Mechanical Engineering Commons^™

Phase Field Modeling Of Shear Yielding And Crazing In Glassy Polymer, Yunzhe Mao

Open Access Theses

Glassy polymers are very important in industrial and commercial components manufacturing. For instance, it is used to manufacture polymer-matrix composites, the type of composite used in the Dreamliner 787. But this kind of material is also limited by its tendency to fail in brittle manner. In this study, we use phase field model to characterize the yielding condition of glassy amorphous polymer under a wide range of loading conditions. The main failure mechanisms in amorphous glassy polymers, such as poly-methyl-methacrylate (PMMA), are crazing and shear yielding. Crazing is formed because of the nucleation of micro-voids in the location of stress …

Experimental And Numerical Study Of The Air Distribution In An Airliner Cabin, Wei Liu

Open Access Theses

Nowadays, more people, including those with impaired health or who are otherwise potentially sensitive to the cabin environment, are traveling by air than ever before. The flying public demands a higher comfort level and a cleaner environment because they encounter a combination of environmental factors including low humidity, low air pressure, and sometimes, exposure to air contaminants such as ozone, carbon monoxide, various organic chemicals, and biological agents. Moreover, international air travel has increased the potential risks associated with airborne disease transmission and the release, whether accidentally or intentionally, of noxious substances during flight. Many studies suggest that the risk …

Probabilistic Fault Detection And Diagnostics For Packaged Air-Conditioner Outdoor-Air Economizers, Andrew L. Hjortland

Open Access Theses

Poor economizer control, economizer damper failure, and excess outdoor-air contribute to these performance degradations. In order to promote optimal rooftop air-conditioner (RTU) performance and reduce operating costs, an automated fault detection and diagnostics (AFDD) tool has been designed for RTUs with integrated economizers. Based on previously proposed methods, the proposed method advances the economizer fault detection and diagnosis components by using statistical classifiers in order to provide more robust, probabilistic fault outputs. A set of air-side virtual sensors has also been added to the method in order to expand the applicable range of conditions fault detection and diagnostics can be …

A Novel Three Degree-Of-Freedoms Oscillation System Of Insect Flapping Wings, Yi Qin

Open Access Theses

We propose an oscillation system to replicate the dynamic behavior of flapping wings, inspired by insect flight muscles. In particular, we study the flight of the fruit fly Drosophila virilis . We model the wing as a rigid body with three degree-of-freedom, described by three Euler angles: the stroke angle, the rotation angle and the deviation angle. Insect flight muscles are separated into two types: power muscles and control muscles. One actuator and one torsional spring at the stroke angle act as the power muscles. Two torsional springs at the rotation angle and the deviation angle mimic the control muscles. …

Characterization Of Thermal And Mechanical Properties Of Porous Material For Electronic Cooling Applications, Ninad Tushar Trifale

Open Access Theses

Metal foams are considered beneficial for several applications because of its significantly large surface area for a given volume. Foams form a high thermal conductive network in a thermal interface for electro cooling applications. The porous structures are relatively compliant and can provide for a better contact and thereby have a lower thermal resistance. Porous heat sinks made of aluminum foam have been well studied in the past. It is not only cost effective due to the unique production process, but also attractive for the theoretical modeling study to determine the performance. A study on the thermal and mechanical characterization …

The Influence Of Gaps On The Frequency Response Of A Beamspring Contact System, Wenbin Zhang

Open Access Theses

Some mechanical systems with gaps such as in disc brakes and Cardan joints exhibit nonlinearity under certain load conditions, which is unpredictable and highly sensitive to initial conditions. Previous studies were mainly focused on either a single-degree-of-freedom (DOF) system or a flexible beam with uniform elastic foundation. The analysis of this thesis is a combination of these two where gaps are first introduced to a flexible beam model. A model of a beam resting on compliant foundation with gaps has been developed and analyzed. The assumed modes method is used to derive the equations of motion (EOM's) for the system. …

An Algorithm For Impacting Soft Structures, Tengfei Long

Open Access Theses

Impact among soft structures is often difficult to model because of the geometrical non-linearity involved. There are a number of previous studies of the contact dynamics of rigid bodies, but few has focused on soft structures so far.

This thesis models impact between soft structures without any restraint on their geometries. The goal is to simulate the dynamics involved among soft structures during an impact process. This has been done through designing and implementing an contact algorithm that uses the finite element method along with a three-dimensional solid element to solve the fundamental time integration problem. Modeling of the contact …

Exhaust Thermal Management Using Cylinder Deactivation And Late Intake Valve Closing, Mark E. Magee

Open Access Theses

Progressively stricter emission regulations have compelled diesel engine manufacturers to develop new technologies that reduce harmful pollutants like NOx and soot. While manufacturers have previously been able to meet these regulations through the use of on engine technology such as exhaust gas recirculation and multiple pulse injections, exhaust after treatment systems such as diesel particulate filters and selective catalytic reduction systems have become necessary to meet recent stricter policies. While these after treatment systems are incredibly effective at reducing harmful emissions, to operate effectively the system needs to be above a certain temperature level typically between 250 and 300°C. Many …

Improving Indoor Air Quality Through Botanical Air Filtration In Energy Efficient Residences, Daniel William Newkirk

Open Access Theses

According to the U.S. EPA, the average American spends 90% of their time indoors where pollutants are two to five times more prevalent than outside. The consequences of these pollutants are estimated to cost the U.S. 125 billion dollars in lost health and productivity. Background literature suggests botanical air filtration may be able to solve this problem by leveraging the natural ability of plants to purify indoor air. By improving indoor air quality, energy consumption can also be reduced by bringing in less outside air to dilute contaminants within the space. A botanical air filter, called the Biowall, was designed …

Modeling Tools For Conformal Orthotic Devices, Steven David Riddle

Open Access Theses

The purpose of this thesis is to advance the design of conformal orthotic devices through the development of two modeling tools to address knowledge gaps in the field.

The field of human orthotics has been continually troubled by identifying successful methods of harnessing devices to the body. Past orthotics have utilized a rigid framework with minimal degrees of freedom (DOFs) driven by hard actuators attached to the body at select anchor points. Many devices design the structure and anchor points such that they reduce the degrees of freedom of a targeted joint, limiting the user's mobility and often causing the …

A Study Of Inkjet Printed Line Morphology Using Volatile Ink With Non-Zero Receding Contact Angle For Conductive Trace Fabrication, Chenchao Shou

Open Access Theses

Inkjet printed lines on a homogeneous solid substrate are studied under the condition that ink evaporation is not negligible and the contact angle exhibits hysteresis with non-zero receding contact angle (NRCA). A new family of line instability is discovered, featured by formation of agglomerations within a line. The agglomeration is explained by a hydrodynamic flow that consistently drives a bead on the substrate towards fresh deposited droplets due to concentration-induced surface tension gradient. Morphologies of lines printed with multiple layers are also explored for the purpose of conductive trace fabrication. A non-uniform morphology is observed across a multi-layer line when …

Analysis Of An Actuated Two Segment Leg Model Of Locomotion, Nikhil Vinayak Rao

Open Access Theses

Research studies on dynamic models of legged locomotion have generally focused on telescoping-type leg models. Such telescoping spring loaded inverted pendulum (SLIP) models have been able to accurately predict observed center of mass (CoM) trajectories. There have been comparatively fewer studies on dynamics of locomotion

with segmented legs. Some earlier studies on the dynamics due to leg segmentation appear straightforward. For example, a simple model with the only joint moment being due to a passive springy knee has been shown to behave similarly to a telescoping spring-mass model. However, in real-life animal locomotion, there are multiple joint-moments acting at the …