You searched for +publisher:"Virginia Tech" +contributor:("Ross, Shane D.").
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Virginia Tech
1.
Gargioni, Gustavo.
Multiple Asteroid Retrieval Mission.
Degree: MS, Aerospace Engineering, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/98838 
► In this thesis, the possibility of enabling space-mining for the upcoming decade is explored. Making use of recently-proven reusable rockets, we envision a fleet of…
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▼ In this thesis, the possibility of enabling space-mining for the upcoming decade is explored. Making use of recently-proven reusable rockets, we envision a fleet of spacecraft capable of reaching Near-Earth asteroids, NEAs. To analyze this idea, the goal of this problem is to maximize the asteroid mass retrieved within a spacecraft max life span. Explicitly, the maximum lifetime of the spacecraft fleet is set at 30 years. A fuel supply-chain is proposed and designed so that each spacecraft is refueled before departing for each asteroid. To maximize access to the number of asteroids and retrievable mass for each mission, we propose launching each mission from an orbit with low escape velocity. A location after the Moon, at the L2-Halo orbit, was selected due to its easy access from Low-Earth Orbit and for a synergy with the proposed new space station at the Moon orbit. Using data from NASA databases, we investigated the asteroids in the period between 2030 and 2060 that could be captured and returned with two approaches, MARM-1 and MARM-2. Together, these databases provide all information for every asteroid's close approach known today. Returning the asteroid as a whole is explored in the MARM-1 method, while MARM-2 evaluates the possibility of reaching larger asteroids and returning a fragment of their masses, such that it optimizes the available cargo weight per time of flight of each mission. The following results are compared with previous work from the community. The results show a 96% reduction in the cost per kg, with an enormous increase in retrieved mass. With these results, this thesis shows that not solely energy or dynamic optimization will be responsible for proving space mining feasibility, but rather a combination of those and business best practices. Proving feasibility for space mining is a complex and immense problem. Although this thesis opens new possibilities for future work on the field and sparkes the interest of private endeavors, the final solution for this problem still requires additional exploration.
Advisors/Committee Members: Black, Jo (committeechair), Ross, Shane D. (committee member), England, Scott (committee member).
Subjects/Keywords: Near-Earth Asteroid; Near-Earth Object; Asteroid; S-Type; M-Type; A-Type; Close Approach; Asteroid Return Mission; L2-Halo; Starship; Spacex; Reusability; in-space refueling; CNEOS; Cislunar; NASA; Gateway
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APA (6th Edition):
Gargioni, G. (2020). Multiple Asteroid Retrieval Mission. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/98838
Chicago Manual of Style (16th Edition):
Gargioni, Gustavo. “Multiple Asteroid Retrieval Mission.” 2020. Masters Thesis, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/98838.
MLA Handbook (7th Edition):
Gargioni, Gustavo. “Multiple Asteroid Retrieval Mission.” 2020. Web. 09 Mar 2021.
Vancouver:
Gargioni G. Multiple Asteroid Retrieval Mission. [Internet] [Masters thesis]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/98838.
Council of Science Editors:
Gargioni G. Multiple Asteroid Retrieval Mission. [Masters Thesis]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/98838
Virginia Tech
2.
Shaffer, Irena Marie.
Effects of Echolocation Calls on the Interactions of Bat Pairs using Transfer Entropy Analysis.
Degree: MS, Engineering Mechanics, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/98672
► Manyanimalspeciesexhibitcollectivebehaviorwheregroupsofanimalscoordinatetheir motion, as in flocking or schooling. Many species of bats also demonstrate this behavior. Bats are unique among these animals in that they use…
(more)
▼ Manyanimalspeciesexhibitcollectivebehaviorwheregroupsofanimalscoordinatetheir motion, as in flocking or schooling. Many species of bats also demonstrate this behavior. Bats are unique among these animals in that they use echolocation as their primary means of navigation. Bats produce ultrasonic pulses or calls and listen to the returning echo to "visualize" their environment. Bats using echolocation in large groups run the risk of other bat calls interfering with their ability to hear their own calls. They have developed various waystopreventinterferencewhichmayleadtodifferentbehaviorwhenflyingwithotherbats thanwhenflyingalone. Fielddatafromamaternitycolonyofgraybatswerecollectedusing a system of cameras and microphones. These data were analyzed to quantify the interaction between pairs of bats and to determine the effect echolocation calls have on this interaction. Results show that there is evidence of information transfer about both the speed of the bats and their turning behavior. There was also evidence of a possible leader-follower interaction in some subsets of the data.
Advisors/Committee Members: Abaid, Nicole (committeechair), Ford, W. Mark (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: Transfer entropy; Bat swarms; Animal group interaction; 3D tracking; Microphone arrays
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APA (6th Edition):
Shaffer, I. M. (2020). Effects of Echolocation Calls on the Interactions of Bat Pairs using Transfer Entropy Analysis. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/98672
Chicago Manual of Style (16th Edition):
Shaffer, Irena Marie. “Effects of Echolocation Calls on the Interactions of Bat Pairs using Transfer Entropy Analysis.” 2020. Masters Thesis, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/98672.
MLA Handbook (7th Edition):
Shaffer, Irena Marie. “Effects of Echolocation Calls on the Interactions of Bat Pairs using Transfer Entropy Analysis.” 2020. Web. 09 Mar 2021.
Vancouver:
Shaffer IM. Effects of Echolocation Calls on the Interactions of Bat Pairs using Transfer Entropy Analysis. [Internet] [Masters thesis]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/98672.
Council of Science Editors:
Shaffer IM. Effects of Echolocation Calls on the Interactions of Bat Pairs using Transfer Entropy Analysis. [Masters Thesis]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/98672
Virginia Tech
3.
Epstein, Stephen David.
The Stochastic Dynamics of Optomechanical Sensors for Atomic Force Microscopy.
Degree: MS, Engineering Mechanics, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23730
► This work explores the stochastic dynamics and important diagnostics of a mechanical resonator (nanobeam) used in cavity optomechanical sensors for atomic force microscopy. Atomic force…
(more)
▼ This work explores the stochastic dynamics and important diagnostics of a mechanical resonator (nanobeam) used in cavity optomechanical sensors for atomic force microscopy. Atomic force microscopy (AFM) is a tool to image surface topology down to the level of individual atoms. Conventional AFM has been an essential tool for micro and nanoscale studies in physics, chemistry, and biology. Cavity optomechanical sensors for AFM extend the utility of conventional AFM into a new regime of high sensitivity k is approximately 1 N/m and high frequency f0 is approximately 10 MHz. Cavity optomechanical sensors for AFM are unique because they use near field optics to transduce the position of a nanobeam. The nanobeam is not able to be transduced by more conventional AFM techniques, such as laser interferometry, because the nanobeam is smaller than the spot size of the laser.
This work determines the noise spectrum G of a nanobeam in water and in air. Also important diagnostics of the nanobeam are determined in air and in water. These important diagnostics include the quality factor Q and natural frequency in fluid omega_f. It is found that the nanobeam is overdamped in water. However, the nanobeam is underdamped in air and has quality factor of Q is approximately 4. The noise spectrum is determined from deterministic numerical calculations and the Fluctuation-Dissipation Theorem. This is possible because the same molecular processes, Brownian motion, cause both the fluctuations of the nanobeam and the dissipation of the nanobeam.
Advisors/Committee Members: Paul, Mark R. (committeechair), Ragab, Saad A. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: optomechanics; atomic force microscopy; noise spectrum
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APA (6th Edition):
Epstein, S. D. (2013). The Stochastic Dynamics of Optomechanical Sensors for Atomic Force Microscopy. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23730
Chicago Manual of Style (16th Edition):
Epstein, Stephen David. “The Stochastic Dynamics of Optomechanical Sensors for Atomic Force Microscopy.” 2013. Masters Thesis, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/23730.
MLA Handbook (7th Edition):
Epstein, Stephen David. “The Stochastic Dynamics of Optomechanical Sensors for Atomic Force Microscopy.” 2013. Web. 09 Mar 2021.
Vancouver:
Epstein SD. The Stochastic Dynamics of Optomechanical Sensors for Atomic Force Microscopy. [Internet] [Masters thesis]. Virginia Tech; 2013. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/23730.
Council of Science Editors:
Epstein SD. The Stochastic Dynamics of Optomechanical Sensors for Atomic Force Microscopy. [Masters Thesis]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23730
4.
Orange, Nicholas Brian.
Transfer Entropy Analysis of the Interactions of Flying Bats.
Degree: MS, Engineering Mechanics, 2015, Virginia Tech
URL: http://hdl.handle.net/10919/53955
► In this document, a low-cost, portable, non-invasive method of collecting the 3D trajectories of flying bats is first presented. An array of commercially available camera…
(more)
▼ In this document, a low-cost, portable, non-invasive method of collecting the 3D trajectories of flying bats is first presented. An array of commercially available camera and light components is used alongside a number of well-established calibration and triangulation techniques to resolve the motion of agents through a 3D volume. It is shown that this system is capable of accurately capturing the bats' flight paths in a field experiment. The use of non-visible illumination ensures that a natural cave environment is disturbed as little as possible for behavioral experiments.
Following is a transfer entropy analysis approach applied to the 3D paths of bats flying in pairs. The 3D trajectories are one-dimensionally characterized as inverse curvature time series to allow for entropy calculations. In addition to a traditional formulation of information flow between pair members, a path coupling hypothesis is pursued with time-delay modifications implemented in such a way as to not change the Markovianity of the process. With this modification, trends are found that suggest a leader-follower interaction between the front bat and the rear bat, although statistical significance is not reached due to the small number of pairs considered.
Advisors/Committee Members: Abaid, Nicole (committeechair), Mueller, Rolf (committee member), Hanna, James (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: Transfer Entropy; Animal Behavior; 3D Tracking
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APA ·
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APA (6th Edition):
Orange, N. B. (2015). Transfer Entropy Analysis of the Interactions of Flying Bats. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/53955
Chicago Manual of Style (16th Edition):
Orange, Nicholas Brian. “Transfer Entropy Analysis of the Interactions of Flying Bats.” 2015. Masters Thesis, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/53955.
MLA Handbook (7th Edition):
Orange, Nicholas Brian. “Transfer Entropy Analysis of the Interactions of Flying Bats.” 2015. Web. 09 Mar 2021.
Vancouver:
Orange NB. Transfer Entropy Analysis of the Interactions of Flying Bats. [Internet] [Masters thesis]. Virginia Tech; 2015. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/53955.
Council of Science Editors:
Orange NB. Transfer Entropy Analysis of the Interactions of Flying Bats. [Masters Thesis]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/53955
5.
Chakrabarti, Brato.
Catenaries in Viscous Fluid.
Degree: MS, Engineering Mechanics, 2015, Virginia Tech
URL: http://hdl.handle.net/10919/53832
► Slender structures in fluid flow exhibit a variety of rich behaviors. Here we study the equilibrium shapes of perfectly flexible strings that are moving with…
(more)
▼ Slender structures in fluid flow exhibit a variety of rich behaviors. Here we study the equilibrium shapes of perfectly flexible strings that are moving with a uniform velocity and axial flow in viscous fluid. The string is acted upon by local, anisotropic, linear drag forces and a uniform body force. Generically, the configurations of the string are planar, and we provide analytical expressions for the equilibrium shapes of the string as a first order five parameter dynamical system for the tangential angle of the body (θ). Phase portraits in the angle-curvature (θ,partial
s theta) plane are generated, that can be shown to be π periodic after appropriate scaling and reflection operations. The rich parameter space allows for different kinds of phase portraits that give rise to a variety of curve geometries. Some of these solutions are unstable due to the presence of compressive stresses. Special cases of the problem include sedimenting filaments, dynamic catenaries, and towed strings. We also discuss equilibrium configurations of towed cables and other relevant problems with fixed boundary conditions. Special cases of the boundary value problem involve towing of neutrally buoyant cables and strings with pure axial flow between two fixed points.
Advisors/Committee Members: Hanna, James (committeechair), Ross, Shane D. (committee member), Stremler, Mark A. (committee member).
Subjects/Keywords: Catenary; String; Towing; Dynamical System; Phase Portrait; Viscous Flow
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APA (6th Edition):
Chakrabarti, B. (2015). Catenaries in Viscous Fluid. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/53832
Chicago Manual of Style (16th Edition):
Chakrabarti, Brato. “Catenaries in Viscous Fluid.” 2015. Masters Thesis, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/53832.
MLA Handbook (7th Edition):
Chakrabarti, Brato. “Catenaries in Viscous Fluid.” 2015. Web. 09 Mar 2021.
Vancouver:
Chakrabarti B. Catenaries in Viscous Fluid. [Internet] [Masters thesis]. Virginia Tech; 2015. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/53832.
Council of Science Editors:
Chakrabarti B. Catenaries in Viscous Fluid. [Masters Thesis]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/53832
Virginia Tech
6.
Xie, Xuping.
Large Eddy Simulation Reduced Order Models.
Degree: PhD, Mathematics, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/77626
► This dissertation uses spatial filtering to develop a large eddy simulation reduced order model (LES-ROM) framework for fluid flows. Proper orthogonal decomposition is utilized to…
(more)
▼ This dissertation uses spatial filtering to develop a large eddy simulation reduced order model (LES-ROM) framework for fluid flows. Proper orthogonal decomposition is utilized to extract the dominant spatial structures of the system. Within the general LES-ROM framework, two approaches are proposed to address the celebrated ROM closure problem. No phenomenological arguments (e.g., of eddy viscosity type) are used to develop these new ROM closure models.
The first novel model is the approximate deconvolution ROM (AD-ROM), which uses methods from image processing and inverse problems to solve the ROM closure problem. The AD-ROM is investigated in the numerical simulation of a 3D flow past a circular cylinder at a Reynolds number Re=1000. The AD-ROM generates accurate results without any numerical dissipation mechanism. It also decreases the CPU time of the standard ROM by orders of magnitude.
The second new model is the calibrated-filtered ROM (CF-ROM), which is a data-driven ROM. The available full order model results are used offline in an optimization problem to calibrate the ROM subfilter-scale stress tensor. The resulting CF-ROM is tested numerically in the simulation of the 1D Burgers equation with a small diffusion parameter. The numerical results show that the CF-ROM is more efficient than and as accurate as state-of-the-art ROM closure models.
Advisors/Committee Members: Iliescu, Traian (committeechair), Borggaard, Jeffrey T. (committee member), Gugercin, Serkan (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: Reduced Order Modeling; Large Eddy Simulation; Approximate Deconvolution; Data-Driven Modeling; Stochastic Reduced Order Model; Spatial Filtering; Finite Element; Numerical Analysis
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APA ·
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APA (6th Edition):
Xie, X. (2017). Large Eddy Simulation Reduced Order Models. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/77626
Chicago Manual of Style (16th Edition):
Xie, Xuping. “Large Eddy Simulation Reduced Order Models.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/77626.
MLA Handbook (7th Edition):
Xie, Xuping. “Large Eddy Simulation Reduced Order Models.” 2017. Web. 09 Mar 2021.
Vancouver:
Xie X. Large Eddy Simulation Reduced Order Models. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/77626.
Council of Science Editors:
Xie X. Large Eddy Simulation Reduced Order Models. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/77626
Virginia Tech
7.
Gonzalez-Rocha, Javier.
Sensing Atmospheric Winds from Quadrotor Motion.
Degree: PhD, Aerospace Engineering, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/98657
► Wind observations that are critical for understanding meteorological processes occurring inside of the Earth's atmospheric boundary layer (ABL) are sparse due to limitations of conventional…
(more)
▼ Wind observations that are critical for understanding meteorological processes occurring inside of the Earth's atmospheric boundary layer (ABL) are sparse due to limitations of conventional atmospheric sensors. In this dissertation, dynamic systems and estimation theory are combined with experimental methods to exploit the flight envelope of multirotor UAS for wind sensing. The parameters of three quadrotor motion models, consisting of a kinematic particle model, a dynamic particle model, and a dynamic rigid body model, are characterized to measure wind velocity in hovering flight. Parameter characterizations are realized using data from wind tunnel, steady level flight tests and system identification experiments. Model-based wind estimations algorithms are developed using the kinematic particle model directly and by synthesizing state observers for the dynamic particle and rigid body models separately. For comparison purposes, the frequency response characteristic of the dynamic particle and rigid body models is examined to determine the range of wind fluctuations that each model can resolve. Performance comparisons demonstrate that the rigid body model to resolve higher wind fluctuations and yield more accurate wind estimates. The dissertation extends the rigid body wind estimation algorithm to estimate wind velocity profiles of the horizontal wind vector. The rigid body wind estimation algorithms is used to answer science questions about about the drift of a person in water.
Advisors/Committee Members: Sultan, Cornel (committeechair), Woolsey, Craig A. (committeechair), Black, Jonathan T. (committee member), De Wekker, Stephan F.J. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: Unmanned Aircraft Systems; State Estimation; System Identification
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APA ·
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APA (6th Edition):
Gonzalez-Rocha, J. (2020). Sensing Atmospheric Winds from Quadrotor Motion. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/98657
Chicago Manual of Style (16th Edition):
Gonzalez-Rocha, Javier. “Sensing Atmospheric Winds from Quadrotor Motion.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/98657.
MLA Handbook (7th Edition):
Gonzalez-Rocha, Javier. “Sensing Atmospheric Winds from Quadrotor Motion.” 2020. Web. 09 Mar 2021.
Vancouver:
Gonzalez-Rocha J. Sensing Atmospheric Winds from Quadrotor Motion. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/98657.
Council of Science Editors:
Gonzalez-Rocha J. Sensing Atmospheric Winds from Quadrotor Motion. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/98657
Virginia Tech
8.
Fino, Peter C.
Longitudinal Locomotor and Postural Control Following Mild Traumatic Brain Injury.
Degree: PhD, Mechanical Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/73775
► Millions of people sustain a mild traumatic brain injury (concussion) each year. While most clinical signs and symptoms resolve within 7-10 days for the majority…
(more)
▼ Millions of people sustain a mild traumatic brain injury (concussion) each year. While most clinical signs and symptoms resolve within 7-10 days for the majority of typical concussions, some gait and balance tasks have shown abnormalities lasting beyond the resolution of clinical symptoms. These abnormalities can persist after athletes have been medically cleared for competition, yet the implications of such changes are unclear. Most prior research has examined straight gait and standard measures of balance, yet there is a lack of knowledge regarding potential persistent effects on non-straight maneuvers or on indicators of motor control variability or complexity. To expand the knowledge of post-concussion locomotor and postural changes, this investigation examined the recovery of recently concussed athletes longitudinally, over the course of one year, in three domains: 1) path selection and body kinematics during turning gait, 2) non-linear local dynamic stability during straight gait, and 3) postural control complexity during quiet standing. Compared to matched health controls, concussed athletes exhibited significant and persistent differences in turning kinematics, local dynamic stability, and postural complexity over the initial six weeks following injury. These motor differences may increase the risk of injury to concussed athletes who are cleared to return to play. Given the persistent nature of these effects, future clinical tests may benefit from incorporating gait assessments before returning athletes to competition. Future research should prospectively and longitudinally monitor locomotor and postural control in conjunction with structural and functional changes within the brain to better understand the pathophysiology of concussions and potential rehabilitation strategies.
Advisors/Committee Members: Nussbaum, Maury A. (committeechair), Brolinson, P. Gunnar (committeechair), Queen, Robin M. (committee member), Sturges, Robert H. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: concussion; brain injury; gait; turning; local dynamic stability; balance; postural stability
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APA ·
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Export
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APA (6th Edition):
Fino, P. C. (2016). Longitudinal Locomotor and Postural Control Following Mild Traumatic Brain Injury. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/73775
Chicago Manual of Style (16th Edition):
Fino, Peter C. “Longitudinal Locomotor and Postural Control Following Mild Traumatic Brain Injury.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/73775.
MLA Handbook (7th Edition):
Fino, Peter C. “Longitudinal Locomotor and Postural Control Following Mild Traumatic Brain Injury.” 2016. Web. 09 Mar 2021.
Vancouver:
Fino PC. Longitudinal Locomotor and Postural Control Following Mild Traumatic Brain Injury. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/73775.
Council of Science Editors:
Fino PC. Longitudinal Locomotor and Postural Control Following Mild Traumatic Brain Injury. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/73775
Virginia Tech
9.
Kappiyoor, Ravi.
Mechanical Properties of Elastomeric Proteins.
Degree: PhD, Engineering Mechanics, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/54563
► When we stretch and contract a rubber band a hundred times, we expect the rubber band to fail. Yet our heart stretches and contracts the…
(more)
▼ When we stretch and contract a rubber band a hundred times, we expect the rubber band to fail. Yet our heart stretches and contracts the same amount every two minutes, and does not fail. Why is that? What causes the significantly higher elasticity of certain molecules and the rigidity of others? Equally importantly, can we use this information to design materials for precise mechanical tasks? It is the aim of this dissertation to illuminate key aspects of the answer to these questions, while detailing the work that remains to be done.
In this dissertation, particular emphasis is placed on the nanoscale properties of elastomeric proteins. By better understanding the fundamental characteristics of these proteins at the nanoscale, we can better design synthetic rubbers to provide the same desired mechanical properties.
Advisors/Committee Members: Puri, Ishwar K. (committeechair), Dudek, Daniel M. (committeechair), Ross, Shane D. (committee member), Xing, Jianhua (committee member), Stremler, Mark A. (committee member).
Subjects/Keywords: Protein elasticity; molecular dynamics; nanoscale material properties
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APA (6th Edition):
Kappiyoor, R. (2014). Mechanical Properties of Elastomeric Proteins. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/54563
Chicago Manual of Style (16th Edition):
Kappiyoor, Ravi. “Mechanical Properties of Elastomeric Proteins.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/54563.
MLA Handbook (7th Edition):
Kappiyoor, Ravi. “Mechanical Properties of Elastomeric Proteins.” 2014. Web. 09 Mar 2021.
Vancouver:
Kappiyoor R. Mechanical Properties of Elastomeric Proteins. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/54563.
Council of Science Editors:
Kappiyoor R. Mechanical Properties of Elastomeric Proteins. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/54563
Virginia Tech
10.
Basu, Saikat.
Dynamics of vortices in complex wakes: modeling, analysis, and experiments.
Degree: PhD, Engineering Mechanics, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/51749
► The thesis develops singly-periodic mathematical models for complex laminar wakes which are formed behind vortex-shedding bluff bodies. These wake structures exhibit a variety of patterns…
(more)
▼ The thesis develops singly-periodic mathematical models for complex laminar wakes which are formed behind vortex-shedding bluff bodies. These wake structures exhibit a variety of patterns as the bodies oscillate or are in close proximity of one another. The most well-known formation comprises two counter-rotating vortices in each shedding cycle and is popularly known as the vk vortex street. Of the more complex configurations, as a specific example, this thesis investigates one of the most commonly occurring wake arrangements, which consists of two pairs of vortices in each shedding period. The paired vortices are, in general, counter-rotating and belong to a more general definition of the 2P mode, which involves periodic release of four vortices into the flow. The 2P arrangement can, primarily, be sub-classed into two types: one with a symmetric orientation of the two vortex pairs about the streamwise direction in a periodic domain and the other in which the two vortex pairs per period are placed in a staggered geometry about the wake centerline. The thesis explores the governing dynamics of such wakes and characterizes the corresponding relative vortex motion.
In general, for both the symmetric as well as the staggered four vortex periodic arrangements, the thesis develops two-dimensional potential flow models (consisting of an integrable Hamiltonian system of point vortices) that consider spatially periodic arrays of four vortices with their strengths being +/-1 and +/-2. Vortex formations observed in the experiments inspire the assumed spatial symmetry. The models demonstrate a number of dynamic modes that are classified using a bifurcation analysis of the phase space topology, consisting of level curves of the Hamiltonian. Despite the vortex strengths in each pair being unequal in magnitude, some initial conditions lead to relative equilibrium when the vortex configuration moves with invariant size and shape.
The scaled comparisons of the model results with experiments conducted in a flowing soap film with an airfoil, which was imparted with forced oscillations, are satisfactory and validate the reduced order modeling framework. The experiments have been performed by a collaborator group at the Department of Physics and Fluid Dynamics at the Technical University of Denmark (DTU), led by Dr. Anders Andersen. Similar experiments have also been run at
Virginia Tech as part of this dissertation and the preliminary results are included in this treatise.
The thesis also employs the same dynamical systems techniques, which have been applied to study the 2P regime dynamics, to develop a mathematical model for the P+S mode vortex wakes, with three vortices present in each shedding cycle. The model results have also been compared favorably with an experiment and the predictions regarding the vortex circulation data match well with the previous results from literature.
Finally, the thesis introduces a novel concept of clean and renewable energy extraction from vortex-induced vibrations of bluff bodies. The slow-moving…
Advisors/Committee Members: Stremler, Mark A. (committeechair), Jung, Sunghwan (committee member), Iliescu, Traian (committee member), Ross, Shane D. (committee member), Ragab, Saad A. (committee member).
Subjects/Keywords: Vortex dynamics; Point vortices; Bluff body wake; Fluid-structure interactions; Vortex-induced vibrations
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APA (6th Edition):
Basu, S. (2014). Dynamics of vortices in complex wakes: modeling, analysis, and experiments. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/51749
Chicago Manual of Style (16th Edition):
Basu, Saikat. “Dynamics of vortices in complex wakes: modeling, analysis, and experiments.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/51749.
MLA Handbook (7th Edition):
Basu, Saikat. “Dynamics of vortices in complex wakes: modeling, analysis, and experiments.” 2014. Web. 09 Mar 2021.
Vancouver:
Basu S. Dynamics of vortices in complex wakes: modeling, analysis, and experiments. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/51749.
Council of Science Editors:
Basu S. Dynamics of vortices in complex wakes: modeling, analysis, and experiments. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/51749
Virginia Tech
11.
Tehrani, Mehran.
Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation.
Degree: PhD, Engineering Mechanics, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/49547
► For many decades, fiber reinforced polymers (FRPs) have been extensively utilized in load-bearing structures. Their formability and superior in-plane mechanical properties have made them a…
(more)
▼ For many decades, fiber reinforced polymers (FRPs) have been extensively utilized in load-bearing structures. Their formability and superior in-plane mechanical properties have made them a viable replacement for conventional structural materials. Â A major drawback to FRPs is their weak interlaminar properties (e.g., interlaminar fracture toughness). The need for lightweight multifunctional structures has become vital for many applications and hence alleviating the out-of-plane mechanical (i.e., quasi-static, vibration, and impact) and electrical properties of FRPs while retaining minimal weight is the subject of many ongoing studies. The primary objective of this dissertation is to investigate the fundamental processes for developing hybrid, multifunctional composites based on surface grown carbon nanotubes (CNTs) on carbon fibersýarns. This study embraces the development of a novel low temperature synthesis technique to grow CNTs on virtually any substrate. The developed method graphitic structures by design (GSD) offers the opportunity to place CNTs in advantageous areas of the composite (e.g., at the ply interface) where conventional fiber architectures are inadequate. The relatively low temperature of the GSD (i.e. 550 C) suppresses the undesired damage to the substrate fibers. GSD carries the advantage of growing uniform and almost aligned CNTs at pre-designated locations and thus eliminates the agglomeration and dispersion problems associated with incorporating CNTs in polymeric composites. The temperature regime utilized in GSD is less than those utilized by other synthesis techniques such as catalytic chemical vapor deposition (CCVD) where growing CNTs requires temperature not less than 700 C. It is of great importance to comprehend the reasons for and against using the methods involving mixing of the CNTs directly with the polymer matrix, to either fabricate nanocomposites or three-phase FRPs. Hence, chapter 2 is devoted to the characterization of CNTs-epoxy nanocomposites at different thermo-mechanical environments via the nanoindentation technique. Improvements in hardness and stiffness of the CNTs-reinforced epoxy are reported. Long duration (45 mins) nanocreep tests were conducted to study the viscoelastic behavior of the CNT-nanocomposites. Finally, the energy absorption of these nanocomposites is measured via novel nanoimpact testing module. Chapter 3 elucidates a study on the fabrication and characterization of a three phase CNT-epoxy system reinforced with woven carbon fibers. Tensile test, high velocity impact (~100 ms-1), and dynamic mechanical analysis (DMA) were employed to examine the response of the hybrid composite and compare it with the reference CFRP with no CNTs. Quasi-static shear punch tests (QSSPTs) were also performed to determine the toughening and damage mechanisms of both the CNTs-modified and the reference CFRP composites during transverse impact loading. The synthesis of CNTs at 550 C via GSD is the focus of chapter 4. The GSD technique was adjusted to grow…
Advisors/Committee Members: Al-Haik, Marwan (committeechair), Jung, Sunghwan (committee member), Case, Scott W. (committee member), Ross, Shane D. (committee member), Hajj, Muhammad R. (committee member).
Subjects/Keywords: multiscale composites; carbon nanotubes; mechanical characterization; finite element method
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APA (6th Edition):
Tehrani, M. (2012). Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/49547
Chicago Manual of Style (16th Edition):
Tehrani, Mehran. “Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation.” 2012. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/49547.
MLA Handbook (7th Edition):
Tehrani, Mehran. “Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation.” 2012. Web. 09 Mar 2021.
Vancouver:
Tehrani M. Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/49547.
Council of Science Editors:
Tehrani M. Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/49547
Virginia Tech
12.
Sharma, Harsh Apurva.
Structure-preserving Numerical Methods for Engineering Applications.
Degree: PhD, Aerospace Engineering, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/99912
► Accurate numerical simulation of dynamical systems over long time horizons is essential in applications ranging from particle physics to geophysical fluid flow to space hazard…
(more)
▼ Accurate numerical simulation of dynamical systems over long time horizons is essential in applications ranging from particle physics to geophysical fluid flow to space hazard analysis. In many of these applications, the governing physical equations derive from a variational principle and their solutions exhibit physically meaningful invariants such as momentum, energy, or vorticity. Unfortunately, most traditional numerical methods do not account for the underlying geometric structure of the physical system, leading to simulation results that may suggest nonphysical behavior. In this dissertation, tools from geometric mechanics and computational methods are used to develop numerical integrators that respect the qualitative features of the physical system. The research presented here focuses on numerical schemes derived from variational principles– schemes that are general enough to apply to a large class of engineering problems. Energy-preserving algorithms are developed for mechanical systems by exploiting the underlying geometric properties. Numerical performance comparisons demonstrate that these algorithms provide almost exact energy preservation and lead to more accurate prediction. The advantages of these methods in the numerical simulation are illustrated by various representative examples from engineering applications, which include limit cycle oscillations of an aeroelastic system, dynamics of a neutrally buoyant underwater vehicle, and optimization for spherical shape correlation and matching.
Advisors/Committee Members: Patil, Mayuresh J. (committeechair), Woolsey, Craig A. (committeechair), Ross, Shane D. (committee member), Lee, Taeyoung (committee member), Sultan, Cornel (committee member).
Subjects/Keywords: Structure-preserving methods; Geometric numerical integration; Variational integrators; Lie group methods
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APA (6th Edition):
Sharma, H. A. (2020). Structure-preserving Numerical Methods for Engineering Applications. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/99912
Chicago Manual of Style (16th Edition):
Sharma, Harsh Apurva. “Structure-preserving Numerical Methods for Engineering Applications.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/99912.
MLA Handbook (7th Edition):
Sharma, Harsh Apurva. “Structure-preserving Numerical Methods for Engineering Applications.” 2020. Web. 09 Mar 2021.
Vancouver:
Sharma HA. Structure-preserving Numerical Methods for Engineering Applications. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/99912.
Council of Science Editors:
Sharma HA. Structure-preserving Numerical Methods for Engineering Applications. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/99912
13.
Yeaton, Isaac J.
The Dynamics of Non-Equilibrium Gliding in Flying Snakes.
Degree: PhD, Mechanical Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/82493
► This dissertation addresses the question, how and why do 'flying' snakes (Chrysopelea) undulate through the air? Instead of deploying paired wings or wing-like surfaces, flying…
(more)
▼ This dissertation addresses the question, how and why do 'flying' snakes (Chrysopelea) undulate through the air? Instead of deploying paired wings or wing-like surfaces, flying snakes jump, splay their ribs into a bluff-body airfoil, and undulate through the air. Aerial undulation is the dominant feature of snake flight, but its effects on locomotor performance and stability are unknown. Chapter 2 describes a new non-equilibrium framework to analyze gliding animals and how the pitch angle affects their translational motion. Chapter 3 combines flying snake glide experiments and detailed dynamic modeling to address what is aerial undulation and how each kinematic component affects rotational stability and translational performance. Chapter 4 combines the kinematic data of Chapter 3, with elements of the non-equilibrium framework of Chapter 2, to examine the kinematics of snake flight in greater detail. This chapter also tests if our current understanding of flying snake aerodynamics is sufficient to explain the observed center of mass motion.
Advisors/Committee Members: Ross, Shane D. (committeechair), Socha, John J. (committeechair), Paul, Mark R. (committee member), Abaid, Nicole (committee member), Woolsey, Craig A. (committee member).
Subjects/Keywords: Flying snake; animal locomotion; gliding flight; dynamical systems
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APA (6th Edition):
Yeaton, I. J. (2018). The Dynamics of Non-Equilibrium Gliding in Flying Snakes. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/82493
Chicago Manual of Style (16th Edition):
Yeaton, Isaac J. “The Dynamics of Non-Equilibrium Gliding in Flying Snakes.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/82493.
MLA Handbook (7th Edition):
Yeaton, Isaac J. “The Dynamics of Non-Equilibrium Gliding in Flying Snakes.” 2018. Web. 09 Mar 2021.
Vancouver:
Yeaton IJ. The Dynamics of Non-Equilibrium Gliding in Flying Snakes. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/82493.
Council of Science Editors:
Yeaton IJ. The Dynamics of Non-Equilibrium Gliding in Flying Snakes. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/82493
Virginia Tech
14.
Mukherjee, Saikat.
Front Propagation and Feedback in Convective Flow Fields.
Degree: PhD, Engineering Mechanics, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/98594
► Quantification of transport of reacting species in the presence of a flow field is important in many problems of engineering and science. A front is…
(more)
▼ Quantification of transport of reacting species in the presence of a flow field is important in many problems of engineering and science. A front is described as a moving interface between two different states of a system such as between the products and reactants in a chemical reaction. An example is a line of wildfire which separates burnt and fresh vegetation and propagates until all the fresh vegetation is consumed. In this dissertation the propagation of reacting fronts in the presence of convective flow fields of varying complexity is studied. It is found that the spatial variations in a convective flow field affects the burning and propagation of fronts by reorienting the geometry of the front interface. The velocity of the propagating fronts and its dependence on the spatial variation of the flow field is quantified. In certain scenarios the propagating front feeds back to the flow by inducing a local flow that interacts with the background convection. The rich and emergent dynamics resulting from this front induced feedback is quantified and it is found that feedback enhances the burning and propagation of fronts. Finally, the properties of pattern forming fronts are studied for fronts which leave a trail of spatial structures behind as they propagate for example in dendritic solidification and crystal growth. Pattern forming fronts of convection rolls are studied and the velocity of the front and spatial distribution of the patterns left behind by the front is quantified.
This research was partially supported by DARPA Grant No. HR0011-16-2-0033. The numerical computations were done using the resources of the Advanced Research Computing center at
Virginia Tech.
Advisors/Committee Members: Paul, Mark R. (committeechair), Stremler, Mark A. (committee member), Ross, Shane D. (committee member), Tafti, Danesh K. (committee member), Jung, Sunghwan (committee member).
Subjects/Keywords: Reaction-Advection-Diffusion; Front Propagation; Rayleigh-B�nard convection
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APA (6th Edition):
Mukherjee, S. (2020). Front Propagation and Feedback in Convective Flow Fields. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/98594
Chicago Manual of Style (16th Edition):
Mukherjee, Saikat. “Front Propagation and Feedback in Convective Flow Fields.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/98594.
MLA Handbook (7th Edition):
Mukherjee, Saikat. “Front Propagation and Feedback in Convective Flow Fields.” 2020. Web. 09 Mar 2021.
Vancouver:
Mukherjee S. Front Propagation and Feedback in Convective Flow Fields. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/98594.
Council of Science Editors:
Mukherjee S. Front Propagation and Feedback in Convective Flow Fields. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/98594
Virginia Tech
15.
Bozorg Magham, Amir Ebrahim.
Atmospheric Lagrangian transport structures and their applications to aerobiology.
Degree: PhD, Engineering Mechanics, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/56482
► Exploring the concepts of long range aerial transport of microorganisms is the main motivation of this study. For this purpose we use theories and concepts…
(more)
▼ Exploring the concepts of long range aerial transport of microorganisms is the main motivation of this study. For this purpose we use theories and concepts of dynamical systems in the context of geophysical fluid systems. We apply powerful notions such as finite-time Lyapunov exponent (FTLE) and the associated Lagrangian coherent structures (LCS) and we attempt to provide mathematical explanations and frameworks for some applied questions which are based on realistic concerns of atmospheric transport phenomena. Accordingly, we quantify the accuracy of prediction of FTLE-LCS features and we determine the sensitivity of such predictions to forecasting parameters. In addition, we consider the spatiotemporal resolution of the operational data sets and we propose the concept of probabilistic source and destination regions which leads to the definition of stochastic FTLE fields. Moreover, we put forward the idea of using ensemble forecasting to quantify the uncertainty of the forecast results. Finally, we investigate the statistical properties of localized measurements of atmospheric microbial structure and their connections to the concept of local FTLE time-series.
Results of this study would pave the way for more efficient models and management strategies for the spread of infectious diseases affecting plants, domestic animals, and humans.
Advisors/Committee Members: Ross, Shane D. (committeechair), Schmale, David G. III (committeechair), Iliescu, Traian (committee member), Stremler, Mark A. (committee member), Paul, Mark R. (committee member).
Subjects/Keywords: Finite-time Lyapunov exponent (FTLE); Lagrangian coherent structure (LCS); chaotic atmospheric transport; unresolved turbulence; stochastic FTLE field; ensemble forecasting; uncertainty analysis; local FTLE time-series; maximal diversity monitoring
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APA (6th Edition):
Bozorg Magham, A. E. (2014). Atmospheric Lagrangian transport structures and their applications to aerobiology. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/56482
Chicago Manual of Style (16th Edition):
Bozorg Magham, Amir Ebrahim. “Atmospheric Lagrangian transport structures and their applications to aerobiology.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/56482.
MLA Handbook (7th Edition):
Bozorg Magham, Amir Ebrahim. “Atmospheric Lagrangian transport structures and their applications to aerobiology.” 2014. Web. 09 Mar 2021.
Vancouver:
Bozorg Magham AE. Atmospheric Lagrangian transport structures and their applications to aerobiology. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/56482.
Council of Science Editors:
Bozorg Magham AE. Atmospheric Lagrangian transport structures and their applications to aerobiology. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/56482
Virginia Tech
16.
Whitehead, John Gardner.
An examination of the kinematics and behavior of mallards (Anas platyrhynchos) during water landings.
Degree: PhD, Biological Sciences, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/99383
► Control of landing is an important ability for any flying animal. However, with the exception of perch landing, we know very little about how birds…
(more)
▼ Control of landing is an important ability for any flying animal. However, with the exception of perch landing, we know very little about how birds and other flyers land on a variety of different surfaces. Here, we aim to extend our knowledge in this area by focusing on how mallard ducks land on water. This dissertation addresses the following questions. Do mallards regulate landing speed and trajectory the same way as pigeons? At what speeds, angles, and postures do mallards land on water? Can mallards adjust landing behavior to avoid collisions with other birds on the water surface? Chapter 2 determines how mallards regulate landings and how it is similar and different from pigeons and several other flyers. Chapter 3 describes the speeds, angles, and postures used by mallards to land on water. In addition, this chapter finds evidence for at least two different categories of landing performed by mallards. Chapter 4 provides evidence that mallards avoid situations in which a collision with another bird is likely. However, it is unclear if this is an active choice made by the mallard or due to other circumstances related to the landing behavior. Overall, this dissertation illustrates how the landing behavior of mallards is similar to what has been documented in other animals. However there are significant differences such as higher impact speeds, and shallower angles. Both of which are likely related to the ability of water to absorb a greater amount of the impact forces than a perch or the ground would.
Advisors/Committee Members: Socha, John J. (committeechair), Moore, Ignacio T. (committeechair), Jung, Sunghwan (committee member), Walters, Jeffrey R. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: Mallards; kinematics; flight; landing; Tau Theory; obstacle avoidance
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APA (6th Edition):
Whitehead, J. G. (2020). An examination of the kinematics and behavior of mallards (Anas platyrhynchos) during water landings. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/99383
Chicago Manual of Style (16th Edition):
Whitehead, John Gardner. “An examination of the kinematics and behavior of mallards (Anas platyrhynchos) during water landings.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/99383.
MLA Handbook (7th Edition):
Whitehead, John Gardner. “An examination of the kinematics and behavior of mallards (Anas platyrhynchos) during water landings.” 2020. Web. 09 Mar 2021.
Vancouver:
Whitehead JG. An examination of the kinematics and behavior of mallards (Anas platyrhynchos) during water landings. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/99383.
Council of Science Editors:
Whitehead JG. An examination of the kinematics and behavior of mallards (Anas platyrhynchos) during water landings. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/99383
17.
Tahmasian, Sevak.
Design, Analysis, and Optimization of Vibrational Control Strategies.
Degree: PhD, Engineering Mechanics, 2015, Virginia Tech
URL: http://hdl.handle.net/10919/52564
► This dissertation presents novel vibrational control strategies for mechanical control-affine systems with high-frequency, high-amplitude inputs. Since these control systems use high-frequency, zero-mean, periodic inputs, averaging…
(more)
▼ This dissertation presents novel vibrational control strategies for mechanical control-affine systems with high-frequency, high-amplitude inputs. Since these control systems use high-frequency, zero-mean, periodic inputs, averaging techniques are widely used in the analysis of their dynamics. By studying their time-averaged approximations, new properties of the averaged dynamics of this class of systems are revealed. Using these properties, the problem of input optimization of vibrational control systems was formulated and solved by transforming the problem to a constrained optimization one.
Geometric control theory provides powerful tools for studying the control properties of control-affine systems. Using the concepts of vibrational and geometric controls and averaging tools, a closed-loop control strategy for trajectory tracking of a class of underactuated mechanical control-affine systems is developed. In the developed control law, the fact that for underactuated systems, the actuated coordinates together with the corresponding generalized velocities can be considered as generalized inputs for the unactuated dynamics plays the main role. Using the developed control method, both actuated and unactuated coordinates of the system are able to follow slowly time-varying prescribed trajectories on average. The developed control method is applied for altitude control of flapping wing micro-air vehicles by considering the sweeping (flapping) angle of the wings as the inputs. Using the feathering (pitch) angles of the wings as additional inputs, and using non-symmetric flapping, the control method is then extended for three-dimensional flight control of flapping wing micro-air vehicles.
Advisors/Committee Members: Woolsey, Craig A. (committeechair), Hajj, Muhammad R. (committee member), Ross, Shane D. (committee member), Paul, Mark R. (committee member).
Subjects/Keywords: Vibrational Control; Geometric Control; Averaging; Mechanical Control-Affine Systems; Underactuated Mechanical Systems; Input Optimization; Biomimetic Systems
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APA (6th Edition):
Tahmasian, S. (2015). Design, Analysis, and Optimization of Vibrational Control Strategies. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/52564
Chicago Manual of Style (16th Edition):
Tahmasian, Sevak. “Design, Analysis, and Optimization of Vibrational Control Strategies.” 2015. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/52564.
MLA Handbook (7th Edition):
Tahmasian, Sevak. “Design, Analysis, and Optimization of Vibrational Control Strategies.” 2015. Web. 09 Mar 2021.
Vancouver:
Tahmasian S. Design, Analysis, and Optimization of Vibrational Control Strategies. [Internet] [Doctoral dissertation]. Virginia Tech; 2015. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/52564.
Council of Science Editors:
Tahmasian S. Design, Analysis, and Optimization of Vibrational Control Strategies. [Doctoral Dissertation]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/52564
Virginia Tech
18.
Nolan, Peter Joseph.
Experimental and Theoretical Developments in the Application of Lagrangian Coherent Structures to Geophysical Transport.
Degree: PhD, Engineering Mechanics, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/88986
► How particles are moved by fluid flows, such as the oceanic currents and the atmospheric winds, is a problem with important implications for fields as…
(more)
▼ How particles are moved by fluid flows, such as the oceanic currents and the atmospheric winds, is a problem with important implications for fields as diverse as: agriculture, aviation, human health, disaster response, and weather forecasting. Because these fluid flows tend to change over time, predicting how particles will be moved by these flows can often be challenging. Fortunately, mathematical tools exist which can reveal important geometric features in these flows. These geometric features can help us to visualize regions where particles are likely to come together or spread apart, as they are moved by the flow. In the past, these geometric features have been uncovered by using methods which look at the trajectories of particles in the flow. These methods are referred to as Lagrangian, in honor of the Italian mathematician Joseph-Louis Lagrange. Unfortunately, calculating the trajectories of particles can be a time consuming and computationally expensive process. Recently, new methods have been developed which look at how the speed of the flow changes in space. These new methods are referred to as Eulerian, in honor of the Swiss mathematician Leonhard Euler. These new Eulerian methods are faster and less expensive to calculate, while still revealing important geometric features within the flow. Because these Eulerian methods are so new, there is still much that we do not know about them and their connection to the older Lagrangian methods. This dissertation will fill in some of this gap and provide a mathematical bridge between these two methodologies. This dissertation is composed of three projects. These projects represent theoretical, numerical, and experimental advances in the understanding of these new Eulerian methods and their relationship to the older Lagrangian methods. The first project explores the deep mathematical relationship that exists between Eulerian and Lagrangian diagnostic tools. It mathematically proves that some of the new Eulerian diagnostics are the limit of Lagrangian diagnostics as the trajectory’s integration times is decreased to zero. Taking advantage of this discovery, a new Eulerian diagnostic is developed, called infinitesimal-time Lagrangian coherent structures. The second project develops a technique for estimating local Eulerian diagnostics using wind speed measures from a single fixed-wing unmanned aircraft system (UAS) flying in a circular path. Using computer simulations, we show that the Eulerian diagnostics as calculated from UAS measurements provide a reasonable estimate of the true local Eulerian diagnostics. Furthermore, we show that these Eulerian diagnostics can be used to estimate the local Lagrangian diagnostics. The third project applies these Eulerian diagnostics to real-world wind speed measurements. These results are then compared to Eulerian diagnostics that were calculated from a computer simulation to look for indications of Lagrangian diagnostics.
Advisors/Committee Members: Ross, Shane D. (committeechair), Schmale, David G. III (committee member), Iliescu, Traian (committee member), Foroutan, Hosein (committee member), Woolsey, Craig A. (committee member).
Subjects/Keywords: Lagrangian coherent structures; geophysical fluid mechanics; dynamical systems
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APA (6th Edition):
Nolan, P. J. (2019). Experimental and Theoretical Developments in the Application of Lagrangian Coherent Structures to Geophysical Transport. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/88986
Chicago Manual of Style (16th Edition):
Nolan, Peter Joseph. “Experimental and Theoretical Developments in the Application of Lagrangian Coherent Structures to Geophysical Transport.” 2019. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/88986.
MLA Handbook (7th Edition):
Nolan, Peter Joseph. “Experimental and Theoretical Developments in the Application of Lagrangian Coherent Structures to Geophysical Transport.” 2019. Web. 09 Mar 2021.
Vancouver:
Nolan PJ. Experimental and Theoretical Developments in the Application of Lagrangian Coherent Structures to Geophysical Transport. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/88986.
Council of Science Editors:
Nolan PJ. Experimental and Theoretical Developments in the Application of Lagrangian Coherent Structures to Geophysical Transport. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/88986
19.
Pietsch, Renee.
Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environments.
Degree: PhD, Biological Sciences, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/70915
► Aquatic environments contain a great diversity of microorganisms, some of which may be aerosolized and transported long distances through the atmosphere. The bacterium Pseudomonas syringae…
(more)
▼ Aquatic environments contain a great diversity of microorganisms, some of which may be aerosolized and transported long distances through the atmosphere. The bacterium Pseudomonas syringae can be found in aquatic environments and in the atmosphere and may express an ice nucleation protein (bacteria expressing the protein are Ice+ and bacteria not expressing the protein are Ice-). Ice+ bacteria may be involved in cloud formation and precipitation processes due to their ability to freeze water at warmer temperatures. Freshwater aerosolization processes are not well understood, particularly the role the Ice+ phenotype may play. Water samples were collected from Claytor Lake,
Virginia, USA and screened for Ice+ P. syringae. Results indicated that between 6% and 15% of Pseudomonas colonies assayed were Ice+. Preliminary phylogenetic analysis of cts (citrate synthase) sequences from strains of P. syringae showed a surprising diversity of phylogenetic subgroups present in the lake. A Collison nebulizer was used to aerosolize an Ice+ and an Ice- strain of P. syringae under artificial laboratory conditions. The aerosolization of P. syringae was not influenced by water temperature between 5° and 30°C. In general, the culturability (viability) of P. syringae in aerosols increased with temperature between 5 and 30°C. The Ice+ strain was aerosolized in greater numbers than the Ice- strain at all temperatures studied, suggesting a possible connection between the Ice+ phenotype and aerosol production. A quantitative empirical assessment of aerosolized droplets was generated using a laboratory flume and high-speed video. Droplet diameter and initial velocity upon leaving the water surface were examined at four wind speeds (3.5, 4.0, 4.5, and 5.0 m/s), and the results showed that droplet diameter and velocity had a gamma distribution and droplet mass flux increased exponentially with wind speed. An estimate of the potential amount of bacteria capable of aerosolizing was made for each wind speed. An interdisciplinary unit for advanced high school students has been developed presenting biological aerosolization and ice nucleation. This interdisciplinary work combines modeling and experimental approaches across biology and engineering interfaces, with the goal of increasing our understanding of microbial aerosols from aquatic environments that may impact our planet's water cycle.
Advisors/Committee Members: Brown, Bryan L. (committeechair), Schmale, David G. III (committeechair), Ross, Shane D. (committeechair), Vinatzer, Boris A. (committee member), Strickland, Michael (committee member).
Subjects/Keywords: ice nucleation; Pseudomonas syringae; bioprecipitation; aerosolization; water cycle; interdisciplinary curricula
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APA (6th Edition):
Pietsch, R. (2016). Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environments. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/70915
Chicago Manual of Style (16th Edition):
Pietsch, Renee. “Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environments.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/70915.
MLA Handbook (7th Edition):
Pietsch, Renee. “Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environments.” 2016. Web. 09 Mar 2021.
Vancouver:
Pietsch R. Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environments. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/70915.
Council of Science Editors:
Pietsch R. Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environments. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/70915
Virginia Tech
20.
Hartman, Timothy Benjamin.
Geometrically Nonlinear Stress Recovery in Composite Laminates.
Degree: PhD, Engineering Mechanics, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/50597
► Composite laminates are increasingly being used as primary load bearing members in structures. Â However, because of the directional dependence of the properties of composite materials,…
(more)
▼ Composite laminates are increasingly being used as primary load bearing members in structures. Â However, because of the directional dependence of the properties of composite materials, additional failure modes appear that are absent in homogeneous, isotropic materials. Â Therefore, a stress analysis of a composite laminate is not complete without an accurate representation of the transverse (out-of-plane) stresses. Stress recovery is a common method to estimate the transverse stresses from a plate or shell analysis. Â This dissertation extends stress recovery to problems in which geometric nonlinearities, in the sense of von K\\árm\\án, Â are important. Â The current work presents a less complex formulation for the stress recovery procedure for plate geometries, compared with other implementations, and results in a post-processing procedure which can be applied to data from any plate analyses; analytical or numerical methods, resulting in continuous or discretized data. Recovered transverse stress results are presented for a variety of geometrically nonlinear example problems: a semi-infinite plate subjected to quasi-static transverse and shear loading, and a finite plate subjected to both quasi-static and dynamic transverse loading. Â For all cases, the corresponding results from a fully three-dimensional stress analysis are shown alongside the distributions from the stress recovery procedure. Â Good agreement is observed between the stresses obtained from each method for the cases considered. Discussion is included regarding the applicability and accuracy of the technique to varying plate geometries and varying degrees of nonlinearity, as well as the viability of the procedure in replacing a three-dimensional analysis in regard to the time required to obtain a solution. The proposed geometrically nonlinear stress recovery procedure results in estimations for transverse stresses which show good correlation to the three-dimensional finite element solutions. Â The procedure is accurate for quasi-static and dynamic loading cases and proves to be a viable replacement for more computationally expensive analyses.
Advisors/Committee Members: Case, Scott W. (committeechair), Hyer, Michael W. (committeechair), Batra, Romesh C. (committee member), West, Robert L. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: composite laminate; stress recovery; geometrically nonlinear; transverse stress; interlaminar stress
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APA (6th Edition):
Hartman, T. B. (2013). Geometrically Nonlinear Stress Recovery in Composite Laminates. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/50597
Chicago Manual of Style (16th Edition):
Hartman, Timothy Benjamin. “Geometrically Nonlinear Stress Recovery in Composite Laminates.” 2013. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/50597.
MLA Handbook (7th Edition):
Hartman, Timothy Benjamin. “Geometrically Nonlinear Stress Recovery in Composite Laminates.” 2013. Web. 09 Mar 2021.
Vancouver:
Hartman TB. Geometrically Nonlinear Stress Recovery in Composite Laminates. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/50597.
Council of Science Editors:
Hartman TB. Geometrically Nonlinear Stress Recovery in Composite Laminates. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/50597
Virginia Tech
21.
Li, Qian.
Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints.
Degree: PhD, Engineering Mechanics, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/82923
► Fiber-reinforced rubberlike materials (FRRM) commonly used in tires undergo large deformations, and exhibit different response in tension and compression along the fiber direction. Assuming that…
(more)
▼ Fiber-reinforced rubberlike materials (FRRM) commonly used in tires undergo large deformations, and exhibit different response in tension and compression along the fiber direction. Assuming that the response of a fiber-reinforced rubberlike material can be modeled as transversely isotropic with the fiber direction as the axis of transverse isotropy, we express the stored energy function, W, in terms of the five invariants of the right Cauchy-Green strain tensor and the fiber direction, and account for different response in tension and compression along the fiber direction. It has been shown in the literature that in shear-dominated deformations, the 5th invariant, I5, significantly contribution to the stress-strain curve. We have implemented the constitutive relation in the commercial software, LS-DYNA. The numerical solutions of several boundary value problems studied here agree with their analytical solutions derived by using Ericksen's inverse approach, in which a part of the solution is assumed and unknowns in the presumed solution are then found by analyzing the pertinent boundary value problem. However, computed results have not been compared with experimental findings.
For W of the FRRMs an expression that is a complete quadratic function of the five invariants is also examined. Homogeneous deformations such as simple extension, simple shear, and biaxial loading problems are studied to delineate the mechanical behaviors of FRRMs. Consistency with the infinitesimal deformation theory requires that linear terms in the 4th and 5th invariants, I4 and I5, be included in the expression for W. Stability analysis of deformations reveals the qualitative changes triggered by the second order terms of the quadratic function. Analytical solutions for inflation, extension and twist deformations caused by internal pressure, end torque, and axial force for a pressurized cylindrical laminate are derived using Ericksen's inverse method. Effects of fiber orientations on the mechanical behaviors of a +/-α angle-ply cylindrical tube are investigated using the derived analytical solutions.
The T-peel test, widely used for characterizing adhesion across a plethora of adhesives, adherends, and geometries, results in a range of responses that may complicate meaningful interpretation of the test data. This research effort, involving several specific specimen types, was undertaken to investigate concerns that commonly used configurations may not always result in plateaus in the force-displacement response. We experimentally and numerically study debonding of T-peel specimens having 75 mm bond length and 0.81 mm thick adherends made of either 6061 aluminum (Al) or one of the three steels (G70 70U hot dip galvanized, E60 elctrogalvanized (EGZ), 1010 cold-rolled steel (CRS) bonded with either LORD® 406 or Maxlokâ„¢ acrylic adhesive. For the EGZ and the Al adherends, specimens with a bond length of 250 mm and adherend thickness of 1.60 mm are also examined. Effects of adherend materials and thicknesses, bond lengths, and…
Advisors/Committee Members: Batra, Romesh C. (committeechair), Dillard, David A. (committeechair), Cramer, Mark S. (committee member), Ross, Shane D. (committee member), West, Robert L. (committee member).
Subjects/Keywords: fiber-reinforced rubberlike material; user-defined subroutine; finite deformations; transversely isotropic material; T-peel specimens; finite element analysis
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APA (6th Edition):
Li, Q. (2018). Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/82923
Chicago Manual of Style (16th Edition):
Li, Qian. “Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/82923.
MLA Handbook (7th Edition):
Li, Qian. “Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints.” 2018. Web. 09 Mar 2021.
Vancouver:
Li Q. Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/82923.
Council of Science Editors:
Li Q. Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/82923
Virginia Tech
22.
Lin, Binbin.
Movement and Structure of Atmospheric Populations of Fusarium.
Degree: PhD, Plant Pathology, Physiology, and Weed Science, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23203
► Fusarium is one of the most important genera of fungi on earth. Many species of Fusarium are well-suited for atmospheric dispersal, yet little is known…
(more)
▼ Fusarium is one of the most important genera of fungi on earth. Many species of Fusarium are well-suited for atmospheric dispersal, yet little is known about their aerobiology. Previous research has shown that large-scale features known as atmospheric transport barriers (Lagrangian coherent structures) guide the transport and mixing of atmospheric populations of Fusarium. The overall goal of this work is to expand our knowledge on the movement and structure of atmospheric populations of Fusarium. The first objective was to monitor changes in colony forming units (CFUs) in atmospheric populations of Fusarium over small time intervals (10 min to several hours). We hypothesized that consecutive collections of Fusarium with unmanned aerial vehicles (UAVs) demonstrate small variations in colony counts. To test this hypothesis, sampling devices on UAVs were separated into two groups, four inner sampling devices opened during the first 10 minutes and four outer sampling devices opened during the second 10 minutes. Results indicated that (1) consecutive collections of Fusarium at 100 m demonstrated small variations in counts and (2) the similarity between collections decreased as the time between sampling intervals increased. The second objective was to determine the structure of atmospheric populations of Fusarium species and relate this to potential source regions. We hypothesized that diverse atmospheric populations of Fusarium are associated with multiple source regions. To test this hypothesis, Fusarium samples were collected with UAVs and identified to the level of species by sequencing a portion of the translation elongation factor 1-alpha gene (TEF-1•). Potential source regions were identified using the atmospheric transport model HYSPLIT. Results indicated that (1) diverse atmospheric populations of Fusarium appeared to be associated with multiple source regions, and (2) the number of Fusarium species collected with UAVs increased with back-trajectory distance of the sampled air. The third objective was to examine the associations between concentrations of populations of Fusarium at ground level (1 m) and in the lower atmosphere (100 m). We hypothesized that concentrations of Fusarium in the atmosphere vary between 1m and 100m. To test this hypothesis, Fusarium was collected with a Burkard volumetric sampler (BVS) and UAVs. Colony counts were converted to spore concentrations (spores per cubic meter of air). Sampling efficiency was used to correct spore concentrations. Results indicated that (1) the distribution of spore concentrations was similar for both samplers over different times of the day, (2) spore concentrations were generally higher in the fall, spring, and summer, and lower in the winter, and (3) spore concentrations were generally higher with BVS samplers than those with UAVs for both hourly and seasonal data. The fourth objective was to assess the ability of strains of Fusarium collected in the lower atmosphere to cause plant disease. We hypothesized that certain isolates of Fusarium collected with…
Advisors/Committee Members: Schmale, David G. III (committeechair), Ross, Shane D. (committeechair), Baudoin, Antonius B. (committee member), Vinatzer, Boris A. (committee member).
Subjects/Keywords: Fusarium; plant pathogen; aerobiology; aerobiological sampling; Burkard volumetric sampler; BVS; unmanned aerial vehicle; UAV
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APA (6th Edition):
Lin, B. (2013). Movement and Structure of Atmospheric Populations of Fusarium. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23203
Chicago Manual of Style (16th Edition):
Lin, Binbin. “Movement and Structure of Atmospheric Populations of Fusarium.” 2013. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/23203.
MLA Handbook (7th Edition):
Lin, Binbin. “Movement and Structure of Atmospheric Populations of Fusarium.” 2013. Web. 09 Mar 2021.
Vancouver:
Lin B. Movement and Structure of Atmospheric Populations of Fusarium. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/23203.
Council of Science Editors:
Lin B. Movement and Structure of Atmospheric Populations of Fusarium. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23203
Virginia Tech
23.
Bahmani, Fatemeh.
Three Problems Involving Compressible Flow with Large Bulk Viscosity and Non-Convex Equations of State.
Degree: PhD, Engineering Mechanics, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/25885
► We have examined three problems involving steady flows of Navier-Stokes fluids. In each problem non-classical effects are considered. In the first two problems, we consider…
(more)
▼ We have examined three problems involving steady flows of Navier-Stokes fluids. In each problem non-classical effects are considered. In the first two problems, we consider fluids which have bulk viscosities which are much larger than their shear viscosities. In the last problem, we examine steady supersonic flows of a Bethe-Zel'dovich-Thompson (BZT) fluid over a thin airfoil or turbine blade. BZT fluids are fluids in which the fundamental derivative of gasdynamics changes sign during an isentropic expansion or compression.
In the first problem we consider the effects of large bulk viscosity on the structure of the inviscid approximation using the method of matched asymptotic expansions. When the ratio of bulk to shear viscosity is of the order of the square root of the Reynolds number we find that the bulk viscosity effects are important in the first corrections to the conventional boundary layer and outer inviscid flow. At first order the outer flow is found to be frictional, rotational, and non-isentropic for large bulk viscosity fluids. The pressure is found to have first order variations across the boundary layer and the temperature equation is seen to have two additional source terms at first order when the bulk viscosity is large.
In the second problem, we consider the reflection of an oblique shock from a laminar flat plate boundary layer. The flow is taken to be two-dimensional, steady, and the gas model is taken to be a perfect gas with constant Prandtl number. The plate is taken to be adiabatic. The full Navier-Stokes equations are solved using a weighted essentially non-oscillatory (WENO) numerical scheme. We show that shock-induced separation can be suppressed once the bulk viscosity is large enough.
In the third problem, we solve a quartic Burgers equation to describe the steady, two-dimensional, inviscid supersonic flow field generated by thin airfoils. The Burgers equation is solved using the WENO technique. Phenomena of interest include the partial and complete disintegration of compression shocks, the formation of expansion shocks, and the collision of expansion and compression shocks.
Advisors/Committee Members: Cramer, Mark S. (committeechair), Ragab, Saad A. (committee member), Ross, Shane D. (committee member), Paul, Mark R. (committee member), Jung, Sunghwan (committee member).
Subjects/Keywords: Compressible flow; shock; boundary layer; WENO; CFD; bulk viscosity; BZT fluids
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MLA ·
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Export
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APA (6th Edition):
Bahmani, F. (2013). Three Problems Involving Compressible Flow with Large Bulk Viscosity and Non-Convex Equations of State. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/25885
Chicago Manual of Style (16th Edition):
Bahmani, Fatemeh. “Three Problems Involving Compressible Flow with Large Bulk Viscosity and Non-Convex Equations of State.” 2013. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/25885.
MLA Handbook (7th Edition):
Bahmani, Fatemeh. “Three Problems Involving Compressible Flow with Large Bulk Viscosity and Non-Convex Equations of State.” 2013. Web. 09 Mar 2021.
Vancouver:
Bahmani F. Three Problems Involving Compressible Flow with Large Bulk Viscosity and Non-Convex Equations of State. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/25885.
Council of Science Editors:
Bahmani F. Three Problems Involving Compressible Flow with Large Bulk Viscosity and Non-Convex Equations of State. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/25885
Virginia Tech
24.
Kalhor, Roozbeh.
Energy Absorption of Metal-FRP Hybrid Square Tubes.
Degree: PhD, Engineering Mechanics, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/74960
► Lower-cost manufacturing methods have increased the anticipation for economical mass production of vehicles manufactured from composite materials. One of the potential applications of composite materials…
(more)
▼ Lower-cost manufacturing methods have increased the anticipation for economical mass production of vehicles manufactured from composite materials. One of the potential applications of composite materials in vehicles is in energy-absorbing components such as hollow shells and struts (these components may be in the form of circular cylindrical shells, square and rectangular tubes, conical shells, and frusta). However, constructions which result in brittle fracture of the composite tubes in the form of circumferential or longitudinal corner crack propagation may lead to unstable collapse failure mode and concomitant very low energy absorption. As a result, metal-composite hollow tubes have been developed that combine the benefits of stable ductile collapse of the metal (which can absorb crushing energy in a controlled manner) and the high strength-to-weight ratio of the composites. The relative and absolute thicknesses of metal or FRP section has a substantial effect on energy absorption of the hybrid tubes. In particular, likelihood of delamination occurrence raises with increase in FRP thickness. This can reduce the energy absorption capability of the metal-FRP hybrid tubes. Additionally, adding a very thick FRP section may result in a global buckling failure mode (rather than local folding). Until now, there are no studies specifically addressing the effect of FRP thickness on energy absorption of hybrid tubes. In this study, the effects of fiber orientation and FRP thickness (the number of layers) on the energy absorption of S2-glass/epoxy-304 stainless steel square tubes were experimentally investigated. In addition, a new geometrical trigger was demonstrated which has positive effects on the collapse modes, delamination in the FRP, and the crush load efficiency of the hybrid tube.
To complete this study, a new methodology including the combination of experimental results, numerical modeling, and a multi-objective optimization process was introduced to obtain the best combination of design variables for hybrid metal-composite tubes for crashworthiness applications. The experimental results for the S2 glass/epoxy-304 stainless steel square tubes with different configurations tested under quasi-static compression loading were used to validate numerical models implemented in LS-DYNA software. The models were able to capture progressive failure mechanisms of the hybrid tubes. In addition, the effects of the design variables on the energy absorption and failure modes of the hybrid tubes were explained. Subsequently, the results from the numerical models were used to obtain optimum crashworthiness functions. The load efficiency factor (the ratio of mean crushing load to maximum load) and ratio between the difference of mean crushing load of hybrid and metal tube and thickness of the FRP section were introduced as objective functions. To connect the variables and the functions, back-propagation artificial neural networks (ANN) were used. The Non-dominated Sorting Genetic Algorithm–II (NSGAII) was applied to the…
Advisors/Committee Members: Case, Scott W. (committeechair), Al-Haik, Marwan (committee member), Ross, Shane D. (committee member), Seidel, Gary D. (committee member).
Subjects/Keywords: Energy absorption; Axial crushing; Metal-composite square hybrid tubes; Neural networks; Multi-objective optimization
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APA (6th Edition):
Kalhor, R. (2017). Energy Absorption of Metal-FRP Hybrid Square Tubes. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/74960
Chicago Manual of Style (16th Edition):
Kalhor, Roozbeh. “Energy Absorption of Metal-FRP Hybrid Square Tubes.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/74960.
MLA Handbook (7th Edition):
Kalhor, Roozbeh. “Energy Absorption of Metal-FRP Hybrid Square Tubes.” 2017. Web. 09 Mar 2021.
Vancouver:
Kalhor R. Energy Absorption of Metal-FRP Hybrid Square Tubes. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/74960.
Council of Science Editors:
Kalhor R. Energy Absorption of Metal-FRP Hybrid Square Tubes. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/74960
25.
Naik, Shibabrat.
Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics.
Degree: PhD, Engineering Mechanics, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/73364
► This dissertation presents geometric approaches of understanding chaotic transport in phase space that is fundamental across many disciplines in physical sciences and engineering. This approach…
(more)
▼ This dissertation presents geometric approaches of understanding chaotic transport in phase space that is fundamental across many disciplines in physical sciences and engineering. This approach is based on analyzing phase space transport using boundaries and regions inside these boundaries in presence of perturbation.
We present a geometric view of defining such boundaries and study the transport that occurs by crossing such phase space structures. The structure in two dimensional non-autonomous system is the codimension 1 stable and unstable manifolds associated with the hyperbolic fixed points. The manifolds separate regions with varied dynamical fates and their time evolution encodes how the initial conditions in a given region of phase space get transported to other regions. In the context of four dimensional autonomous systems, the corresponding structure is the stable and unstable manifolds of unstable periodic orbits which reside in the bottlenecks of energy surface. The total energy and the cylindrical (or tube) manifolds form the necessary and sufficient condition for global transport between regions of phase space.
Furthermore, we adopt the geometric view to define escaping zones for avoiding transition/escape from a potential well using partial control. In this approach, the objective is two fold: finding the minimum control that is required for avoiding escape and obtaining discrete representation called disturbance of continuous noise that is present in physical sciences and engineering. In the former scenario, along with avoiding escape, the control is constrained to be smaller than the disturbance so that it can not exactly cancel out the disturbances.
Advisors/Committee Members: Ross, Shane D. (committeechair), Paul, Mark R. (committee member), Jung, Sunghwan (committee member), Woolsey, Craig A. (committee member), Puri, Ishwar K. (committee member).
Subjects/Keywords: Invariant manifolds; Phase space transport; Escaping dynamics; Partial control
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APA (6th Edition):
Naik, S. (2016). Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/73364
Chicago Manual of Style (16th Edition):
Naik, Shibabrat. “Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/73364.
MLA Handbook (7th Edition):
Naik, Shibabrat. “Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics.” 2016. Web. 09 Mar 2021.
Vancouver:
Naik S. Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/73364.
Council of Science Editors:
Naik S. Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/73364
Virginia Tech
26.
David, Ray.
Impact of Meteorological Conditions and Maturity of Perithecia on the Release of Fusarium graminearum Ascospores.
Degree: PhD, Civil Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/79695
► The global food supply is being stressed by climate change, a growing population, and harmful diseases. One risk to vital cereal crops such as wheat…
(more)
▼ The global food supply is being stressed by climate change, a growing population, and harmful diseases. One risk to vital cereal crops such as wheat and barley is Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium graminearum. Ascospores of the fungus are released from perithecia on the residues of corn and small grains and can be transported long distances (>500 m) through the atmosphere. The overall objective of this work was to assess the influence of meteorological conditions and perithecial maturity on ascospore release. The research focuses on F. graminearum because of its damaging impact to staple crops and the global ubiquity of FHB.
The first specific objective was to apply state-of-the-science techniques to identify causal meteorological variables of ascospore release. We analyzed field measurements of airborne ascospores against meteorological conditions at
Virginia Tech's Kentland Farm, Blacksburg,
Virginia, USA and used convergent cross mapping and multivariate state space reconstruction to identify significant causal agents within this complicated natural and dynamic system. We identified relative humidity, solar radiation, wind speed, and air temperature as predictors of ascospore release.
Our second research objective was to understand the impact of varying meteorological conditions on ascospore release under controlled environmental conditions. We assessed ascospore release in a chamber with controlled temperature (15°C and 25°C) and relative humidity (60%, 75%, and 95%). Ascospores released from ascospore-producing structures (perithecia) were captured on microscope slides placed inside of 3D-printed ascospore discharge devices. Results showed the sensitivity of ascospore release to relative humidity and temperature, with cool temperature and high relative humidity resulting in greater quantities of ascospores released.
Our third research objective was to determine the relationship between the maturity, the number of ascospores, and the hardness of perithecia. A mechanical compression testing instrument was used to investigate the hardness of perithecia at various stages of maturity, producing a mean perithecium compression constant quantifying the uniaxial compression force required to rupture a perithecium. Results indicated that old perithecia contain the greatest amount of ascospores and exhibit increased resiliency, requiring greater forces to rupture, compared to young perithecia.
This research has illustrated the complexities of F. graminearum ascospore release by describing the impact of several meteorological conditions and perithecial maturity on the timing and quantity of released ascospores. Collectively, our results may inform wheat growers on the nature and timing of ascospore release, which could help inform FHB management decisions in the future.
Advisors/Committee Members: Schmale, David G. III (committeechair), Marr, Linsey C. (committeechair), Pruden, Amy (committee member), Kolivras, Korine N. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: bioaerosol; fungus; spore release; Fusarium head blight; causality analysis
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APA (6th Edition):
David, R. (2016). Impact of Meteorological Conditions and Maturity of Perithecia on the Release of Fusarium graminearum Ascospores. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/79695
Chicago Manual of Style (16th Edition):
David, Ray. “Impact of Meteorological Conditions and Maturity of Perithecia on the Release of Fusarium graminearum Ascospores.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/79695.
MLA Handbook (7th Edition):
David, Ray. “Impact of Meteorological Conditions and Maturity of Perithecia on the Release of Fusarium graminearum Ascospores.” 2016. Web. 09 Mar 2021.
Vancouver:
David R. Impact of Meteorological Conditions and Maturity of Perithecia on the Release of Fusarium graminearum Ascospores. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/79695.
Council of Science Editors:
David R. Impact of Meteorological Conditions and Maturity of Perithecia on the Release of Fusarium graminearum Ascospores. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/79695
Virginia Tech
27.
Rogers, Andrew Charles.
Optimization-Based Guidance for Satellite Relative Motion.
Degree: PhD, Aerospace Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/79455
► Spacecraft relative motion modeling and control promises to enable or augment a wide range of missions for scientific research, military applications, and space situational awareness.…
(more)
▼ Spacecraft relative motion modeling and control promises to enable or augment a wide range of missions for scientific research, military applications, and space situational awareness. This dissertation focuses on the development of novel, optimization-based, control design for some representative relative-motion-enabled missions. Spacecraft relative motion refers to two (or more) satellites in nearly identical orbits. We examine control design for relative configurations on the scale of meters (for the purposes of proximity operations) as well as on the scale of tens of kilometers (representative of science gathering missions). Realistic control design for satellites is limited by accurate modeling of the relative orbital perturbations as well as the highly constrained nature of most space systems. We present solutions to several types of optimal orbital maneuvers using a variety of different, realistic assumptions based on the maneuver objectives.
Initially, we assume a perfectly circular orbit with a perfectly spherical Earth and analytically solve the under-actuated, minimum-energy, optimal transfer using techniques from optimal control and linear operator theory. The resulting open-loop control law is guaranteed to be a global optimum. Then, recognizing that very few, if any, orbits are truly circular, the optimal transfer problem is generalized to the elliptical linear and nonlinear systems which describe the relative motion. Solution of the minimum energy transfer for both the linear and nonlinear systems reveals that the resulting trajectories are nearly identical, implying that the nonlinearity has little effect on the relative motion. A continuous-time, nonlinear, sliding mode controller which tracks the linear trajectory in the presence of a higher fidelity orbit model shows that the closed-loop system is both asymptotically stable and robust to disturbances and un-modeled dynamics.
Next, a novel method of computing discrete-time, multi-revolution, finite-thrust, fuel-optimal, relative orbit transfers near an elliptical, perturbed orbit is presented. The optimal control problem is based on the classical, continuous-time, fuel-optimization problem from calculus of variations, and we present the discrete-time analogue of this problem using a transcription-based method. The resulting linear program guarantees a global optimum in terms of fuel consumption, and we validate the results using classical impulsive orbit transfer theory. The new method is shown to converge to classical impulsive orbit transfer theory in the limit that the duration of the zero-order hold discretization approaches zero and the time horizon extends to infinity. Then the fuel/time optimal control problem is solved using a hybrid approach which uses a linear program to solve the fuel optimization, and a genetic algorithm to find the minimizing time-of-flight. The method developed in this work allows mission planners to determine the feasibility for realistic spacecraft and motion models.
Proximity operations for robotic…
Advisors/Committee Members: Woolsey, Craig A. (committeechair), McGwier, Robert W. (committeechair), Ross, Shane D. (committee member), Earle, Gregory D. (committee member), Black, Jonathan T. (committee member).
Subjects/Keywords: Model predictive control; astrodynamics; optimal control; optimization; proximity operations
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APA (6th Edition):
Rogers, A. C. (2016). Optimization-Based Guidance for Satellite Relative Motion. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/79455
Chicago Manual of Style (16th Edition):
Rogers, Andrew Charles. “Optimization-Based Guidance for Satellite Relative Motion.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/79455.
MLA Handbook (7th Edition):
Rogers, Andrew Charles. “Optimization-Based Guidance for Satellite Relative Motion.” 2016. Web. 09 Mar 2021.
Vancouver:
Rogers AC. Optimization-Based Guidance for Satellite Relative Motion. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/79455.
Council of Science Editors:
Rogers AC. Optimization-Based Guidance for Satellite Relative Motion. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/79455
28.
Nave Jr, Gary Kirk.
Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies.
Degree: PhD, Engineering Mechanics, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/84945
► This dissertation presents useful nonlinear models for fluid forcing on a moving body in two distinct contexts, and methods for analyzing the geometric structure within…
(more)
▼ This dissertation presents useful nonlinear models for fluid forcing on a moving body in two distinct contexts, and methods for analyzing the geometric structure within those and other mathematical models. This manuscript style dissertation presents three works within the theme of understanding fluid forcing and geometric structure.
When a bluff body is free to move in the presence of an incoming bluff body wake, the average forcing on the body is dependent on its position relative to the upstream bluff body. This position-dependent forcing can be conceptualized as a stiffness, much like a spring. This work presents an updated model for the quasi-steady fluid forcing of a wake and extends the notion of wake stiffness to consider a nonlinear spring. These results are compared with kinematic experimental results to provide an example of the application of this framework.
Fluid force models also play a role in understanding the behavior of passive aerodynamic gliders, such as gliding animals or plant material. The forces a glider experiences depend on the angle that its body makes with respect to its direction of motion. Modeling the glider as capable of pitch control, this work considers a glider with a fixed angle with respect to the ground. Within this model, all trajectories in velocity space collapse to a 1-dimensional invariant manifold known as the terminal velocity manifold. This work presents methods to identify the terminal velocity manifold, investigates its properties, and extends it to a 2-dimensional invariant manifold in a 3-dimensional space.
Finally, in the search for manifolds such as the terminal velocity manifold, this dissertation introduces a new diagnostic for identifying the low dimensional geometric structure of models. The trajectory divergence rate uses instantaneous vector field information to identify regions of large normal stretching and strong normal convergence between nearby invariant manifolds. This work lays out the mathematical basis of the trajectory divergence rate and shows its application to approximate a variety of structures including slow manifolds and Lagrangian coherent structures.
This dissertation applies nonlinear theoretical and numerical techniques to analyze models of fluid forcing and their geometric structure. The tools developed in this dissertation lay the groundwork for future research in the fields of flow-induced vibration, plant and animal biomechanics, and dynamical systems.
Advisors/Committee Members: Ross, Shane D. (committeechair), Stremler, Mark A. (committeechair), Abaid, Nicole (committee member), Socha, John J. (committee member), Woolsey, Craig A. (committee member).
Subjects/Keywords: Fluid-structure interaction; phase space structure; computational geometry; nonlinear dynamics
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APA (6th Edition):
Nave Jr, G. K. (2018). Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/84945
Chicago Manual of Style (16th Edition):
Nave Jr, Gary Kirk. “Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/84945.
MLA Handbook (7th Edition):
Nave Jr, Gary Kirk. “Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies.” 2018. Web. 09 Mar 2021.
Vancouver:
Nave Jr GK. Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/84945.
Council of Science Editors:
Nave Jr GK. Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/84945
Virginia Tech
29.
Yang, Wenchao.
Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow.
Degree: PhD, Engineering Mechanics, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/97563
► The wake of a bluff body is a representative issue in vortex dynamics that plays a central role in civil engineering, ocean engineering and thermal…
(more)
▼ The wake of a bluff body is a representative issue in vortex dynamics that plays a central role in civil engineering, ocean engineering and thermal engineering. In this work, a flowing soap film was used to investigate the wakes of multiple stationary circular cylinders and of a single oscillating cylinder. Corresponding computer simulations were also conducted. Vortex formation of a stationary circular cylinder was analyzed by proper orthogonal decomposition (POD). The POD analysis was used to define an unsteady vortex formation length, which suggests a relationship between the vortex formation length of a single cylinder and the critical spacing of two cylinders in a tandem arrangement. A systematic parametric study of the wake structure was conducted for a controlled transversely oscillating cylinder. Neural network and support vector machine codes assisted the wake classification procedure and the identification of boundaries between different wake regimes. The phase map of the vortex shedding regimes for the (quasi) two-dimensional experiment qualitatively agrees with previous three-dimensional experiments. The critical spacings of two identical tandem circular cylinders in a flowing soap film system were determined using visual inspections of the wake patterns and calculations of the Strouhal frequencies. The dimensionless spacing was both increased and decreased quasi-statically. Hysteresis was observed in the flow patterns and Strouhal numbers. This study appears to provide the first experimental evidence of critical spacing values that agree with published computational results. The wake interaction between a stationary upstream circular disk and a free downstream circular disk was also investigated. With the ability to tie together the wake structure and the object motion, the relationship between energy generation and flow structure in the simplified reduced order model system was studied. The research results find the optimal efficiency of the energy harvesting system by a parametric study.
Advisors/Committee Members: Stremler, Mark A. (committeechair), Hanna, James (committee member), Jung, Sunghwan (committee member), Ross, Shane D. (committee member), Yue, Pengtao (committee member).
Subjects/Keywords: Wake interaction; Flow-induced vibration; Vortex dynamics
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APA (6th Edition):
Yang, W. (2018). Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/97563
Chicago Manual of Style (16th Edition):
Yang, Wenchao. “Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/97563.
MLA Handbook (7th Edition):
Yang, Wenchao. “Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow.” 2018. Web. 09 Mar 2021.
Vancouver:
Yang W. Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/97563.
Council of Science Editors:
Yang W. Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/97563
Virginia Tech
30.
Peebles, Alexander Thomas.
Development and Validation of Clinically Feasible Methods to Assess Landing Mechanics in Patients Following Anterior Cruciate Ligament Reconstruction.
Degree: PhD, Biomedical Engineering, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/98810
► The anterior cruciate ligament (ACL) is a bundle of connective tissue that helps stabilize the knee joint. ACL injuries are common in sport, and ACL…
(more)
▼ The anterior cruciate ligament (ACL) is a bundle of connective tissue that helps stabilize the knee joint. ACL injuries are common in sport, and ACL reconstruction surgery is the most widely used treatment strategy for patients who wish to return to playing sports. Unfortunately, even after ACL surgery and rehabilitation, many patients who return to sport wind up getting hurt again and developing severe joint pain down the road. Previous research has identified movement and loading patterns which are associated with this increased risk for further injury in patients following ACL reconstruction. For example, patients who have increased asymmetry when landing from a jump, where they shift weight away from their surgical limb and towards their non-surgical limb, have an increased likelihood of sustaining a second ACL injury to either their surgical or non-surgical leg. Assessing movement during rehabilitation could help identify patients who exhibit poor movement mechanics and improve movement to reduce their risk for second injuries. However, there are not currently methods available to reliably assess movement that are feasible for widespread use in non-research settings (i.e. physical therapy clinics). The purpose of this project was to identify and develop methods to assess movement which are accurate and feasible to use in a clinical setting. In this dissertation, we first determined the accuracy of using wireless force sensing shoe insoles to measure how hard and how symmetrically people contact the ground when they land from a jump. Second, we developed a new method to measure knee motion using videos collected with low-cost cameras (e.g. iPad), and determined the accuracy of this method compared to a three-dimensional motion capture system. For the last part of this dissertation we demonstrated that the aforementioned methods could be used to identify deficits in landing mechanics in patients following ACL reconstruction in a non-research setting. When comparing ACL reconstruction patients with uninjured controls, we found movement and loading asymmetries which were expected and which are associated with the risk for second ACL injuries and early onset knee osteoarthritis. This project is an important step towards being able to assess landing mechanics in patients recovering from an ACL reconstruction, which could improve our ability to prevent subsequent injuries in this clinical population.
Advisors/Committee Members: Queen, Robin M. (committeechair), Miller, Thomas K. (committee member), Schmitt, Daniel (committee member), Ross, Shane D. (committee member), Socha, John J. (committee member).
Subjects/Keywords: Biomechanics; Rehabilitation; Injury Prevention
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APA ·
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APA (6th Edition):
Peebles, A. T. (2020). Development and Validation of Clinically Feasible Methods to Assess Landing Mechanics in Patients Following Anterior Cruciate Ligament Reconstruction. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/98810
Chicago Manual of Style (16th Edition):
Peebles, Alexander Thomas. “Development and Validation of Clinically Feasible Methods to Assess Landing Mechanics in Patients Following Anterior Cruciate Ligament Reconstruction.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 09, 2021.
http://hdl.handle.net/10919/98810.
MLA Handbook (7th Edition):
Peebles, Alexander Thomas. “Development and Validation of Clinically Feasible Methods to Assess Landing Mechanics in Patients Following Anterior Cruciate Ligament Reconstruction.” 2020. Web. 09 Mar 2021.
Vancouver:
Peebles AT. Development and Validation of Clinically Feasible Methods to Assess Landing Mechanics in Patients Following Anterior Cruciate Ligament Reconstruction. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 09].
Available from: http://hdl.handle.net/10919/98810.
Council of Science Editors:
Peebles AT. Development and Validation of Clinically Feasible Methods to Assess Landing Mechanics in Patients Following Anterior Cruciate Ligament Reconstruction. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/98810
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Open Access Theses and Dissertations
