Date of Award

Fall 2022

Document Type

Open Access Dissertation


Mechanical Engineering

First Advisor

Nikolaos Vitzilaios


Uncrewed Aircraft Systems (UAS) are becoming increasingly popular for infrastructure inspections since they offer increased safety, decreased costs and consistent results, compared to traditional methods. However, there are still many open challenges before fully autonomous, reliable, and repeatable UAS inspections. While a UAS platform has increased mobility and can easily approach hard to reach areas, it has limited range and payload capacity and is susceptible to environmental disturbances. Therefore, current operations are limited to Visual Line of Sight (VLOS) manual inspections that usually result in just a qualitative (visual) assessment of the structure.

The objective of this work is to propose solutions to these limitations in an effort to improve the effectiveness of UAS as an autonomous inspection platform. First, a heterogeneous marsupial robotic system is proposed as a solution to the limited range and flight time of UAS. The proposed system uses an Autonomous Surface Vehicle (ASV) to ferry the UAS close to the area of interest, where the latter can perform an inspection. Combining these two different platforms in a single system takes advantage of the individual strengths resulting on a platform that has the reach and high point of view of a UAS but has the range and operation time of the ASV. The proposed system was extensively tested over a six-month period in field deployments at Lake Murray and at the Congaree River, SC, USA, to validate its capabilities.

As a solution to go beyond visual UAS inspections, a UAS equipped with a Stereo Digital Image Correlation (StereoDIC) system is proposed. StereoDIC is a non-contact non-destructive evaluation method that can accurately measure displacements, strains, strain rates, and geometry profiles. StereoDIC has become a method of choice in experimental mechanics with most studies performed in controlled lab environments with controlled lighting and stationary cameras positioned in the appropriate distance from the measured object.

A prototype is built and tested in a lab setting to investigate its effectiveness and understand the challenges that might arise from the deployment of such a system. A comparative study using a stationary StereoDIC system validates the accuracy of the measurements while the acquisition of measurements showing the onset and evolution of defects and the dynamic response of the structure during a harmonic oscillation verifies the ability of the system to produce a quantitative assessment.

Finally, using the lessons learned from the lab experiments, a new, upgraded, StereoDIC enabled UAS is developed for outdoor deployment and infrastructure inspection. To allow safe field deployments, the new system features a state estimation framework enabling operation in GNSS degraded environments while also estimating any external disturbances acting on the platform. These disturbances are utilized by the controller to make the platform adaptable to challenging weather conditions. The new system was deployed over an eight-month period at a railroad bridge in Columbia, SC. Initial data were collected that guided the investigations of effective speckle pattern applications. Experimental results from bridge measurements, while loaded from crossing trains, are presented and discussed.


© 2022, Michail Kalaitzakis