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Virginia Tech
1.
Fergusson, Austin David.
Non-equilibrium Dynamics of Nanoscale Soft Matter Deformation.
Degree: MS, Engineering Mechanics, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/50500 
► Life is soft. From the fluid-like structure of lipid bilayers to the flexible folding of proteins, the realm of nanoscale soft matter is a complex…
(more)
▼ Life is soft. From the fluid-like structure of lipid bilayers to the flexible folding of proteins, the realm of nanoscale soft matter is a complex and vibrant area of research. The lure of personalized medicine, advanced sensing technology, and understanding life at a fundamental level pushes research forward. This work considers to areas: (1) lipid bilayer dynamics in the presence of substrate defects and (2) the inverse temperature transition of elastic proteins. Molecular dynamics simulations as well as umbrella sampling were employed. The behavior of the bilayers discussed in the work provides evidence that small defects on confining surfaces can promote nucleation of lipid tethers. Results the second part of this work indicate elastin-like peptides experiencing inverse temperature transitions may be capable of performing amounts of work similar to RNA polymerase; additionally, resilin's inverse temperature transition may be closely linked to the molecule's ability to efficiently transmit energy through the similar coil-β secondary structure transition seen in both cases. These insights into the inverse transition temperature are relevant for the design of bio-inspired sensors and energy storage devices.
Advisors/Committee Members: Holmes, Douglas P. (committeechair), Jung, Sunghwan (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: lipid bilayer; elastin; resilin; inverse temperature transition; umbrella sampling; potential of mean force
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APA (6th Edition):
Fergusson, A. D. (2014). Non-equilibrium Dynamics of Nanoscale Soft Matter Deformation. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/50500
Chicago Manual of Style (16th Edition):
Fergusson, Austin David. “Non-equilibrium Dynamics of Nanoscale Soft Matter Deformation.” 2014. Masters Thesis, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/50500.
MLA Handbook (7th Edition):
Fergusson, Austin David. “Non-equilibrium Dynamics of Nanoscale Soft Matter Deformation.” 2014. Web. 06 Mar 2021.
Vancouver:
Fergusson AD. Non-equilibrium Dynamics of Nanoscale Soft Matter Deformation. [Internet] [Masters thesis]. Virginia Tech; 2014. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/50500.
Council of Science Editors:
Fergusson AD. Non-equilibrium Dynamics of Nanoscale Soft Matter Deformation. [Masters Thesis]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/50500
2.
Chatterjee, Krishnashis.
Analytical and Experimental Investigation of Insect Respiratory System Inspired Microfluidics.
Degree: PhD, Engineering Mechanics, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/85688
► Microfluidics or the study of fluids at the microscale has gained a lot of interest in the recent past due to its various applications starting…
(more)
▼ Microfluidics or the study of fluids at the microscale has gained a lot of interest in the recent past due to its various applications starting from electronic chip cooling to biomedical diagnostic devices and exoplanetary chemical analysis. Though there has been a lot of advancements in the functionality and portability of microfluidic devices, little has been achieved in the improvement of the peripheral machinery needed to operate these devices. On the other hand insects can expertly manipulate fluids, in their body, at the microscale with the help of their efficient respiratory capabilities. In the present study we mimic some essential features of the insect respiratory system by incorporating them in microfluidic devices. The feasibility of practical application of these techniques have been tested, at first, analytically by mathematically modeling the fluid flow in insect respiratory tract mimetic microchannels and tubes and then by fabricating, testing and analyzing the functionality of microfluidic devices. The mathematical models, using slip boundary conditions, showed that the volumetric fluid flow through a trachea mimetic tube decreased with the increase in the amount of slip. Apart from that it also revealed a fundamental difference between shear and pressure driven flow at the microscale. The microfluidic devices exhibited some unique characteristic features never seen before in valveless microfluidic devices and have the potential in reducing the actuation overhead. These devices can be used to simplify the operating procedure and subsequently decrease the production cost of microfluidic devices for various applications.
Advisors/Committee Members: Staples, Anne E. (committeechair), Davalos, Rafael V. (committee member), Socha, John J. (committee member), Ragab, Saad A. (committee member), Untaroiu, Alexandrina (committee member).
Subjects/Keywords: Microfluidics; insect-inspired; microscale pumping; slip boundary conditions; single actuation; frequency dependent flow control
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APA (6th Edition):
Chatterjee, K. (2018). Analytical and Experimental Investigation of Insect Respiratory System Inspired Microfluidics. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/85688
Chicago Manual of Style (16th Edition):
Chatterjee, Krishnashis. “Analytical and Experimental Investigation of Insect Respiratory System Inspired Microfluidics.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/85688.
MLA Handbook (7th Edition):
Chatterjee, Krishnashis. “Analytical and Experimental Investigation of Insect Respiratory System Inspired Microfluidics.” 2018. Web. 06 Mar 2021.
Vancouver:
Chatterjee K. Analytical and Experimental Investigation of Insect Respiratory System Inspired Microfluidics. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/85688.
Council of Science Editors:
Chatterjee K. Analytical and Experimental Investigation of Insect Respiratory System Inspired Microfluidics. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/85688
Virginia Tech
3.
Chien, Ssu-Ying.
Compressible Lubrication Theory in Pressurized Gases.
Degree: PhD, Engineering Mechanics, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/88868
► Lubrication theory plays a fundamental role in all mechanical design as well as applications to biomechanics. All machinery are composed of moving parts which must…
(more)
▼ Lubrication theory plays a fundamental role in all mechanical design as well as applications to biomechanics. All machinery are composed of moving parts which must be protected against wear and damage. Without eective lubrication, maintenance cycles will be shortened to impractical levels resulting in increased costs and decreased reliability. The focus of the work presented here is on the lubrication of rotating machinery found in advanced power systems and designs involving micro-turbines. One of the earliest studies of lubrication is due to Osborne Reynolds in 1886 who recorded what is now regarded as the canonical equation governing all lubrication problems; this equation and its extensions have become known as the Reynolds equation. In the past century, Reynolds equation has been extended to include three-dimensional eects, unsteadiness, turbulence, variable material properties, non-newtonian uids, multi-phase ows, wall slip, and thermal eects. The bulk of these studies have focused on highly viscous liquids,
e.g., oils. In recent years there has been increasing interest in power systems using new working uids, micro-turbines and non-fossil fuel heat sources. In many cases, the design of these systems employs the use of gases rather than liquids. The advantage of gases over liquids include the reduction of weight, the reduction of adverse eects due to fouling, and compatibility with power system working uids. Most treatments of gas lubrication are based on the ideal, i.
e., low pressure, gas theory and straightforward retro-tting of the theory of liquid lubrication. However, the 21st Century has seen interest in gas lubrication at high pressures. At pressures and temperatures corresponding to the dense and supercritical gas regime, there is a strong dependence on gas properties and even singular behavior of fundamental transport properties. Simple extrapolations of the intuition and analyses of the ideal gas or liquid phase theory are no longer possible. The goal of this dissertation is to establish the correct form of the Reynolds equation valid for both low and high pressure gases and to explore the dynamics predicted by this new form of the Reynolds equation. The dissertation addresses ve problems involving our new Reynolds equation. In the rst, we establish the form appropriate for the simple benchmark problem of two-dimensional journal bearings. It is found that the material response is completely determined by a single thermodynamic parameter referred to as the eective bulk modulus. The validity of our new Reynolds equation has been established using solutions to the full Navier-Stokes-Fourier equations. We have also provided analytical estimates for the range of validity of this Reynolds equation and provided a systematic derivation of the energy equation valid whenever the Reynolds equation holds. The next three problems considered here derive local and global results of interest in high speed lubrication studies. The results are based on a perturbation analysis of our Reynolds and energy equation…
Advisors/Committee Members: Cramer, Mark S. (committeechair), Yue, Pengtao (committee member), Thangjitham, Surot (committee member), Abaid, Nicole (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: Fluid mechanics; Supercritical fluids; Compressible lubrication; Low Reynolds number
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APA (6th Edition):
Chien, S. (2019). Compressible Lubrication Theory in Pressurized Gases. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/88868
Chicago Manual of Style (16th Edition):
Chien, Ssu-Ying. “Compressible Lubrication Theory in Pressurized Gases.” 2019. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/88868.
MLA Handbook (7th Edition):
Chien, Ssu-Ying. “Compressible Lubrication Theory in Pressurized Gases.” 2019. Web. 06 Mar 2021.
Vancouver:
Chien S. Compressible Lubrication Theory in Pressurized Gases. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/88868.
Council of Science Editors:
Chien S. Compressible Lubrication Theory in Pressurized Gases. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/88868
Virginia Tech
4.
Jin, Hanxiang.
Surface Patterning and Rotordynamic Response of Annular Pressure Seals Used in Turbomachinery.
Degree: PhD, Engineering Mechanics, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/96731
► This dissertation focused on understanding the correlations between surface patterning and rotordynamic responses in the annular pressure seals. The annular pressure seals are a specific…
(more)
▼ This dissertation focused on understanding the correlations between surface patterning and rotordynamic responses in the annular pressure seals. The annular pressure seals are a specific type of rotordynamic component that was designed to prevent the fluid leakage from high pressure stage to low pressure stage in turbomachinery. As the working fluid enters the cavities and recirculates, the kinetic energy is reduced, resulting in a reduction of leakage flow through the annular pressure seals. Rotordynamic instability becomes an issue that may be related to the annular pressure seals in some cases. In recent years, rotordynamic components with higher rotor speeds and higher power densities are commonly used in industrial applications. These features could lead to increased instability risk in rotor-bearing systems as fluids-structure interactions take place. Therefore, high precision modeling of the rotodynamic components is required to predict the instability issues in high performance rotordynamic design. The instability issue may potentially be eliminated in design stage by varying the characteristics of the potentially unstable components. In this study, the surface patterning and rotordynamic responses were investigated for several different annular pressure seal models with a hybrid Bulk Flow/Computational Fluid Dynamics method. This dissertation provides for the first time regression models for rotordynamic coefficients that can be used as optimization guidelines. Research topics related to the annular pressure seals were presented in this dissertation as well. The reduced order model of both hole-pattern seals and labyrinth seals were investigated. The results showed that the flow field representing the flow dynamics in annular pressure seals can be expressed as a combination of first three proper orthogonal decomposition modes. In addition, supercritical state of carbon dioxide (sCO2) process fluid was examined to better understand the effects of working fluid on annular pressure seals. The results showed that the performance and stability in the annular pressure seals using sCO2 as process fluid can both be improved.
Advisors/Committee Members: Untaroiu, Alexandrina (committeechair), Staples, Anne E. (committee member), Iliescu, Traian (committee member), Boreyko, Jonathan B. (committee member), Untaroiu, Costin D. (committee member).
Subjects/Keywords: Fluid Dynamics; Annular Pressure Seals; Rotordynamics; Labyrinth Seals; Hole-pattern Seals; Reduced Order Modeling
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APA (6th Edition):
Jin, H. (2020). Surface Patterning and Rotordynamic Response of Annular Pressure Seals Used in Turbomachinery. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/96731
Chicago Manual of Style (16th Edition):
Jin, Hanxiang. “Surface Patterning and Rotordynamic Response of Annular Pressure Seals Used in Turbomachinery.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/96731.
MLA Handbook (7th Edition):
Jin, Hanxiang. “Surface Patterning and Rotordynamic Response of Annular Pressure Seals Used in Turbomachinery.” 2020. Web. 06 Mar 2021.
Vancouver:
Jin H. Surface Patterning and Rotordynamic Response of Annular Pressure Seals Used in Turbomachinery. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/96731.
Council of Science Editors:
Jin H. Surface Patterning and Rotordynamic Response of Annular Pressure Seals Used in Turbomachinery. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/96731
Virginia Tech
5.
Zhang, Peng.
Interfacial Dynamics and Applications in Optofluidics.
Degree: PhD, Engineering Mechanics, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/80443
► High quality (Q) factor whispering gallery modes (WGMs) can induce nonlinear effects in liquid droplets through mechanisms such as radiation pressure, light scattering, thermocapillarity, Kerr…
(more)
▼ High quality (Q) factor whispering gallery modes (WGMs) can induce nonlinear effects in liquid droplets through mechanisms such as radiation pressure, light scattering, thermocapillarity, Kerr nonlinearity, and thermal effect. However, such nonlinear effects have yet to be thoroughly investigated and compared in the literature. In this study, we first investigate a micron-sized liquid spherical resonator and present an approximated solution for the resonator interface deformation due to the radiation pressure. We then derive an analytical approach that can exactly calculate the droplet deformation induced by the radiation pressure. The accuracy of the analytical solution is confirmed through numerical analyses based on the boundary element method. We show that the nonlinear optofluidic effect induced by the radiation pressure is stronger than the Kerr effect and the thermal effect under a large variety of realistic conditions. Using liquids with ultra-low and experimentally attainable interfacial tension, we further confirm the prediction that it may only take a few photons to produce measurable WGM resonance shift through radiation pressure induced droplet deformation.
Similar to the radiation pressure, the scattering force in the droplet can induce a rotational fluid motion which also leads to the interface deformation. The interface deformation can also be produced by the thermocapillarity as a result of the WGM energy absorption and temperature increase. In this study, we provide a numerical scheme to calculate the fluid motion and quantify the nonlinearity induced by the optical scattering force and thermocapillarity. The magnitude of the optofluidic nonlinearities induced by the radiation pressure, thermocapillary effect, light scattering and Kerr effect are compared. We show that the radiation pressure due to the WGM produces the strongest nonlinear optofluidic effect.
Advisors/Committee Members: Jung, Sunghwan (committeechair), Staples, Anne E. (committee member), Abaid, Nicole (committee member), Xu, Yong (committee member), De Vita, Raffaella (committee member).
Subjects/Keywords: Optofluidics; Interfacial dynamics; BEM
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APA (6th Edition):
Zhang, P. (2016). Interfacial Dynamics and Applications in Optofluidics. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/80443
Chicago Manual of Style (16th Edition):
Zhang, Peng. “Interfacial Dynamics and Applications in Optofluidics.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/80443.
MLA Handbook (7th Edition):
Zhang, Peng. “Interfacial Dynamics and Applications in Optofluidics.” 2016. Web. 06 Mar 2021.
Vancouver:
Zhang P. Interfacial Dynamics and Applications in Optofluidics. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/80443.
Council of Science Editors:
Zhang P. Interfacial Dynamics and Applications in Optofluidics. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/80443
Virginia Tech
6.
San, Omer.
Multiscale Modeling and Simulation of Turbulent Geophysical Flows.
Degree: PhD, Engineering Science and Mechanics, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/28031
► The accurate and efficient numerical simulation of geophysical flows is of great interest in numerical weather prediction and climate modeling as well as in numerous…
(more)
▼ The accurate and efficient numerical simulation of geophysical flows is of great interest in numerical weather prediction and climate modeling as well as in numerous critical areas and industries, such as agriculture, construction, tourism, transportation, weather-related disaster management, and sustainable energy technologies. Oceanic and atmospheric flows display an enormous range of temporal and spatial scales, from seconds to decades and from centimeters to thousands of kilometers, respectively. Scale interactions, both spatial and temporal, are the dominant feature of all aspects of general circulation models in geophysical fluid dynamics. In this thesis, to decrease the cost for these geophysical flow computations, several types of multiscale methods were systematically developed and tested for a variety of physical settings including barotropic and stratified wind-driven large scale ocean circulation models, decaying and forced two-dimensional turbulence simulations, as well as several benchmark incompressible flow problems in two and three dimensions. The new models proposed here are based on two classes of modern multiscale methods: (i) interpolation based approaches in the context of the multigrid/multiresolution methodologies, and (ii) deconvolution based spatial filtering approaches in the context of large eddy simulation techniques. In the first case, we developed a coarse-grid projection method that uses simple interpolation schemes to go between the two components of the problem, in which the solution algorithms have different levels of complexity. In the second case, the use of approximate deconvolution closure modeling strategies was implemented for large eddy simulations of large-scale turbulent geophysical flows. The numerical assessment of these approaches showed that both the coarse-grid projection and approximate deconvolution methods could represent viable tools for computing more realistic turbulent geophysical flows that provide significant increases in accuracy and computational efficiency over conventional methods.
Advisors/Committee Members: Staples, Anne E. (committeechair), Stremler, Mark A. (committee member), De Vita, Raffaella (committee member), Iliescu, Traian (committee member), Ragab, Saad A. (committee member).
Subjects/Keywords: Geophysical Flows; Physical Oceanography; Multiscale Modeling; Multigrid; Large Eddy Simulation; Computational Fluid Dynamics
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APA (6th Edition):
San, O. (2012). Multiscale Modeling and Simulation of Turbulent Geophysical Flows. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/28031
Chicago Manual of Style (16th Edition):
San, Omer. “Multiscale Modeling and Simulation of Turbulent Geophysical Flows.” 2012. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/28031.
MLA Handbook (7th Edition):
San, Omer. “Multiscale Modeling and Simulation of Turbulent Geophysical Flows.” 2012. Web. 06 Mar 2021.
Vancouver:
San O. Multiscale Modeling and Simulation of Turbulent Geophysical Flows. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/28031.
Council of Science Editors:
San O. Multiscale Modeling and Simulation of Turbulent Geophysical Flows. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/28031
Virginia Tech
7.
Foster, Erich Leigh.
Finite Elements for the Quasi-Geostrophic Equations of the Ocean.
Degree: PhD, Mathematics, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/19362
► The quasi-geostrophic equations (QGE) are usually discretized in space by the finite difference method. The finite element (FE) method, however, offers several advantages over the…
(more)
▼ The quasi-geostrophic equations (QGE) are usually discretized in space by the finite difference method. The finite element (FE) method, however, offers several advantages over the finite difference method, such as the easy treatment of complex boundaries and a natural treatment of boundary conditions [Myers1995]. Despite these advantages, there are relatively few papers that consider the FE method applied to the QGE. Most FE discretizations of the QGE have been developed for the streamfunction-vorticity formulation. The reason is simple: The streamfunction-vorticity formulation yields a second order \\emph{partial differential equation (PDE)}, whereas the streamfunction formulation yields a fourth order PDE. Thus, although the streamfunction-vorticity formulation has two variables (q and \ψ) and the streamfunction formulation has just one (\ψ), the former is the preferred formulation used in practical computations, since its conforming FE discretization requires low-order (C
0) elements, whereas the latter requires a high-order (C
1) FE discretization. We present a conforming FE discretization of the QGE based on the Argyris element and we present a two-level FE discretization of the Stationary QGE (SQGE) based on the same conforming FE discretization using the Argyris element. We also, for the first time, develop optimal error estimates for the FE discretization QGE. Numerical tests for the FE discretization and the two-level FE discretization of the QGE are presented and theoretical error estimates are verified. By benchmarking the numerical results against those in the published literature, we conclude that our FE discretization is accurate. �Furthermore, the numerical results have the same convergence rates as those predicted by the theoretical error estimates.
Advisors/Committee Members: Iliescu, Traian (committeechair), Adjerid, Slimane (committee member), Burns, John A. (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: Quasi-geostrophic equations; finite element method; Argyris element; wind-driven ocean currents.
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APA (6th Edition):
Foster, E. L. (2013). Finite Elements for the Quasi-Geostrophic Equations of the Ocean. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/19362
Chicago Manual of Style (16th Edition):
Foster, Erich Leigh. “Finite Elements for the Quasi-Geostrophic Equations of the Ocean.” 2013. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/19362.
MLA Handbook (7th Edition):
Foster, Erich Leigh. “Finite Elements for the Quasi-Geostrophic Equations of the Ocean.” 2013. Web. 06 Mar 2021.
Vancouver:
Foster EL. Finite Elements for the Quasi-Geostrophic Equations of the Ocean. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/19362.
Council of Science Editors:
Foster EL. Finite Elements for the Quasi-Geostrophic Equations of the Ocean. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/19362
Virginia Tech
8.
Garrett, Joel Frederick.
Microfluidic Flow Creation in the Insect Respiratory System.
Degree: PhD, Biomedical Engineering, 2021, Virginia Tech
URL: http://hdl.handle.net/10919/101784
► The insect respiratory system works through the direct delivery of oxygen to the tissues. This occurs via a complex network of pumps, tubes, valves, and…
(more)
▼ The insect respiratory system works through the direct delivery of oxygen to the tissues. This occurs via a complex network of pumps, tubes, valves, and other structures that facilitate flow. These mechanisms allow insects to survive and prosper under a wide range of environmental and physiological conditions. While these structures have been studied extensively in a wide range of insect species, there are still many aspects of the respiratory system that remain unexplored. Here, we use the Madagascar hissing cockroach to examine how both bulk flow and diffusion are created in some types of insect respiratory systems. First, in Chapter One, we studied the animal under normal environmental conditions in order to determine how abdominal pumping, tracheal tube collapse, and spiracular valving are coordinated. Then, in Chapter Two, we exposed the animals to a range of oxygen concentrations to identify how the animals respond to varying environmental conditions. Finally, in Chapter Three, we constructed a simulated insect respiratory system to parametrically study the effects of network geometry and valve timing on the creation of advective and diffusive flow. By combining these three studies, we were able to improve our understanding of flow creation in the insect respiratory system.
Advisors/Committee Members: Davalos, Rafael V. (committeechair), Socha, John (committeechair), Staples, Anne E. (committee member), Harrison, Jon F. (committee member), Stremler, Mark A. (committee member).
Subjects/Keywords: microfluidics; entomology; engineering; simulation
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APA (6th Edition):
Garrett, J. F. (2021). Microfluidic Flow Creation in the Insect Respiratory System. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/101784
Chicago Manual of Style (16th Edition):
Garrett, Joel Frederick. “Microfluidic Flow Creation in the Insect Respiratory System.” 2021. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/101784.
MLA Handbook (7th Edition):
Garrett, Joel Frederick. “Microfluidic Flow Creation in the Insect Respiratory System.” 2021. Web. 06 Mar 2021.
Vancouver:
Garrett JF. Microfluidic Flow Creation in the Insect Respiratory System. [Internet] [Doctoral dissertation]. Virginia Tech; 2021. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/101784.
Council of Science Editors:
Garrett JF. Microfluidic Flow Creation in the Insect Respiratory System. [Doctoral Dissertation]. Virginia Tech; 2021. Available from: http://hdl.handle.net/10919/101784
9.
Zhang, Di.
Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics.
Degree: PhD, Aerospace Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/81137
► Wind energy industry thrived in the last three decades, environmental concerns and government regulations stimulate studies on wind farm location selection and wind turbine design.…
(more)
▼ Wind energy industry thrived in the last three decades, environmental concerns and government regulations stimulate studies on wind farm location selection and wind turbine design. Full-scale experiments and high-fidelity simulations are restrictive due to the prohibitively high cost, while the model-scale experiments and low-fidelity calculations miss key flow physics of unsteady high Reynolds number flows.
A hybrid RANS/LES turbulence model integrated with transition formulation is developed and tested by a surrogate model problem through joint experimental and computational fluid dynamics approaches. The model problem consists of a circular cylinder for generating coherent unsteadiness and a downstream airfoil in the cylinder wake. The cylinder flow is subcritical, with a Reynolds number of 64,000 based upon the cylinder diameter.
The quantitative dynamics of vortex shedding and Reynolds stresses in the cylinder near wake were well captured, owing to the turbulence-resolving large eddy simulation method that was invoked in the wake. The power spectrum density of velocity components showed that the flow fluctuations were well-maintained in cylinder wake towards airfoil and the hybrid model switched between RANS/LES mode outside boundary layer as expected. According to the experimental and simulation results, the airfoil encountered local flow angle variations up to ±50 degrees, and the turbulent airfoil boundary layer remained attached. Inspecting the boundary layer profiles over one shedding cycle, the oscillation about mean profile resembled the Stokes layer with zero mean. Further processing the data through phase-averaging technique found phase lags along the chordwise locations and both the phase-averaged and mean profiles collapsed into the Law of Wall in the range of 0 < y+ < 50. The features of high blade loading fluctuations due to unsteadiness and transitional boundary layers are of interest in the aerodynamic studies of full-scale wind turbine blades, making the model problem a comprehensive benchmark case for future model development and validation.
Advisors/Committee Members: Paterson, Eric G. (committeechair), Lowe, Kevin T. (committee member), Devenport, William J. (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: Hybrid RANS/LES; DES; Wind Energy; Boundary Layer Transition
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APA (6th Edition):
Zhang, D. (2017). Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/81137
Chicago Manual of Style (16th Edition):
Zhang, Di. “Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/81137.
MLA Handbook (7th Edition):
Zhang, Di. “Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics.” 2017. Web. 06 Mar 2021.
Vancouver:
Zhang D. Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/81137.
Council of Science Editors:
Zhang D. Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/81137
Virginia Tech
10.
Rao, Pradeep Chandrakant.
Study of the dynamics of transport and mixing using set oriented methods.
Degree: PhD, Engineering Mechanics, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/54552
► Efficient mixing can be achieved in flows where turbulence is absent, if the trajectories of passively advected particles in the flow are chaotic. The chaotic…
(more)
▼ Efficient mixing can be achieved in flows where turbulence is absent, if the trajectories of passively advected particles in the flow are chaotic. The chaotic nature of particle trajectories results in exponential stretching of material lines in the flow. Thus the interface along which diffusion occurs is stretched exponentially leading to efficient mixing. It has been demonstrated recently that regions in flow fields that exhibit poor mixing and non-chaotic particle trajectories can have an important bearing on the overall dynamics and transport of the entire domain.
The space-time trajectories of physical stirrers or elliptic points in two dimensional flows can be classified according to braid groups. One can predict a lower bound on the topological entropy (i.
e. exponential rate of stretching of material lines) of flows (hf ) by applying the Thurston-Nielsen classification theorems to these braids. This gives a reduced order model for the dynamics of transport of the entire flow field using just a few points. Recent work has shown that this methodology can be used to estimate a lower bound on hf using the
braids formed by Almost Cyclic Sets (ACS) in certain periodic Stokes' flows. These ACS are closely related to Almost Invariant Sets (AIS) which are identified using a probabilistic set oriented method that makes use of the descritised Perron-Frobenius operator of the flow map.
This work extends this approach to flows at non-zero Reynolds numbers, which take into account the effects of inertia. The role of Finite Time Coherent Structures (FTCS) in the dynamics of flow fields is also investigated. Unlike ACS, the FTCS approach is more general as it can be applied to aperiodic flow fields. Further, the relationship between mixing efficiency and the topological entropy of flow fields at non-zero Reynolds numbers is also studied.
Advisors/Committee Members: Stremler, Mark A. (committeechair), Paul, Mark R. (committee member), Ross, Shane D. (committee member), Ragab, Saad A. (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: Chaotic advection; mixing; coherent sets
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APA (6th Edition):
Rao, P. C. (2014). Study of the dynamics of transport and mixing using set oriented methods. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/54552
Chicago Manual of Style (16th Edition):
Rao, Pradeep Chandrakant. “Study of the dynamics of transport and mixing using set oriented methods.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/54552.
MLA Handbook (7th Edition):
Rao, Pradeep Chandrakant. “Study of the dynamics of transport and mixing using set oriented methods.” 2014. Web. 06 Mar 2021.
Vancouver:
Rao PC. Study of the dynamics of transport and mixing using set oriented methods. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/54552.
Council of Science Editors:
Rao PC. Study of the dynamics of transport and mixing using set oriented methods. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/54552
Virginia Tech
11.
Chaurasia, Adarsh Kumar.
Computational Micromechanics Analysis of Deformation and Damage Sensing in Carbon Nanotube Based Nanocomposites.
Degree: PhD, Engineering Mechanics, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/79789
► The current state of the art in structural health monitoring is primarily reliant on sensing deformation of structures at discrete locations using sensors and detecting…
(more)
▼ The current state of the art in structural health monitoring is primarily reliant on sensing deformation of structures at discrete locations using sensors and detecting damage using techniques such as X-ray, microCT, acoustic emission, impedance methods etc., primarily employed at specified intervals of service life. There is a need to develop materials and structures with self-sensing capabilities such that deformation and damage state can be identified in-situ real time. In the current work, the inherent deformation and damage sensing capabilities of carbon nanotube (CNT) based nanocomposites are explored starting from the nanoscale electron hopping mechanism to effective macroscale piezoresistive response through finite elements based computational micromechanics techniques. The evolution of nanoscale conductive electron hopping pathways which leads to nanocomposite piezoresistivity is studied in detail along with its evolution under applied deformations. The nanoscale piezoresistive response is used to evaluate macroscale nanocomposite response by using analytical micromechanics methods. The effective piezoresistive response, obtained in terms of macroscale effective gauge factors, is shown to predict the experimentally obtained gauge factors published in the literature within reasonable tolerance. In addition, the effect of imperfect interface between the CNTs and the polymer matrix on the mechanical and piezoresistive properties is studied using coupled electromechanical cohesive zone modeling. It is observed that the interfacial separation and damage at the nanoscale leads to a larger nanocomposite irreversible piezoresistive response under monotonic and cyclic loading because of interfacial damage accumulation. As a sample application, the CNT-polymer nanocomposites are used as a binding medium for polycrystalline energetic materials where the nanocomposite binder piezoresistivity is exploited to provide inherent deformation and damage sensing. The nanocomposite binder medium is modeled using electromechanical cohesive zones with properties obtained through the Mori-Tanaka method allowing for different local CNT volume fractions and orientations. Finally, the traditional implementation of Material Point Method (MPM) is extended for composite problems with large deformation (
e.g. large strain nanocomposite sensors with elastomer matrix) allowing for interfacial discontinuities appropriately. Overall, the current work evaluates nanocomposite piezoresistivity using a multiscale modeling framework and emphasizes through a sample application that nanocomposite piezoresistivity can be exploited for inherent sensing in materials.
Advisors/Committee Members: Seidel, Gary D. (committeechair), Staples, Anne E. (committee member), Batra, Romesh C. (committee member), Kapania, Rakesh K. (committee member), Case, Scott W. (committee member).
Subjects/Keywords: Carbon Nanotube; Nanocomposite; Piezoresistivity; Electron Hopping; Computational Micromechanics; Strain Sensing; Damage Sensing; Cohesive Zone; Interface Damage; Material Point Method
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APA (6th Edition):
Chaurasia, A. K. (2016). Computational Micromechanics Analysis of Deformation and Damage Sensing in Carbon Nanotube Based Nanocomposites. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/79789
Chicago Manual of Style (16th Edition):
Chaurasia, Adarsh Kumar. “Computational Micromechanics Analysis of Deformation and Damage Sensing in Carbon Nanotube Based Nanocomposites.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/79789.
MLA Handbook (7th Edition):
Chaurasia, Adarsh Kumar. “Computational Micromechanics Analysis of Deformation and Damage Sensing in Carbon Nanotube Based Nanocomposites.” 2016. Web. 06 Mar 2021.
Vancouver:
Chaurasia AK. Computational Micromechanics Analysis of Deformation and Damage Sensing in Carbon Nanotube Based Nanocomposites. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/79789.
Council of Science Editors:
Chaurasia AK. Computational Micromechanics Analysis of Deformation and Damage Sensing in Carbon Nanotube Based Nanocomposites. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/79789
Virginia Tech
12.
Dibelka, Jessica Anne.
Mechanics of Hybrid Metal Matrix Composites.
Degree: PhD, Engineering Mechanics, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/50579
► The appeal of hybrid composites is the ability to create materials with properties which normally do not coexist such as high specific strength, stiffness, and…
(more)
▼ The appeal of hybrid composites is the ability to create materials with properties which normally do not coexist such as high specific strength, stiffness, and toughness. One possible application for hybrid composites is as backplate materials in layered armor. Fiber reinforced composites have been used as backplate materials due to their potential to absorb more energy than monolithic materials at similar to lower weights through microfragmentation of the fiber, matrix, and fiber-matrix interface. Composite backplates are traditionally constructed from graphite or glass fiber reinforced epoxy composites. However, continuous alumina fiber-reinforced aluminum metal matrix composites (MMCs) have superior specific transverse and specific shear properties than epoxy composites. Unlike the epoxy composites, MMCs have the ability to absorb additional energy through plastic deformation of the metal matrix. Although, these enhanced properties may make continuous alumina reinforced MMCs advantageous for use as backplate materials, they still exhibit a low failure strain and therefore have low toughness. One possible solution to improve their energy absorption capabilities while maintaining the high specific stiffness and strength properties of continuous reinforced MMCs is through hybridization. To increase the strain to failure and energy absorption capability of a continuous alumina reinforced Nextel" MMC, it is laminated with a high failure strain Saffil® discontinuous alumina fiber layer. Uniaxial tensile testing of hybrid composites with varying Nextel" to Saffil® reinforcement ratios resulted in composites with non-catastrophic tensile failures and an increased strain to failure than the single reinforcement Nextel" MMC. The tensile behavior of six hybrid continuous and discontinuous alumina fiber reinforced MMCs are reported, as well as a description of the mechanics behind their unique behavior. Additionally, a study on the effects of fiber damage induced during processing is performed to obtain accurate as-processed fiber properties and improve single reinforced laminate strength predictions. A stochastic damage evolution model is used to predict failure of the continuous Nextel" fabric composite which is then applied to a finite element model to predict the progressive failure of two of the hybrid laminates.
Advisors/Committee Members: Case, Scott W. (committeechair), Lattimer, Brian Y. (committee member), Staples, Anne E. (committee member), Batra, Romesh C. (committee member), Carter, Robert H. (committee member).
Subjects/Keywords: continuous fiber; discontinuous fiber; alumina; aluminum matrix; progressive failure
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APA (6th Edition):
Dibelka, J. A. (2013). Mechanics of Hybrid Metal Matrix Composites. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/50579
Chicago Manual of Style (16th Edition):
Dibelka, Jessica Anne. “Mechanics of Hybrid Metal Matrix Composites.” 2013. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/50579.
MLA Handbook (7th Edition):
Dibelka, Jessica Anne. “Mechanics of Hybrid Metal Matrix Composites.” 2013. Web. 06 Mar 2021.
Vancouver:
Dibelka JA. Mechanics of Hybrid Metal Matrix Composites. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/50579.
Council of Science Editors:
Dibelka JA. Mechanics of Hybrid Metal Matrix Composites. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/50579
Virginia Tech
13.
Hosseinzadegan, Hamid.
A Physio-chemical Predictive Model of Dynamic Thrombus Formation and Growth in Stenosed Vessels.
Degree: PhD, Mechanical Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/89325
► According to the World Health Organization (WHO), Cardiovascular Disease (CVD) is the leading cause of death in the world. Biomechanics and fluid dynamics of blood…
(more)
▼ According to the World Health Organization (WHO), Cardiovascular Disease (CVD) is the leading cause of death in the world. Biomechanics and fluid dynamics of blood flow play an important role in CVD mediation. Shear stress plays a major role in platelet-substrate interactions and thrombus formation and growth in blood flow, where under both pathological and physiological conditions platelet adhesion and accumulation occur. In this study, a three-dimensional dynamic model of platelet-rich thrombus growth in stenosed vessels using computational fluid dynamics (CFD) methods is introduced. Platelet adhesion, aggregation and activation kinetics are modeled by solving mass transport equations for blood components involved in thrombosis. The model was first verified under three different shear conditions and at two heparin levels. Three-dimensional simulations were then carried out to evaluate the performance of the model for severely damaged (stripped) aortas with mild and severe stenosis degrees. For these cases, linear shear-dependent functions were developed for platelet-surface and platelet-platelet adhesion rates. It was confirmed that the platelet adhesion rate is not only a function of Reynolds number (or wall shear rate) but also the stenosis severity of the vessel. General correlations for adhesion rates of platelets as functions of stenosis and Reynolds number were obtained based on these cases. The model was applied to different experimental systems and shown to agree well with measured platelet deposition. Then, the Arbitrary Lagrangian Eulerian (ALE) formulation was used to model dynamic growth by including geometry change in the simulation procedure. The wall boundaries were discretely moved based on the amount of platelet deposition that occurs on the vessel wall. To emulate the dynamic behavior of platelet adhesion kinetics during thrombus growth, the validated model for platelet adhesion, which calculates platelet-surface adhesion rates as a function of stenosis severity and Reynolds number, was applied to the model. The model successfully predicts the nonlinear growth of thrombi in the stenosed area. These simulations provide a useful guide to understand the effect of growing thrombus on platelet deposition rate, platelet activation kinetics and occurrence of thromboembolism (TE) in highly stenosed arteries.
Advisors/Committee Members: Tafti, Danesh K. (committeechair), Qiao, Rui (committee member), Staples, Anne E. (committee member), Behkam, Bahareh (committee member), Chappell, John C. (committee member), Grant, John W. (committee member).
Subjects/Keywords: Numerical modeling; Atherosclerosis; Platelet adhesion; Platelet activation; Embolism
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APA (6th Edition):
Hosseinzadegan, H. (2017). A Physio-chemical Predictive Model of Dynamic Thrombus Formation and Growth in Stenosed Vessels. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/89325
Chicago Manual of Style (16th Edition):
Hosseinzadegan, Hamid. “A Physio-chemical Predictive Model of Dynamic Thrombus Formation and Growth in Stenosed Vessels.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/89325.
MLA Handbook (7th Edition):
Hosseinzadegan, Hamid. “A Physio-chemical Predictive Model of Dynamic Thrombus Formation and Growth in Stenosed Vessels.” 2017. Web. 06 Mar 2021.
Vancouver:
Hosseinzadegan H. A Physio-chemical Predictive Model of Dynamic Thrombus Formation and Growth in Stenosed Vessels. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/89325.
Council of Science Editors:
Hosseinzadegan H. A Physio-chemical Predictive Model of Dynamic Thrombus Formation and Growth in Stenosed Vessels. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/89325
Virginia Tech
14.
Stewart, Kelley Christine.
Hydrodynamics of Cardiac Diastole.
Degree: PhD, Mechanical Engineering, 2011, Virginia Tech
URL: http://hdl.handle.net/10919/26837
► Left ventricular diastole (filling) is a complex process with many features and coupled compensatory mechanisms which coordinate to maintain optimal filling and ejection of the…
(more)
▼ Left ventricular diastole (filling) is a complex process with many features and coupled compensatory mechanisms which coordinate to maintain optimal filling and ejection of the left ventricle. Diastolic filling is controlled by the left ventricular recoil, relaxation, and compliance as well as atrial and ventricular pressures making left ventricular diastolic dysfunction very difficult to understand and diagnose. An improved understanding of these unique flows is important to both the fundamental mechanics of the cardiac diastolic filling as well as the development of novel and accurate diagnostic techniques.
This work includes studies of in-vivo and in-vitro vortex rings. Vortex rings created in the left ventricle past the mitral valve during diastole are produced in a confined domain and are influenced by the left ventricular walls. Therefore, an in-vitro analysis of the formation and decay of vortex rings within confined cylindrical domains using particle image velocimetry was conducted. Varying mechanisms of vortex ring breakdown were observed over a wide range of Reynolds numbers, and an analytical model for vortex ring circulation decay of laminar vortex rings was developed. Also, in this work a novel method for analyzing color M-mode echocardiography data using a newly developed automated algorithm is introduced which examines the pressure gradients and velocities within the left ventricle. From this analysis, a new diagnostic filling parameter is introduced which displays a greater probability of detection of diastolic dysfunction over the conventionally used diagnostic parameter.
Advisors/Committee Members: Vlachos, Pavlos P. (committeechair), Staples, Anne E. (committee member), Paul, Mark R. (committee member), Little, William C. (committee member), Jung, Sunghwan (committee member), Ball, Kenneth S. (committee member).
Subjects/Keywords: heart failure; echocardiography; diastole; vortex rings
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APA (6th Edition):
Stewart, K. C. (2011). Hydrodynamics of Cardiac Diastole. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/26837
Chicago Manual of Style (16th Edition):
Stewart, Kelley Christine. “Hydrodynamics of Cardiac Diastole.” 2011. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/26837.
MLA Handbook (7th Edition):
Stewart, Kelley Christine. “Hydrodynamics of Cardiac Diastole.” 2011. Web. 06 Mar 2021.
Vancouver:
Stewart KC. Hydrodynamics of Cardiac Diastole. [Internet] [Doctoral dissertation]. Virginia Tech; 2011. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/26837.
Council of Science Editors:
Stewart KC. Hydrodynamics of Cardiac Diastole. [Doctoral Dissertation]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/26837
Virginia Tech
15.
Aboelkassem, Yasser.
Novel Bioinspired Pumping Models for Microscale Flow Transport.
Degree: PhD, Engineering Science and Mechanics, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/28674
► Bioinspiration and biomimetics are two increasingly important fields in applied science and mechanics that seek to imitate systems or processes in nature to design improved…
(more)
▼ Bioinspiration and biomimetics are two increasingly important fields in applied science and mechanics that seek to imitate systems or processes in nature to design improved engineering devices. Here, we are inspired and motivated by microscale internal flow transport phenomena in insect tracheal networks, which are observed to be induced by the rhythmic tracheal wall contractions. These networks have been shown to mange fluid very efficiently compared to current state-of-the-art microfluidic devises.
This dissertation presents two versions of a novel bioinspired pumping mechanism that is neither peristaltic nor belongs to impedance mismatch class of pumping mechanisms. The insect-inspired pumping models presented here are expected to function efficiently in the microscale flow regime in a simple channel/tube geometries or a complex network of channels. The first pumping approach shows the ability of inducing a unidirectional net flow by using an inelastic tube or channel with at least two moving contractions. The second pumping approach presents a new concept for directional pumping, namely ``selective pumping in a network.". The results presented here might help in mimicking features of physiological systems in insects and guide efforts to fabricate novel microfluidic devices with improved efficiency.
In this study, both theoretical analysis and Stokeslets-meshfree computational methods are used to solve for the 2D and 3D viscous flow transport in several micro-geometries (tubes, channels and networks) with prescribed moving wall contractions. The derived theoretical analysis is based on both lubrication theory and quasi-steady approximations at low Reynolds numbers. The meshfree numerical method is based on the method of fundamental solutions (MFS) that uses a set of singularized force elements ``Stokeslets'' to induce the flow motions. Moreover, the passive particle tracking simulation approach in the Lagrangian frame of reference is also used to strengthen and support our pumping paradigm developed in this dissertation.
Advisors/Committee Members: Staples, Anne E. (committeechair), Stremler, Mark A. (committee member), Socha, John J. (committee member), Jung, Sunghwan (committee member), Davalos, Rafael V. (committee member), De Vita, Raffaella (committee member).
Subjects/Keywords: Bioinspiration; Biomimetics; Physiological System in Insects; Stokeslets; Meshfree; Microscale Flow Transport; Collapsible Tubes; Microfluidics
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APA (6th Edition):
Aboelkassem, Y. (2012). Novel Bioinspired Pumping Models for Microscale Flow Transport. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/28674
Chicago Manual of Style (16th Edition):
Aboelkassem, Yasser. “Novel Bioinspired Pumping Models for Microscale Flow Transport.” 2012. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/28674.
MLA Handbook (7th Edition):
Aboelkassem, Yasser. “Novel Bioinspired Pumping Models for Microscale Flow Transport.” 2012. Web. 06 Mar 2021.
Vancouver:
Aboelkassem Y. Novel Bioinspired Pumping Models for Microscale Flow Transport. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/28674.
Council of Science Editors:
Aboelkassem Y. Novel Bioinspired Pumping Models for Microscale Flow Transport. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/28674
Virginia Tech
16.
Dupuis, Eric Donald.
Electroelastic Modeling and Testing of Direct Contact Ultrasonic Clothes Drying Systems.
Degree: PhD, Engineering Mechanics, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/99280
► Energy efficient appliances and devices are becoming increasingly necessary as emissions from electricity production continue to increase the severity of global warming. Many of such…
(more)
▼ Energy efficient appliances and devices are becoming increasingly necessary as emissions from electricity production continue to increase the severity of global warming. Many of such appliances have not been substantially redesigned since their creation in the early 1900s. One device in particular which has arguably changed the least and consumes the most energy during use is the electric clothes dryer. The common form of this technology in the United States relies on the generation of thermal energy by passing electrical current through a metal. The resulting heat causes liquid within the clothing to evaporate where the humid air is ejected from the control volume. While the conversion of energy from electrical to thermal through a heating element is efficient, the drying characteristics of fabrics in a warm humid environment are not, and much of the heat inside of the volume does not perform drying as efficiently as possible.
In 2016, researchers at Oak Ridge National Laboratory in Knoxville, Tennessee, proposed an alternative mechanism for the drying of clothes which circumvents the need for thermal energy. This method is called direct-contact ultrasonic clothes drying, and utilizes a vibrating disk made of piezoelectric and metal materials to physically turn the water retained in clothing into a mist, which can be vented away leaving behind dry fabric. This method results in the water leaving the fabric at room temperature, rather than being heated, which bypasses the need for a substantial amount of energy to convert from the liquid to gas phase. The first ever prototype dryer shows the potential of being twice as efficient as conventional dryers.
This investigation is based around improving the device atomizing the water within the clothing, as well as understanding physical processes behind the ultrasonic drying process. These tasks will be conducted through experimental measurements and mathematical models to predict the behavior of the atomizing device, as well as computer software for both the parameters experimentally measured, and items which cannot be measured such as the flow in very small channels. The conclusions of this study will be recommendations for the future development of direct contact ultrasonic drying technology.
Advisors/Committee Members: Shahab, Shima (committeechair), Momen, Ayyoub Mehdizadeh (committee member), Abaid, Nicole (committee member), Vlaisavljevich, Eli (committee member), Staples, Anne E. (committee member), Patel, Viral K. (committee member).
Subjects/Keywords: Ultrasonic drying; vibrations; piezoelectric; electromechanical; microchannel
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APA (6th Edition):
Dupuis, E. D. (2020). Electroelastic Modeling and Testing of Direct Contact Ultrasonic Clothes Drying Systems. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/99280
Chicago Manual of Style (16th Edition):
Dupuis, Eric Donald. “Electroelastic Modeling and Testing of Direct Contact Ultrasonic Clothes Drying Systems.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/99280.
MLA Handbook (7th Edition):
Dupuis, Eric Donald. “Electroelastic Modeling and Testing of Direct Contact Ultrasonic Clothes Drying Systems.” 2020. Web. 06 Mar 2021.
Vancouver:
Dupuis ED. Electroelastic Modeling and Testing of Direct Contact Ultrasonic Clothes Drying Systems. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/99280.
Council of Science Editors:
Dupuis ED. Electroelastic Modeling and Testing of Direct Contact Ultrasonic Clothes Drying Systems. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/99280
17.
Izadi, Saeed.
Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber.
Degree: PhD, Engineering Mechanics, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/81539
► Atomistic modeling and simulation methods enable a modern molecular approach to bio-medical research. Issues addressed range from structure-function relationships to structure-based drug design. The ability…
(more)
▼ Atomistic modeling and simulation methods enable a modern molecular approach to bio-medical research. Issues addressed range from structure-function relationships to structure-based drug design. The ability of these methods to address biologically relevant problems is largely determined by their accurate treatment of electrostatic interactions in the target biomolecular structure. In practical molecular simulations, the electrostatic charge density of molecules is approximated by an arrangement of fractional "point charges" throughout the molecule. While chemically intuitive and straightforward in technical implementation, models based exclusively on atom-centered charge placement, a major workhorse of the biomolecular simulations, do not necessarily provide a sufficiently detailed description of the molecular electrostatic potentials for small systems, and can become prohibitively expensive for large systems with thousands to millions of atoms. In this work, we propose a rigorous and generally applicable approach, Optimal Point Charge Approximation (OPCA), for approximating electrostatic charge distributions of biomolecules with a small number of point charges to best represent the underlying electrostatic potential, regardless of the distance to the charge distribution. OPCA places a given number of point charges so that the lowest order multipole moments of the reference charge distribution are optimally reproduced. We provide a general framework for calculating OPCAs to any order, and introduce closed-form analytical expressions for the 1-charge, 2-charge and 3-charge OPCA. We demonstrate the advantage of OPCA by applying it to a wide range of biomolecules of varied sizes. We use the concept of OPCA to develop a different, novel approach of constructing accurate and simple point charge water models. The proposed approach permits a virtually exhaustive search for optimal model parameters in the sub-space most relevant to electrostatic properties of the water molecule in liquid phase. A novel rigid 4-point Optimal Point Charge (OPC) water model constructed based on the new approach is substantially more accurate than commonly used models in terms of bulk water properties, and delivers critical accuracy improvement in practical atomistic simulations, such as RNA simulations, protein folding, protein-ligand binding and small molecule hydration. We also apply our new approach to construct a 3-point version of the Optimal Point Charge water model, referred to as OPC3. OPCA can be employed to represent large charge distributions with only a few point charges. We use this capability of OPCA to develop a multi-scale, yet fully atomistic, generalized Born approach (GB-HCPO) that can deliver up to 2 orders of magnitude speedup compared to the reference MD simulation. As a practical demonstration, we exploit the new multi-scale approach to gain insight into the structure of million-atom 30-nm chromatin fiber. Our results suggest important structural details consistent with experiment: the linker DNA fills the core region and…
Advisors/Committee Members: Onufriev, Alexey V. (committeechair), Davalos, Rafael V. (committee member), Bevan, David R. (committee member), Ross, Shane D. (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: Molecular Modeling; Explicit Solvent Model; Force Field; Implicit Solvent Model; Point Charge Approximation; Multipole Moments; Electrostatics; Water Models; Multi-scale Models
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APA (6th Edition):
Izadi, S. (2016). Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/81539
Chicago Manual of Style (16th Edition):
Izadi, Saeed. “Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/81539.
MLA Handbook (7th Edition):
Izadi, Saeed. “Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber.” 2016. Web. 06 Mar 2021.
Vancouver:
Izadi S. Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/81539.
Council of Science Editors:
Izadi S. Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/81539
18.
Park, David.
The Application of the Solar Chimney for Ventilating Buildings.
Degree: PhD, Mechanical Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/73418
► This study sought to demonstrate the potential applications of the solar chimney for the naturally ventilating a building. Computational fluid dynamics (CFD) was used to…
(more)
▼ This study sought to demonstrate the potential applications of the solar chimney for the naturally ventilating a building. Computational fluid dynamics (CFD) was used to model various room configurations to assess ventilation strategies. A parametric study of the solar chimney system was executed, and three-dimensional simulations were compared and validated with experiments. A new definition for the hydraulic diameter that incorporated the chimney geometry was developed to predict the flow regime in the solar chimney system. To mitigate the cost and effort to use experiments to analyze building energy, a mathematical approach was considered. A relationship between small- and full-scale models was investigated using non-dimensional analysis. Multiple parameters were involved in the mathematical model to predict the air velocity, where the predictions were in good agreement with experimental data as well as the numerical simulations from the present study.
The second part of the study considered building design optimization to improve ventilation using air changes per hour (ACH) as a metric, and air circulation patterns within the building. An upper vent was introduced near the ceiling of the chimney system, which induced better air circulation by removing the warm air in the building. The study pursued to model a realistic scenario for the solar chimney system, where it investigated the effect of the vent sizes, insulation, and a reasonable solar chimney size. It was shown that it is critical to insulate the backside of the absorber and that the ratio of the conditioned area to chimney volume should be at least 10.
Lastly, the application of the solar chimney system for basement ventilation was discussed. Appropriate vent locations in the basement were determined, where the best ventilation was achieved when the duct inlet was located near the ceiling and the exhaust vent was located near the floor of the chimney. Sufficient ventilation was also achieved even for scenarios of a congested building when modeling the presence of multiple people.
Advisors/Committee Members: Battaglia, Francine (committeechair), Behkam, Bahareh (committee member), Kornhauser, Alan A. (committee member), Huxtable, Scott T. (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: Natural ventilation; solar chimney; buoyancy-driven flow; building energy; basement
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APA (6th Edition):
Park, D. (2016). The Application of the Solar Chimney for Ventilating Buildings. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/73418
Chicago Manual of Style (16th Edition):
Park, David. “The Application of the Solar Chimney for Ventilating Buildings.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/73418.
MLA Handbook (7th Edition):
Park, David. “The Application of the Solar Chimney for Ventilating Buildings.” 2016. Web. 06 Mar 2021.
Vancouver:
Park D. The Application of the Solar Chimney for Ventilating Buildings. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/73418.
Council of Science Editors:
Park D. The Application of the Solar Chimney for Ventilating Buildings. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/73418
19.
Free, Jillian Chodak.
Rapid Modelling of Nonlinearities in Heat Transfer.
Degree: PhD, Mechanical Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/74885
► Heat transfer systems contain many sources of nonlinearity including temperature dependent material properties, radiation boundary conditions, and internal source terms. Despite progress in numerical simulations,…
(more)
▼ Heat transfer systems contain many sources of nonlinearity including temperature dependent
material properties, radiation boundary conditions, and internal source terms. Despite progress in numerical simulations, producing accurate models that can predict these complex behaviors are still encumbered by lengthy processing times. Accurate models can be produced quickly by utilizing projection Reduced Order Modeling (ROM) techniques. For discretized systems, the Singular Value Decomposition technique is the preferred approach but has had limited success on treating nonlinearities. In this research, the treatment of nonlinear temperature dependent material properties was incorporated into a ROM. Additional sources of nonlinearities such as radiation boundary conditions, temperature dependent source heating terms, and complex geometry were also integrated. From the results, low conductivity, highly nonlinear material properties were predicted by the ROM within 1% of full order models, and additional nonlinearities were predicted within 8%. A study was then done to identify initial snapshots for use in developing a ROM that can accurately predict results across a wide range of inputs. From this, a step function was identified as being the most accurate and computationally efficient. The ROM was further investigated by a discretization study to assess computational gains in both 1D and 3D models as a function of mesh density. The lower mesh densities in the 1D and 3D ROMs resulted in moderate computational times (up to 40 times faster). However, highly discretized systems such as 5000 nodes in 1D and 125000 nodes in 3D resulted in computational gains on the order of 2000 to 3000 times faster than the full order model.
Advisors/Committee Members: Lattimer, Brian Y. (committeechair), Diller, Thomas E. (committee member), Huxtable, Scott T. (committee member), Ekkad, Srinath (committee member), Staples, Anne E. (committee member).
Subjects/Keywords: heat transfer; nonlinearities; material properties; radiation; source heating; reduced order model; proper orthogonal decomposition
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APA ·
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MLA ·
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APA (6th Edition):
Free, J. C. (2017). Rapid Modelling of Nonlinearities in Heat Transfer. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/74885
Chicago Manual of Style (16th Edition):
Free, Jillian Chodak. “Rapid Modelling of Nonlinearities in Heat Transfer.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/74885.
MLA Handbook (7th Edition):
Free, Jillian Chodak. “Rapid Modelling of Nonlinearities in Heat Transfer.” 2017. Web. 06 Mar 2021.
Vancouver:
Free JC. Rapid Modelling of Nonlinearities in Heat Transfer. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/74885.
Council of Science Editors:
Free JC. Rapid Modelling of Nonlinearities in Heat Transfer. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/74885
20.
Nasr Azadani, Leila.
Advanced Spectral Methods for Turbulent Flows.
Degree: PhD, Engineering Mechanics, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/47676
► Although spectral methods have been in use for decades, there is still room for innovation, refinement and improvement of the methods in terms of efficiency…
(more)
▼ Although spectral methods have been in use for decades, there is still room for innovation, refinement and improvement of the methods in terms of efficiency and accuracy, for generalized homogeneous turbulent flows, and especially for specialized applications like the computation of atmospheric flows and numerical weather prediction. In this thesis, two such innovations are presented. First, inspired by the adaptive mesh refinement (AMR) technique, which was developed for the computation of fluid flows in physical space, an algorithm is presented for accelerating direct numerical simulation (DNS) of isotropic homogeneous turbulence in spectral space. In the adaptive spectral resolution (ASR) technique developed here the spectral resolution in spectral space is dynamically refined based on refinement criteria suited to the special features of isotropic homogeneous turbulence in two, and three dimensions. Applying ASR to computations of two- and three-dimensional turbulence allows significant savings in the computational time with little to no compromise in the accuracy of the solutions. In the second part of this thesis the effect of explicit filtering on large eddy simulation (LES) of atmospheric flows in spectral space is studied. Apply an explicit filter in addition to the implicit filter due to the computational grid and discretization schemes in LES of turbulent flows allows for better control of the numerical error and improvement in the accuracy of the results. Explicit filtering has been extensively applied in LES of turbulent flows in physical space while few studies have been done on explicitly filtered LES of turbulent flows in spectral space because of perceived limitations of the approach, which are shown here to be incorrect. Here, explicit filtering in LES of the turbulent barotropic vorticity equation (BVE) as a first model of the Earth's atmosphere in spectral space is studied. It is shown that explicit filtering increases the accuracy of the results over implicit filtering, particularly where the location of coherent structures is concerned.
Advisors/Committee Members: Staples, Anne E. (committeechair), Paul, Mark R. (committee member), Iliescu, Traian (committee member), Tafti, Danesh K. (committee member), Ross, Shane D. (committee member).
Subjects/Keywords: Turbulent Flows; Spectral Methods; Large Eddy Simulation; Direct Numerical Simulation
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APA (6th Edition):
Nasr Azadani, L. (2014). Advanced Spectral Methods for Turbulent Flows. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/47676
Chicago Manual of Style (16th Edition):
Nasr Azadani, Leila. “Advanced Spectral Methods for Turbulent Flows.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/47676.
MLA Handbook (7th Edition):
Nasr Azadani, Leila. “Advanced Spectral Methods for Turbulent Flows.” 2014. Web. 06 Mar 2021.
Vancouver:
Nasr Azadani L. Advanced Spectral Methods for Turbulent Flows. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/47676.
Council of Science Editors:
Nasr Azadani L. Advanced Spectral Methods for Turbulent Flows. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/47676
21.
Kim, Seong Jin.
Fluid Dynamics in Liquid Entry and Exit.
Degree: PhD, Engineering Mechanics, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/88757
► Interaction between a solid body and a liquid-air interface plays an important role in multiphase flows, which includes numerous engineering applications such as mineral flotation,…
(more)
▼ Interaction between a solid body and a liquid-air interface plays an important role in multiphase flows, which includes numerous engineering applications such as mineral flotation, dip coating operations, and air-to-sea and sea-to-air projectiles. It is also crucial in animal behaviors like the locomotion of water-walking animals, the plunge-diving of birds, and the jumping out of water of marine creatures. Depending on the moving direction of a solid, such diverse phenomena can be classified into two categories; liquid-entry and liquid-exit. Liquid-entry, or more widely called water-entry, is the behavior of a solid object entering liquid from air. The opposite case is referred to as liquid-exit.
Liquid-entry has been extensively studied, especially focusing on cavity formation and the estimation on capillary and hydrodynamic forces on a solid object. However, as the behavior of a triple contact line has not been understood on a sinking object, previous studies were limited to the special case of hydrophobic object to fix the contact line. Moreover, a more recent study pointed out the important role of contact line behavior to characterize the performance of film flotation, which is one of the direct applications of liquid-entry. However, there are no existing previous studies on the dynamics of the contact line on a sinking object. This subject will be first discussed in Chapter 2.
In Chapters 3 and 4, the topics related to liquid-exit will be discussed, where a solid sphere exits out of a liquid toward air with constant velocity, acceleration, or deceleration. Chapter 3 will focus on the penetration and bouncing behaviors of a solid sphere while impacting a liquid-air interface. The solid sphere experiences the resistance of surface tension and gravity while impacting the interface. Thus, liquid-exit spheres should have enough momentum to penetrate the interface to overcome these resistances, which indicates that the critical momentum exits. This understanding would give a mechanistic explanation as to why some aquatic species, especially plankton, are able to jump out of water while the others cannot despite their similar size. This study can help to understand the particle-bubble interaction for froth flotation applications, in which the particle tends to attach to the bubble.
In the last Chapter, the formation of a liquid column during the liquid-exit will be discussed. It has been observed that the evolution of a liquid column strongly depends on experimental conditions, especially the acceleration of a solid sphere. The pinch-off dynamics of a liquid column is categorized as two branches: upper and lower pinch-off's. The pinch-off location affects the entrained liquid volume adhered to the solid object, which is directly related to the uniform quality of a dip-coating operation. In addition to the pinch-off location and time in relation to the aforementioned experimental conditions will be discussed.
In summary, studies in the present dissertation are designed and performed to provide…
Advisors/Committee Members: Jung, Sunghwan (committeechair), Lu, Chang (committee member), Staples, Anne E. (committee member), Abaid, Nicole (committee member), Cramer, Mark S. (committee member).
Subjects/Keywords: Surface tension; water-exit; water-entry; contact line
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APA ·
Chicago ·
MLA ·
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CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Kim, S. J. (2017). Fluid Dynamics in Liquid Entry and Exit. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/88757
Chicago Manual of Style (16th Edition):
Kim, Seong Jin. “Fluid Dynamics in Liquid Entry and Exit.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 06, 2021.
http://hdl.handle.net/10919/88757.
MLA Handbook (7th Edition):
Kim, Seong Jin. “Fluid Dynamics in Liquid Entry and Exit.” 2017. Web. 06 Mar 2021.
Vancouver:
Kim SJ. Fluid Dynamics in Liquid Entry and Exit. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 06].
Available from: http://hdl.handle.net/10919/88757.
Council of Science Editors:
Kim SJ. Fluid Dynamics in Liquid Entry and Exit. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/88757
. 
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