Mongkolwongrojn, Mongkol

Preferred name

Alternative Name

Mongkolwongrojn, M.

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School of Engineering

mongkol.mo@kmitl.ac.th

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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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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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Thermoelastohydrodynamic analysis of journal bearings with non-Newtonian Carreau fluids
(2010-06-24)
Mongkolwongrojn, M.
;
Aiumpornsin, C.
The paper focuses on the solution of a numerical model to explore the journal bearing performance under transient thermal elastohydrodynamic lubrication with non-Newtonian lubricants based on Carreau viscosity model. The newly derived time-dependent modified Reynolds equation and the adiabatic energy equation have been formulated using a non-Newtonian Carreau viscosity model. The simultaneous systems consisting of the modified Reynolds equation, elasticity equation and energy equation with initial conditions were solved numerically using the multi-grid multi-level method with full approximation technique. The analysis showed that the fluid characteristics as defined by the Carreau model, led to large differences in minimum film thickness and maximum temperature rise for bearing liners with low elastic modulus. Copyright © 2009 by ASME.
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Influence of speed-up and speed-down on internal stresses of wound rolls in web handling process
(2012-02-23)
Mongkolwongrojn, Mongkol
;
Jeenkour, Puttha
In web winding process, the effects of speed-up and speed-down on internal stresses of wound roll have been investigated. The air-entrainment can be obtained theoretically using the modified nonlinear Hakiel model. In this research work, air-entrainment model established by Hamrock and Dowson was applied to estimate the initial air film layers into a wound roll in the winding system with a nip-roller. Moreover, the characteristics of a wound roll were examined under varying tension and varying speed conditions. The numerical results showed the radial stress, tangential stress, and friction force distributions at central inside a wound roll under the condition for a wound roll without wrinkle and slippage phenomena. © (2012) Trans Tech Publications.
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Theoretical analysis of flying characteristics for air-helium filled HDD
(2014-01-01)
Mongkolwongrojn, Mongkol
;
Kuanoon, Kunchit
This paper presents the flying characteristics of air-helium filled hard disk drive for a self-acting two rails flat slider bearing. Numerical scheme based on the finite difference with multigrid multi-level technique were implemented for the ultra-low flying height sliders. The characteristics of air-helium filled HDD have been examined in this research work. The results shown that the change of flying height is significantly for various fraction of air-helium filled, at various operating conditions such as temperature velocity and mass of slider. Increase of velocity, flying height increase. Increase both the temperature and the mass load, flying height decrease. Increasing of fraction in helium gas, the flying height decreases rapidly for 40% to 60% of fraction in helium filled. The flying height for air-helium filled magnetic flat slider head equal to 1.3 nm at trailing edge with mass load 12 mN and velocity 20 m/s. The spacing for helium filled hard disk drive is lower than 3 nm when compared with conventional air filled hard disk drive. © (2014) Trans Tech Publications, Switzerland.
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Effect of solid particle on TEHL under line contact with solid-liquid lubricant
(2012-04-04)
Rattapasakorn, S.
;
Mongkolwongrojn, M.
The two infinitely long surfaces in line contact under thermoelastohydrodynamic lubrication with solid-liquid lubricants were investigated. The time-dependent modified Reynolds equation elasticity equation and the adiabatic energy equation have been formulated and solved numerically with initial conditions using multi-grid multi-level method with full approximation technique. The characteristics of the two surfaces in line contact under thermoelastohydrodynamic lubrication were presented as; film pressure, film temperature and oil film thickness profiles. The results of solid-liquid lubricants with micro-particle and nano-particle under thermal elastohydrohynamic lubrication were compared with the case of pure liquid lubricant. © (2012) Trans Tech Publications, Switzerland.
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Elastohydrodynamic lubrication of cylindrical roller in line contact
(2004-09-27)
Mongkolwongrojn, Mongkol
;
Yawong, Somnuk
Elastohydrodynamic lubrication is defined as thin film lubrication considering the elastic deformation of material under contact stress. This paper presents the application of finite difference and Newton Raphson method to calculate the Reynolds equation of a cylindrical roller on flat surface numerically. The lubricant is a compressible fluid and operated at isothermal condition. Calculation results show that the film pressure of the lubricants in line contact under elastohydrodynamic lubrication is decreased when the increase of load, on the other hand, the film thickness will be increase as the velocity increase. At severe conditions, the film pressure will be increased approach the Hertzian contact pressure. At constant load and velocity the film pressure increase gradually at lubricant inlet and reach the maximum pressure to form pressure spike at minimum film thickness.
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Compensation and estimation of friction by using extended Kalman filter
(2006-12-01)
Gomonwattanapanich, Opart
;
Pattanapukdee, Adual
;
Mongkolwongrojn, Mongkol
A friction exists in every mechanical system. The phenomenon of friction is complicated and difficult to measure the exact value. In this paper, the compensation and estimation of friction by using Extended Kalman Filter (EKF) have been introduced and investigated. The study plant is a second order system with low-pass PD controller. The actual friction of the plant is assumed to be the modified Tustin friction model. The simulations are conducted for three cases of the input signal: sinusoidal, triangular, square, and two cases of compensation: no friction compensation and with friction compensation. The performances of the system are indicated by root-mean-square error (RMS Error) and peak error (Peak Error). The studies show that the system with the friction compensation by using EKF has the better performances than the system with no friction compensation. The RMS Errors of the system are decrease by 90.4 %, 89.2 %, and 12.5 % for sinusoidal, triangular, and square input signals, respectively. Also, the Peak Errors are decrease by 65.9 % and 58.7 % for sinusoidal and triangular input signals, respectively. For square input signal, there is no significant decrease of the Peak Error due to the high overshoot of the system with friction compensation. © 2006 ICASE.
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Effects of surface roughness on elastohydrodynamic lubrication in elliptical contact with non-Newtonian fluids
(2012-04-04)
Rattapasakorn, S.
;
Panichakorn, J.
;
Mongkolwongrojn, M.
This paper presents the effect of surface roughness on the performance characteristics of elastohydrodynamic lubrication with non-Newtonian fluid base on Carreau viscosity model in elliptical contact. The time independent modified Reynolds equation and elastic equation were formulated for compressible fluid. Perturbation method, Newton Raphson method and full adaptive multigrid method were implemented to obtain the film pressure, film thickness profiles and friction coefficient in the contact region at various amplitude of combined surface roughness, applied loads, speeds and elliptic ratio. Simulation results show surface roughness amplitude has significant affected the film pressure in the contact region. The minimum film thickness decreases but friction coefficient increases when the combined roughness and applied loads increases. The minimum film thickness and friction coefficient both increase as the relative velocity of the ball and the plate is increase. For increasing the elliptic ratio, the minimum film thickness increases but the friction coefficient decreases. © (2012) Trans Tech Publications, Switzerland.
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Transient response of head slider with geometry change in head surface of magnetic storage systems
(2002-01-01)
Mongkolwongrojn, M.
;
Gunnuang, W.
In this study, the dynamic flying characteristics of the worn head sliders are investigated theoretically due to the change in head geometry caused by head and disk contact. The film shapes can be approximated as taper- Truncated cycloidal-flat film. Two-dimensional time dependent modified Reynolds equation included molecular slip effect are formulated with neglected the roughness effect. The motion of head slider was assumed to have two degree of freedom in this work. Finite difference approximation with Newton Raphson iterative technique and the fourth order Runge-Kutta method were implemented to obtain the transient response of the slider head with various change in head geometry numerically and compared with IBM3380 type head The simulation results show the film shape has affects significantly on the static and dynamic characteristic of slider head in magnetic storage systems.

Mongkolwongrojn, Mongkol

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