Announcements

Author: Lautaro Cilenti

Date: Wednesday, September 07, 2022 at 11:00 am

Location: Martin Hall, Room EGR-2164

Committee Members:

Professor Balakumar Balachandran, Mechanical Engineering, Chair/Advisor
Associate Professor Maria Cameron, Mathematics, Co-Chair/Advisor
Professor Eyad Abed, Electrical and Computer Engineering, Dean’s Representative
Professor Amr Baz, Mechanical Engineering
Associate Professor Jin-Oh Hahn, Mechanical Engineering
Assistant Professor Eleonora Tubaldi, Mechanical Engineering

Title of Paper: INFLUENCE OF NOISE ON RESPONSE LOCALIZATIONS IN MECHANICAL OSCILLATOR ARRAYS

Abstract: 

The dynamics of mechanical systems such as turbomachinery and vibration energy harvesting systems (VEH) consisting of one or multiple cantilever structures are often modeled by arrays of
periodically driven coupled nonlinear oscillators. It is known that such systems may have multiple stable vibration modes. Some of these stable modes are localized vibrations that are characterized by high amplitude vibrations of a subset of the system, with the rest of the system being in a state of either low amplitude vibrations or no vibrations. On one hand, these localized vibrations can be detrimental to mechanical integrity of turbomachinery, while on the other hand, the vibrations can be potentially desirable for increasing energy yield in VEHs. Transitions into or out of localized vibrations may occur under the influence of random factors.

A combination of experimental and numerical studies have been performed in this dissertation to study the associated transition times and probability of transitions of these mechanical systems. These include the following: (i) a numerical methodology based on the Path Integral Method to quantify the probability of transitions due to noise, (ii) a numerical methodology based on the Action Plot Method to quantify the quasipotential and most probable transition paths in nonlinear systems with periodic external excitations, and (iii) experimental evidence and stochastic simulations of the influence of noise on response localizations of rotating macro-scale cantilever structures. The methodology and results discussed in this dissertation provide insights relevant to the stochastic nonlinear dynamics community, and more broadly, designers of mechanical systems with potentially undesirable stochastic nonlinear behavior. 

Name: Kunal Ahuja

Title of Dissertation: ULTRA-THIN ON-CHIP ALD LIPON CAPACITORS FOR HIGH ENERGY AND HIGH-FREQUENCY APPLICATIONS 

Date, time, location: August 4th, 1-3pm in EGR 2164 (https://umd.zoom.us/j/9523406285)

List of all committee members: 

• Professor F. Patrick McCluskey, Chair/Advisor
• Professor Gary Rubloff, Co-Chair
• Professor Peter Sandborn
• Professor Keith Gregorczyk
• Professor Hugh Bruck
• Professor Aris Christou
• Professor Sang Bok Lee (Dean’s Representative)

Abstract: Liquid electrolytes dominate the supercapacitor market due to their high ionic conductivity leading to high energy and power density metrics. However, with the increase in demand for portable and implantable consumer electronics, all solid-state supercapacitor systems with high safety are an attractive option from both application perspectives and their similar charge storage mechanism. For solid state ionic capacitors, there remains significant room for innovation to increase the ionic conductivity and capacitor architecture to enhance the performance of these devices. Nano-structuring along with advanced manufacturing techniques such as atomic layer deposition (ALD) are powerful tools to augment the performance metrics of these all-solid-state capacitors that can compete with state-of-the-art liquid electrolyte-based supercapacitors. This dissertation has two primary objectives; 1) Study the behavior of polymorphs of ALD LiPON as a capacitor material and 2) Enhance the performance metrics using advanced materials and 3D nanostructuring for improved energy storage and high-frequency applications.

In this work, ALD LiPON-based solid state capacitors are fabricated with a gold current collector to study the behavior of the solid electrolyte. LiPON shows a dual energy storage behavior, in low frequency (<10 kHz), LiPON shows an ionic behavior with electric double layer type energy storage, beyond this frequency, LiPON shows an electrostatic behavior with a dielectric constant of 14. The capacitor stack’s thin film structure and dual frequency behavior allow for extended frequency operation of these capacitors (100 Hz to 2000 MHz). Next, LiPON’s energy storage metrics are enhanced using pseudocapacitive energy storage behavior and enhanced surface area in ALD oxy-TiN. Finally, new fabrication techniques and ALD recipes are developed and optimized for integration into 3D templates. For fabrication of these capacitors, the material’s chemistry is analyzed, and ALD techniques are developed to enhance the deposition of electrode/electrolyte materials and current collectors into the 3D nanostructures. The intermixing during the ALD processes are studied to understand the behavior and reliability of these thin films. This work highlights LiPON characteristics as a capacitor material for high-energy and high-frequency applications. Though incomplete, we discuss progress towards the development of all ALD solid-state 3D supercapacitors that can compete against state-of-the-art capacitors available in the market.

Name: Zhaoxi Yao

Title of Dissertation: Thermal Management of Integrated motors for Electric Propulsion

Date, time, location: August 5, 2:00 PM to 4:00 PM in EGR 2162

List of all committee members: 

• Professor F. Patrick McCluskey, Chair/Advisor
• Professor Michael Ohadi
• Professor Amir Riaz
• Professor Hugh Bruck
• Professor Christopher Cadou (Dean’s Representative)

Abstract: Electrification of traditional combustion power units has been a major trend. The low emissions, low noise and high efficiency characteristic of electrified power, fit the vision of a low carbon emission future. The development of high power density electric motors is key to facilitating large scale, heavy duty applications. The demand for dense power leads to significant heat flux, causing thermal management to become one of the main obstacles in developing high power density electric motors. Multiple components in the motor generate heat. For example, the motor of interest in this paper is a 1 MW, high power density, surface mounted permanent magnet motor, with a segmented and laminated stator on the outside, and a laminated rotor on the inside. Heat is generated in the stator winding, stator core, magnets, rotor core as well as the motor drive. For high speed motors, windage loss could also be significant in the air gap. Among the heat-generating components, the stator winding is the primary heat source.

For this study, a comprehensive thermal management solution was developed. The power density of the motor, based on active mass, exceeded 22 kW/kg and majority of the loss came from the stator windings. Thus, a dedicated direct winding cooling combined with an integrated cooling jacket were deployed. Multiple winding cooling schemes were explored, such as investment-casted cooling channels in potting, hollow conductors, flooded slots and Litz-wire-wrapped cooling tubes. The flooded slots with scaffolding-shaped spacer were chosen in the end, which demonstrate good thermal performance, low pumping power, pressure requirements and low risk of partial discharge as the dielectric coolant also served as liquid insulation. A cooling jacket with integrated power module cooling was designed to cool the stator core and power modules. The cooling jacket included a compression sleeve, which served as the mechanical support to hold the stator segments as well as the cooling surface for the stator cores, and nine cold plates, hosting 18 power modules on top, placed around the curved outer surface of the motor. The cooling concepts were designed, simulated and validated by testing. A functioning prototype was constructed and in the process of testing.

Name: Anthony Devlin Larosa

Title of Thesis: DESIGN OF A LOW-COST PORTABLE HANDHELD SPECTROMETER FOR AEROSOL OPTICAL DEPTH MEASUREMENTS

Date, time, location: 08/05, 2:00 PM, EGR 2164 (DeWalt Seminar Room)

List of all committee members: 

• Professor Miao Yu, Chair and Advisor
• Professor Mario Dagenais
• Assistant Professor Avik Dutt

Abstract: The impact aerosols have on human health and the climate continues to be a central topic in scientific research. The quantification of aerosol abundance in the atmosphere is a key factor in understanding the climate, Earth’s radiative budget, and their impacts to human health. This research focuses on the development and comprehensive assessment of a handheld field instrument that measures aerosol optical thickness. The challenges associated with designing a low-cost, durable handheld system with highly sensitive electronics, which is capable of direct-sun measurements, are investigated. The thesis work can be summarized as follows. First, the electrical, mechanical, and optical integration needed for the instrument development is discussed and presented. Second, the sensitivities of a compact micro spectrometer are analyzed in both the laboratory and field deployment studies. The spectrometer and the fully integrated instrument are characterized in terms of its spectral resolution, sensitivity, thermal characteristics, and stability. Finally, after successful performance characterization, the capabilities of the instrument for field measurements are explored by taking direct sun measurements. The results demonstrate that the instrument has great potential to be used as a rigorous scientific device or a citizen science, educational instrument for aerosol optical depth measurements.

Name: Neda Shafiei

Title: Estimating The Reliability of a New Consumer Product Using User Survey Data and Reliability Test Data

Date: 7/27/2022 at 11am via Zoom only

Zoom Link: https://umd.zoom.us/j/9968970907

Committee Members:

Mohammad Modarres, Chair

Jefferey Herrmann

Abhijit Dasgupta

Katrina Groth

Vasiliy Krivtsov

Mohamad Al-Sheikhly, Dean’s Representative

Abstract: Collecting data for estimating the reliability of a new consumer product is challenging. Using test data for estimating reliability is usually insufficient because, in reliability tests, the number of samples, test stress levels, and test times are restricted. Collecting and analyzing reliability data of the same class of product obtained from user surveys offer a cost-effective and quick way to obtain the field prior reliability characteristics of the new device. User survey data, however, is biased. This dissertation provides a guideline for designing a reliability-informed survey. An approach is proposed that corrects any bias in the survey responses through the Kullback-Leibler (KL) divergence method and uses bias-corrected survey data and test data about the similar product and test data about the new product to estimate the reliability model. The approach considers a product with many or several cycles to failure. The application of the approach is illustrated using the simulated survey and test datasets for a consumer electronic product with the failure mode of cracking caused by accidental drops.

Name: Kit Pan Wong

Title of dissertation: Distributed fiber-optic sensors for pressure and strain measurements during slamming of a flexible plate

Date & location: July 25^th, 2022 10am EST, Martin Hall 2164

https://umd.zoom.us/j/3669032774?pwd=WG9IalhCK1lZTWozM1VXUlhQM1Z4UT09
Meeting ID: 366 903 2774
Passcode: 2021088

Committee members:

Professor Miao Yu, Chair
Professor James Duncan
Professor Kenneth Kiger
Professor Nikhil Chopra
Professor Stuart Laurence (Dean’s Representative)

Abstract:
The investigation of fluid-structure interaction during the impact of a flexible plate on a water surface has received much attention. Measurement of highly transient, distributed strain and pressure of the plate during the slamming event is of great interest. Multiplexed fiber Bragg grating (FBG) strain sensors provide a promising solution for such measurement since these sensors are inherently waterproof and are immune to electromagnetic interference. However, in order to monitor the highly transient, distributed strain and pressure responses (up to 20 kHz), high-speed interrogation of multiplexed sensors is required, which is challenging by using commercial optical interrogators. Furthermore, it is challenging to use conventional piezoelectric sensors for pressure measurement on a flexible plate due to the intrusiveness of their size.
In this dissertation work, a distributed fiber optic sensor system is explored for strain and pressure measurement on a flexible plate during slamming. First, a high-speed optical interrogation system for multiplexed FBG strain sensors and Fabry-Perot pressure sensors is developed. The interrogation system employs a piezoelectric-transducer-controlled Fabry-Perot tunable filter. By operating the tunable filter at its resonant frequency and demodulating the sensor signal based on a peak tracing method, the system can operate at the interrogation speed of 100 kHz, an interrogation range of 98 nm, and an interrogation resolution of 5 pm. To demonstrate its capability, the interrogation system is used to monitor the vibrational responses of a cantilever plate under impact loading and the measurement of vibration modes up to 6.785 kHz.  The system is also demonstrated to be able to interrogate Fabry-Perot acoustic pressure sensors for up to 20 kHz. Second, miniature Fabry-Perot pressure sensors with temperature compensation are developed based on the additive manufacturing technique. Two types of miniature Fabry-Perot pressure sensors (a single cavity FP sensor and a dual cavity FP sensor) were designed and developed. Due to the large coefficient of thermal expansion of the polymer material, the change of the optical path length induced by the temperature can result in a large error in the pressure measurement. By characterizing the pressure and temperature sensitivity of the sensor, the experimental result shows the temperature compensated pressure response of the FP sensor agreed well with the reference sensor. Finally, the experimental study of the impact of a flexible plate on a water surface is carried out by using the distributed fiber optic strain and pressure measurement system.  With multiplexed FBG strain sensors and FP pressure sensors mounted on the flexible plate, the dynamic strain and pressure responses occurred on the plate during the slamming event were successfully monitored. The maximum strain increased with increasing impact speeds, which was in good agreement with the behavior of the measured maximum deflection. The high-speed spectral domain optical interrogation system with FBG strain sensors and FP sensors can serve as a useful measurement tool for a better understanding of the fluid-structure interaction.

Name: Connor Quigley

Date & Time: July 25th, 2022 at 10am in EGR-2162 

Zoom Meeting: https://umd.zoom.us/j/2010401689 | Meeting ID: 201 040 1689

Thesis Title: Developments in Carbon Rod Analysis for Sporting Goods Applications

Advisory Committee:

Professor Peter Chung, Chair/Advisor

Professor Abhijit Dasgupta

Professor Jeffery Herrmann

Abstract:

In sporting goods manufacturing, such as in fishing rod design, new products are created using an Edisonian process. By changing the layup and geometry of the carbon fiber prepreg layup, a rod can be constructed that lend itself to a specific application. This thesis will present an integrated computational materials engineering (ICME) approach for carbon fiber fishing rods using simulation theory and experiments. The computations are based on the finite element method (FEM), including the use of integrated Euler-Bernoulli beam theory in MATLAB.  The experimental methodology uses three-point bending (3PB) flexure test analysis to determine values for Young’s Modulus which are then incorporated into numerical solutions and modelling.  Discretized values for Young’s Modulus are used in thin-walled tapered cylindrical Euler-Bernoulli beam models through integrated second area moment of inertia and non-integrated approaches.  The 3PB flexural experiments performed on a test rod section demonstrate correlation to FEM solutions, along with convergence between non-integrated and integrated beam models.  A modal analysis on the beam provides insight to the free-vibrational effects of a fishing rod under differing user-induced boundary conditions.  Through this ICME approach, rod manufactures can understand properties in rod prototypes and better develop future rod models.