Taqi Ahmad Cheema

Tribological performance evaluation and sensitivity analysis of piston ring lubricating film with deformed cylinder liner

The interface between piston ring and cylinder liner is lubricated with an oil film to improve wear resistance and operating life of the engine. The high combustion pressure, variable loadings, manufacturing errors, and thermal distortions in the engine cylinder deform the cylinder liner, thus making a significant effect on the lubricant performance. To investigate the effects of cylinder liner deformation on the piston ring lubrication, a 2D model of elastohydrodynamic lubrication under fully flooded conditions was considered. Various elliptically deformed profiles of the cylinder liner were tested to evaluate conformability, lubricating film thickness, friction, power loss, and lubrication flow rate for a complete four-stroke engine cycle. Comparative analysis of the simulation results was conducted to evaluate the dependency of engine performance on deformed bore shape. Results showed that the lubricating film thickness and engine performance parameters strongly depend on the cylinder liner shape and the degree of distortion.

Effect of Paddle-Wheel Pulsating Velocity on the Hydrodynamic Performance of High-Rate Algal Ponds

AbstractHigh-rate algae ponds (HRAPs) are widely used in increasing biofuel production because of their effective design in terms of cost and power consumption. Using modeling and simulation techniques is an economical approach for improving the design of raceways. Previous modeling studies reported the use of a flat velocity profile, thus failing to depict the real phenomena involved. However, in practice, the rotating paddle wheel in HRAPs produces a pulsating velocity that is necessary for culture growth. In this study, the hydrodynamic characteristics of algal ponds were investigated using a coupling algorithm to map the effects of a two-dimensional paddle wheel on a three-dimensional raceway model. HRAPs with and without paddle wheels were compared in terms of hydrodynamic mixing, dead zones, and power consumption. The results revealed that compared with a flat velocity at the inlet, the pulsating velocity of a paddle wheel produced a large dead zone volume with reduced power consumption, shear stres...

Development of dual micro-PIV system for simultaneous velocity measurements: optical arrangement techniques and application to blood flow measurements

Blood rheological characteristics can significantly vary with the motion of red blood cells (RBCs) in plasma. Moreover, RBCs show a complicated behavior in micro vessels. Thus, the determination of either plasma or blood cell velocity distribution has been the primary objective in blood flow analysis. However, the conditions during blood flow analyses are different from the actual physiological conditions, wherein the motion of the two distinct blood phases simultaneously occurs. In this study, we used an in vitro micro-particle image velocimetry, which is a reliable velocity field measurement technique, to evaluate the velocity distribution of plasma and blood cells simultaneously. Blood flow through a rectangular microchannel was determined using special optical filter arrangements and by assuming two different hematocrit values. Using the proposed technique, the averaged parabolic velocity profiles for the RBCs and plasma were successfully obtained and compared. The developed simultaneous measurement technique can be used to predict blood cell and plasma behaviors simultaneously with high accuracy under given clinical conditions.

Two-dimensional numerical simulation of the red blood cell floating in a plasma-alcohol solution through stenosis in a microvessel

A two-dimensional computational model of a single red blood cell (RBC) floating in a plasma-alcohol solution through a microchannel with stenosis was created using the Arbitrary Lagrangian-Eulerian (ALE) method with moving mesh for a fluid structure interaction problem. Cell deformability and stability were studied in a plasma-alcohol solution at different fluid flow conditions during movement through the channel with stenosis. Different results were obtained for different input parameters. Motion through 45% and 70% stenoses with the high and law velocities of the RBC and different viscosities was analyzed and successfully simulated. Results show that changes in RBC deformability were due to the effects of alcohol. Changes in behavior during motion were also observed. At low shear rate and high surrounding fluid viscosity the RBC showed a tendency to rotate during movement. The proposed model with its coupling of structural and fluid analysis techniques could be useful to understand the effect of alcohol on the RBC passing through stenosis.

Numerical investigation of hyperelastic wall deformation characteristics in a micro-scale stenotic blood vessel

Stenosis is the drastic reduction of blood vessel diameter because of cholesterol accumulation in the vessel wall. In addition to the changes in blood flow characteristics, significant changes occur in the mechanical behavior of a stenotic blood vessel. We conducted a 3-D study of such behavior in micro-scale blood vessels by considering the fluid structure interaction between blood flow and vessel wall structure. The simulation consisted of one-way coupled analysis of blood flow and the resulting structural deformation without a moving mesh. A commercial code based on a finite element method with a hyperelastic material model (Neo-Hookean) of the wall was used to calculate wall deformation. Three different cases of stenosis severity and aspect ratios with and without muscles around the blood vessel were considered. The results showed that the wall deformation in a stenotic channel is directly related to stenosis severity and aspect ratio. The presence of muscles reduces the degree of deformation even in very severe stenosis.

Fluid-solid interaction based morphological investigation of hyperelastic stenotic structure under turbulent pulsatile flow

Abstract The accumulation of low density lipoproteins, which form different geometrical stenotic structures, affects not only the blood fluid dynamics but also the structural properties of the arterial wall. A fluid structure interaction study was conducted to investigate the morphology of the stenotic structure in a two-dimensional axisymmetric arterial model. Three different stenotic structures were subjected to turbulent flow. Using pulsatile velocity and pressure waveforms as the physiological boundary conditions, the fluid dynamic and structural properties of an arterial wall with a hyperelastic material model were calculated.

Numerical investigation of stress–strain and deformation characteristics imposed upon automatic screener rakes

Abstract Automatic bar type screeners are used as a primary filtration device in water flowing channels to remove unwanted solid materials from the influent. To reduce manpower, automatic mechanisms are used to clean screeners that are clogged with debris of various sizes. The rake experiences fatigue loading when water passes through the gate during the cleaning process. Therefore, the components must be designed to withstand the induced stresses. The teeth or pin is the crucial component in completing the function of the rake. However, it may rupture under periodic loadings. Replacing the pin requires a considerable amount of time and immense manpower. To solve this problem, this study first performs a structural analysis to predict stress distribution and total deformation on the individual pins under various types of loadings. A rake pin design with a rib is analyzed for the same loadings; the design demonstrated improved stress distribution with significantly small deformation. The results show that the mid-section of the rake, which is the most stress intensive region, must be carefully loaded to avoid fracture.

Effects of thermal material properties on precision of transient temperatures in pulsed laser welding of Ti6Al4V alloy

This study investigates the effect of temperature-dependent material properties on the precision of a simulation in pulsed laser beam welding of Ti6Al4V alloy. Ti6Al4V is one of the most extensively used titanium alloys. The precision in transient temperature distributions developed in the thermal modeling part of a sequentially coupled thermo-mechanical simulation is crucial to the end results of structural mechanics. The temperature profile obtained by a finite element model at two distinct locations is validated by experimental results using temperature-dependent material properties. Then, the effect of assuming constant room temperature values for thermal conductivity, specific heat, and density on the temperature distribution is studied at different welding speeds. Temperature distributions are unaffected by the constant density assumption. The constant thermal conductivity assumption underestimates the peak temperatures far from the weld region, whereas the constant specific heat assumption overestimates these temperatures. This effect becomes prominent at low welding speeds. The temperature profile when conductivity and specific heat are assumed to be constant is nearly similar to that in the case of constant conductivity when conductivity and specific heat are assumed constant. Therefore, conductivity is the dominant variable. The constant conductivity assumption also restricts the heat flow from the weld to the edge region, thus increasing the size of the weld pool. This effect also becomes increasingly prominent at low welding speeds.

A New Methodology for Aerodynamic Design and Analysis of a Small Scale Blended Wing Body

The blended wing body (BWB) concept is a relatively new concept of an aircraft. The wings and the fuselage blend into one integral structure greatly reduce drag and increases lift thus making it a highly efficient design. The aim of the research was to design a radio controlled small scale BWB aircraft for use over long ranges at low altitudes in order to deliver payloads. The BWB was divided into the center body and the outer wing. Four airfoils, HS522, LA2573A, NACA 25111 and MH78 were analyzed in XFLR5. In consideration of their lift and moment characteristics, NACA 25111 and MH78 were selected for the center body and the wing respectively. The stall speed and wing loading were the primary factors used in determining the area and size of the aircraft which converged to a design having a five feet wingspan. Center of gravity was placed ahead of aerodynamic center to provide static and dynamic stability in pitch. Twist, dihedral and sweep were given to increase stability and controllability. The final design was tested in XFLR5 for stability and in commercial computational fluid dynamic code ANSYS-Fluent for comparison. These simulation results were compared to wind tunnel tests of a 20% scaled down prototype. 3D Panel Method results in XFLR5 were found to be very close to wind tunnel results but CFD results were seen to be not conforming to the wind tunnel results after 10° angle of attack. Thus, CFD was deemed to be unnecessary for designing a plane of this size. Ultimately, a larger test prototype was made out of polystyrene foam and a successful flight was achieved.

Numerical investigation of basin geometries for vortex generation in a gravitational water vortex power plant

To improve the efficiency of a gravitational water vortex turbine, the production of a strong vortex, capable of driving a runner for the generation of electricity is very important. Various design configurations have been investigated using the computational fluid dynamics approach. A cylindrical tank with a discharge hole at the bottom center is the most suitable configuration to generate a water vortex. The results show variations in vortices formed under different basin parameters such as inlet velocity, basin height, outlet diameter, inlet channel width, inlet channel depth and mass flow rate. It is concluded that the optimized design parameters improve the efficiency of the plant to a significant extent by the generation of a strong vortex with air core.