Author: Segen Sara A. Habte

Name: Keshav Rajasekaran

Title: Bio-Inspired flow sensors and their application in Unmanned Air Vehicles

Date: 07/22/2022

Time: 9AM – 11AM

Location: EGR 2164

Committee members:

Professor Miao Yu, Chair

Professor Sarah Bergbreiter, Co-Chair

Professor Don Devoe

Professor Nikhil Chopra 

Professor Ryan Sochol

Professor Pamela Abshire (Dean’s Representative)

Abstract:

Small-scale unmanned air vehicles require lightweight, compact, and low-power sensors that encompass various sensing modalities to enable flight control and navigation in challenging environments. Flow sensing is one such modality that has attracted much interest in recent years. Previously reported flow sensors are mostly fabricated by using the traditional MEMS process and have been primarily used to measure underwater flows.
The overall goal of this dissertation is to develop novel bio-inspired directional flow sensors based on additive manufacturing techniques and explore the application of directional flow sensors for use in micro air vehicles. Three major research thrusts are pursued. First, a micro-scale artificial hair sensor is developed for two-dimensional directional flow sensing. The sensor structure is fabricated by using nano-scale 3D printing, which allows high-precision fabrication with a good device to device uniformity. The performance of the sensor is thoroughly studied in deflection experiments with a probe station and in airflow tests.  
The sensor is integrated with a micro air vehicle (MAV), and detection of flow separation is demonstrated. Second,  flow detection on MAVs with a pair of all elastomer strain sensors is investigated. The soft flow sensors are integrated with an MVA, and the abilities of the sensors for obstacle and gust detection are demonstrated. Finally, the use of bio-inspired flow sensors on a micro air vehicle for performing simple control tasks is explored. The experimental results demonstrate that the sensors are capable of early disturbance warnings, and the sensor output can be used to perform simple navigation tasks, for example, following a wall.

Name: Lena Johnson

Title: Evaluating Flight Time in a Flapping-Wing UAV Through Intermittent Gliding and Flapping

Time: July, 22 4:00-6:00pm EGR-2162 DeWalt Meeting Room

Committee Members: 

– Dr. Hugh Bruck: Committee Chair

– Dr. Derek Paley: Dean’s Representative

– Dr. Miao Yu

– Dr. Yancy Diaz-Mercado

– Dr. Nikhil Chopra

Abstract:

Unmanned Aerial Vehicles (UAVs) are increasingly being used for applications that require longer, reliable flight duration and distances. The greatest limitation to achieving these desired flights is the current on board battery technology which, restricted by internal chemistry and external size, can only provide a finite amount of power over time. Efforts to increase the battery’s efficiency and energy storage tend to rely on cumbersome methods that add weight and/or complexity to the system. However natural flyers, though also limited by a finite amount of internal energy gained through food consumption, are able to extend their flights through techniques that either utilize their inherent aerodynamic advantages or advantageously employ atmospheric phenomena. Flapping-Wing UAVs (FWUAVs) are as limited by their onboard battery as any other type of UAV, but because of their bio-inspired functionality are uniquely suited to utilize natural flight extension methods. Therefore, this PhD presents an analysis of the exploration of bio-inspired, hybrid flapping/gliding, also known as intermittent gliding, techniques to improve the flight performance of a FWUAV. Robo Raven is the FWUAV that was chosen as the research platform for this work. It was developed by researchers at the University of Maryland to perform prolonged, untethered flights and exhibit a flight proficiency that combined the maneuverability of rotary-wing flight with the efficiency of fixed-wing flight.
The technique to improve FWUAV flight time, presented in this work incorporates (1) the modeling of Robo Raven’s flapping/gliding potential through the development of a state-space representation directly linking Robo Raven’s onboard battery dynamics with its aerodynamic performance, (2) the use of the state-space model to characterize the effect of intermittent gliding techniques on flight performance through simulation, (3) the real-world characterization of the simulation and of intermittent gliding techniques through flight demonstrations, and (4) the development of a design space by which the effect of wing design on gliding performance might be explored and lead to the potential tailoring of wing design to desired flight performance. The expected outcome of this technique is scientific analysis of the extension of Robo Raven’s flight time without added complexity of weight of the battery system.

Name: Gyeong Sung Kim

Title of dissertation: Heat and mass transfer analysis and performance improvement study for air gap membrane distillation

Defense Date: 7/21/2022 at 10am

Location: Rm. 4164B, Glenn L. Martin Hall

Zoom link : https://umd.zoom.us/j/3218334573?pwd=TkJFbkozbllBTi9qQlNpOFJGVG12QT09

Committee members: 

Professor Reinhard K. Radermacher, Chair
Professor Kenneth Yu, Dean’s Representative
Professor Jungho Kim
Professor Peter Sandborn
Professor Bao Yang
Research Professor Yunho Hwang

Abstract:

Seawater desalination method can be largely divided into evaporation- and membrane-based techniques. From decades ago, the global installation capacity of reverse-osmosis membrane-based seawater desalination (SWRO) started outgrowing that of the evaporative desalination plant due to its higher energy efficiency and it became the mainstream technology in the 20th century. However, small-scale SWRO facilities installed on South Korean islands are not competitive compared to the thermally driven evaporation method as their specific energy consumption (SEC) values are highly ranging in 9 – 19 kWh∙m^(-3) and there have been frequent maintenance events.

By taking the advantages of direct utilization of renewable and thermal energy, air gap membrane distillation (AGMD) is investigated in this study as an improved approach.  From the preliminary experimental study, it was found that the lower air-gap pressure of AGMD helps to increase its water productivity. However, most of the heat and mass transfer models in AGMD used the constant atmospheric pressure for the air gap.  Therefore, new models considering the pressure effect of the air gap are needed. Since maintaining a vacuum pressure in the gap requires additional energy, a vacuum technique consuming less energy is also needed.  In addition to controlling the total pressure of the gap, condensation augmentation on the cooling surface on one side of the gap is critical since the vapor flux is dependent on the vapor pressure in the gap. As the preliminary experimental study showed that the dropwise condensation mode dominates the condensation of AGMD, the effect of gap size between the condensation surface and hydrophobic membrane is needed to be investigated.

Therefore, this research was performed with the following objectives: (i) experimental investigation and mass transfer model development for vacuum applied AGMD (V-AGMD), (ii) development of a wave-powered desalination system using V-AGMD, (iii) experimental investigation of condensation in AGMD, and (iv) development of condensation enhancement technology for AGMD. From the modeling and experimental research, this study made the following major research outcomes and observations. First, a straightforward mass transfer model was developed by using the concept of Kinetic Theory of Evaporation and temperature fraction value between the fluid temperatures of feed and coolant, based on the AGMD experimental results. This model was evaluated experimentally and showed an excellent prediction of water flux in various air-gap pressures without measuring each temperature of the interface of the feed-membrane-air-cooling surface-coolant. Second, considering that the air gap of AGMD can be operated in a vacuum state using wave power, a novel wave powered AGMD desalination device was proposed and evaluated for island’s dwellers. Third, during the whole AGMD tests, only dropwise condensation (DWC) modes were observed on the stainless-steel condensing wall. Therefore, experiments were conducted to understand the physical pattern of DWC from nucleation to departure. After testing various temperature and humidity conditions, it was confirmed that the average size of the water droplets followed the power law for each case. Fourth, as the periodic cleaning of the condensate wall of AGMD could improve the production of condensate, an experimental study was subsequently performed for the condensation augmentation using an electrohydrodynamic (EHD) method. By both cleaning periodically and applying 2.5 kV and 5.0 kV EHD field on the condensing surface in a thermos-hygrostat chamber, water production rate was increased by 32% and 88%, respectively.

This study concluded that the performance of an AGMD desalination system can be improved by applying a vacuum or an EHD device in its air gap. Therefore, pilot-scale experiments will be conducted as future studies to evaluate the commercial viability of the improved system.

Name: Bahram Parvinian

Defense Date: July 7^th, 2022 at 10am

Location: Glenn L. Martin Hall, EGR-2162

Committee Members:

Professor Jin-Oh Hahn, Advisor/Chair

Professor Yang Tao, Dean’s Representative

Professor Balakumar Balachandran

Professor Yancy Diaz-Mercado

Professor Monifa Vaughn-Cooke

Professor Pras Pathmanathan

Title: A FRAMEWORK FOR CREDIBILITY ASSESSMENT OF SUBJECT-SPECIFIC PHYSIOLOGICAL MODELS 

Abstract:

Physiological closed-loop controllers and decision support systems are medical devices that enable some degree of automation to meet the needs of patients in resource-limited environments such as critical care and surgical units. Traditional methods of safety and effectiveness evidence generation such as pre-clinical animal and human clinical studies are cost prohibitive and may not fully capture different performance attributes of such complex safety-critical systems primarily due to subject variability. In silico studies using subject-specific physiological models (SSPMs) may provide a versatile platform to generate pre-clinical and clinical safety evidence for medical devices and help reduce the size and scope of animal studies and/or clinical trials. To achieve such a goal, the credibility of the SSPMs must be established for the purpose it is intended to serve. While in the past decades significant research has been dedicated towards development of tools and methods for development and evaluation of SSPMs, adoption of such models remains limited, partly due to lack of trust in SSPMs for safety-critical applications. This may be due to a lack of a cohesive and disciplined credibility assessment framework for SSPMs.

In this dissertation a novel framework is proposed for credibility assessment of SSPMs. The framework combines various credibility activities in a unified manner to avoid or reduce resource intensive steps, effectively identify model or data limitations, provide direction as to how to address potential model weaknesses, and provide much needed transparency in the model evaluation process to the decision-makers. To identify various credibility activities, the framework is informed by an extensive literature review of more mature modeling spaces focusing on non-SSPMs as well as a literature review identifying gaps in the published work related to SSPMs. The utility of the proposed framework is successfully demonstrated by its application towards credibility assessment of a CO₂ ventilatory gas exchange model intended to predict physiological parameters, and a blood volume kinetic model intended to predict changes in blood volume in response to fluid resuscitation and hemorrhage. The proposed framework facilitates development of more reliable SSPMs and will result in increased adoption of such models to be used for evaluation of safety-critical medical devices such as Clinical Decision Support (CDS) and Physiological Closed-Loop Controlled (PCLC) systems.

Name: Azin Sadat Mousavi

Defense Date: July 5^th, 2022 at 2 pm

Location: Glenn L. Martin Hall, EGR-2164

Committee Members:

Associate Professor Jin-Oh Hahn, Advisor/Chair

Professor Alison Flatau, Dean’s Representative

Professor Balakumar Balachandran

Professor Hosam Fathy

Professor Miao Yu

Title: Ballistocardiography: Mathematical Modeling, Analysis, and Application to Cardiovascular Health Monitoring

Abstract:

The main goal of this thesis is to improve the early detection and management of cardiovascular disease by developing novel ultra-convenient CV health and risk predictor monitoring techniques based on a physiological signal called ballistocardiogram (BCG). BCG is the recording of heart-induced body movements. It has great potential to enable ultra-convenient CV health monitoring because of its close association with cardiac functions and its amenity for convenient measurement (i.e., measurement form factors including weighing scales and wearables). Nonetheless, the shortage of physical understanding of the BCG is a serious challenge that has hampered its effective use in CV health and risk assessment. The scope of this thesis can be explained under three themes: (i) physics-based modeling of BCG, (ii) BCG recording, and (iii) challenges in wearable BCG-based cuffless blood pressure monitoring.

In the first part of the thesis, a closed-form physics-based model is developed to estimate BCG from a single blood pressure waveform and investigate the feasibility of this model in the estimation of CV risk predictors. This model is inspired by our team’s prior hypothesis that the main mechanism for the genesis of head-to-foot BCG is the pressure gradients in the ascending and descending aorta (the major artery in the body). In addition, a systematic BCG feature selection approach was introduced leveraging the closed-form BCG model. This model-based approach is superior to previous ad-hoc feature selection techniques in that it incorporates physiological knowledge of the arterial system and unlike ad-hoc approaches which are data specific its findings can be generalized to different independent datasets.

BCG waveforms recorded with different sensors and devices have morphological differences. Therefore, the next part of this work is dedicated to the study of different BCG recording devices and the construction of a BCG measurement apparatus that enables the recording of true BCG (as estimated in the mathematical model). The efficacy of the BCG recording apparatus in measuring BCG is shown in two human and animal experiments.

Finally, BCG can enable cuff-less blood pressure (BP) tracking by virtue of two perks. It can easily be instrumented using wearables and it can be used as a proximal timing reference to calculate pulse transit time (PTT) which is the basis of the most common technique for cuff-less BP tracking.  However, most wearable BCG-based studies for cuff-less BP monitoring, have resorted to one posture (standing with hands placed on the sides). Therefore, in this work, the effect of posture on wrist BCG-PPG PTT was investigated. This work revealed the posture-induced changes in PTT and PAT in-depth for the first time, by invoking and quantifying the effect of possible physical mechanisms responsible for such changes.