Mechanical Engineering

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    Center for Engineering Concepts Development (CECD) 20th Anniversary Celebration and Middleton Luncheon
    (2019-04-17) Anand, Davinder; Hazelwood, Dylan
    The Center for Engineering Concepts Development (CECD) celebrated its distinguished history and two decades of accomplishments with the 20th Anniversary and Middleton Luncheon on April 17, 2019. The event opened with welcoming remarks from CECD director, Dr. Davinder Anand, and hosted guest speakers U.S. Senator Chris Van Hollen (D-Md.) and Maryland State Senator Thomas “Mac” Middleton (D-Charles Co.), who were early supporters of the research center. Included are remarks, presentation slides, program and CECD overview, and pictures from the April 17th 2019 CECD 20th Anniversary Celebration and Middleton Luncheon.
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    INVESTIGATION OF JP-8 AUTOIGNITION UNDER VITIATED COMBUSTION CONDITIONS
    (2011) Fuller, Casey Charles; Jackson, Gregory S.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Limited data on jet fuel ignition and oxidation at low-O2, vitiated conditions has hindered the validation of kinetic models for combustion under such conditions. In this study, ignition delay time experiments of JP-8 have been performed with vitiated air at low pressures. Initially, the effects of temperature, equivalence ratio, and mole fractions of vitiated components on JP-8 ignition at 1 atm were screened to discover that temperature, O2 and NO have the largest significance. A following detailed investigation examined the effect on JP-8 ignition of larger concentrations of NO (0 - 1000 ppm) at lower temperatures (700 - 900 K), pressure (0.5 - 1.0 atm) and O2 mole fractions (12 - 20%). Results show that even trace amounts of NO dramatically enhance the oxidation of JP-8 with reduction in ignition delay time of up to 80%. Significant coupling exists between NO and the other design variables (temperature, oxygen level and pressure) as related to the effect of NO on ignition. An empirical model relating temperature, O2 and NO to ignition delay time of JP-8 has also been developed.
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    INVESTIGATION OF HOUSEHOLD REFRIGERATOR WITH ALTERNATIVE LOW GLOBAL WARMING POTENTIAL REFRIGERANTS
    (2011) Leighton, Daniel Thomas; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Steady-state and transient thermodynamic models of the refrigeration system were created in order to predict the performance of household refrigerators using different refrigerant types. The models were validated with experimental data taken from a commercially available household refrigerator charged with HFC-134a. The models were then used to simulate the drop-in performance of several alternative low global warming potential (GWP) refrigerants in the household refrigerator. The alternative refrigerant of strongest interest was HFO-1234yf, which was evaluated as a direct drop-in replacement for HFC-134a. HFO-1234yf was found to be a suitable replacement for HFC-134a, with similar performance characteristics and a decrease in overall system efficiency of less than 2%. A parametric study of HFC-134a/HFO-1234yf blends was also conducted in order to evaluate their potential as non-flammable, low GWP replacements for HFC-134a.
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    A BAYESIAN FRAMEWORK FOR STRUCTURAL HEALTH MANAGEMENT USING ACOUSTIC EMISSION MONITORING AND PERIODIC INSPECTIONS
    (2011) Rabiei, Masoud; Modarres, Mohammad; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Many aerospace and civil infrastructures currently in service are at or beyond their design service-life limit. The ability to assess and predict their state of damage is critical in ensuring the structural integrity of such aging structures. The empirical models used for crack growth prediction suffer from various uncertainties; these models are often based on idealized theories and simplistic assumptions and may fail to capture the underlying physics of the complex failure mechanisms. The other source of uncertainty is the scarcity of relevant material-level test data required to estimate the parameters of empirical models. To avoid in-service failure, the structures must be inspected routinely to ensure no damage of significant size is present in the structure. Currently, the structure has to be taken off line and partly disassembled to expose the critical areas for nondestructive inspection (NDI). This is an expensive and time-consuming process. Structural health monitoring (SHM) is an emerging research area for online assessment of structural integrity using appropriate NDI technology. SHM could have a major contribution to the structural diagnosis and prognosis. Empirical models, offline periodic inspections and online SHM systems can each provide an independent assessment of the structural integrity; in this research, a novel structural health management framework is proposed in which the Bayesian knowledge fusion technique is used to combine the information from all sources mentioned above in a systematic manner. This work focuses on monitoring fatigue crack growth in metallic structures using acoustic emission (AE) technology. Fatigue crack growth tests with real-time acoustic emissions monitoring are conducted on CT specimens made of 7075 aluminum. Proper filtration of the resulting AE signals reveals a log-linear relationship between fracture parameters (da/dN and ΔK ) and select AE features; a flexible statistical model is developed to describe the relationship between these parameters. Bayesian regression technique is used to estimate the model parameters using experimental data. The model is then used to calculate two important quantities that can be used for structural health management: (a) an AE-based instantaneous damage severity index, and (b) an AE-based estimate of the crack size distribution at a given point in time, assuming a known initial crack size distribution. Finally, recursive Bayesian estimation is used for online integration of the structural health assessment information obtained from various sources mentioned above. The evidence used in Bayesian updating can be observed crack sizes and/or crack growth rate observations. The outcome of this approach is updated crack size distribution as well as updated model parameters. The model with updated parameters is then used for prognosis given an assumed future usage profile.
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    HOTSPOT REMEDIATION USING GERMANIUM SELF COOLING TECHNOLOGY
    (2011) Nochetto, Horacio; Bar-Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Localized thermoelectric "self cooling" in semiconductor materials is among the most promising approaches for the remediation of on-chip hot spots resulting from the shrinking feature sizes and faster switching speeds of nanoelectronic components. Self cooling in a germanium chip is investigated, using 3-dimensional, thermal-electric, coupled numerical simulations, for a range of systems and geometric parameters. The results suggest that localized cooling, associated with the introduction of an electric current on the back surface of a germanium chip, can effectively reduce the hot spot temperature rise on the active side of the chip. It was found that self cooling in a 100µm thick chip could provide between 3.9ºC and 4.5ºC hotspot temperature reduction. When using a germanium layer above an electrically insulated silicon layer, self-cooling was found to yield an additional 1ºC to 2º C temperature reduction. A streamlined computational tool is developed to facilitate the identification of optimal cooling parameters.
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    EFFECT OF KINEMATIC VARIATIONS ON VISCOUS PUMPING BY A ROBOTIC GILL PLATE ARRAY
    (2011) Larson, Mary Alexandra; Kiger, Kenneth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    As the Reynolds number of a system decreases, traditional pumping techniques become less effective. In nature, oscillating appendage systems exhibit distinct patterns of movement based on their Reynolds number. Studies of pumping by mayfly nymph gill arrays have shown different kinematics over Reynolds numbers from 2 to 22. To understand why and how this pumping mechanism might be optimized, a robotic oscillating plate array was constructed allowing stroke and pitch variation as well as phase lag variation between adjacent gills. Stereoscopic PIV was used to obtain three dimensional velocity data, allowing computation of the net pumping rate and flow induced dissipation for five cases, focusing on the role of the gill plate interactions and their dependence on the phase lag. The results indicate that mayfly gills most likely use a phase lag of 90° because it produces the highest net mass flow rate and has the highest specific flux efficiency.
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    Microfabrication and Analysis of Manifold Microchannel Coolers for Power Electronics
    (2011) Boteler, Lauren Marie; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This research presents the analysis and realization of a single phase high performance manifold microchannel cooler for improving the thermal and hydrodynamic performance of multi-chip power electronic modules. This heat exchanger, microfabricated directly into the substrate, enables higher power density electronic products by more efficiently removing the high levels of heat generated. The improved thermal performance and efficiency of the heat exchanger is demonstrated using both numerical and experimental techniques. The improved heat removal is due to the reduction in the number of packaging layers between the device and the heat exchanger and by improvement in convective heat transfer. In addition, the efficiency of the device is enhanced by minimizing fluid pressure drop through the use of large manifold channels to transport fluid to the cooling area and smaller crossover microchannels in the active cooling area. This combination of channels also improves the uniformity of the temperature distribution across the device. The manifold microchannel coolers were fabricated and tested both with and without electrical isolation between the chip and the coolant. Experimentally, the coolers without electrical isolation demonstrated thermal resistivity values as low as 0.06 K/(W/cm2), which is up to a 50X improvement over a standard power package with significant size and weight reduction. The coolers with an incorporated aluminum nitride electrical isolation layer experimentally demonstrated up to a 15X improvement. In addition to experimental results, the interaction between the manifold channels and multiple microchannels was numerically modeled and compared to simpler, one-dimensional approximations based on the Hagen-Poiseuille equation. The comparison shows that the one-dimensional model, while under-predicting total pressure drops, can provide insight into the effect of varying dimensions on system performance. The numerical models were used to identify the impact of varying dimensions across the entire length of the cooler, and a sensitivity analysis was performed with respect to system pressure drop, thermal resistance and uniformity. Additionally, large microchannel velocity gradients, some larger than 10X, were observed along the length of the device which impacts the chip non-uniformity. The simulations showed that when comparing the manifolded design to a comparable straight microchannel cooler, there is a 38X reduction in system pressure drop for similar thermal performance.
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    MODELING CRUTCH COMPENSATION OF HIP ABDUCTOR WEAKNESS AND PARALYSIS
    (2011) Borrelli, James Rocco; Balachandran, Balakumar; Haslach Jr, Henry W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Hip abductor weakness or paralysis is prevalent in the half a million cases of low level spinal injuries in the United States alone. Crutches are often used as an ambulatory aid by individuals with this type of permanent disability. This study investigates whether using a crutch with a wide stance, as opposed to a conventional vertical stance, returns the hip rotation and pelvic obliquity to a more normal range of motion for individuals with weak or paralyzed hip abductors. An inverse dynamics six link model of the body with ten degrees of freedom and a forward dynamics six link model with six degrees of freedom were used to simulate the swing and stance phases of gait with hip abductor weakness/paralysis while using either compensatory motions (hip hiking or lateral displacement of the torso) or crutches. The forward dynamics model characterizes the effect of hip abductor weakness on the gait kinematics hip rotation and pelvic obliquity. The model also characterizes the effect of compensatory motions and crutch use on gait with paralyzed hip abductors. The inverse dynamics model calculates the time varying body weight that must be supported on a contralateral crutch to achieve normal gait kinematics even with paralyzed hip abductors. The forward dynamics model predicts that hip abductor paralysis reduces the range of pelvic obliquity and increases the range of hip rotation. The model also predicts that compensatory motions and crutch use restore the range of motion of hip rotation and pelvic obliquity in gait with paralyzed hip abductors to more normal. The inverse dynamics model predicts that the portion of body weight that must be supported on a crutch for normal gait kinematics with paralyzed hip abductors is lowered by using a wide crutch stance. This study suggests that contralateral crutch use replaces the need for the compensatory motions hip hiking and lateral displacement of the torso while restoring the range of hip rotation and pelvic obliquity to more normal ranges in an individual with weak or paralyzed hip abductors. Furthermore, angling the crutch side-to-side restores the range while supporting less body weight on a contralateral crutch.
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    Prognostics of Insulated Gate Bipolar Transistors
    (2011) Patil, Nishad Kashinath; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Insulated gate bipolar transistors (IGBTs) are the devices of choice for medium and high power, low frequency applications. IGBTs have been reported to fail under excessive electrical and thermal stresses in variable speed drives and are considered as reliability problems in wind turbines, inverters in hybrid electric vehicles and railway traction motors. There is a need to develop methods to detect anomalous behavior and predict the remaining useful life (RUL) of IGBTs to prevent system downtime and costly failures. In this study, a framework for prognostics of IGBTs was developed to provide early warnings of failure and predict the remaining useful life. The prognostic framework was implemented on non punch through (NPT) IGBTs. Power cycling of IGBTs was performed and the gate-emitter voltage, collector-emitter voltage, collector-emitter current and case temperature was monitored in-situ during aging. The on-state collector-emitter current (ICE(ON)) and collector-emitter voltage (VCE(ON)) were identified as precursors to IGBT failure. Electrical characterization and X-ray analysis was performed before and after aging to map degradation in the devices to observed trends in the precursor parameters. A Mahalanobis distance based approach was used for anomaly detection. The initial ICE(ON) and VCE(ON) parameters were used to compute the healthy MD distance. This healthy MD distance was transformed and the mean and standard deviation of the transformed MD data was obtained. The μ+3σ upper bound obtained from the transformed healthy MD was then used as a threshold for anomaly detection. This approach was able to detect anomalous behavior in IGBTs before failure. Upon anomaly detection, a particle filter approach was used for predicting the remaining useful life of the IGBTs. A system model was developed using the degradation trend of the VCE(ON) parameter. This model was obtained by a least squares regression of the IGBT degradation curve. The tracking and prediction performance of the model with the particle filter was demonstrated.
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    Fiber Optical Tweezers for Microscale and Nanoscale Particle Manipulation and Force Sensing
    (2011) Liu, Yuxiang; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Optical tweezers have been an important tool in biology and physics for studying single molecules and colloidal systems. Most of current optical tweezers are built with microscope objectives, which are: i) expensive, ii) bulky and hard to integrate, iii) sensitive to environmental fluctuations, iv) limited in terms of working distances from the substrate, and v) rigid with the requirements on the substrate (transparent substrate made with glass and with a fixed thickness). These limitations of objective-based optical tweezers prevent them from being miniaturized. Fiber optical tweezers can provide a solution for cost reduction and miniaturization, and these optical tweezers can be potentially used in microfluidic systems. However, the existing fiber optical tweezers have the following limitations: i) low trapping efficiency due to weakly focused beams, ii) lack of the ability to control the positions of multiple particles simultaneously, and iii) limited functionalities. The overall objective of this dissertation work is to further the fundamental understanding of fiber optical tweezers through experimental study and modeling, and to develop novel fiber optical tweezers systems to enhance the capability and functionalities of fiber optical tweezers as microscale and nanoscale manipulators/sensors. The contributions of this dissertation work are summarized as follows: i) An enhanced understanding of the inclined dual-fiber optical tweezers (DFOTs) system has been achieved. Stable three dimensional (3D) optical trapping of a single micron-sized particle has been experimentally demonstrated. This is the first time that the trapping efficiency has been calibrated and the stiffness of the trap has been obtained in the experiments, which has been carried out by using two methods: the drag force method and power spectrum analysis. Such calibration enables the system to be used as a picoNewton-level force sensor in addition to a particle manipulator. The influence of system parameters on the trapping performance has been carefully investigated through both experimental and numerical studies. ii) Multiple traps have been created and carefully studied with the inclined DFOTs for the first time. Three traps, one 3D trap and two 2D traps, have been experimentally created at different vertical levels with adjustable separations and positions. iii) Multiple functionalities have been achieved and studied for the first time with the inclined DFOTs. Particle separation, grouping, stacking, rod alignment, rod rotation, and optical binding have been experimentally demonstrated. The multiple functionalities allow the inclined DFOTs to find applications in the study of interaction forces in colloidal systems as well as parallel particle manipulation in drug delivery systems. iv) Far-field superfocusing effect has been investigated and successfully demonstrated with a fiber-based surface plasmonic (SP) lens for the first time. A planar SP lens with a set of concentric nanoscale rings on a fiber endface has been developed. For the first time, a focus size that is comparable to the smallest achievable focus size of high NA objective lenses has been achieved with the fiber-based SP lens. The fiber-based SP lens can bridge the nanoscale particles/systems and the macroscale power sources/detectors, which has been a long standing challenge for nanophotonics. In addition to optical trapping, the fiber-based SP lens will impact many applications including high-resolution lithography, high-resolution fluorescence detection, and sub-wavelength imaging. v) Trapping ability enhanced with the fiber-based SP lens has been successfully demonstrated. With the help of the fiber-based SP lens, the trapping efficiency of fiber optical tweezers has been significantly enhanced, which is comparable with that of objective-based optical tweezers. A submicron-sized bacterium has been successfully trapped in three dimensions for the first time with optical tweezers based on single fibers.