Theses and Dissertations at Montana State University (MSU)
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Item Modeling snow water equivalent in complex mountainous terrain(Montana State University - Bozeman, College of Letters & Science, 2023) Beck, Madeline Makenzie; Chairperson, Graduate Committee: Eric A. Sproles; This is a manuscript style paper that includes co-authored chapters.The water stored in seasonal mountain snowpacks is a vital resource that approximately 20% of the world's population relies on for freshwater availability. However, accurately quantifying the amount of water stored in a snowpack, known as snow water equivalent (SWE), is difficult. The longest employed technique to quantify SWE is manual measurements. However, manual measurements of SWE are time intensive. As a result, researchers can collect relatively few point-based measurements across spatially extensive and complex regions. Automated weather stations may provide additional measurements of SWE and meteorological conditions but are expensive and difficult to maintain. Thus, reliable measurements of snow characteristics like SWE are scarce across time and space. A lack of extensive measurements causes data from few points to be extrapolated across spatially heterogeneous environments which increases uncertainty in estimates of water availability. Recent advances in satellite remote sensing allow researchers to observe snowpack dynamics across spatially continuous scales instead of relying solely on point-based measurements. However, current satellite technologies are incapable of collecting high- resolution snow data at the hillslope scale. Previous work has shown the importance of high elevation, hillslope-scale water storage reservoirs. Uncrewed aerial vehicles (UAVs) address the limitations of satellite remote sensing on the hillslope scale and are used to create high accuracy (<5 cm) models of snow depth. However, these models of snow depth provide no information on the amount of water stored without a value for snow bulk density. Thus, to capture hillslope dynamics of SWE, researchers must pair high-resolution models of snow depth with either directly measured or modeled bulk density of snow. This master's thesis integrates UAV-derived measurements of snow depth with modeled snow bulk density values to create continuous representations of hillslope-scale SWE across 9 flight dates. We found that each density modeling approach consistently underestimated SWE for the field site for each flight date except one. Further, each method of modeling snow bulk density was statistically indiscernible from each other. These findings highlight the heterogeneity of snow in mountainous terrain. In future work, bulk density models can be further parameterized to better represent site-specific values of SWE.Item Full scale component level testing & severity analysis of phantom 3 UAV to Cessna 182b aircraft collisions(Montana State University - Bozeman, College of Engineering, 2021) Hayes, Benjamin Woodruff; Chairperson, Graduate Committee: Robb LarsonUnmanned Aircraft Systems (UAS) are more attainable now than ever before. With uses ranging from re-forestation, agriculture, film-making, and recreation; a significant amount of airspace is being occupied by UAS. To better understand the risks posed by UAS to other aircraft, the Alliance for System Safety of UAS through Research Excellence (ASSURE) was created. One aspect of ASSURE's agenda is to conduct air to air collision studies using Finite Element Analysis (FEA) in combination with full scale collision data. Montana State University contracted with ASSURE to conduct component level testing for the project, and provide data for validating FEA models being developed at the National Institute of Aviation Research (NIAR). Component level testing consisted of the following aircraft components: Cessna 182B struts, wings, and windscreens. In order to accurately simulate in-flight geometry, fixtures were custom fabricated to individually mount aircraft components. High velocity impact data was collected via load cells, high speed video, and Digital Image Correlation (DIC). A drone launching system developed during an MSU conducted research effort was used to launch Phantom 3 quadcopter UAVs as projectiles for component level tests. For all tests, the impact was captured from two viewpoints using high speed video, and reaction force data was collected using load cells at critical attachment points. For wing and windscreen testing, 2-D DIC and 3-D DIC were used respectively to capture displacements during the collision. Testing showed that struts received mainly superficial damage, but that both wings and windscreens exhibited the potential for catastrophic failure.Item An operational methodology for validating satellite-based snow albedo measurements using a UAV(Montana State University - Bozeman, College of Letters & Science, 2021) Mullen, Andrew Louiselle; Chairperson, Graduate Committee: Eric A. Sproles; Eric A. Sproles, Jordy Hendrikx, Joseph A. Shaw and Charles K. Gatebe were co-authors of the article, 'An operational methodology for validating satellite-based snow albedo measurements using a UAV' submitted to the journal 'Frontiers in remote sensing' which is contained within this thesis.The albedo, or reflectivity, of seasonal snowpack directly controls the timing and magnitude of snowmelt and runoff. Snow albedo is affected by a large number of snow physical and environmental properties that vary considerably at multiple spatiotemporal scales. This variability introduces a high degree of uncertainty into existing modeling techniques. Models for snowmelt that require snow albedo can be improved by incorporating satellite measurements to inform and update estimates of this snow property. However, satellite measurements are susceptible to a multitude of error sources, which requires them to be calibrated and validated by means of ground-based measurements. Ground-based measurements from automated weather stations are often located at sparsely-distributed monitoring sites in homogeneous meadow environments. These spatially restricted in-situ data provide biased validation and calibration data that are not representative of the heterogeneous landscapes that comprise many seasonally snow-covered watersheds. In order to provide comprehensive validation and calibration of satellite albedo products, multiple near-surface measurements should be taken across large areas to capture the high degree of spatial variability that snow albedo can exhibit. UAV albedo measurements can be used to bridge the scaling gap between satellite and point-based measurements. Since these platforms are in a novel stage, the requisite methodologies for topographic correction and comparison to gridded albedo products do not exist. Additionally, there lacks a general understanding of the spatial scaling of albedo measurements in heterogeneous terrain. This research aims to develop these methodologies and provide a comprehensive understanding of how to deploy these platforms and properly interpret their measurements. We first developed and validated a topographic correction using ground-based measurements of snow albedo in a sloping alpine meadow. Sensitivity analyses on both ground validation measurements and UAV-based albedo surveys in our alpine study area highlight the implications of using different user-defined parameters for the proposed topographic correction and satellite comparison methods. Improvements to the methodology can be made in the way it accounts for trees, shading, and cloud cover. This research develops the initial steps requisite to the operationalization of UAV albedo measurements and standardization of the techniques.Item Reduced-order aeroelastic modeling of a torsionally compliant UAV rotor blade(Montana State University - Bozeman, College of Engineering, 2021) Marks, Montana William; Chairperson, Graduate Committee: Mark JankauskiSmall-scale quadrotor helicopters, or quadcopters, have increased in popularity significantly in the past decade. These unmanned aerial vehicles (UAVs) have a wide range of applications - from aerial photography and cinematography to agriculture. Increasing flight time and payload capacity are of the utmost importance when designing these systems, and reducing vehicle weight is the simplest method for improving these performance metrics. However, lighter components and structures are often more flexible and may deform during operation. This is especially the case for flexible UAV blade rotor behavior during flight. Modeling rotor blade deformations is non-trivial due to the coupling between the structure and the surrounding flow, which is called Fluid-Structure Interaction (FSI). Several methods exist for FSI modeling where the most common involves integrating Finite Element and Computational Fluid Dynamics solvers. However, these higher-fidelity models are computationally expensive and are not ideal for parametric studies that consider variable rotor geometry, material properties or other physical characteristics. This research develops low-order modeling techniques that can be leveraged by UAV rotor designers. Here, a reduced-order FSI model of a small-scale UAV rotor blade is developed using Lagrangian mechanics paired with a blade element model. The rotor blade is discretized into rectangular elements along the span. Each blade element is constrained to uni-axial rotation about the span-wise axis and is treated as a torsional stiffness element. The quasi-static equilibrium state of the structure due to aerodynamic forces at user-defined operational conditions is then determined. The model presented is capable of producing a converged solution in as little as 0.016 seconds, as opposed to higher-order FSI models, which can take up to several orders of magnitude longer to solve. It is determined that the deflection of a flexible blade can reduce the total aerodynamic lift from 18-25% when compared to a rigid blade with the same initial geometry. It is shown that the model allows a user to tailor the initial pre-twist of the flexible rotor blade such that losses in lift are reduced to 0.68-5.7%.Item Cessna 182b windscreen material model development and full scale UAS to aircraft impact testing facility(Montana State University - Bozeman, College of Engineering, 2020) Arnold, Forrest Jacob; Chairperson, Graduate Committee: Douglas S. CairnsUnmanned Aircraft Systems (UAS) have become popular in the last decade. More than 1.5 million have been registered by the Federal Aviation Administration (FAA) since 2015. In order to understand the risk UAS pose to manned aircraft and make informed regulation decisions, the FAA has created air to air collision studies. As a part of the FAA general aviation air to air collision research, a Cessna 182 windscreen material model and a full scale impact testing facility were required. A Finite Element Crash Model of a Cessna 182 is in development as a part of the general aviation air to air collision research. The National Institute for Aviation Research at Wichita State University is managing development of the model. In support of that work, an LS-DYNA material model of the Poly(Methyl methacrylate) windscreen was developed. Results from tensile testing at multiple strain rates were used to develop material models using MAT_124 and MAT_187. A model of an impact tower was created to compare the material models to test results. The material models were tuned to better fit the impact tower test results. MAT_187 has more flexible material inputs, which allowed it to outperform MAT_124. A full scale impact testing facility was developed to support Finite Element model validation and direct testing of UAS to aircraft impact. A slingshot style launcher was designed and built to launch common quadcopter style UAS. Testing has shown that the launcher is capable of 120 knots with the accuracy required to repeatably hit the leading edge of a wing. Additionally, the launch site required a system for instrumented testing to compare experimental results with finite element results. A system was developed to allow flexible fixturing, impact speed and orientation measurement, and inclusion of load cells and strain gauges.Item Toward the design and characterization of a dynamically similar artificial insect wing(Montana State University - Bozeman, College of Engineering, 2019) Reid, Heidi Elita; Chairperson, Graduate Committee: Mark JankauskiMicro air vehicles (MAVs) are a useful tool for numerous tasks, such as environmental mapping, search and rescue, and military reconnaissance. As MAV applications require them to operate at smaller and smaller length scales, traditional propulsion mechanisms (e.g. fixed wings, rotating propellers) cannot meet these demands. Conversely, flapping wing micro air vehicles (FWMAVs) can to realize flight at sub centimeter-lengths. However, FWMAVs face design challenges that preclude autonomous flight, including inefficient energetics and reliable on-board sensing. A comprehensive understanding of flying insect biomechanics may provide valuable design insights to help overcome the challenges experienced by FWMAVs. Insect wings have biological sensors that provide feedback to control attitude and wing deformation improves both inertial and aerodynamic power economy. Consequently, the insect wing can guide the design FWMAV-employed artificial insect wings. The present work aims to (1) dynamically characterize real insect wings via experimental modal analysis, and (2) develop dynamically similar artificial wings to be used on FWMAVs or in controlled studies. To our knowledge, no existing artificial insect wing models are isospectral and isomodal with respect to their biological counterparts. Isomodality and isospectrality imply they have identical frequency response functions and vibration mode shapes, and thus will deform similarly under realistic flapping conditions. We measured the frequency response function and vibration modes of fresh Manduca sexta forewings using an electrodynamic shaker and planar scanning vibrometer and estimated the wings' mass distribution via a cut-and-weigh procedure. Based upon our results, we designed and constructed the artificial wings using fused filament fabrication to print a polylactic acid vein structure, based upon the actual vein size and arrangement present in biological wings. Thin polymer films were manually layered over the vein structure and trimmed to fit the wing boundaries to produce a flat wing structure. We determined that the biological and artificial wings have nearly identical natural frequencies, damping ratios, gain, and shape for the first vibration mode. The second mode exhibited complex modal behavior previously unreported in literature, which likely has significant implications to flapping wing aerodynamics. We demonstrate the feasibility of fabricating economical, realistic artificial wings for robotic applications moving forward.Item Simulation, design and validation of a solid oxide fuel cell powered propulsion system for an unmanned aerial vehicle(Montana State University - Bozeman, College of Engineering, 2009) Lindahl, Peter Allan; Chairperson, Graduate Committee: Steven R. ShawThis thesis presents a physically-based model for design and optimization of a fuel cell powered electric propulsion system for an Unmanned Aerial Vehicle (UAV). Components of the system include a Solid Oxide Fuel Cell (SOFC) providing power, motor controller, Brushless DC (BLDC) motor, and a propeller. Steady-state models for these components are integrated into a simulation program and solved numerically. This allows an operator to select constraints and explore design trade-offs between components, including fuel cell, controller, motor and propeller options. We also presents a graphical procedure using the model that allows rapid assessment and selection of design choices, including fuel cell characteristics and hybridization with multiple sources. To validate this simulation program, a series of experiments conducted on an instrumented propulsion system in a low-speed wind tunnel is provided for comparison. These experimental results are consistent with model predictions.