Mountain Scholar :: Browsing by Author "Bradley, Thomas, advisor"

Browsing by Author "Bradley, Thomas, advisor"

Now showing 1 - 20 of 34

Open Access
A modeling tool for household biogas burner flame port design
(Colorado State University. Libraries, 2017) Decker, Thomas J., author; Bradley, Thomas, advisor; Prapas, Jason, committee member; Sharvelle, Sybil, committee member
Anaerobic digestion is a well-known and potentially beneficial process for rural communities in emerging markets, providing the opportunity to generate usable gaseous fuel from agricultural waste. With recent developments in low-cost digestion technology, communities across the world are gaining affordable access to the benefits of anaerobic digestion derived biogas. For example, biogas can displace conventional cooking fuels such as biomass (wood, charcoal, dung) and Liquefied Petroleum Gas (LPG), effectively reducing harmful emissions and fuel cost respectively. To support the ongoing scaling effort of biogas in rural communities, this study has developed and tested a design tool aimed at optimizing flame port geometry for household biogas-fired burners. The tool consists of a multi-component simulation that incorporates three-dimensional CAD designs with simulated chemical kinetics and computational fluid dynamics. An array of circular and rectangular port designs was developed for a widely available biogas stove (called the Lotus) as part of this study. These port designs were created through guidance from previous studies found in the literature. The three highest performing designs identified by the tool were manufactured and tested experimentally to validate tool output and to compare against the original port geometry. The experimental results aligned with the tool's prediction for the three chosen designs. Each design demonstrated improved thermal efficiency relative to the original, with one configuration of circular ports exhibiting superior performance. The results of the study indicated that designing for a targeted range of port hydraulic diameter, velocity and mixture density in the tool is a relevant way to improve the thermal efficiency of a biogas burner. Conversely, the emissions predictions made by the tool were found to be unreliable and incongruent with laboratory experiments.
Open Access
Aircraft survivability modeling, evaluation, and optimization for multi-UAV operational scenarios
(Colorado State University. Libraries, 2021) Lunsford, Ian, author; Bradley, Thomas, advisor; Borky, John, committee member; Shahroudi, Kamran, committee member; Arabi, Mazdak, committee member
The unmanned aerial vehicle (UAV) has become a prominent aircraft design throughout aerospace applications including commercial, civilian, and military. A UAV is preferred in some missions and applications due to its unique abilities compared to manned aircraft. This dissertation aims to define an improved understanding of the concepts and modeling of aircraft survivability, as applied to UAVs. Traditionally, survivability as a field has defined and considered survivability primarily in the context of manned aircraft, and single aircraft. With UAV's increasing importance in multi-UAV operational scenarios, it has become increasingly important to understand aircraft survivability for singles and groups of UAVs. This research effort has been structured into three research questions defining contributions in survivability modeling, validation, and UAV aircraft design. Research Question 1 seeks to demonstrate the feasibility of a parametric model of UAV survivability. The result is a UAV survivability model and simulation which illustrates key tradeoffs within UAV survivability. The effects on survivability on UAV design characteristics (speed, wing area, drag and lift coefficients) is quantified specific to the detailed lethal envelope simulation method. Research Question 2 aims to verify and validate the UAV survivability simulation, providing evidence of the predictive capability of the survivability simulation results. Evidence is presented for verification and validation through comparison to previous modeling efforts, through solicitation of expert opinion, and through parameter variability and sensitivity analysis. Lastly, Research Question 3 seeks to apply the simulation results to multi-UAV tactical evaluation and single aircraft design. The results illustrate the level of improvement that can be realized through UAV design including armoring (a 25% survivability improvement through 1000kg of armoring), speed increases (a 100 mph increase in cruise speed realizes a 14% decrease in killability), and other relevant design variables. Results also demonstrate that multi-UAV tactics can improve the survivability of UAVs in combat. Loyal wingman tactics are simulated to increase the survivability of a C-130J (equivalent UAV) from 19.8% to 40.0%. Other single UAV tactics such as fuel dumping, afterburners are evaluated under the same framework for their relative effectiveness. This dissertation answers the described research questions by presenting an aircraft survivability evaluation approach that relates survivability with modern UAV applications, emerging threats, multi-UAV tactics, and UAV design. Aircraft survivability encounters with modern UAV countermeasures are considered and simulated. UAV metrics of performance are modeled and simulated to describe aircraft design parameters sensitive to improving aircraft survivability. By evaluating aircraft survivability with a modern multi-UAV tactical perspective, this study seeks to provide the UAV designer with more complete vision of survivability-derived design criteria.
Open Access
An analysis of the costs and performance of vehicles fueled by alternative energy carriers
(Colorado State University. Libraries, 2024) Lynch, Alexander, author; Bradley, Thomas, advisor; Coburn, Tim, committee member; Olsen, Daniel B., committee member
The transportation sector stands at the crossroads of new challenges and opportunities, driven by the pressing need to mitigate environmental impacts, enhance energy efficiency, and ensure sustainable mobility solutions. This transition will occur across diverse transportation modes, each with distinct characteristics and challenges. From light duty vehicles embracing electrification to maritime transport adopting alternative fuel engines, the push for low-carbon technology is reshaping the landscape of transportation. In this context, it is necessary to conduct a review and assessment of technologies, environmental benefits, and costs of alternative fuels and powertrains across a broad set of applications in the transportation sector. This study seeks to perform this assessment by combining bottom-up cost analysis, environmental assessments, and reviews of the literature to examine the techno-economic aspects of various fuel and powertrain options in the transportation sector. This approach involves detailed evaluations of individual components and systems to model the cost structures and efficiency profiles of vehicles. The results illustrated in this thesis will be embedded into adoption models to enable governments, utilities, private fleets, and other shareholders to make informed transportation planning decisions.
Open Access
An enterprise system engineering analysis of KC-46A maintenance program decision-making
(Colorado State University. Libraries, 2023) Blond, Kyle E., author; Bradley, Thomas, advisor; Ender, Tommer, committee member; Conrad, Steven, committee member; Herber, Daniel, committee member; Ozbek, Mehmet, committee member
The KC-46A Pegasus is a United States Air Force (USAF) tanker, transport, and medical evacuation commercial derivative aircraft based on the Boeing 767. It is a top acquisition priority to modernize the USAF's refueling capabilities and is governed by a lifecycle sustainment strategy directed by USAF commercial variant policies aligned to Federal Aviation Administration (FAA) policy. While this strategy provides robust mechanisms to manage the KC-46A's performance during its operations and support phase, opportunity exists for the KC-46A sustainment enterprise to better achieve reliability, availability, maintainability, and cost (RAM C) objectives through enhancing KC-46A maintenance program decision making in the context of USAF and FAA policies. This research characterizes the KC-46A maintenance program as an industrial enterprise system governing the maintenance, repair, overhaul, and modification of KC-46A aircraft. Upon this basis, enterprise systems engineering (ESE) characterizes the KC-46A maintenance program and identifies decision making improvement opportunities in its management. Canonical ESE viewpoints are tailored to abstract the organizations, processes, and information composing KC-46A maintenance program decision making and model how decision support methods can better achieve KC-46A sustainment enterprise objectives. A decision making framework then evaluates the RAM C performance of KC-46A maintenance tasks as part of the KC-46A Continued Analysis and Surveillance System (CASS) program. The framework's heuristics classify the compliance, effectiveness, and optimality of a maintenance task to prescribe KC-46A CASS responses. A rule based expert system applies this framework and serves as the knowledge engine for the KC-46A CASS decision support system referred to as the "Pegasus Fleet Management Tool." A focus group of KC-46A sustainment experts evaluated the framework and produced consensus that it advances the state of the art in KC-46A maintenance program decision making. A business case analysis roadmaps the programmatic and technical activities required to implement the framework in PFMT and improve KC-46A sustainment.
Open Access
Avoiding technical bankruptcy in system development: a process to reduce the risk of accumulating technical debt
(Colorado State University. Libraries, 2023) Kleinwaks, Howard, author; Bradley, Thomas, advisor; Batchelor, Ann, advisor; Marzolf, Gregory, committee member; Wise, Daniel, committee member; Turner, John F., committee member
The decisions made early in system development can have profound impacts on later capabilities of the system. In iterative systems development, decisions made in each iteration produce impacts on every future iteration. Decisions that have benefits in the short-term may damage the long-term health of the system. This phenomenon is known as technical debt. If not carefully managed, the buildup of technical debt within a system can lead to technical bankruptcy: the state where the system development can no longer proceed with its lifecycle without first paying back some of the technical debt. Within the schedule constrained development paradigm of iteratively and incrementally developed systems, it is especially important to proactively manage technical debt and to understand the potential long-term implications of decisions made to achieve short-term delivery goals. To enable proactive management of technical debt within systems engineering, it is first necessary to understand the state of the art with respect to the application of technical debt methods and terminology within the field. While the technical debt metaphor is well-known within the software engineering community, it is not as well known within the systems engineering community. Therefore, this research first characterizes the state of technical debt research within systems engineering through a literature review. Next, the prevalence of the technical debt metaphor among practicing systems engineers is established through an empirical survey. Finally, a common ontology for technical debt within systems engineering is proposed to enable clear and concise communication about the common problems faced in different systems engineering development programs. Using the research on technical debt in systems engineering and the ontology, this research develops a proactive approach to managing technical debt in iterative systems development by creating a decision support system called List, Evaluate, Achieve, Procure (LEAP). The LEAP process, when used in conjunction with release planning methods, can identify the potential for technical debt accumulation and eventually technical bankruptcy. The LEAP process is developed in two phases: a qualitative approach to provide initial assessments of the state of the system and a quantitative approach that models the effects of technical debt on system development schedules and the potential for technical bankruptcy based on release planning schedules. Example applications of the LEAP process are provided, consisting of the development of a conceptual problem and real applications of the process at the Space Development Agency. The LEAP process provides a novel and mathematical linkage of the temporal and functional dependencies of system development with the stakeholder needs, enabling proactive assessments of the ability of the system to satisfy those stakeholder needs. These assessments enable early identification of potential technical debt, reducing the risk of negative long-term impacts on the system health.
Open Access
Case study of the real world integration of fuel cell plug-in hybrid electric vehicles and their effect on hydrogen refueling locations in the Puget Sound region
(Colorado State University. Libraries, 2014) Bucher, Jake Duvall, author; Bradley, Thomas, advisor; Anderson, Charles, committee member; Suryanarayanan, Siddarth, committee member
The personal vehicle transportation fleet relies heavily on non-renewable and pollutive sources of fuel, such as petroleum. However, with harsher restrictions from the Environmental Protection Agency's (EPA) Corporate Average Fuel Economy (CAFE) and California Air Resource Board's (CARB) Zero Emission Vehicle (ZEV) standards coupled with growing sales for alternative fueled vehicles, the automotive industry has begun to shift toward more renewable and clean sources of energy to power vehicles. The fuel cell plug-in hybrid electric vehicle (FCPHEV) architecture provides a unique and promising solution to decreasing the dependence of vehicles on petroleum and decreasing the amount of pollution emitted from tailpipes. Until recently, the FCPHEV architecture had only been developed in concept cars and paper studies. However, recent studies have confirmed the capability of the FCPHEV concept in terms of its economics, environmental benefits, and real-world viability. From this concept it becomes important to understand how daily commuters will benefit from driving a FCPHEV using real world driving data. Through the use of geographic information system (GIS) data of vehicle travel in the Puget Sound area from the National Renewable Energy Laboratory (NREL) a model of electrical and hydrogen energy consumption of a fleet of FCPHEVs can be constructed. This model can be modified to model the driving, charging and fueling habits of drivers using four different all-electric driving ranges, and using either a normal plug-in hybrid control strategy or a control strategy that focuses on highway fuel cell operation. These comparisons are used to analyze the driving habits of daily commuters while using a FCPHEV, and the effect of the FCPHEV architecture on the location of hydrogen refueling. The results of this thesis help to define FCPHEV energy management strategies and show that the FCPHEV architecture can concentrate the location of hydrogen refueling to predictable areas and aid in the development of the hydrogen refueling infrastructure.
Open Access
Comparative analysis of model-based systems engineering and traditional systems engineering approaches for architecting robotic space systems through knowledge categorization, automatic information transfer, and automatic knowledge processing measures
(Colorado State University. Libraries, 2021) Younse, Paulo, author; Bradley, Thomas, advisor; Borky, John, committee member; Sega, Ron, committee member; Reising, Steven, committee member
Robotic space systems have enabled us to explore the far reaches of our solar system. However, these missions are high-cost, high-risk, and prone to accidents due to their complex nature. As these systems continue to grow even more capable and complex, spacecraft costs and mission success risk are also expected to grow. Current systems engineering approaches are finding it challenging to manage this growth in system complexity. Model-Based Systems Engineering (MBSE) offers techniques to aid in the development of complex systems, aiming to reduce design errors, reduce cost through prevention of costly rework, and improve system quality and project performance over traditional systems engineering techniques. Robotic space systems have much to benefit from an MBSE approach due to their intrinsic complexity, particularly if MBSE is implemented during the early architecting phase of the project. Case studies from the literature assert that there are benefits to using MBSE when applied to developing complex systems. However, none of these studies perform in-depth quantitative comparative analysis of applying MBSE vs. non-MBSE approaches, and there currently is a lack of substantial and compelling evidence to establish broad adoption of MBSE within the systems engineering community. This research measures the benefits of MBSE approaches over traditional, non-MBSE approaches for architecting robotic space systems though comparative analysis, focusing on quantitative evidence supporting how MBSE better describes, develops, and evaluates the system architecture, all which can aid in the adoption of MBSE within the robotics space systems domain. These advantages will be investigated through studying 1) how an MBSE approach better captures the information content for describing a robotic space system architecture relative to a non-MBSE approach, 2) how an MBSE approach reduces the implementation effort required to developing a robotic space system architecture relative to a non-MBSE approach, and 3) how an MBSE approach more efficiently evaluates a robotic space system architecture relative to a non-MBSE approach. A Mars orbiting sample Capture and Orient Module (COM) system for a Capture, Contain, and Return System (CCRS) payload concept for the notional Mars Sample Return (MSR) campaign develop at the NASA Jet Propulsion Laboratory was used as a case study to investigate the advantages of MBSE. The MBSE approach provided measurable advantages to architecting the COM robotic space system in terms of a higher fraction of formally captured architecture content in the appropriate knowledge category, a higher quantity of automatic information transfer between architecting tasks, and a higher quantity of automatic knowledge processing during modeling and simulation activities.
Open Access
Comprehensive concept-phase system safety analysis for hybrid-electric vehicles utilizing automated driving functions
(Colorado State University. Libraries, 2019) Knopf, Matthew David, author; Bradley, Thomas, advisor; Olsen, Daniel, committee member; Pasricha, Sudeep, committee member
Automotive system safety (SS) analysis involving automated driving functions (ADFs) and advanced driver assistance systems (ADAS) is an active subject of research but highly proprietary. A comprehensive SS analysis and a risk informed safety case (RISC) is required for all complex hybrid-vehicle builds especially when utilizing ADFs and ADAS. Industry standard SS procedures have been developed and are accessible but contain few detailed instructions or references for the process of completing a thorough automotive SS analysis. In this work, a comprehensive SS analysis is performed on an SAE-Level 2 autonomous hybrid-vehicle architecture in the concept phase which utilizes lateral and longitudinal automated corrective control actions. This paper first outlines a proposed SS process including a cross-functional SS working group procedure, followed by the development of an item definition inclusive of the ADFs and ADAS and an examination of 5 hazard analysis and risk assessment (HARA) techniques common to the automotive industry that were applied to 11 vehicle systems, and finally elicits the safety goals and functional requirements necessary for safe vehicle operation. The results detail functional failures, causes, effects, prevention, and mitigation methods as well as the utility of, and instruction for completing the various HARA techniques. The conclusion shows the resulting critical safety concerns for an SAE Level-2 autonomous system can be reduced through the use of the developed list of 116 safety goals and 950 functional safety requirements.
Open Access
Design and construction of electric motor dynamometer and grid attached storage laboratory
(Colorado State University. Libraries, 2011) Lutz, Markus, author; Bradley, Thomas, advisor; Zimmerle, Daniel, committee member; Young, Peter, committee member
The purpose of this thesis is to describe the design and development of a laboratory facility to both educate students on electric vehicle components as well as allow researchers to gain experimental results of grid-attached-storage testing. With the anticipated roll out of millions of electric vehicles, manufacturers of such vehicles need educated hires with field experience. Through instruction with this lab, Colorado State University plans to be a major resource in equipping the future electric vehicle work force with necessary training and hands-on experience using real world, full-scale, automotive grade electric vehicle components. The lab also supports research into grid-attached-storage. This thesis explains the design objectives, challenges, selections, construction and initial testing of the lab, and also provides context for the types of education and research which can be performed utilizing the laboratory.
Open Access
Development of a human factors hazard model for use in system safety analysis
(Colorado State University. Libraries, 2021) Birch, Dustin Scott, author; Bradley, Thomas, advisor; Miller, Erika, committee member; Cale, James, committee member; Ozbek, Mehmet, committee member
Traditional methods for Human Reliability Analysis (HRA) have been developed with specific applications or industries in mind. Additionally, these methods are often complicated, time consuming, costly to apply, and are not suitable for direct comparison amongst themselves. The proposed Human Factors Hazard Model (HFHM) utilizes the established and time-tested probabilistic analysis tools of Fault Tree Analysis (FTA) and Event Tree Analysis (ETA), and integrates them with a newly developed Human Error Probability (HEP) predictive tool. This new approach is developed around Performance Shaping Factors (PSFs) relevant to human behavior, as well as specific characteristics unique to a system architecture and its corresponding operational behavior. This updated approach is intended to standardize, simplify, and automate the approach to modeling the likelihood of a mishap due to a human-system interaction during a hazard event. The HFHM is exemplified and automated within a commercial software tool such that trade and sensitivity studies can be conducted and validated easily. The analysis results generated by the HFHM can be used as a standardized guide to SE analysts as a well as design engineers with regards to risk assessment, safety requirements, design options, and needed safety controls within the system architecture. Verification and evaluation of the HFHM indicate that it is an effective tool for HRA and system safety with results that accurately predict HEP values that can guide design efforts with respect to human factors. In addition to the development and automation of the HFHM, application within commonly used system safety Hazard Analysis Techniques (HATs) is established. Specific utilization of the HFHM within system or subsystem level FTA and Failure Mode and Effects Analysis (FMEA) is established such that human related hazards can more accurately be accounted for in system design safety analysis and lifecycle management. Lastly, integration of the HFHM within Model-Based System Engineering (MBSE) emphasizing an implementation into the System Modeling Language (SysML) is established using a combination of existing hazard analysis libraries and custom designed libraries within the Unified Modeling Language (UML). The FTA / ETA components of the hazard model are developed within SysML partially utilizing the RAAML (Risk Analysis and Assessment Modeling Language) currently under development by the Object Management Group (OMG), as well as a unique recursive analysis library. The SysML model successfully replicates the probabilistic calculation results of the HFHM as generated by the native analytical model. The SysML profiles developed to implement HFHM have application in integration of conventional system safety analysis as well as requirements engineering within lifecycle management.
Open Access
Energy management of a university campus utilizing short-term load forecasting with an artificial neural network
(Colorado State University. Libraries, 2012) Palchak, David, author; Bradley, Thomas, advisor; Suryanarayanan, Siddharth, advisor; Zimmerle, Daniel, committee member; Young, Peter, committee member
Electrical load forecasting is a tool that has been utilized by distribution designers and operators as a means for resource planning and generation dispatch. The techniques employed in these predictions are proving useful in the growing market of consumer, or end-user, participation in electrical energy consumption. These predictions are based on exogenous variables, such as weather, and time variables, such as day of week and time of day as well as prior energy consumption patterns. The participation of the end-user is a cornerstone of the Smart Grid initiative presented in the Energy Independence and Security Act of 2007, and is being made possible by the emergence of enabling technologies such as advanced metering infrastructure. The optimal application of the data provided by an advanced metering infrastructure is the primary motivation for the work done in this thesis. The methodology for using this data in an energy management scheme that utilizes a short-term load forecast is presented. The objective of this research is to quantify opportunities for a range of energy management and operation cost savings of a university campus through the use of a forecasted daily electrical load profile. The proposed algorithm for short-term load forecasting is optimized for Colorado State University's main campus, and utilizes an artificial neural network that accepts weather and time variables as inputs. The performance of the predicted daily electrical load is evaluated using a number of error measurements that seek to quantify the best application of the forecast. The energy management presented utilizes historical electrical load data from the local service provider to optimize the time of day that electrical loads are being managed. Finally, the utilization of forecasts in the presented energy management scenario is evaluated based on cost and energy savings.
Open Access
Enhancing the test and evaluation process: implementing agile development, test automation, and model-based systems engineering concepts
(Colorado State University. Libraries, 2020) Walker, Joshua T., author; Borky, John, advisor; Bradley, Thomas, advisor; Chong, Edwin, committee member; Ghosh, Sudipto, committee member; Jayasumana, Anura, committee member
With the growing complexity of modern systems, traditional testing methods are falling short. Test documentation suites used to verify the software for these types of large, complex systems can become bloated and unclear, leading to extremely long execution times and confusing, unmanageable test procedures. Additionally, the complexity of these systems can prevent the rapid understanding of complicated system concepts and behaviors, which is a necessary part of keeping up with the demands of modern testing efforts. Opportunities for optimization and innovation exist within the Test and Evaluation (T&E) domain, evidenced by the emergence of automated testing frameworks and iterative testing methodologies. Further opportunities lie with the directed expansion and application of related concepts such as Model-Based Systems Engineering (MBSE). This dissertation documents the development and implementation of three methods of enhancing the T&E field when applied to a real-world project. First, the development methodology of the system was transitioned from Waterfall to Agile, providing a more responsive approach when creating new features. Second, the Test Automation Framework (TAF) was developed, enabling the automatic execution of test procedures. Third, a method of test documentation using the Systems Modeling Language (SysML) was created, adopting concepts from MBSE to standardize the planning and analysis of test procedures. This dissertation provides the results of applying the three concepts to the development process of an airborne Electronic Warfare Management System (EWMS), which interfaces with onboard and offboard aircraft systems to receive and process the threat environment, providing the pilot or crew with a response solution for the protection of the aircraft. This system is representative of a traditional, long-term aerospace project that has been constantly upgraded over its lifetime. Over a two-year period, this new process produced a number of qualitative and quantitative results, including improving the quality and organization of the test documentation suite, reducing the minimum time to execute the test procedures, enabling the earlier identification of defects, and increasing the overall quality of the system under test. The application of these concepts generated many lessons learned, which are also provided. Transitioning a project's development methodology, modernizing the test approach, and introducing a new system of test documentation may provide significant benefits to the development of a system, but these types of process changes must be weighed against the needs of the project. This dissertation provides details of the effort to improve the effectiveness of the T&E process on an example project, as a framework for possible implementation on similar systems.
Open Access
High efficiency thermoelectric devices fabricated using quantum well confinement techniques
(Colorado State University. Libraries, 2011) Jurgensmeyer, Austin Lee, author; Williams, John, advisor; Bradley, Thomas, advisor; Evangelista, Paul, committee member
Experimental results are presented of thermoelectric materials, specifically two-dimensional quantum well confinement structures, formed by ion beam sputter deposition methods. Applications of these thermoelectric devices include nearly any system that generates heat including waste heat. The targeted applications of this research include harvesting of waste heat from stand-alone generator systems and automobiles. Thermoelectric generator modules based on an in-plane orientation of nano-scale, thin-film, superlattices have demonstrated very high performance and are appropriate for a wide range of waste heat recovery applications. In this project, the first, fast, ion-beam-based deposition process was developed for producing Si/SiC (n-type) and B4C/B9C (p-type) superlattices. The deposition process uses low-cost powder targets, a simplified substrate holder with embedded heater, a QCM deposition rate monitor, and stepper-motor-controlled masks. Deposition times for individual layers are shown to be significantly shorter than those achieved in magnetron-based systems. As an example of the speed of the process, a 10-nm thick Si layer can be deposited in as little as 20 sec while a SiC layer can be deposited in less than 100 sec. Electrical resistivities, thermal conductivities and Seebeck coefficients are reported for the deposited films as well as their respective non-dimensional figures of merit (zT). Figures of merit (zT) approaching 20 at modest temperatures of ~600 K were observed. These measurements are made in-plane where enhanced Seebeck values and reduced electrical resistivities have also been reported in the literature. A method for directly measuring thermal conductivity in the plane of the superlattice is described that uses MEMs-based SiN cantilevers. Results are presented for various deposition variables, including film thickness, temperature, deposition energy, and material. Scanning white light interferometry (SWLI) and scanning electron microscopy (SEM) were used to characterize film thickness. In addition to the experimental effort, an analysis was performed to predict the performance of a thermoelectric module fabricated with the superlattice films deposited on ceramic substrates. Thermal efficiencies approaching 15% are predicted for modest cold and hot side temperatures. Thermal conduction through the substrate was found to be the largest factor limiting the performance of the modeled thermoelectric modules.
Open Access
Implementation and evaluation of backward facing fuel consumption simulation and testing methods
(Colorado State University. Libraries, 2019) Johnson, Troy, author; Bradley, Thomas, advisor; Pasricha, Sudeep, committee member; Weinberger, Chris, committee member
The Colorado State University Vehicle Innovations Team (VIT) participates in numerous Advanced Vehicle Technology Competitions (AVTC's) as well as several hybrid-electric vehicle projects with outside sponsors. This study seeks to develop and quantify the accuracy of simulation and testing methods that will be used in the VIT's predictive optimal energy management strategy research that is to be used in these projects. First, a backward facing vehicle simulation model is built and populated with real-world OBD-II drive data collected from a 2019 Toyota Tacoma. This includes the creation of both an engine speed vs accelerator position vs engine load map as well as an engine speed vs engine load vs engine fuel rate map. Acceleration events (AE's) are performed with a baseline shift schedule and vehicle performance is recorded. The backward facing vehicle simulation model is used to predict how a modified shift schedule will affect the vehicle's fuel consumption. Further AE's are performed with the modified shift schedule and the performance data is compared to the vehicle simulation. The backward facing simulation model was capable of predicting average engine speed within 0.3 RPM, average engine load within 5.2%, and average total fuel consumption within 0.2 grams of the actual testing data. This study concludes that the vehicle simulation methods are capable of predicting fuel consumption changes within 1.4% of what is actual measured during real-world testing with a 95% confidence.
Open Access
In-vehicle validation of energy consumption modeling and simulation
(Colorado State University. Libraries, 2020) DiDomenico, Gabriel, author; Bradley, Thomas, advisor; Quinn, Jason, committee member; Pasricha, Sudeep, committee member
The Colorado State University (CSU) Vehicle Innovation Team (VIT) participated in the first Department of Energy (DOE) Advanced Vehicle Technology Competitions (AVTC) in 1988. Since then, it has participated in the next iterations of the competition as well as other advanced vehicle technology projects. This study aims to validate the team's mathematical modeling and simulation of electrical energy consumption of the EcoCAR 3 competition (academic years 2014-2018) as well as the testing methods used for validation. First, baseline simulation results are obtained by simulating a 0-60 mph wide open throttle (WOT, or 100% APP) acceleration event (AE) with the product being the electrical energy economy in Wh/mi. The baseline model (representing the baseline control strategy and vehicle parameters) is also simulated for 0-40 mph and 0-20 mph AEs. These tests are replicated in the actual vehicle, a 2016 P2 PHEV Chevrolet Camaro entirely designed and built by CSU's VIT. Next, the same AEs are again tested with a changed acceleration rate due to the APP being limited to 45%. The velocity profiles from these tests are used as feedback for the model and the tests are replicated in simulation. Finally, the baseline model is altered in 3 additional ways in order to understand their effect on electrical energy consumption: the mass is increased, then the auxiliary low voltage (LV) load is increased and then the transmission is restricted to only 1 gear. These simulations are again replicated in-vehicle in order to validate the model's capability in predicting changes in electrical energy consumption as certain vehicle parameters are changed. This study concludes that model is able to predict these changes within 6.5%, or ±30.2 Wh/mi with 95% confidence.
Open Access
Innovative hydrogen station operation strategies to increase availability and decrease cost
(Colorado State University. Libraries, 2019) Kurtz, Jennifer, author; Bradley, Thomas, advisor; Willson, Bryan, committee member; Suryanarayanan, Siddharth, committee member; Ozbek, Mehmet, committee member
Major industry, government, and academic teams have recently published visions and objectives for widespread use of hydrogen in order to enable international energy sector goals such as sustainability, affordability, reliability, and security. Many of these visions emphasize the important and highly-scalable use of hydrogen in fuel cell electric cars, trucks, and buses, supported by public hydrogen stations. The hydrogen station is a complicated system composed of various storage, compression, and dispensing sub-systems, with the hydrogen either being delivered via truck or produced on-site. As the number of fuel cell electric vehicles (FCEVs) on roads in the U.S. have increased quickly, the number of hydrogen stations, the amount of hydrogen dispensed, and the importance of their reliability and availability to FCEV drivers has also increased. For example, in California, U.S., the number of public, retail hydrogen stations increased from zero to more than 30 in less than 2 years, and the annual hydrogen dispensed increased from 27,400 kg in 2015 to nearly 105,000 kg in 2016, and more than 913,000 kg in 2018, an increase of nearly 9 times in 2 years for retail stations. So, although government, industry, and academia have studied many aspects of hydrogen infrastructure, much of the published literature does not address hydrogen station operational and system innovations even though FCEV and hydrogen stations have some documented problems with reliability, costs, and maintenance in this early commercialization phase. In general, hydrogen station research and development has lagged behind the intensive development effort that has been allocated to hydrogen FCEVs. Based on this understanding of the field, this research aims to identify whether integrating reliability engineering analysis methods with extensive hydrogen station operation and maintenance datasets can address the key challenge of station reliability and availability. The research includes the investigation and modeling of real-world hydrogen station operation and maintenance. This research first documents and analyzes an extensive dataset of hydrogen station operations to discover the state-of-the-art of current hydrogen station capabilities, and to identify performance gaps with key criteria like cost, reliability, and safety. Secondly, this research presents a method for predicting future hydrogen demand in order to understand the impact of the proposed station operation strategies on data-driven decision-making for low-impact maintenance scheduling, and optimized control strategies. Finally, based on an analysis indicating the need for improved hydrogen station reliability, the research applies reliability engineering principles to the hydrogen station application through development and evaluation of a prognostic health management system.
Open Access
Investigation of indirect (secondary loop) refrigeration systems in commercial food service buildings
(Colorado State University. Libraries, 2016) Anderson, Chris, author; Bradley, Thomas, advisor; Bandhauer, Todd, committee member; Cross, Jennifer, committee member
Indirect (secondary loop) refrigeration systems have recently received increased attention due to their well-known effects on reducing refrigerant losses, particularly in commercial food sales buildings. Although their effects on operating costs, particularly in terms of energy efficiency, are less definitive, there is potential that indirect refrigeration systems might offer significant energy efficiency improvements in food service buildings. The aim of this thesis was to determine the feasibility of an indirect (secondary loop) refrigeration system for a food service building, specifically a Starbucks coffee shop. Six commercial refrigeration units were installed in a laboratory setting. The units were first tested with their air-cooled condensers to establish a baseline. Then, each unit was retrofitted with a water-cooled condenser, and all six water-cooled condensers were connected in series to form a secondary loop system and tested again. The results of this laboratory testing were used to create a predictive model to estimate the payback period for installing the system in different Starbucks coffee shop locations around the country. The model predicted the major requirements for a two year payback period to be high energy costs (>$0.22/kWh), a warm to hot climate (AC runtime > 20 hours per day), and a sufficiently large store (containing multiple large food cases or ice machines).
Open Access
Low work function, long lifetime filament for electron beam-based, wire-fed metal additive manufacturing
(Colorado State University. Libraries, 2018) Nguyen, Bao Gia, author; Bradley, Thomas, advisor; Williams, John, advisor; de la Venta Granda, Jose, committee member
Tantalum filaments are used in electron beam additive manufacturing to thermionically emit electrons that are used to build near-net shape, metal parts. High operating temperatures are required to emit electrons which consequently limits the lifetime of these filaments. This thesis presents the thermionic emission characteristics of drop-in filament replacements that incorporate barium calcium aluminate cermets. Barium calcium aluminate is a low work function material used with hollow cathodes in electric propulsion devices to provide very long service lifetimes by acting as a moderate temperature, electron source. A marriage of these two technologies may limit downtime and increase the productivity and output of electron beam additive manufacturing. Results of extended runtime tests are presented from configurations that immerse the modified filament in plasma and operate it as a vacuum emitter. The effect of contamination by air and fabrication methods are examined and evaluated based on effective work function and current density measurements. The latter includes formation methods for barium diffusion orifices as well as surface preparation methods for cermets. The experimental data collected were used to validate a predictive model that evaluates emission current densities, in both temperature and space-charge limited conditions, and effective work functions based on the fractional surface coverage of barium over a tantalum substrate.
Open Access
Managing risk in commercial-off-the-shelf based space hardware systems
(Colorado State University. Libraries, 2024) Herbert, Eric W., author; Bradley, Thomas, advisor; Sega, Ronald, advisor; Herber, Daniel, committee member; Shahroudi, Kamran, committee member; Wise, Daniel, committee member
The space industry is experiencing a dynamic renaissance. From 2005 to 2021, the industry has exhibited a 265% increase in commercial and government investment [1]. The demand is forecasted to continue its upward trajectory by an added 55% by 2026 [1]. So, the aerospace industry continually seeks innovative space hardware solutions to reduce cost and to shorten orbit insertion schedules. Using Commercial-Off-the-Shelf (COTS) components to build space-grade hardware is one method that has been proposed to meet these goals. However, using non-space-grade COTS components requires designers to identify and manage risks differently early in the development stages. Once the risks are identified, then sound and robust risk management efforts can be applied. The methods used must verify that the COTS are reliable, resilient, safe, and able to survive rigorous and damaging launch and space environments for the mission's required longevity or that appropriate mitigation measures can be taken. This type of risk management practice must take into consideration form-fit-function requirements, mission objectives, size-weight-and-performance (SWaP) constraints, how the COTS will perform outside of its native applications, manufacturing variability, and lifetime expectations, albeit using a different lens than those traditionally used. To address these uncertainties associated with COTS the space industry can employ a variety of techniques like performing in-depth component selections, optimizing designs, instituting robust stress screening, incorporating protective and preventative measures, or subjecting the hardware to various forms of testing to characterize the hardware's capabilities and limitations. However, industrial accepted guidance to accomplish this does not reside in any standard or guide despite space program policies encouraging COTS use. One reason is because companies do not wish to reveal their proprietary methods used to evaluate COTS which, if broadcast, could benefit their market competition. Another is that high value spacecraft sponsors still cling to low-risk time consuming and expensive techniques that require the use of space hardware built with parts that have historical performance pedigrees. Keeping this data hidden does not help the space industry, especially when there is a push to field space systems that are built with modern technologies at a faster rate. This is causing a change in basic assumptions as stakeholders begin to embrace using parts from other industries such as the automotive, aviation, medical, and the like on a more frequent basis. No longer are COTS relegated to use in CubeSats or research and development spacecraft that have singular and limited missions that are expected to function for a brief period. This is because COTS that are produced for terrestrial markets are equally as dependable because of the optimized manufacturing and quality control techniques that reduce product variability. This increases the use of COTS parts in space hardware designs where until recently space programs had dared not to tread. But using COTS does come with a unique set of uncertainties and risks that still need to be identified and mitigated. Despite legacy risk management tools being mature and regularly practiced across a diverse industrial field, there is not a consensus on which risk management tools are best to use when evaluating COTS for space hardware applications. However, contained within technical literature amassed over the last twenty-plus years there exists significant systems engineering controls and enablers that can be used to develop robust COTS-use risk management frameworks. The controls and enablers become the basis to identify where aleatory and epistemic uncertainties exist within a COTS-based space system hardware design. With these statements in mind, unique activities can be defined to analyze, evaluate, and mitigate the uncertainties and the inherent risks to an acceptable level or to determine if a COTS-based design is not appropriate. These concepts were explored and developed in this research. Specifically, a series of COTS centric risk management frameworks were developed that can be used as a roadmap when considering integrating COTS into space hardware designs. From these frameworks unique risk evaluation processes were developed that identified the unique activities needed to effectively evaluate the non-space grade parts being considered. The activities defined in these risk evaluation processes were tailored to uncover as much uncertainty as possible so that appropriate risk mitigation techniques could be applied, design decisions could be quickly made from an informed perspective, and spacecraft fielding could be accomplished at an accelerated rate. Instead of taking five to ten years to field a spacecraft, it can now take less than one to three years. Thus, if effectively used, COTS integration can be a force multiplier throughout the space industry. But first, the best practices learned over the last few decades must be collected, synthesized, documented, and applied. To validate the risk frameworks discussed, a COTS-based space-grade secondary lithium-ion battery was chosen to demonstrate that the concepts could work. Unique risk evaluation activities were developed that took into consideration the spacecraft's mission, environment, application, and lifetime (MEAL) [2] attributes to characterize the battery's COTS cells, printed circuit board, electrical design, and electrical-electronic-electromechanical (EEE) performance, strengths, and weaknesses. The activities defined and executed included risk evaluation activities that included a variety of modeling, analyses, non-destructive examinations, destructive physical assessments, environmental testing, worst case scenario testing, and manufacturing assessments. These activities were developed based on the enablers and controls extracted from the data that was resident in the literature that was reviewed. The techniques employed proved quite successful in uncovering and mitigating numerous aleatory and epistemic uncertainties. The mitigation of these uncertainties significantly improved the battery's design and improved the battery's performance. As a result, the COTS-based battery was successfully built, qualified, and flown on a fleet of launch vehicles and payloads. The information that follows documents how the risk management frameworks were created, what influenced its architecture, and how these were successfully validated. Validating the COTS centric risk management framework was important because it demonstrated the risk management frameworks' utility to uncover uncertainty. It also proved that methods exist that can be readily employed that are not typically within the scope of traditional space hardware design and qualification techniques. This is important because it provides the industry a new set of systems engineering tools that can be employed to limit the impact of supply chain constraints, reduce reliance on expensive low-yield hardware procurement practices, and minimize the amount of obsolete hardware in designs which tend to constrain the space system hardware's performance. As a result, the techniques developed in this research start to fill a gap that exists in the space industry's systems engineering toolbox.
Open Access
Manufacturing and testing of spline geometry using carbon fiber reinforced composite
(Colorado State University. Libraries, 2016) Jambor, Eric, author; Bradley, Thomas, advisor; Radford, Donald, committee member; Heyliger, Paul, committee member
A model and manufacturing process for the design of carbon fiber reinforced composite spline shafts is developed and validated to investigate the feasibility of using composite splines for use in power transmission applications. Composite torque tubes for power transmission have been employed in various industries for over three decades and have shown up to a 50% mass decrease compared to steel shafts designed for the same use. One limiting factor for the amount of weight reduction achievable is the mechanism used to transfer power to and from the composite tube. Most composite shafts use adhesive bonding, fasteners, press fits, or some combination to join a steel or aluminum yolk or spline to the end of the tube. This research will investigate the feasibility of eliminating these mechanisms by replacing them by molding in splines to the composite torque tube. This will additionally reduce part count and manufacturing time as well as eliminating the heavy metal inserts. To achieve this, an analytical model is developed to investigate the strength of composite spline teeth of involute geometry as well as a composite torque tube. Due to the complex nature of designing with composites these models are supplemented by material models using a composite software package and finite element models (FEM). The involute splined shaft was then manufactured using an iterative approach to refine the sample quality and tested in torsion to failure. Although the peak failure torque had a large range over the samples it can be concluded that with improvements in the manufacturing process using molded composite splines is a feasible method of torque transfer. This can be concluded from the failure modes of the splined shaft as they indicate that the splines were able to adequately transfer the load to the torque tube.