Mechanical Engineering

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    BAYESIAN BELIEF NETWORK AND FUZZY LOGIC ADAPTIVE MODELING OF DYNAMIC SYSTEM: EXTENSION AND COMPARISON
    (2010) CHENG, PING DANNY; MODARRES, MOHAMMAD; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this thesis is to develop, expand, compare and contrast two methodologies, namely BBN and FLM, which are used in the modeling of the dynamics of physical system behavior and are instrumental in a better understanding on the POF. The paper begins with an introduction of the proposed approaches in the modeling of complex physical systems, followed by a quick literature review of FLM and BBN. This thesis uses an existing pump system [3] as a case study, where the resulting NPSHA data obtained from the applications of BBN and FLM are compared with the outputs derived from the implementation of a Mathematical Model. Based on these findings, discussions and analyses are made, including the identification of the respective strengths and weaknesses posed by the two methodologies. Last but not least, further extensions and improvements towards this research are discussed at the end of this paper.
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    End-of-Life and Constant Rate Reliability Modeling for Semiconductor Packages Using Knowledge-Based Test Approaches
    (2009) Yang, Liyu; Bernstein, Joseph B; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    End-of-life and constant rate reliability modeling for semiconductor packages are the focuses of this dissertation. Knowledge-based testing approaches are applied and the test-to-failure approach is approved to be a reliable approach. First of all, the end-of-life AF models for solder joint reliability are studied. The research results show using one universal AF model for all packages is flawed approach. An assessment matrix is generated to guide the application of AF models. The AF models chosen should be either assessed based on available data or validated through accelerated stress tests. A common model can be applied if the packages have similar structures and materials. The studies show that different AF models will be required for SnPb solder joints and SAC lead-free solder joints. Second, solder bumps under power cycling conditions are found to follow constant rate reliability models due to variations of the operating conditions. Case studies demonstrate that a constant rate reliability model is appropriate to describe non solder joint related semiconductor package failures as well. Third, the dissertation describes the rate models using Chi-square approach cannot correlate well with the expected failure mechanisms in field applications. The estimation of the upper bound using a Chi-square value from zero failure is flawed. The dissertation emphasizes that the failure data is required for the failure rate estimation. A simple but tighter approach is proposed and provides much tighter bounds in comparison of other approaches available. Last, the reliability of solder bumps in flip chip packages under power cycling conditions is studied. The bump materials and underfill materials will significantly influence the reliability of the solder bumps. A set of comparable bump materials and the underfill materials will dramatically improve the end-of-life solder bumps under power cycling loads, and bump materials are one of the most significant factors. Comparing to the field failure data obtained, the end-of-life model does not predict the failures in the field, which is more close to an approximately constant failure rate. In addition, the studies find an improper underfill material could change the failure location from solder bump cracking to ILD cracking or BGA solder joint failures.
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    Methodology for Detection and Assessment of the Impact Of Informal Processes On Organizational Output
    (2009) Ross, Lesa Moore; Mosleh, Ali; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This research focuses on the detection and assessment of informal processes within an organization. Informal processes are defined as activities that are not formalized with respect to the inputs, resources, and/or controls; or an activity that deviates from a formal process. Informal processes affect all aspects of an organization's business. Informal processes cannot be eliminated (nor should they necessarily be). The question becomes how can we identify the informal processes and assess their impact on our system/s safety? The research reported in this paper is aimed at providing an answer to this question. A theoretical foundation in the area of organizational culture, structures and practices culminating in the SoTeRiA (Socio-Technical Risk Analysis) framework provides the general model for this research. A comprehensive methodology for the detection, identification and assessment of informal processes is presented which will allow an organization to benefit from positive informal processes, while resolving detrimental informal processes to preclude their use. Two detection methods have been developed - an indirect detection method (questionnaire completed by a management representative) and a direct detection method (process audit). A methodology has been developed to be utilized as a guideline in the performance of process audits that encompasses process element identification, process interactions, and the usage of document trees. A methodology for the assessment of the impact of informal processes on an organization has been developed that will enable businesses and organization's to have more accurate and complete data from which to make their decisions regarding the state of the organization. To assess the impact of informal processes, Bayesian Belief Networks were utilized to determine the probability of the process output failure with the inclusion of informal processes and then after the informal processes were brought into the formal system. The application of this methodology has proven that when either informal processes that are beneficial to an organization are brought into the formal system, or detrimental informal processes are eliminated, the probability of the output failure decreases. The methodology presented provides a comprehensive approach to the understanding, detection, and assessment of informal processes in an organization.
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    Development and Validation of Methodology for Fix Effectiveness Projection During Product Development
    (2009) Brown, Stephen Mark; Mosleh, Ali; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    One of the challenges that design and reliability engineers face is how to accurately project fix effectiveness during reliability planning of a product development project. All reliability projection methods currently in use require estimates of the fix effectiveness factors (FEF) in their mathematical formulation. Obviously, required test results from multiple test phases are unavailable at the onset of a project and therefore practice is to rely on engineers' subjective assessment FEFs. Such estimates are often inaccurate and mostly optimist, resulting in potentiality significant project risks in the form of delays, additional development costs, and costs associated with field failures, returns, and market position. This dissertation provides a methodology that significantly improves the accuracy of FEF estimates and also the resulting reliability metrics such as projected failures rates and MTBFs. The methodology identifies key "performance shaping factors" (PSF) that enhances or impedes an engineer's ability to "fix" a problem, and puts that information into a "causal model" via Bayesian Belief Networks (BBN) to predict FEFs. Tests and confirmation of the methodology for various products and diverse industries show a systematic error reduction in FEF estimates over the current use of unstructured subjective estimates. A second major contribution of the research is an investigation of the effect of interdependencies among various FEFs in projecting the reliability of the same product or several different products by the same organization. Independence is currently assumed by all reliability projection methods. The research (i) shows that FEFs are indeed dependent, (ii) provides a composite BBN model showing the level of dependency among two different fix activities, and (iii) quantifies the impact that fix effectiveness factors have on MTBF projections. The research therefore presents an important augmentation to the current IEC standard for reliability growth, Crow-AMSAA model, showing how to include dependent FEFs in the calculation of failure intensity.
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    Measurements and Analysis of Extinction in Vitiated Flame Sheets
    (2009) Williamson, Justin Wade; Marshall, Andre W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Accidental fires present many challenging hazards to people and property. The thermal and toxic effects of fires are significantly affected by the ventilation conditions supplied to the fire. Vitiation is a consequence of limited ventilation, where the products of combustion mix with the unburned reactants prior to reaction. Vitiation results in diluting and preheating the reactants, significantly enhancing the behavior of the fire. An interesting effect of vitiation is the increased propensity of the flame to experience extinction, either locally or globally. Likewise, there are other factors that can increase the propensity for extinction, including losses due to incomplete chemical kinetics, radiation, and conduction. These extinction events have a direct impact on the thermal and toxic hazards associated with accidental fires by creating holes in the reaction surface. This research provides a detailed analysis of local flame extinction by examining the behavior of counterflow flames undergoing kinetic losses, radiation losses, and vitiation. A thorough review of flame extinction theory was conducted to determine the appropriate parameters necessary for characterizing local flame extinction conditions. Simple scaling arguments are presented to demonstrate that each of these parameters is significant in accidental fires. Counterflow methane-air diffusion flames have been studied experimentally and numerically with OPPDIF to systematically examine the effects of each parameter on local flame extinction. Furthermore, a model is presented, which uses reactant composition and temperature in the vicinity of the flame, net radiation losses from the flame, and the local scalar dissipation rate as inputs to model local extinction conditions. The proposed model is suitable for integration into Computational Fluid Dynamics (CFD) codes used to predict the hazards associated with accidental fires.
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    Automatic Generation of Generalized Event Sequence Diagrams for Guiding Simulation Based Dynamic Probabilistic Risk Assessment of Complex Systems
    (2007-11-27) Nejad-Hosseinian, Seyed Hamed; Mosleh, Ali; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Dynamic probabilistic risk assessment (DPRA) is a systematic and comprehensive methodology that has been used and refined over the past two decades to evaluate the risks associated with complex systems such as nuclear power plants, space missions, chemical plants, and military systems. A critical step in DPRA is generating risk scenarios which are used to enumerate and assess the probability of different outcomes. The classical approach to generating risk scenarios is not, however, sufficient to deal with the complexity of the above-mentioned systems. The primary contribution of this dissertation is in offering a new method for capturing different types of engineering knowledge and using them to automatically generate risk scenarios, presented in the form of generalized event sequence diagrams, for dynamic systems. This new method, as well as several important applications, is described in detail. The most important application is within a new framework for DPRA in which the risk simulation environment is guided to explore more interesting scenarios such as low-probability/high-consequence scenarios. Another application considered is the use of the method to enhance the process of risk-based design.
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    Hybrid Causal Logic Methodology for Risk Assessment
    (2007-11-27) Wang, Chengdong; Mosleh, Ali; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Probabilistic Risk Assessment is being increasingly used in a number of industries such as nuclear, aerospace, chemical process, to name a few. Probabilistic Risk Assessment (PRA) characterizes risk in terms of three questions: (1) What can go wrong? (2) How likely is it? (3) What are the consequences? Probabilistic Risk Assessment studies answer these questions by systematically postulating and quantifying undesired scenarios in a highly integrated, top down fashion. The PRA process for technological systems typically includes the following steps: objective and scope definition, system familiarization, identification of initiating events, scenario modeling, quantification, uncertainty analysis, sensitivity analysis, importance ranking, and data analysis. Fault trees and event trees are widely used tools for risk scenario analysis in PRAs of technological systems. This methodology is most suitable for systems made of hardware components. A more comprehensive treatment of risks of technical systems needs to consider the entire environment within which such systems are designed and operated. This environment includes the physical environment, the socio-economic environment, and in some cases the regulatory and oversight environment. The technical system, supported by an organization of people in charge of its operation, is at the cross-section of these environments. In order to develop a more comprehensive risk model for these systems, an important step is to extend the modeling capabilities of the conventional Probabilistic Risk Assessment methodology to also include risks associated with human activities and organizational factors in addition to hardware and software failures and adverse conditions of the physical environment. The causal modeling should also extend to the influence of regulatory and oversight functions. This research offers such a methodology. It proposes a multi-layered modeling approach so that most the appropriate techniques are applied to different individual domains of the system. The approach is called the Hybrid Causal Logic (HCL) methodology. The main layers include: (a) A model to define safety/risk context. This is done using a technique known as event sequence diagram (ESD) method that helps define the kinds of accidents and incidents that can occur in relation to the system being considered; (b) A model that captures the behaviors of the physical system (hardware, software, and environmental factors) as possible causes or contributing factors to accidents and incidents delineated by the event sequence diagrams. This is done by common system modeling techniques such as fault tress (FT); and (c) A model to extend the causal chain of events to their potential human and organizational roots. This is done using Bayesian belief networks (BBN). Bayesian belief networks are particularly useful as they do not require complete knowledge of the relation between causes and effects. The integrated model is therefore a hybrid causal model with the corresponding sets of taxonomies and analytical and computational procedures. In this research, a methodology to combine fault trees, event trees or event sequence diagrams, and Bayesian belief networks has been introduced. Since such hybrid models involve significant interdependencies, the nature of such dependencies are first determined to pave the way for developing proper algorithmic solutions of the logic model. Major achievements of this work are: (1) development of the Hybrid Causal Logic model concept and quantification algorithms; (2) development and testing of computer implementation of algorithms (collaborative work); (3) development and implementation of algorithms for HCL-based importance measures, an uncertainty propagation method the BBN models, and algorithms for qualitative-quantitative Bayesian belief networks; and (4) development and testing of the Integrated Risk Information System (IRIS) software based on HCL methodology.
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    Design of a dielectrophoretic cell loading device
    (2007-08-09) Urdaneta, Mario Gustavo; Smela, Elisabeth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In recent years there has been an increasing interest in studying individual cells, and structures that physically entrap one or few cells have been developed for this purpose, but the approaches to load cells into these structures leave a lot to be desired. This dissertation discusses the design of a device that loads cells suspended in a solution into microvials using a combination of dielectrophoresis and fluid flow, which offers significant advantages over previous loading approaches. The basic concept is to use fluid flow and dielectrophoretic forces to position a given cell above a given vial, within an array of similar vials, and then bringing the cell into the vial. The loading of several cells flowing in a channel into a vial in a matter of seconds is demonstrated. The design of the loading device spurred the development of novel topics in the area of dielectrophoresis. The structures into which cells are loaded produce "parasitic cages". The effect of multiple electric fields and at multiple frequencies had to be explored to eliminate the parasitic cages, and new theory was developed to describe the phenomenon in a straight forward and convenient way. The design process of dielectrophoretic structures known as flow through sorters was simplified significantly using a method that relies on non dimensional analysis and a figure of merit. These topics investigated have broader applications than just loading cells into vials. The dissertation demonstrates technologies and design and fabrication methods key to the cell loading design. The dissertation ends by describing the design of a device that can be implemented to load cells into vials on integrated circuit chips and outlining this device's expected characteristics and performance based on the theory and methods presented through the dissertation.
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    On the Theoretical Foundations and Principles of Organizational Safety Risk Analysis
    (2007-08-02) Mohaghegh-Ahmadabadi, Zahra; Mosleh, Ali; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This research covers a targeted review of relevant theories and technical domains related to the incorporation of organizational factors into technological systems risk. In the absence of a comprehensive set of principles and modeling guidelines rooted in theory and empirical studies, all models look equally good, or equally poor, with very little basis to discriminate and build confidence. Therefore, this research focused on the possibility of improving the theoretical foundations and principles for the field of Organizational Safety Risk Analysis. Also, a process for adapting a hybrid modeling technique, in order to operationalize the theoretical organizational safety frameworks, is proposed. Candidate ingredients are techniques from Risk Assessment, Human Reliability, Social and Behavioral Science, Business Process Modeling, and Dynamic Modeling. Then, as a realization of aforementioned modeling principles, an organizational safety risk framework, named Socio-Technical Risk Analysis (SoTeRiA)is developed. The proposed framework considers the theoretical relation between organizational safety culture, organizational safety structure/practices, and organizational safety climate, with specific distinction between safety culture and safety climate. A systematic view of safety culture and safety climate fills an important gap in modeling complex system safety risk, and thus the proposed organizational safety risk theory describing the theoretical relation between two concepts to bridge this gap. In contrast to the current safety causal models which do not adequately consider the multilevel nature of the issue, the proposed multilevel causal model explicitly recognizes the relationships among constructs at multiple levels of analysis. Other contributions of this research are in implementing the proposed organizational safety framework in the aviation domain, particularly the airline maintenance system. The US Federal Aviation Administration (FAA), which has sponsored this research over the past three years, has recognized the issue of organizational factors as one of the most critical questions in the quest to achieve 80% reduction in aviation accidents. An example of the proposed hybrid modeling environment including an integration of System Dynamics (SD), Bayesian Belief Network (BBN), Event Sequence Diagram (ESD), and Fault Tree (FT), is also applied in order to demonstrate the value of hybrid frameworks. This hybrid technique integrates deterministic and probabilistic modeling perspectives, and provides a flexible risk management tool.
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    Waking Effectiveness of Emergency Alerting Devices for the Hearing Able, Hard of Hearing, and Deaf Populations
    (2007-04-25) Ashley, Erin Mack; Milke, James; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The study presented measures the awakening effectiveness of a number of commercially available emergency alerting devices. Three groups of varying hearing levels were tested: hearing able, hard of hearing, and deaf. The devices evaluated are a typical audible smoke detector, a strobe light, and a bed shaker. The subjects were monitored for sleep stage during the single night tests and the emergency alerting devices were activated in Stage 2, Delta and REM stages of sleep. Results indicate that the audible smoke detector was most effective for the hearing able population and least effective for the deaf population. The recommended alternative to the audible smoke detector, the strobe, was the least effective device when measured against the total United States population. The vibratory tactile devices were most effective across all hearing categories and sleep stage. When the tactile signal of the bed shaker was modified to vibrate intermittently, all persons were effectively aroused. The research shows that the standard audible detector recommended for placement in all American homes is only effective in awakening those without hearing loss. The strobe is recommended by building and fire codes when hearing deficits are present but did not sufficiently awaken any population. Tactile devices can provide a sufficient means for awakening all populations regardless of hearing level, age or race