Department: Mechanical Engineering ![[clear]](close-x.png "Remove this limiter")
84 matches in the database.
These are records: 1 - 30.
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1.
Abu-Mahfouz, Issam Abdullah.
Routes to chaos in rotor dynamics.
Degree: PhD, Mechanical Engineering, 1993, Case Western Reserve University
► The behavior of three fundamental nonlinear rotordynamical systems are investigated with particular…
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▼ The behavior of three fundamental nonlinear rotordynamical systems are investigated with particular attention on the routes to chaotic motion: (1) Rotor-stator rub-impact interaction modeled by a Hertzian contact radial force and a Coulomb friction tangential force; (2) Dynamically unstable hydrodynamic journal bearing; (3) Statically and dynamically unstable pivoted-pad journal bearings (PPJB). In each of these systems the dynamical disturbance is from rotor unbalance. A quite extensive numerical experimentation for a wide range of parameters yields results rich in subharmonic, quasiperiodic and chaotic motions. Orbital motions, phase-portraits for the pads in terms of their angular pitching velocity and amplitude, Poincare′ maps and bifurcation diagrams are used as qualitative descriptors to observe the evolution of chaos in the systems considered. Numerical evidence of different routes to and out of chaos are delineated and categorized. Feigenbaum type, period-doubling (period-halving), quasiperiodic with period locking, and sudden (crisis) sequences of bifurcation leading to and out of chaotic regions are produced. These rotor dynamical phenomena are potentially of considerable value as a diagnostic tool in assessing condition monitoring signals that are now routinely taken on modern rotating machinery. Although the systems considered are relatively simple and very important in rotor dynamics, their chaotic behavior has not been investigated before. The present work presents new insights significant to understanding highly complicated nonlinear behaviors of rotor dynamics. This work also provides a strong motivation for further work on chaos content of rotordynamical systems, particularly for higher order systems, i.e., multi-bearing flexible rotors
Advisors/Committee Members: Adams, M. L.
Subjects: Engineering, Mechanical
Keywords: Rotor dynamics; Chaotic motion
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2.
Anderson, Eric James.
BRIDGING THE GAP IN UNDERSTANDING BONE AT MULTIPLE LENGTH SCALES USING FLUID DYNAMICS.
Degree: PhD, Mechanical Engineering, 2007, Case Western Reserve University
► Fluid flow through the network of pathways in bone tissue is hypothesized…
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▼ Fluid flow through the network of pathways in bone tissue is hypothesized to play an integral role in transducing external mechanical forces from the skeletal level down to the cells embedded deep within bone tissue. Communicating these external forces to bone cells is thought to be the mechanism by which bone is regenerated, and thus has major implications in fighting bone disease as well as repairing defects or damage to the tissue. This research pursues the role of fluid flow in bone remodeling and looks to bridge the gap between tissue and cellular level knowledge using computational fluid dynamics modeling of Navier-Stokes equations as well as experimental validations of applicable models. Using physiologic model geometries of increasing complexity, the following work predicts currently immeasurable propeties of this tissue such as permeability or cell communication, as well as the resultant mechanical forces as they exist at the cellular and subcellular levels. The mechanical environment of the osteocyte is described, where the mode and magnitude of force on the cell varies spatio-temporally. Both the hydrodynamic pressure and imparted shear stress are found on the cell surface, where the cell body experiences a nearly constant pressure and virtually zero shear stress while the cell processes are exposed to high gradients of both shear stress and pressure. This differentiation between types and location of forces has possible implications in cell physiology and the types of receptors or mechanosensors present on the cell. In addition, along the cell processes, which radiate from the cell body, subcellular geometries near the lower continuum-limit yield small discontinuities in the annular wall that are foundt o amplify peak shear stresses up to five times that of previous predictions. This result gives insight into a major paradox that has existed in bone and suggests a bridge between theoretical predictions and laboratory measurements of the necessary mechanical force for cell stimulation, where previous in vitro measurements have been an order of magnitude higher than in vivo predictions. This knowledge of the cell's mechanical environment is used to improve and design applications for laboratory cell studies and tissue growth in vitro.
Advisors/Committee Members: Knothe Tate, Melissa L.
Keywords: mechanotransduction; bone fluid flow; computational fluid dynamics; osteocyte
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3.
Barnhart, Paul Joseph.
Experimental investigation of unsteady shock wave turbulent boundary layer interactions about a blunt fin.
Degree: PhD, Mechanical Engineering, 1995, Case Western Reserve University
► A series of experiments were performed to investigate the effects of Mach…
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▼ A series of experiments were performed to investigate the effects of Mach number variation on the characteristics of the unsteady shock wave/turbulent boundary layer interaction generated by a blunt fin. A single blunt fin hemi-cylindrical leading edge diameter size was used in all of the experiments which covered the Mach number range from 2.0 to 5.0. The measurements in this investigation included surface flow visualization, static and dynamic pressure measurements, both on centerline and off-centerline of the blunt fin axis. Surface flow visualization and static pressure measurements showed that the spatial extent of the shock wave/turbulent boundary layer interaction increased with increasing Mach number. The maximum static pressure, normalized by the incoming static pressure, measured at the peak location in the separated flow region ahead of the blunt fin was found to increase with increasing Mach number. The mean and standard deviations of the fluctuating pressure signals from the dynamic pressure transducers were found to collapse to self-similar distributions as a function of the distance perpendicular to the separation line. The standard deviation of the pressure signals showed initial peaked distributions, with the maximum standard deviation poin t corresponding to the location of the separation line at Mach number 3.0 to 5.0. At Mach 2.0 the maximum standard deviation point was found to occur significantly upstream of the separation line. The intermittency distributions of the separation shock wave motion were found to be self-similar profiles for all Mach numbers. The intermittent region length was found to increase with Mach number and decrease with interaction sweepback angle. For Mach numbers 3.0 to 5.0 the separation line was found to correspond to high intermittencies, or equivalently to the downstream locus of the separation shock wave motion. The Mach 2.0 tests, however, showed that the intermittent region occurs significantly upstream of the separation line. Power spectral densities measured in the intermittent regions were found to have self-similar frequency distributions when compared as functions of a Strouhal number for all Mach numbers and interaction sweepback angles. The maximum zero-crossing frequencies were found to correspond with the peak frequencies in the power spectra measured in the intermittent region
Advisors/Committee Members: Greber, Isaac.
Subjects: Engineering, Mechanical
Keywords: Shock wave boundary layer; Blunt fin
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4.
Bartolotta, Paul Anthony.
Fatigue behavior and life prediction of a silicon carbide/titanium-24aluminum-11niobium composite under isothermal conditions.
Degree: PhD, Mechanical Engineering, 1991, Case Western Reserve University
► Metal Matrix Composites (MMC) and Intermetallic Matrix Composites (IMC) have been identified…
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▼ Metal Matrix Composites (MMC) and Intermetallic Matrix Composites (IMC) have been identified as potential material candidates for advanced aerospace applications. They are especially attractive for high temperature applications which require a low density material that maintains its structural integrity at elevated temperatures. High temperature fatigue resistance plays an important role in determining the structural integrity of a material. There are several fundamental issues that surface when considering high temperature fatigue response of MMC's and IMC's. Among them are test technique, failure criterion and life prediction. This study attempts to examine the relevance of these concepts as they pertain to an IMC material, specifically unidirectional SiC fiber reinforced titanium aluminide. As a part of this study, a series of strain- and load-controlled fatigue tests were conducted on unidirectional SiC/Ti-24Al-11Nb (atomic %) composite at 425 and 815°C. Several damage mechanism regimes were identified by using a strain-based representation of the data, Talreja's fatigue life diagram concept. Results from these tests were then used to address issues of test control modes, definition of failure and testing tech niques. Finally, a strain-based life prediction method was proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the "Universal Slopes" method, the model utilizes the composite's tensile properties to estimate life. Factors such as fiber volume ratio (V f), number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model parameters were determined by using fatigue data at temperatures of 425 and 815°C. Fatigue life data from two independent sources were used to verify the model at temperatures of 650 and 760°C. Cross-ply life data from specimens with ply lay-ups of (0/90) 2s and (0/±45/90) 2s at 760°C were also predicted. Correlation between experimental and predicted lives was found to be very reasonable.
Advisors/Committee Members: Kicher, T. P.
Keywords: Fatigue behavior; life prediction; silicon carbide/titanium-24aluminum-11niobium; isothermal
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5.
Boonpongmanee, Thaveesak.
NUMERICAL AND EXPERIMENTAL INVESTIGATION OF HEAT AND MASS TRANSFER IN ROTATING SYSTEMS.
Degree: PhD, Mechanical Engineering, 2005, Case Western Reserve University
► Heat and mass transfer processes in rotating cells are investigated numerically and…
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▼ Heat and mass transfer processes in rotating cells are investigated numerically and experimentally. The experiments are also performed with gas evolution. umerical simulations are performed to study the velocity and temperature fields in detail. Based on the numerical results and scaling analysis, the basic flow structure and heat and mass transfer rate are discussed. There exist velocity boundary layers, called the Ekman layers, due to the Coriolis force. In addition, we have thermal boundary layers in the heat transfer experiment and solutal boundary layers in the mass transfer experiment. The flow can be classified into two different regimes depending on the ratio of the Ekman layer thickness to the thermal or solutal boundary layer thickness. The Ekman suction driven convection regime occurs when the boundary layer ratio is less than unity, which is the case in the present heat transfer experiment. In this regime, the flow is very much suppressed by the Coriolis force. The thermal boundary layer thickness and the heat transfer rate are controlled by the Ekman suction flow. The computed Nusselt numbers agree well with the present experimental data. The experiment shows that the flow becomes oscillatory under certain conditions, probably due to the Coriolis force. When the boundary layer ratio is greater than unity, we have the centrifugal buoyancy driven convection regime. This happens in the present mass transfer experiment with an electrochemical system. The basic characteristics of the flow are similar to those for buoyancy driven convection in rectangular enclosures, and the mass transfer rate is not affected by the Coriolis force. However, the Coriolis force is still important away from the solutal boundary layer. It is shown that unsteady secondary cells appear because of the Coriolis force. The effect of gas evolution is investigated experimentally in the heat and mass transfer experiments. It is found that the heat transfer rate is not much affected by the gas evolution but the mass transfer is substantially increased by the bubbles.
Advisors/Committee Members: Kamotani, Yasuhiro.
Subjects: Engineering, Mechanical
Keywords: Heat transfer, mass transfer, rotating, electrochemical, coriolis force, Ekman layer, bubble generation
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6.
Bruckner, Robert Jack.
Simulation and Modeling of the Hydrodynamic, Thermal, and Structural Behavior of Foil Thrust Bearings.
Degree: PhD, Mechanical Engineering, 2004, Case Western Reserve University
► A simulation and modeling effort is conducted on foil gas thrust bearings.…
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▼ A simulation and modeling effort is conducted on foil gas thrust bearings. A foil bearing is a self acting hydrodynamic device capable of separating stationary and rotating components of rotating machinery by a film of air or other gaseous “lubricant”. Although simple in appearance these bearings have proven to be complicated devices. They are sensitive to fluid structure interaction, use a compressible gas as a lubricant, may not be in the fully continuum range, and operate in the range where viscous heat generation is significant. These factors provide a challenge to the simulation and modeling task. The conservation equations of mass, momentum, and energy are applied to the problem. The traditional Reynolds equation is developed with the addition of a Knudsen number effect due to thin film thicknesses. The energy equation is simplified by applying the thin layer assumptions such that fluid properties do not vary through the film. Heat transfer between the lubricant and the surroundings is also taken into consideration. The structural deformations of the bearing are modeled with a single partial differential equation. The equation models the top foil as a thin, bending dominated membrane whose deflections are governed by the biharmonic equation. A linear superposition of hydrodynamic load and compliant foundation reaction is included. The stiffness of the compliant foundation is modeled after a set of discrete springs that support the topfoil. The system of governing equations is solved numerically by a computer program written in the Mathematica computing environment. A generalized hydrodynamic analysis is conducted to systematically analyze each of the individual effects included in the development of the governing equations. Previous analytic work on foil thrust bearings includes the modeling of the Reynolds equation with an isothermal density model and an additional model to predict top foil deflections. This work finds a substantial difference between bearing performance based on traditional lubricant models and that based on the energy equation model. Qualitative and quantitative comparisons are produced that demonstrate the utility of the current approach, which couples the Reynolds, energy, and structural equations.
Advisors/Committee Members: Prahl, Joseph M.
Subjects: Engineering, Mechanical
Keywords: Foil Bearing, Thrust Bearing, Hydrodnamics, Thermodynamics, Fluid-Structure Interaction
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7.
Chang, Qingming.
LATTICE BOLTZMANN METHOD (LBM) FOR THERMAL MULTIPHASE FLUID DYNAMICS.
Degree: PhD, Mechanical Engineering, 2006, Case Western Reserve University
► A multiphase lattice Boltzmann method (MLBM) based on the HSD model has…
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▼ A multiphase lattice Boltzmann method (MLBM) based on the HSD model has been adapted for the solution of multiphase fluid dynamics problem. The interactions between particles are expressed through a mean-field approximation and exclusion-volume effect. The behavior of interface is obtained as part of the solution of the lattice Boltzmann equations. No a priori assumptions and artificial treatment are made regarding the shape and dynamic roles of the interface. Interfacial tension dynamics is validated through a series of test running of three-dimensional wave dispersion. The MLBM is also extended to thermal multiphase LBM (TMLBM) which includes the effects of interfacial tension and its dependence on temperature by a hybrid scheme. The key point for this scheme is combining a micro-scale description of the flow with a macroscopic energy transport equation. Applying the TMLBM, a systematic investigation of fluid dynamics in a two-layer immiscible fluid system is undertaken starting with Rayleigh-Benard convection. A parametric study of the effects of thermally induced density change, buoyancy, surface tension variation with temperature on interface dynamics, flow regimes and heat transfer is presented. Further investigation of TMLBM is applied to a two-layer immiscible fluid system with density inversion in which density inverse assumption holds for the lower layer fluid. The evaluation of the effects of density distribution parameter, Rayleigh number, size aspect ratio and Marangoni number on convection flow and heat transfer is presented. Interaction between gravity-induced and vibration-induced thermal convection in a two-layer fluid system has also be studied by TMLBM. The vibrations considered correspond to sinusoidal translations of a rigid cavity at a fixed frequency and is parallel to temperature gradient. The ability of applied vibration to enhance the flow, heat transfer and interface distortion is investigated. Comparisons of two-phase fluid system with single-phase fluid system are discussed. Finally, a nearest-neighbor molecular interaction force is introduced into LB equation to model the adhesive forces between the fluid and solid surface. The behavior of a micron-scale fluid droplet on a heterogeneous surface is investigated. The dependence of spreading/breakup behavior of a hemispherical droplet on the structure and wettability of the surface and gravity is investigated.
Advisors/Committee Members: Alexander, J. Iwan D.
Keywords: Lattice Boltzmann Method, Multiphase fluid dynamics, Droplet Spreading dynamics, Two-phase Rayleigh-Benard Convection, Thermovibrational Convection, Micro-scale Fluidics
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8.
Chao, Liyung.
Lateral g-jitter effects on liquid motion and thermocapillary convection in an open square container under weightless condition.
Degree: PhD, Mechanical Engineering, 1991, Case Western Reserve University
► Lateral g-jitter effects on liquid motion in an open container under weightless…
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▼ Lateral g-jitter effects on liquid motion in an open container under weightless condition are studied numerically and analytically. A hysteresis parameter is incorporated into the numerical scheme to allow for different kinds of contact line conditions. The disturbing, damping, resonant, hysteresis and depth effects on free surface deformation are investigated in detail. The importance of g-jitter with resonant frequencies and low frequencies is also shown. Based on the former results, the influence of g-jitter on steady thermocapillary convection is also studied numerically. It is found that the g-jitter and thermocapillary flow interact most intensely only in the free surface layer region, the influence of g-jitter diminishes very fast as the depth increases. The g-jitter disturbance of local conduction heat transfer along a crystal growth front is also examined.
Advisors/Committee Members: Ostrach, Simon.
Keywords: Lateral g-jitter effects liquid motion thermocapillary convection open square container weightless condition
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9.
Chen, Jiunn-Liang.
Dynamics and control of structurally flexible multibody systems.
Degree: PhD, Mechanical Engineering, 1992, Case Western Reserve University
► This dissertation is concerned with the dynamic modeling and control of multibody,…
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▼ This dissertation is concerned with the dynamic modeling and control of multibody, open-chained, structurally flexible, mechanical systems where the bodies are connected by revolute joints. The equations of motion are formulated based on a matrix form of Lagrange's equations for inertial quasi-coordinates. Each body is treated as a substructure of the system. For the purposes of simulation and control, the equations of motion are separated into two sets of equations using a perturbation approach: one to describe large rigid-body motions of the articulated system and the other to describe small linear motions of the bodies about the large motions. The kinematic equations including the relationship between quasi-coordinates and Euler angles describing the motion of each joint are considered independently and used to formulate the equations of motion. Biologically natural control strategies such as Uniform Damping Control and a new approach which we call Projection PD Control are used for vibration suppression and for tracking the prescribed motions. Finally, case studies and numerical examples are performed.
Advisors/Committee Members: Quinn, Roger D.
Keywords: structurally flexible; multibody systems
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10.
Chen, Rong-Che.
Experimental and numerical studies of solid-liquid multiphase flow in pipes.
Degree: PhD, Mechanical Engineering, 1991, Case Western Reserve University
► A unique refractive index matched facility for studying solid-liquid multiphase flow has…
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▼ A unique refractive index matched facility for studying solid-liquid multiphase flow has been developed. The refractive index matching of the solid and the liquid allows the use of non-intrusive Laser Doppler Velocimetry (LDV) to measure the solid and the liquid velocities. Silica gel particles of mean diameter 40 microns and 50% sodium iodide solution in water (refractive index ∼eq 1.4429) are used as the refractive index matched solid and liquid respectively. A two color back scatter mode LDV is used for making velocity measurements of both liquid and solid phases. Tests were conducted for solid-liquid slurry flows in a one inch diameter pipe with volumetric solid concentration levels of 5%, 15%, 25% and 30% in the Reynolds number range of 500 to 15000. The Reynolds number is based on the mean velocity of slurry, the pipe diameter and the liquid viscosity. Measurements included mapping of the solid and liquid velocities and obtaining the pressure drop data. A comparison between axial velocity profiles along the vertical and horizontal diameters associated with the observation of the height of settled solid particles on the bottom of pipe was used for demarcating flow regimes. The four flow regimes, stationary bed flow, saltation flow, heterogeneous flow and homogeneous flow, w ere identified with respect to Reynolds number. Pressure drop measurements were made by using inclined tube manometer. The comparison of friction factor with Turian's correlation shows very good agreement in the homogeneous flow regime. A signal processing technique utilizing histogram of velocity measurements made at a point and signal amplitude discrimination was successfully used for differentiating between the solid and liquid velocities. Differences between the solid and liquid velocities were observed for the saltation flow and heterogeneous flow regimes for 15% and 25% slurries. No velocity difference between solid and liquid was detected for slurries flow in the homogeneous flow regime for all solid concentrations. A numerical model based on the transport equations and empirical coefficients for interphase interactions was successfully developed for predicting flow properties of a slurry in the homogeneous flow regime for solid concentration up to 25% by volume. This numerical model provides the velocity profile for each phase, the solid concentration distribution, the turbulent kinetic energy and the dissipation rate of turbulence for homogeneous flow of slurry. The axial velocity profile compared well with the experimental data.
Advisors/Committee Members: Kadambi, Jaikrishnan R.
Keywords: Experimental and numerical studies of solid-liquid multiphase flow in pipes.
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11.
Chhatpar, Siddharth R.
Localization for Robotic Assemblies with Position Uncertainty.
Degree: PhD, Mechanical Engineering, 2006, Case Western Reserve University
► This dissertation deals with the class of robotic assemblies where position uncertainty…
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▼ This dissertation deals with the class of robotic assemblies where position uncertainty far exceeds assembly clearance, and visual assistance is not available to resolve the uncertainty. Our research is motivated by actual assemblies from vehicular transmissions that fall under this class. For this class of assemblies, the focus shifts from the dynamics of the assembly to the problem of searching for part alignment. A novel idea is introduced to transform the search for part alignment into one of localizing the peg-hole misalignment on the hyper-surface formed in the peg-hole contact configuration space (C-space). This idea is developed into an intelligent localization strategy for resolving the uncertainty in the relative configuration of parts. The strategy is to explore the assembly contact C-space and match observations to a pre-acquired map of the C-space. The implementation of our localization strategy is described using both analytical and sampled maps of the contact C-space. Thus, one can either model the contact C-space using equations of the three-dimensional volumetric intersections of the mating parts, or sample it using a robot or CAD model. However, a sampled map does not provide a complete representation of the continuous contact C-space. Hence, the concepts of assembly sufficiency, goal region, and approximate localization are introduced to help in localizing sufficiently for assembly. With increasing dimensionality of the assembly uncertainty and small assembly clearances, the computational load becomes large and uneven over the localization period. An algorithm, termed the cell approach, is developed to implement the localization strategy in stages of increasing resolution, thus distributing the computational load more evenly. To make the localization strategy more robust, the application of particle filtering for robotic assemblies with position uncertainty was pioneered in this dissertation. Particle filtering is a probabilistic scheme that maintains a set of weighted particles, where each particle represents an estimate of the relative peg-hole configuration; it can handle errors in actuation and observation, and also errors in mapping. Moreover, the number of particles can be adjusted to accommodate the computational resources available. The ideas presented in this dissertation were validated with mathematical analyses, computer simulations, and actual robotic assemblies.
Advisors/Committee Members: Branicky, Michael S.
Keywords: Localization; Robotic Assembly; Particle Filter; Configuration Space; Sampled Maps
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12.
Chinnapalaniandi, Periasamy.
An experimental study of particle-laden jet interactions with cocurrent flows.
Degree: PhD, Mechanical Engineering, 1992, Case Western Reserve University
► The interactions of particle laden jet with cocurrent flow was studied experimentally.…
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▼ The interactions of particle laden jet with cocurrent flow was studied experimentally. To improve sorbent utilization, in induct flue gas desulfurization processes where sorbent particle-laden jet is injected into cocurrent flowing flue gas, an understanding of particle and fluid interaction within the turbulent mixing zone is necessary. To improve the understanding of this phenomenon, one needs to obtain measurements of the particle size, velocity, concentration, and gas phase velocity within the shear layer region of particle-laden jet. A particle injection test facility was designed specifically to study the interaction of particle laden jets using non-intrusive, laser-based optical techniques. Spherical glass particles in the size range of 2-100 μm were used. The mass loading was varied between 0 to 10. Particle Dynamics Analyzer, which utilizes phase Doppler interferometry and laser Doppler anemometry was used for measuring the particle velocities, sizes, and concentration as well as gas phase velocities in the flow field. Phase discrimination between the particle phase and gas phase was accomplished by utilizing particle velocity and size statistics. Single phase, particle and gas phases mean velocities and fluctuating turbulent intensities, and concentration profile s were obtained. Single phase velocity measurements were used as baseline data for comparison with particle laden flows. The decay rate of mean gas phase centerline velocity for particle laden flows less than that for single phase flows. This resulted from the momentum transfer from particles to the gas phase. The axial and radial rms velocities of the particle and gas phases decrease with increase in mass loading. The spreading rate of particle laden jet is also reduced. This decrease resulted from the reduction in the radial fluctuating velocity. Entrainment increases with higher jet velocity and reduced mass loading. Higher mass loading reduces the turbulence level; therefore there is a reduction in mixing and entrainment. For the range of particle sizes used, larger particles tend to concentrate around the centerline of the jet. For higher mass loading the particles are concentrated in a smaller radial distance and there is a resulting reduction in dispersion and mixing of particles.
Advisors/Committee Members: Kadambi, JaiKrishnan R.
Keywords: particle-laden; jet interactions; cocurrent flows
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13.
Choi, Jongung.
LOCOMOTION CONTROL EXPERIMENTS IN COCKROACH ROBOT WITH ARTIFICIAL MUSCLES.
Degree: PhD, Mechanical Engineering, 2005, Case Western Reserve University
► This dissertation describes experimental efforts to improve the control and mechanical designs…
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▼ This dissertation describes experimental efforts to improve the control and mechanical designs of a biologically-inspired hexapod robot. Robot V is modeled after the Blaberus discoidalis cockroach. It uses Festo pneumatic muscle actuators with two-way solenoid valves activated by Pulse-Width-Modulation. Robot 5 is capable of rudimentary walking without sensors, but walking with style requires proprioceptors to measure joint angles and load. Control circuits are described in this thesis that coordinate the robot’s joints and legs using sensor data. The Modified Moore Penrose method is used to solve the inverse kinematics problem for each of the robot’s legs at a number of foot positions within the legs’ workspaces. These solutions are used to train neural networks that then are used to solve the inverse kinematics problems on line as the robot moves. A Cruse controller is used to coordinate the legs into insect gaits. These controllers are tested in a dynamic simulation that models the robot’s dynamics, actuators and valves. The simulated Robot V walks successfully. The control strategies were then implemented and tested in Robot V. The robot was shown to move its legs in insect gaits while it was supported in the air such that its feet could not touch the ground. Load feedback must be implemented before it will walk well on the ground. The robot’s design was compared to Robot III and a number of problems with Robot V’s design were discovered during experimentation.
Advisors/Committee Members: Quinn, Roger D.
Subjects: Engineering, Mechanical
Keywords: Bio-inspired robot; Walking robot; Hexapod robot; Locomotion control
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14.
Cho, Soo-Yong.
Three dimensional compressible turbulent flow computations for a diffusing S-duct with/without vortex generators.
Degree: PhD, Mechanical Engineering, 1993, Case Western Reserve University
► Numerical investigations on a diffusing S-duct with/without vortex generators and a straight…
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▼ Numerical investigations on a diffusing S-duct with/without vortex generators and a straight duct with vortex generators are presented. The investigation consists of solving the full three-dimensional unsteady compressible mass averaged Navier-Stokes equations. An implicit finite volume lower-upper time marching code (RPLUS3D) has been employed and modified. A three-dimensional Baldwin-Lomax turbulence model has been modified in conjunction with the flow physics. A model for the analysis of vortex generators in a fully viscous subsonic internal flow is evaluated. A vortical structure for modelling the shed vortex is used as a source term in the computation domain. The injected vortex paths in the straight duct are compared with the analysis by two kinds of prediction models. The flow structure by the vortex generators are investigated along the duct. Computed results of the flow in a circular diffusing S-duct provide an understanding of the flow structure within a typical engine inlet system. These are compared with the experimental wall static-pressure, static- and total-pressure field, and secondary velocity profiles. Additionally, boundary layer thickness, skin friction values, and velocity profiles in wall coordinates are presented. In order to investigate the e ffect of vortex generators, various vortex strengths are examined in this study. The total-pressure recovery and distortion coefficients are obtained at the exit of the S-duct. The numerical results clearly depict the interaction between the low velocity flow by the flow separation and the injected vortices.
Advisors/Committee Members: Greber, Isaac.
Subjects: Engineering, Aerospace
Keywords: dimensional compressible turbulent flow computations diffusing S-duct vortex generators
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15.
Cooke, Malcolm Norman.
Novel Stereolithographic Manufacture of Biodegradable Bone Tissue Scaffolds.
Degree: PhD, Mechanical Engineering, 2004, Case Western Reserve University
► This research concentrates on both design and manufacturing methodologies for the implementation…
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▼ This research concentrates on both design and manufacturing methodologies for the implementation of stereolithography (SLA) to produce well controlled, custom designed, porous scaffolds in the biodegradable, biocompatible polymer, poly(propylene fumarate) for both in vitro and in vivo studies. Initially, proof of concept trials were undertaken in a custom designed build tank retro-fitted to a standard SLA 250/40 SLA machine to determine stereolithography process feasibility. The results of the initial trials enabled the build process to be scaled-up and implemented on a dedicated Viper Si2 SLA machine. Poly(propylene fumarate) (PPF) and diethyl fumarate (DEF) ratios were adjusted to improve scaffold build quality, which is particularly important for the control of porosity when manufacturing porous scaffolds. Design methodologies are developed that allow three-dimensional porous volumes to be created using hexagonal and plate and post unit cells. Porous scaffolds were designed using this approach by populating a three-dimensional volume from which the scaffold was produced. Two porous scaffold designs were created for an in vitro cell attachment study and for an in vivo toxicity study using a rat dorsal flap animal model. A further set of in vivo animal studies (dog, rat, and rabbit) motivated the design of custom specific porous scaffolds for each animal model. The scaffold designs were based on three-dimensional, computer tomography scan data which was translated and imported into a 3D computer aided design (CAD) environment for the design of porosity to suit each custom scaffold. The CAD data was used to control the SLA process, finally resulting in poly(propylene fumarate), custom porous sterilizable and implantable scaffolds. The preliminary results from the in vitro and in vivo studies are encouraging. This work represents an advancement of knowledge and capability in the design and manufacture of custom porous scaffolds and provides a guide for further research towards the goal of repairing critical-sized cranial defects and other bony defects using tissue engineering technology.
Advisors/Committee Members: Rimnac, Clare M.
Keywords: Tissue engineering; Poly(propylene fumarate); Biodegradable scaffolds; Biocompatible porous scaffolds; Stereolithography; Rapid prototyping
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16.
De Anna, Russell Gerard.
Direct numerical simulation of boundary-layer flow over surface roughness.
Degree: PhD, Mechanical Engineering, 1993, Case Western Reserve University
► Results from a direct numerical simulation of transitional flow over a surface…
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▼ Results from a direct numerical simulation of transitional flow over a surface with spherical roughness elements of height k and a surface with random roughness of maximum height ± kmax are presented. Periodic boundary conditions in the streamwise and spanwise directions simulate an infinite array of roughness elements, while a body force, designed to yield the streamwise Blasius velocity in the absence of roughness, maintains the flow. At k/δ* = 0.72, the mean velocity field in the spherical roughness domain contains secondary flow patterns within the region below 2k, for Reynolds numbers, Ukk/ν, between 90 and 225. The streamwise vorticity at these low Reynolds numbers is simply a result of the fluid's continuity and does not indicate rotating fluid or effects of inertia. The spheres distort the original Blasius profile into a mildly inflected layer containing low-momentum regions behind each sphere. These regions engender unsteady disturbances near the wall; however, the distribution of body force with vertical position above the wall is such that growth is suppressed in this region. Growth does occur in the unstable layer above the spheres where the body force is larger. The disturbance frequency is fixed by both the mean, streamwise velocity in the most unstable layer and the spacing between spheres; it is n ot the blunt-body vortex-shedding frequency expected for isolated bodies. When an oscillating component was added to the steady, Blasius body force, the response was independent of both forcing frequency and amplitude and, once again, depended on the mean velocity and the spacing between spheres. At kmax/δ* = 0.5, the random roughness flow field contains oscillation frequencies near the Tollmien-Schlichting band, which is also the passing frequency associated with the domain's streamwise length and the local advection velocity, for Reynolds numbers, Ukmaxkmax/ν, in the range from 60 to 120, corresponding to Reδ* in the range from 310 to 620. At Rekmax = 30, the flow remained steady
Advisors/Committee Members: Reshotko, Eli.
Subjects: Physics, Fluid and Plasma
Keywords: Boundary-layer flow; Surface roughness
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17.
Demko, Michael Thomas.
Novel Thermal Characterization Methods for Micro/Nanomaterials.
Degree: MS, Mechanical Engineering, 2008, Case Western Reserve University
► Thermal characterization of micro/nanomaterials and their bulk composites is critical to further…
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▼ Thermal characterization of micro/nanomaterials and their bulk composites is critical to further development of numerous applications including electronics, thermal insulation and MEMS devices. Even though there are numerous methods reported in the literature describing characterization of thermal properties, complexities associated with these techniques often render them inappropriate for various sample geometries and sizes, thermal conductivity ranges, and surface characteristics; novel techniques are commonly invented or adapted for specific needs. For this work, a non-contact photothermal measurement technique, the numerical mirage method, is presented, which provides increased accuracy and additional ease of use as compared with previous mirage methods or other photothermal measurements. Additionally, a novel thermal characterization method is presented for use with individual micro/nanowires, providing a simple, reliable, repeatable method for measuring wire thermal diffusivities. Each method is verified by testing materials with known thermal properties, and good agreement with reference values has been obtained.
Advisors/Committee Members: Abramson, Alexis.
Subjects: Mechanical engineering
Keywords: photothermal; mirage; thermal; diffusivity; nanowire; heat transfer; measurement
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18.
Dowell, John P.
Thermal Cracks in Diesel Engine Crankshafts.
Degree: PhD, Mechanical Engineering, 2004, Case Western Reserve University
► Diesel engine crankshafts serve the function of transmitting torque generated by the…
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▼ Diesel engine crankshafts serve the function of transmitting torque generated by the power cylinders to the driven machinery. During the re-qualification of the crankshaft at overhaul, there may be small cracks found in the crankshaft. These cracks, known as “heat checks” in the industry, may render the crankshaft unfit for replacement in an engine, thereby representing a financial loss to the owner of the engine. The focus of this work is on the crankshafts, bearings and lubricating oils used in the diesel engines made by GE Rail, a manufacturer of locomotives. A metallurgical analysis of the thermal cracks in a typical crankshaft was made. Bearing rig tests were configured and executed to measure the relative tendency of different shaft materials (heat treatment) to seize and crack when running with different bearing materials and lubricating oils. Transient thermal and elastic-plastic analyses were used to verify the hypothesis of thermal shock. A one-dimensional generalized plane strain model of a long cylinder subjected to a transient heat flux on the outside diameter proved useful in understanding the sensitivity of different geometry and material parameters to the thermal shock mechanism. The finite element method and bearing back temperature measurements were used to estimate the heat flux from actual bearing seizure events. It was determined that the thermal cracks in the surface of the crankshaft journals are the result of a thermal shock mechanism. The rapid heating of the journal due to contact with the bearing will cause a temperature gradient that may be sufficient to cause constrained plasticity near the surface of the shaft. Subsequent cooling of the shaft may result in “reverse yielding” of the shaft surface and the generation of tensile hoop stresses that are sufficient to crack the material. Prior experience and some experimental evidence obtained in this work suggest that case hardening of the crankshaft may exacerbate the tendency to crack under thermal shock.
Advisors/Committee Members: Kicher, Thomas P.
Subjects: Engineering, Mechanical
Keywords: diesel engine; crankshaft; thermal cracks; heat checks; thermal shock; journal bearings
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19.
Dykas, Brian David.
FACTORS INFLUENCING THE PERFORMANCE OF FOIL GAS THRUST BEARINGS FOR OIL-FREE TURBOMACHINERY APPLICATIONS.
Degree: PhD, Mechanical Engineering, 2006, Case Western Reserve University
► The operating characteristics of foil gas thrust bearings are explored experimentally and…
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▼ The operating characteristics of foil gas thrust bearings are explored experimentally and analytically to ascertain the physical mechanisms that limit bearing performance. Measurements of bearing power loss and load capacity made in a variety of configurations highlight several important factors which influence performance. Consistent with conventional hydrodynamic theory, surface condition of the foil and surface condition of the runner have a large influence on bearing performance. Furthermore, active thermal management via cooling air flow and passive thermal management via conduction through the runner have a large influence. Thermal effects are shown to be more pronounced at higher loads where gas film heat generation and resulting thermoelastic distortion are larger, but smooth lubricious surfaces are needed to achieve these loads. With non-optimal surface conditions such as high levels of roughness, it is shown that asperity contact dominates over thermal deformation. This dissertation quantifies the effects of these non-ideal surface conditions on the load capacity of foil thrust bearings. It is determined that both smooth, low friction surfaces combined with adequate thermal management are necessary to support large loads at high speeds. Furthermore, analysis and modeling suggest that enhanced thermal management is possible by optimizing the thermal characteristics of the runner, an approach not yet exploited by the foil bearing community.
Advisors/Committee Members: Prahl, Joseph M.
Keywords: foil bearings, gas bearings, air bearings, thrust bearings, oil-free turbomachinery
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20.
Ergin, Fahrettin Gökhan.
Roughness Induced Transition.
Degree: PhD, Mechanical Engineering, 2005, Case Western Reserve University
► Surface roughness has numerous different effects on boundary layer stability. For roughness…
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▼ Surface roughness has numerous different effects on boundary layer stability. For roughness amplitudes lower than a critical level, the velocity disturbances roughness creates in laminar boundary layers experience a transient algebraic growth followed by exponential decay without leading to transition. When the critical level is exceeded unsteady disturbances are amplified and the flow rapidly transitions to turbulence. Whether the flow remains laminar or becomes turbulent is solely determined by the receptivity of the initial disturbance. Two experiments are performed that address two fundamental problems related to roughness induced disturbances. One examines the disturbances produced by subcritical elements. The other identifies the instability mechanism responsible for breakdown in the wake of supercritical roughness elements. For subcritical conditions, multiple component velocity measurements are obtained in a flat plate boundary layer in the wake of an array of subcritical cylindrical elements. These data reveal the topology of the steady horseshoe vortex that exists in the wake of roughness elements and leads to transient growth of streamwise and spanwise velocity disturbances. A theoretical technique that quantifies the receptivity of velocity disturbances to surface roughness requires the complete velocity field as input and the data obtained here are suitable for this purpose. For supercritical conditions, velocity measurements are obtained above and below the critical roughness height Reynolds number, Rek. The steady disturbance field reveals local shear layers in the wall-normal and spanwise directions and the unsteady disturbance filed reveals evidence of hairpin vortices observed in flow visualization studies. The locations of maximum fluctuation intensity correspond to the locations of local inflection points of the steady velocity field suggesting that the fluctuations result from a Kelvin-Helmholz-type instability. Rapid transition takes place at Rek = 334 but not below this value. The disturbances’ energy growth rates indicate that the transition scenario can be understood as a competition between the unsteady disturbances’ growth and the rapid relaxation of the steady flow that tends to stabilize these disturbances.
Advisors/Committee Members: White, Edward B.
Subjects: Engineering, Mechanical
Keywords: Laminar to turbulent transition; Surface roughness; Roughness receptivity; Transient growth; Bypass transition
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21.
Espenschied, Kenneth Scot.
Biologically-inspired control of an insect-like hexapod robot on rough terrain.
Degree: PhD, Mechanical Engineering, 1994, Case Western Reserve University
► There are three sections to this document: Application of a stick-insect based…
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▼ There are three sections to this document: Application of a stick-insect based controller for the locomotion of a 12 degree-of-freedom (DOF) hexapod robot, the use of a simulation in the design of an 18 DOF hexapod robot and its locomotion controller, and the construction of an 18 DOF robot and a corresponding controller for locomotion on rough terrain. The stick insect controller used on the 12 DOF robot is derived from the mechanisms believed to be responsible for the coordination of the stick insect. The robot walks in a continuum of insect-like gaits in a straight line on a flat surface. A previously developed simulation of an 18 DOF hexapod was modified to include models of the motors and transmissions to be used in the 18 DOF robot. The stick insect controller used on the 12 DOF robot was modified to allow general locomotion on a plane, and this was applied to the control of the simulated hexapod. The user inputs for this controller were forward velocity, lateral velocity, and rate of yaw.
Advisors/Committee Members: Quinn, Roger D.
Subjects: Engineering, Mechanical
Keywords: Hexapod robot, insect-like
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22.
Esteki, Ali.
Dynamic model of the hand with application in functional neuromuscular stimulation.
Degree: PhD, Mechanical Engineering, 1995, Case Western Reserve University
► A dynamic model of hand was generated and used to study potential…
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▼ A dynamic model of hand was generated and used to study potential hand functions on hand positioning and grasp force and the outcome of surgeries such as tendon transfers and joint fusions, in situations typical of those encountered in FNS. In the model, the hand is being treated as a multi-body system including rigid segments (phalanges and palm) connected by joints. Each joint is subjected to muscle moments, produced by a muscle model, passive joint moment and external force moments. The external forces are the result of interaction forces between the hand segments and a grasped fixed or movable object. In particular, the model was used to study the non-prehensile tip and palmar pinch movements, and to simulate prehensile lateral and palmar grasp functions of the hand. A quasi-linear viscoelastic model was found to described the joint passive moment. Model simulations showed that, in the absence of external forces, tip pinch posture is not obtained using only the extrinsic muscles. The currently used tendon transfer methods were found useful in normal hands but not significantly effective in quadriplegic hands. It was also found that activation of multiple thumb muscles (ADP, APB and FPL) without surgical alterations can provide functional lateral pinch with about 70% more grip force than the currently used method with joint fusion. A grasp protocol was introduced and shown successful in palmar grasp and hold of movable cylindrical objects using only extrinsic muscles
Advisors/Committee Members: Mansour, Joseph M.
Subjects: Engineering, Biomedical
Keywords: Hand functions; Neuromuscular stimulation
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23.
Ferkul, Paul Vincent.
A model of concurrent flow flame spread over a thin solid fuel.
Degree: PhD, Mechanical Engineering, 1993, Case Western Reserve University
► A numerical model is developed to examine laminar flame spread and extinction…
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▼ A numerical model is developed to examine laminar flame spread and extinction over a thin solid fuel in low-speed concurrent flows. The model provides a more precise fluid-mechanical description of the flame by incorporating an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point. Parabolic equations are used to treat the downstream flame, which has a higher flow Reynolds number. The parabolic and elliptic regions are coupled smoothly by an appropriate matching of boundary conditions. The solid phase consists of an energy equation with surface radiative loss and a surface pyrolysis relation. Steady spread with constant flame and pyrolysis lengths is found possible for thin fuels and this facilitates the adoption of a moving coordinate system attached to the flame with the flame spread rate being an eigenvalue. Calculations are performed in purely forced flow in a range of velocities which are lower than those induced in a normal gravity buoyant environment. Both quenching and blowoff extinction are observed. The results show that as flow velocity or oxygen percentage is reduced, the flame spread rate, the pyrolysis length, and the flame length all decrease, as expected. The flame standoff distance from the solid and the reaction zone thickness, however, first increase with decreasing flow velocity, but eventually decrease very near the quenching extinction limit. The short, diffuse flames observed at low flow velocities and oxygen levels are consistent with available experimental data. The maximum flame temperature decreases slowly at first as flow velocity is reduced, then falls more steeply close to the quenching extinction limit. Low velocity quenching occurs as a result of heat loss. At low velocities, surface radiative loss becomes a significant fraction of the total combustion heat release. In addition, the shorter flame length causes an increase in the fraction of conduction downstream compared to conduction to the fuel. These heat losses lead to lower flame temperatures, and ultimately, extinction. This extinction mechanism differs from that of blowoff, where the flame is unable to be stabilized due to the high flow velocity.
Advisors/Committee Members: T'ien, James S.
Keywords: model concurrent flow flame spread over thin solid fuel
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24.
Fu, Shuzhen.
Mechanical studies of the intramuscular electrode leads.
Degree: PhD, Mechanical Engineering, 1992, Case Western Reserve University
► The intramuscular electrode lead (made by the multi-strand wire) is used for…
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▼ The intramuscular electrode lead (made by the multi-strand wire) is used for functional electrical stimulation. In this investigation of the electrode, the biomedical origin has been abstraction into mechanical problems. It is important to understand the studies only focus the mechanical behavior of the electrode, therefore, the applications of the studies are limited. The studies illustrate the quality of the electrode is mainly judged by its flexibility and longevity which are functions of the mechanical properties of the electrode and loading conditions. The mechanical properties of the electrode largely depend on the strand wire manufacturing process and the geometric configuration of the electrode. The residual stress which is a "by-product" from winding process largely affected the electrodes' fatigue life. Although the size of the double helix electrode is more than twice of the single helix electrode, it still becomes the best choice in terms of it's flexibility and life expectancy, both of which were proven by experiments and patient implantation.
Advisors/Committee Members: Kicher, Thomas P.
Keywords: Mechanical studies intramuscular electrode leads
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25.
Guo, Jenq-Shan.
Characteristics of the nonlinear hysteresis loop for rotor-bearing instability.
Degree: PhD, Mechanical Engineering, 1995, Case Western Reserve University
► The nonlinear hysteresis loop of a simple-cylindrical-journal-bearing supported rotordynamic system is characterized…
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▼ The nonlinear hysteresis loop of a simple-cylindrical-journal-bearing supported rotordynamic system is characterized by the Hopf-bifurcation and Saddle-Node bifurcation speeds. The nonlinearity of this system occurs in the journal-bearing fluid-film forces, and requires the imbedding of a solution for the Reynolds lubrication education within a numerical integration scheme of the coupled motion equations in order to perform proper simulations. These show that under a light bearing static load, the Saddle-Node and Hopf bifurcations coalesce to a single speed at essentially two times the self-excited vibration frequency (i.e., the lowest natural frequency) At higher bearing loads, the classical instability threshold speed (i.e., Hopf bifurcation) occurs at progressively higher rotor speeds. However, the disappearance speed (Saddle Node of the periodic orbit) of the nonlinear limit cycle occurs at progressively lower rotor speeds, asymptotically approaching approximately 1.725 times the lowest natural frequency. By adding a rotor unbalance force to the model, exploratory simulations have been made to determine the extent to which chaos signal processing in the normal speed-up or coast-down vibration of actual machines could be used to locate this lower speed bound of the instability hysteresis loop. Laboratory experiments were performed and these agree quite well with simuiation results
Advisors/Committee Members: Adams, M. L.
Subjects: Engineering, Aerospace
Keywords: Nonlinear hysteresis loop; Instability threshold speed; Rotor-bearing instability
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26.
Gurun, Akif Murat.
Interactions of Tollmien-Schlichting Waves and Stationary Transient Disturbances.
Degree: PhD, Mechanical Engineering, 2006, Case Western Reserve University
► Numerical simulations have shown that stationary, spanwise periodic transient disturbances are capable…
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▼ Numerical simulations have shown that stationary, spanwise periodic transient disturbances are capable of suppressing the growth of Tollmien-Schlichting (TS) waves in boundary layers. A natural implication is that the deliberate introduction of transient disturbances may delay TS-dominated transition. This experimental study investigates the interactions of these two types of disturbances and the breakdown of TS waves with and without transient disturbances. TS waves are created using a combination of acoustic forcing and a two-dimensional roughness strip while transient disturbances are created using a spanwise array of cylindrical roughness elements. It is found that in the presence of stationary transient disturbances, wall-normal velocity profiles of the unsteady TS-like waves are modulated and their growth rate is reduced. The modulated wall-normal velocity profiles have a characteristic M-shaped appearance and this shape appears to be mainly due to the component of the unsteady disturbances that varies on the spanwise wavelength of the stationary disturbances and higher spanwise harmonics of this wavelength. An important finding with respect to transition control applications is that the receptivity of the TS waves is reduced when the spanwise roughness array is present. The underlying mechanism responsible for this reduction is not yet known. Additionally, it has been found that unsteady disturbance amplitudes at breakdown are reduced when transient disturbances are introduced and, therefore, the breakdown location is actually moved upstream when care is taken to match initial unsteady disturbance amplitudes. It is concluded that even though TS growth is reduced, transition to turbulence is not successfully delayed.
Advisors/Committee Members: White, Edward B.
Keywords: Transition; Boundary Layers; Tollmien-Schlicting Waves; Transient Growth; Turbulence; Secondary Instability; Wind Tunnel; Transition Delay; Data Acquisition
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27.
Hagigat, Michael Kent.
Influence of non classical friction on the rubbing and impact behavior of rotor dynamic systems.
Degree: PhD, Mechanical Engineering, 1994, Case Western Reserve University
► A nonlinear finite element model for simulating the effects of rubbing and…
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▼ A nonlinear finite element model for simulating the effects of rubbing and impact on rotor dynamics has been developed. The nonlinear model is used to conduct a series of forced transient analyses of a rotating system under the influence of rubbing and impact using the modal and the Average Acceleration direct numerical integration methods. The modal method is shown to be more efficient than the Average Acceleration method. The first approach for modeling the friction forces is the application of Coulomb friction law. Simulation results show the rotating system to be unstable for all ranges of Coulomb coefficient of friction. In contrast, experimental results have shown that the system under study is stable under the influence of rubbing and impact for the simulation conditions. A second approach for modeling the friction forces is employed for the purpose of investigating the differences between the experimental and the simulation results. The second approach consists of an artificial simulation of a Stick-Slip phenomenon by setting the Coulomb coefficient of friction to a value of zero for certain time intervals. The artificial Stick-Slip simulation has a stabilizing effect on the system. The third approach for modeling the friction forces is the application of an advanced fri ction model simulating the Stick-Slip phenomena. The system appears to be completely stable for a dry metal to metal rubbing and impact condition. The results of the simulation using the advanced friction model are close to experimental results. The surface finish of the contacting metals were found to have a negligible effect on the results of the simulation.
Advisors/Committee Members: Mullen, Robert L.
Subjects: Engineering, Mechanical
Keywords: non classical friction rotor dynamic system
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28.
Han, Bai.
An Experimental and Computational study on Burner-Generated Low Stretch Gaseous Diffuion Flames.
Degree: PhD, Mechanical Engineering, 2005, Case Western Reserve University
► The study of low-stretch flames is essential for the fundamental understanding of…
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▼ The study of low-stretch flames is essential for the fundamental understanding of the flame radiation effects on flame response and extinction limits. Low-stretch flames are also relevant to fire safety in reduced gravity environment and large buoyant fires, where localized areas of low stretch are attainable. An experimental study of the dynamics and structure of low-stretched diffusion flames is carried out by using various advanced optical diagnostics, along with a quasi-one-dimensional simulation with detailed chemical kinetics, thermodynamic/transport properties, narrowband radiation model, and gray surface radiation treatment. In the present study, ultra-low stretch flames are established in normal gravity by bottom burning of a methane/nitrogen mixture discharged from a porous spherically symmetric burner of large radius of curvature. With the radius of curvature of ~400 cm, quasi-one-dimensional diffusion flames of equivalent stretch rate as low as ~2 s-1 can be stabilized. Using this novel burner, the current study aims to improve our understanding of diffusion combustion, by expanding the available experimental data regarding the structure and response of diffusion flames to the previously-unexplored low-stretch rate regime. Several advanced non-intrusive optical diagnostics techniques are used to study the flame structure. Gas phase temperatures are measured by Raman scattering, while the burner surface temperatures are measured by infra-red imaging. OH-PLIF and chemiluminescence imaging techniques are used to help characterize the reaction zone of the flames. A flame stability diagram mapping the response of the ultra-low stretch diffusion flame to varying fuel injection speed and nitrogen dilution is explored. In this diagram, the sooting and extinction limit boundaries are identified. Various near-extinction multi-dimensional flame patterns under different experimental conditions are observed, and their evolutions are studied using direct chemiluminescence and OH-PLIF imaging. The experimental results on quasi-one-dimensional flame structure allow direct comparison with a detailed quasi-one-dimensional numerical model including the radiative interactions of flame and gray surface. The numerical modeling is demonstrated to be able to simulate the low-stretch flame structure. Using current modeling, the extinction limits under different conditions are also examined. The results are consistent with experimental observations.
Advisors/Committee Members: Sung, Chih-Jen.
Subjects: Engineering, Mechanical
Keywords: Low stretch; Diffusion Flame
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29.
Handschuh, Robert Frederick.
Thermal behavior of spiral bevel gears.
Degree: PhD, Mechanical Engineering, 1993, Case Western Reserve University
► A study of the thermal behavior of spiral bevel gears is presented.…
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▼ A study of the thermal behavior of spiral bevel gears is presented. The study includes both experimental and analytical results. Experimental data was taken using thermocoupled test hardware as well as an infrared microscope. Many operational parameters were varied to investigate their effects on the thermal behavior. The data taken was also used to validate the boundary conditions applied to the analytical model. A finite element based solution sequence was developed. A three-dimensional model is based on modeling the manufacturing process for these gears. Contact between the meshing gears is found using tooth contact analysis to describe the location, curvatures, orientations, and surface velocities. This information is then used in a three-dimensional Hertzian contact analysis to predict contact ellipse size, and maximum pressure. From these results an estimate of the heat flux magnitude and location on the finite element model are made. The finite element model uses time averaged boundary conditions to permit the solution to attain steady state in a computationally efficient manner. Then time and position varying boundary conditions are applied to the model for analysis of the cyclic heating and cooling due to the gears meshing and transferring heat to the surroundings respectively. The model is run in this mode until the temperature behavior stabi lizes. The transient flash temperature on the surface is therefore described. The analysis can be used to predict overall expected thermal behavior of spiral bevel gears. The experimental and analytical results were compared for this study and to a limited number of other studies. The experimental and analytical results were basically within 10% of each other for the cases compared. The experimental comparison was for bulk thermocouple locations and data taken with an infrared microscope. A limited number of studies that the results attained herein were compared to predicted the same basic behavior.
Advisors/Committee Members: Kicher, Thomas P.
Keywords: Thermal behavior spiral bevel gears
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30.
Hu, Didi.
Thermocapillary flows in an enclosure of unit order aspect ratio.
Degree: PhD, Mechanical Engineering, 1990, Case Western Reserve University
► Steady thermocapillary flows in a two-dimensional rectangular enclosure of unit order aspect…
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▼ Steady thermocapillary flows in a two-dimensional rectangular enclosure of unit order aspect ratio are studied for fluids of small, unit order, and large Prandtl numbers. Scaling analysis is applied to obtain velocity and length scales for different flow regimes along with the dimensionless parameters that define these regimes. The scaling analysis in this work is for the entire range of the Reynolds number and the influence of the flow on the driving force, which leads to a change in the thermal signature, is also incorporated. Numerical simulations are performed and agreements are found between the results from the scaling analysis and the results from the numerical simulations. The analysis also predicts the behavior of the thermocapillary flow in the range of Marangoni number at which present numerical schema are incapable of simulating.
Advisors/Committee Members: Ostrach, Simon.
Keywords: Thermocapillary flows unit order aspect ratio
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