770 research outputs found
Data supporting University of Southampton Doctoral thesis 'Simulation of Lubricant Properties and their Interactions with Surfaces'
No full textThis very large dataset (539 GB) is available on request in part or whole please complete the form for access https://library.soton.ac.uk/datarequest
The folders 2_feb_supp4_results.zip up to retrieve_200_reax_comp_archer.zip, include files and results of Chapter 5 of the thesis (Confined NEMD simulations).
The folders 24_Oct_20_3more_temps_pao2_viscos_t150_1_6.50.zip up to finalextra16_t100_9000.zip, include files and results of Chapter 4 of the thesis (Bulk NEMD simulations).
The folders 26_Oct_glyc_t30dens1_10k_1.zip up to the end of the list, include files and results of Chapter 3 of the thesis (EMD simulations)*.
*Note: The last two zips in this list, 9_jan_21_young_file_retrieve_100_ft2_lite_sim_ReaxFF_compression.zip and 9_jan_21_young_file_retrieve_200_ft1_lite_sim_ReaxFF_compression.zip belong to Chapter 5 of the thesis (Confined NEMD simulations)
</span
Simulation of Lubricant Properties and their Interactions with Surfaces
No full textThe behaviour of lubricants at operational conditions, such as at high temperatures and pressures, is a topic of great industrial interest. In particular, viscosity and the viscosity-pressure relation are especially important for applications and their determination by computational simulations is very desirable. In this thesis we evaluate methods to compute these quantities based on fully atomistic molecular dynamics simulations which are computationally demanding but also have the potential to be most accurate. We tested several molecules that are used as lubricants, such as 9,10-dimethyloctadecane, main component of PAO-2 base oil, which was used as the main lubricant for our simulations. The methods used for the viscosity simulations are the Green-Kubo equilibrium molecular dynamics (EMD-GK), the direct computation of viscosity from shear during non-equilibrium MD (NEMD) and the use of confined NEMD, where the fluid is confined within explicitly defined iron oxide wall surfaces, at pressures of up to 1.0 GPa and various temperatures (40-150 degrees Celsius). We present the theory behind these methods and investigate how the simulation parameters affect the results obtained, to ensure viscosity convergence with respect to the simulation intervals and all other parameters. We show that by using each method in its regime of applicability, we can achieve good agreement between simulated and measured values. NEMD simulations at high pressures captured zero shear viscosity successfully, while at 40 degrees Celsius EMD-GK is only applicable to pressures up to 0.3 GPa, where the viscosity is lower. In NEMD, longer and multiply repeated simulations reduce the standard deviation of viscosity, which is essential at lower pressures. Additionally, by using confined NEMD simulations, it was demonstrated that the film thickness of the fluid affects viscosity, and as we increase the number of lubricant molecules, we approach the viscosity value of the bulk fluid derived from NEMD simulations.Another aspect of these methods is the choice of the utilised force field for the atomic interactions. This was investigated by selecting three different commonly used force fields. We have explored several methods for calculating viscosity and we obtained results of particular industrial interest.<br/
Data supporting the thesis 'Simulations of rheological properties of lubricants under operational conditions'
No full textThe dataset is divided in
IDEAL : This folder contains the data regarding the result chapter on Ideal mixtures of two esters obtained via LAMMPS software. It contains the input files, output files, jupyter notebooks with the analysis as well as molecular dynamics trajectories and files to reproduce the simulations and data.
MIXTURE2: This folder contains the data regarding the mixture 2 (non-ideal mixtures result chapter) obtained via LAMMPS software. Specifically, it contains the input files, output files, jupyter notebooks with the analysis as well as molecular dynamics trajectories and files to reproduce the simulations and data.
MIXTURE2: This folder contains the data regarding the mixture 2 (non-ideal mixtures result chapter) obtained via LAMMPS software. Specifically, it contains the input files, output files, jupyter notebooks with the analysis as well as molecular dynamics trajectories and files to reproduce the simulations and data.
Bicyclo_Butylbenzene: This folder contains the data regarding the two of the component of the mixtures used in the non-ideal mixtures result chapter obtained via LAMMPS software. Specifically, it contains the input files, output files, jupyter notebooks with the analysis as well as molecular dynamics trajectories and files to reproduce the simulations and data.
Non_ideal_1_2_4GPa and non_ideal_1bar_05GPa : These folders contain the data regarding the mixture 1 of the non-ideal result chapter obtained via LAMMPS software. Specifically, it contains the input files, output files, jupyter notebooks with the analysis as well as molecular dynamics trajectories and files to reproduce the simulations and data.
CONFINED: This folder contains the data regarding the result chapter on confined system obtained via LAMMPS software. It contains the input files, output files, jupyter notebooks with the analysis as well as molecular dynamics trajectories and files to reproduce the simulations and data. Part of the data necessary to reproduce the data in chapter have been published in another thesis, ref. to doi:10.5258/SOTON/D2436
Hematite: This folder contains the data regarding the result chapter on hematite+zddp obtained via the ONETEP software. It contains the input files, output files, jupyter notebooks with the analysis as well as pseudopotential and any file needed to reproduce the work.
this large dataset 515GB is available 'on request' due to size. Please complete the request form at
https://library.soton.ac.uk/datarequest</span
Evaluation of methods for viscosity simulations of lubricants at different temperatures and pressures: a case study on PAO-2
No full textThe behavior of lubricants at operational conditions, such as at high pressures, is a topic of great industrial interest. In particular, viscosity and the viscosity-pressure relation are especially important for applications and their determination by computational simulations is very desirable. In this study we evaluate methods to compute these quantities based on fully atomistic molecular dynamics simulations which are computationally demanding but also have the potential to be most accurate. We used the 9,10-dimethyloctadecane molecule, main component of PAO-2 base oil as the lubricant for our tests. The methods used for the viscosity simulations are the Green-Kubo equilibrium molecular dynamics (EMD-GK) and non-equilibrium molecular dynamics (NEMD), at pressures of up to 1.0 GPa and various temperatures (40-150 degrees Celsius). We present the theory behind these methods and investigate how the simulation parameters affect the results obtained, to ensure viscosity convergence with respect to the simulation intervals and all other parameters. We show that by using each method in its regime of applicability, we can achieve good agreement between simulated and measured values. NEMD simulations at high pressures captured zero shear viscosity successfully, while at 40 degrees Celsius EMD-GK is only applicable to pressures up to 0.3 GPa, where the viscosity is lower. In NEMD, longer and multiply repeated simulations improve the confidence interval of viscosity, which is essential at lower pressures. Another aspect of these methods is the choice of the utilized force field for the atomic interactions. This was investigated by selecting two different commonly used force fields
Babel, or the local distortion of the Greek language
No full textTitle: Βαβυλωνία ἤ ἡ κατά τόπους διαφθορά τῆς ἑλληνικῆς γλώσσας. Κωµωδία (Babel, or the local distortion of the Greek language: A comedy) Originally published: Ναύπλιο (Nafplio), Τυπογραφεῖsο Κωνσταντίνου Τόµπρα ἐκ Κυδωνιῶν καὶ Κωνσταντίνου Ἰωαννίδη ἐκ Σµύρνης, 1836 Language: Greek The excerpt used is from D. C. Vyzantios, Βαβυλωνία, introduction by Spyros Evangelatos (Athens: Εστία, 1993), pp.1–3. About the author Dimitrios Vyzantios (pseudonym of Dimitrios K. Hatziaslanis) [1790, Constantin..
Dimitrios Tsamis Karatasos : a symbol of Greek, Serbian and Bulgarian friendship
No full textTwo Serbian texts extol the contribution of Dimitrios Tsamis Karatasos to the Balkan joint effort to throw off the Ottoman yoke. These texts are analysed by the author within the historical framework of their period, so that the man’s personality and work may be accurately evaluated from a fresh viewpoint. More specifically, the author conducts a research on the tombstone of Dimitrios Tsamis Karatasos, which he discovered himself at Naoussa, and the octet engraved on it, which is also published here. The work is illustrated by seven plates, of which four have not been published previously
The Remains of authoritarianism : bureaucracy and civil society in post-authoritarian Greece
No full textDimitrios A. Sotiropoulos. 30 cm. He presented this paper at a seminar held at the Center on October 21, 1994. - T.p. Includes bibliographical references (p. 31-35
Calculating shear viscosity with confined non-equilibrium molecular dynamics: a case study on hematite - PAO-2 lubricant
No full textThe behaviour of confined lubricants at the atomic scale as affected by the interactions at the surface-lubricant interface is relevant in a range of technological applications in areas such as the automotive industry. In this paper, by performing fully atomistic molecular dynamics, we investigate the regime where the viscosity starts to deviate from the bulk behaviour, a topic of great practical and scientific relevance. The simulations consist of setting up a shear flow by confining the lubricant between iron oxide surfaces. By using confined Non-Equilibrium Molecular Dynamics (NEMD) simulations at a pressure range of 0.1-1.0 GPa at 100 °C, we demonstrate that the film thickness of the fluid affects the behaviour of viscosity. We find that by increasing the number of lubricant molecules, we approach the viscosity value of the bulk fluid derived from previously published NEMD simulations for the same system. These changes in viscosity occurred at film thicknesses ranging from 10.12 to 55.93 Å. The viscosity deviations at different pressures between the system with the greatest number of lubricant molecules and the bulk simulations varied from −16% to 41%. The choice of the utilized force field for treating the atomic interactions was also investigated.</p
Computing viscosities of mixtures of ester-based lubricants at different temperatures
No full textSynthetic esters are used as lubricants for applications at high temperatures, but their development can be a trial and error process. In this context, molecular dynamics simulations could be used as a tool to investigate the properties of new lubricants, in particular viscosity. We employ nonequilibrium molecular dynamics (NEMD) simulations to predict bulk Newtonian viscosities of a set of mixtures of two esters, di(2-ethylhexyl) sebacate (DEHS) and di(2-ethylhexyl) adipate (DEHA) at 293 and 343 K as well as equilibrium molecular dynamics (EMD) and NEMD at 393 K and compare these to experimental measurements. The simulations predict mixture densities within 5% of the experimental values, and we are able to retrieve between 99% and 75% of the experimental viscosities for all ranges of temperature. Experimental viscosities show a linear trend which we are able to capture using NEMD at low temperature and EMD at high temperature. Our work shows that, using EMD and NEMD simulations, and the workflows we developed, we can obtain reliable estimates of the viscosities of mixtures of industrially relevant ester-based lubricants at different temperatures
Erratum: Korkovelos, A., et al. The role of open access data in geospatial electrification planning and the achievement of SDG7. An OnSSET-based case study for Malawi. <i>Energies</i> 2019, 12(7), 1395
No full textThe authors wish to make a change in author names (adding new author—Dimitrios Mentis) to this paper
- …
