Mongkolwongrojn, Mongkol

Preferred name

Alternative Name

Mongkolwongrojn, M.

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School of Engineering

mongkol.mo@kmitl.ac.th

Now showing 1 - 10 of 37

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Transient EHL of two surfaces under elliptical contact with non-Newtonian lubricant
(2012-02-23)
Mongkolwongrojn, Mongkol
;
Panichakorn, Jesda
This paper presents the effects of a sudden load change and sudden speed change on the performance characteristics of two surfaces under elliptical contact with elastohydrodynamic lubrication. The non-Newtonian lubricant for the research work are modeled based on Carreau viscosity model. The time dependent modified Reynolds equation and elastic equation were formulated for compressible fluid. Perturbation method, Newton Raphson method and full adaptive multigrid method were implemented and solved to obtain the film pressure, film thickness profiles and friction coefficient in the contact regime at various applied loads and speeds. Simulation results show the friction coefficient increase significantly under sudden loads. The minimum film thickness and friction coefficient both decrease significantly as speed is decreased. © (2012) Trans Tech Publications.
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Influence of surface roughness in TEHL with non-Newtonian liquid/solid lubricants under sudden load change
(2008-05-16)
Mongkolwongrojn, Mongkol
;
Aiumpornsin, Chatchai
This paper describes the influence of surface roughness on thermoelastohydrodynamic (TEHL) lubrication characteristics of a sliding line contact under sudden load change. The surface roughness is a harmonic wave in the transverse direction. The time-dependent Reynolds equation with non-Newtonian liquid-solid fluids has been formulated using a power law model. The constitutive equation of the liquid-solid lubricants was formulated based on experimental data. The simultaneous systems of modified Reynolds, elasticity and energy equations with initial conditions were solved numerically. The static and dynamic characteristics of the thermoelastohydrodynamic line contact with rough surfaces under sudden load change have been investigated numerically to determine the distribution of pressure, film thickness and temperature. The transient response of the lubricated line contact between a infinitely long cylinder surface and a flat plate was simulated under a heavy step load function. This simulation showed a significant effect of surface roughness and solid particles on thermoelastohydrodynamic lubrication under sudden load change. Copyright © 2007 by ASME.
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Theoretical investigation of transient elastohydrodynamic lubrication with newtonian solid-liquid lubricants
(2006-10-01)
Mongkolwongrojn, M.
;
Thammakosol, K.
This paper reports a theoretical investigation of transient elastohydrodynamic lubrication of a line contact. A time-dependent Reynolds equation and elasticity equations for compressible solid-liquid lubricants were solved using finite volume and multigrid techniques. The lubricants used were mineral oils mixed with very small solid particles, MoS<inf>2</inf> and FIFE which can be treated as Newtonian fluids. The two surfaces were initially at rest and in contact. The transient oil film pressure and oil film thickness were calculated numerically. This simulation showed the significant effects of solid particles on the lubrication characteristics. Copyright © 2006 John Wiley & Sons, Ltd.
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Transient elastohydrodynamic lubrication in artificial knee joint with non-Newtonian fluids
(2010-05-01)
Mongkolwongrojn, Mongkol
;
Wongseedakaew, Khanittha
;
Kennedy, Francis E.
This paper presents the transient analysis of a human artificial knee joint under elastohydrodynamic lubrication (EHL) for point contact with non-Newtonian lubricants. The artificial knee joints use ultra high molecular weight polyethylene (UHMWPE) against metal with time-varying speed and load during walking. This numerical simulation employed a perturbation method, Newton Raphson method and multigrid method with full approximation technique to solve simultaneously both the time-dependent Reynolds equation, with non-Newtonian fluid based on a Carreau model, and the elasticity equation. The general numerical schemes are implemented to investigate the characteristics of elastohydrodynamic lubrication in human artificial knee joints; profiles of pressure and film thickness are determined, with varying material and lubricant properties, applied loads and speeds. The results show that the elastohydrodynamic fluid film thickness between the metallic component of the artificial knee joint and the soft polyethylene bearing becomes larger as the contact area increases and the fluid film pressure decreases. At the beginning of the first walking cycle, the film thickness is lower than in subsequent cycles because of the time required to develop the fluid film; after the first cycle, the fluid film is similar for every cycle and is dependent on transient applied load and speed during human movement. © 2009 Elsevier Ltd. All rights reserved.
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Elastohydrodynamic lubrication of rough surfaces under oscillatory line contact with non-newtonian lubricant
(2008-09-01)
Mongkolwongrojn, Mongkol
;
Wongseedakaew, Khanittha
;
Kennedy, Francis E.
This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.
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Theoretical characteristics of hydrodynamic journal bearings lubricated with soybean-based oil
(2002-01-01)
Mongkolwongrojn, M.
;
Arunmetta, P.
Vegetable-based oils are not only biodegradable but also environmentally advantageous, and the range of lubrication applications offered by them continues to grow. Recently, vegetable-based oils have been combined with synthetic esters to produce modified vegetable-based oils. This paper presents an investigation of the theoretical characteristics of hydrodynamic journal bearings lubricated with non-Newtonian soybean-based oil. The soybean-based oil was mixed with synthetic esters and silicone oil. The relationship between the shear stress and shear strain rate of the oil was obtained experimentally. The time-dependent modified Reynolds equation including non-Newtonian effects was formulated for short circular journal bearings. The perturbation technique was applied to the Reynolds equation to obtain zero- and first-order pressure equations. The finite difference method was used to calculate the pressure distribution numerically. The static and dynamic characteristics, such as pressure distribution, Sommerfeld number, attitude angle, and spring and damping coefficients, were obtained numerically. It was found that the nonlinear factors of the non-Newtonian soybean-based oil strongly affected the performance characteristics of the journal bearings.
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Lubrication and wear of artificial knee joint materials in a rolling/sliding tribotester
(2007-04-01)
Kennedy, Francis E.
;
Van Citters, Douglas W.
;
Wongseedakaew, Khanittha
;
Mongkolwongrojn, Mongkol
This paper describes the influence of lubrication on wear during testing of materials for artificial knee joints in a rolling/sliding tribotester built to simulate contact conditions in a total knee replacement. The test configuration consists of parallel cylinders (pucks) of ultrahigh molecular weight polyethylene (UHMWPE) and polished cobalt-chrome alloy in oscillatory rolling/sliding contact in a bath of dilute (25%) bovine serum. Wear tests of three different UHMWPE materials were run under constant load at 40% sliding for 1.5 million oscillation cycles at 1.5 cycles/s. Wear of the UHMWPE was determined by measuring the profile of the cylindrical contact surface of the puck before and after each test. Profile measurements were repeated after at least 53 days to eliminate the contribution from creep. Differences between initial and final profiles were attributed to wear of the UHMWPE. It was found that the largest wear depth in the lubricated tests occurred near the ends of the oscillatory contact area, while dry (unlubricated) tests of the same materials showed a peak wear depth near the center of the contact area. In the lubricated tests, the worn depth was lowest for the most heavily irradiated material. Analysis of the elastohydrodynamic lubrication in the rolling/sliding contact was carried out assuming a line-contact situation with smooth cylindrical surfaces. The time-dependent modified Reynolds equation and the elasticity equation with initial conditions were solved numerically using a multigrid technique with full approximation scheme, and using a Newton Raphson method to solve the highly nonlinear system of equations. The thickness of the lubricating film of bovine serum was determined for points along the length of the wear track. It was found that the smallest film thickness (h<inf>min</inf>) occurs very close to the location in the oscillating contact where the greatest wear occurs, owing to the very low entraining velocity near the ends of the oscillation cycle. The coefficient (K) for wear of the UHMWPE was found to be relatively constant over the central section of the oscillatory motion, but increased to a higher value where h<inf>min</inf> decreased to near zero. Thus, the important influence of lubrication on wear of artificial knee bearings was demonstrated. Copyright © 2007 by ASME.
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Static Characteristics of High-Speed Slider Bearings Lubricated with Non-Newtonian Fluids (In the Case of Infinitely Long Bearings)
(1995-01-01)
Hashimoto, Hiromu
;
Mongkolwongrojn, Mongkol
In this paper, the static characteristics of infinitely long slider bearings lubricated with non-Newtonian fluids are examined theoretically by considering the fluid inertia effects. In the derivation of the modified Reynolds equation, the fluid inertia terms in the momentum equation for the lubricant film are averaged over the film thickness, and the Rabinowitsch empirical model is used as a constitutive equation of non-Newtonian fluids. Applying the modified Reynolds equation to the infinitely long slider bearings, the film pressure, load carrying capacity, friction force and inlet flow rate are obtained under various values of the dimensionless nonlinear factor and film thickness ratio, and the effects of fluid inertia on these static characteristics are discussed. © 1995, The Japan Society of Mechanical Engineers. All rights reserved.
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Effect of bearing materials on journal bearings under TEHL with lubricant based on Carreau model
(2020-02-17)
Gunnuang, Waleephan
;
Aiumbhornsin, Chatchai
;
Wongsa-Ngam, Jittraporn
;
Mongkolwongrojn, Mongkol
This work presents a transient analysis of journal bearings under thermal elastohydrodynamic lubrication (TEHL) based on the Carreau model. The effects of the elastic modulus of the bearing liner have been investigated using numerical simulations. A time-dependent modified Reynolds equation and an adiabatic energy equation based on the Carreau model have been formulated and numerically solved to examine the performance of the journal bearings. The results show that the minimum film thickness and the friction coefficient both increase with decreasing bearing liner elastic modulus. In contrast, the dimensionless load carrying capacity, dimensionless maximum film temperature, and dimensionless maximum film pressure all decrease with decreasing bearing liner elastic modulus. The stability regions tend to decrease in size for journal bearings under TEHL, especially for journal bearings composed of soft materials.
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Effect of Al2O3 nanoparticles additives on thermo-elastohydrodynamic with Newtonian lubricant
(2013-10-04)
Rattapasakorn, Sountaree
;
Mongkolwongrojn, Mongkol
This paper presents the effect of Al<inf>2</inf>O<inf>3</inf> nanoparticles additives on thermo-elastohydrodynamic with Newtonian lubricant. The modified Reynolds equation and energy equation have been formulated and solved numerically with initial conditions using multi-grid multi-level method. Simulation results show the operating with Al<inf>2</inf>O<inf>3</inf> nanoparticles blended particularly with SAE-90 lubricant. The maximum pressure and temperature decreases, as compared to SAE-90 oil without nanoparticles additives. © (2013) Trans Tech Publications, Switzerland.

Mongkolwongrojn, Mongkol

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