Theses/Dissertations - Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/2104/4817

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The influence of load on kinematics of computer-simulated sagittal-plane lifting.
(2006-05-11T17:03:31Z) Newman, Patrick S.; Garner, Brian Alan, 1966-; Mechanical Engineering.; Baylor University. Dept. of Mechanical Engineering.
Researchers have shown that lifting kinematics change predictably with increased load. To test whether these kinematics patterns are intrinsic or voluntary, a computer model was developed to simulate lifting in the sagittal plane. The eight-degree-of-freedom model included the ankle, knee, hip, shoulder, elbow, neck, and two back joints. Strength limits were assigned to model joints according to position-dependent average male data obtained from the literature. Using both forward and inverse dynamics approaches, the model was programmed to lift various loads while tracking lift kinematics measured from a human subject. Simulation results suggest that, contrary to common hypotheses, observed lifting patterns are not dictated by physical law (intrinsic) but are chosen for efficiency and stability (voluntary). In this study, a method for isolating kinematic dependencies is introduced. It is anticipated that the results will help in the understanding of motion perception, lifting technique, and low-back pain.
The design and validation of an impinging jet test facility.
(2006-05-28T01:13:46Z) Robertson, Peter R.; Van Treuren, Kenneth W.; Mechanical Engineering.; Baylor University. Dept. of Mechanical Engineering.
An experimental jet impingement facility was constructed with the capability of conducting a detailed analysis of the local heat transfer coefficients beneath an array of large impinging jets. The facility was validated with initial heat transfer studies that determined an appropriate jet discharge coefficient of 0.802 and created a correlation relating local jet Reynolds number and stagnation point heat transfer. The correlation matched closely with previous studies. The thermal effects of impinging jets were visualized by liquid crystal thermography. The resulting thermal footprints of downstream jets revealed the first known documented case of the heat transfer effects of horseshoe vortices on the target surface. This phenomenon was identified and discussed.
A linked-plane obstacle-set algorithm for modeling broad muscle paths : application to the deltoid muscle.
(2008-10-01T19:03:48Z) Xu, Bo, 1984-; Garner, Brian Alan, 1966-; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Computer modeling is commonly used to simulate muscle paths for the study of human biomechanics. Because some muscles, such as broad muscles, have complex morphology, modeling the paths of these muscles can be challenging. The aim of this study is to develop a new algorithm that quickly and realistically models the wrapping paths of broad muscles. The algorithm treats the muscle as a series of elastic bands wrapping around sphere-shaped obstacles. Each band is constrained to lie in its own plane and wrap around its own sphere. Each band plane forms a given angle with respect to the adjacent band plane, with the first band plane forming an optimized angle with respect to a fixed reference plane. The optimization seeks to minimize the sum total of all band lengths. The new algorithm accounts for tissue connectivity between muscle fibers in broad muscles, and can reproduce realistic muscle moment arm simulations.
Converting coconut husks into binderless particle board.
(2009-04-01T18:45:23Z) Greer, Stanton.; Bradley, Walter Lee, 1943-; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Coconuts grow abundantly in tropical regions, and the coconut husk is often discarded as waste. However, a new application has increased interest in developing this previously underutilized resource. Coconut pith has chemical reactivity due to its high lignin and phenolic content and can be hot-pressed into binderless particle board with excellent commercial potential. This initial investigation into proof of concept and production details determines the key processing variables and discusses the important findings of the concurrent research done by the Common Fund for Commodities. The objective of this research is to identify the best production paths to make high quality "Cocoboard" at the lowest possible price.
Experimental and numerical study on flow control using obliquely aligned elements.
(2010-06-23T12:33:08Z) Narvaez, Gilberto.; McClain, Stephen Taylor.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
The use of micro-electromechanical system devices (MEMS) have been studied extensively in literature for control of flow separation and transitioning to turbulent flow. However, there is limited information about how obliquely aligned roughness elements affect the boundary layer development and induce turbulence. The purpose of this study was to measure the transverse flow and turbulent intensities produced by an array of 0°, 5°, 10°, and 15° obliquely-aligned elliptical control elements in turbulent flow at 2, 5, and 10 m/s on a flat plate. The resulting boundary-layer measurements demonstrate the ability of the control elements to produce tailored secondary flows. Since the test coupon was of finite span, results demonstrate that controlled vortices can also be generated using the arrays. Additionally, CFD simulations were performed and compared to the experimental results using the realizable k-ε turbulence model in ANSYS FLUENT 12.0 with solutions converging to residuals less than 1x10⁻⁶ for flow and turbulence quantities.
Non-deterministic modeling of the bulk thermal and electrical conductivity for dense thin film carbon nanotube networks.
(2011-05-12T15:14:17Z) Ashtekar, Nikhil A.; Jack, David Abram, 1977-; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Thin films composed of single-walled carbon nanotubes, enjoy very high thermal and electrical conductivities, well beyond that of polymer matrix composites, and are very light in weight. Before these materials can experience industrial acceptance the underlying mechanisms dictating their performance must be understood. This research project intends to characterize using a physics based model the bulk thermal and electrical behavior of a neat carbon nanotube network conditions involving stochastic distributions of length, diameter, chirality, orientation obtained from the literature along with theoretical values of the inter-tube distance distribution obtained from in-house studies obtained through MD simulations. The work presents step by step development of the fully three dimensional model for linear, steady state loadings. Case studies using models are presented to better understand the dependence of the bulk thermal and electrical conductivity on the nanoscale parameters, such as bundle length, bundle diameter, orientation, volume fraction. The model is also used to investigate the sensitivity of the thermal and electrical conductivity on select stochastic parameters.
Design and experimental testing of small-scale wind turbines.
(2011-05-12T15:31:46Z) Gregg, Jason R.; Van Treuren, Kenneth W.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Due to the increasing environmental and economic cost of fossil fuels, alternative sources of energy are needed. One such source is energy wind energy. Much of the current wind turbine research focuses on large-scale wind turbines. An alternative approach is small-scale wind turbines designed specifically to produce power at low wind speeds. This thesis investigates the design and testing of these turbines. Concerns specific to small-scale design, such as low Reynolds number flow, separation, and low wind speed power generation are addressed. A test apparatus was developed to validate the design procedure, and specific methods to increase power generation under these conditions, such as spanwise and axial roughness, two, three, and four-bladed systems and tip-speed ratios of 1, 3, and 7, were investigated. While many of these methods increased system efficiency, roughness was found to dramatically improve performance, reaching up to 126% increase in power output at a wind speed of 10 mph.
The effect of roughness element thermal conductivity on turbulent convection.
(2011-05-12T15:41:42Z) Mart, Steven Robert.; McClain, Stephen Taylor.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Many flows of engineering interest occur over surfaces that exhibit roughness with thermal conductivities much lower than common metals and alloys. This is especially true of in-service gas turbine blades with surface depositions. Depending on the local convection coefficients, low thermal conductivity deposits may create situations where temperature changes along the heights of the elements are important and must be considered in predicting the overall surface convection coefficient. Using four test plates constructed with hexagonal distributions of hemispheres or cones made of either aluminum or ABS plastic, a series of experiments were performed in the Baylor University Subsonic Wind Tunnel to investigate the effects of roughness element thermal conductivities on turbulent convection. Results indicate that the packing density of the elements and the enhancement on the floor of the roughness distribution compete with the roughness element thermal conductivity in determining the overall convection enhancement.
Experimental and numerical investigation of high temperature jet impingement for turbine cooling applications.
(2011-05-12T15:42:00Z) Martin, Evan L.; Wright, Lesley Mae.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Modern gas turbine engines commonly operate at temperatures above the melting point of the turbine’s blades and vanes. Internal and external cooling of the blades is required for sustained operation and prolonged engine life. Jet impingement, an aggressive form of cooling, is typically used in the airfoil leading edge which is exposed to extreme heat loads. A parametric study is used to experimentally and numerically investigate high temperature jet impingement in the blade leading edge. The effects of jet Reynolds number (Rejet), jet-to-target surface spacing (ℓ/d), jet-to-jet spacing (s/d), jet-to-target surface curvature (D/d), and jet temperature on stagnation Nusselt numbers are evaluated in a high temperature test apparatus. The facility is validated against correlations developed in previous studies. The experimental study is complimented with CFD simulations performed using commercially available software. Nusselt number results show strong dependence on Reynolds number and geometry yet little or no dependence on jet temperature.
Optimization of muscle physiological parameters for a computer model of the human shoulder girdle.
(2011-05-12T15:54:16Z) White, Joel D.; Garner, Brian Alan, 1966-; Skurla, Carolyn Patlovany.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
The shoulder girdle serves as the platform for all human upper extremity movement and plays an integral role in providing the large range of motion of the shoulder joint. However, computer models representing human upper-extremity biomechanics have suffered from a lack of published data relating to the shoulder girdle. The aim of this study was to validate an existing human upper-extremity model in light of newly-published strength data for twelve shoulder shrugging exercises at various shoulder girdle positions. The three-dimensional model accounted for motions of the clavicle, scapula, and humerus, and was actuated by 19 muscle bundles. The model was used to simulate each of the reported shrugging exercises, while the model’s muscle physiological parameters were optimized to minimize error between the simulated and experimental strength measures. The optimized model accurately reproduced the experimental shoulder elevation and depression strengths, but tended to overachieve for retraction and underachieve for protraction exercises.
Modeling of flexible fiber motion and prediction of material properties.
(2011-09-14) Zhang, Cong, 1986-; Jack, David Abram, 1977-; Engineering.; Baylor University. Dept. of Mechanical Engineering.
This work employs the rod chain model of Wang et al. (2006) to study the motion of discrete flexible fibers. Results are presented for both individual fibers and a stochastic distribution of fibers to study the variations in the transient effects between the rigid and the flexible fiber systems. Results demonstrate that the observed period decreases as the fiber flexure increases, and provide insight into the modifications required for the orientation distribution function of flexible suspensions. To demonstrate the importance in studying the alterations in the transient effects on a processed part, a study of the cured composite stiffness is presented for the flexible fiber system using the micro-mechanical approach of Hsiao and Daniel (1996) along with an adapted version of the rigid fiber micromechanical approach discussed by Jack and Smith (2008).
Design and validation of new testing apparatus for testing helical compression springs under combined axial, shear, torsion, and bending loads.
(2011-09-14) Kelley, Jace Dane.; Skurla, Carolyn Patlovany.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Helical compression springs are normally used to provide a linear force response to compressive displacement. However, compression springs can be used to provide lateral force and rotational torque responses to lateral and angular displacements. The purpose of this thesis is to take advantage of improvements in mechanical testing equipment to develop a testing apparatus that can mechanically test helical compression springs under varying amounts of complex three-dimensional displacements. A testing apparatus was constructed using a custom six axis load cell and a commercial MTS system. The calibration and validation of the custom load cell is presented. One compression spring was tested under different combinations of axial, shear, and torsional displacements to validate the design of the jig. The results indicated varying levels of interdependence between the loading modes on the spring’s net force response; however, the spring’s compressive response appears to be independent of torsion and shear displacement.
Designing, constructing, and testing a second-generation prototype mechanical hippotherapy horse.
(2011-09-14) Benoit, Heather Denae.; Garner, Brian Alan, 1966-; Engineering.; Baylor University. Dept. of Mechanical Engineering.
The use of horses as a means of therapy has been documented for some time. To determine why this type of therapy works and to provide a means of expanding its accessibility, a mechanical horse has been developed. Data collected on the movement of live horses during a previous study was used as a target motion in the development of a prototype mechanical horse. This mechanism was designed to be capable of reproducing that motion. For this prototype, the base remains stationary and a suspended saddle seat moves in a pattern replicating that of a live horse. The saddle is suspended by eight cables which are displaced by eight distinct cams. The cam set can be exchanged for various cam sets which correspond to different prescribed movements. Testing revealed good agreement between the motion of the prototype and the target, but improvements can be made in the measure of z-translation.
Investigation of dense suspension rotary diffusion models for fiber orientation predictions during injection molding of short-fiber reinforced polymeric composites.
(2011-09-14) Agboola, Babatunde O.; Jack, David Abram, 1977-; Engineering.; Baylor University. Dept. of Mechanical Engineering.
There is a need for physics-based mathematical models for the design of industrial short-fiber reinforced composites (SFRC) to predict the fiber orientation within the part. Traditional models for fiber interactions use the isotropic rotary diffusion model of Folgar and Tucker, but there is considerable interest to use the Phelps and Tucker anisotropic rotary diffusion model. Both models predict the flow induced orientation, which directly determines the resulting stiffness of an injection molded part. These two models are investigated in the present work. A number of fourth order orientation tensor closure approximations are investigated for both diffusion models, with the goal being to suggest the more effective and efficient closure approximation for a variety of flow conditions. Differences in the resulting elastic properties predicted from the two rotary diffusion models are observed. These observations raise questions as to which diffusion model should be used commercially for injection molded SFRCs.
Experimental investigation of leading edge jet impingement with varying jet geometries and inlet supply conditions for turbine cooling applications.
(2012-08-08) Jordan, C. Neil.; Wright, Lesley Mae.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Jet impingement is often employed within the leading edge of modern gas turbine airfoils to combat the extreme heat loads incurred within this region. This experimental investigation employs a transient liquid crystal technique to obtain detailed Nusselt number distributions on a concave, cylindrical surface that models the leading edge of a turbine blade. The effect of hole shape, varying edge conditions at the jet orifice, as well as varying inlet crossflow conditions are investigated. Cylindrical and racetrack shaped jets with three inlet and exit conditions are investigated for each jet shape: a square edge, a partially filleted edge, and a fully filleted edge. Results show that racetrack shaped jets generally provide enhanced heat transfer when compared to the cylindrical holes. However, engine designers should be cautious when introducing edge fillets and inlet crossflow, as these modifications generally degrade the heat transfer from the leading edge target surface.
Aerodynamic design considerations for small-scale, fixed-pitch, horizontal-axis wind turbines operating in class 2 winds.
(2012-08-08) Burdett, Timothy A.; Van Treuren, Kenneth W.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Renewable sources of energy, such as wind, are necessary to meet the growing demand as conventional energy sources are depleted. Very little research has been accomplished to improve wind turbine performance in Class 2 winds. This work experimentally analyzed techniques to improve the aerodynamic performance of small-scale, fixed-pitch, horizontal-axis wind turbines in Class 2 winds. Experimental data for the S823 airfoil was taken for Reynolds numbers from 50,000 to 200,000. A trip strip was shown to improve airfoil performance for Reynolds numbers below 100,000. Additional wind tunnel studies validated the wind turbine testing procedure. Using blade element theory (BET) and blade element momentum theory (BEMT), wind turbine blades with optimum angle of twist were designed and tested. Results suggest the BEMT-optimized blades will perform better at the design point. The sensitivity of the design angle on power production was also examined, resulting in negligible difference for the conditions tested.
Response of passive surface hairs in steady and unsteady Falkner-Skan boundary layers.
(2012-11-29) Case, Lance C.; McClain, Stephen Taylor.; Engineering.; Baylor University. Dept. of Mechanical Engineering.
Arrays of biologically inspired artificial hair sensors for flow detection are being considered to provide small unmanned aerial vehicles greater platform stability through gust mitigation. Analytical models of hair sensor response to flow conditions have been previously developed, but fundamental assumptions of those models have remained essentially unvalidated. A model adaptation for non-wall-orthogonal fiber deflection was developed due to the geometric nature of the attached fibers. The current work seeks to validate this hair sensor model with wind tunnel testing results of hair sensor response to flows. Because the hair sensor arrays are not yet active, an optical fiber displacement measurement scheme and image analysis algorithms were developed to compute fiber deflection response to steady and unsteady flow conditions. Results indicate agreement between model predictions and experimental results sufficient for future sensor design employing the adapted model.
Investigation of induced thermo-mechanical response and cure kinetics during processing of carbon fiber reinforced plastics.
(2013-05-15) Mailen, Russell.; Jack, David Abram, 1977-; Mechanical Engineering.; L-3 Communications.; Birkeland Current.; Baylor University. Dept. of Mechanical Engineering.
The manufacture of laminated composite materials using a thermosetting resin matrix is a complex process that can be understood with a knowledge of cure kinetics, heat transfer, and structural mechanics. During laminate manufacture, reinforcing fibers are impregnated with resin and subjected to catalytic conditions. Under these conditions, the resin transforms from liquid to solid as polymer chains form a crosslinked network. During this process, the phenomenological events of gelation and vitrification influence the ability to process the resin. Prediction of these events with kinetic modeling allows the optimization of the manufacturing process and insight into the final material properties. This thesis investigates the application of kinetic models to, specifically, the Pro-Set 117LV/229 epoxy system. Additionally, it is demonstrated that residual stresses develop in laminated composite as cure progresses. The residual stress state is affected by the processing history of the component and has an impact on component dimensionality and strength.
Convective heat transfer from realistic ice roughness distributions.
(2013-09-16) Tecson, Joshua Logan.; McClain, Stephen Taylor.; Mechanical Engineering.; Baylor University. Dept. of Mechanical Engineering.
As supercooled water droplets impinge the surfaces of in-flight aircraft, a layer of accreted ice will form. In the initial stages of the accretion process, the ice will form as a distributed surface roughness. Ice accretions degrade the aerodynamic performance and safety of an aircraft. Icing effects are simulated and mitigated during aircraft design through the use of computational ice accretion codes. A significant area for improvement of these codes exists in the simplistic characterization of convective heat transfer from ice roughness. A better characterization of convective heat transfer must be obtained for flows over surfaces with realistic ice roughness properties and relevant thermal boundary conditions. A series of steady state experiments was performed in a wind tunnel on a flat plate with two realistic ice roughness surfaces. Using an infrared camera, detailed maps of convective heat transfer coefficients were obtained for the surfaces.
The use of the flexural modulus in the comparison of fiber orientation models for concentrated suspensions in short fiber-filled thermoplastics.
(2013-09-24) Lewis, Benjamin W.; Jack, David Abram, 1977-; Mechanical Engineering.; Baylor University. Dept. of Mechanical Engineering.
Advances in modeling spatially varying fiber orientation within an injection molded thermoplastic composite part have led to better structural designs and manufacturing efficiencies by optimizing mold designs and processing parameters. With recent improvements in processing tolerances, the accuracy of classical fiber interaction models warrant further investigation. The isotropic diffusion fiber interaction model of Folgar-Tucker (1984) has been commonly used for decades. Recent objective modifications include the reduced strain closure of Wang, et al. (2008) and the anisotropic rotary diffusion model of Phelps and Tucker (2009). This thesis investigates the impact these diffusion models have on final processed part structural performance. A proposed macroscopic methodology that takes into account the microstructure of fiber orientation is suggested through the use of the flexural modulus for comparisons with experimental testing. Results indicate that the flexural modulus has limited use for diffusion model validation, and alternative macroscopic methods to identify fiber interaction models are suggested.

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