calculated with Equilibrium Molecular Dynamics Simulations. Lubricants 2023, 11, 183. https://doi.org/10.3390/lubricants11040183

AMA Style

Toraman G, Verstraelen T, Fauconnier D. Impact of Ad Hoc Post-Processing Parameters on the Lubricant Viscosity Calculated with Equilibrium Molecular Dynamics Simulations. Lubricants. 2023; 11(4):183. https://doi.org/10.3390/lubricants11040183

Chicago/Turabian Style

Toraman, Gözdenur, Toon Verstraelen, and Dieter Fauconnier. 2023. "Impact of Ad Hoc Post-Processing Parameters on the Lubricant Viscosity Calculated with Equilibrium Molecular Dynamics Simulations" Lubricants 11, no. 4: 183. https://doi.org/10.3390/lubricants11040183

APA Style

Toraman, G., Verstraelen, T., & Fauconnier, D. (2023). Impact of Ad Hoc Post-Processing Parameters on the Lubricant Viscosity Calculated with Equilibrium Molecular Dynamics Simulations. Lubricants, 11(4), 183. https://doi.org/10.3390/lubricants11040183

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop