Mechanical Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2263
Browse
10 results
Search Results
Item ELECTRICAL AND STRUCTURAL FORMATION OF TRANSIENT LIQUID PHASE SINTER (TLPS) MATERIALS DURING EARLY PROCESSING STAGE(2023) Nave, Gilad; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The growing demands of electrification are driving research into new electronic materials. These electronic materials must have high electrical conductivity, withstand harsh environments and high temperatures and demonstrate reliable solutions as part of complete electronic packaging solutions. This dissertation focuses on characterizing the initial stage of the manufacturing process of Transient Liquid Phase Sinter (TLPS) alloys in a paste form as candidates for Pb-free high-temperature and high-power electronic materials.The main objective of this dissertation work is to investigate the factors and decouple the multiple cross effects occurring during the first stage of TLPS processing in order to improve the understanding of material evolution. The work proposes, develops, and conducts in-situ electrical resistivity tests to directly measure material properties and analyze the dynamics at different stages of the material's evolution. The research explores various factors, including alloying elements, organic binders, and heating rates, to understand their effects on the development of electrical performance in electronic materials. More specifically, the work examines the performance of Ag-In, Ag-Sn and Cu-Sn TLPS paste systems. Additionally, packing density and changes in cross-section are investigated using imaging techniques and image processing to gain insights into the early formation of the material's structural backbone. An Arrhenius relationship together with Linear Mixed Models (LMM) techniques are used to extract the activation energies involved with each of the processing stages. The study then develops procedures to model different states of the TLPS microstructures at different heating stages based on experimentally observed data. Using these models, the study uses Finite Element Method (FEM) analysis to verify the experimental results and gain a better understanding and visualization into the involved mechanisms. This investigation not only sheds light on the material's behavior but also has implications for robust additive manufacturing (AM) applications.Item Modeling of Falling-Particle Solar Receivers for Hydrogen Production and Thermochemical Energy Storage(2014) Oles, Andrew; Jackson, Gregory S.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)One of the most important components in a solar-thermal power plant is the central receiver where concentrated solar energy is absorbed in a medium for storage and eventual use in power generation or fuel production. Current state-of-the-art receivers are not appropriate for future power-plant designs due to limited operating temperatures. The solid-particle receiver (SPR) has been proposed as an alternative architecture that can achieve very high temperatures (above 1500 °C) with high efficiency, while avoiding many of the thermal stress issues that plague alternative architectures. The SPR works by having a flow of solid particles free-fall through a cavity receiver while directly illuminated to absorb the solar energy. Because of the high operating temperatures that can be achieved, along with the ability to continuously flow a stream of solid reactant, the SPR has the potential for use as a reactor for either chemical storage of solar energy or fuel production as part of a solar water-splitting cycle. While the operation of the SPR is relatively simple, analysis is complicated by the many physical phenomena in the receiver, including radiation-dominated heat transfer, couple gas-particle flow, and inter-phase species transport via reaction. This work aims to demonstrate a set modeling tools for characterizing the operation of a solid particle receiver, as well as an analysis of the key operating parameters. A inert receiver model is developed using a semi-empirical gas-phase model and the surface-to-surface radiation model modified to account for interaction with the particle curtain. A detailed thermo-kinetic model is developed for undoped-ceria, a popular material for research into solar fuel production. The inert-receiver model is extended to integrate this kinetic model, and further used to evaluate the potential of perovskite materials to enhance the storage capability of the receiver. A modified undoped ceria model is derived and implemented via custom user functions in the context of a computational fluid dynamics simulation of the receiver using the discrete-ordinates method for radiation transfer. These modeling efforts provide a basis for in-depth analysis of the key operating parameters that influence the performance of the solid-particle receiver.Item Simulation and Analysis of Energy Consumption for an Energy-Intensive Academic Research Building(2014) Levy, Jared Michael; Ohadi, Michael M.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The University of Maryland's Jeong H. Kim Engineering Building is a state-of-the-art academic research facility. This thesis describes an energy analysis and simulation study that serves to identify energy saving opportunities and optimum operation of the building to achieve its goals of high energy efficiency and substantial CO2 emission reduction. A utility analysis, including a benchmarking study, was completed to gauge the performance of the facility and a detailed energy model was developed using EnergyPlus to mimic current operation. The baseline energy model was then used to simulate eight energy efficiency measures for a combined energy savings of 16,760 MMBtu, reducing annual energy use by 25.3%. The simple payback period for the proposed measures as a single project is estimated to be less than one year. Due to the high-tech and unique usage of the Kim Engineering Building, including cleanrooms and research labs, this thesis also contributes to the development of energy consumption benchmarking data available for such facilities.Item DYNAMIC BEHAVIOR OF OPERATING CREW IN COMPLEX SYSTEMS: AN OBJECT-BASED MODELING & SIMULATION APPROACH(2013) Azarkhil, Mandana; Mosleh, Ali; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High-risk environments such as the control room of Nuclear Power Plants are extremely stressful for the front line operators; during accidents and under high task load situations, the operators are solely responsible for the ultimate decision-making and control of such complex systems. Individuals working as a team constantly interact with each other and therefore introduce team related issues such as coordination, supervision and conflict resolution. The aggregate impact of multiple human errors inside communication and coordination loops in a team context can give rise to complex human failure modes and failure mechanisms. This research offers a model of operating crew as an interactive social unit and investigates the dynamic behavior of the team under upset situations through a simulation method. The domain of interest in this work is the class of operating crew environments that are subject to structured and regulated guidelines with formal procedures providing the core of their response to accident conditions. In developing the cognitive models for the operators and teams of operators, their behavior and relations, this research integrates findings from multiple disciplines such as cognitive psychology, human factors, organizational factors, and human reliability. An object-based modeling methodology is applied to represent system elements and different roles and behaviors of the members of the operating team. The proposed team model is an extended version of an existing cognitive model of individual operator behavior known as IDAC (Information, Decision, and Action in Crew context). Scenario generation follows DPRA (Dynamic Probabilistic Risk Assessment) methodologies. The method capabilities are demonstrated through building and simulating a simplified model of a steam/power generating plant. Different configurations of team characteristics and influencing factors have been simulated and compared. The effects of team factors and crew dynamics on system risk with main focus on team errors, associated causes and error management processes and their impact on team performance have been studied through a large number of simulation runs. The results are also compared with several theoretical models and empirical studies.Item MODELING OF A COMBINED HEAT AND POWER UNIT AND EVALUATION OF SYSTEM PERFORMANCE IN BUILDING APPLICATIONS(2010) Bush, John; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents a validated model of a 4 kilowatt combined heat and power (CHP) system derived from laboratory experiments. The model is tuned to match steady state experimental tests, and validated with transient experimental results. Further simulations are performed using a modeled thermal storage system, and implementing the CHP system into a building model to evaluate the feasibility of CHP in the mid-Atlantic region, as well as the Great Lakes region. The transient simulation outputs are within 4.8% of experimental results for identical load profiles for a simulated summer week, and within 2.2% for a spring or autumn week. When integrated with a building model, the results show 23.5% cost savings on energy in the mid-Atlantic region, and 29.7% savings in the Great Lakes region.Item Generic Dynamic Model for a Range of Thermal System Components(2010) Xuan, Shenglan; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The simulation of a thermal system consists of a simulation of its components and their interactions. The advantages of thermal system simulations have been widely recognized. They can be used to explore the performance of a newly designed system, to identify whether the design meets the design criteria, to develop and test controls, and to optimize the system by minimizing the cost or power consumption, and maximizing the energy efficiency and/or capacity. Thermal system simulations can also be applied to existing systems to explore prospective modifications and improvements. Much research has been conducted on aspects of thermal system and component simulation, especially for steady-state simulation. Recently, transient simulations for systems and components have gained attention, since dynamic modeling assists the understanding of the operation of thermal systems and their controls. This research presents the development of a generic component model that allows users to easily create and customize any thermal component with a choice of working fluids and levels of complexity for either transient or steady-state simulation. The underlying challenge here is to design the code such that a single set of governing equations can be used to accurately describe the behavior of any component of interest. The inherent benefits to this approach are that maintenance of the code is greatly facilitated as compared to competing approaches, and that the software is internally consistent. This generic model features a user-friendly description of component geometry and operating conditions, interactive data input and output, and a robust component solver. The open literature pertaining to thermal component models, especially the components of vapor compression systems, is reviewed and commented on in this research. A theoretical evaluation of the problem formulation and solution methodology is conducted and discussed. A generic structure is proposed and developed to simulate thermal components by enabling and disabling a portion of the set of governing equations. In addition, a system solver is developed to solve a system composed of these components. The component/system model is validated with experimental data, and future work is outlined.Item A Predictive Model of Nuclear Power Plant Crew Decision-Making and Performance in a Dynamic Simulation Environment(2009) Coyne, Kevin; Mosleh, Ali; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The safe operation of complex systems such as nuclear power plants requires close coordination between the human operators and plant systems. In order to maintain an adequate level of safety following an accident or other off-normal event, the operators often are called upon to perform complex tasks during dynamic situations with incomplete information. The safety of such complex systems can be greatly improved if the conditions that could lead operators to make poor decisions and commit erroneous actions during these situations can be predicted and mitigated. The primary goal of this research project was the development and validation of a cognitive model capable of simulating nuclear plant operator decision-making during accident conditions. Dynamic probabilistic risk assessment methods can improve the prediction of human error events by providing rich contextual information and an explicit consideration of feedback arising from man-machine interactions. The Accident Dynamics Simulator paired with the Information, Decision, and Action in a Crew context cognitive model (ADS-IDAC) shows promise for predicting situational contexts that might lead to human error events, particularly knowledge driven errors of commission. ADS-IDAC generates a discrete dynamic event tree (DDET) by applying simple branching rules that reflect variations in crew responses to plant events and system status changes. Branches can be generated to simulate slow or fast procedure execution speed, skipping of procedure steps, reliance on memorized information, activation of mental beliefs, variations in control inputs, and equipment failures. Complex operator mental models of plant behavior that guide crew actions can be represented within the ADS-IDAC mental belief framework and used to identify situational contexts that may lead to human error events. This research increased the capabilities of ADS-IDAC in several key areas. The ADS-IDAC computer code was improved to support additional branching events and provide a better representation of the IDAC cognitive model. An operator decision-making engine capable of responding to dynamic changes in situational context was implemented. The IDAC human performance model was fully integrated with a detailed nuclear plant model in order to realistically simulate plant accident scenarios. Finally, the improved ADS-IDAC model was calibrated, validated, and updated using actual nuclear plant crew performance data. This research led to the following general conclusions: (1) A relatively small number of branching rules are capable of efficiently capturing a wide spectrum of crew-to-crew variabilities. (2) Compared to traditional static risk assessment methods, ADS-IDAC can provide a more realistic and integrated assessment of human error events by directly determining the effect of operator behaviors on plant thermal hydraulic parameters. (3) The ADS-IDAC approach provides an efficient framework for capturing actual operator performance data such as timing of operator actions, mental models, and decision-making activities.Item DEEP SUBMICRON CMOS VLSI CIRCUIT RELIABILITY MODELING, SIMULATION AND DESIGN(2005-11-29) Li, Xiaojun; Bernstein, Joseph B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)CMOS VLSI circuit reliability modeling and simulation have attracted intense research interest in the last two decades, and as a result almost all IC Design For Reliability (DFR) tools now try to incrementally simulate device wearout mechanisms in iterative ways. These DFR tools are capable of accurately characterizing the device wearout process and predicting its impact on circuit performance. Nevertheless, excessive simulation time and tedious parameter testing process often limit popularity of these tools in product design and fabrication. This work develops a new SPICE reliability simulation method that shifts the focus of reliability analysis from device wearout to circuit functionality. A set of accelerated lifetime models and failure equivalent circuit models are proposed for the most common MOSFET intrinsic wearout mechanisms, including Hot Carrier Injection (HCI), Time Dependent Dielectric Breakdown (TDDB), and Negative Bias Temperature Instability (NBTI). The accelerated lifetime models help to identify the most degraded transistors in a circuit in terms of the device's terminal voltage and current waveforms. Then corresponding failure equivalent circuit models are incorporated into the circuit to substitute these identified transistors. Finally, SPICE simulation is performed again to check circuit functionality and analyze the impact of device wearout on circuit operation. Device wearout effects are lumped into a very limited number of failure equivalent circuit model parameters, and circuit performance degradation and functionality are determined by the magnitude of these parameters. In this new method, it is unnecessary to perform a large number of small-step SPICE simulation iterations. Therefore, simulation time is obviously shortened in comparison to other tools. In addition, a reduced set of failure equivalent circuit model parameters, rather than a large number of device SPICE model parameters, need to be accurately characterized at each interim wearout process. Thus device testing and parameter extraction work are also significantly simplified. These advantages will allow circuit designers to perform quick and efficient circuit reliability analyses and to develop practical guidelines for reliable electronic designs.Item Advances to a Computer Model Used in the Simulation and Optimization of Heat Exchangers(2005-08-11) Schwentker, Robert Andrew; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heat exchangers play an important role in a variety of energy conversion applications. They have a significant impact on the energy efficiency, cost, size, and weight of energy conversion systems. CoilDesigner is a software program introduced by Jiang (2003) for simulating and optimizing heat exchangers. This thesis details advances that have been made to CoilDesigner to increase its accuracy, flexibility, and usability. CoilDesigner now has the capability of modeling wire-and-tube condensers under both natural and forced convection conditions on the air side. A model for flat tube heat exchangers of the type used in automotive applications has also been developed. Void fraction models have been included to aid in the calculation of charge. In addition, the ability to model oil retention and oil's effects on fluid flow and heat transfer has been included. CoilDesigner predictions have been validated with experimental data and heat exchanger optimization studies have been performed.Item Vehicle Path Optimization of Emergency Lane Change Maneuvers for Vehicle Simulation(2005-08-23) O'Hara, Steven Robert; Schultz, Gregory A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Driver-based handling tests, such as the Double Lane Change (DLC) maneuver are subjective in nature and depend largely on driver skill and road conditions. They also suffer from poor repeatability. Implementation of these tests on hardware-in-the-loop simulators can also produce subjective results if the steer profiles are not systematically generated. This research produced a vehicle path optimization model that generated optimal paths for handling tests based on minimizing the maximum curvature during the maneuver. This approach lessened the dynamics of the vehicle and increased the chances of successful test results at given speeds. Excel's Solver was used for the optimization. The model results were compared to field test and hardware-in-the-loop test results, showing potential for reductions in lateral acceleration and vehicle side-slip.