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Virginia Tech
1.
Battista, Thomas Andrew.
Lagrangian Mechanics Modeling of Free Surface-Affected Marine Craft.
Degree: PhD, Aerospace and Ocean Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/82928 
► Although ships have been used for thousands of years, modeling the dynamics of marine craft has historically been restricted by the complex nature of the…
(more)
▼ Although ships have been used for thousands of years, modeling the dynamics of marine craft has historically been restricted by the complex nature of the hydrodynamics. The principal challenge is that the vehicle motion is coupled to the ambient fluid motion, effectively requiring one to solve an infinite dimensional set of equations to predict the hydrodynamic forces and moments acting on a marine vehicle. Additional challenges arise in parametric modeling, where one approximates the fluid behavior using reduced-order ordinary differential equations. Parametric models are typically required for model-based state estimation and feedback control design, while also supporting other applications including vehicle design and submarine operator training.
In this dissertation, Lagrangian mechanics is used to derive nonlinear, parametric motion models for marine craft operating in the presence of a free surface. In Lagrangian mechanics, one constructs the equations of motion for a dynamic system using a system Lagrangian, a scalar energy-like function canonically defined as the system kinetic energy minus the system potential energies. The Lagrangian functions are identified under ideal flow assumptions and are used to derive two sets of equations. The first set of equations neglects hydrodynamic forces due to exogenous fluid motions and may be interpreted as a nonlinear calm water maneuvering model. The second set of equations incorporates effects due to exogenous fluid motion, and may be interpreted as a nonlinear, unified maneuvering and seakeeping model. Having identified the state- and time-dependent model parameters, one may use these models to rapidly simulate surface-affected marine craft maneuvers, enabling model-based control design and state estimation algorithms.
Advisors/Committee Members: Woolsey, Craig A. (committeechair), Valentinis, Francis (committeechair), Brizzolara, Stefano (committee member), Paterson, Eric G. (committee member).
Subjects/Keywords: Lagrangian Mechanics; Potential Flow Hydrodynamics; Fluid-Body Interactions
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APA (6th Edition):
Battista, T. A. (2018). Lagrangian Mechanics Modeling of Free Surface-Affected Marine Craft. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/82928
Chicago Manual of Style (16th Edition):
Battista, Thomas Andrew. “Lagrangian Mechanics Modeling of Free Surface-Affected Marine Craft.” 2018. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/82928.
MLA Handbook (7th Edition):
Battista, Thomas Andrew. “Lagrangian Mechanics Modeling of Free Surface-Affected Marine Craft.” 2018. Web. 15 Nov 2019.
Vancouver:
Battista TA. Lagrangian Mechanics Modeling of Free Surface-Affected Marine Craft. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/82928.
Council of Science Editors:
Battista TA. Lagrangian Mechanics Modeling of Free Surface-Affected Marine Craft. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/82928
Virginia Tech
2.
Clark, Ian Andrew.
A Study of Bio-Inspired Canopies for the Reduction of Roughness Noise.
Degree: MS, Aerospace and Ocean Engineering, 2015, Virginia Tech
URL: http://hdl.handle.net/10919/51178
► The wings of most species of owl have been shown to possess three unique physical attributes which allow them to hunt in effective silence: a…
(more)
▼ The wings of most species of owl have been shown to possess three unique physical attributes which allow them to hunt in effective silence: a comb of evenly-spaced bristles along the wing leading-edge; a compliant and porous fringe of feathers at the trailing-edge; and a velvety down material distributed over the upper wing surface. This investigation focuses on the last of the mechanisms as a means to reduce noise from flow over surface roughness. A microscopic study of several owl feathers revealed the structure of the velvety down to be very similar to that of a forest or a field of crops. Analogous surface treatments (suspended canopies) were designed which simulated the most essential geometric features of the velvety down material.
The
Virginia Tech Anechoic Wall-Jet Facility was used to perform far-field noise and surface pressure fluctuation measurements in the presence of various combinations of rough surfaces and suspended canopies. All canopies were demonstrated to have a strong influence on the surface pressure spectra, and attenuations of up to 30 dB were observed. In addition, all canopies were shown to have some positive effects on far-field noise, and optimized canopies yielded far-field noise reductions of up to 8 dB across all frequencies at which roughness noise was observed. This development represents a new passive method for roughness noise control with possibility for future optimization and application to engineering structures.
Advisors/Committee Members: Devenport, William J. (committeechair), Alexander, William Nathan (committee member), Paterson, Eric G. (committee member).
Subjects/Keywords: Roughness Noise; Bio-Inspired; Noise Reduction; Noise Control; Canopies
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APA (6th Edition):
Clark, I. A. (2015). A Study of Bio-Inspired Canopies for the Reduction of Roughness Noise. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/51178
Chicago Manual of Style (16th Edition):
Clark, Ian Andrew. “A Study of Bio-Inspired Canopies for the Reduction of Roughness Noise.” 2015. Masters Thesis, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/51178.
MLA Handbook (7th Edition):
Clark, Ian Andrew. “A Study of Bio-Inspired Canopies for the Reduction of Roughness Noise.” 2015. Web. 15 Nov 2019.
Vancouver:
Clark IA. A Study of Bio-Inspired Canopies for the Reduction of Roughness Noise. [Internet] [Masters thesis]. Virginia Tech; 2015. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/51178.
Council of Science Editors:
Clark IA. A Study of Bio-Inspired Canopies for the Reduction of Roughness Noise. [Masters Thesis]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/51178
Virginia Tech
3.
McCall, Andrew James.
Multi-level Parallelism with MPI and OpenACC for CFD Applications.
Degree: MS, Aerospace and Ocean Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/78203
► High-level parallel programming approaches, such as OpenACC, have recently become popular in complex fluid dynamics research since they are cross-platform and easy to implement. OpenACC…
(more)
▼ High-level parallel programming approaches, such as OpenACC, have recently become popular in complex fluid dynamics research since they are cross-platform and easy to implement. OpenACC is a directive-based programming model that, unlike low-level programming models, abstracts the details of implementation on the GPU. Although OpenACC generally limits the performance of the GPU, this model significantly reduces the work required to port an existing code to any accelerator platform, including GPUs. The purpose of this research is twofold: to investigate the effectiveness of OpenACC in developing a portable and maintainable GPU-accelerated code, and to determine the capability of OpenACC to accelerate large, complex programs on the GPU. In both of these studies, the OpenACC implementation is optimized and extended to a multi-GPU implementation while maintaining a unified code base. OpenACC is shown as a viable option for GPU computing with CFD problems.
In the first study, a CFD code that solves incompressible cavity flows is accelerated using OpenACC. Overlapping communication with computation improves performance for the multi-GPU implementation by up to 21%, achieving up to 400 times faster performance than a single CPU and 99% weak scalability efficiency with 32 GPUs.
The second study ports the execution of a more complex CFD research code to the GPU using OpenACC. Challenges using OpenACC with modern Fortran are discussed. Three test cases are used to evaluate performance and scalability. The multi-GPU performance using 27 GPUs is up to 100 times faster than a single CPU and maintains a weak scalability efficiency of 95%.
Advisors/Committee Members: Roy, Christopher John (committeechair), Paterson, Eric G. (committee member), De Sturler, Eric (committee member).
Subjects/Keywords: Graphics processing unit; Directive-based programming; OpenACC; Lid-driven cavity; Multi-GPU; Parallel computing
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APA (6th Edition):
McCall, A. J. (2017). Multi-level Parallelism with MPI and OpenACC for CFD Applications. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78203
Chicago Manual of Style (16th Edition):
McCall, Andrew James. “Multi-level Parallelism with MPI and OpenACC for CFD Applications.” 2017. Masters Thesis, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/78203.
MLA Handbook (7th Edition):
McCall, Andrew James. “Multi-level Parallelism with MPI and OpenACC for CFD Applications.” 2017. Web. 15 Nov 2019.
Vancouver:
McCall AJ. Multi-level Parallelism with MPI and OpenACC for CFD Applications. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/78203.
Council of Science Editors:
McCall AJ. Multi-level Parallelism with MPI and OpenACC for CFD Applications. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/78203
Virginia Tech
4.
Li, Jiahui.
Verification and Validation Study of OpenFOAM on the Generic Prismatic Planing Hull Form.
Degree: MS, Aerospace and Ocean Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/89904
► In this research, hydrodynamic analysis, verification and validation will be performed on Generic Prismatic Planing Hull (GPPH) using OpenFOAM v1806 solver interFoam. The numerical simulation…
(more)
▼ In this research, hydrodynamic analysis, verification and validation will be performed on Generic Prismatic Planing Hull (GPPH) using OpenFOAM v1806 solver interFoam. The numerical simulation will be compared with the experimental result, which is a new set of high-quality experimental tests performed on a large model of a high deadrise prismatic planing hull with flat of chine, tested from pre-planing to fully planing regimes. Firstly, the mesh convergence study and Verification and Validation (VandV) study are performedonthebasisoffixedattitudesimulations. Threegridsarechosenandusedtoperform the free attitude simulations at the highest speed. Then, mesh convergence study is conducted for the results of highest speed free body simulations, which helps us to choose two grids for other speeds simulations. By performing free attitude simulations using two grids, resistance, heave, trim angle, wetted chine length, and wetted keel length are calculated and compared at seven different tested speeds. Computational Fluid Dynamics (CFD) results analysisregardspressuredistributiononthebottomofthehullandinparticularareasofinterest(flatofchine, sprayarea, etc.), frictioncoefficientandvolumefractionoffluidinareas where the free surface undergoes violent deformations (overturning wave at the chine and in the wake, spray jet development area). Different algorithms for dynamic mesh simulation and their effect on the quality of CFD predictions are also investigated.
Advisors/Committee Members: Brizzolara, Stefano (committeechair), Brown, Alan J. (committee member), Paterson, Eric G. (committee member).
Subjects/Keywords: Planing Hull; GPPH; OpenFOAM; URANS
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APA ·
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APA (6th Edition):
Li, J. (2019). Verification and Validation Study of OpenFOAM on the Generic Prismatic Planing Hull Form. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/89904
Chicago Manual of Style (16th Edition):
Li, Jiahui. “Verification and Validation Study of OpenFOAM on the Generic Prismatic Planing Hull Form.” 2019. Masters Thesis, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/89904.
MLA Handbook (7th Edition):
Li, Jiahui. “Verification and Validation Study of OpenFOAM on the Generic Prismatic Planing Hull Form.” 2019. Web. 15 Nov 2019.
Vancouver:
Li J. Verification and Validation Study of OpenFOAM on the Generic Prismatic Planing Hull Form. [Internet] [Masters thesis]. Virginia Tech; 2019. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/89904.
Council of Science Editors:
Li J. Verification and Validation Study of OpenFOAM on the Generic Prismatic Planing Hull Form. [Masters Thesis]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/89904
Virginia Tech
5.
Bay, Raymond James.
Improved Design Method for Cambered Stepped Hulls with High Deadrise.
Degree: MS, Aerospace and Ocean Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/90298
► Eugene Clement created a design method for swept-back cambered step hulls with deadrise. The cambered step is designed to carry 90% of the planing vessels…
(more)
▼ Eugene Clement created a design method for swept-back cambered step hulls with deadrise.
The cambered step is designed to carry 90% of the planing vessels weight with the remaining
10% being support by a stern mounted hydrofoil. The method requires multiple design
iterations in order to achieve an optimal design. Clement stated that the method was not
suitable for cambered planing surfaces with high deadrise angles greater than 15 degrees.
The goal of this thesis is to create a design procedure for swept-back cambered planing
surfaces with high deadrise angles that does not require multiple iterations to obtain an
optimal design. Computational fluid dynamics (CFD) program STAR CCM+ is used to
generate a database for performance characteristics for a wide range of designs varying
deadrise angle, load requirements, trim angle, and different camber values. The simulations
are first validated with experimental data for two different cambered steps designed by
Stefano Brizzolara and tested in the tow tank at the United States Naval Academy. A series
of validation studies utilizing fixed and overset meshes led to a final simulation set up with an
overset mesh that allowed for accurate prediction of drag, trim moment, wetted keel length,
and the wake profile aft of the cambered planing surface. The database is fitted such that
the final equations for optimal design values such as camber, trim angle, drag (shear and
pressure), wetted keel length, wetted surface area, and trim moment are in terms of deadrise
angle and lift. The optimized design equations are validated with CFD simulation.
Advisors/Committee Members: Brizzolara, Stefano (committeechair), Paterson, Eric G. (committee member), Brown, Alan J. (committee member).
Subjects/Keywords: CFD; Planing Surface; Cambered Step Hull
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APA (6th Edition):
Bay, R. J. (2019). Improved Design Method for Cambered Stepped Hulls with High Deadrise. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/90298
Chicago Manual of Style (16th Edition):
Bay, Raymond James. “Improved Design Method for Cambered Stepped Hulls with High Deadrise.” 2019. Masters Thesis, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/90298.
MLA Handbook (7th Edition):
Bay, Raymond James. “Improved Design Method for Cambered Stepped Hulls with High Deadrise.” 2019. Web. 15 Nov 2019.
Vancouver:
Bay RJ. Improved Design Method for Cambered Stepped Hulls with High Deadrise. [Internet] [Masters thesis]. Virginia Tech; 2019. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/90298.
Council of Science Editors:
Bay RJ. Improved Design Method for Cambered Stepped Hulls with High Deadrise. [Masters Thesis]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/90298
Virginia Tech
6.
Cole, Robert Edward.
Numerical Modeling of Air Cushion Vehicle Flexible Seals.
Degree: PhD, Aerospace and Ocean Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/83828
► Air cushion vehicle flexible seals operate in a complex and chaotic environment dominated by fluid-structure interaction. An efficient means to explore interdependencies between various governing…
(more)
▼ Air cushion vehicle flexible seals operate in a complex and chaotic environment dominated by fluid-structure interaction. An efficient means to explore interdependencies between various governing parameters that affect performance is through high fidelity numerical simulation. As previous numerical efforts have employed separate iterative partitioned solvers, or have implemented simplified physics, the approaches have been complex, computationally expensive, or of limited utility. This research effort performs numerical simulations to verify and validate the commercial multi-physics tool STAR-CCM+ as a stand-alone partitioned approach for fluid-structure interaction problems with or without a free surface. A dimensional analysis is first conducted to identify potential non-dimensional forms of parameters related to seal resistance. Then, an implicit, Reynolds-averaged Navier-Stokes finite volume fluid solver is coupled to an implicit, nonlinear finite element structural solver to successfully replicate benchmark results for an elastic beam in unsteady laminar flow. To validate the implementation as a seal parameter exploratory tool, a planer bow seal model is developed and results are obtained for various cushion pressures and inflow speeds. Previous numerical and experimental results for deflection and resistance are compared, showing good agreement. An uncertainty analysis for inflow velocity reveals an inversely proportional resistance dependency. Using Abaqus/Explicit, methodologies are also developed for a two-way, loosely coupled explicit approach to large deformation fluid-structure interaction problems, with and without a free surface. Following numerous verification and validation problems, Abaqus is ultimately abandoned due to the inability to converge the fluid pressure field and achieve steady state. This work is a stepping stone for future researchers having interests in ACV seal design and other large deformation, fluid-structure interaction problems. By modeling all necessary physics within a verified and validated stand-alone approach, a designer's ability to comprehensively investigate seal geometries and interactions has never been more promising.
Advisors/Committee Members: Neu, Wayne L. (committeechair), Paterson, Eric G. (committee member), Wang, Kevin Guanyuan (committee member), Smith, Richard W. (committee member).
Subjects/Keywords: fluid-structure interaction; computational fluid dynamics; hydrodynamic resistance; air cushion vehicles
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APA (6th Edition):
Cole, R. E. (2018). Numerical Modeling of Air Cushion Vehicle Flexible Seals. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/83828
Chicago Manual of Style (16th Edition):
Cole, Robert Edward. “Numerical Modeling of Air Cushion Vehicle Flexible Seals.” 2018. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/83828.
MLA Handbook (7th Edition):
Cole, Robert Edward. “Numerical Modeling of Air Cushion Vehicle Flexible Seals.” 2018. Web. 15 Nov 2019.
Vancouver:
Cole RE. Numerical Modeling of Air Cushion Vehicle Flexible Seals. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/83828.
Council of Science Editors:
Cole RE. Numerical Modeling of Air Cushion Vehicle Flexible Seals. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/83828
Virginia Tech
7.
Nastasi, Kevin Michael.
Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness.
Degree: PhD, Aerospace and Ocean Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/84931
► As resident space object populations grow, and satellite propulsion capabilities improve, it will become increasingly challenging for space-reliant nations to maintain space situational awareness using…
(more)
▼ As resident space object populations grow, and satellite propulsion capabilities improve, it will become increasingly challenging for space-reliant nations to maintain space situational awareness using current human-in-the-loop methods. This dissertation develops several real-time adaptive approaches to autonomous sensor network management for tracking multiple maneuvering and non-maneuvering satellites with a diversely populated Space Object Surveillance and Identification network. The proposed methods integrate suboptimal Partially Observed Markov Decision Processes (POMDPs) with covariance inflation or multiple model adaptive estimation techniques to task sensors and maintain viable orbit estimates for all targets. The POMDPs developed in this dissertation use information-based and system-based metrics to determine the rewards and costs associated with tasking a specific sensor to track a particular satellite. Like in real-world situations, the population of target satellites vastly outnumbers the available set of sensors. Robust and adaptable tasking algorithms are needed in this scenario to determine how and when sensors should be tasked. The strategies developed in this dissertation successfully track 207 non-maneuvering and maneuvering spacecraft using only 24 ground and space-based sensors. The results show that multiple model adaptive estimation coupled with a multi-metric, suboptimal POMDP can effectively and efficiently task a diverse network of sensors to track multiple maneuvering spacecraft, while simultaneously monitoring a large number of non-maneuvering objects. Overall, this dissertation demonstrates the potential for autonomous and adaptable sensor network command and control for real-world space situational awareness.
Advisors/Committee Members: Black, Jonathan T. (committeechair), Paterson, Eric G. (committee member), Psiaki, Mark L. (committee member), Canfield, Robert Arthur (committee member).
Subjects/Keywords: Sensor Network Management; Remote Sensing; Adaptive Estimation; Astrodynamics; Space Situational Awareness; Autonomy
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APA (6th Edition):
Nastasi, K. M. (2018). Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/84931
Chicago Manual of Style (16th Edition):
Nastasi, Kevin Michael. “Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness.” 2018. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/84931.
MLA Handbook (7th Edition):
Nastasi, Kevin Michael. “Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness.” 2018. Web. 15 Nov 2019.
Vancouver:
Nastasi KM. Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/84931.
Council of Science Editors:
Nastasi KM. Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/84931
Virginia Tech
8.
Awasthi, Manuj.
Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities.
Degree: PhD, Aerospace and Ocean Engineering, 2015, Virginia Tech
URL: http://hdl.handle.net/10919/64158
► Measurements have been performed to understand the sound source mechanism in turbulent boundary layer flow over two and three-dimensional surface discontinuities whose height is smaller…
(more)
▼ Measurements have been performed to understand the sound source mechanism in turbulent boundary layer flow over two and three-dimensional surface discontinuities whose height is smaller than the incoming boundary layer thickness. The work was performed in two different types of boundary layers: a wall-jet flow and a conventional high Reynolds boundary layer. In the wall-jet flow, measurements of far field sound from two-dimensional forward facing steps, gaps with rounded corners and swept forward facing steps with rounded corners were made. The sound from a forward facing step is shown to exhibit effects of non-compactness. Rounding the step corner results in consistent drop in sound levels but the directivity of the sound field remains unchanged. The sound from gaps is dominated by the forward step component and remains unaffected by rounding of the backward step portion. The sound from swept forward facing steps was found to approximately obey an acoustic sweep independence principle up to a sweep angle of 30 deg when the spanwise inhomogeneity in the flow is accounted for using a simple source distribution model. Sweep independence is also observed for steps with corner rounding radii up to 25% of the step height.
The work performed in the high Reynolds number boundary layer included measurements on forward facing steps with rounded corners and a three-dimensional circular embossment with the same height as the forward step. The highest Reynolds number based on discontinuity height achieved in this work was approximately 93,000. The results show that rounding the forward step corner has the same qualitative effect on far field sound as in the wall-jet boundary layer. Quantitatively, for similar boundary layer edge velocity the sound is higher than in the wall-jet flow. The near field measurements show that the separation bubble downstream of the step shrinks as the step corner is rounded while the bubble upstream remains unaffected by it. The unsteady surface force in the lower half of the vertical face of the step was found to be independent of corner rounding. The force on the downstream surface shows similar character within the separation bubble for each rounding but decays faster with increasing downstream distance due to reduced bubble size. The unsteady force measurements were applied to the theory of Glegg et al. (2014) and the resultant of the unsteady forces on the vertical face and downstream surface placed at the top corner of the step is shown to qualitatively describe the far field sound. The acoustic sweep independence principle was applied to the far field sound from the circular embossment and it has been shown that the sound from the three-dimensional geometry can be predicted with reasonable accuracy using sound from a two-dimensional forward step with the same span.
Advisors/Committee Members: Devenport, William J. (committeechair), Paterson, Eric G. (committee member), Glegg, Stewart (committee member), Lowe, Kevin T. (committee member), Alexander, William Nathan (committee member).
Subjects/Keywords: Forward step noise; gap noise; swept forward step noise; circular embossment noise; surface pressure fluctuations and unsteady surface force
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APA (6th Edition):
Awasthi, M. (2015). Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/64158
Chicago Manual of Style (16th Edition):
Awasthi, Manuj. “Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities.” 2015. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/64158.
MLA Handbook (7th Edition):
Awasthi, Manuj. “Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities.” 2015. Web. 15 Nov 2019.
Vancouver:
Awasthi M. Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities. [Internet] [Doctoral dissertation]. Virginia Tech; 2015. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/64158.
Council of Science Editors:
Awasthi M. Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities. [Doctoral Dissertation]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/64158
Virginia Tech
9.
Sun, Rui.
Particle-Resolving Simulations of Dune Migration: Novel Algorithms and Physical Insights.
Degree: PhD, Aerospace and Ocean Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/78260
► Sediment transport is ubiquitous in aquatic environments, and the study of sediment transport is important for both engineering and environmental reasons. However, the understanding and…
(more)
▼ Sediment transport is ubiquitous in aquatic environments, and the study of sediment transport is important for both engineering and environmental reasons. However, the understanding and prediction of sediment transport are hindered by its complex dynamics and regimes. In this dissertation, the open-source solver SediFoam is developed for high-fidelity particle-resolving simulations of various sediment transport problems based on open-source solvers OpenFOAM and LAMMPS. OpenFOAM is a CFD toolbox that can perform three-dimensional flow simulations on unstructured mesh; LAMMPS is a massively parallel DEM solver for molecular dynamics. To enable the particle-resolving simulation of sediment transport on an arbitrary mesh, a diffusion-based algorithm is used in SediFoam to obtain the averaged Eulerian fields from discrete particle data. The parallel interface is also implemented for the communication of the two open-source solvers. Extensive numerical simulations are performed to validate the capability of SediFoam in the modeling of sediment transport problems. The predictions of various sediment transport regimes, including `flat bed in motion', `small dune' and `vortex dune', are in good agreement of with the experimental results and those obtained by using interface resolved simulations. The capability of the solver in the simulation of sediment transport in the oscillatory boundary layer is also demonstrated. Moreover, this well-validated high-fidelity simulation tool has been used to probe the physics of particle dynamics in self-generated bedforms in various hydraulic conditions. The results obtained by using SediFoam not only bridge the gaps in the experimental results but also help improve the engineering practice in the understanding of sediment transport. By using the particle-resolving simulation results and the insights generated therein, the closure terms in the two-fluid models or hydro-morphodynamic models can be improved, which can contribute to the numerical modeling of sediment transport in engineering scales.
Advisors/Committee Members: Xiao, Heng (committeechair), Liu, Yang (committee member), Wang, Kevin Guanyuan (committee member), Irish, Jennifer L. (committee member), Paterson, Eric G. (committee member).
Subjects/Keywords: Sediment Transport; CFD – DEM; Particle-Resolving Simulations; Multiphase Flow; Dune Migration
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APA (6th Edition):
Sun, R. (2017). Particle-Resolving Simulations of Dune Migration: Novel Algorithms and Physical Insights. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78260
Chicago Manual of Style (16th Edition):
Sun, Rui. “Particle-Resolving Simulations of Dune Migration: Novel Algorithms and Physical Insights.” 2017. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/78260.
MLA Handbook (7th Edition):
Sun, Rui. “Particle-Resolving Simulations of Dune Migration: Novel Algorithms and Physical Insights.” 2017. Web. 15 Nov 2019.
Vancouver:
Sun R. Particle-Resolving Simulations of Dune Migration: Novel Algorithms and Physical Insights. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/78260.
Council of Science Editors:
Sun R. Particle-Resolving Simulations of Dune Migration: Novel Algorithms and Physical Insights. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/78260
Virginia Tech
10.
Bassler, Christopher Colby.
Analysis and Modeling of Hydrodynamic Components for Ship Roll Motion in Heavy Weather.
Degree: PhD, Aerospace and Ocean Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23258
► Ship roll motion has been the subject of many studies, because of the complexities associated with this mode of ship motion, and its impact on…
(more)
▼ Ship roll motion has been the subject of many studies, because of the complexities associated with this mode of ship motion, and its impact on operability, safety, and survivability. Estimation and prediction of the energy transfer and dissipation of the hydrodynamic components, added inertia and damping, is essential to accurately describe the roll motions of a ship. This is especially true for ship operations in moderate to extreme sea conditions. In these conditions, a complex process of energy transfer occurs, which alters the physical behavior of the hydrodynamic components, and ultimately affects the amplitude of ship roll motion. Bilge keels have been used on ships for nearly two centuries, to increase damping and reduce the severity of roll motions experienced by a ship in waves. Because ship motions are more severe in extreme sea conditions, large roll angles may occur. With the possibility of crew injury, cargo damage, or even capsize, it is important to understand the behavior of the roll added inertia and damping for these conditions. Dead ship conditions, where ships may experience excitation from beam, or near beam, seas present a worst case scenario in heavy weather. The behavior of a ship in this condition should be considered in both the design and assessment of seakeeping performance. In this study, hydrodynamic component models of roll added inertia and roll damping were examined and assessed to be unsuitable for accurate prediction of ship motions in heavy weather. A series of model experiments and numerical studies were carried out and analyzed to provide improved understanding of the essential physical phenomena which affect the hydrodynamic components and occur during large amplitude roll motion. These observations served to confirm the hypothesis that the existing models for roll added inertia and damping in large amplitude motions are not sufficient. The change in added inertia and damping behavior for large roll motion is largely due to the effects of hull form geometry, including the bilge keels and topside geometry, and their interactions with the free surface. Therefore, the changes in added inertia and damping must be considered in models to describe and predict roll motions in severe wave environments. Based on the observations and analysis from both experimental and numerical methods, several time-domain model formulations were proposed and examined to model hydrodynamic components of large amplitude roll motions. These time-domain formulations included an analytical model with memory effects, a piecewise formulation, and several possibilities for a bilge keel force model. Although a piecewise model for roll damping was proposed, which can improve the applicability of traditional formulations for roll damping to heavy weather conditions, a further attempt was undertaken to develop a more detailed model specifically for the bilge keel force. This model was based on the consideration of large amplitude effects on the hydrodynamic components of the bilge keel force. Both…
Advisors/Committee Members: Brown, Alan J. (committeechair), Reed, Arthur M. (committee member), Neu, Wayne L. (committee member), Paterson, Eric G. (committee member).
Subjects/Keywords: ship motions; seakeeping; roll motion; roll damping; added mass; added inertia; bilge keel; dead ship condition; beam seas; larg
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APA (6th Edition):
Bassler, C. C. (2013). Analysis and Modeling of Hydrodynamic Components for Ship Roll Motion in Heavy Weather. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23258
Chicago Manual of Style (16th Edition):
Bassler, Christopher Colby. “Analysis and Modeling of Hydrodynamic Components for Ship Roll Motion in Heavy Weather.” 2013. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/23258.
MLA Handbook (7th Edition):
Bassler, Christopher Colby. “Analysis and Modeling of Hydrodynamic Components for Ship Roll Motion in Heavy Weather.” 2013. Web. 15 Nov 2019.
Vancouver:
Bassler CC. Analysis and Modeling of Hydrodynamic Components for Ship Roll Motion in Heavy Weather. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/23258.
Council of Science Editors:
Bassler CC. Analysis and Modeling of Hydrodynamic Components for Ship Roll Motion in Heavy Weather. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23258
11.
Wu, Jinlong.
Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning.
Degree: PhD, Aerospace and Ocean Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/85129
► Reynolds-Averaged Navier-Stokes (RANS) simulations are widely used for engineering design and analysis involving turbulent flows. In RANS simulations, the Reynolds stress needs closure models and…
(more)
▼ Reynolds-Averaged Navier-Stokes (RANS) simulations are widely used for engineering design and analysis involving turbulent flows. In RANS simulations, the Reynolds stress needs closure models and the existing models have large model-form uncertainties. Therefore, the RANS simulations are known to be unreliable in many flows of engineering relevance, including flows with three-dimensional structures, swirl, pressure gradients, or curvature. This lack of accuracy in complex flows has diminished the utility of RANS simulations as a predictive tool for engineering design, analysis, optimization, and reliability assessments. Recently, data-driven methods have emerged as a promising alternative to develop the model of Reynolds stress for RANS simulations. In this dissertation I explore two physics-informed, data-driven frameworks to improve RANS modeled Reynolds stresses. First, a Bayesian inference framework is proposed to quantify and reduce the model-form uncertainty of RANS modeled Reynolds stress by leveraging online sparse measurement data with empirical prior knowledge. Second, a machine-learning-assisted framework is proposed to utilize offline high-fidelity simulation databases. Numerical results show that the data-driven RANS models have better prediction of Reynolds stress and other quantities of interest for several canonical flows. Two metrics are also presented for an a priori assessment of the prediction confidence for the machine-learning-assisted RANS model. The proposed data-driven methods are also applicable to the computational study of other physical systems whose governing equations have some unresolved physics to be modeled.
Advisors/Committee Members: Xiao, Heng (committeechair), Paterson, Eric G. (committeechair), Roy, Christopher John (committee member), Lowe, Kevin T. (committee member).
Subjects/Keywords: Turbulence modeling; RANS; Model-form uncertainty; Data-driven; Uncertainty quantification; Bayesian Inference; Machine learning
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APA (6th Edition):
Wu, J. (2018). Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/85129
Chicago Manual of Style (16th Edition):
Wu, Jinlong. “Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning.” 2018. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/85129.
MLA Handbook (7th Edition):
Wu, Jinlong. “Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning.” 2018. Web. 15 Nov 2019.
Vancouver:
Wu J. Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/85129.
Council of Science Editors:
Wu J. Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/85129
Virginia Tech
12.
Jones, Matthew Cecil.
Accelerating Conceptual Design Analysis of Marine Vehicles through Deep Learning.
Degree: PhD, Aerospace and Ocean Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/89341
► Evaluation of the flow field imparted by a marine vehicle reveals the underlying efficiency and performance. However, the relationship between precise design features and their…
(more)
▼ Evaluation of the flow field imparted by a marine vehicle reveals the underlying efficiency and performance. However, the relationship between precise design features and their impact on the flow field is not well characterized. The goal of this work is first, to investigate the thermally-stratified near field of a self-propelled marine vehicle to identify the significance of propulsion and hull-form design decisions, and second, to develop a functional mapping between an arbitrary vehicle design and its associated flow field to accelerate the design analysis process. The unsteady Reynolds-Averaged Navier-Stokes equations are solved to compute near-field wake profiles, showing good agreement to experimental data and providing a balance between simulation fidelity and numerical cost, given the database of cases considered. Machine learning through convolutional networks is employed to discover the relationship between vehicle geometries and their associated flow fields with two distinct deep-learning networks. The first network directly maps explicitly-specified geometric design parameters to their corresponding flow fields. The second network considers the vehicle geometries themselves as tensors of geometric volume fractions to implicitly-learn the underlying parameter space. Once trained, both networks effectively generate realistic flow fields, accelerating the design analysis from a process that takes days to one that takes a fraction of a second. The implicit-parameter network successfully learns the underlying parameter space for geometries within the scope of the training data, showing comparable performance to the explicit-parameter network. With additions to the size and variability of the training database, this network has the potential to abstractly generalize the design space for arbitrary geometric inputs, even those beyond the scope of the training data.
Advisors/Committee Members: Paterson, Eric G. (committeechair), Devenport, William J. (committee member), Pitt, Jonathan (committee member), Roy, Christopher John (committee member).
Subjects/Keywords: near wake; machine learning; deep learning; adversarial network; OpenFOAM
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APA (6th Edition):
Jones, M. C. (2019). Accelerating Conceptual Design Analysis of Marine Vehicles through Deep Learning. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/89341
Chicago Manual of Style (16th Edition):
Jones, Matthew Cecil. “Accelerating Conceptual Design Analysis of Marine Vehicles through Deep Learning.” 2019. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/89341.
MLA Handbook (7th Edition):
Jones, Matthew Cecil. “Accelerating Conceptual Design Analysis of Marine Vehicles through Deep Learning.” 2019. Web. 15 Nov 2019.
Vancouver:
Jones MC. Accelerating Conceptual Design Analysis of Marine Vehicles through Deep Learning. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/89341.
Council of Science Editors:
Jones MC. Accelerating Conceptual Design Analysis of Marine Vehicles through Deep Learning. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/89341
Virginia Tech
13.
Webster III, John Ackroyd.
Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling.
Degree: PhD, Aerospace and Ocean Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/93038
► Small-scale marine propellers operate at low Reynolds numbers, where laminar-turbulent transition of the boundary layer can impact the distributions of pressure and shear stress on…
(more)
▼ Small-scale marine propellers operate at low Reynolds numbers, where laminar-turbulent
transition of the boundary layer can impact the distributions of pressure and shear stress
on the blade surface. Marine propellers operating at low Reynolds numbers are subject to
laminar-turbulent transition of the boundary layer, which impacts the distributions of pressure
and shear stress on the blade surface. To design efficient propellers for operation at
low Reynolds numbers, transitional effects must be included in the evaluations of propeller
performance. In this work, transition modeling techniques in Reynolds Averaged Navier-
Stokes computational fluid dynamics (RANS CFD) are utilized to evaluate and design propellers
operating at low Reynolds numbers. The Galilean invariant γ transition model with
an extension for crossflow transition is coupled to the SSG (Speziale, Sarkar, Gatski) /LRR
(Launder, Reece, Rodi) -ω Reynolds stress transport turbulence model, with validation cases
performed for flate plate boundary layers, 2-dimensional airfoils, a 3-dimensional wing, and
6:1 prolate spheroids. The performance of the coupled SSG/LRR-ω-γ Reynolds stress transition
model for propellers with flow transition is then evaluated using experimental surface
streamline and force data from four model-scale marine propellers. A method for the design
of low Reynolds number marine propellers is presented using a transition-sensitive lifting line
method coupled with the panel method code XFOIL. Initial geometries generated using the
lifting-line method are then optimized in RANS CFD using the 2 equation γ-Reθ transition
model and an adjoint method to warp the propeller shape to improve the efficiency. Two
design studies are performed, including an open water propeller, and a propeller designed
for a small autonomous underwater vehicle.
Advisors/Committee Members: Neu, Wayne L. (committeechair), Brizzolara, Stefano (committeechair), Stilwell, Daniel J. (committee member), Woolsey, Craig A. (committee member), Paterson, Eric G. (committee member).
Subjects/Keywords: Marine Propulsion; Transition Modeling; Hydrodynamics
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APA (6th Edition):
Webster III, J. A. (2019). Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/93038
Chicago Manual of Style (16th Edition):
Webster III, John Ackroyd. “Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling.” 2019. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/93038.
MLA Handbook (7th Edition):
Webster III, John Ackroyd. “Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling.” 2019. Web. 15 Nov 2019.
Vancouver:
Webster III JA. Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/93038.
Council of Science Editors:
Webster III JA. Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/93038
14.
Zhang, Di.
Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics.
Degree: PhD, Aerospace and Ocean 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 November 15, 2019.
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. 15 Nov 2019.
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 2019 Nov 15].
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
15.
He, Long.
Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation.
Degree: PhD, Mechanical Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/91400
► Gas-solid flow is fundamental to many industrial processes. Extensive experimental and numerical studies have been devoted to understand the interphase momentum and heat transfer in…
(more)
▼ Gas-solid flow is fundamental to many industrial processes. Extensive experimental and numerical studies have been devoted to understand the interphase momentum and heat transfer in these systems. Most of the studies have focused on spherical particle shapes, however, in most natural and industrial processes, the particle shape is seldom spherical. In fact, particle shape is one of the important parameters that can have a significant impact on momentum, heat and mass transfer, which are fundamental to all processes. In this study particle-resolved simulations are performed to study momentum and heat transfer in flow through a fixed random assembly of ellipsoidal particles with sphericity of 0.887. The incompressible Navier-Stokes equations are solved using the Immersed Boundary Method (IBM). A Framework for generating particle assembly is developed using physics engine PhysX. High-order boundary conditions are developed for immersed boundary method to resolve the heat transfer in the vicinity of fluid/particle boundary with better accuracy. A complete framework using particle-resolved simulation study assembly of particles with any shape is developed. The drag force of spherical particles and ellipsoid particles are investigated. Available correlations are evaluated based on simulation results and recommendations are made regarding the best combinations. The heat transfer in assembly of ellipsoidal particle is investigated, and a correlation is proposed for the particle shape studied. The lift force, lateral force and torque of ellipsoid particles in assembly and their variations are quantitatively presented and it is shown that under certain conditions these forces and torques cannot be neglected as is done in the larger literature.
Advisors/Committee Members: Tafti, Danesh K (committeechair), Dancey, Clinton L (committee member), Batra, Romesh C (committee member), Paul, Mark R (committee member), Paterson, Eric G (committee member).
Subjects/Keywords: immersed boundary method; Immersed boundary method; Non-spherical particle; Momentum transfer; Heat transfer; Nusselt number
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APA (6th Edition):
He, L. (2018). Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/91400
Chicago Manual of Style (16th Edition):
He, Long. “Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation.” 2018. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/91400.
MLA Handbook (7th Edition):
He, Long. “Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation.” 2018. Web. 15 Nov 2019.
Vancouver:
He L. Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/91400.
Council of Science Editors:
He L. Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/91400
16.
Cadel, Daniel R.
Advanced Instrumentation and Measurements Techniques for Near Surface Flows.
Degree: PhD, Aerospace and Ocean Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/72968
► The development of aerodynamic boundary layers on wind turbine blades is an important consideration in their performance. It can be quite challenging to replicate full…
(more)
▼ The development of aerodynamic boundary layers on wind turbine blades is an important consideration in their performance. It can be quite challenging to replicate full scale conditions in laboratory experiments, and advanced diagnostics become valuable in providing data not available from traditional means. A new variant of Doppler global velocimetry (DGV) known as cross-correlation DGV is developed to measure boundary layer profiles on a wind turbine blade airfoil in the large scale
Virginia Tech Stability Wind Tunnel. The instrument provides mean velocity vectors with reduced sensitivity to external conditions, a velocity measurement range from 0ms^-1 to over 3000ms^-1, and an absolute uncertainty. Monte Carlo simulations with synthetic signals reveal that the processing routine approaches the Cramér-Rao lower bound in optimized conditions. A custom probe-beam technique is implanted to eliminate laser flare for measuring boundary layer profiles on a DU96-W-180 wind turbine airfoil model. Agreement is seen with laser Doppler velocimetry data within the uncertainty estimated for the DGV profile.
Lessons learned from the near-wall flow diagnostics development were applied to a novel benchmark model problem incorporating the relevant physical mechanisms of the high amplitude periodic turbulent flow experienced by turbine blades in the field. The model problem is developed for experimentally motivated computational model development. A circular cylinder generates a periodic turbulent wake, in which a NACA 63215b airfoil with a chord Reynolds number Re_c = 170, 000 is embedded for a reduced frequency k = (pi)fc/V = 1.53. Measurements are performed with particle image velocimetry on the airfoil suction side and in highly magnified planes within the boundary layer. Outside of the viscous region, the Reynolds stress profile is consistent with the prediction of Rapid Distortion Theory (RDT), confirming that the redistribution of normal stresses is an inviscid effect. The fluctuating component of the phase- averaged turbulent boundary layer profiles is described using the exact solution to laminar Stokes flow. A phase lag similar to that in laminar flow is observed with an additional constant phase layer in the buffer region. The phase lag is relevant for modeling the intermittent transition and separation expected at full scale.
Advisors/Committee Members: Lowe, Kevin T. (committeechair), Borgoltz, Aurelien (committee member), Devenport, William J. (committee member), Paterson, Eric G. (committee member), Ng, Wing Fai (committee member).
Subjects/Keywords: Doppler global velocimetry; particle image velocimetry; wind turbine aerodynamics; unsteady boundary layers
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APA (6th Edition):
Cadel, D. R. (2016). Advanced Instrumentation and Measurements Techniques for Near Surface Flows. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/72968
Chicago Manual of Style (16th Edition):
Cadel, Daniel R. “Advanced Instrumentation and Measurements Techniques for Near Surface Flows.” 2016. Doctoral Dissertation, Virginia Tech. Accessed November 15, 2019.
http://hdl.handle.net/10919/72968.
MLA Handbook (7th Edition):
Cadel, Daniel R. “Advanced Instrumentation and Measurements Techniques for Near Surface Flows.” 2016. Web. 15 Nov 2019.
Vancouver:
Cadel DR. Advanced Instrumentation and Measurements Techniques for Near Surface Flows. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2019 Nov 15].
Available from: http://hdl.handle.net/10919/72968.
Council of Science Editors:
Cadel DR. Advanced Instrumentation and Measurements Techniques for Near Surface Flows. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/72968
. 
Open Access Theses and Dissertations
