Matching Items (119)

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Improving damage detection and localization in complex composites

Description

The goal of this research is to couple a physics-based model with adaptive algorithms to develop a more accurate and robust technique for structural health monitoring (SHM) in composite structures.

The goal of this research is to couple a physics-based model with adaptive algorithms to develop a more accurate and robust technique for structural health monitoring (SHM) in composite structures. The purpose of SHM is to localize and detect damage in structures, which has broad applications to improvements in aerospace technology. This technique employs PZT transducers to actuate and collect guided Lamb wave signals. Matching pursuit decomposition (MPD) is used to decompose the signal into a cross-term free time-frequency relation. This decoupling of time and frequency facilitates the calculation of a signal's time-of-flight along a path between an actuator and sensor. Using the time-of-flights, comparisons can be made between similar composite structures to find damaged regions by examining differences in the time of flight for each path between PZTs, with respect to direction. Relatively large differences in time-of-flight indicate the presence of new or more significant damage, which can be verified using a physics-based approach. Wave propagation modeling is used to implement a physics based approach to this method, which is coupled with adaptive algorithms that take into account currently existing damage to a composite structure. Previous SHM techniques for composite structures rely on the assumption that the composite is initially free of all damage on both a macro and micro-scale, which is never the case due to the inherent introduction of material defects in its fabrication. This method provides a novel technique for investigating the presence and nature of damage in composite structures. Further investigation into the technique can be done by testing structures with different sizes of damage and investigating the effects of different operating temperatures on this SHM system.

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Created

Date Created
  • 2015-05

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Analysis of FDM-Enabled Thermoplastics as Hybrid Rocket Fuel

Description

In this analysis, materials capable of being 3D printed such as acrylonitrile-butadiene styrene (ABS), polyethylene terephthalate-glycol (PETG), and polylactic acid (PLA) were analyzed mathematically to determine their potential application as

In this analysis, materials capable of being 3D printed such as acrylonitrile-butadiene styrene (ABS), polyethylene terephthalate-glycol (PETG), and polylactic acid (PLA) were analyzed mathematically to determine their potential application as a fuel source for a hybrid rocket engine currently being developed by Daedalus Astronautics. By developing a 3D printed fuel option, new fuel grain geometries can be manufactured and tested that have the potential to greatly improve regression and flow characteristics of hybrid rockets. In addition, 3D printed grains have been shown to greatly reduce manufacturing time while improving grain-to-grain consistency. In the end, it was found that ABS, although the most difficult material to work with, would likely provide the best results as compared to an HTPB baseline. This is because after conducting a heat conservation analysis similar to that employed by NASA's chemical equilibrium with applications code (CEA), ABS was shown to operate at similarly high levels of specific impulse at approximately the same oxidizer-to-fuel ratio, meaning the current Daedalus test setup for HTPB would be applicable to ABS. In addition, PLA was found to require a far lower oxidizer-to-fuel ratio to achieve peak specific impulse than any of the other fuels analyzed leading to the conclusion that in a flight-ready engine it would likely require less oxidizer and pressurization mass, and therefore, less overall system mass, to achieve thrust levels similar to ABS and HTPB. By improving the thrust-to-weight ratio in this way a more efficient engine could be developed. Following these results, future works will include the hot-fire testing of the four fuel options to verify the analysis method used. Additionally, the ground work has been set for future analysis and development of complex fuel port geometries which have been shown to further improve flight characteristics.

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Created

Date Created
  • 2017-05

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A Space Elevator to Mars: Calculating Space Flight Trajectories

Description

Human habitation of other planets requires both cost-effective transportation and low time-of-flight for human passengers and critical supplies. The current methods for interplanetary orbital transfers, such as the Hohmann transfer,

Human habitation of other planets requires both cost-effective transportation and low time-of-flight for human passengers and critical supplies. The current methods for interplanetary orbital transfers, such as the Hohmann transfer, require either expensive, high fuel maneuvers or extended space travel. However, by utilizing the high velocities of a super-geosynchronous space elevator, spacecraft released from an apex anchor could achieve interplanetary transfers with minimal Delta V fuel and time of flight requirements. By using Lambert’s Problem and Free Release propagation to determine the minimal fuel transfer from a terrestrial space elevator to Mars under a variety of initial conditions and time-of-flight constraints, this paper demonstrates that the use of a space elevator release can address both needs by dramatically reducing the time-of-flight and the fuel budget.

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Created

Date Created
  • 2020-05

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An Automated Test System for Terahertz Receiver Characterization

Description

An automated test system was developed to characterize detectors for the Kilopixel Array Pathfinder Project (KAPPa). KAPPa is an astronomy instrument that detects light at terahertz wavelengths using a 16-pixel

An automated test system was developed to characterize detectors for the Kilopixel Array Pathfinder Project (KAPPa). KAPPa is an astronomy instrument that detects light at terahertz wavelengths using a 16-pixel heterodyne focal plane array. Although primarily designed for the KAPPa receiver, the test system can be used with other instruments to automate tests that might be tedious and time-consuming by hand. Mechanical components of the test setup include an adjustable structure of aluminum t-slot framing that supports a rotating chopper. Driven by a stepper motor, the chopper alternates between blackbodies at room temperature and 77 K. The cold load consists of absorbing material submerged in liquid nitrogen in an open Styrofoam cooler. Scripts written in Matlab and Python control the mechanical system, interface with receiver components, and process data. To calculate the equivalent noise temperature of a receiver, the y-factor method is used. Test system operation was verified by sweeping the local oscillator frequency and power level for two room temperature Schottky diode receivers from Virginia Diodes, Inc. The test system was then integrated with the KAPPa receiver, providing a low cost, simple, adaptable means to measure noise with minimal user intervention.

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Created

Date Created
  • 2014-05

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An Assessment of the Performance of Machine Learning Techniques When Applied to Trajectory Optimization

Description

Prior research has confirmed that supervised learning is an effective alternative to computationally costly numerical analysis. Motivated by NASA's use of abort scenario matrices to aid in mission operations and

Prior research has confirmed that supervised learning is an effective alternative to computationally costly numerical analysis. Motivated by NASA's use of abort scenario matrices to aid in mission operations and planning, this paper applies supervised learning to trajectory optimization in an effort to assess the accuracy of a less time-consuming method of producing the magnitude of delta-v vectors required to abort from various points along a Near Rectilinear Halo Orbit. Although the utility of the study is limited, the accuracy of the delta-v predictions made by a Gaussian regression model is fairly accurate after a relatively swift computation time, paving the way for more concentrated studies of this nature in the future.

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Created

Date Created
  • 2018-05

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Automated Generation of Aircraft Wing Structures

Description

This paper describes the development of a software tool used to automate the preliminary design of aircraft wing structure. By taking wing planform and aircraft weight as inputs, the tool

This paper describes the development of a software tool used to automate the preliminary design of aircraft wing structure. By taking wing planform and aircraft weight as inputs, the tool is able to predict loads that will be experienced by the wing. An iterative process is then used to select optimal material thicknesses for each section of the design to minimize total structural weight. The load analysis checks for tensile failure as well as Euler buckling when considering if a given wing structure is valid. After running a variety of test cases with the tool it was found that wing structure of small-scale aircraft is predominantly buckling driven. This is problematic because commonly used weight estimation equations are based on large scale aircraft with strength driven wing designs. Thus, if these equations are applied to smaller aircraft, resulting weight estimates are often much lower than reality. The use of a physics-based approach to preliminary sizing could greatly improve the accuracy of weight predictions and accelerate the design process.

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Created

Date Created
  • 2019-12

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The Effect of Spoilers on Vehicle Aerodynamics and Performance

Description

An understanding of aerodynamics is crucial for automobile performance and efficiency. There are many types of “add-on” aerodynamic devices for cars including wings, splitters, and vortex generators. While these have

An understanding of aerodynamics is crucial for automobile performance and efficiency. There are many types of “add-on” aerodynamic devices for cars including wings, splitters, and vortex generators. While these have been studied extensively, rear spoilers have not, and their effects are not as widely known. A Computational Fluid Dynamics (CFD) and wind tunnel study was performed to study the effects of spoilers on vehicle aerodynamics and performance. Vehicle aerodynamics is geometry dependent, meaning what applies to one car may or may not apply on another. So, the Scion FRS was chosen as the test vehicle because it is has the “classic” sports car configuration with a long hood, short rear, and 2+2 passenger cabin while also being widely sold with a plethora of aftermarket aerodynamic modifications available. Due to computing and licensing restrictions, only a 2D CFD simulation was performed in ANSYS Fluent 19.1. A surface model of the centerline of the car was created in SolidWorks and imported into ANSYS, where the domain was created. A mesh convergence study was run to determine the optimum mesh size, and Realizable k-epsilon was the chosen physics model. The wind tunnel lacked equipment to record quantifiable data, so the wind tunnel was utilized for flow visualization on a 1/24 scale car model to compare with the CFD.

0° spoilers reduced the wake area behind the car, decreasing pressure drag but also decreasing underbody flow, causing a reduction in drag and downforce. Angled spoilers increased the wake area behind the car, increasing pressure drag but also increasing underbody flow, causing an increase in drag and downforce. Longer spoilers increased these effects compared to shorter spoilers, and short spoilers at different angles did not create significantly different effects. 0° spoilers would be best suited for cases that prioritize fuel economy or straight-line acceleration and speed due to the drag reduction, while angled spoilers would be best suited for cars requiring downforce. The angle and length of spoiler would depend on the downforce needed, which is dependent on the track.

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Created

Date Created
  • 2019-12

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Communications Between Air Traffic Controllers and Pilots During Simulated Arrivals: Relation of Closed Loop Communication Deviations to Loss of Separation

Description

Communications between air traffic controllers and pilots are critical to national airspace traffic management. Measuring communications in real time made by pilots and air traffic controllers has the potential to

Communications between air traffic controllers and pilots are critical to national airspace traffic management. Measuring communications in real time made by pilots and air traffic controllers has the potential to predict human error. In this thesis a measure for Deviations from Closed Loop Communications is defined and tested to predict a human error event, Loss of Separation (LOS). Six retired air traffic controllers were recruited and tested in three conditions of varying workload in an Terminal Radar Approach Control Facility (TRACON) arrival radar simulation. Communication transcripts from simulated trials were transcribed and coding schemes for Closed Loop Communication Deviations (CLCD) were applied. Results of the study demonstrated a positive correlation between CLCD and LOS, indicating that CLCD could be a variable used to predict LOS. However, more research is required to determine if CLCD can be used to predict LOS independent of other predictor variables, and if CLCD can be used in a model that considers many different predictor variables to predict LOS.

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Created

Date Created
  • 2020

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Unique Design Discoveries for a Modern Mach 1.3 Airliner Including Anomalies in the Shock Wave Formation Along a Highly Swept Blunt Leading Edge Wing

Description

The process of designing any real world blunt leading-edge wing is tedious andinvolves hundreds, if not thousands, of design iterations to narrow down a single design.
Add in the complexities

The process of designing any real world blunt leading-edge wing is tedious andinvolves hundreds, if not thousands, of design iterations to narrow down a single design.
Add in the complexities of supersonic flow and the challenge increases exponentially.
One possible, and often common, pathway for this design is to jump straight into detailed
volume grid computational fluid dynamics (CFD), in which the physics of supersonic
flow are modeled directly but at a high computational cost and thus an incredibly long
design process. Classical aerodynamics experts have published work describing a process
which can be followed which might bypass the need for detailed CFD altogether.

This work outlines how successfully a simple vortex lattice panel method CFDcode can be used in the design process for a Mach 1.3 cruise speed airline wing concept.
Specifically, the success of the wing design is measured in its ability to operate subcritically (i.e. free of shock waves) even in a free stream flow which is faster than the
speed of sound. By using a modified version of Simple Sweep Theory, design goals are
described almost entirely based on defined critical pressure coefficients and critical Mach
numbers. The marks of a well-designed wing are discussed in depth and how these traits
will naturally lend themselves to a well-suited supersonic wing.

Unfortunately, inconsistencies with the published work are revealed by detailedCFD validation runs to be extensive and large in magnitude. These inconsistencies likely
have roots in several concepts related to supersonic compressible flow which are
explored in detail. The conclusion is made that the theory referenced in this work by the
classical aerodynamicists is incorrect and/or incomplete. The true explanation for the
perplexing shock wave phenomenon observed certainly lies in some convolution of the
factors discussed in this thesis. Much work can still be performed in the way of creating
an empirical model for shock wave formation across a highly swept wing with blunt
leading-edge airfoils.

Contributors

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Created

Date Created
  • 2020

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Numerical modelling of galvanic structural joints subjected to combined environmental and mechanical loading

Description

Dissimilar metal joints such as aluminum-steel joints are extensively used in automobile, naval and aerospace applications and these are subjected to corrosive environmental and mechanical loading resulting in eventual failure

Dissimilar metal joints such as aluminum-steel joints are extensively used in automobile, naval and aerospace applications and these are subjected to corrosive environmental and mechanical loading resulting in eventual failure of the structural joints. In the case of aluminum alloys under aggressive environment, the damage accumulation is predominantly due to corrosion and is accelerated in presence of other metals. During recent years several approaches have been employed to develop models to assess the metal removal rate in the case of galvanic corrosion. Some of these models are based on empirical methods such as regression analysis while others are based on quantification of the ongoing electrochemical processes. Here, a numerical model for solving the Nernst- Planck equation, which captures the electrochemical process, is implemented to predict the galvanic current distribution and, hence, the corrosion rate of a galvanic couple. An experimentally validated numerical model for an AE44 (Magnesium alloy) and mild steel galvanic couple, available in the literature, is extended to simulate the mechano- electrochemical process in order to study the effect of mechanical loading on the galvanic current density distribution and corrosion rate in AE44-mild steel galvanic couple through a multiphysics field coupling technique in COMSOL Multiphysics®. The model is capable of tracking moving boundariesy of the corroding constituent of the couple by employing Arbitrary Langrangian Eulerian (ALE) method.Results show that, when an anode is under a purely elastic deformation, there is no apparent effect of mechanical loading on the electrochemical galvanic process. However, when the applied tensile load is sufficient to cause a plastic deformation, the local galvanic corrosion activity at the vicinity of the interface is increased remarkably. The effect of other factors, such as electrode area ratios, electrical conductivity of the electrolyte and depth of the electrolyte, are studied. It is observed that the conductivity of the electrolyte significantly influences the surface profile of the anode, especially near the junction. Although variations in electrolyte depth for a given galvanic couple noticeably affect the overall corrosion, the change in the localized corrosion rate at the interface is minimal. Finally, we use the model to predict the current density distribution, rate of corrosion and depth profile of aluminum alloy 7075-stainless steel 316 galvanic joints, which are extensively used in maritime structures.

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Created

Date Created
  • 2015