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University of Oklahoma
1.
LaBryer, Allen Russell.
Optimal Spatiotemporal Reduced Order Modeling for Nonlinear Dynamical Systems.
Degree: PhD, 2012, University of Oklahoma
URL: http://hdl.handle.net/11244/318987
► We investigate the performance of the subgrid-scale models with under-resolved simulations (in space and time) and various discretization schemes. For the canonical Duffing and van…
(more)
▼ We investigate the performance of the subgrid-scale models with under-resolved simulations (in space and time) and various discretization schemes. For the canonical Duffing and van der Pol oscillators, the subgrid-scale models are found to improve the accuracy of under-resolved time-marching and time-spectral simulations by one to two orders of magnitude. The models are also found to improve the reliability of predictions for both regular and chaotic response types by eliminating the onset of artificial regularity due to strong numerical damping with a coarse temporal grid. For the viscous Burgers flow and nonlinear beam problems, both subgrid spatial and temporal scales prove to be important as finite-difference-based simulations are expedited by coarsening the computational grid in space and time. For the viscous Burgers flow, the subgrid spatial and temporal models alone appear to be insufficient for error reduction, but when used in conjunction, the models are shown to improve statistical descriptions of the flow by five-fold. For the nonlinear beam, we perform a set of numerical experiments designed to capture the complex bifurcation behavior of the beam response. Maps for the Lyapunov exponents are also obtained with greater accuracy by including the subgrid-scale models. We find that a specified level of accuracy can be obtained one to two orders of magnitude faster by including the models instead of refining the computational grid.
Advisors/Committee Members: Attar, Peter J||Vedula, Prakash (advisor).
Subjects/Keywords: Nonlinear systems; Differentiable dynamical systems
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APA (6th Edition):
LaBryer, A. R. (2012). Optimal Spatiotemporal Reduced Order Modeling for Nonlinear Dynamical Systems. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/318987
Chicago Manual of Style (16th Edition):
LaBryer, Allen Russell. “Optimal Spatiotemporal Reduced Order Modeling for Nonlinear Dynamical Systems.” 2012. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/318987.
MLA Handbook (7th Edition):
LaBryer, Allen Russell. “Optimal Spatiotemporal Reduced Order Modeling for Nonlinear Dynamical Systems.” 2012. Web. 27 Feb 2021.
Vancouver:
LaBryer AR. Optimal Spatiotemporal Reduced Order Modeling for Nonlinear Dynamical Systems. [Internet] [Doctoral dissertation]. University of Oklahoma; 2012. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/318987.
Council of Science Editors:
LaBryer AR. Optimal Spatiotemporal Reduced Order Modeling for Nonlinear Dynamical Systems. [Doctoral Dissertation]. University of Oklahoma; 2012. Available from: http://hdl.handle.net/11244/318987

University of Oklahoma
2.
Heck, Margaret.
Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics.
Degree: PhD, 2015, University of Oklahoma
URL: http://hdl.handle.net/11244/23321
► Computational fluid dynamics is used to study two distinct areas of engineering interest: microfluidic systems involving superhydrophobic surfaces and blood pumps. Superhydrophobic surfaces, which can…
(more)
▼ Computational fluid dynamics is used to study two distinct areas of engineering interest: microfluidic systems involving superhydrophobic surfaces and blood pumps. Superhydrophobic surfaces, which can induce slip at fluid-solid interfaces, are modeled using mixed free-shear and no-slip boundary conditions. Despite remarkable effort to include the effects of surface topology and various flow and physical properties in models describing fluid slip over these surfaces, the mathematical description of flow over mixed slip boundaries is still incomplete. Critical configurations of roughness necessary to achieve drag reduction in micro-channels are established. The effects of roughness shape and size on drag for both Newtonian and non-Newtonian fluid flow are also considered in depth. Based on these findings, similarity theory is used to develop a model to describe drag reduction as a function of channel geometry. The principles used in the development of these models are then applied to the more complicated system of a centrifugal blood pump. The effects of the non-Newtonian rheological behavior, hematocrit, temperature, and turbulence on pump performance and subsequent blood damage is quantified over a wide range of operating conditions.
Advisors/Committee Members: Papavassiliou, Dimitrios (advisor), Lobban, Lance (committee member), O'Rear, Edgar (committee member), Schmidtke, David (committee member), Vedula, Prakash (committee member).
Subjects/Keywords: Computational fluid dynamics; microfluidics; blood pump
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APA ·
Chicago ·
MLA ·
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CSE |
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APA (6th Edition):
Heck, M. (2015). Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/23321
Chicago Manual of Style (16th Edition):
Heck, Margaret. “Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics.” 2015. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/23321.
MLA Handbook (7th Edition):
Heck, Margaret. “Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics.” 2015. Web. 27 Feb 2021.
Vancouver:
Heck M. Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics. [Internet] [Doctoral dissertation]. University of Oklahoma; 2015. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/23321.
Council of Science Editors:
Heck M. Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics. [Doctoral Dissertation]. University of Oklahoma; 2015. Available from: http://hdl.handle.net/11244/23321

University of Oklahoma
3.
Ozcelik, Orhan.
Experimental and Numerical Studies on the Structural Dynamics of Flapping Beams.
Degree: PhD, 2015, University of Oklahoma
URL: http://hdl.handle.net/11244/14580
► The nonlinear structural dynamics of slender cantilever beams in flapping motion is studied through experiments, numerical simulations, and perturbation analyses. A flapping mechanism which imparts…
(more)
▼ The nonlinear structural dynamics of slender cantilever beams in flapping motion is studied through experiments, numerical simulations, and perturbation analyses.
A flapping mechanism which imparts a periodic flapping motion of certain amplitude and frequency on the clamped boundary of the appended cantilever beam is constructed. Centimeter-size thin aluminum beams are tested at two amplitudes and frequencies up to, and slightly above, the first bending mode to collect beam tip displacement and surface bending strain data. Experimental data analyzed in time and frequency domains reveal a planar, single stable (for a given flapping amplitude-frequency combination) periodic beam response with superharmonic resonance peaks. Numerical simulations performed with a nonlinear beam finite element corroborate the experiments in general with the exception of the resonance regions where they overpredict the experiments. The discrepancy is mainly attributed to the use of a linear viscous damping model in the simulations. Nonlinear response dynamics predicted by the simulations include symmetric periodic, asymmetric periodic, quasi-periodic, and aperiodic motions.
To investigate the above-mentioned discrepancy between experiment and simulation, linear and nonlinear damping force models of different functional forms are incorporated into a nonlinear inextensible beam theory. The mathematical model is solved for periodic response by using a combination of Galerkin and a time-spectral numerical scheme; two reduced order methods which, along with the choice of the inextensible beam model, facilitate parametric study and analytical analysis. Additional experiments are conducted in reduced air pressure to isolate the air damping from the material damping. The frequency response curves obtained with different damping models reveal that, when compared to the linear viscous damping, the nonlinear external damping models better represent the experimental damping forces in the regions of superharmonic and primary resonances. The effect of different damping models on the stability of the periodic solutions are investigated using the Floquet theory. The mathematical models with nonlinear damping yield stable periodic solutions which is in accord with the experimental observation.
The effect of excitation and damping parameters on the steady-state superharmonic and primary resonance responses of the flapping beam is further investigated through perturbation analyses. The resonance solutions of the spatially-discretized equation of motion (via 1-mode Galerkin approximation of the inextensible beam model), which involves both quadratic and cubic nonlinear terms, are constructed as first-order uniform asymptotic expansions via the method of multiple time scales. The critical excitation amplitudes leading to bistable solutions are identified and are found to be consistent with the experimental and numerical results. The approximate analytical results indicate that a second harmonic is required in the boundary actuation spectra in order…
Advisors/Committee Members: Attar, Peter J. (advisor), Altan, M. Cengiz (committee member), Baldwin, J. David (committee member), Shambaugh, Robert L. (committee member), Vedula, Prakash (committee member).
Subjects/Keywords: Engineering, Mechanical.; Engineering, Aerospace.; Structural Dynamics; Flapping; Cantilever Beams
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
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APA (6th Edition):
Ozcelik, O. (2015). Experimental and Numerical Studies on the Structural Dynamics of Flapping Beams. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/14580
Chicago Manual of Style (16th Edition):
Ozcelik, Orhan. “Experimental and Numerical Studies on the Structural Dynamics of Flapping Beams.” 2015. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/14580.
MLA Handbook (7th Edition):
Ozcelik, Orhan. “Experimental and Numerical Studies on the Structural Dynamics of Flapping Beams.” 2015. Web. 27 Feb 2021.
Vancouver:
Ozcelik O. Experimental and Numerical Studies on the Structural Dynamics of Flapping Beams. [Internet] [Doctoral dissertation]. University of Oklahoma; 2015. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/14580.
Council of Science Editors:
Ozcelik O. Experimental and Numerical Studies on the Structural Dynamics of Flapping Beams. [Doctoral Dissertation]. University of Oklahoma; 2015. Available from: http://hdl.handle.net/11244/14580

University of Oklahoma
4.
Pandya, Soham.
Wellbore Cleanout in Inclined and Horizontal Wellbores – The Effects of Fluid Rheology, Inclination, and Solids Density.
Degree: PhD, 2019, University of Oklahoma
URL: http://hdl.handle.net/11244/321402
► Recent technical improvements in the drilling process have allowed drilling of high inclination and horizontal wells with longer laterals. The frequency of such wells has…
(more)
▼ Recent technical improvements in the drilling process have allowed drilling of high inclination and horizontal wells with longer laterals. The frequency of such wells has increased over time due to their advantage of increased contact area with the reservoir. However, the complexity of these wells results in more well completion problems such as deposition of solids in the wellbore and increased Non-Productive Time (NPT). The reduction of NPT depends on factors influencing the mechanism of solids transport. The dominance of gravity over buoyancy forces the solids to settle vertically downwards irrespective of the direction of the flow. However, the distance required for solids to settle downwards is significantly reduced in directional and horizontal wells. Moreover, the fluid flow in these wells has a reduced velocity component in the vertical direction. The substantial reduction of the vertical component of fluid velocity, which prevents solids from settling, results in rapid solids deposition and bed build up. Also, the forces acting on the flow protruding particle of the bed determine the erosion mechanism of solids bed formed in inclined and horizontal wells.
This study undertakes an experimental approach to solve the problem of optimization of wellbore cleanout process in deviated and horizontal well sections. In addition, Computational Fluid Dynamics (CFD) approach is incorporated to interpret and explain experimental observations. Experimental investigations were carried out using a large-scale flow loop. Bed-erosion experiments were conducted in an eccentric annulus (140 mm × 60 mm annular geometry and 10.36 m long section) to study the effects of several influencing factors (fluid rheology, inclination, and solid density) on wellbore cleanout efficiency. The effects of these factors were analyzed in terms of normalized bed erosion curves (reduction of bed height with time) and cleanout efficiency (percentage removal of solids weight).
Experimental results demonstrated that high-viscosity fluids are superior cleanout medium at low inclinations due to their better solids suspension capability while low-viscosity fluids have greater erosion capability and thereby perform well at high inclinations and horizontal configuration. CFD simulations show that low-viscosity fluids have significantly greater local velocity in the vicinity of the bed than highly viscous fluids, even though the viscous fluid exhibit a higher bed shear stress. The analysis indicates that the local fluid velocity is more important than bed shear stress in eroding the bed. Besides this, the density of solids was found to have a moderate effect on the hole cleaning process, and solids with higher density were slightly more difficult to remove from the wellbore section.
Furthermore, experimental results are analyzed by developing a dimensionless relationship between various influential parameters. The correlation developed is capable of upscaling the lab-scale model to field scale. This was validated by comparing the results obtained…
Advisors/Committee Members: Ahmed, Ramadan (advisor), Shah, Subhash (committee member), Vedula, Prakash (committee member), Teodoriu, Catalin (committee member), Salehi, Saeed (committee member).
Subjects/Keywords: Engineering, Petroleum.; Energy.; Operations Research.; Physics, General.
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
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APA (6th Edition):
Pandya, S. (2019). Wellbore Cleanout in Inclined and Horizontal Wellbores – The Effects of Fluid Rheology, Inclination, and Solids Density. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/321402
Chicago Manual of Style (16th Edition):
Pandya, Soham. “Wellbore Cleanout in Inclined and Horizontal Wellbores – The Effects of Fluid Rheology, Inclination, and Solids Density.” 2019. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/321402.
MLA Handbook (7th Edition):
Pandya, Soham. “Wellbore Cleanout in Inclined and Horizontal Wellbores – The Effects of Fluid Rheology, Inclination, and Solids Density.” 2019. Web. 27 Feb 2021.
Vancouver:
Pandya S. Wellbore Cleanout in Inclined and Horizontal Wellbores – The Effects of Fluid Rheology, Inclination, and Solids Density. [Internet] [Doctoral dissertation]. University of Oklahoma; 2019. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/321402.
Council of Science Editors:
Pandya S. Wellbore Cleanout in Inclined and Horizontal Wellbores – The Effects of Fluid Rheology, Inclination, and Solids Density. [Doctoral Dissertation]. University of Oklahoma; 2019. Available from: http://hdl.handle.net/11244/321402

University of Oklahoma
5.
JIN, XIAOCHUN.
AN INTEGRATED GEOMECHANICS AND PETROPHYSICS STUDY OF HYDRAULIC FRACTURING IN NATURALLY FRACTURED RESERVOIRS.
Degree: PhD, 2014, University of Oklahoma
URL: http://hdl.handle.net/11244/10343
► Production enhancement of tight reservoirs requires in-depth analysis of mechanisms governing hydraulic fracturing, especially in naturally fractured reservoirs. This study is dedicated to the optimization…
(more)
▼ Production enhancement of tight reservoirs requires in-depth analysis of mechanisms governing hydraulic fracturing, especially in naturally fractured reservoirs. This study is dedicated to the optimization of hydraulic fracturing and drilling by integrating both rock fracture mechanics and petrophysics study.
Fracture twist near the borehole adversely impair production rate or induce premature screenout, and is analyzed in terms of mixed-mode fracture propagation. The best fracture propagation criterion is selected by comparing experimental and theoretical fracture initiation angles, suggestions regarding the alleviation of fracture twist are summarized by sensitivity analysis.
Accurate estimation of fracture gradient is critical for both drilling and hydraulic fracturing. Fracture gradient by traditional methods is greatly overestimated due to the ignorance of preexisting fractures, nonlinear near wellbore stress concentration acting on fracture surfaces, and nonlinear fluid pressure distribution inside fractures. A weight function method is firstly introduced to petroleum engineering for the calculation of stress intensity factor where there are preexisting fractures intersecting borehole. Weight function parameters of a pair of symmetrical fractures emanating from borehole are derived and verified against existing models. The weight function parameters are applied to predict breakdown pressure of preexisting fractures. The simulation results are compared against both measured breakdown pressure in both fields and laboratory and results of classical fracture models. The proven weight function method shows a great potential in improving the accuracy of breakdown pressure prediction.
Screening fracture candidates plays a central role in hydraulic fracturing design. Identification of fracture barrier helps prevent freshwater aquifer from contamination and undesirable water breakthrough due to unintentional cross of fracture barriers. New definition of brittleness is developed and benchmarked for unconventional shale. Correlations of brittleness with neutron porosity and compressional slowness are built for predicting brittleness in the fields lacking specific logging data, and saving cost of logging service. Fracability index model is firstly developed for screening fracturing candidates and fracture barrier identification by integrating brittleness and fracture energy (or fracture toughness, Young’s modulus, tensile strength). Its interpretation result is proven by logging interpretation. It is found that it is not always right that formations with high brittleness are good fracturing candidates. The fracability index model refines the formation evaluation and narrows the thickness of target interval.
This research establishes a comprehensive understanding regarding fracture twist, mixed-mode fracture propagation, fracture gradient prediction, fracturing candidate selection by integrating theoretical modeling, experimental efforts, and logging interpretation. The methodologies will not only help engineers…
Advisors/Committee Members: SHAH, SUBHASH (advisor), ROEGIERS, JEAN-CLAUDE (committee member), GHASSEMI, AHMAD (committee member), DEVEGOWDA, DEEPAK (committee member), VEDULA, PRAKASH (committee member).
Subjects/Keywords: Engineering; Petroleum.
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
JIN, X. (2014). AN INTEGRATED GEOMECHANICS AND PETROPHYSICS STUDY OF HYDRAULIC FRACTURING IN NATURALLY FRACTURED RESERVOIRS. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/10343
Chicago Manual of Style (16th Edition):
JIN, XIAOCHUN. “AN INTEGRATED GEOMECHANICS AND PETROPHYSICS STUDY OF HYDRAULIC FRACTURING IN NATURALLY FRACTURED RESERVOIRS.” 2014. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/10343.
MLA Handbook (7th Edition):
JIN, XIAOCHUN. “AN INTEGRATED GEOMECHANICS AND PETROPHYSICS STUDY OF HYDRAULIC FRACTURING IN NATURALLY FRACTURED RESERVOIRS.” 2014. Web. 27 Feb 2021.
Vancouver:
JIN X. AN INTEGRATED GEOMECHANICS AND PETROPHYSICS STUDY OF HYDRAULIC FRACTURING IN NATURALLY FRACTURED RESERVOIRS. [Internet] [Doctoral dissertation]. University of Oklahoma; 2014. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/10343.
Council of Science Editors:
JIN X. AN INTEGRATED GEOMECHANICS AND PETROPHYSICS STUDY OF HYDRAULIC FRACTURING IN NATURALLY FRACTURED RESERVOIRS. [Doctoral Dissertation]. University of Oklahoma; 2014. Available from: http://hdl.handle.net/11244/10343

University of Oklahoma
6.
Razi, Mani.
ADAPTIVE GRID BASED FINITE DIFFERENCE METHODS FOR SOLUTION OF HYPERBOLIC PDES: APPLICATION TO COMPUTATIONAL MECHANICS AND UNCERTAINTY QUANTIFICATION.
Degree: PhD, 2015, University of Oklahoma
URL: http://hdl.handle.net/11244/14579
► Novel finite-difference based numerical methods for solution of linear and nonlinear hyperbolic partial differential equations (PDEs) using adaptive grids are proposed in this dissertation. The…
(more)
▼ Novel finite-difference based numerical methods for solution of linear and nonlinear hyperbolic partial differential equations (PDEs) using adaptive grids are proposed in this dissertation. The overall goal of this research is to improve the accuracy and/or computational efficiency of numerical solutions via the use of adaptive grids and suitable modifications of a given low-order order finite-difference scheme. These methods can be grouped in two broad categories. The first category of adaptive FD methods proposed in the dissertation attempt to reduce the truncation error and/or enhance the accuracy of the underlying numerical schemes via grid distribution alone. Some approaches for grid distribution considered include those based on (i) a moving uniform mesh/domain, (ii) adaptive gradient based refinement (AGBR) and (iii) unit local Courant-Freidrich-Lewy (CFL) number. The improvement in the accuracy which is obtained using these adaptive methods is limited by the underlying scheme formal order of accuracy. In the second category, the CFL based approach proposed in the first category was extended further using defect correction in order to improve the formal order of accuracy and computational efficiency significantly (i.e. by at least one order or higher). The proposed methods in this category are constructed based upon the analysis of the leading order error terms in the modified differential equation associated with the underlying partial differential equation and finite difference scheme. The error terms corresponding to regular and irregular perturbations are identified and the leading order error terms associated with regular perturbations are eliminated using a non-iterative defect correction approach while the error terms associated with irregular perturbations are eliminated using grid adaptation. In the second category of methods involving defect correction (or reduction of leading order terms of truncation error), we explored two different approaches for selection of adaptive grids. These are based on (i) optimal grid dis- tribution and (ii) remapping with monotonicity preserving interpolation. While the first category of methods may be preferred in view of ease of implementation and lower computational complexity, the second category of methods may be preferred in view of greater accuracy and computational efficiency. The two broad categories of methods, which have been applied to problems involving both bounded and unbounded domains, were also extended to multidimensional cases using a dimensional splitting approaches.
The performance of these methods was demonstrated using several example problems in computational uncertainty quantification (CUQ) and computational mechanics. The results of the application of the proposed approaches all indicate improvement in both the accuracy and computational efficiency (by about three orders of magnitude in some selected cases) of underlying schemes. In the context of CUQ, all three proposed adaptive finite different solvers are combined with the…
Advisors/Committee Members: Attar, Peter J. (advisor), Vedula, Prakash (advisor), Altan, Cengiz (committee member), Parthasarathy, Ramkumar (committee member), Papavassiliou, Dimitrios (committee member).
Subjects/Keywords: Hyperbolic Partial Differential Equation; Uncertainty Qunatification; Grid Adaptation; Defect Correction
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Razi, M. (2015). ADAPTIVE GRID BASED FINITE DIFFERENCE METHODS FOR SOLUTION OF HYPERBOLIC PDES: APPLICATION TO COMPUTATIONAL MECHANICS AND UNCERTAINTY QUANTIFICATION. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/14579
Chicago Manual of Style (16th Edition):
Razi, Mani. “ADAPTIVE GRID BASED FINITE DIFFERENCE METHODS FOR SOLUTION OF HYPERBOLIC PDES: APPLICATION TO COMPUTATIONAL MECHANICS AND UNCERTAINTY QUANTIFICATION.” 2015. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/14579.
MLA Handbook (7th Edition):
Razi, Mani. “ADAPTIVE GRID BASED FINITE DIFFERENCE METHODS FOR SOLUTION OF HYPERBOLIC PDES: APPLICATION TO COMPUTATIONAL MECHANICS AND UNCERTAINTY QUANTIFICATION.” 2015. Web. 27 Feb 2021.
Vancouver:
Razi M. ADAPTIVE GRID BASED FINITE DIFFERENCE METHODS FOR SOLUTION OF HYPERBOLIC PDES: APPLICATION TO COMPUTATIONAL MECHANICS AND UNCERTAINTY QUANTIFICATION. [Internet] [Doctoral dissertation]. University of Oklahoma; 2015. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/14579.
Council of Science Editors:
Razi M. ADAPTIVE GRID BASED FINITE DIFFERENCE METHODS FOR SOLUTION OF HYPERBOLIC PDES: APPLICATION TO COMPUTATIONAL MECHANICS AND UNCERTAINTY QUANTIFICATION. [Doctoral Dissertation]. University of Oklahoma; 2015. Available from: http://hdl.handle.net/11244/14579

University of Oklahoma
7.
Ozbenli, Ersin.
Consideration of Lie Symmetry Groups in Computational Fluid Dynamics.
Degree: PhD, 2018, University of Oklahoma
URL: http://hdl.handle.net/11244/316323
► Lie symmetries are fundamental properties of differential equations that are often not actively considered in construction of numerical schemes relevant to computational fluid dynamics (CFD).…
(more)
▼ Lie symmetries are fundamental properties of differential equations that are often not actively considered in construction of numerical schemes relevant to computational fluid dynamics (CFD). While many of these numerical schemes in CFD are constructed based on consideration of a desired order of accuracy and have shown promising results, these schemes usually do not accurately represent fundamental symmetry (or invariance) properties of underlying governing equations. The overall objective of this dissertation is to address this limitation via development of numerical schemes that not only preserve Lie symmetries of underlying differential equations but also ensure a desired order of accuracy.
In this regard, novel methodologies for construction of high order accurate invariant numerical schemes, based on the method of equivariant moving frames, are introduced. Formulation of high order accurate invariant schemes presented in this work involves consideration of (a) modified equations (via perturbation or defect correction) and/or (b) compact schemes. Modified forms of equations are used not only to achieve a desired order of accuracy in associated invariant schemes but also to systematically select convenient moving frames. Further, in the construction of invariant compact schemes, extended symmetry groups of differential equations are considered where point transformations based on these extended groups are used to transform existing base schemes to their invariant forms. Construction and performance of symmetry preserving numerical schemes are discussed for a variety of linear and nonlinear canonical problems (such as linear advection-diffusion equation in 1D/2D, inviscid Burgers' equation, viscous Burgers' equation along with application to Euler equations in 1D/2D). The overall quality of results obtained from constructed invariant numerical schemes is often found to be notably better than that of standard, non-invariant base numerical schemes. Such improvements in results are particularly more significant when error measures based on symmetry properties of underlying differential equations are considered.
Advisors/Committee Members: Vedula, Prakash (advisor), Altan, M. Cengiz (committee member), Papavassiliou, Dimitrios (committee member), Merchan-Merchan, Wilson E. (committee member), Garg, Jivtesh (committee member).
Subjects/Keywords: Computational Fluid Dynamics; Lie Symmetry Groups; Invariant Numerical Schemes; Symmetry Preservation in Numerical Schemes
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Ozbenli, E. (2018). Consideration of Lie Symmetry Groups in Computational Fluid Dynamics. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/316323
Chicago Manual of Style (16th Edition):
Ozbenli, Ersin. “Consideration of Lie Symmetry Groups in Computational Fluid Dynamics.” 2018. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/316323.
MLA Handbook (7th Edition):
Ozbenli, Ersin. “Consideration of Lie Symmetry Groups in Computational Fluid Dynamics.” 2018. Web. 27 Feb 2021.
Vancouver:
Ozbenli E. Consideration of Lie Symmetry Groups in Computational Fluid Dynamics. [Internet] [Doctoral dissertation]. University of Oklahoma; 2018. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/316323.
Council of Science Editors:
Ozbenli E. Consideration of Lie Symmetry Groups in Computational Fluid Dynamics. [Doctoral Dissertation]. University of Oklahoma; 2018. Available from: http://hdl.handle.net/11244/316323

University of Oklahoma
8.
Heck, Margaret.
Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics.
Degree: PhD, 2015, University of Oklahoma
URL: http://hdl.handle.net/11244/32571
► Computational fluid dynamics is used to study two distinct areas of engineering interest: microfluidic systems involving superhydrophobic surfaces and blood pumps. Superhydrophobic surfaces, which can…
(more)
▼ Computational fluid dynamics is used to study two distinct areas of engineering interest: microfluidic systems involving superhydrophobic surfaces and blood pumps. Superhydrophobic surfaces, which can induce slip at fluid-solid interfaces, are modeled using mixed free-shear and no-slip boundary conditions. Despite remarkable effort to include the effects of surface topology and various flow and physical properties in models describing fluid slip over these surfaces, the mathematical description of flow over mixed slip boundaries is still incomplete. Critical configurations of roughness necessary to achieve drag reduction in micro-channels are established. The effects of roughness shape and size on drag for both Newtonian and non-Newtonian fluid flow are also considered in depth. Based on these findings, similarity theory is used to develop a model to describe drag reduction as a function of channel geometry. The principles used in the development of these models are then applied to the more complicated system of a centrifugal blood pump. The effects of the non-Newtonian rheological behavior, hematocrit, temperature, and turbulence on pump performance and subsequent blood damage is quantified over a wide range of operating conditions.
Advisors/Committee Members: Papavassiliou, Dimitrios (advisor), Lobban, Lance (committee member), O'Rear, Edgar (committee member), Schmidtke, David (committee member), Vedula, Prakash (committee member).
Subjects/Keywords: Computational fluid dynamics; microfluidics; blood pump
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Manager
APA (6th Edition):
Heck, M. (2015). Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/32571
Chicago Manual of Style (16th Edition):
Heck, Margaret. “Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics.” 2015. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/32571.
MLA Handbook (7th Edition):
Heck, Margaret. “Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics.” 2015. Web. 27 Feb 2021.
Vancouver:
Heck M. Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics. [Internet] [Doctoral dissertation]. University of Oklahoma; 2015. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/32571.
Council of Science Editors:
Heck M. Investigation of Flow through Complicated Microfluidic Devices and over Micropatterned Surfaces using Computational Fluid Dynamics. [Doctoral Dissertation]. University of Oklahoma; 2015. Available from: http://hdl.handle.net/11244/32571

University of Oklahoma
9.
Wang, Yunxiang.
SHAPE SENSITIVITY ANALYSIS FOR THREE-DIMENSIONAL MULTI-SCALE CRACK PROPAGATION PROBLEMS USING THE BRIDGING SCALE METHOD.
Degree: PhD, 2014, University of Oklahoma
URL: http://hdl.handle.net/11244/10337
► During the past two decades, a variety of concurrent multi-scale simulation methods have been developed, such as the bridging scale method, in which MD simulation…
(more)
▼ During the past two decades, a variety of concurrent multi-scale simulation methods have been developed, such as the bridging scale method, in which MD simulation is performed only at localized areas of interest, while the response of rest of the domain is solved by using finite element method (FEM). This thesis presents a shape sensitivity analysis approach for multi-scale crack propagation problems based on the bridging scale method. The objective is to reveal the impact of macroscopic shape change on the speed of crack growth at microscopic level. Two major challenges exist in shape sensitivity analysis of coupled atomistic/continuum crack propagation problems, namely the discrete nature of the MD simulation and the non-differentiability of the performance measure of crack propagation speed. In this thesis, the shape sensitivity expressions are derived using direct differentiation method by taking material derivative of a continuum variational formulation of the bridging scale. To get around the discontinuity issue in continuum shape design due to the discrete nature of the MD simulation, the design velocity fields are defined in a way that the shape of the MD region does not change. The derived shape sensitivity formulation can be used to analytically compute the sensitivity coefficients of structural responses at the atomistic level. In addition, a performance measure that quantifies the speed of crack is established to support the sensitivity calculation for crack propagation speed. To overcome the non-differentiability of crack speed in design space, a hybrid method that combines analytical sensitivity analysis and regression analysis is developed. The proposed analytical sensitivity approach and hybrid method are implemented numerically in a nano-beam example, and the accuracy is verified using overall finite difference results.
The analytical sensitivity expressions in this thesis are formulated based on a rigorous mathematical foundation, and is generalized for three-dimensional structures with arbitrary geometric shape. In calculating the sensitivity of crack speed, the hybrid method with regression analysis is much more efficient than overall finite difference. The major contributions of this thesis are: first, it demonstrates the feasibility of shape design of coupled atomistic/continuum systems for the first time; and second, the proposed sensitivity approach accurately predicts the correlation between macroscopic shape change and microscopic crack propagation speed, and therefore establishes the foundation of multi-scale residual-life-based structural optimization without involving traditional fracture mechanics theory.
Advisors/Committee Members: Chang, Kuang-Hua (advisor), Attar, Peter (committee member), Gramoll, Kurt (committee member), Muraleetharan, Kanthasamy (committee member), Vedula, Prakash (committee member).
Subjects/Keywords: Engineering; Mechanical.
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MLA ·
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APA (6th Edition):
Wang, Y. (2014). SHAPE SENSITIVITY ANALYSIS FOR THREE-DIMENSIONAL MULTI-SCALE CRACK PROPAGATION PROBLEMS USING THE BRIDGING SCALE METHOD. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/10337
Chicago Manual of Style (16th Edition):
Wang, Yunxiang. “SHAPE SENSITIVITY ANALYSIS FOR THREE-DIMENSIONAL MULTI-SCALE CRACK PROPAGATION PROBLEMS USING THE BRIDGING SCALE METHOD.” 2014. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/10337.
MLA Handbook (7th Edition):
Wang, Yunxiang. “SHAPE SENSITIVITY ANALYSIS FOR THREE-DIMENSIONAL MULTI-SCALE CRACK PROPAGATION PROBLEMS USING THE BRIDGING SCALE METHOD.” 2014. Web. 27 Feb 2021.
Vancouver:
Wang Y. SHAPE SENSITIVITY ANALYSIS FOR THREE-DIMENSIONAL MULTI-SCALE CRACK PROPAGATION PROBLEMS USING THE BRIDGING SCALE METHOD. [Internet] [Doctoral dissertation]. University of Oklahoma; 2014. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/10337.
Council of Science Editors:
Wang Y. SHAPE SENSITIVITY ANALYSIS FOR THREE-DIMENSIONAL MULTI-SCALE CRACK PROPAGATION PROBLEMS USING THE BRIDGING SCALE METHOD. [Doctoral Dissertation]. University of Oklahoma; 2014. Available from: http://hdl.handle.net/11244/10337

University of Oklahoma
10.
Nguyen, Quoc.
Study of transport phenomena in turbulent channel flows using Direct Numerical Simulation and Lagrangian Scalar Tracking.
Degree: PhD, 2016, University of Oklahoma
URL: http://hdl.handle.net/11244/34749
► In this study, Direct Numerical Simulation (DNS) and Lagrangian Scalar Tracking (LST) method are used simultaneously to study fundamental transport phenomena in turbulent channel flows.…
(more)
▼ In this study, Direct Numerical Simulation (DNS) and Lagrangian Scalar Tracking (LST) method are used simultaneously to study fundamental transport phenomena in turbulent channel flows. Area of study covers drag reduction in turbulence, flow-induced particles separation in wall turbulence, and probability density function model of a puff of particles diffusing from a channel wall.
Advisors/Committee Members: Papavassiliou, Dimitrios (advisor), Vedula, Prakash (committee member), O' Rear, Edgar (committee member), Wang, Bin (committee member), Shambaugh, Robert (committee member).
Subjects/Keywords: Engineering; Chemical.
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
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APA (6th Edition):
Nguyen, Q. (2016). Study of transport phenomena in turbulent channel flows using Direct Numerical Simulation and Lagrangian Scalar Tracking. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/34749
Chicago Manual of Style (16th Edition):
Nguyen, Quoc. “Study of transport phenomena in turbulent channel flows using Direct Numerical Simulation and Lagrangian Scalar Tracking.” 2016. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/34749.
MLA Handbook (7th Edition):
Nguyen, Quoc. “Study of transport phenomena in turbulent channel flows using Direct Numerical Simulation and Lagrangian Scalar Tracking.” 2016. Web. 27 Feb 2021.
Vancouver:
Nguyen Q. Study of transport phenomena in turbulent channel flows using Direct Numerical Simulation and Lagrangian Scalar Tracking. [Internet] [Doctoral dissertation]. University of Oklahoma; 2016. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/34749.
Council of Science Editors:
Nguyen Q. Study of transport phenomena in turbulent channel flows using Direct Numerical Simulation and Lagrangian Scalar Tracking. [Doctoral Dissertation]. University of Oklahoma; 2016. Available from: http://hdl.handle.net/11244/34749

University of Oklahoma
11.
Kiran, Raj.
STUDY OF FLUID DYNAMICS EFFECTS FOR LOSS OF WELL CONTROL INCIDENTS IN SUBSEA WELLS.
Degree: PhD, 2019, University of Oklahoma
URL: http://hdl.handle.net/11244/319699
► The safety of well operations has become the focal point of the research paradigm since the Deepwater Horizon incident. The risks of wellbore blowouts cannot…
(more)
▼ The safety of well operations has become the focal point of the research paradigm since the Deepwater Horizon incident. The risks of wellbore blowouts cannot be neglected in any drilling operation, which makes the discharge of fluids a likely scenario. One of the critical observations while tackling the well control operation during the Deepwater Horizon incident was the fluid discharge rate with subsonic and sonic velocity. Lack of a comprehensive tool to estimate the worst-case discharge scenario constrained the tackling operations and exacerbated the side effects of blowouts. Keeping this in mind, an experimental and numerical investigation of multiphase flow was conducted, and consequently, an integrated reservoir and hydrodynamic model was developed to estimate the worst-case discharge (WCD).
A new multiphase vertical flow-loop was constructed, which included annulus and pipe as test sections. The flow loop was equipped with sensors and instruments to capture the flow characteristics. The experiments were conducted at high superficial gas (0-160m/s) and liquid velocity (0-2.35 m/s) to measure the pressure drop and liquid holdup. The high-speed video recording was implemented to capture the photographic images of flow dynamics. Experimental data were analyzed to understand the flow characteristics during high-velocity inlet conditions. Numerical investigations were carried out using computational fluid dynamics (CFD) and mechanistic modeling to mimic the experimental data.
The experimental results show the friction dominated trend of pressure gradients. The CFD modeling in ANSYS Fluent suggests that the volume of fluid multiphase flow model with different turbulence models can identify the flow regimes in high-velocity flow conditions. Furthermore, several mechanistic and empirical models were tested to verify the aptness in WCD estimation. Finally, the suitable hydrodynamic model was incorporated in the newly developed tool to characterize the discharge rates. A new sonic correlation was developed based on which it can be established whether the sonic condition achieved in the well or not. These features were included in an integrated hydrodynamic and reservoir tool that can simulate the real-time event of WCD scenario. A sensitivity analysis was conducted to establish confidence in the software. The results were in good agreement with the commercial software in the base cases.
The novelty in this approach is the integrated use of numerical and experimental investigation to mimic the real field conditions of WCD especially for flow with Mach number greater than 0.3 (subsonic and sonic conditions). The new models and techniques can be used in flow characterization of high superficial gas velocity multiphase flow and estimation of flow rates during the worst case discharge.
Advisors/Committee Members: Salehi, Saeed (advisor), Vedula, Prakash (committee member), Ahmed, Ramadan (committee member), Teodoriu, Catalin (committee member), Misra, Siddharth (committee member).
Subjects/Keywords: Petroleum; Worst case discharge; Multiphase flow; Annulus
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
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APA (6th Edition):
Kiran, R. (2019). STUDY OF FLUID DYNAMICS EFFECTS FOR LOSS OF WELL CONTROL INCIDENTS IN SUBSEA WELLS. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/319699
Chicago Manual of Style (16th Edition):
Kiran, Raj. “STUDY OF FLUID DYNAMICS EFFECTS FOR LOSS OF WELL CONTROL INCIDENTS IN SUBSEA WELLS.” 2019. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/319699.
MLA Handbook (7th Edition):
Kiran, Raj. “STUDY OF FLUID DYNAMICS EFFECTS FOR LOSS OF WELL CONTROL INCIDENTS IN SUBSEA WELLS.” 2019. Web. 27 Feb 2021.
Vancouver:
Kiran R. STUDY OF FLUID DYNAMICS EFFECTS FOR LOSS OF WELL CONTROL INCIDENTS IN SUBSEA WELLS. [Internet] [Doctoral dissertation]. University of Oklahoma; 2019. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/319699.
Council of Science Editors:
Kiran R. STUDY OF FLUID DYNAMICS EFFECTS FOR LOSS OF WELL CONTROL INCIDENTS IN SUBSEA WELLS. [Doctoral Dissertation]. University of Oklahoma; 2019. Available from: http://hdl.handle.net/11244/319699

University of Oklahoma
12.
Wang, Huiyu.
Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes.
Degree: PhD, 2020, University of Oklahoma
URL: http://hdl.handle.net/11244/324967
► Electromagnetic-based energy harvesting materials and devices have emerged as a prominent research area in the last ten years, especially systems using ferrofluidic induction—a process that…
(more)
▼ Electromagnetic-based energy harvesting materials and devices have emerged as a prominent research area in the last ten years, especially systems using ferrofluidic induction—a process that generates voltage via the pulsation of a ferrofluid (iron-based nanofluid) through a solenoid. This work includes the development of an analytical model and computational modeling methods to investigate ferrofluid pulsating flow within an energy harvesting device and the mass and heat transfer performance of a two-phase closed thermosyphon (TPCT) and oscillating heat pipe (OHP). First, an analytical model is proposed to predict the induced electromotive force (EMF) based on the flow behavior and magnetic properties of a pulsating ferrofluid energy harvesting device. The model identifies key parameters for describing and optimizing induction for ferrofluid pulsing through a solenoid. Data from a previously documented experimental study was used to validate the analytical model, and both the experimental data and analytical model show the same trends with the induced EMF increasing as a function of pulsating frequency and magnetic field strength as a higher percentage of the ferrofluid nanoparticle moments are aligned. Second, computational fluid dynamics (CFD) simulations were performed to predict the heat transfer performance of a TPCT. Simulations were performed using a three-dimensional finite-volume flow solver (ANSYS Fluent) with a pressure-based scheme for the solution of the continuity and momentum equations, volume-of-fluid method for resolution of the liquid-vapor phase interface, and a temperature-dependent model for interphase mass transfer by evaporation and condensation. Different model and numerical scheme combinations were investigated to identify an efficient and consistently accurate method using currently available software tools. To address issues with previously published simulation methods violating the conservation of mass, a new variable saturation temperature model was tested along with mass transfer coefficients based on the vapor-liquid density ratio and more physically realistic boundary conditions. The variable saturation temperature model significantly mitigated mass and energy imbalance in the simulations, for both constant heat flux and convection condenser boundary conditions. In addition, for the VOF discretization the Geo-Reconstruct scheme was found to be more accurate than the Compressive scheme available in Fluent without additional computational cost. Third, simulations of a vertical OHP were performed using the CFD methodology developed for the TPCT system. Results show simulations using appropriate values for the evaporation and condensation mass transfer time relaxation parameters and the new variable saturation temperature model are in good agreement with the available experimental data. For the OHP system, using the Compressive discretization scheme for the VOF model allowed for computationally efficient simulation. It is believed that the advances in analytical and computational modeling…
Advisors/Committee Members: Walters, D. Keith (advisor), Walters, Keisha B. (advisor), Ruyle, Jessica E. (committee member), Shabgard, Hamidreza (committee member), Vedula, Prakash (committee member), Garg, Jivtesh (committee member).
Subjects/Keywords: Heat Transfer; Computational fluid dynamics (CFD); Electrodynamic energy harvesting
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Wang, H. (2020). Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/324967
Chicago Manual of Style (16th Edition):
Wang, Huiyu. “Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes.” 2020. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/324967.
MLA Handbook (7th Edition):
Wang, Huiyu. “Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes.” 2020. Web. 27 Feb 2021.
Vancouver:
Wang H. Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes. [Internet] [Doctoral dissertation]. University of Oklahoma; 2020. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/324967.
Council of Science Editors:
Wang H. Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes. [Doctoral Dissertation]. University of Oklahoma; 2020. Available from: http://hdl.handle.net/11244/324967

University of Oklahoma
13.
Jamal, Tausif.
Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework.
Degree: PhD, 2020, University of Oklahoma
URL: http://hdl.handle.net/11244/324966
► Reynolds Averaged Navier-Stokes (RANS) models still represent the most common turbulence modeling technique used in Computational Fluid Dynamics (CFD) today. RANS models are preferred primarily…
(more)
▼ Reynolds Averaged Navier-Stokes (RANS) models still represent the most common turbulence modeling technique used in Computational Fluid Dynamics (CFD) today. RANS models are preferred primarily due to their relatively low computational demand and ease of use. The general RANS framework utilizes the ensemble averaged form of the Navier Stokes equations in which all turbulent scales are modelled, and hence requires reduced computational effort compared to scale resolving methods. Despite their popularity, RANS models have been found to perform poorly in flows with separated shear layers, unsteady wakes, and temporally evolving flows. There has been ongoing progress towards high-fidelity methods such as Large Eddy Simulation (LES) to more accurately represent these flow features. LES models apply filters to the equations of fluid motion to resolve the large turbulent structures that are responsible for energy transfer. The smaller scales however, are represented using a sub-grid scale (SGS) model. LES models perform well in separated shear layers where large eddies dictate the energy and momentum transfer, due to the small time and length scales associated with near wall flow. The costs associated with LES are a major limiting factor in their adoption in industrial and academic research. This has led to the development of Hybrid RANS-LES (HRL) models which offer improved performance over RANS models while being relatively inexpensive compared to LES models. The hybrid modeling approach aims to provide the best of both worlds. In hybrid models, LES models are used far away from the wall to resolve large scale structures primarily responsible for the transfer of momentum and energy, while the wall bounded turbulence is treated using a RANS model. However, HRL models suffer from inherent drawbacks associated with their handling of RANS to LES transition in addition to a high degree of grid sensitivity. The present study proposes advanced turbulence modeling strategies within the hybrid RANS-LES class of models. Major contributions include: (i) evaluation of RANS and hybrid RANS-LES models for separated and non-stationary flows, (ii) development of time-filtering techniques for the dynamic Hybrid RANS-LES (DHRL) model to improve predictive capabilities for non-stationary periodic and non-periodic flows, and (iii) a new variant of the DHRL model for complex turbulent flows to address a known weakness in the DHRL formulation.
First, the performance of the DHRL model is evaluated against popular RANS and HRL models for flow over a three-dimensional axisymmetric hill. DHRL model results indicate superior prediction of mean flow statistics and turbulent stresses. However, some discrepancy in Reynolds stress prediction and the lack of a smooth LES-mode away from the wall is observed. Second, static and dynamic time filters are implemented to extend the DHRL model from an ensemble averaged framework to a non-stationary framework. Results once again indicate superior model performance when compared to other models investigated.…
Advisors/Committee Members: Walters, Dibbon K. (advisor), O'Rear, Edgar (committee member), Walters, Keisha B. (committee member), Garg, Jivtesh (committee member), Shabgard, Hamidreza (committee member), Vedula, Prakash (committee member).
Subjects/Keywords: Computational Fluid Dynamics; Turbulence Modeling; Numerical Methods; Mechanical Engineering
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Jamal, T. (2020). Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/324966
Chicago Manual of Style (16th Edition):
Jamal, Tausif. “Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework.” 2020. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/324966.
MLA Handbook (7th Edition):
Jamal, Tausif. “Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework.” 2020. Web. 27 Feb 2021.
Vancouver:
Jamal T. Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework. [Internet] [Doctoral dissertation]. University of Oklahoma; 2020. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/324966.
Council of Science Editors:
Jamal T. Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework. [Doctoral Dissertation]. University of Oklahoma; 2020. Available from: http://hdl.handle.net/11244/324966
14.
Lu, Xu.
Improving High-Resolution Tropical Cyclone Prediction using a Cycled, GSI-Based Hybrid Ensemble-Variational Data Assimilation System for HWRF with Vortex Scale Observations.
Degree: PhD, 2019, University of Oklahoma
URL: http://hdl.handle.net/11244/322825
► A Gridpoint Statistical Interpolation analysis system (GSI)-based, continuously cycled, dual-resolution hybrid ensemble-variational (EnVar) data assimilation (DA) system is developed for the Hurricane Weather Research and…
(more)
▼ A Gridpoint Statistical Interpolation analysis system (GSI)-based, continuously cycled, dual-resolution hybrid ensemble-variational (EnVar) data assimilation (DA) system is developed for the Hurricane Weather Research and Forecasting (HWRF) Model. The newly developed DA system is then used in this dissertation to address a few scientific and technical challenges in assimilating the vortex-scale observations to improve the numerical prediction of TCs.
In the dissertation, the newly developed DA system is described first. Then, the next part addresses how various data assimilation configurations impact the vortex scale observation assimilation and the subsequent prediction using the DA system. It is found that (1) dual-resolution EnVar DA improves the analyzed storm structure and short-term maximum wind speed (Vmax) and minimum sea level pressure (MSLP) forecasts compared to coarser, single-resolution EnVar DA, but track and radius of maximum wind (RMW) forecasts do not improve. (2) Additionally, applying vortex relocation (VR) and vortex modification (VM) on the control background before DA improves the analyzed storm, overall track, RMW, MSLP, and Vmax forecasts. Further applying VR on the ensemble background improves the analyzed storm and forecast biases for MSLP and Vmax. (3) Also, using four-dimensional (4D) EnVar to assimilate tail Doppler radar (TDR) data improves the analyzed storm and short-term MSLP and Vmax forecasts compared to three-dimensional (3D) EnVar although 4DEnVar slightly degrades the track forecast. (4) Finally, a diagnostic on why advanced DA can improve the TC intensity forecast for Edouard (2014) is provided.
In the third part, using the further upgraded DA system, the deficiency of the numerical model physics was discussed. Although the DA produces realistic 3D analyses to initialize the model, persistent Vmax spin-down is found during the rapid intensification of hurricane Patricia (2015). Diagnostics reveal that the spin-down issue is likely attributed to the deficient HWRF model physics which are unable to maintain the realistic 3D structures from the DA analysis. The horizontal diffusion is too strong to maintain the realistically observed vertical oscillation of radial wind near the eyewall region. The vertical diffusion profile cannot produce a sufficiently strong secondary circulation connecting the realistically elevated upper-level outflow produced in the DA analysis. Further investigations with different model physics parameterizations demonstrate that spin-down can be alleviated by modifying model physics. In particular, a modified turbulent mixing parameterization scheme together with a reduced horizontal diffusion is found to significantly alleviate the spin-down issue and to improve the intensity forecast. Additional experiments show that the peak simulated intensity and rapid intensification (RI) rate can be further improved by increasing the model resolution. But the model resolution is not as important as model physics in the spin-down alleviation.
The…
Advisors/Committee Members: Wang, Xuguang (advisor), Vedula, Prakash (committee member), Biggerstaff, Michael (committee member), Sakaeda, Naoko (committee member), Wicker, Louis (committee member).
Subjects/Keywords: Data Assimilation; Hurricane; Vortex Scale Observations
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Lu, X. (2019). Improving High-Resolution Tropical Cyclone Prediction using a Cycled, GSI-Based Hybrid Ensemble-Variational Data Assimilation System for HWRF with Vortex Scale Observations. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/322825
Chicago Manual of Style (16th Edition):
Lu, Xu. “Improving High-Resolution Tropical Cyclone Prediction using a Cycled, GSI-Based Hybrid Ensemble-Variational Data Assimilation System for HWRF with Vortex Scale Observations.” 2019. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/322825.
MLA Handbook (7th Edition):
Lu, Xu. “Improving High-Resolution Tropical Cyclone Prediction using a Cycled, GSI-Based Hybrid Ensemble-Variational Data Assimilation System for HWRF with Vortex Scale Observations.” 2019. Web. 27 Feb 2021.
Vancouver:
Lu X. Improving High-Resolution Tropical Cyclone Prediction using a Cycled, GSI-Based Hybrid Ensemble-Variational Data Assimilation System for HWRF with Vortex Scale Observations. [Internet] [Doctoral dissertation]. University of Oklahoma; 2019. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/322825.
Council of Science Editors:
Lu X. Improving High-Resolution Tropical Cyclone Prediction using a Cycled, GSI-Based Hybrid Ensemble-Variational Data Assimilation System for HWRF with Vortex Scale Observations. [Doctoral Dissertation]. University of Oklahoma; 2019. Available from: http://hdl.handle.net/11244/322825

University of Oklahoma
15.
Yoon, Jangho.
Nonlinear Bayesian Estimation via Solution of The Fokker-Planck Equation.
Degree: PhD, 2009, University of Oklahoma
URL: http://hdl.handle.net/11244/320209
► Then, new proposed filtering methods are applied to several challenging problems such as i) the bearing-only tracking problem, ii) the relative orbit position estimation problem,…
(more)
▼ Then, new proposed filtering methods are applied to several challenging problems such as i) the bearing-only tracking problem, ii) the relative orbit position estimation problem, and iii) the orbit determination problem to demonstrate their advantages. Simulation results indicate that the performance of the proposed filters are better than existing nonlinear filtering methods, such as the Extended Kalman Filter especially with less measurement updates.
Advisors/Committee Members: Xu, Yunjun||Vedula, Prakash (advisor).
Subjects/Keywords: Bayesian statistical decision theory; Nonlinear theories; Filters (Mathematics); Fokker-Planck equation; Stochastic differential equations; Differential equations, Nonlinear
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APA ·
Chicago ·
MLA ·
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CSE |
Export
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Manager
APA (6th Edition):
Yoon, J. (2009). Nonlinear Bayesian Estimation via Solution of The Fokker-Planck Equation. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/320209
Chicago Manual of Style (16th Edition):
Yoon, Jangho. “Nonlinear Bayesian Estimation via Solution of The Fokker-Planck Equation.” 2009. Doctoral Dissertation, University of Oklahoma. Accessed February 27, 2021.
http://hdl.handle.net/11244/320209.
MLA Handbook (7th Edition):
Yoon, Jangho. “Nonlinear Bayesian Estimation via Solution of The Fokker-Planck Equation.” 2009. Web. 27 Feb 2021.
Vancouver:
Yoon J. Nonlinear Bayesian Estimation via Solution of The Fokker-Planck Equation. [Internet] [Doctoral dissertation]. University of Oklahoma; 2009. [cited 2021 Feb 27].
Available from: http://hdl.handle.net/11244/320209.
Council of Science Editors:
Yoon J. Nonlinear Bayesian Estimation via Solution of The Fokker-Planck Equation. [Doctoral Dissertation]. University of Oklahoma; 2009. Available from: http://hdl.handle.net/11244/320209
.