M.S. - Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10125/2096

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On the geometry of load paths
(University of Hawai'i at Manoa, 2025) Freitas, Christopher John; Kobayashi, Marcelo H.; Mechanical Engineering
This thesis develops a novel framework for defining and analyzing structural load paths using variational principles. Load paths describe the internal transmission of forces within a structure and are fundamental to understanding structural behavior, optimization, and design. Traditional optimization methods like SIMP and level set techniques typically rely on stress approximations, often yielding impractical or non-intuitive results. However, approximations based on internal loads have proven to be more accurate and may illustrate more meaningful approaches. This work formulates load paths as geodesics governed by the stress field, drawing analogies from differential geometry. Two types of formulation are discussed, the Lagrangian and the Hamiltonian. The Lagrangian formulation interprets load paths as curves that minimize a Lagrangian functional, analogous to minimizing the action in mechanics, while the Hamiltonian formulation introduces complementary insights via energy conservation and contravariant stress tensors. First, examples are given for each system separately, while application to an ESAVE wing structure is used to demonstrate how these load path formulations can guide structural design. Numerical solutions are obtained using finite element analysis and differential equation solvers, followed by design optimization using MSC.Nastran. The study also draws analogies with the Schwarzschild metric to further interpret geodesic behavior in structural systems. Ultimately, this approach offers a physically intuitive and computationally tractable means to identify meaningful load paths, potentially enhancing structural optimization methods and practical design workflows.
A semi-automated handheld active needle device for percutaneous image-guided interventions
(University of Hawai'i at Manoa, 2025) Kinder, Josh; Konh, Bardia; Mechanical Engineering
This thesis presents the design and preliminary evaluation of novel brachytherapy (BT)systems intended to improve anatomical conformity, placement precision, and procedural safety in high-dose-rate (HDR) treatments for prostate and cervical cancer. Traditional applicators often rely on rigid, manually inserted components, which limit adaptability and reduce dose accuracy in patients with complex anatomical and disease variations. To address these limitations, a semi- automated active needle system was developed for prostate HDR BT, integrating a custom 3D- printed template and preplanned curvilinear trajectories based on patient-specific magnetic resonance imaging (MRI) data. Phantom and air testing demonstrated sub-millimeter tip displacement accuracy, validating the system’s precision. Building on this foundation, a handheld tendon-driven steerable needle device was created for real-time use under transrectal ultrasound (TRUS) guidance. This system features a joystick-controlled actuation mechanism and a modular TRUS attachment to support intraoperative visualization and navigation. For cervical cancer treatment, a modular applicator was designed incorporating adjustable vaginal spreaders, a controllable tandem channel, and support for 2 mm steerable needles. The design accommodates ovoid separation from 25 mm to 45 mm. The performance and range of motion were validated for TRUS imaging compatibility. Future development will focus on interfacing the cervical applicator with externally controlled telescopic pre-curved tandems and incorporating mechanisms for active adjustment of ovoid geometry. Collectively, these systems demonstrate the feasibility of integrating flexible, image-guided instrumentation into HDR BT workflows, offering a pathway toward more personalized, precise, and patient-specific cancer treatment solutions.
Development and validation of a digital twin system model for a piezoelectric sensor
(University of Hawai'i at Manoa, 2025) Okura, Kailer; Brown, Joseph J.; Mechanical Engineering
This study presents a multiphysics modeling framework for a piezoelectric force sensor embedded within an automotive tire system, combining finite element and circuit simulation with empirical validation. The project had three primary objectives: (1) to modify an exist- ing two-dimensional axisymmetric tire model in COMSOL® to accommodate localized point loading, (2) to develop a virtual representation of a multilayer piezoelectric sensor capable of predicting voltage output under mechanical stress, and (3) to validate this model utilizing experimental techniques. To address the tire modeling challenge, the axisymmetric geometry was extruded into a complete three-dimensional model to enable the simulation of discrete contact forces. A simplified pseudo-tire model, constructed with linear elastic materials, was able to converge under internal pressure and contact loading, producing a peak von Mises stress of 2 × 10^{2} N/m^{2} and a maximum displacement of 3 × 10^{-2} m at 5 kPa of interior air pressure. For the sensor, a two-dimensional COMSOL model was coupled with an LTspice® circuit to capture electromechanical coupling and time-dependent electrical behavior. The COMSOL simulation produced a peak voltage of 33.55 V and an integrated charge of 1.25 × 10^{−8} C under a ±500 N force sweep. Experimental validation using three- point bending and a voltage follower circuit yielded a capped sensor output of approximately 5 V at 250 N. Comparison between the COMSOL and experimental force–displacement data showed partial agreement, with a standard deviation of 2.71 N and a 24.23 % error. While the simulation accurately captured the sensor’s early behavior, it lacked the nonlinear plateau observed in the experimental results. This discrepancy suggests that future work should in- corporate parasitic loss mechanisms. This integrated modeling approach lays the foundation for digital twin frameworks in next-generation intelligent tire systems.
Efficacy of curvilinear catheter implantation for prostate cancer interventions
(University of Hawai'i at Manoa, 2025) Imanaka, Rex R.; Konh, Bardia; Mechanical Engineering
High-dose-rate (HDR) brachytherapy (BT) is a widely utilized treatment for patients with intermediate- and high-risk prostate cancer. Despite its proven efficacy, it is often associated with side effects such as edema, urinary incontinence, and sexual dysfunction. A key limitation of HDR BT, however, lies in the risk of delivering excessive radiation to nearby organs-at-risk (OARs), including the urethra, bladder, and rectum. To minimize radiation exposure to OARs and improve patient outcomes, curvilinear catheter implantation has been investigated as an alternative to conventional rectilinear techniques. Unlike rectilinear catheter placement, curvilinear implantation enables the catheters to better conform to the natural contours of the prostate. This enhanced conformity allows for more precise dose delivery, reducing radiation exposure to surrounding OARs, while also potentially decreasing the number of needles required for the procedure. Despite its clear advantages, curvilinear catheter implantation has not been widely adopted in clinical practice due to challenges related to needle control, precise placement, and insertion accuracy. This work represents the culmination of a series of studies that: (i) evaluate the effectiveness of curvilinear catheter application, (ii) explore methods to control the initial needle insertion angle, (iii) develop robotic systems for precise needle insertion, and (iv) support the training of new physicians in curvilinear catheter implantation techniques.
Experimental evaluation of process-property relationships in bound powder extrusion based metal additive manufacturing
(University of Hawai'i at Manoa, 2025) Lorenzo, Kendall; Ray, Tyler; Mechanical Engineering
Additive manufacturing (AM) techniques permit the fabrication of intricate geometries that are challenging or impossible to produce using traditional subtractive methods (e.g., machining). Bound powder extrusion (BPE), an AM variant, extends this capability to functional metal components in a process akin to the production of polymer parts via consumer-grade printers. AM-fabricated parts differ fundamentally from wrought materials: each exhibits unique characteristics due to inherent defects like porosity, residual stresses, and orientation-dependent mechanical properties stemming from the layer-by layer build process. In BPE, this anisotropy manifests as significant variations in strength and ductility with printing direction, introducing variability and uncertainty that demand thorough characterization for reliable part qualification and engineering deployment. Despite BPE's potential, detailed studies on the mechanical properties of its metal outputs are sparse, with existing data showing inconsistencies from differing processing and testing conditions; even scarcer are systematic explorations of orientation effects essential for design optimization. To address these deficiencies, I undertook a comprehensive evaluation of 17-4PH stainless steel components produced via the Markforged MetalX system, printing specimens in 0°, 45°, and 90° orientations relative to the build direction. These were subjected to tensile testing, hardness measurements, surface roughness profiling, and corrosion assessments, with all metrics benchmarked against wrought 17-4PH. Through these efforts, it was observed that essential, orientation-resolved property insights absent in the literature that will aid in enabling evidence-based design of BPE components, expanded characterizations across Markforged alloys to foster comprehensive material databases, and enable broader utilization in industrial applications.
Exploring planetary surfaces: Active learning for resource mapping with autonomous rovers
(University of Hawai'i at Manoa, 2025) Akins, Sapphira; Zhu, Frances; Mechanical Engineering
The exploration of planetary surfaces presents unique challenges that necessitate autonomous decision-making to optimize scientific data collection. Such data collection is necessary to facilitate technological advancements and increase our knowledge of planetary bodies. This thesis investigates the use of active learning algorithms to enhance the efficiency of planetary surface exploration, with a particular focus on Gaussian Processes (GPs) and cost-aware query policies that ensure efficiency and minimization of annotation costs. By employing active learning techniques, autonomous robotic agents can select informative sampling locations, reducing the number of samples and distance required while maximizing scientific findings. Through a combination of simulation studies and real-world experiments, this research evaluates the performance differences of GPs and Bayesian Neural Networks (BNNs) in constrained trajectory exploration. The findings indicate that GPs consistently achieve faster convergence, require fewer samples, and result in shorter travel distances compared to BNNs. Despite the flexibility of BNNs in modeling complex spatial distributions, they exhibit higher computational demands and reduced reliability in sparse-data environments. A field demonstration conducted on Mauna Kea, a recognized lunar analog site on the island of Hawai'i, further validates the applicability of active learning algorithms in real-world planetary exploration settings. The results highlight the potential of GP-based active learning in reducing mission duration and optimizing energy efficiency for autonomous robotic explorers. Along with this, in-situ testing was completed in a sand court at the University of Hawai'i at Manoa where various query policies were tested on their efficiency at minimizing costs associated with data collection. This work contributes to the development of intelligent exploration strategies for planetary surface missions. A future research direction includes additional real-time deployment of active learning algorithms, particularly with fully autonomous rovers in lunar regolith testbeds with scientific instrumentation planned for use on a space mission.
Design and optimization of compliant mechanisms for mechanical attachment systems
(University of Hawai'i at Manoa, 2025) Laudone, Russell; Brown, Joseph; Mechanical Engineering
Bistable compliant mechanisms offer a promising alternative to traditional fasteners and adhesives for mechanical attachment, enabling lightweight, reusable locking systems across diverse applications. This work presents two compliant locking mechanisms: one tool-less and in-plane for aerospace thermal protection systems, and another tool-actuated and out-of- plane for modular panel assemblies. The aerospace mechanism was prototyped in polylactic acid (PLA) and optimized using a hyperelastic solid model with a yield constraint, applying sequential sweeps of geometric parameters. The resulting design achieved a retention force of 53.41 N with a mass of 47.3 g and a 789 mm2 footprint, offering rapid tile exchange without adhesives. The modular panel system created a physical model inspired by industry needs and, separately, introduced an updated computational framework using particle swarm op- timization (PSO) coupled with FEniCSx simulations to enable multi-dimensional geometry tuning for material-dependent design. PSO-FEniCSx algorithm explored a three-parameter solution space, including band thickness, band angle, and side shuttle length, using a swarm of 16-particle’s evolving over 12 iterations. The best configuration, with band thickness “t” = 1.3 mm, band angle ”θ” = 78.85◦, and side shuttle length “ssl” = 29.66 mm, achieved a peak retention force of 66.33 N while remaining below the 95% yield stress threshold. Experimental validation confirmed that PSO accurately characterizes structures based on maximum force. However, it was found that the FEniCSx boundary conditions did not cor- rectly accurately represent deformation at the side walls during geometry transformation. To resolve this discrepancy, replacement of fixed conditions with a pin support is recommended. These results demonstrate that bistable compliant structures can be computationally opti- mized and physically tuned to meet application-specific requirements in both aerospace and architectural contexts.
Design and fabrication of a modular, low-cost aerosol jet printer
(University of Hawai'i at Manoa, 2025) Viernes, Kian; Ray, Tyler; Mechanical Engineering
Flexible electronics that conform to non-planar surfaces represent an important frontier in device engineering, with applications spanning wearable systems, biomedical interfaces, and structural monitoring. Fabrication of these systems requires manufacturing approaches that can precisely pattern functional materials onto diverse substrates. Aerosol jet printing (AJP) offers distinctive capabilities in this domain, using aerodynamic focusing to direct aerosolized functional inks with high spatial precision onto both planar and non-planar surfaces. We report the development of a modular, low-cost aerosol jet printer (LC-AJP) constructed from commercial off-the-shelf components, open-source software, and custom 3D-printed elements. Despite its modest cost (<$1,200), the system achieves sub-50 µm resolution in printed features. We demonstrate material versatility by successfully printing with silver nanoparticle inks, PEDOT conducting polymer, and carbon black composites, enabling fabrication of functional temperature sensors. The modular architecture facilitates rapid innovation, exemplified by our implementation of a 4-in-1 multi-nozzle configuration that quadruples production throughput by simultaneously printing four identical structures. This accessible platform establishes a foundation for broader adoption of advanced manufacturing techniques for flexible electronics, with opportunities for further refinement in resolution, materials compatibility, and integration with complementary fabrication methods.
Development and Design of a Compact Laparoendoscopic Single-Site Robotic Surgical System Integrating ROS2 Middleware
(University of Hawai'i at Manoa, 2024) Trafford, Sean; Berkelman, Peter J.; Mechanical Engineering
Minimally invasive surgery aims to further this by performing procedures with the least number of incisions necessary. Single-port laparoscopy takes this a step further by having every instrument used in the procedure operate from inside just a single small incision. While minimally invasive surgery has been shown to have beneficial outcomes in regards to the speed, quality, and cosmetics of the healing process, it is heavily restricted by the prerequisite skill required by the surgeon. To this end, Robotic surgical systems can be used to lower the skill floor. The surgical system presented in this thesis was built upon a previous University of Hawai‘i at Manoa system [1], designed to have a similar level of performance to other systems on the market, such as the Intuitive Surgical Inc. da Vinci RAS, while reducing the cost and total volume taken up by the system. While the goals of cost and volume were solved by the previous iteration of the surgical system, it introduced a brand new problem of longevity. To remedy this, new components possessing similar dimensions to the components of the original system were used, but with 6061 aluminum as the primary material used, rather than ABS P-430 plastic. A new control system was also created which utilizes a damped-least squares algorithm to calculate the inverse kinematics based on the motions of a Geomagic/Sensable Phantom Omni controller, and using velocity control to further adjust the positioning. Finally, rather than operating from multiple computers simultaneously, Robotic Operating System 2 (ROS2) middleware was implemented to allow for the simultaneous operation of two arms through multi-core processing, the transference of positional data between the two control algorithms, and any additional programs. Through the use of a Northern Digital Polaris Vicra optical tracker, spatial data for the system was taken for movement along a preset path, and free hand taken from the controller, both over a time of 70 seconds. The results in both cases displayed a visual reduction in positional drifting when compared to the results of previous systems, with the preset path never visually achieving more than a drift of 0.5 mm off the path before self-correcting, with an average deviation from the path of 0.434 mm. The free hand data, also displayed a visual improvement by maintaining the same path for the duration of the experiment, rather than permanently drifting in a single direction, with an average deviation from the path of 1.953 mm. While the motion tracking data does show a promising improvement compared to the previous UH Mānoa system, additional practical testing and structural refinements will be required to determine if the surgical system is ready to enter pre-clinical development.
MARINE VEHICLE CHARACTERIZATION AND IMPLEMENTING VARIOUS LEVELS OF AUTONOMY
(University of Hawai'i at Manoa, 2024) Ng, Patrick Julian; Krieg, Michael; Mechanical Engineering
Remotely operated vehicles (ROVs) are marine submersible robots that serve a variety of purposes in industry and research. These unmanned vessels harness human judgment and precision to perform tasks within extreme environments like the deep sea, polar, and volcanic regions of the ocean. Some examples of their usages are to survey the ocean floor, maintain pipelines and collect scientific data in the form of sediment and hydrothermal vent plume samples and optical observations of marine wildlife. Training of ROV pilots is typically very expensive and time-consuming because of the highly specialized skill requirements. A novel system was proposed by collaborators from the University of Florida (UF) and the University of Hawai‘i at M ̄anoa (UHM) for piloting ROVs with an intuitive augmented/virtual reality (AR/VR) interface that uses a hybrid autopilot. To demonstrate the feasibility of this system the group at UHM altered the ArduSub firmware of the commercially available BlueROV2 (BROV2) Heavy to enable model-based quantitative control. Error feedback control for the hybrid autopilot was implemented using Robot Operating System (ROS) in a modular manner that enabled various levels of autonomy to assist ROV pilots. Alongside the development of the custom firmware and hybrid autopilot, the software-in-the-loop (SITL) simulation environment was also updated with an experimentally determined hydrodynamic model using onboard sensor- based system identification techniques As much as sixty percent improvement of relative error when predicting vehicle behavior compared to the original SITL model. The calibration process of the hybrid autopilot involved iteratively cycling between SITL and water tank testing. It was demonstrated that this procedure was an effective method for achieving precision control of the BROV2.
Development of a Thermal Dummy Cell (TDC) for Pouch Cells in Lithium-Ion Battery Thermal Management Systems
(University of Hawai'i at Manoa, 2024) Bahrami, Armida; Dubarry, Matthieu; Mechanical Engineering
Lithium-ion (Li-ion) batteries have become indispensable in various sectors, including consumer electronics, automotive, and renewable energy storage, due to their high energy density, long service life, and efficiency. Effective thermal management is crucial to ensure the safety, performance, and longevity of these batteries. This thesis focuses on developing a segmented Thermal Dummy Cell (TDC) specifically for pouch cells—a novel and pioneering design that has never been constructed before. Unlike cylindrical and prismatic cells, which have been extensively studied, pouch cells have lacked sufficient research in thermal management, leaving a critical gap in the literature. Previous studies have developed TDCs for cylindrical and prismatic cells, providing valuable insights into the thermal behavior of these battery types. However, this research introduces the first-ever segmented TDC tailored for pouch cells, featuring independent control over each heating segment. This allows for precise temperature management that closely simulates real-world battery conditions. The system incorporates Pulse Width Modulation (PWM) control and advanced data monitoring, capturing essential parameters such as temperature, current, voltage, and power in real time. The thesis begins with a comprehensive review of existing literature on TDCs for cylindrical and prismatic cells, identifying the methodologies and findings that can be applied to pouch cells. It then details the iterative design process of the pouch cell TDC, including the challenges encountered and the solutions implemented. The final prototype consists of 11 heating pads arranged in a 3x3 grid for the body and 2 additional pads for the tabs, controlled via Arduino and PWM to achieve precise temperature control. Extensive calibration and testing were conducted to ensure the TDC accurately mimics the thermal behavior of real pouch cells. The results demonstrate that the TDC provides a reliable and safe means of studying thermal management strategies for pouch cells. By enabling individual control of heating segments, the system offers in-depth insights into localized thermal effects, making it ideal for research aimed at improving battery safety and efficiency. This development enables safer and more accurate studies of thermal behavior without the risks associated with live cells. This research represents a significant advancement in the field of battery thermal management by offering a novel tool for researchers and engineers. It serves as a key step forward in understanding and controlling the complex thermal dynamics of lithium-ion batteries, ultimately contributing to the evolution of energy storage technologies.
Stress Corrosion Cracking and Hydrogen Embrittlement Atmospheric Corrosion Testing of Control and Prototype Steels
(University of Hawai'i at Manoa, 2024) Maruno, Tyler; Hihara, Lloyd; Mechanical Engineering
The United States Department of Defense has begun the formulation of a new generation of high strength steels for naval applications, emphasizing superior hardness, toughness, and ballistic resistance. Whilst these metals have been designed with a focus on strength, their corrosion behavior is largely unknown and must be characterized prior to widespread application. This research involved the design of an experiment to test the stress corrosion cracking and hydrogen embrittlement susceptibility of HY-100, HSLA-150, 10Ni QQT, and 10 Ni QQLT steels. A modified version of the standardized four-point bend test in which samples are stressed to 90% of their yield strength was designed to be implemented in numerous microclimates across the State of Hawai’i. In addition, microstructural analysis was performed via metallurgical techniques, while the corrosion behavior was quantified via electrochemical polarization. Inclusions were characterized in each steel, with directional, structural, and elemental analyses performed. Aluminum and iron containing oxides were identified in each metal, with 10Ni steels showing the highest frequency of inclusion clusters. Potentiodynamic polarization testing provided information pertaining to the corrosion rates of each steel along with zinc and magnesium in three solutions simulating freshwater, acidic, and saline environments. While all four steels produced similar galvanic potential and current density results, magnesium was shown to induce the highest levels of hydrogen liberation on the steels with rates consistently two orders of magnitude greater than that due to zinc. Combined, the information obtained as related to stress corrosion cracking, hydrogen embrittlement, and material characterization serve as integral pieces necessary to validate and further refine the next generation of high strength steels for defense applications.
Solar-Thermal Desalination with Reduced Graphene Nanocomposites and Hydrophobic Polymers for Enhanced Evaporation and Dropwise Condensation
(University of Hawai'i at Manoa, 2024) Blanks, Sean Allen; Lee, Woochul; Mechanical Engineering
Interfacial solar-thermal desalination is an off-grid passively operated method of producing pure drinking water. It shows especially high promise in providing an inexpensive sustainable desalination solution for currently underserved dispersed communities who are unable to adequately secure drinking water and lack the infrastructure to justify traditional large scale energy intensive desalination plants. The aim of this thesis is the fabrication of an inexpensive high efficiency interfacial solar-thermal desalination prototype capable of producing pure drinking water. To meet this aim, the independent development of both a high efficiency evaporator and condensing surface were approached utilizing benign fabrication methods. Improving upon previous solar-to-vapor efficiencies through improved substrate wettability and coating photothermal absorption efficiency, a carbon based solar-thermal evaporator derived from an Aquazone dip coat of reduced graphene oxide (rGO) and polydimethylsiloxane (PDMS) nanocomposite achieved an average solar-to-vapor conversion efficiency of 69.7%. To capitalize on the high vaporization efficiency, a polyvinyl chloride cover treated with a hydrophobic polymer coating for enhanced drop wise condensation was employed for water collection with a measured condensation efficiency of 86.0%. The resulting prototype demonstrated high efficiency through improvement of both condensation and evaporation. Further, the prototype successfully produced pure water from local seawater, meeting water quality standards provided by both the Environmental Protection Agency National Primary Drinking Water Regulations and the Standards and Guidelines for Contaminants in Massachusetts Drinking Waters. Based off this investigation it was also found there exists great potential with bridging the gap from in-situ prototypes productivity to the potential efficiencies of promised from lab values.
SYSTEM IDENTIFICATION OF AN UNINHABITED SURFACE VEHICLE
(University of Hawai'i at Manoa, 2024) Jones, Kai; Trimble, A Zachary; Mechanical Engineering
Uninhabited Surface Vehicles (USVs) require a robust and capable Guidance, Navigation, and Control (GNC) system to operate effectively. GNC requires a model of the USV’s dynamics for state estimation, control, and other applications. Data-driven modeling, the process of determining practical models from data, is a re-emerging method and active field of research for modeling system dynamics. The purpose of this research is to explore the use of PySINDy, an open-source Python module that implements the Sparse Identification of Nonlinear Dynamics (SINDy) data-driven system identification method, to generate a generalizable and interpretable model of a Wave Adaptive Modular Vessel (WAM-V). PySINDy is equipped with tools to simplify the modeling process, such as a library class to initialize a matrix of nonlinear terms for SINDy to create models from, a fit function that incorporates control inputs and time series data to infer a model from, and a score function that evaluates the model’s performance against validation data using ?2 as the scoring metric. First, existing examples of PySINDy’s capabilities are explored and demonstrate that the algorithm can produce the underlying model of a numerically simulated Lorenz system with: no noise (?2=1.00), with an external force acting on the system (?2=0.99), with “low” and “high” level noise (R5% ?????2=0.99; R60% ?????2=0.78), and with filtered low and high noise (?5% ?????2=1.00; ?60% ?????2=0.99). These test cases illustrate SINDy’s ability to generate effective models in various circumstances expected by a real system as indicated by the high ?2 values. Second, with a baseline understanding of SINDy’s capabilities, Blanke’s simplified version of Norrbin’s second-order nonlinear model, suggested as a representative maneuvering model for simulation in Fossen1, is utilized to simulate the dynamics of a WAM-V. Like the Lorenz system case studies, simulated data with low- and high-level noises are filtered and used to generate models which score ?5% ?????2=0.81 and ?75% ?????2=0.78 indicating SINDy’s capability to generate effective models for a potentially representative USV and confirm that straight-line and turning circle maneuvers provide enough data variety to sufficiently capture the system’s behavior. Third, and finally, the same procedure is replicated in a real-world experiment by recording and subsequently estimating the full state data of a WAM-V at Sand Island in calm water (i.e. no waves - wind and current disturbances were present). SINDy generated a second-order nonlinear cross-coupled modulus model with a model score of ?2=0.28. Due to the low validation score, the time-constant of the generated model, which is approximately 14s, is estimated by analyzing the model’s rise time from a step input and the quality of the model is also validated by its ability to predict the state of the system over 3 time-constants (i.e. 36 s). This time horizon was applied to create a sliding window on the validation dataset with 0-36 s, 12-48 s, and 24-60 s windows where the initial conditions of the model are updated at the beginning of each time window and results in an ?2 score of 0.32, 0.28, and 0.29 respectively.
CREVICE AND GALVANIC ATMOSPHERIC CORROSION TESTING OF CONTROL AND PROTOTYPE STEELS
(University of Hawai'i at Manoa, 2024) Qu, Linda; Hihara, Lloyd H.; Mechanical Engineering
The United States Navy aims to develop new high strength steels with superior mechanical properties for naval applications. A novel nickel-based steel is being researched as a suitable candidate to replace currently used high strength steels. As an emerging steel alloy, it is necessary to evaluate its corrosion performance which may vary depending on the composition and environment. This research investigated four steels consisting of a control steel, HY-100, and three prototype steels of a modified HSLA, 10Ni QQT, and 10Ni QQLT. Material characterization of the steels was conducted through an analysis of the steel microstructure utilizing metallography, and a study of the corrosion behavior via electrochemical polarization. Metallographic imaging revealed the microstructural characteristics of the steels. Microstructural morphologies were identified, along with an observed reduction in grain size of the 10Ni steels relative to the HY-100 and HSLA steels. Potentiodynamic polarization testing provided an estimation of the corrosion rates of each steel in three different solutions simulating freshwater, acidic, and saline environments. Acidic environments of pH 3 proved to be the most corrosive towards the steels. Furthermore, the galvanic corrosion of the steels coupled to nickel aluminum bronze (NAB) and low voltage aluminum (LV Al) was investigated. LV Al had minimal galvanic effect on the steels in the pH 3 solution, but was effective in promoting cathodic protection in the neutral solutions in certain conditions. However, the galvanic coupling of NAB displayed significant galvanic corrosion rates of the steels in aerated conditions.
AUTONOMOUS STRUCTURAL LAYOUT AND TOPOLOGY OPTIMIZATION
(University of Hawai'i at Manoa, 2024) Melnichenko, Igor Olegovich; Kobayashi, Marcelo H.; Mechanical Engineering
This thesis utilizes a biology-inspired method for topology optimization in structures. Themethod is adapted from an existing method that utilizes cellular division to generate topology maps for structures. These maps are generated from genomes that are created by a genetic algorithm. Once the topologies are created, they go through sizing optimization and are then evaluated based on their weight. The weight is returned to the genetic algorithm as fitness to optimize the topologies further. This method adds two new features to the optimization process. One of the features is to allow the genetic algorithm to control whether any specific load-bearing substructure within the structure is an I-beam or a truss. The other feature is to let the genetic algorithm also optimize the topology of the truss sub-structure. Optimization runs were performed on a desktop computer with a small population size and then at a supercomputing facility with a larger population. The results of these runs were compared against a baseline design with a conventional topology. Weight reductions of about 4% were achieved.
Development of 3D Printable Ceramic Nano-Paste and Associated Ceramic 3D Printer for Manufacturing and Testing of High-Performance Ceramic Nanocomposites
(University of Hawai'i at Manoa, 2024) Meyer, Liam; Nejhad, Mehrdad; Mechanical Engineering
This thesis presents a comprehensive research on the development of Ceramic Nano-Pastes (CNPs) and their applications in the manufacturing of high-performance ceramic nanocomposite parts via injection molding and 3D printing. A commercially available Liquid Deposition Modeling (LDM) 3D Printer is modified to 3D Print a specially formulated CNP with minimum shrinkage, and surface and internal flaws while maintaining optimal printability. This study also introduces the development of a Laboratory-Scale Roll-to-Roll (R2R) CNP Prepregging System aimed to automate the process of prepregging fiber fabrics. The mechanical properties of parts produced by both the Modified 3D Printer and the Laboratory-Scale Roll-to-Roll (R2R) CNP Prepregging System are assessed using ASTM four-point bending tests for Ceramic Matrix Composites (CMCs) and Continuous Fiber Ceramic Composites (CFCCs), with results benchmarked against traditional manufacturing methods. Results indicate that the Injection Molding and 3D Printing ASTM samples manufactured employing CNPs show comparable and in some cases superior qualities when compared to a part manufactured through Compaction Molding, (i.e., a more traditional method to produce these ceramic composites parts made from similar CNP compositions). Although a 24--meter- long roll of CNP-based prepregged carbon fiber fabric was successfully produced from the automated R2R system, its quality reveals potentials for improvements. The Continuous Fiber Ceramic Composites (CFCCs) derived from this R2R ceramic composite prepreg contained a reduced fiber volume fraction (i.e., a higher matrix volume fraction), due to the oversaturation of the fabric, resulting in lower performance when compared with those made by the traditional manual/hand wet layup technique, indicating rooms for further optimizations to produce parts with improved qualities, properties, and performances.
Development of Carbon-Nanotube based Nanoforest Derivatives for Manufacturing and Testing of Polymer Nanocomposite Prepregs, Film Stacking, and Powder Processing
(University of Hawai'i at Manoa, 2024) Tribble, Connor Kekoa; Ghasemi Nejhad, Mehrdad N.; Mechanical Engineering
An existing Chemical Vapor Deposition (CVD) furnace was modified to include semi-automatic features to provide optimized CVD operation. The process of manufacturing and transferring Carbon Nanotube (CNT) based Nanoforest III (NFIII) for the specific use of high-temperature polymeric polyimide composite Prepregs such as Carbon/RM-1100 and Carbon/AFR-PE-4 prepreg systems has been established and employed in this research to manufacture high-performance composite materials. Several methods were optimized including: substrate preparation, CVD water injection times for best Nanoforest delamination, as well as the best methods and parameters for a hot press for transferring the CNT-based Nanoforest onto carbon fiber prepreg systems, mentioned above. To establish the quality and performance of the manufactured composite parts, ASTM Double Cantilevered Beam (DCB) samples, with and without Nanoforests, were manufactured and tested and found that, for example, the Mode I Opening Fracture Toughness improves between about 30% to 45% for the samples with CNT-based Nanoforests as compared with those without Nanoforest for various materials systems used in this research. Next, several composite panels were manufactured for various ASTM testing to specified dimensions and geometries with and without Nanoforest in between the layers. Finally, a Powder-Processing similar to a Film-Stacking composite manufacturing was established, where BMI (Bismaleimide – another high-temperature polymer) powder processing combined with dry Carbon Fabric, with and without CNT-based Nanoforest grown on the fabrics, was developed, followed by its DCB testing and results.
TECHNO-ECONOMIC ASSESSMENT OF GREEN FUEL PRODUCTION USING RENEWABLE ENERGY
(University of Hawai'i at Manoa, 2024) Soltanifar, Fatemeh; Ghorbani, Reza; Mechanical Engineering
A multi-generation system, driven by photovoltaic panels, is proposed for production of methanol as the green fuel, and CO2 capture at the same time. Using MATLAB software program, the system is analyzed from technical, energy, economic, and environmental points of view to be applied for a residential building complex in Honolulu, Hawaii, the USA. The impact of the fraction of produced H2 from the whole production used for green fuel production (XH2) is studied, and the optimal value of XH2 has been found. After that, the optimal condition is compared with the base case, where no green fuel happens. According to the results, for the whole investigated range for XH2, which covers from 0.20 to 0.50, payback period is in a very good range, increasing from 3.477 to 4.599 years. In addition, according to the conducted parametric study, the best value of XH2 is found 0.40. Using the multi-generation system in the optimal condition is accompanied by a trade-off. One the one hand, as an unfavorable impact, size of system components increases, where payback period goes up from 3.034 to 4.123 years compared to the base case. On the other hand, as benefits, 11.80 tons methanol is produced and 23.19 tons CO2 has been captured in a year. The benefits are accompanied by almost 1 year increase in the payback period, which makes the trade-off with the favor of application of the optimized proposed system. Therefore, the optimized proposed system could be introduced as a totally justifiable system from both economic and environmental aspects.
FACTORIAL INVESTIGATION OF PRESSURIZED SLOW PYROLYSIS FOR CARBONIZATION OF SOLID WASTE
(University of Hawai'i at Manoa, 2024) Castillo, Christian Jayme Agbalog; Turn, Scott Q.; Mechanical Engineering
Many wastes, containing plastics and other materials, in the globe are sent to landfills where they degrade overtime and emit hazardous gases that contribute to greenhouse gases. Military forward operating bases (FOB) have adopted similar waste disposal methods by collecting their waste in burn pits and setting the waste on fire until it burns away completely. However, many soldiers stationed at these FOBs have developed illnesses such as lung cancer which are reportedly linked to these burn pits. Researchers are seeking solutions to manage the effects of waste disposal at military bases. Constant volume carbonization (CVC) and high pressured pyrolysis of biomass, such as wood, have been studied and shown to improve the quality of charcoal from the biomass by reduce its volatile matter and improving its fixed carbon content through pyrolysis. In this study, CVC experiments were conducted on waste materials based on compositions reported in FOBs to determine pyrolysis capabilities in mitigating waste disposal. Co-pyrolysis of polystyrene (PS) with biomass showed potential of devolatilization of plastic through the chemical bonding of the materials. The focused waste materials included dog food, fiber trays, Norwegian birch wood, PS, and rubber. Test variables studied on constant volume waste pyrolysis include reaction time, initial pressure, sandbath temperature, and waste composition to analyze the variable effective. Evaluation of the waste mitigation was done through product yield recovery, proximate analysis of char products, fixed carbon yield determination, derivative thermogravimetric analysis, gas chromatography, and mass spectrometry.

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