Saad Ahmed - Academia.edu (original) (raw)

Papers by Saad Ahmed

Volume 1: Symposia, Parts A and B, 2012

ABSTRACT

Volume 2: Fora, 2009

ABSTRACT

2003 International Joint Power Generation Conference, 2003

Volume 2: Fora, Parts A and B, 2007

ASME 1997 Turbo Asia Conference, 1997

Pathology, 2014

ABSTRACT Introduction: Benign symmetric lipomatosis is a rare disease. Its aetiopathogenesis is u... more ABSTRACT Introduction: Benign symmetric lipomatosis is a rare disease. Its aetiopathogenesis is uncertain although it has been linked to chronic alcoholism, disturbance in lipid metabolism, and autonomic and mitochondrial dysfunctions. Familial and syndromic associations have also been made. Its main characteristic is the overgrowth of fat in form of an unencapsulated lesion. Most of the cases reported are in the head and neck region. We report a case that occurred in the breasts. Patient: A 62-year-old man presented to our hospital with a 3 year history of painless progressive, soft swellings of the breasts bilaterally. History, systemic examination, biochemical and radiological assessment did not reveal anything suggestive of abnormal lipid metabolism or of liver or endocrine disorders. He was not on any medications except for the here oft used herbal blends. A clinical diagnosis of gynaecomastia was made. Partial mastectomy with sparing of the nipple-areolar complex area was done. Grossly, we found huge unencapsulated masses measuring: right (30 x 30 x 13 cm) and left (31 x 30 x 12 cm). Cut sections revealed homogeneous, yellow, greasy tissues. Microscopy showed unencapsulated sheets of mature adipocytes with scanty, delicate, fibro-vascular connective tissue stroma exclusive of any epithelial elements. The patient had done very well since discharge from the hospital. Conclusion: Benign symmetric lipomatosis may occur in the male breast and thus constitute a mimic of bilateral gynaecomastia.

Journal of Biomechanics, 1983

The velocity field in the neighborhood of axisymmetric constrictions in rigid tubes was investiga... more The velocity field in the neighborhood of axisymmetric constrictions in rigid tubes was investigated using laser Doppler anemometry and flow visualization. Upstream flow conditions were steady; and Reynolds numbers were in the range 500-2000, values which are representative of the larger arteries in humans. Stenoses of 25, 50 and 75% area reduction were studied. Velocity profiles are presented in sufficient detail to allow comparison with computational biofluid dynamics models. Wall shear stresses were estimated from the near wall velocity gradient, and the nature of observed poststenotic flow disturbances is discussed. Results indicate that flow disturbances of discrete oscillation frequency may be more valuable than turbulence as an indicator of early stages of stenosis development. Additionally, despite the fact that poststenotic turbulence exists for the higher degrees of stenosis and Reynolds numbers, the resulting wall shear stresses are only three to four times greater than the Poiseuille value and are considerably less than the wall shear stress within the stenosis itself.

Journal of Biomechanics, 1983

Instantaneous velocities in the field distal to contoured axisymmetric stenoses were measured wit... more Instantaneous velocities in the field distal to contoured axisymmetric stenoses were measured with a laser Doppler anemometer. Upstream flow conditions were steady and spanned a range of Reynolds numbers from 500 to 2000. Autocorrelation functions and spectra of the velocity were employed to descrtbe the nature of fluid dynamic disturbances.

Journal of Biomechanics, 1984

The pulsatile flow field distal to axisymmetric constrictions in a straight tube was studied usin... more The pulsatile flow field distal to axisymmetric constrictions in a straight tube was studied using laser Doppler anemometry. The upstream centerline velocity waveform was sinusoidal at a frequency parameter of 7.5 and mean Reynolds number of 600. Stenosis models of 25, 50 and 75% area reduction were employed and velocity data were derived by ensemble averaging methods. Extensive measurements of the pulsatile velocity profiles are reported, and wall shear rates were computed from the near wall velocity profile gradients. The experiments indicate that a permanent region of poststenotic flow separation does not exist even for the severest constriction, in contrast to results for steady flow. Values of wall shear stress were greatest near the throat of the constriction and were relatively low in the poststenotic region, including the region of most intense flow disturbance. Turbulence was found only for the 75% stenosis model and was created only during a segment of the cycle. Although much emphasis has been placed upon turbulence in the detection of arterial stenoses, particularly as identified by Doppler ultrasound spectral broadening, the present study implies that identification of flow disturbances of an organized nature may be more fundamental in recognizing mild to moderate disease. Additionally, the relationship of these flow field results to the animal aortic coarctation model often employed in atherogenesis studies is discussed.

Journal of Aircraft, 2000

An experimental investigation has been conducted on a two-dimensional NACA 0024 airfoil equipped ... more An experimental investigation has been conducted on a two-dimensional NACA 0024 airfoil equipped with a leading-edgerotating cylinder. The airfoil was tested for different values of leading-edgerotations and ap de ection angles. The effects of the angle of attack ®, the cylinder surface velocity ratio Uc/U, and the ap de ection angle ± on lift and drag coef cients, the size of the separated ow region, and the stall angle of attack are included. The effect of Uc/U on the boundary-layer growth and turbulence intensity are also shown. Experimental results, for example, showed that the leading-edge rotating cylinder increases the lift coef cient of a NACA 0024 airfoil from 0.85 at Uc/U = 0 to 1.63 at Uc /U = 4 and delays the stall angle of attack by about 160%. Smoke-wire ow visualization results were also used to demonstrate the strong effect of the leading-edge rotating cylinder on the size of the recirculation region.

Journal of Aircraft, 1995

Energy, 1998

Simultaneous two-component laser-Doppler-velocimeter measurements were made in an axisymmetric su... more Simultaneous two-component laser-Doppler-velocimeter measurements were made in an axisymmetric sudden expansion to measure the flow properties of a confined, isothermal flow-field of a research dump combustor. Measurements of mean velocities, Reynolds stresses, and triple products were carried out at axial distances ranging from 0.38H (H=step height) to 18H downstream of the dump plane. Detailed experimental data are provided to help

Applied Mechanics and Materials, 2013

Applied Mechanics and Materials, 2013

ABSTRACT The direct contact heat transfer technique gives better heat transfer rates. In this pap... more ABSTRACT The direct contact heat transfer technique gives better heat transfer rates. In this paper, the operation of a simple system was simulated under different operating conditions.During the charging mode of the operation, refrigerant R134a is injected into water stored in an evaporator to exchange directly heat with the water and form clathrates.Later, the clathrate is used tocool water which is used for air-conditioning purposes. Direct contact charging and/or discharging eliminate the necessity of a heatexchanger inside the storage tank and leads to an effective heat transfermethod. The results indicate that the performance of the system depends on the refrigerant type, compressor speed and the mass flow rate of the refrigerant.

Applied Mechanics and Materials, 2013

ABSTRACT This research work investigates the heat transfer characteristics of a direct contact he... more ABSTRACT This research work investigates the heat transfer characteristics of a direct contact heat exchanger. A cold two phase refrigerant R134a is injected into water stored in an evaporator to exchange directly heat with the water and form clathrates during the charging mode of the operation. The clathrate is used later for obtaining chilled water for air-conditioning purposes. It was found that the performance of the system depends on the refrigerant, its ratio to water, compressor speed and the mass flow rate of the refrigerant.

AIAA Journal, 1987

Jets discharging normally into a swirling crossflow are investigated experimentally. Total jet to... more Jets discharging normally into a swirling crossflow are investigated experimentally. Total jet to total swirling flow axial momentum ratios of 0.43 and 0.96 are examined. A vane swirler with an overall swirl number of 2.25 is used to generate the crossflow in a 125-mm i.d. tube. The jet nozzle with an exit diameter of 8.73 mm is mounted at one tube diameter downstream of the swirler. A one-color, one-component laser Doppler anemometer, operating in the forward scatter mode, is used to measure the flow field downstream of the jet. Results show that the jet does not penetrate deeply into the tube. Instead, it moves downstream along a spiral created by the swirling flow in the absence of the jet. Consequently, the disturbances created by the jet are limited to a small region around the jet, and the reversed flow region along the tube core created by the swirling motion still remains intact. The turbulence field of the swirling flow is affected more by the jet than the mean flowfield. However, the disturbances created by the jet die off quickly. At two tube diameters away from the jet and farther downstream, the mean flow and turbulence fields exhibit behavior characteristic of the swirling flow alone. This demonstrates that the decay of the jet is fairly complete within this region. Finally, as the jet momentum is increased, the jet's effect is also noted in regions other than along the jet trajectory. This indicates jetbifurcation behavior at high jet momentum.

Experiments in Fluids, 1986

Abstract. The presem investigation reports on the near field behavior of gas jets in a long confi... more Abstract. The presem investigation reports on the near field behavior of gas jets in a long confinement and points out the differences between this type of jet flow and those of free jets and jets in a short confinement. The jet, with a diameter of 8.73 mm, is aligned concentrically with a ...

Volume 1: Symposia, Parts A and B, 2012

ABSTRACT

Volume 2: Fora, 2009

ABSTRACT

2003 International Joint Power Generation Conference, 2003

Volume 2: Fora, Parts A and B, 2007

ASME 1997 Turbo Asia Conference, 1997

Pathology, 2014

ABSTRACT Introduction: Benign symmetric lipomatosis is a rare disease. Its aetiopathogenesis is u... more ABSTRACT Introduction: Benign symmetric lipomatosis is a rare disease. Its aetiopathogenesis is uncertain although it has been linked to chronic alcoholism, disturbance in lipid metabolism, and autonomic and mitochondrial dysfunctions. Familial and syndromic associations have also been made. Its main characteristic is the overgrowth of fat in form of an unencapsulated lesion. Most of the cases reported are in the head and neck region. We report a case that occurred in the breasts. Patient: A 62-year-old man presented to our hospital with a 3 year history of painless progressive, soft swellings of the breasts bilaterally. History, systemic examination, biochemical and radiological assessment did not reveal anything suggestive of abnormal lipid metabolism or of liver or endocrine disorders. He was not on any medications except for the here oft used herbal blends. A clinical diagnosis of gynaecomastia was made. Partial mastectomy with sparing of the nipple-areolar complex area was done. Grossly, we found huge unencapsulated masses measuring: right (30 x 30 x 13 cm) and left (31 x 30 x 12 cm). Cut sections revealed homogeneous, yellow, greasy tissues. Microscopy showed unencapsulated sheets of mature adipocytes with scanty, delicate, fibro-vascular connective tissue stroma exclusive of any epithelial elements. The patient had done very well since discharge from the hospital. Conclusion: Benign symmetric lipomatosis may occur in the male breast and thus constitute a mimic of bilateral gynaecomastia.

Journal of Biomechanics, 1983

The velocity field in the neighborhood of axisymmetric constrictions in rigid tubes was investiga... more The velocity field in the neighborhood of axisymmetric constrictions in rigid tubes was investigated using laser Doppler anemometry and flow visualization. Upstream flow conditions were steady; and Reynolds numbers were in the range 500-2000, values which are representative of the larger arteries in humans. Stenoses of 25, 50 and 75% area reduction were studied. Velocity profiles are presented in sufficient detail to allow comparison with computational biofluid dynamics models. Wall shear stresses were estimated from the near wall velocity gradient, and the nature of observed poststenotic flow disturbances is discussed. Results indicate that flow disturbances of discrete oscillation frequency may be more valuable than turbulence as an indicator of early stages of stenosis development. Additionally, despite the fact that poststenotic turbulence exists for the higher degrees of stenosis and Reynolds numbers, the resulting wall shear stresses are only three to four times greater than the Poiseuille value and are considerably less than the wall shear stress within the stenosis itself.

Journal of Biomechanics, 1983

Instantaneous velocities in the field distal to contoured axisymmetric stenoses were measured wit... more Instantaneous velocities in the field distal to contoured axisymmetric stenoses were measured with a laser Doppler anemometer. Upstream flow conditions were steady and spanned a range of Reynolds numbers from 500 to 2000. Autocorrelation functions and spectra of the velocity were employed to descrtbe the nature of fluid dynamic disturbances.

Journal of Biomechanics, 1984

The pulsatile flow field distal to axisymmetric constrictions in a straight tube was studied usin... more The pulsatile flow field distal to axisymmetric constrictions in a straight tube was studied using laser Doppler anemometry. The upstream centerline velocity waveform was sinusoidal at a frequency parameter of 7.5 and mean Reynolds number of 600. Stenosis models of 25, 50 and 75% area reduction were employed and velocity data were derived by ensemble averaging methods. Extensive measurements of the pulsatile velocity profiles are reported, and wall shear rates were computed from the near wall velocity profile gradients. The experiments indicate that a permanent region of poststenotic flow separation does not exist even for the severest constriction, in contrast to results for steady flow. Values of wall shear stress were greatest near the throat of the constriction and were relatively low in the poststenotic region, including the region of most intense flow disturbance. Turbulence was found only for the 75% stenosis model and was created only during a segment of the cycle. Although much emphasis has been placed upon turbulence in the detection of arterial stenoses, particularly as identified by Doppler ultrasound spectral broadening, the present study implies that identification of flow disturbances of an organized nature may be more fundamental in recognizing mild to moderate disease. Additionally, the relationship of these flow field results to the animal aortic coarctation model often employed in atherogenesis studies is discussed.

Journal of Aircraft, 2000

An experimental investigation has been conducted on a two-dimensional NACA 0024 airfoil equipped ... more An experimental investigation has been conducted on a two-dimensional NACA 0024 airfoil equipped with a leading-edgerotating cylinder. The airfoil was tested for different values of leading-edgerotations and ap de ection angles. The effects of the angle of attack ®, the cylinder surface velocity ratio Uc/U, and the ap de ection angle ± on lift and drag coef cients, the size of the separated ow region, and the stall angle of attack are included. The effect of Uc/U on the boundary-layer growth and turbulence intensity are also shown. Experimental results, for example, showed that the leading-edge rotating cylinder increases the lift coef cient of a NACA 0024 airfoil from 0.85 at Uc/U = 0 to 1.63 at Uc /U = 4 and delays the stall angle of attack by about 160%. Smoke-wire ow visualization results were also used to demonstrate the strong effect of the leading-edge rotating cylinder on the size of the recirculation region.

Journal of Aircraft, 1995

Energy, 1998

Simultaneous two-component laser-Doppler-velocimeter measurements were made in an axisymmetric su... more Simultaneous two-component laser-Doppler-velocimeter measurements were made in an axisymmetric sudden expansion to measure the flow properties of a confined, isothermal flow-field of a research dump combustor. Measurements of mean velocities, Reynolds stresses, and triple products were carried out at axial distances ranging from 0.38H (H=step height) to 18H downstream of the dump plane. Detailed experimental data are provided to help

Applied Mechanics and Materials, 2013

Applied Mechanics and Materials, 2013

ABSTRACT The direct contact heat transfer technique gives better heat transfer rates. In this pap... more ABSTRACT The direct contact heat transfer technique gives better heat transfer rates. In this paper, the operation of a simple system was simulated under different operating conditions.During the charging mode of the operation, refrigerant R134a is injected into water stored in an evaporator to exchange directly heat with the water and form clathrates.Later, the clathrate is used tocool water which is used for air-conditioning purposes. Direct contact charging and/or discharging eliminate the necessity of a heatexchanger inside the storage tank and leads to an effective heat transfermethod. The results indicate that the performance of the system depends on the refrigerant type, compressor speed and the mass flow rate of the refrigerant.

Applied Mechanics and Materials, 2013

ABSTRACT This research work investigates the heat transfer characteristics of a direct contact he... more ABSTRACT This research work investigates the heat transfer characteristics of a direct contact heat exchanger. A cold two phase refrigerant R134a is injected into water stored in an evaporator to exchange directly heat with the water and form clathrates during the charging mode of the operation. The clathrate is used later for obtaining chilled water for air-conditioning purposes. It was found that the performance of the system depends on the refrigerant, its ratio to water, compressor speed and the mass flow rate of the refrigerant.

AIAA Journal, 1987

Jets discharging normally into a swirling crossflow are investigated experimentally. Total jet to... more Jets discharging normally into a swirling crossflow are investigated experimentally. Total jet to total swirling flow axial momentum ratios of 0.43 and 0.96 are examined. A vane swirler with an overall swirl number of 2.25 is used to generate the crossflow in a 125-mm i.d. tube. The jet nozzle with an exit diameter of 8.73 mm is mounted at one tube diameter downstream of the swirler. A one-color, one-component laser Doppler anemometer, operating in the forward scatter mode, is used to measure the flow field downstream of the jet. Results show that the jet does not penetrate deeply into the tube. Instead, it moves downstream along a spiral created by the swirling flow in the absence of the jet. Consequently, the disturbances created by the jet are limited to a small region around the jet, and the reversed flow region along the tube core created by the swirling motion still remains intact. The turbulence field of the swirling flow is affected more by the jet than the mean flowfield. However, the disturbances created by the jet die off quickly. At two tube diameters away from the jet and farther downstream, the mean flow and turbulence fields exhibit behavior characteristic of the swirling flow alone. This demonstrates that the decay of the jet is fairly complete within this region. Finally, as the jet momentum is increased, the jet's effect is also noted in regions other than along the jet trajectory. This indicates jetbifurcation behavior at high jet momentum.

Experiments in Fluids, 1986

Abstract. The presem investigation reports on the near field behavior of gas jets in a long confi... more Abstract. The presem investigation reports on the near field behavior of gas jets in a long confinement and points out the differences between this type of jet flow and those of free jets and jets in a short confinement. The jet, with a diameter of 8.73 mm, is aligned concentrically with a ...