Ph.D. - Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10125/2097

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Failure as a design feature: A computational framework for fracture-driven optimization
(University of Hawai'i at Manoa, 2026) Nakamura, Matthew T.; Brown, Joseph J.; Mechanical Engineering
Traditional structural design focuses on preventing fracture, limiting applicability in systems that require controlled, predictable failure. This dissertation developed a dual-physics optimization framework that couples finite element analysis (FEA) with peridynamic fracture simulation to design structures where engineered failure is a primary objective.
Discovering self-assembly properties of patchy particles using inverse design
(University of Hawai'i at Manoa, 2026) Snyder, Gregory Alonzo; Du, Chrisy; Mechanical Engineering
Soft materials, including colloids, polymers, and biological assemblies, exhibit complex self-organizationdriven by weak, highly tunable interactions. Their ability to form structures across length scales makes them central to the study of self-assembly and materials design. Within this class, patchy particles provide a coarse-grained, minimal, and highly tunable model for directional interactions, retaining only essential features, such as building-block geometry and binding specificity. These particles can be engineered to assemble into targets ranging from finite clusters to bulk crystals, spanning synthetic colloids and biological analogs such as viral capsids. Despite this flexibility, the design space is effectively unbounded, yielding a high-dimensional landscape that can be systematically explored using inverse design techniques. Although prior work has developed frameworks for targeted assembly, the interplay between key design parameters remains poorly understood. Here, we address this gap using differentiable molecular dynamics with JAX- MD. We show that the design landscape is governed by structural floppiness, and that stiff and sloppy parameter directions can be identified through Hessian analysis of the full optimization space.
Experimentation and simulation of the evolution of stress in fillet-welded A36 steel patch plates due to crevice corrosion
(University of Hawai'i at Manoa, 2026) Ling, Sonya; Hihara, Lloyd; Mechanical Engineering
Industry has used A36 steel for structural purposes to include buildings, bridges, and structural membrane for tanks because of its material properties (tensile and yield strength), and its machinability and weldability. A36 is a mild, low carbon steel alloy that corrodes when mitigation is not in place and corrosion products can occupy up to five times the volumetric space. This unique characteristic of expansion can become problematic when corrosion occurs in a crevice. For example, industry uses fillet-welded A36 patch plates as repairs to existing material that produces a crevice. When corrosion occurs, the resulting expansion can propagate stress and plastic strains to the weld-plate interface and cause permanent deformation. This can undermine the structural and material integrity of the weld and plate system. The impact is investigated using Finite Elemental Analysis (FEA) to validate and evaluate the corrosion effects on the weld and plate system for defect sizes of ¼, ½, 1-, and 2- inch diameter holes and the effectiveness of Jotun 86, an inorganic zinc silicate corrosion inhibiting coating. This study utilizes data collected through experimental testing through environmental exposure in the presence of corrosive chlorides, for 24 months, and lab exposure testing that replicates prolonged, accelerated periods of time for 300 cycles. A validation test and COMSOL Solid Mechanics FEA was performed to find agreement between the model and the controlled experiment. The model was refined and executed for the experimental plate configurations and the resulting FEA von Mises stress, equivalent plastic strain, and displacement plots were used to determine the effect of crevice corrosion and the effectiveness of the use of a coating. COMSOL was also used to model and simulate the patch plate as the resulting corrosion cell. COMSOL Corrosion Module modeled a thin, 10 µm, and thick, maximum displacement observed ~10 mils (≈254 µm), electrolyte film, and the impact of film thickness on the corrosion potential and current density of the plate and hole sizes were evaluated.
Multiscale nonlinear mechanics optimization for micromechanical interlocking structures
(University of Hawai'i at Manoa, 2026) Heyes, Corrisa; Brown, Joseph J.; Mechanical Engineering
Heterogeneous integration in microelectronics packaging demands attachment methods that accommodate substrate warpage and coefficient-of-thermal-expansion mismatch without the rigidity of solder joints, the high-temperature damage of reflow, or the irreversibility of chemical adhesives. Micromechanical interlocking structures offer structural attachment through geometry rather than chemistry, providing a candidate path to reusable, thermally robust, alignment-tolerant interconnects. Whether any specific μMIS geometry can be designed, fabricated, and deployed to meet these demands at microscale is the question this dissertation addresses. This work develops the framework and experimental infrastructure needed to answer it at stated parameters with quantified confidence.Three independent physical characterizations establish the operating constraints. Measurement-grounded pre-contact adhesion model identifies a 100 nm surface-to-surface separation as the operational boundary below which van der Waals forces become design-governing, setting a geometric requirement on the μMIS engagement surface. Misalignment sensitivity analysis quantifies the insertion force amplification that radial offsets produce in cantilever arrays, producing both a practical alignment tolerance threshold and the lateral load estimate that feeds the structural design budget. Macroscale buckling study identifies process-generated residual stress, rather than insertion force, as the binding structural constraint on prior thin-shell μMIS pillars, motivating the solid-pillar construction that the optimization framework subsequently requires of all candidates. These findings feed a three-level nested optimization framework adapted from the multiscale composition paradigm, in which geometric screening, fabrication regulation, and macroscale-analog performance evaluation pass candidate sets and accumulated scores forward through successive operators with hard-gate reduction and continuous scoring at each level. The framework inputs are grounded by two experimental programs: a large-format microscale fabrication testbed on a multiphoton 3D lithography platform that documents feature-resolution, shape-fidelity, lacing-severity, and inter-structure-spacing limits from a single print run as active constraints on the candidate set; and a macroscale analog characterization of seven geometry families across FDM and SLA campaigns that provides directly measured retention and insertion force data as the Level 3 performance inputs. Applied to 540 specimens across 13 geometry families, the framework converges on a hemisphere-on-pillar geometry at specimen D0500 31 (Rxy = 7.5 μm, Rz = 22.5 μm, pillar diameter 10 μm, pillar height 24.75 μm) with 99.2% robustness across the tested cross-operator weight perturbation space. A class-level microscale realization of the hemisphere family is fabricated on the multiphoton platform, and direct confocal characterization of the as-fabricated structures establishes the geometric transfer fidelity coefficients carried forward into the microscale force density estimate. The dissertation delivers a reproducible, auditable design workflow for μMIS that produces a geometry recommendation at stated parameters with characterized sensitivity, a microscale realization with direct geometric fidelity measurement, and a path forward to close the validation gap this work leaves open. The framework identifies a manufacturable hemisphere geometry whose snap-fit functionality is inferred from macroscale analog measurements through geometric scaling arguments; direct microscale force-displacement characterization remains the principal open question for future work.
Bio-inspired low Reynolds number oscillatory flow for fluid transport, locomotion, and particle detection
(University of Hawai'i at Manoa, 2025) Hayashi, Rintaro; Takagi, Daisuke; Mechanical Engineering
Flows at low Reynolds numbers are dominated by viscosity, governed by the linear and time-reversible Stokes equations. In this regime, actuation and sensing mechanisms that rely on inertial effects lose much of their effectiveness, motivating the development of alternative approaches that instead exploit viscous effects. Understanding physical processes in these environments is important for applications such as microfluidics, where channel dimensions and flow speeds naturally place devices in the Stokes regime, as well as for the design of microscale pumps, swimmers, and sensors. Copepods are small aquatic organisms that effectively generate feeding currents, swim, and detect suspended particles by oscillating their appendages. Drawing inspiration from copepod biomechanics, this dissertation develops minimal models and scaled tabletop experiments that demonstrate flow generation, locomotion, and particle detection in the low Reynolds number regime. First, we demonstrate that asynchronous oscillations of rigid rods generate swirling flow fields and net fluid transport, establishing a minimal system for pumping and mixing in highly viscous environments. Second, we demonstrate low Reynolds number swimming using rigid arms and show that only asynchronous oscillatory motion with distinct orientation angles generates net displacement, which is enhanced near bounding walls. Third, we demonstrate pressure-based imaging of an inert sphere suspended in a highly viscous fluid, enabling object detection and image reconstruction from pressure signals alone. Together, these studies show that simple rigid-body oscillations can achieve flow generation, locomotion, and particle detection at low Reynolds numbers, providing a foundation for studying more complex systems and motivating the design of pumps, swimmers, and sensors for microfluidic and other viscous-flow systems.
Dynamic compressed sensing and coverage optimization for multi-agent systems
(University of Hawai'i at Manoa, 2025) Shriwastav, Sachin; Zhu, Frances; Mechanical Engineering
Sensing is a critical application in most real-life scenarios. Collecting and predicting data of large-scale dynamics quickly using very few sensors is a crucial problem in real-life applications. As we navigate this landscape of sensor-based systems, this dissertation addresses the challenges, intricacies, and details of various critical applications, starting with the pursuit of optimal coverage, robust recovery from sensor loss, and exploring an area of non-uniform coverage importance. The spotlight then shifts to dynamic compressed sensing to replace multiple static sensors with a single mobile robot, examining its applications and extending its principles to multi-robot coordination, exploring an unknown flow environment, and adaptive trajectory optimization to develop the low-rank model of the flow. Two fixed-wing unmanned aerial vehicle (UAV) area coverage algorithms are introduced in Chapters 2 and 3, leveraging their endurance advantages for long-term and large-scale deployment. The homogeneous approach deploys a UAV fleet using hexagon and square packing for continuous coverage, producing resilience against simultaneous multiple node loss. The heterogeneous approach starts with uniform coverage of an arbitrarily shaped area and enables localized and distributed recovery from multiple node failures. Chapter 4 introduces an algorithm that optimizes paths for a mobile robot exploring a target area with nonuniform importance, considering power constraints and limited movement ability at each time step to maximize coverage and net importance reward. While effective, these approaches have substantial data and communication requirements and necessitate a large sensor fleet size for the first two approaches. The core of this thesis, the dynamic compressed sensing (DCS) algorithm, is then introduced in Chapter 5. DCS is an extension of the well-established compressed sensing approach. Optimal sensing locations are identified using the fluid flow field properties to guide the planning of an optimal path for a sensor-equipped autonomous vehicle, replacing the conventional static sensors for efficient reconstruction performance using reduced sampling. The path aims for spatiotemporal efficiency, ensuring the vehicle is at crucial locations during the flow’s temporal cycle. The algorithm uses proper orthogonal decomposition (POD) techniques on known target flow fields to evaluate dataset-specific POD bases, determining when to visit subsets of locations for minimal error. Subsequently, an optimal path for fuel and time is devised for the vehicle to autonomously visit these locations at specified points in the flow cycle to capture the desired information. The multi-agent coordination dynamic compressed sensing (MAC-DCS) to explore unknown environments using a fleet of mobile robots and develop the low-rank model of the flow is discussed in Chapter 6. MAC-DCS compares various sensor deployment methods (random static, compressed sensing static, passive drifters, and random straight shooting trajectories) and reconstruction techniques (Gaussian process regression, data-based and true POD modes) for flow field estimation in a double-gyre environment to study the effect of dividing the spatiotemporal sensing load amongst the varying fleet size of static sensors or mobile robots. The simulations are extended to a real-world scale with measurement noise, and other practicalities, such as the effect of background flow, are considered to assess the efficacy of the MAC-DCS approach. This research offers a scalable solution for dynamic environmental monitoring. This applies to various scenarios, including well-studied flow fields like ocean gyres and currents and less-explored phenomena such as lava flows, floods, hurricanes, and more. MAC-DCS can significantly enhance the capabilities of data-driven sensing and modeling in fluid dynamics and atmospheric science. The preliminary results of a potential extension of this work, online dynamic compressed sensing (Online DCS), are introduced in future work (Chapter 7). Online DCS is a dynamic flow field sampling algorithm that employs static sensors and a mobile robot for collaborative measurements for low-rank model development in an unknown flow environment. The static sensors provide infinite temporal resolution measurements, and the mobile robot enhances spatial coverage through trajectories divided into fixed-interval segments, followed by an iterative predict-measure cycle. After each segment, the collected data modifies the low-rank flow model basis. The next robot waypoint is determined, and the prediction cycle uses the low-rank basis to forecast flow maps for the upcoming segment. Convergence is characterized by the narrowing progressive error, and iterations are terminated at a specified error threshold. The low-rank model identifies the flow behavior and potentially the underlying mathematical framework. The key contributions of this dissertation work include (i) resilient coverage algorithms to recover from simultaneous multiple node failures, (ii) optimal trajectory optimization for exploring an area of non-uniform coverage importance, (iii) optimized sensing locations for the DCS algorithm, prioritizing mobile robot visits over static sensors, (iv) time and energy optimal trajectory for efficient flow reconstruction, (v) MAC-DCS and Online DCS algorithms for developing the low-rank model of an unknown flow, and crucially, (v) collaborative coordination of sensor fleet for enhanced efficiency and application range.
Tendon-driven notched needle manipulation, guidance, and modeling in soft tissue under real-time ultrasound tracking
(University of Hawai'i at Manoa, 2025) Padasdao, Blayton Kenji; Konh, Bardia; Mechanical Engineering
Today, several medical diagnosis and therapeutic cancer interventions are performed using needles via percutaneous surgical procedures. The success of these procedures highly depends on the accurate placement of the needle tip at target positions. Improving targeting accuracy necessitates improvements in medical imaging and needle steering techniques. The former provides an improved vision on the target (i.e., cancerous tissue) and the needle, while the latter enables an enhanced interventional tool. In spite of considerable advancements in the medical imaging field, the structure of the needle itself has remained unchanged. In the past decade, research works have suggested passive or active navigation of the needle inside the tissue to improve targeting accuracy. In addition, to provide actuation and control for needle steering, an active needle has been introduced that’s actuated by internal tendons. This work is the culmination of studies involving the robot-assisted tracking system to (i) estimate the 3D shape of the active needle inside phantom tissue using 2D transverse ultrasound imaging, (ii) predict the 3D needle shape for real-time tracking, (iii) steer the active needle for patients with pubic arch interference, (iv) estimate tissue movement during an active needle insertion task, (v) model and control for bidirectional manipulation, (vi) perform a systematic 12-core transperineal prostate biopsy with minimal active needle insertions to avoid puncturing organs-at-risk, (vii) develop a mechanics-based model for needle-tissue interactions and (viii) autonomous control of the needle utilizing MRI-conditional parts.
Chemotactic behavior for a self-phoretic janus particle near a patch source of fuel
(University of Hawai'i at Manoa, 2025) Mancuso, Viviana; Uspal, William E.; Mechanical Engineering
Many biological microswimmers are capable of chemotaxis, i.e., they can sense an ambient chemical gradient and adjust their motility mechanism to move towards or away from the source of the gradient. Synthetic active colloids endowed with chemotactic behavior hold considerable promise for targeted drug delivery and the realization of programmable and reconfigurable materials. Here, we study the chemotactic behavior of a Janus particle, which converts "fuel" molecules, released at an axisymmetric chemical patch located on a planar wall, into "product" molecules at its catalytic cap and moves by self-phoresis induced by the product. The chemotactic behavior is characterized as a function of the interplay between the rates of release (at the patch) and the consumption (at the particle) of fuel, as well as of details of the phoretic response of the particle (i.e., its phoretic mobility). Among others, we find that, under certain conditions, the particle is attracted to a stable "hovering state" in which it aligns its axis normal to the wall and rests (positions itself) at an activity-dependent distance above the center of the patch.
THIN FILM GAS ADSORPTION MEASUREMENT AND CONTROL
(University of Hawai'i at Manoa, 2024) Pham, Thi Kieu Ngan; Brown, Joseph; Mechanical Engineering
The science of interfaces investigates the intermediation among distinctly different phases, enabling the observation of many intriguing phenomena spanning scales from micrometers, nanometers, and even to the sub-atomic level. The interaction of gaseous molecules with solid surfaces underlies efforts in understanding and engineering the adsorption and permeation of gaseous molecules through outer layer(s) of solid phase materials for the applications of sensing, storing, filtering, etc. This knowledge underlies today’s robust growth of core industrial technologies such as batteries for electric vehicles, hydrogen storage as a source of clean energy, gas sensing for wearable devices and safety purposes, and gas filter membranes. In this dissertation, we expand the use of a well-known gravimetric detection device with high sensitivity – the Quartz Crystal Microbalance – to detailed examination of the gas-solid interface during physisorption. The first project presented in this dissertation (Chapter 1): Design of an environmental chamber for gas adsorption detection with Quartz Crystal Microbalance, helps create a well-controlled and stable environment around the Quartz Crystal Microbalance as the adsorption experiment takes place. The chamber’s temperature, pressure, in and out flows were controlled and thermodynamic information of the cyclohexane adsorption on gold surface of QCM was successfully collected. This ensures the feasibility of the environmental chamber encapsulating the QCM for different gas adsorption experiment conditions. The understanding of gaseous molecule interaction with thin film was elaborated and analytically represented through the second work (Chapter 2): (II) Analytical study of H2 adsorption on MgB2 thin film. This work focused on H2 adsorption on MgB2 because MgB2 is a prominent hydrogen storage material listed by Department of Energy, with interesting its metallic-like and layered structure are interesting to look into. A parallel effort of chapter 2 is the third project (Chapter 3): (III) Develop an ultrathin v film of MgB2 on QCM surface. This project serves as a crucial step for consequential hydrogen adsorption on MgB2 which is to transfer the MgB2 film onto the QCM surface. Dip coating of MgB2 in co-solvent proved to provide an ultra-thin film of 5 nm of MgB2 on QCM surface with negligible coffee ring effect. The final project is presented in Chapter 4: (IV) Study of film conductivity change at gaseous partial pressure variation. This effort demonstrated joint operation of electrical conductivity and gravimetric measurements within the QCM environmental chamber, thereby observing a unique resistivity effect dependent on film composition and adsorption state. The changes of Au and AuPd thin film resistivity were evaluated under exposure to ethanol and cyclohexane vapors. A significantly larger change in sheet resistance of ethanol adsorption on AuPd, as compared with sheet resistance change of ethanol adsorption on Au or Pd films alone, emphasized the synergistic effect of bimetallic AuPd. Overall, this dissertation provides a comprehensive experimental and analytical foundation for characterization of sensing and adsorbing materials. This dissertation prepared the fundamental theory and experimental techniques for study of adsorption enhancement through external electric field effects, but detailed study of this topic remains future work. Further interfacing design is needed; first, continuity testing must be achieved for sequential gas adsorption experiments. The collective goal of the following research projects, presented below in this report, has been to demonstrate and test the capabilities of quartz crystal microbalance apparatus as a high-productivity experimental platform in gas adsorption on thin films, through use of the QCM test platform to deepen the understanding of surface science as gaseous molecules interact with thin solid films.
Using Battery Energy Storage Systems to Address the Needs of Different Types of Grid Participants
(University of Hawai'i at Manoa, 2024) Angelo, Michael S.; Ghorbani, Reza; Mechanical Engineering
This work presents two research contributions, which are then applied to two use cases to demonstrate their efficacy in identifying opportunities for battery energy storage (BES) systems. The first contribution is a modified version of the Hilbert Huang Transform (HHT) signal processing technique, which proposes a new stoppage criterion to help mitigate the impacts of the emergence of end effects within the analysis of the intermodal functions (IMFs) to provide greater assurance that any identified IMFs are meaningful, and proposes statistical analysis, rather than the typically used marginal Hilbert spectrum, to characterize variability in time-series energy data. The modified HHT analysis is used to identify locations where there is high variability in net energy flows on the interties between balancing authorities (BAs) directly interconnected with the California Independent System Operator (CAISO) to help down-select to find individual tie points where large amounts of generation are interconnected with large amount of load. The second contribution presents a novel methodology for modelling the optimal charging and dispatch of BES systems on the grid. The methodology is unique in that it sets up the optimization as a type of scheduling problem that can be solved quickly without the need for complex and often times costly optimization software while also accounting for modelled generation, charging the BES from both the grid and on-site generation, and negative electricity prices. The model can be applied anywhere there is information on future prices for grid services that can be delivered by a BES system and can be used with actual forecasted pricing values or expected pricing based on probability models. In this work, the charging / dispatch methodology for the BES system is used to determine the optimal size of BES system with a two-part optimization that consists of a financial model that estimates the capacities of the BES system devices that maximize net present value (NPV). The methods developed in this work can support grid operators’ long-term grid planning efforts and operational reliability models because they help identify locations where BES systems have the potential to enhance grid reliability. They can also be used to assists grid planners, operators, IPPs, and utility customers by providing insight into how IPPs and utility customers are financially incentivized to size and operate their BES systems. This work found that, among BAs directly intertied with the CAISO, historically, the highest variability in energy flows occurs between the CAISO and Los Angeles Department of Water and Power (LDWP). For those BAs, the highest transfer in energy was into LDWP from the CAISO through the Sylmar switching station. Further investigation indicated reliability concerns and the need for additional energy flows and capacity to deliver energy at the evening peak. The charging / dispatch model for the BES system with the financial model this work determined that, in most cases and project financing structures, a 1-hr BES with varying amount of solar generation is economically incentivized depending on project costs and financing structure.
THERMAL TRANSPORT IN POLYMER NANOFIBER AND POLYMER NANOCOMPOSITES
(University of Hawai'i at Manoa, 2025) Nguyen, Anh Tuan; Lee, Woochul; Mechanical Engineering
Effective thermal management plays a vital role in the development of electronic devices as it directly affects the devices’ lifetime, performance, and reliability. As electronic devices are more miniaturized and integrated, heat dissipation in these devices becomes more challenging. Among many materials systems, polymers have been shown to be a potential candidate due to their excellent properties, including light weight, low cost, easy to manufacture, and excellent chemical stability. However, intrinsic thermal conductivity of polymer is relatively low and not sufficient. Thus, enhancing thermal conductivity of polymer is crucial for expanding polymers applications in thermal field. In this dissertation, I present various methods to enhance thermal conductivity of polymer-based materials. In the first method, intrinsic thermal conductivity of polyethylene oxide (PEO) polymer is enhanced by engineering the internal structures. Specifically, the effect of PEO molecular weight and molecular concentration on the thermal conductivity of PEO nanofiber is investigated. In the second method, thermal conductivity is increased by creating polymer nanocomposites with the addition of thermally conductive fillers. Here, I present the fabrication of polymer nanocomposites from epoxy and boron nitride nanotube (BNNT) filler. The surface of BNNT is functionalized to improve its dispersion in the epoxy matrix. The effect of interface between functionalized BNNT and polymer matrix to the thermal conductivity of polymer nanocomposites is discussed. The results from our study could contribute to the application expansion of polymer-based materials where high thermal conductivity is required such as electronic packaging and thermal interface materials. Further, this work can be served as guidance for investigating thermal transport of other polymers and polymer nanocomposites systems.
SYNTHETIC VOLTAGE DATASETS FOR ARTIFICIAL INTELLIGENCE-BASED LI-ION DIAGNOSIS AND PROGNOSIS: INVESTIGATION OF THREE DIFFERENT BLENDING CONDITIONS
(University of Hawai'i at Manoa, 2024) Beck, David; Dubarry, Matthieu MD; Mechanical Engineering
Lithium-ion batteries are a cornerstone of modern energy storage systems and play a crucial role in the transition towards a sustainable energy future. Their performance and longevity are impacted by various parameters such as composition, architecture, environment, and degradation mechanisms. In addition, the degradation might not be uniformly distributed across the components of the battery, leading to inhomogeneities.This research delves into the effect of three specific blending conditions on the voltage response of lithium-ion batteries: active material blends, lithium plating, and inhomogeneous degradation. This aspect is key as the voltage response of a cell is used for conducting diagnoses and prognoses. By integrating experimental data with simulations from the alawa model, we aim to enhance our understanding of battery behavior, particularly focusing on effects these blending conditions have on the overall voltage response. Through experimental tests, we have gained an understanding of the observable effects, ultimately aiming to improve state of the art battery models to make them more accurate for generating synthetic data. The latter is essential to properly validate battery diagnosis and prognosis methodologies.
Biophysical Study Of Tear Film Lipid Layer
(University of Hawaii at Manoa, 2023) Xu, Xiaojie; Zuo, Yi; Mechanical Engineering
Tear film lipid layer (TFLL) is the outmost layer of the tear film. The current consensus is that the 40-nm thick TFLL consists of two sublayers, i.e., a polar lipid layer covering the air-water surface of the cornea, and a nonpolar lipid layer that resides upon the polar lipids and is directly exposed to air. The polar lipids account for 20 mol% of the TFLL, including ~ 12 mol% phospholipids, and ~ 4 mol% (O-acyl)-ω-hydroxy fatty acids (OAHFAs), which belongs to a newly discovered class of endogenous lipids termed fatty acid esters of hydroxy fatty acids (FAHFAs). The nonpolar lipids account for 80 mol% of the TFLL, with wax esters (WEs, accounting for ~ 43 mol%) and cholesteryl esters (CEs, accounting for ~39 mol%) being the most prevalent nonpolar lipid classes. The major physiological function of the TFLL is to stabilize the tear film by reducing surface tension and retarding evaporation of the aqueous layer. Dysfunction of the TFLL leads to dysfunctional tear syndrome, with the dry eye disease (DED) being the most prevalent eye disease affecting 10-30% of the world population. It is estimated that the DED directly and indirectly causes a $55 billion annual economic burden in the United States alone. To date, except for treatments alleviating the dry eye symptoms, effective therapeutic interventions in treating the DED are still lacking. Therefore, there is an urgent need to better understand the biophysical function of the TFLL and to develop translational solutions in effectively managing the DED. The focus of this dissertation is to study biophysical properties of the TFLL using a newly developed experimental methodology called constrained drop surfactometry (CDS). Main contributions fell into the following four headings: 1. Study of the composition-functional correlations of a model TFLL, under physiologically relevant conditions. For the first time, this study unveiled that the primary biophysical function of FAHFAs is to optimize the interfacial rheological properties of the TFLL. 2. Study of the polymorphism and collapse mechanism of FAHFA monolayers. This study revealed that FAHFA molecules at the air-water surface demonstrate unique polymorphic behaviors, which can be explained by configurational transitions of the molecules under various lateral pressures. 3. Development of a novel ventilated, closed-chamber, droplet evaporimeter with a constant surface area. This droplet-based evaporimeter is capable of a rigorous control of environmental conditions, including the temperature, relative humidity, airflow rate, surface area, and surface pressure, thus allowing for reproducible water evaporation measurements over a time period of only 5 minutes. The volumetric evaporation rate of this droplet evaporimeter is less than 2.7 μL/min, comparable to the basal tear production of healthy adults. This study demonstrated that the TFLL resists water evaporation with a combined mechanism by increasing film compactness of the polar lipid film at the air-water surface, and, to a lesser extent, by increasing film thickness of the nonpolar lipid film. 4. Comparative study of the dynamic surface activity, interfacial rheology, evaporation resistance, and ultrastructure of the meibomian lipid films extracted from wild type (WT) and Soat1 knockout (KO) mice. Inactivation of Soat1 gene led to a complete stoppage of CE production in meibomian glands and a severe change in the eye phenotype in experimental animals. Lipidomic analysis with ultrahigh-pressure liquid chromatography ̶ mass spectrometry showed that the pool of cholesterol rose seven times in the KO mice compared with their WT siblings, and, an almost complete ablation of CEs longer than C18-C20 was observed. This study revealed novel experimental evidence about the composition-structure-functional correlations of the meibomian lipid films. Overall, research in this dissertation advanced the biophysical understanding of the TFLL, and provided novel implications in the pathophysiological and translational understanding of DED.
Analytical and numerical studies of the effect of shape on microswimmer propulsion
(University of Hawaii at Manoa, 2023) Poehnl, Ruben; Uspal, William E.; Mechanical Engineering
The shape of an active colloid has an enormous effect on the motion of the particle and allows for significantly more variation in its design and application. In this thesis, the dynamics of both convex (spheroidal) and concave (helical and toroidal) particles are investigated with analytical and numerical methods. Starting with an individual particle, it is shown that breaking symmetries of the particle shape can enlarge the possibilities for particle motion, both for self-diffusiophoretic microswimmers and within the more general ``squirmer model''. These results are then extended to include pair interactions. For interacting spheroids, two types of stable pair configurations can exist: co-moving "head-to-tail`` and stationary "head-to-head" pairs. We also consider the interaction of a torus and sphere, with a view towards designing "lock-and-key" interactions.
Renewable Energy Trading in Real Time Using Simulated Clients and Energy Markets
(University of Hawaii at Manoa, 2023) Sariri, Shawyun; Ghorbani, Reza; Mechanical Engineering
Renewable energy has long been seen as a way to alleviate reliance on fossil fuels, this has become even more imperative as the frequency of natural disasters has increased, and the consequences of climate change have become more abundant. However, renewable integration is not a straightforward process as many factors, such as geography, resource availability, cost, legislation, climate, and the stochastic nature of renewables play a factor in what sources can be utilized and in what quantities. Regions cannot go to 100% renewables overnight; a more realistic approach would be to blend already existing grid infrastructure with sustainable energy sources. Because the current grid infrastructure was not initially designed to handle renewable integration, it is important to understand how sustainable sources can work with existing infrastructure. This research proposes a potential testbed to study the effects of how homes can become prosumers to not only lower costs and integrate renewable energy, but to also provide resilience to the power grid. A real-time model is examined to show the potential for a home to produce and sell energy in the current grid as well as how this idea can be integrated into the current grid infrastructure. In addition, a renewable energy marketplace is explored to understand how energy vendors and consumers can interact in real time.
Soft, Epidermal Systems for Clinical Diagnostics
(University of Hawaii at Manoa, 2023) Wu, Chung-Han; Ray, Tyler R.; Mechanical Engineering
Advancements in digital health and manufacturing technologies have enabled the development of wearable systems that can monitor various physiological parameters and biomarkers in a non-invasive and comfortable way. Through the integration of soft, flexible materials, these systems can be seamlessly deployed on the skin, allowing for imperceptible and comfortable monitoring of health conditions. This paper presents several novel strategies and has led to significant advancements in the development of soft, epidermal systems.One novel contribution of this work is the use of skin-interfaced wearable systems with integrated microfluidic structures and sensing capabilities for sweat monitoring from natural physiological processes. The introduction of 3D printing has also established a unique class of epidermal microfluidic devices, such as the 'sweatainer', which facilitates the chronological collection of multiple independent sweat samples during on-body field tests with a true 3D design space for microfluidics that is inaccessible to most commercially available 3D printing machines. The development of a wearable patch-like sensor containing the accelerometer, gyroscope, and optical Photoplethysmography (PPG) sensing modules has also been shown to be a significant contribution, allowing for the 'Always-On' Imperceptible Monitoring (AIM) of heart rate. This sensor can be worn on multiple body locations, including the forearm, shank, and sacrum which are seldom discussed, and enables accurate HR estimation during a variety of intense physical activities. PPG-based heart rate algorithms containing multiple levels of motion artifact correction are also presented, using complementary motion data to minimize the effects of motion artifacts in 1-hour cyclical activities. The results demonstrate an improvement in HR estimation over commercial devices such as the Apple Watch, and set the foundation for advancing remote monitoring of physiology and activity. Overall, this research has shown that the recent advancements in digital health and manufacturing technologies have led to the development of non-invasive, comfortable, imperceptible, and wireless soft, epidermal systems that can monitor various physiological parameters and sweat biomarkers. The use of these systems has led to the collection of biometric information such as heart rate, sweat, and body motion data from healthy adults and patients undergoing cardiac rehabilitation, offering new insights into fatigue study and patient recovery assessment. This research has revealed novel insights and perspectives on the potential applications of soft, epidermal systems in medical and fitness-related domains. These findings underscore the significance of continued research in medical and fitness-related fields to further explore the capabilities and possibilities of such soft, epidermal systems.
Laboratory and Computational Study on Galvanic and Local Corrosion of Aluminum Alloy 6061-T6 Coupled to Non-Passivating and Passivating Alloys
(University of Hawaii at Manoa, 2022) Wohner, Natalie Yvonne Danielle; Hihara, Lloyd H.; Mechanical Engineering
Corrosion of Aluminum Alloy (AA) 6061-T6 coupled to non-passivating and passivating alloys was studied concerning galvanic effects on local corrosion. In this work, local and galvanic corrosion was quantified, the effects of cathode material on local electrolyte pH were explored, and a relationship between pH and self-corrosion of AA6061-T6 was established. In addition, a finite element thin film model for simulating the galvanic corrosion of Aluminum Alloys based on pH-dependent corrosion kinetics was developed to show trends in corrosion rates for acidic electrolytes. Marine and aerospace structures often combine lightweight aluminum alloys with dissimilar metals to optimize mechanical performance and reduce costs. Unfortunately, the exposure of such dissimilar couples in a harsh environment can cause severe corrosion damage to the aluminum structure due to its position in the galvanic series. Atmospheric field tests are typically performed to estimate the performance of galvanic couples in natural environments; however, these tests are time-consuming and costly. In addition, field tests only provide limited insights into the accelerated, localized corrosion damage to aluminum alloys when coupled to dissimilar metals. Computational modeling offers a complementary approach to studying the corrosion behavior of galvanic couples at a lower cost and an enhanced understanding of localized corrosion. Experimental and numerical studies quantified galvanic corrosion of AA6061-T6 coupled to 316 stainless steel, copper, titanium alloy Ti6Al4V, and 316 stainless steel coated with titanium nitride, chromium nitride, and a sol-gel nano-coating. To validate the thin film model, numerical results were compared with laboratory tests of galvanic couples exposed for 21 days in a controlled environment at 90% relative humidity and 30◦C. Galvanic currents were measured during the exposure time, and the aluminum alloy’s total mass loss was determined to quantify the corrosion damage. Exposure tests showed that galvanic corrosion accounts for less than 15% of the total corrosion of AA6061-T6 and that most aluminum corrosion damage was caused by local corrosion. In addition, immersion experiments of AA6061-T6 galvaniccouples in gelled 3.15 wt.% NaCl solutions showed that galvanic coupling influences the evolution of electrolyte pH leading to severe acidification at the aluminum anode surface and alkalization around the cathode. The solution pH at the aluminum surface was decreased by galvanic action and depended on galvanic couple materials and design. To quantify the effect of acidity on self-corrosion of AA6061-T6, potentiodynamic polarization tests were performed in aerated and deaerated 3.15 wt.% NaCl solution adjusted to different pH. Anodic dissolution reactions and cathodic oxygen reduction reactions show significantly higher anodic and cathodic currents for more acidic solutions due to the instability of the passive oxide film of aluminum. This film is stable in near-neutral solutions and unstable in highly acidic solutions. As a result, the breakdown of the passive film increases the effective area contributing to anodic or cathodic currents. Observations from experimental work were implemented into the finite element thin film model using COMSOL Multiphysics to predict the self-corrosion and galvanic interaction of aluminum alloy AA6061-T6 coupled to noble metals in severe marine environments. The model results show galvanic interaction accounts for most corrosion in neutral pH. However, in acidic solutions, the corrosion of aluminum is mainly caused by local corrosion, which results in accelerated corrosion rates. The numerical result agrees with our experimental findings and underlines the importance of accounting for local corrosion when predicting the galvanic compatibility of aluminum alloys.
Experimental Analysis and Finite Element Modeling of the Lateral Friction Surfacing Process
(University of Hawaii at Manoa, 2022) Seidi, Ebrahim; Miller, Scott F.; Mechanical Engineering
Lateral friction surfacing is a novel method of friction surfacing for solid-state metal deposition, in which the radial surface of the rotating consumable tool is forced into the substrate surface, facilitating material transfer. Frictional heat enables plastic deformation, which results in depositing the consumable material on the substrate surface, and a layer of tool material is transferred from the consumable rod to the substrate surface as the tool moves across. The process is carried out at temperatures below the melting point of the consumable material, resulting in a solid-state deposition process. In this method, there is no external source of heat energy, and all the heat energy required in this method is generated by friction. This technique is an excellent alternative to creating thin and ultra-smooth metallic deposit layers for repairing damaged surfaces or improving corrosion and wear resistance. Also, there is no flash formed in this technique which reduces material consumption.In this study, a comprehensive assessment through conducting real-time force measurement, surface roughness measurement, hardness testing, corrosion performance analysis, optical microscopy, infrared thermography, scanning electron microscopy, and energy-dispersive X-ray spectroscopy was performed to characterize the lateral friction surfacing of various materials. Furthermore, the LFS process was investigated via thermo-mechanical modeling using ABAQUS software to analyze the mechanical and thermal responses. In order to evaluate the model, an experimental study using the same materials and process parameters was conducted. The results showed that the lateral friction surfacing approach is capable of producing coating layers with complete coverage, roughness values of less than 1 µm, and coating thickness values as low as 16 µm. Furthermore, this technique results in a deposition process with lower generated process temperatures than conventional friction surfacing, which mitigates the thermal impacts on the microstructures, mechanical properties, and metallurgical characteristics of the deposits. The finite element modeling proved that this novel technique generates low process temperature localized in a small area, and the temperature rapidly decreases as the distance from the processing zone slightly increases. The quality of the fabricated deposits was found to be dependent on several important process parameters such as pressing force, table traverse speed, spindle speed, and tool/substrate materials. Therefore, these parameters can be utilized as the controlling process parameters to achieve the desired quality. This study revealed that high input energy provided by high normal forces and tool rotational speeds might result in failure in the deposition process of materials with lower thermal conductivity and melting point, which emphasizes on limitations for the process parameters during the process. On the other hand, increasing the input energy by adopting higher forces and rotational speeds may lead to deposition of materials with higher melting points. The cross-sections SEM analysis of various deposits was conducted, and results exhibited a clear interface without any unbonded regions between deposits of some materials such as AA2011 and AA6061 and the steel substrate; however, cracks and unbonded regions at the interface of AA7075 deposit and steel substrate were observed. Moreover, the SEM results revealed no elemental diffusion of consumable materials to the substrate, which indicates that the LFS process temperature was low enough to avoid plasticizing the substrate and intermixing between the consumable material and substrate. The EDS analysis showed that excess Si in the plasticized consumable material results in large Si-rich particles forming in the deposition of different aluminum alloys, such as AA6061 and AA6063. Moreover, the EDS analysis revealed the presence of a large amount of Fe in most of the coatings fabricated on steel substrates, indicating that the substrate material was rubbed off during the LFS process due to high tool speed and force at the tool/substrate interface, and the substrate material was transferred to the deposits. Furthermore, the multilayer deposition of AA6061 onto AISI 1018 through the lateral friction surfacing process was performed to assess the potential application of this technique for fabricating multilayer deposits and additive manufacturing purposes. The multi-pass deposition of AA6061 through LFS did not result in a trend of increasing coating thickness due to the formation of a reverse material transferring process from the coating to the radial surface of the rod.
Shape Memory Alloy Actuator Control For 3D Steering Of Active Surgical Needle In Minimal Invasive Surgeries
(University of Hawaii at Manoa, 2021) Karimi, Saeed; Konh, Bardia; Mechanical Engineering
Minimally Invasive Surgery (MIS) is defined as a surgical procedure that is associated with lower postoperative patient’s morbidity, compared to the conventional approach for the same diagnostic/therapeutic operation. Minimally invasive percutaneous interventional procedures for diagnostics and therapeutics are practiced in a variety of medical procedures such as brachytherapy, biopsy, and thermal ablation. The clinical outcome in such procedures is subjected to precise navigation and accurate placement of the needle at specific target locations within the soft tissue. Active needle steering increases the target placement accuracy, and consequently improves the clinical outcome. In this work, a 3D steerable active flexible needle with multiple interacting Shape Memory Alloy (SMA)-wire actuators is introduced. A self-sensing resistive-based feedback loop control system was designed and implemented to control the SMA’s actuation. The needle tip position was controlled through the feedback loop control system using the electrical resistance measurements of the SMA-wire actuators. Concomitant actuation and sensing capabilities of SMAs were used in the control system to realize a desired 3D motion at the needle tip. The controller was then tested on a 1:4 scaled prototype of the active needle for reference path tracking. This work demonstrates the 3D steerable active needle manipulation via precision control of interacting SMA-wire actuators.
Analytical Spacecraft Trajectory Optimization
(University of Hawaii at Manoa, 2021) Morrison-Fogel, Dylan Nevada; Azimov, Dilmurat; Mechanical Engineering
This monograph examines the problem of trajectory optimization for spacecraft operating within a Newtonian field. Background information of the problem formulation is provided, including the overall investigation objective. A survey of previous works is provided with regards to optimization by means of indirect and direct methods. A formulation of spacecraft equations of motion is provided following definitions of applicable coordinate systems. Specific methods of optimization are conferred in their numerical form, with most attention given to shooting methods for the reason that it was the dominant method used to obtain research results. Direct optimization through collocation is addressed in terms of Runge-Kutta and trapezoidal methods. The document further addresses the conditions of optimality in numerical form, discussing formulation of a performance index for optimality and then classifying applicable conditions of optimality into either first-order or higher-order. Trajectories constructed are either coplanar, in polar coordinates, or non-coplanar, in spatial (spherical) coordinates. Planar maneuvers are designed by first applying optimality conditions to properly formulate equations of motion and costate equations. The two-point boundary value problem resulting from this methodology is solved for the specific cases of constant thrust, switching thrust (also known as bang-off-bang), and variable specific impulse using numerical methods. Problem types in which singular arcs may occur are addressed using Intermediate Thrust arc segments in the form of Lawden Spirals, for which explicit analytical solutions are derived. Intermediate Thrust trajectories are performed using one, two, or three intermediate thrust arcs, contributing various levels of initial or final orbit definition between elliptical Keplerian orbits. In addition to juxtaposition of performance throughout the various trajectory designs, existence of viable solutions in the case of three Intermediate Thrust arc segments is derived in terms of compulsory terminal orbit conditions. Spatial maneuvers are considered for continuous thrust and Intermediate Thrust trajectories between non-coplanar elliptical orbits following a similar optimality conditions application as that of planar maneuvers. Equations of spacecraft motion are defined and costate equations derived in addition to first integrals of the system and invariant relations. Mass-flow rate of a free time horizon Intermediate Thrust arc is obtained through invariant relations, expressed as a function of current state and Lagrange multipliers. Fuel efficiency of trajectories for non-coplanar maneuvers are compared for the constant thrust and Intermediate Thrust cases, as well as to a case of direct optimization methods. Additionally, an amelioration to Lawden Spirals is offered through formulation of explicit state expressions for Intermediate Thrust arcs of non-coplanar operations.

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