Ph.D. - Mechanical Engineering

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

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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.
Autonomous and Integrated Guidance, Navigation, and Control System for Fuel-optimal Atmospheric Entry, Descent, and Landing Maneuver
(University of Hawaii at Manoa, 2021) Jo, Minji; Azimov, Dilmurat; Mechanical Engineering
In the history of mankind, observation and exploration of the universe have been continuously developed, and the curiosity of mankind about the unknown world will not cease. We have been sending exploration vehicles to an unknown planet beyond just looking, and we are looking forward to manned Mars landing probes like human-crewed lunar landings. It is essential to develop the entry, descent, and landing (EDL) system with autonomous capabilities to realize this. Therefore, the autonomous and integrated guidance, navigation, and control (GNC) system for fuel-optimal atmospheric EDL maneuver is designed, developed, and proposed in this study. The challenges facing the EDL system development are associated with increased landed mass capability, improved landed accuracy, and landing at the desired altitude. Also, to safely land on Mars' surface, the kinetic energy of the lander must be used up perfectly and safely. However, Mars' atmosphere imposes difficulties for a safe landing. A fuel-optimal trajectory must be developed, and the desired altitude and velocity at the landing site with consideration of Mars' atmosphere characteristics must be achieved to overcome these difficulties. For this, in this study, semi-analytical solutions to the optimal control problem for 3-dimensional fuel-efficient planetary landing trajectories with constant exhaust velocity and limited mass-flow rate in a drag-existing central Newtonian field are presented. The first-order optimality conditions reduce the problem to a Hamiltonian canonical system to design and synthesize feasible and extremal planetary EDL trajectories. The proposed solutions allow us to describe the state vector and Lagrange multipliers in terms of time and characteristics of switching function to determine the number and sequence of thrust arcs. These solutions describe new extremal trajectories based on the analysis of first- and second-order optimality conditions. The results of this work can be used to support mission design analysis and synthesis of fuel-efficient trajectories. For the autonomous capability, the GNC system was integrated with the proposed EDL trajectories. An extended Kalman filter (EKF) was applied to estimate the position and velocity components as the navigation solutions, and these estimated components were used to the E-guidance as the guidance solutions. Therefore, the feasibility of the autonomous and integrated GNC system for the proposed EDL maneuver was demonstrated. These solutions can be adjusted for maneuvers near other celestial bodies for which a central gravitational acceleration can be dominant. Also, the results of this work can be used to support mission design analysis, and the next generation of missions aim to perform autonomous and precision landing maneuvers, which impose significant challenges on the development of lander's autonomous control and guidance systems.
Integrated Targeting, Guidance, Navigation, and Control for Unmanned Aerial Vehicles
(University of Hawaii at Manoa, 2020) Kawamura, Evan; Azimov, Dilmurat; Mechanical Engineering
The goal of this dissertation research is to demonstrate the integration of targeting, guidance, navigation, and control (TGNC) functions for real-time implementation onboard unmanned aerial vehicles (UAVs) for a wide range of applications. This allows us to create a robust and accurate integrated TGNC software platform for UAVs, which enables them with real-time capabilities and leverages the flight autonomy. Target-relative guidance, real-time targeting and re-targeting capabilities are of great interest in today's UAV technology. This research proposes new guidance and estimation methods as well as new extremal control laws for UAV applications. In particular, this research focuses on quadcopter applications. The proposed guidance methods represent an extension of the existing explicit translational guidance (E-guidance) to include rotational guidance and exponential braking guidance to reach target points. The proposed estimation method is a hierarchical mixture of experts (HME) framework with extended Kalman filters (EKFs) and a modified softmax function to provide state and parameter estimations for navigation solutions. The proposed research utilizes the Hamiltonian formalism with the indirect method to solve the optimal control problem, which replaces existing PID control laws with extremal control laws based on first-order optimality conditions. Three illustrative examples demonstrate integration of targeting, guidance, and control functions for takeoff, waypoint, and roll maneuvers of quadcopters. It is shown that the proposed HME framework with acoustic parameters demonstrates a viable navigation solution. Implementation of the TGNC functions through the proposed HME, target-relative guidance, and extremal control with simulated acoustic parameter measurements demonstrates a completely integrated TGNC software system for quadcopters. Novelties of the proposed research include extension of E guidance, simulating an exponential braking guidance law to reach a target point, determination of the switching function for max-intermediate thrust arcs, and design and validation of a HME framework to provide navigation solutions. The proposed research results can be used to address environmental and agricultural problems that utilize UAVs. This research has been funded, in part, by the NASA EPSCoR ACTUAS (Autonomous Control Theory - Unmanned Aerial Systems) project. The core research contributions are deriving E Guidance for rotational maneuvers extending E Guidance to higher order integration methods, integrating E Guidance with extremal control satisfies the boundary conditions to yield an extremal for the guided trajectory, and incorporating acoustics with EKFs in HME shows the impact of considering several different models and parameters to have accurate state estimation. Future work may encompass determining accurate dynamic thrust and acoustic models and considering second-order conditions to determine optimal control with a corresponding trajectory.
Convergent Pose And Twist Estimation For Velocity-denied Mobile Robots Based On A Cascading, Dual-frame, Motion-tracking Estimator
(University of Hawaii at Manoa, 2019) Yamamoto, Brennan Eugene; Trimble, A. Z.; Mechanical Engineering
Advancements in micro-fabrication and micro-electromechanical systems, increased market demand, and economies of scale have lowered the cost for global navigation satellite system (GNSS) and inertial measurement unit (IMU) sensor systems to levels cost-relevant for average consumers. The combination of GNSS+IMU can provide basic robot localization information, but cannot measure linear velocity, which is essential for autonomous mobile robot operation. Unfortunately, linear velocity sensors like wheeled odometers, air speed, optical flow, or doppler velocity log sensors are situationally applicable and/or cost prohibitive for many robot applications; these robots can be entitled “velocity-denied”. In this work I propose a state estimation algorithm based on a cascading, dual-frame, motion-tracking estimator that is capable of providing accurate pose (positions) and twist (velocities) estimates for velocity-denied robot platforms, by probabilistically estimating the unobserved velocity state based on the time-varying information extracted from the measured position and acceleration states. Because this state estimator is based on a kinematic, motion-tracking state-transition model, it does not require dynamical information about the robot platform or the forces acting on it. I first demonstrate this state estimator algorithm on simulated mobile robot data and then on real data collected from a GNSS+IMU robot sensor system. I show that this state estimation algorithm consistently maintains a dead-reckoning pose accuracy of <1 m of the post-interpolated pose measurements, and provides hidden a linear velocity accuracy of <±1 m/s.
Constant-Volume Carbonization of Biomass
(University of Hawaii at Manoa, 2018-08) Legarra Arizaleta, Maider; Mechanical Engineering
Carbonization in constant-volume reactors has received little attention in current biomass pyrolysis research. In this conversion process, volatiles linger in close proximity to the carbonaceous solid material resulting in long vapor residence times and high partial pressures. The formation of additional secondary charcoal through heterogeneous reactions between the pyrolyzing charcoal and the tarry vapors is therefore greatly enhanced minimizing carbon losses in the form of gases and liquids. The result is the relatively quick formation of a charcoal product with a higher fixed-carbon yield and a lower content of volatiles compared to charcoals derived from conventional, hydrothermal carbonization or flash carbonization processes. This work presents the effect of processing conditions (pressure, temperature, heating rate, reaction time, biomass loading) and fuel properties (biomass type and particle size) on product yields and char properties in constant-volume carbonization processes. Raising the pre-test system pressure with an inert gas from 0 to 2.17 MPa did not significantly affected product yields or char proximate analysis. It seems that the volatiles partial pressures, rather than the total system pressure, accounts for the dominant effect on the high yields and fixed-carbon contents reported for constant-volume carbonization processes. Raising the reaction time from 30 to 190 minutes and the temperature in a 300-550°C range improved fixed-carbon contents and reduced volatiles while maintaining fixed-carbon yields near theoretical limiting values. In contrast with flash-carbonization or traditional carbonization observations which showed a beneficial effect of the use of larger particles, constant-volume carbonization manifested higher fixed-carbon contents and yields (or similar under certain conditions) when using smaller biomass particles, offering possibilities for smaller, lower-grade biomass to produce a charcoal high in fixed-carbon. A fascinating phenomenon has been reported from certain constant-volume carbonization experiments. Under specific heating rate, pressure and temperature conditions, the particulate biomass seems to exhibit a transient plastic phase that converts it into a single solid piece of char. The roles of pressure, temperature, heating rate, particle size and mass loading in the formation of this transient liquid phase are briefly summarized.
Constrained Drop Surfactometer for Studying Interfacial Structure and Rheology
(University of Hawaii at Manoa, 2017-12) Yang, Jinlong; Mechanical Engineering
Measurements of surface tension and interfacial rheology of liquid-fluid surfaces play an important role in a variety of scientific and industrial fields, such as smart material, thin film, soft matter, microfluidics, and biophysics. Being a miniaturized experimental platform for studying surface phenomena, droplets hold great advantages over the traditional experimental methods, such as the classical Langmuir trough, in determining surface tension and interfacial rheological properties. The focus of this thesis was to develop a novel droplet-based experimental platform called the constrained drop surfactometer (CDS) for studying surface tension and interfacial rheology. Axisymmetric drop shape analysis (ADSA) was used as a numerical algorithm to determine the dynamic surface tension as a function of time and surface area variations. We first proposed a new dimensionless parameter, called the Neumann number, N e ≡ Δ ρ g R0H / γ, to replace the classical Bond number for evaluating the accuracy of ADSA upon reducing drop volume. We then developed a closed-loop ADSA (CL-ADSA) algorithm for determining and controlling droplet parameters, including the volume, surface area, and surface tension, in real-time. With the CL-ADSA, the CDS was transformed from a traditional surface tension measurement methodology to a sophisticated experimental platform for manipulating millimeter-sized single droplets in real-time. We have demonstrated the accuracy, robustness, versatility, and automation of this droplet manipulation technique. Finally, we engaged the combination of CDS and CL-ADSA in studying interfacial rheology. Understanding the interfacial rheology of complex fluids plays a central role in a range of applications such as food processing, detergency, coating, cosmetic, and pharmacology. For the first time, our methodological advance permitted direct control of surface area oscillated in a sinusoidal pattern, thus resulting in a precise evaluation of the surface dilational rheological properties of complex fluids, including surfactants and proteins. Our results showed that the CDS, together with the CL-ADSA, holds great promise for advancing the study of interfacial structure and rheology.

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