@article{stewart_weisler_anderson_bryant_peters_2020, title={Dynamic Modeling of Passively Draining Structures for Aerial-Aquatic Unmanned Vehicles}, volume={45}, ISSN={["1558-1691"]}, DOI={10.1109/JOE.2019.2898069}, abstractNote={In the design of hybrid unmanned aerial and underwater vehicles, buoyancy management and weight are two major factors. Large wing volumes used by unmanned air vehicles to fly efficiently drive vehicle buoyancy up, preventing them from submerging. Heavy active buoyancy control systems can overcome this, but cost weight, energy, and time to transition between underwater operation and flight. An alternative design, consisting of a passively flooding and draining wing, is presented in this paper. Relevant dynamic parameters for a full vehicle dynamic model are identified. A dynamic model of a draining structure is developed and verified experimentally on both a simple cylinder and a full wing structure. With proper tuning, the model captures the salient dynamic behavior of passive draining during vehicle egress. A prototype unmanned aerial and underwater vehicle was built, flown, and used to collect flight test data. The model is used to accurately predict the takeoff performance of the vehicle. As given, the model can be incorporated into a full vehicle dynamic model to aid in the design, simulation, and control of hybrid unmanned aerial and underwater vehicles with passively draining components.}, number={3}, journal={IEEE JOURNAL OF OCEANIC ENGINEERING}, author={Stewart, William and Weisler, Warren and Anderson, Mark and Bryant, Matthew and Peters, Kara}, year={2020}, month={Jul}, pages={840–850} }
 @article{stewart_weisler_macleod_powers_defreitas_gritter_anderson_peters_gopalarathnam_bryant_et al._2018, title={Design and demonstration of a seabird-inspired fixed-wing hybrid UAV-UUV system}, volume={13}, ISSN={1748-3190}, url={http://dx.doi.org/10.1088/1748-3190/aad48b}, DOI={10.1088/1748-3190/aad48b}, abstractNote={This paper looks to the natural world for solutions to many of the challenges associated with the design of fixed-wing cross-domain vehicles. One example is the common murre, a seabird that flies from nesting locations to feeding areas, dives underwater to catch prey and returns. This hunting expedition provides an outline of a possible mission for a cross-domain vehicle. While the challenges of cross-domain vehicles are many, the focus of this paper was on buoyancy management and propulsion. Potential solutions to each challenge, inspired by multiple animals that cross between aerial and underwater domains, are investigated. From these solutions, three design concepts are considered, a quadrotor/fixed-wing hybrid, a vertical takeoff and landing (VTOL) tailsitter aircraft, and a waterjet-assisted takeoff vehicle. A comparison was made between the capability of each concept to complete two missions based on the common murres’ hunting expedition. As a result of this comparison, the VTOL tailsitter design was selected for further study. In-depth design was conducted and a prototype vehicle was built. The completed vehicle prototype successfully conducted submerged operation as well as four air flights. Flights consisted of egress from water, flight in air, ingress into water in each flight, and water locomotion. A total of 11 min, 23 s of flight time was recorded as well as underwater swims down to 12 ft (3.7 m) below the surface.}, number={5}, journal={Bioinspiration & Biomimetics}, publisher={IOP Publishing}, author={Stewart, William and Weisler, Warren and MacLeod, Marc and Powers, Thomas and Defreitas, Aaron and Gritter, Richard and Anderson, Mark and Peters, Kara and Gopalarathnam, Ashok and Bryant, Matthew and et al.}, year={2018}, month={Aug}, pages={056013} }
 @article{weisler_stewart_anderson_peters_gopalarathnam_bryant_2018, title={Testing and Characterization of a Fixed Wing Cross-Domain Unmanned Vehicle Operating in Aerial and Underwater Environments}, volume={43}, ISSN={0364-9059 1558-1691 2373-7786}, url={http://dx.doi.org/10.1109/JOE.2017.2742798}, DOI={10.1109/JOE.2017.2742798}, abstractNote={This paper presents test results and performance characterization of the first fixed-wing unmanned vehicle capable of full cross-domain operation in both the aerial and underwater environments with repeated transition and low-energy loitering capabilities. This vehicle concept combines the speed and range of an aircraft with the persistence, diving capabilities, and stealth of a submersible. The paper describes the proof-of-concept vehicle including its concept of operations, the approaches employed to achieve the required functions, and the main components and subsystems. Key subsystems include a passively flooding and draining wing, a single motor and propeller combination for propulsion in both domains, and aerodynamic–hydrodynamic control surfaces. Experiments to quantify the vehicle performance, control responses, and energy consumption in underwater, surface, and flight operation are presented and analyzed. Results of several full-cycle tests are presented to characterize and illustrate each stage of operation including surface locomotion, underwater locomotion, water egress, flight, and water ingress. In total, the proof-of-concept vehicle demonstrated 12 full-cycle cross-domain missions including both manually controlled and autonomous operation.}, number={4}, journal={IEEE Journal of Oceanic Engineering}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Weisler, Warren and Stewart, William and Anderson, Mark B. and Peters, Kara J. and Gopalarathnam, Ashok and Bryant, Matthew}, year={2018}, month={Oct}, pages={969–982} }
 @inproceedings{stewart_van hoe_van steenberge_schultz_peters_2015, title={Correction factors for cross-correlation processing of FBG sensor network data}, volume={9436}, url={http://dx.doi.org/10.1117/12.2084829}, DOI={10.1117/12.2084829}, abstractNote={This paper outlines a demodulation technique developed for low-bandwidth, high sensor density fiber Bragg grating (FBG) applications. Currently there are no such demodulation techniques that can be easily scaled to large networks of sensors. The technique takes advantage of known differences in FBG spectral profiles to uniquely identify each multiplexed grating. Known grating profiles are individually cross-correlated with the measured spectrum to locate each Bragg peak. Cross-correlation was used because of its rapid processing speed. This paper covers preliminary experimental validations to identify accuracy limits, as well as investigations into a correction factor for improved accuracy.}, booktitle={Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2015}, publisher={SPIE}, author={Stewart, William and Van Hoe, Bram and Van Steenberge, Geert and Schultz, Stephen and Peters, Kara}, editor={Peters, Kara J.Editor}, year={2015}, month={Mar} }
 @article{stewart_van hoe_van steenberge_schultz_peters_2015, title={Spectral profile tracking of multiplexed fiber Bragg grating sensors}, volume={357}, ISSN={["1873-0310"]}, DOI={10.1016/j.optcom.2015.08.083}, abstractNote={Abstract This paper outlines a demodulation technique for fiber Bragg grating (FBG) sensors based on combined spectral profile division multiplexing and wavelength division multiplexing. The advantage to this technique is that more FBG sensors can be compressed in a fixed bandwidth, as compared to pure wavelength division multiplexing, in which separate wavelength window is required for each sensor. To identify each FBG sensor, the cross-correlation algorithm of the original sensor spectral profile with the measured full-spectrum from the sensor array is calculated for rapid signal processing. The demodulation method is tested on simulated and experimental data. The demodulation generally performed well, except for cases where a significant amount of spectral distortion due to multiplexing was present. Finally, a correction factor based on the prior location of each sensor at the previous time step is added to compensate for inherent uncertainties in the cross-correlation algorithm. The correction factor improved some predictions, but made others worse, and therefore needs further investigation for practical applications.}, journal={OPTICS COMMUNICATIONS}, author={Stewart, William and Van Hoe, Bram and Van Steenberge, Geert and Schultz, Stephen and Peters, Kara}, year={2015}, month={Dec}, pages={113–119} }