International Journal of Non-Linear Mechanics, 2005
A mathematical formulation for the contact of rough surfaces is presented. The derivation of the ... more A mathematical formulation for the contact of rough surfaces is presented. The derivation of the contact model is facilitated through the definition of plastic asperities that are assumed to be embedded at a critical depth within the actual surface asperities. The surface asperities ...
Manipulating flexible objects stirs a great deal of interest due to the potential applications in... more Manipulating flexible objects stirs a great deal of interest due to the potential applications in industry. Most previous research work with multiple manipulators, however, focused on developing control strategies for the manipulation of rigid bodies. This paper seeks to develop simple yet practical and efficient control scheme that enables cooperating arms to handle a flexible beam. Specifically the problem studied herein is that of two arms rigidly grasping a flexible beam and capable of generating forces/moments in such a way as to move a flexible beam along a predefined trajectory. The paper develops a sliding mode control law that provides robustness against model imperfection and uncertainty. It also provides an implicit stability proof. Given the bounds of uncertainty in the model of the flexible beam and choosing a switching surface that enforces trajectory tracking, a control algorithm is designed to push the states to remain on the switching surface. Simulation results for two three joint arms moving a flexible beam are presented to validate the theoretical results.
International Journal of Vehicle Noise and Vibration, Mar 20, 2015
The reduction of disc brake squeal is an important technological subject in terms of making vehic... more The reduction of disc brake squeal is an important technological subject in terms of making vehicles quieter. Modelling and simulation is necessary for designing quiet brakes and for treating noisy brakes. The finite element method (FEM) is commonly used to simulate and predict the disc brake squeal using a complex eigenvalue analysis. In this paper, an approach to examine the disc brake squeal based on the complex eigenvalue analysis is proposed in which a positive real part indicates that the corresponding eigenmode is unstable and in turn squeal may occur. The influences of brake design parameters upon the squeal are investigated and several structural modifications on the brake pad are proposed to reduce the squeal. The predicted results show that the geometric characteristics of the pad would affect the squeal propensity, and the combination of chamfer and slot is effective to suppress squeal at some eigenmodes.
Diffusion and Defect Data Solid State Data Part B Solid State Phenomena, 2009
Page 1. The Effect of Controlled Frequency and Amplitude of Vibration on Friction Jamil Abdo 1, a... more Page 1. The Effect of Controlled Frequency and Amplitude of Vibration on Friction Jamil Abdo 1, a , Amer Al-Yhmadi 1, b 1Mechanical Engineering Dept., Sultan Qaboos University, PO Box 33, AlKhod 123, Oman ajdabdo@squ.edu.om, bamery@squ.edu.om ...
Journal of Environmental Science and Health Part a Toxic Hazardous Substances Environmental Engineering, Feb 1, 2007
Data on the concentrations of non-methane hydrocarbons (NMHC), nitrogen oxide (NO), nitrogen diox... more Data on the concentrations of non-methane hydrocarbons (NMHC), nitrogen oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), and meteorological parameters (air temperature and solar radiation) were used to predict the concentration of tropospheric ozone using the Design-Ease software. These data were collected on hourly basis over a 12-month period. Sampling of the data was conducted automatically. The effect of the NMHC, NO, NO2,CO, temperature and solar radiation variables in predicting ozone concentrations was examined under two scenarios: (i) when NO is included with the absence of NO2; and (ii) when NO2 is addressed with the absence of NO. The results of these two scenarios were validated against ozone actual data. The predicted concentration of ozone in the second scenario (i.e., when NO2 is addressed) was in better agreement with the real observations. In addition, the paper indicated that statistical models of hourly surface ozone concentrations require interactions and non-linear relationships between predictor variables in order to accurately capture the ozone behavior.
Experiments were conducted to determine the effects of frequency and amplitude of vibration on fr... more Experiments were conducted to determine the effects of frequency and amplitude of vibration on friction. The experimental analysis also seeks to take into account a variety of factors influencing the coefficient of friction such as normal load and surface roughness. An in-house pin-on-disc apparatus was constructed with a spindle speed control and applied forced-feedback to perform the tests. The response surface methodology is utilized to investigate the effects of the factors and their cross influence on the coefficient of friction for the Steel C1020 and Aluminum 7079. The analysis of variance is done on the experimental data to evaluate the statistical significance of the model. The response equation for the coefficient of friction of Steel C1020 and Aluminum 7079 were determined. The ranges of frequency and amplitude of vibration were 120 -600 Hz and 15 -225 µm, respectively. Studies have shown that the coefficient of friction decreases with the increase of frequency and amplitude of vibration within the observed ranges for both metals whereas the in case of Aluminum 7079 the coefficient of friction is about 13 % when it compares with the coefficient of friction of Steel C1020.
Page 1. 1 15th ASCE Engineering Mechanics Conference June 2-5, 2002, Columbia University, New Yor... more Page 1. 1 15th ASCE Engineering Mechanics Conference June 2-5, 2002, Columbia University, New York, NY Theoretical Modeling and Experimental Technique to Study of Contact Load Ratio – Friction Function Jamil A. Abdo 1 and Kambiz Farhang 2 ...
Noise and vibration is an increasingly important consideration in the design and study of disc br... more Noise and vibration is an increasingly important consideration in the design and study of disc brakes. Certain vibrations may only result in minor annoying squeals, while others may be severe enough to result in structural damage or failure. In either case, it is desirable to predict the conditions under which these vibrations arise, so that they may be controlled, or eliminated.
General solution to overcome stern and frequently occurring drilling problems lies in controlling... more General solution to overcome stern and frequently occurring drilling problems lies in controlling the rheology of drilling fluids. Pipe sticking, lost circulation, erosion, formation damage, thermal instability, poor hole cleaning, high torque and drag are few problems that incurs enormous costs on overall drilling operations in form of expensive drilling fluids, breakdowns, fluid loss, high power requirement, and mainly limited functionality. The nanotechnological research leading to create tailored made nanoparticles is a promising step change research for smart fluids development. The nano particles based drilling mud enables the design and development of new drilling muds for efficient drilling operations at significantly low cost. Use of nano based drilling muds has long been in discussion and some researchers have tested in laboratory but no mathematical and analytical model reported. Based on initial studies and easy availability we selected Attapulgite and after milling, characterization, surface treatment, and adding into drilling muds showed useful results. We initiated developing a scheme, starting from synthesis and characterization of nanoparticles, measurement and optimization of properties by response surface technique, establishing correlation between rheological properties, ultimately leading to performance tests at well simulators. Preliminary results of Attapulgite crop up hopes of testing more nanomaterials for further improvement.
It is well recognized that the contact stiffness, true contact area, and the contact force are am... more It is well recognized that the contact stiffness, true contact area, and the contact force are among the key features in the study of friction system behavior. This paper presents the development of formulae for the mechanical component of dry-friction at the interface of two microscopic rough surfaces. Elastic deformation under the influence of the contact forces is considered. The elastic contact model formulation between interacting asperities is not assumed to occur only at asperity peaks, thus allowing the possibility of oblique contacts wherein the local contact surfaces are no longer parallel to the mean planes of the mating surfaces. It is shown that the approach enables the separation of the contact area into its normal and tangential projections and the contact force into its normal and tangential components. The mathematical model of contact is utilized to develop formulae for normal and tangential contact stiffness. The analytical method is used to estimate contact stiffness components. Contact parameter values for the sample are derived from the surface profile data taken from a 1.0 mm by 10 mm test area. The profile is measured using a Mahr profilometer. A computer program is written and used to analyze the profile data. The analysis yields the asperity density, average asperity radius, and the standard deviation for each test area.
The physical changes in the braking material due to wear will reduce the brake lifetime and chang... more The physical changes in the braking material due to wear will reduce the brake lifetime and change both the material properties and braking capacity. Humidity has great effects on the coefficient of friction and wear. In this study the wear and friction behavior of a new and old generation of carbon-carbon composite were investigated. Identical samples were tested on a subscale dynamometer at different humidity, environment, and operating conditions. The friction coefficient was recorded and wear was measured. Visual examination, surface topography characterization, microscopy and spectroscopy techniques were used to determine the friction and wear mechanisms. Scanning Electron Microscopy, Raman Spectroscopy, and X-Rays were also used. The change in wear and friction coefficient with energy input were studies and wear transitional zones were detected. It is shown that friction, and wear are dependant on bulk material properties, environment (humid, dry and inert) and the produced friction film. It was shown that the relative humidity has strong influence on the tribological behavior of the old and new generation of composites. Wear and friction transitional zones were detected for both type of Composite.
Annals of hepatology: official journal of the Mexican Association of Hepatology
Background & aim: Despite treatment with glucocorticoids, mortality remains high in patients with... more Background & aim: Despite treatment with glucocorticoids, mortality remains high in patients with severe alcoholic hepatitis. Oxidative stress and depletion of mitochondrial glutathione are implicated factors in liver injury. The aim of this study was to evaluate the impact of the addition of metadoxine, a drug which possesses a multifactorial mechanism of action, including antioxidant properties, to standard treatment with glucocorticoids in patients with severe alcoholic hepatitis. Material and methods: This randomized open label clinical trial was performed in Mexico's General Hospital (Registry Key DIC/10/107/03/043). We randomized 70 patients with severe alcoholic hepatitis. The first group received prednisone (40 mg/day), and the second group received prednisone (40 mg/day) plus metadoxine tablets (500 mg three times daily). The duration of treatment in both groups was 30 days. Survival at 30 and 90 days, development of complications, adverse events and response to treatme...
Attapulgite (ATT) is purified, synthesized, characterized, functionalized, and tested in nano-for... more Attapulgite (ATT) is purified, synthesized, characterized, functionalized, and tested in nano-form (10–25 nm diameter) for its effectiveness to tailor the rheology of drilling fluids swiftly to reduce friction, discourage use of other expensive additives, and improve functionality. A schematic procedure for purification and synthesis of ATT to nano-level for uniform dispersion is established. X-ray diffraction and scanning electron microscopy (SEM) are utilized to analyze the nano-attapulgite (NATT) structure. The effects of NATT-modified drilling fluids on the tribological properties mainly the coefficient of friction (COF) between the drillstring and the wellbore are established. OFITE Lubricity Tester is used to measure the COF values of the test samples. To test for the performance of the NATT-modified drilling fluids, an in-house experimental setup that imitates the wellbore being drilled in the presence of surrounding drilling fluid was developed and utilized to investigate th...
International Journal of Non-Linear Mechanics, 2005
A mathematical formulation for the contact of rough surfaces is presented. The derivation of the ... more A mathematical formulation for the contact of rough surfaces is presented. The derivation of the contact model is facilitated through the definition of plastic asperities that are assumed to be embedded at a critical depth within the actual surface asperities. The surface asperities ...
Manipulating flexible objects stirs a great deal of interest due to the potential applications in... more Manipulating flexible objects stirs a great deal of interest due to the potential applications in industry. Most previous research work with multiple manipulators, however, focused on developing control strategies for the manipulation of rigid bodies. This paper seeks to develop simple yet practical and efficient control scheme that enables cooperating arms to handle a flexible beam. Specifically the problem studied herein is that of two arms rigidly grasping a flexible beam and capable of generating forces/moments in such a way as to move a flexible beam along a predefined trajectory. The paper develops a sliding mode control law that provides robustness against model imperfection and uncertainty. It also provides an implicit stability proof. Given the bounds of uncertainty in the model of the flexible beam and choosing a switching surface that enforces trajectory tracking, a control algorithm is designed to push the states to remain on the switching surface. Simulation results for two three joint arms moving a flexible beam are presented to validate the theoretical results.
International Journal of Vehicle Noise and Vibration, Mar 20, 2015
The reduction of disc brake squeal is an important technological subject in terms of making vehic... more The reduction of disc brake squeal is an important technological subject in terms of making vehicles quieter. Modelling and simulation is necessary for designing quiet brakes and for treating noisy brakes. The finite element method (FEM) is commonly used to simulate and predict the disc brake squeal using a complex eigenvalue analysis. In this paper, an approach to examine the disc brake squeal based on the complex eigenvalue analysis is proposed in which a positive real part indicates that the corresponding eigenmode is unstable and in turn squeal may occur. The influences of brake design parameters upon the squeal are investigated and several structural modifications on the brake pad are proposed to reduce the squeal. The predicted results show that the geometric characteristics of the pad would affect the squeal propensity, and the combination of chamfer and slot is effective to suppress squeal at some eigenmodes.
Diffusion and Defect Data Solid State Data Part B Solid State Phenomena, 2009
Page 1. The Effect of Controlled Frequency and Amplitude of Vibration on Friction Jamil Abdo 1, a... more Page 1. The Effect of Controlled Frequency and Amplitude of Vibration on Friction Jamil Abdo 1, a , Amer Al-Yhmadi 1, b 1Mechanical Engineering Dept., Sultan Qaboos University, PO Box 33, AlKhod 123, Oman ajdabdo@squ.edu.om, bamery@squ.edu.om ...
Journal of Environmental Science and Health Part a Toxic Hazardous Substances Environmental Engineering, Feb 1, 2007
Data on the concentrations of non-methane hydrocarbons (NMHC), nitrogen oxide (NO), nitrogen diox... more Data on the concentrations of non-methane hydrocarbons (NMHC), nitrogen oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), and meteorological parameters (air temperature and solar radiation) were used to predict the concentration of tropospheric ozone using the Design-Ease software. These data were collected on hourly basis over a 12-month period. Sampling of the data was conducted automatically. The effect of the NMHC, NO, NO2,CO, temperature and solar radiation variables in predicting ozone concentrations was examined under two scenarios: (i) when NO is included with the absence of NO2; and (ii) when NO2 is addressed with the absence of NO. The results of these two scenarios were validated against ozone actual data. The predicted concentration of ozone in the second scenario (i.e., when NO2 is addressed) was in better agreement with the real observations. In addition, the paper indicated that statistical models of hourly surface ozone concentrations require interactions and non-linear relationships between predictor variables in order to accurately capture the ozone behavior.
Experiments were conducted to determine the effects of frequency and amplitude of vibration on fr... more Experiments were conducted to determine the effects of frequency and amplitude of vibration on friction. The experimental analysis also seeks to take into account a variety of factors influencing the coefficient of friction such as normal load and surface roughness. An in-house pin-on-disc apparatus was constructed with a spindle speed control and applied forced-feedback to perform the tests. The response surface methodology is utilized to investigate the effects of the factors and their cross influence on the coefficient of friction for the Steel C1020 and Aluminum 7079. The analysis of variance is done on the experimental data to evaluate the statistical significance of the model. The response equation for the coefficient of friction of Steel C1020 and Aluminum 7079 were determined. The ranges of frequency and amplitude of vibration were 120 -600 Hz and 15 -225 µm, respectively. Studies have shown that the coefficient of friction decreases with the increase of frequency and amplitude of vibration within the observed ranges for both metals whereas the in case of Aluminum 7079 the coefficient of friction is about 13 % when it compares with the coefficient of friction of Steel C1020.
Page 1. 1 15th ASCE Engineering Mechanics Conference June 2-5, 2002, Columbia University, New Yor... more Page 1. 1 15th ASCE Engineering Mechanics Conference June 2-5, 2002, Columbia University, New York, NY Theoretical Modeling and Experimental Technique to Study of Contact Load Ratio – Friction Function Jamil A. Abdo 1 and Kambiz Farhang 2 ...
Noise and vibration is an increasingly important consideration in the design and study of disc br... more Noise and vibration is an increasingly important consideration in the design and study of disc brakes. Certain vibrations may only result in minor annoying squeals, while others may be severe enough to result in structural damage or failure. In either case, it is desirable to predict the conditions under which these vibrations arise, so that they may be controlled, or eliminated.
General solution to overcome stern and frequently occurring drilling problems lies in controlling... more General solution to overcome stern and frequently occurring drilling problems lies in controlling the rheology of drilling fluids. Pipe sticking, lost circulation, erosion, formation damage, thermal instability, poor hole cleaning, high torque and drag are few problems that incurs enormous costs on overall drilling operations in form of expensive drilling fluids, breakdowns, fluid loss, high power requirement, and mainly limited functionality. The nanotechnological research leading to create tailored made nanoparticles is a promising step change research for smart fluids development. The nano particles based drilling mud enables the design and development of new drilling muds for efficient drilling operations at significantly low cost. Use of nano based drilling muds has long been in discussion and some researchers have tested in laboratory but no mathematical and analytical model reported. Based on initial studies and easy availability we selected Attapulgite and after milling, characterization, surface treatment, and adding into drilling muds showed useful results. We initiated developing a scheme, starting from synthesis and characterization of nanoparticles, measurement and optimization of properties by response surface technique, establishing correlation between rheological properties, ultimately leading to performance tests at well simulators. Preliminary results of Attapulgite crop up hopes of testing more nanomaterials for further improvement.
It is well recognized that the contact stiffness, true contact area, and the contact force are am... more It is well recognized that the contact stiffness, true contact area, and the contact force are among the key features in the study of friction system behavior. This paper presents the development of formulae for the mechanical component of dry-friction at the interface of two microscopic rough surfaces. Elastic deformation under the influence of the contact forces is considered. The elastic contact model formulation between interacting asperities is not assumed to occur only at asperity peaks, thus allowing the possibility of oblique contacts wherein the local contact surfaces are no longer parallel to the mean planes of the mating surfaces. It is shown that the approach enables the separation of the contact area into its normal and tangential projections and the contact force into its normal and tangential components. The mathematical model of contact is utilized to develop formulae for normal and tangential contact stiffness. The analytical method is used to estimate contact stiffness components. Contact parameter values for the sample are derived from the surface profile data taken from a 1.0 mm by 10 mm test area. The profile is measured using a Mahr profilometer. A computer program is written and used to analyze the profile data. The analysis yields the asperity density, average asperity radius, and the standard deviation for each test area.
The physical changes in the braking material due to wear will reduce the brake lifetime and chang... more The physical changes in the braking material due to wear will reduce the brake lifetime and change both the material properties and braking capacity. Humidity has great effects on the coefficient of friction and wear. In this study the wear and friction behavior of a new and old generation of carbon-carbon composite were investigated. Identical samples were tested on a subscale dynamometer at different humidity, environment, and operating conditions. The friction coefficient was recorded and wear was measured. Visual examination, surface topography characterization, microscopy and spectroscopy techniques were used to determine the friction and wear mechanisms. Scanning Electron Microscopy, Raman Spectroscopy, and X-Rays were also used. The change in wear and friction coefficient with energy input were studies and wear transitional zones were detected. It is shown that friction, and wear are dependant on bulk material properties, environment (humid, dry and inert) and the produced friction film. It was shown that the relative humidity has strong influence on the tribological behavior of the old and new generation of composites. Wear and friction transitional zones were detected for both type of Composite.
Annals of hepatology: official journal of the Mexican Association of Hepatology
Background & aim: Despite treatment with glucocorticoids, mortality remains high in patients with... more Background & aim: Despite treatment with glucocorticoids, mortality remains high in patients with severe alcoholic hepatitis. Oxidative stress and depletion of mitochondrial glutathione are implicated factors in liver injury. The aim of this study was to evaluate the impact of the addition of metadoxine, a drug which possesses a multifactorial mechanism of action, including antioxidant properties, to standard treatment with glucocorticoids in patients with severe alcoholic hepatitis. Material and methods: This randomized open label clinical trial was performed in Mexico's General Hospital (Registry Key DIC/10/107/03/043). We randomized 70 patients with severe alcoholic hepatitis. The first group received prednisone (40 mg/day), and the second group received prednisone (40 mg/day) plus metadoxine tablets (500 mg three times daily). The duration of treatment in both groups was 30 days. Survival at 30 and 90 days, development of complications, adverse events and response to treatme...
Attapulgite (ATT) is purified, synthesized, characterized, functionalized, and tested in nano-for... more Attapulgite (ATT) is purified, synthesized, characterized, functionalized, and tested in nano-form (10–25 nm diameter) for its effectiveness to tailor the rheology of drilling fluids swiftly to reduce friction, discourage use of other expensive additives, and improve functionality. A schematic procedure for purification and synthesis of ATT to nano-level for uniform dispersion is established. X-ray diffraction and scanning electron microscopy (SEM) are utilized to analyze the nano-attapulgite (NATT) structure. The effects of NATT-modified drilling fluids on the tribological properties mainly the coefficient of friction (COF) between the drillstring and the wellbore are established. OFITE Lubricity Tester is used to measure the COF values of the test samples. To test for the performance of the NATT-modified drilling fluids, an in-house experimental setup that imitates the wellbore being drilled in the presence of surrounding drilling fluid was developed and utilized to investigate th...
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