Mechanical Engineering Commons^™

Dynamics Of 1d Granular Column, Luo Zuo

Dissertations

This dissertation is focused on a discrete element study of the dynamics of a one- dimensional column of inelastic spheres that it subjected to taps by prescribing a half sine wave pulse to supporting floor. Contact interactions obey the Walton-Braun soft-sphere model in which the loading (unloading) path is governing by linear springs of stiffness K1, thereby producing col lisional energy loss through a constant restitution coefficient e. Over a ‘short time scale’, computations are done to examine the floor pulse wave as it propagates through the column contact network. Comparisons of the simulated findings are made with experimental measurements …

Gas-Solid Transport And Reaction Via Intervened Evaporating Sprays, Pengfei He

Dissertations

Fluid catalytic cracking (FCC) is a major process used for converting heavy oils to transportation fuels and light olefins. The gas-solid transport with reaction via intervened evaporating sprays in the FCC riser is specially important but complicated, with coupled mechanisms of chemical reaction and heat, momentum and mass transfer among multiple phases (liquid, solid and gas) in the restriction of wall boundary. Recent developments in FCC process models have progressed along two lines. One aims to develop composition-based kinetic models derived from molecular characterization of petroleum fractions while overlooking the hydrodynamic effect on local catalyst to oil ratio (CTO). The …

Computational Optimization Methods For Modeling The Effect Of Muscle Forces On Bone Strength Adaptation, Catherine Siena Florio

Dissertations

An improved understanding of the mechanical influences that alter the strength of a bone can aid in the refinement of the wide array of currently available techniques to counteract the losses of bone strength that occur due to age or disuse both on Earth and in Space. To address this need, computational modeling methods to quantitatively analyze and compare the effects of mechanical factors on the strength of a targeted bone within a multibone, multimuscle system are developed and implemented in this work. Through a more detailed representation of the system in which the bone acts and the creation of …

Influence Of Lateral Boundaries In Tapped Densification Of Granular Materials, Nathaniel Ching

Theses

Granular systems are widely present in the world. Soil, pharmaceutical pills, and silos filled with grain all are examples of granular systems. Experiments have long established an empirical understanding of granular systems, but an analytical understanding has been much more difficult to establish. One of the behaviors of a granular system that is well documented but poorly understood is the change in density the system undergoes when excited, also known as the densification process.

This thesis investigates the densification process of a tapped granular system using Discrete Element Model (DEM) simulations. Contact interactions in the simulations obey a well-established inelastic …

Adsorption Of Particles On Fluid-Liquid Interfaces, Bhavin Dalal

Dissertations

Particles floating on fluid-liquid interfaces are of considerable interest because of their importance in a range of physical applications and biological processes, e.g., self-- assembly of particles at fluid-fluid interfaces resulting in novel nano structured materials, stabilization of emulsions, formation of pollen and insect egg rafts, etc. The aim of this dissertation is to explore the mechanism by which particles are adsorbed at fluid-liquid interfaces. It is shown that the inertia of a particle plays an important role in its motion in the direction normal to a fluid-liquid interface, and in determining the particles adsorption trajectory and orientation in …

Design And Automated Operation Of A Condensation-Induced Depressurization System, Fen Du

Dissertations

Typical examples of the use of the vacuum environments in industry include vacuum coating, vacuum drying, vacuum packing, vacuum casting, vacuum heat treatment, vacuum cooling for food storage and leakage detection. Most of these applications require a comparatively small volume of vacuum environment. However, there are also many applications where enormous vacuum chambers are needed. For example, a large vacuum chamber is used to simulate the conditions of space.

This study investigates the design and the automated operation of a vacuum generation system based on the idea of the condensation-induced depressurization with prefilled condensable medium in a confined, adiabatic chamber. …

The Mechanical Testing Of Single Nanofiber, Pratik Manohar Dahule

Theses

Polymer nanofibers exhibit properties that make them a favorable material for the development of tissue engineering scaffolds, filtration devices, sensors, and high strength lightweight materials. Perfectly aligned PLLA Nanofibers were fabricated by an electrospinning technique under optimum conditions and the diameter of the electrospun fibers can easily be tailored by adjusting the concentration of the polymer solution. To align the nanofibers, special arrangement was made in terms of two aluminum plates. Good alignment of polymer nanofibers on specimen was confirmed by SEM observation. The effect of different electro-spinning parameters on maximum fiber length, average fiber diameter, diameter uniformity, and fiber …

Dispersion Of Particles On Liquid Surfaces, Sathishkumar Gurupatham

Dissertations

When small particles (e.g., flour, pollen, etc.) come in contact with a liquid surface, they immediately disperse. The dispersion can occur so quickly that it appears explosive, especially for small particles on the surface of mobile liquids like water. This explosive dispersion is the consequence of capillary force pulling particles into the interface causing them to accelerate to a relatively large velocity. The maximum velocity increases with decreasing particle size; for nanometer-sized particles (e.g., viruses and proteins), the velocity on an air-water interface can be as large as 47 m/s. They also oscillate at a relatively high frequency about their …

Modeling Of Non-Uniform Hydrodynamics And Catalytic Reaction In A Solids-Laden Riser, Rajeshkumar Patel

Dissertations

The riser reactors are widely used in a variety of industrial applications such as polymerization, coal combustion and petroleum refinery because of the strong mixing of gas and solids that yields high heat and mass transfer rates, and reaction rates. In a Fluid Catalytic Cracking (FCC) process, the performance of riser reactor is strongly dependent on the interaction between the fluid and catalysts, since the reaction takes place on the active surface of the catalysts. This is why, the local coupling between hydrodynamics and reaction kinetics is critical to the development of riser reaction models. The local gas-solids flow structure …

Design And Fabrication Of A Tapped Densification Apparatus For Bulk Solids, Joshua H. De Jong

Theses

Experiments are commonly used to ascertain the flow properties of bulk solids. One such property is a measurement quantity known as the tapped density. Here, a container of granular material is subjected to a long sequence of discrete taps, after which the bulk density - the total mass divided by the volume occupied –- is determined. Current technology exists to achieve the maximum tap density by subjecting a container to a user defined number of taps at a specific, predetermined amplitude and frequency. However, the final bulk density is known to be dependent on the tap parameters. It can therefore …

Constitutive Modeling Of Glassy Memory Polymers, Mahesh Khanolkar

Dissertations

The aim of this research is to develop constitutive models for non-linear materials. Here, issues related for developing constitutive model for glassy shape memory polymers are addressed in detail. Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such heating the polymer above a transition temperature. Glassy shape memory polymers are called glassy because the temporary shape is fixed by the formation of a glassy solid, while …

Transport Mechanisms And Modeling Of Riser Reactor, Dawei Wang

Dissertations

Riser reactors are extensively employed in various industrial applications. In a riser reactor, the hydrodynamics is closely interacted with kinetic reactions. Common models for the performance prediction of riser reactors overlook this vital coupling effect, which not only miss the important reaction characteristics in the dense-phase transport regime of riser reactors but also misinterpret the kinetic properties via ad hoc adjustments. It is noted that the modeling of hydrodynamics in riser flows has major flaws in its predictability of phase transport in both dense-phase and accelerating regimes where most reactions occur. In addition, with the spray feeding of reactants at …

Stochastic And Deterministic Dynamics Investigation Of The Microstructure Of Granular Materials, Vishagan Ratnaswamy

Theses

Granular materials are ubiquitous in one's daily life. They can be found in the cereal you eat, the sugar you put in your coffee or the sand you walk on in the beach. The study of granular materials has a rich history dating back to the 17th century where Kepler studied the packing of particles. The compaction of granular materials is a problem that is studied by using theory, experiments and simulations. While these studies have yielded some important results, there still are many details about the mechanisms of granular compaction that are unknown.

In this thesis, the density relaxation …

Optimal Synthesis Of Planar Adjustable Mechanisms, Chong Peng

Dissertations

Adjustable mechanisms provide degrees of flexibility while retaining desirable features of one degree of freedom close-loop mechanisms, such as simplicity, stability, and high speed capabilities. By adjusting linkage parameters, additional phases of motions can be achieved using the same hardware. However, an adjustment to the mechanism adds only one or two additional design positions and divides desired positions into "phases", each of which contains only a few positions usually insufficient for industrial applications.

In order to extend the design position limitation of adjustable mechanisms, an optimal synthesis method based on link length structural error is developed and applied to kinematic …

Motion Coordination And Control In The Development Of A Gait Rehabilitation System, Yazan Ahmad Manna

Dissertations

While most take their ability to walk for granted, some are unable to walk due to any number of pathologies, such as traumatic brain injury (TBI), spinal cord injury (SCI), and Parkinson's disease. Decreased activity has been shown to be associated with rapidly deconditioning. Rehabilitation techniques that afford patients the ability to begin reconditioning through walking sooner may ultimately enhance their return to a better quality of life. To assist the functional recovery of such patients, an appropriate afferent input to the spinal cord will help in the therapy of the patient. Manual training is labor intensive, costly, and ergonomically …

Electrohydrodynamic Manipulation Of Multiphase Fluids, Sai C. Nudurupati

Dissertations

In microfluidic devices, the fluid can be manipulated either as continuous streams or droplets. The latter is particularly attractive as individual droplets can not only move but also split and fuse, thus offer a greater flexibility in applications such as a laboratory-on- a-chip. In this thesis, a technique is developed that uses an externally applied electric field for manipulating and removing particles trapped on the surface of a drop. The drop is assumed to be immersed in another liquid with which it is immiscible, and the electric field is generated by placing electrodes on the sides of the microdevice. Both …

Heterogeneous Flow Structure And Gas-Solid Transport Of Riser, Jun You

Dissertations

This study aims to understand physical mechanisms of gas-solid transport and riser flow, investigate heterogeneous flow structures of gas-solid transport and their formation mechanism of the in riser flows, both in axial and radial directions. It provides sound interpretation for the experimental observation and valuable suggestion to riser reactor design. Chemical reaction is also coupled with flow hydrodynamics to board the industrial applications. This study mainly focuses on mathematical modeling approach based upon physical mechanism, and endeavor to validate model prediction against available experimental data.

First of all, most important physical mechanisms including inter-particle collision force, gas/solid interfacial force and …

Electro Hydrodynamic Manipulation Of The Process Of Self-Assembly Of Particles At Fluid-Fluid Interfaces, Muhammad Mansoor Janjua

Dissertations

This dissertation is divided into two parts, first deals with the numerical study of motion of dielectric particles subjected to nonuniform electric fields and second deals with the process of self-assembly of particles at fluid-fluid interfaces and subjected to uniform electric field normal to the interface. In the numerical study, the particles are moved using a direct simulation scheme (DNS) in which the fundamental equations of motion of fluid and solid particles are solved without the use of models. The motion of particles is tracked using a distributed Lagrange multiplier method (DLM) and the electric force acting on the particles …

Experiment And Modeling : Ignition Of Aluminum Particles With A Co2 Laser, Salil Mohan

Dissertations

Aluminum is a promising ingredient for high energy density compositions used in propulsion systems, explosives, and pyrotechnics. Aluminum powder fuel additives enable one to achieve higher combustion enthalpies and reaction temperatures. Therefore, to develop aluminum based novel and customized high density energetic materials, understanding of ignition and combustion kinetics of aluminum powders is required. In most practical systems, metal ignition and combustion occur in environments with rapidly changing temperatures and gas compositions. The kinetics of exothermic reactions in related energetic materials is commonly characterized by thermal analysis, where the heating rates are very low, on the order of 1 -50 …

Kinematic Synthesis Of Planar Four Bar And Geared Five Bar Mechanisms With Structural Constraints, Yahia Mohammad Al-Smadi

Dissertations

In motion generation, the objective is to calculate the mechanism parameters required to achieve or approximate a set of prescribed rigid-body positions. This doctoral dissertation study is aimed to integrate the classical kinematic analysis of a planar four-bar and geared five-bar motion generation with three structural design constraints. These constraints consider driving link static torque, deflection of the crank and buckling of the follower for a given rigid-body load or constant external load.

This kineto-elastostatic analysis is based on the following assumptions to be considered during the analysis; the crank and the follower are elastic members and the coupler is …

Multi-Functional, Self-Sensing And Automated Real-Time Non-Contact Liquid Dispensing System, Qiong Shen

Dissertations

Liquid dispensing in the order of pico-liter has become more and more important in biology, electronics and micro-electronic-mechanical-system (MEMS) during the past two decades due to the rapid progress of researches on the deoxyribonucleic acid (DNA) microarray, compact and low-cost direct write technology (DWT), organic semiconductors and nano-particles.

The existing approaches, commercialized or experimental, to liquid dispensing in minute amounts have one common shortcoming: open loop control, i.e., they have no direct control on the quality of dispensed liquid. In contrast, the SmartPin has intrinsic self-sensing capability to not only control the process of liquid dispensing, but also the results …

Dem Simulated Radial And Axial Pressure In A Cylindrical Granular Column, Meng Cui

Theses

The study of packed beds of granular spheres and their applications are of great interest to industries, and one of the most important subjects that has been studied is cylindrical beds. In 1895, H. A. Janssen discovered that in a vertical cylinder the pressure measured at the bottom does not depend upon the height of the filling in contrast to Newtonian fluids that possess linear hydrostatic pressure equilibrium. One of assumptions of his theory stated that the horizontal pressure is proportional to the vertical. In this thesis, this physical hypothesis is investigated using Discrete Element Simulations of inelastic with a …

Density Relaxation Of Granular Matter Through Monte Carlo And Granular Dynamics Simulations, Oleksandr M. Dybenko

Dissertations

Granular materials are the principal ingredients of the industrial complex involved with the handling and processing of bulk solids including pharmaceuticals, chemicals, agricultural and mining materials. Despite the enormous importance of these materials in society, their behavior is not well-understood; in fact, there is no known model available that is capable of predicting the wide range of phenomenon that have been observed. One of the most important of these is known as density relaxation. Here, a granular material undergoes an increase in solids fraction as a result of the application of discrete taps or continuous vibrations.

In this dissertation, the …

Micro, Meso And Macro Materials Processing Using High-Speed Liquid Projectiles, Veljko Samardzic

Dissertations

The objective of this research is developmentof aknowledge base of materials processing by the impact of high-speed liquid projectiles. The work involved experimental study of generation and applications of high-speed liquid projectiles. The projectiles were generated by the launchers, which used gunpowder as an energy source. The experiments were carried out at the low (O.35g of the powder), middle (1.2g) and high (10g to 70g) levels of energy consumptions and at several different launchers modification.

Experimental investigation of effect of gun powder mass on energy of projectile was conducted for ductile and brittle targets. An array of experimental …

Ignition Of Metal Powder By Electrostatic Discharge Stimulation, Ervin Beloni

Theses

Energetic formulations with metal fuel additives are extensively used in propellants, explosives, pyrotechnics, and incendiaries. Currently, replacement of regular metal powders with nanocomposite metal-based materials is being considered. Such nanocomposite reactive materials are capable of very high reaction rates while maintaining the high combustion enthalpies characteristic of metals. However, such novel reactive nano-materials are often highly sensitive to impact, friction, and electrostatic discharge, making them difficult to handle. In particular, their high electrostatic discharge sensitivity (ESD) was reported. While ESD testing is very common and standardized, the mechanisms of powder ignition by electric spark remain unclear. This project is aimed …

Design Of Gait Rehabilitation System, Andriy Pletenetskyy

Theses

This thesis describes the conceptual design of an innovative robotic rehabilitation machine whose purpose is to help in the recovery of people with motor function disabilities. The machine is smaller, simpler and cheaper than current solutions on the market yet it delivers same functionality.

The conceptual development of the gait rehabilitation system also features a human model with average anthropometric dimensions that allows better visualization and understanding of the actual machine operation. The human model is kinematically coupled to the machine and the whole assembly presents a complex mechanism that closely simulates gait training session.

Three-dimensional modeling and analysis techniques …

Phase Transfer In A Collision Between A Droplet And Solid Spheres, Zheng Shen

Theses

The hydrodynamics of a liquid droplet impinging on a particle is of direct relevance to many engineering applications. The mechanism of heat and mass transfer during the droplet solid collision is essential to the design and operation of many industrial systems. However, very limited systemic research is available to describe the droplet impact on hot solid spheres.

This paper aims to establish a systematic investigation of phase transfer due to the droplet-solid impact, by both experimental and modeling approaches. The targeted phase transfer includes the surface attachment, mass of vaporization, heat transfer to droplet and its partition between vaporization and …

Fully Dense Aluminum-Rich Aluminum Copper Oxide Powders For Energetic Formulations, Demitrios Stamatis

Theses

The thermite reaction between Al and CuO is well known and highly exothermic. For a conventional thermite mixture comprising mixed metal and oxide powders, this reaction is rate limited by the slow heterogeneous mass transfer at the metal and oxide interface. The relatively low reaction rate and a difficult ignition have restricted practical applications for this reaction. For newly developed, nano-composed thermites, the interface area can be substantially increased resulting in a much higher reaction rate and a new range of possible applications. Nanocomposite Al-CuO materials are produced using a technique referred to as arrested reactive milling. Regular metal and …

Direct Simulations Of Cells Motions And Deformations In Flow, Quan Jin

Dissertations

Direct numerical simulations (DNS) are used to study the motions and deformations of blood cells, especially leukocytes, in pressure driven flows in parallel plate channels with both smooth and uneven walls under adhesion force between the leukocytes and the channel wall.

Leukocytes are represented by two composite fluid models. The first model is the compound-drop model in which the cytoplasm and the nucleus are modeled as fluids, and the second one is the drop-rigid-particle model in which the cytoplasm is modeled as a fluid and the nucleus as a rigid particle. The adhesion force is computed using two adhesion force …

Synthesis And Analysis Of Reactive Nanocomposites Prepared By Arrested Reactive Milling, Swati M. Umbrajkar

Dissertations

Different types of reactive nanocomposites have been synthesized by Arrested Reactive Milling (ARM). The technical approach was to increase the interface area available for heterogeneous reaction between solid fuel and oxidizer components. Using aluminum as the main fuel and different metal oxides as oxidizers, highly energetic reactive nanocomposites with different degrees of structural refinement were synthesized. Specifically, stoichiometric Al-MoO₃, Al-CuO, and Al-NaNO₃ material systems were studied in detail.

The correlation of heterogeneous exothermic reactions occurring in the nanocomposite powders upon their heating at low rates and ignition events observed for the same powders heated rapidly was of …