Dissertations / Theses on the topic 'Flow body'
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1
Akbari, Mohammad Hadi. "Bluff-body flow simulations using vortex methods." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq55294.pdf.
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Abramson, Philip S. "Fluidic control of aerodynamic forces and moments on an axisymmetric body." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31707.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Ari Glezer; Committee Member: Bojan Vukasinovic; Committee Member: Mark Costello. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Shanbhogue, Santosh Janardhan. "Dynamics of perturbed exothermic bluff-body flow-fields." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24823.
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Thesis (Ph.D.)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Lieuwen, Tim; Committee Member: Gaeta, Rick; Committee Member: Menon, Suresh; Committee Member: Seitzman, Jerry; Committee Member: Zinn, Ben.
4
Lee, Jongsoo. "Facet model optic flow and rigid body motion." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/53885.
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The dissertation uses the facet model technique to compute the optic flow field directly from a time sequence of image frames. Two techniques, an iterative and a non-iterative one, determine 3D motion parameters and surface structure (relative depth) from the computed optic flow field. Finally we discuss a technique for the image segmentation based on the multi-object motion using both optic flow and its time derivative.
The facet model technique computes optic flow locally by solving over-constrained linear equations obtained from a fit over 3D (row, column, and time) neighborhoods in an image sequence. The iterative technique computes motion parameters and surface structure using each to update the other. This technique essentially uses the least square error method on the relationship between optic flow field and rigid body motion. The non-iterative technique computes motion parameters by solving a linear system derived from the relationship between optic flow field and rigid body motion and then computes the relative depth of each pixel using the motion parameters computed. The technique also estimates errors of both the computed motion parameters and the relative depth when the optic flow is perturbed.Ph. D.
5
He, Kui. "Effect of body force on turbulent pipe flow." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11845/.
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Two non-equilibrium flows, namely, a transient turbulent pipe flow following a sudden change of flow rate and a turbulent pipe flow subjected to a non-uniform body force are systematically studied using direct numerical simulation (DNS). It is revealed that the transient response of a turbulent pipe flow to a sudden increase of flow rate is a laminar-turbulent transition. The response of the flow is not a progressive evolution from the initial turbulence to a new one, but shows a three-stage development, i.e., a pre-transitional stage, a transitional stage and a fully developed stage. This is similar to a typical boundary layer bypass transition with three characteristical regions, i.e., pre-transitional region, transitional region and fully developed region. The results are carefully compared with those of a channel flow of He & Seddighi, J. Fluid Mech. (2013). The statistical and instantaneous behaviours of the two flows are similar in the near-wall region, but there are distinctive differences in the centre of the flow. The transitional critical Reynolds numbers for the transient pipe and channel flow are predicted with the same correlation. The possibility of predicting such transient flow using transitional turbulence modelling, such as γ-Reθ SST, is discussed. The effect of the rate of the change of the flow is also examined. In a fast ramp-up case, the flow is similar to that of a step-change flow, also showing a three-stage development. In a slow ramp-up case, the flow response is not as clear as that in a fast ramp-up case but the main features of the response are similar. A series prescribed body forces are used to emulate flows, which contain features similar to those of real buoyancy-aiding flows. It has been shown that the body force with various amplitudes, coverages and distribution profiles can systematically influence the base flow. The body force influenced flows are classified into four groups, namely, partially laminarized flow, 'completely' laminarized flow, partially recovery flow and strongly recovery flow. A new perspective has been proposed for the partially laminarized flow and 'completely' laminarized flow. In contrast to the conventional view, which views the flow to be re-laminarized, the new theory proves that the turbulence of the flow remains largely unchanged following the imposition of the body force. The body force induces a perturbation flow, which lowers the pressure gradient required to maintain the same Reynolds number. This is the mechanism of turbulence relaminarization. The recovery flows show two-layer turbulence. The outer turbulence is generated by a shear layer in the core of the flow caused by the body force. The inner turbulence is generated in the wall layer, increasing with the outer turbulence. The two layers of turbulence increase hand in hand. The stronger the outer generation, the stronger the inner recovery is. The inner turbulence structure is very similar to an equilibrium turbulent flow. In the region very close to the wall (y+0 < 10), it shows similar budget patterns and flow structures (sweeps and ejections) to those of the base flow. In the region between y+0=10 and the new shear layer, the turbulence structure is complicated, where the turbulence is a mixture of the inner turbulence and the outer turbulence. The transient response of the turbulence to the imposition of a non-uniform body force has been examined. The turbulence decay and recovery features of the flows with non-uniform body forces are studied in detail. It is found that the transient features are mainly determined by the total amplitude of the body force. The higher the amplitude, the stronger the turbulence decay is. In some flows, the near wall turbulence is recovered toward the later stage of the transient process. Under such condition, the inner self-sustaining regeneration interacts strongly with the turbulence from the outer shear layer.
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Pareshkumar, Gordhandas Pattani. "Nonlinear analysis of rigid body-viscous flow interaction." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/27181.
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This thesis decribes the work on extending the finite element method to cover interaction between viscous flow and a moving body. The problem configuration of interest is that of a two-dimensional incompressible flow over a solid body which is elastically supported or alternatively undergoing a specified harmonic oscillation. The problem addressed in this thesis is that of an arbitrarily shaped body undergoing a simple harmonic motion in an otherwise undisturbed fluid. The finite element modelling is based on a velocity-pressure primitive variable representation of the Navier-Stokes equations using curved isoparametric elements with quadratic interpolation for velocities and bilinear for pressure. The problem configuration is represented by a fixed finite element grid but the body moves past the grid. The nonlinear boundary conditions on the moving body are obtained by expanding the relevant body boundary terms to first order in the body amplitude ratio to approximate the velocities at the finite element grid points. The method of averaging is used to analyse the resulting periodic motion of the fluid. The stability of the periodic solutions is studied by introducing small perturbations and applying Floquet theory.
Numerical results are obtained for three different body shapes, namely, (1) a square body oscillating parallel to one of its sides, (2) an oscillating circular body and (3) a symmetric Joukowski profile oscillating parallel to the line of symmetry. The latter case is considered to investigate the flow pattern around an asymmetrical body. In all cases, results are obtained for steady streaming, instantaneous velocity vectors in the fluid domain, added mass, added damping, added force and stability of the flow. A comparision is made between the numerical and published experimental steady streamlines. Very good agreement is obtained for the basic nonlinear phenomenon of steady streaming.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
7
Nicolaou, D. "Internal waves around a moving body." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383254.
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Connell, Benjamin S. H. "Numerical investigation of the flow-body interaction of thin flexible foils and ambient flow." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35706.
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Thesis (Ph. D. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 267-274).
Flow-induced flapping of flexible thin bodies is oft observed in our day-to-day lives in phenomena such as flag flapping, and is important in a host of engineering applications. Despite its prevalence, however, this fundamental problem of fluid-structure interaction is not very well understood. Use of flexible control surfaces in ocean vehicles holds promise for achieving the efficiencies and maneuverability of waterborne animals, but requires an understanding of the natural responses of flexible foils and the associated physics. Likewise, industrial applications such as the handling of flexible textiles and paper benefit from improved understanding of the relationship between the system parameters and the anticipated response of the body. The present work furthers the understanding of the passive flapping problem through the development and application of a nonlinear computational simulation capability. Examining the flapping problem over a wide range of system parameters and responses indicates the influences and trends of the system behavior, and allows investigation of relevant physical mechanisms in the fluid-structure interaction.
(cont.) To pursue this study, the fluid-structure direct simulation (FSDS) capability is developed, coupling a Navier-Stokes fluid-dynamic solver to a geometrically nonlinear thin-body structural solver. The coupled solver is developed in both two dimensions and three dimensions, where the thin foil is free to spanwise variation as a nonlinear plate. The viscous fluid dynamics are solved on a moving grid fitted to the structural boundary. Fluid forcing to the structure is calculated at this boundary and used as external forcing to the structural equations of motion. As both the fluid dynamic and structural solvers use fully implicit backwards difference time integration, they must be solved simultaneously. An iterative approach is used for the simultaneous solution, converging to structural equilibrium with a divergence-free flow field. A detailed study of the canonical problem of a thin flexible foil in uniform flow is first performed in two dimensions, using linear analysis and FSDS simulation, and examining the stability and natural responses as a function of the system parameters. The three relevant nondimensional parameters governing the problem are the Reynolds number, Re = VL/v; the structure-to-fluid mass ratio, ... ;
(cont.) and the nondimensional bending rigidity, ... The flag problem, which has been the subject of recent experimental and numerical studies, is at the limit of vanishing bending rigidity, where the physics are governed by the two parameters of Reynolds number and mass ratio. We find stability of the system to increase for decreasing Reynolds number, decreasing mass ratio, and increasing bending rigidity. Three distinct regimes of response are observed, (I) fixed-point stability, (II) limit-cycle flapping, and (III) chaotic flapping, in order of decreasing stability. Characteristics of the dynamic interaction between the fluid and structure are considered with the modal response and associated flow wake, and the mechanics of the significant physical phenomena of stability hysteresis and chaotic snapping are investigated in detail. The linear analysis is extended to examine the stability of the three-dimensional problem and indicates an increase in stability with spanwise wavenumber. Simulations confirm the relationship between spanwise variation and stability, and display the three-dimensional flapping response and associated wake.
(cont.) Fundamental three-dimensional modes of a spanwise standing wave, spanwise traveling wave, and two-dimensional flapping are revealed along with their unique wake patterns, and the evolution of the system to hybrid modes is displayed. Through this work, we identify for the first time the relationship between the relevant nondimensional parameters of the passive flapping system and the response through the three distinct regimes. The comprehensive study provides new understanding of the physical mechanisms associated with the regime transitions and the flapping dynamics, including chaotic snapping. FSDS allows a first investigation of the three-dimensional passive flapping problem, identifying the stability characteristics and modes of response. The detailed examination and enhanced understanding of the relationship between the relevant nondimensional parameters and the kinematics, forcing, and wake characteristics for the system of a passive flexible foil in uniform flow allows for better engineering of flexible foils for both passive and active applications.
by Benjamin S.H. Connell.
Ph.D.in Ocean Engineering
9
Castledine, Andre J. "Investigation of the fluid flow around blunt body samplers." Thesis, University of Leeds, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305756.
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Whiteman, Jacob T. "Active Flow Control Schemes for Bluff Body Drag Reduction." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1452184221.
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Moorty, Shashi. "A parametric study of rigid body-viscous flow interaction." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26723.
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This thesis presents the numerical solution for two-dimensional incompressible viscous flow over a rigid bluff body which is elastically supported or alternately undergoing a specified harmonic oscillations. Solutions for the related associate flow in which the body is at rest in a two-dimensional incompressible time-dependent viscous flow have also been -obtained. This work is an extension of the work by Pattani [19] to include the effect of a steady far field flow on an oscillating body.
The numerical model utilizes the finite element method based on a velocity-pressure primitive variable representation of the complete Navier-Stokes equations. Curved isoparametric elements with quadratic interpolation for velocities and bilinear interpolation for pressure are used. Nonlinear boundary conditions on the moving body are represented to the first order in the body amplitude parameter. The method of averaging is used to obtain the resulting periodic motion of the fluid. Three non-dimensional parameters are used to completely characterise the flow problem: the frequency Reynolds number Rω , the Reynolds number of steady flow Rℯ₁ and the Reynolds number for time-dependent flow Rℯ₂.
Numerical results are obtained for a circular body, a square body and an equilateral triangular body. A parametric study is conducted for different values of the Reynolds numbers in the viscous flow regime. In all cases, results are obtained for streamlines, streaklines, added mass, added damping, added force and the drag coefficients. The limiting cases of steady flow over a fixed body and an oscillating body in a stationary fluid are checked with known results. Results for the associated flow are also obtained. The transformations derived, between the two associated flows are checked. Good agreement is obtained between the present results and other known results.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
12
De, Vecchi Adelaide. "Wake dynamics of flow past a curved circular cross-section body under cross-flow vibration." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502910.
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Mack, Christoph. "Global stability of compressible flow about a swept parabolic body." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005752.
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Kadja, M. "Computation of recirculating flow in complex domains with algebraic Reynolds stress closure and body fitted meshes." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384419.
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Hinson, Bryan C. "Parametric exploration of wing-body junction flow using computational fluid dynamics." Thesis, Wichita State University, 2012. http://hdl.handle.net/10057/5597.
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In this thesis, wing-body junction flow is studied parametrically using computational fluid dynamics (CFD) in an attempt to understand the effects of junction flow on aircraft drag, with a focus on application to large business jet or commercial transport aircraft. A CFD methodology is validated against detailed experimental data for a junction flow. The same methodology is validated against a high Reynolds number, transonic wind tunnel test of a wing. CFD results for a wing with a leading-edge strake (an aerodynamic surface designed to reduce flow separation, thereby reducing aircraft drag) are presented and compared to experimental data, and the effects of scaling this strake are explored using CFD. The effectiveness of the strake on a swept wing is compared to the same for a straight wing. Finally, the results from this parametric study are successfully applied to sizing a leading-edge strake for a commercial transport aircraft. It is demonstrated that a systematic approach, starting with a simple validated model and building up to a realistic aircraft application, can build confidence in CFD results.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
16
Blank, S. C. "Passive techniques for controlling the flow in supersonic wing - body junctions." Thesis, Cranfield University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260376.
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Shiels, Doug Leonard Anthony. "Simulation of controlled bluff body flow with a viscous vortex method /." Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-03162004-133652.
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Reichstein, Georg A. "Estimation of axial compressor body forces using three-dimensional flow computations." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/47806.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Includes bibliographical references (p. 77-78).
This thesis presents an examination of body force distributions in a single stage low speed compressor. The body force distributions are developed using two different computational procedures, an axisymmetric streamline curvature calculation and an unsteady, three-dimensional flow simulation. A two-dimensional body force representation is defined as a benchmark to evaluate the departures of the computed forces from two-dimensional behavior. The most important contribution to this departure (for both the streamline curvature calculation and the three-dimensional simulation) is identified as the change in streamtube height across the blade rows. The magnitude of the departures increase with blade loading and, for the compressor examined, are smaller than five per cent of the two-dimensional estimate at design but show values up to 50 per cent near stall.
by Georg A. Reichstein.
S.M.
19
Jain, Sunny. "Hypersonic nonequilibrium flow simulations over a blunt body using bgk simulations." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2406.
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Dewitz, Michael B. "The effect of a fillet on a wing/body junction flow." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43843.
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Yeung, Anthony Kwok-Cheung. "Entry flow problem of a liquid body into a suction pipette." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26754.
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The mathematical problem of the pipette aspiration of a liquid sphere is studied in the low Reynolds number limit. Two distinct models are proposed for the deforming body. They are: 1) a liquid droplet of constant viscosity, and 2) a viscoelastic cortex encapsulating an inviscid interior. These models represent energy dissipation distributed in the interior and on the surface of the body, respectively. Because the in-flow rates vary differently with the pipette size for the two models, this is suggested as a means of experimentally identifying the dominant region of viscous dissipation, and thus provide insight into the internal structure of the test sample.
For the droplet problem, the linear Stokes equations are solved in the interior of the deforming body. The solutions, for some specified stress boundary conditions on a sphere, can be expressed as infinite sums of Legendre polynomials.
In solving the surface flow problem, the complexities of the equations necessitate approximate solutions by computational means. A numerical procedure is developed which compares well with analytical results when the latter is available.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Rinehart, Christopher S. "Aerodynamic forces induced by controlled transitory flow on a body of revolution." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42830.
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The aerodynamic forces and moments on an axisymmetric body of revolution are
controlled in a low-speed wind tunnel by induced local flow attachment. Control is
effected by an array of aft-facing synthetic jets emanating from narrow, azimuthally
segmented slots embedded within an axisymmetric backward facing step. The actuation
results in a localized, segmented vectoring of the separated base flow along a rear Coanda
surface and induced asymmetric aerodynamic forces and moments. The observed effects
are investigated in both quasi-steady and transient states, with emphasis on parametric
dependence. It is shown that the magnitude of the effected forces can be substantially
increased by slight variations of the Coanda surface geometry. Force and velocity
measurements are used to elucidate the mechanisms by which the synthetic jets produce
asymmetric aerodynamic forces and moments, demonstrating a novel method to steer
axisymmetric bodies during flight.
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Minelli, Guglielmo. "A LES study of a modified Ahmed body geometry." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/4604/.
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A numerical study using Large Eddy Simulation Coherent Structure Model (LES-CSM), of the flow around a simplified Ahmed body, has been done in this work of thesis.
The models used are two salient geometries from the experimental investigation performed in [1], and consist, in particular, in two notch-back body geometries.
Six simulation are carried out in total, changing Reynolds number and back-light angle of the model’s rear part. The Reynolds numbers used, based on the height of the models and the free stream velocity, are Re = 10000, Re = 30000 and Re = 50000. The back-light angles of the slanted surface with respect to the horizontal roof surface,
that characterizes the vehicle, are taken as B = 31.8◦ and B = 42◦ respectively.
The experimental results in [1] have shown that, depending on the parameter B, asymmetric and symmetric averaged flow over the back-light and in the wake for a symmetric geometry can be observed.
The aims of the present work of master thesis are principally two.
The first aim is to investigate and confirm the influence of the parameter B on the presence of the asymmetry of the averaged flow, and confirm the features described in the experimental results. The second important aspect is to investigate and observe the influence of the second variable, the Reynolds number, in the developing of the
asymmetric flow itself.
The results have shown the presence of the mentioned asymmetry as well as an influence of the Reynolds number on it.
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橋本, 敦., Atsushi HASHIMOTO, 貴広 小林, Takahiro KOBAYASHI, 佳朗 中村, and Yoshiaki NAKAMURA. "遷音速鈍頭2次元物体でのタブによるベース抵抗低減." 日本航空宇宙学会, 2008. http://hdl.handle.net/2237/13873.
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Fleming, Jonathan Lee. "An experimental study of a turbulent wing-body junction and wake flow." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08222009-040300/.
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Meneghini, Julio Romano. "Numerical simulation of bluff body flow control using a discrete vortex method." Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/8441.
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Khan, H. M. "Experimental verification and computational comparison of an Oseen flow slender body theory." Thesis, University of Salford, 2010. http://usir.salford.ac.uk/26758/.
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This project further develops recent work which proposes a new theory that predicts the forces on slender bodies, and slender and thin wings. A steady, incompressible uniform field for high Reynolds numbers (although aerodynamically low-speed) is assumed, through which a slender body with elliptic cross-section moves at a steady constant velocity. The forces on this manoeuvring slender body through fluid at high Reynolds number have been determined in this work. The theory is developed within Oseen flow and models the viscous and vortex wake. The newly developed theory has been applied to cylinder bodies with elliptic cross-section and comparison with experiments and standard Alien and Perkins method has been made. The numerical analysis using ANSYS CFX has been done. The comparison between new theory, experimental results, and numerical analysis has also been done in this work. Xlll
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Kwong, C.-M. "Three-dimensional separated flow prediction on fusiform body using Euler and boundary layer methods." Thesis, University of Salford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234623.
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Sonenblum, Sharon Eve. "Biomechanical responses to seated full body tilt and their relationship to clinical application." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31815.
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Thesis (Ph.D)--Bioengineering, Georgia Institute of Technology, 2010.Committee Chair: Sprigle, Stephen; Committee Member: Brani Vidakovic; Committee Member: Charlie Lachenbruch; Committee Member: John L. Lin; Committee Member: Rudy Gleason. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Akers, Walter John. "Flourescent molecular rotors as mechanosensors in biofluids." Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4114.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2005.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 19, 2007) Vita. Includes bibliographical references.
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Lim, Junghwan 1961. "Evaluation of temperature fields in two dynamic phantoms heated by the ferromagnetic implant hyperthermia." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276908.
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Two experimental dynamic phantoms have been used for studying temperature distributions induced by interstitial ferromagnetic implant hyperthermia at various blood perfusions, Curie point implants, and input power levels. One of the phantoms is an axially perfused hollow cylinder filled with 3 mm diameter glass beads, and the other is a similar cylinder model that is radially perfused. Analytic models have been developed for evaluating temperature profiles within the two phantoms. Experimental results from the phantoms compare reasonably well with the analytical results. A qualitative comparison is made between thermal profiles derived from both a convection energy equation, for a homogeneous porous medium, and a bioheat transfer equation. The adequacy of using a porous material for simulating living tissue is discussed. Parametric studies showing the effects of various implant parameters such as Curie point and applied power are analyzed.
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Ham, Franklin Edward. "Flow simulation using the finite analytic method with multi-block body-fitted grids." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0014/MQ31580.pdf.
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Lin, Xiang Wen. "Numerical study of unsteady heat transfer and fluid flow over a bluff body." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341453.
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Österberg, David. "Multi-Body Unsteady Aerodynamics in 2D Applied to aVertical-Axis Wind Turbine Using a Vortex Method." Thesis, Uppsala universitet, Elektricitetslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-131932.
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Vertical axis wind turbines (VAWT) have many advantages over traditional Horizontalaxis wind turbines (HAWT).One of the more severe problem of VAWTs are the complicated aerodynamicbehavior inherent in the concept. Incontrast to HAWTs the blades experience varying angle of attack during its orbitalmotion. The unsteady flowleads to unsteady loads, and hence, to increased risk for problems with fatigue.A tool for aerodynamic analysis of vertical axis wind turbines has been developed.The model, a Discrete vortex method, relies on conformal maps to simplify the taskto finding the flowaround cylinders. After the simplified problem has been solved with Kutta condition,using the Fast Fouriertransform, the solution is transformed back to the original geometry yielding the flowabout the turbine.The program can be used for quick predictions of the aerodynamic blade loads fordifferent turbines allowing the method to be validated by comparing the predictionsto experimental data from realvertical axis wind turbines. The agreement with experiment is good.
35
Wiratni, Wiratni. "Basic theory and experimental approach to characterize flow and fracture properties of fine powder bulk body." Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=3159.
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Thesis (Ph. D.)--West Virginia University, 2003.Title from document title page. Document formatted into pages; contains xiii, 122 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 100-106).
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Williams, Franklin Pierce. "The numerical simulation of flow through an axisymmetric aortic heart valve." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/9378.
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Eferemo, Daniel. "Numerical investigation of the convective heat transfer coefficient of the human body using a representative cylindrical model." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/26904.
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The principal objective of this study is to investigate, develop and verify a framework for determining the convective heat transfer co-efficient from a cylindrical model that can easily be adaptable to more complex geometry - more specifically the human body geometry. Analysis of the model under forced convection airflow conditions between the transition velocity of about 1m/s - calculated using the Reynolds number - up until 12m/s were carried out. The boundary condition, however, also included differences in turbulence intensities and cylinder orientation with respect to wind flow (seen as wind direction in some texts). A total of 90 Computational Fluid Dynamic (CFD) calculations from these variations were analysed for the model under forced convective flow. Similar analysis were carried out for the model under natural convection with air flow velocity of 0.1m/s. Here, the temperature difference between the model and its surrounding environments and the cylinder orientation with respect to wind flow were varied to allow for a total of 15 CFD analysis. From these analysis, for forced convection, strong dependence of the convective heat transfer coefficient on air velocity, cylinder orientation and turbulence intensity was confirmed. For natural convection, a dependence on the cylinder orientation and temperature difference between the model and its environment was confirmed. The results from the CFD simulations were then compared with those found in texts from literature. Formulas for the convective heat transfer coefficient for both forced and natural convection considering the respective dependent variables are also proposed. The resulting formulas and the step by step CFD process described in this thesis provides a framework for the computation of the convective heat transfer coefficient of the human body via computer aided simulations. This framework can easily be adaptable to the convective heat transfer coefficient calculations of the human body with some geometric modelling adjustments, thus resulting in similar representative equations for a human geometric model.
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Taylor, Ian J. "Study of bluff body flow fields and aeroelastic stability using a discrete vortex method." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/3951/.
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A two dimensional discrete vortex method has been developed to simulate the unsteady, incompressible flow field and aerodynamic loading on bluff bodies. The method has been validated successfully on a range of simple bluff geometries, both stoic and oscillating, and has also been validated on a wider range of problems including static and oscillating suspension bridge deck sections. The results have been compared with experimental data and demonstrate good qualitative and quantitative agreement, and also compare favourably with other computational methods. Most notably, the method has been used to study the aeroelastic stability of a recent bridge deck, with accurate predictions of the critical flutter velocity. The basis of the method is the discretisation of the vorticity field into a series of vortex particles, which are transported in the flow field that they collectively induce. In the method presented herein, the time evolution of the system of particles is calculated by solving the vorticity transport equation in two stages: employing the Biot-Savart law to calculate particle velocities and random walks to simulate flow diffusion. The Lagrangian approach to the calculation avoids the necessity for a calculation grid, and therefore removes some of the problems associated with more traditional grid based methods. These include numerical diffusion and difficulties in resolving small scale vortical structures. In contrast, vortex methods concentrate particles in areas of vorticity, and can provide high quality representations of these small scale structures. Dispensing with a calculation mesh also eases the task of modelling a more arbitrary range of geometries. In particular, vortex methods are well suited to the analysis of moving body problems. Results of the validation exercise are firstly presented for a range of simple bluff geometries to give confidence in the results before moving on to more complex geometries. These results include the effect of incidence on the aerodynamic loading for a stationary square cylinder, and also a study of the effect on aspect ratio for rectangular cylinders. This includes the limiting case of a flat plate. Vortex lock-in is studied on a square cylinder undergoing a forced transverse oscillation, for a range of frequencies and amplitudes. The results in each of these cases are in good agreement with experimental data.
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Johnson, Paula K. "The Effect of Whole Body Vibration on Skin Blood Flow and Nitric Oxide Production." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4120.
Full textAbstract:
Background: Vascular dysfunction due to hyperglycemia in individuals with diabetes is a factor contributing to distal symmetric polyneuropathy (DSP). Reactive oxygen species (ROS) reduce the bioavailability of nitric oxide (NO), a powerful vasodilator, resulting in reduced circulation and nerve ischemia. Increases in blood NO concentrations and circulation have been attributed to whole body vibration (WBV). The purpose of this study was to the determine the effects of low frequency, low amplitude WBV on whole blood NO concentration and skin blood flow (SBF) in individuals with symptoms of DSP. Research Design and Methods: Ten subjects with diabetes and impaired sensory perception in the lower limbs participated in this cross-over study. Each submitted to two treatment conditions, WBV and sham, with a one week washout period between. Blood draws for NO analysis and Doppler laser image scans of SBF were performed before, immediately after and following a 5 minute recovery of each the treatments. Results: Low frequency, low amplitude WBV vibration significantly increased skin blood flow compared to the sham condition (p=0.0115). Whole blood nitric oxide concentrations did not differ between the WBV and sham condition immediately or 5 minutes post-treatment ( p=0.1813) Conclusions: These findings demonstrate that subjects with diabetes respond to whole body vibration with increased skin blood flow compared to sham condition. The implication is that WBV is a potential non-pharmacological therapy for neurovascular complications of diabetes.
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Hajimirzaie, Seyed Mohammad. "Flow structure in the wake of a low-aspect-ratio wall-mounted bluff body." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2509.
Full textAbstract:
The effects of shape and relative submergence (the ratio of flow depth to obstacle height, d/H) were investigated on the wakes around four different low-aspect-ratio wall-mounted obstacles: semi-ellipsoids with the major axes of the base ellipses aligned in the streamwise and transverse directions, two cylinders with aspect ratios matching the ellipsoids. Wake structure of a fully submerged, spherical obstacle was also investigated in the same flow conditions to provide insight into the flow obstacle interaction with ramification to sediment transport. A low-aspect-ratio semi-ellipsoid was chosen as broad representative of a freshwater mussel projecting from a river bed, and a sphere was employed as representative of a boulder. Two cylinders were used due to their similarity to geometries investigated in other studies. Digital Particle Image Velocimetry and thermal anemometry were used to interrogate the flow. For ellipsoids and cylinders, streamwise features observed in the mean wake included counter-rotating distributions of vorticity inducing downwash (tip structures), upwash (base structures), and horseshoe vortices. In particular, the relatively subtle change in geometry produced by the rotation of the ellipsoid from the streamwise to the transverse orientation resulted in a striking modification of the mean streamwise vorticity distribution in the wake. Tip structures were dominant in the former case while base structures were dominant in the latter. A vortex skeleton model of the wake is proposed in which arch vortex structures, shed from the obstacle, are deformed by the competing mechanisms of Biot-Savart self-induction and the external shear flow. An inverse relationship was observed between the relative submergence and the strength of the base structures for the ellipsoids, with a dominant base structure observed for d/H = 1 in both cases. The wake of the sphere is more complex than ellipsoidal geometries. Streamwise features observed in the mean wake including tip, horseshoe structures, and weak upwash. The shedding characteristics and dynamics of the wake were examined. Weak symmetric shedding was observed in the wakes of streamwise and transverse ellipsoids at d/H = 3.9 while cross-spectral measurements confirmed downstream and upstream tilting of arch structures shed by the transverse and streamwise ellipsoids, respectively. Much weaker peaks in the power spectrum were observed for low- and high-aspect-ratio cylinders. While the dominant Strouhal number remained constant as the relative submergence was reduced to d/H = 2.5 for the ellipsoids, it increased abruptly at d/H = 1 and transitioned to an antisymmetric mode. For sphere geometry at d/H = 3.9, a weak dominant frequency was observed close to obstacle junction and the cross-correlation function for symmetric measurements in the wake indicates symmetric shedding. These results demonstrate a means by which to achieve significant modifications to flow structure and transport mechanisms in the flow.
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Nguyen, Matthew P. "Investigation of the Under-Body Flow Field of a Prototype Long-Range Electric Vehicle." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2060.
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This thesis presents changes to the design of the Prototype Vehicles Laboratory (PROVE Lab) Endurance Car, an electric car intended to break the Guinness World Record for the single-charge range of an electric vehicle. The design range is 1609.34 km, however at the design velocity of 104.6 kph, the drag is 196 N; which requires more battery capacity than the 100 kWh maximum of the baseline model. With a fixed frontal area, drag reduction can come from lowered velocity or reduced CD. CD reduction is attempted in four ways: side skirts between the fenders, a raised ride height, an elongated diffuser, and a widened rear. Side skirts were added to move pressure recovery from the front ducts to the diffuser by lowering the pressure between the side skirts; this had the intended effect but increased the tendency of the flow to separation in the already-separated areas. There was no significant change in pressure drag, but the shear drag and downforce increased. The ride height was increased to reduce drag and downforce; this change did not have a significant effect on the resultant forces and the separation on the underbody was largely unchanged. The diffuser was extended by 12.7 cm without modifying the aspect ratio, to lower the divergence angle. The pressure and shear drag reduced by 8 N and 1.1 N, respectively, and downforce decreased by 80 N, but separation in the diffuser was not eliminated. Finally, the fourth strategy reduced the divergence angle to approximately zero degrees by widening the center of the vehicle. This decreased pressure drag by 13 N and downforce by 188 N. Additionally, this strategy allows a larger 180 kWh battery, which permits 1609.34 km of range at 104.6 kph.
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Stenius, Magnus. "The body in pain and pleasure : an ethnography of mixed martial arts." Doctoral thesis, Umeå universitet, Institutionen för kultur- och medievetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-107527.
Full textAbstract:
Mixed Martial Arts (MMA) is a sport on the rise within the field of martial arts in which competitors fight in a cage and utilize full-contact movements using their fists, elbows, and knees as well as kicks, other strikes, and submission techniques to defeat their opponents. MMA has become a modern social movement in combat sports that has become globalized in a short time and is the fastest growing sport in the world. MMA encompasses disciplines from various martial arts and Olympic sports such as boxing, kickboxing, karate, kempo, jiu-jitsu, Muay Thai, tae kwon do, wrestling, sambo, judo, etc. The rounds are five minutes in length and there are typically three rounds in a contest, unless it is a championship fight in which case the contest lasts five rounds. The aim of this study is to analyze the bodily constructions and productions within the MMA culture and especially the constructed human violence associated with the sport. Based on autoethnographic participation in three Swedish MMA clubs, as well as shorter fieldwork case studies conducted in Hong Kong, Japan, Macau, Brazil, and the US, this thesis investigates the interrelationship between MMA, excitement, sensationalism, and the spectacular physical violence that stains the participants’ bodies. Concepts taken from performance ethnography are applied to an analysis of what is reconstructed bodily. This is followed by an analysis that attempts to outline what body-violence means and how this understanding of the informants’ bodies, as well as of the researcher’s body-knowledge, reconstructs the definitions of MMA. A phenomenological approach to the concept of fighting is also included in relation to the MMA landscape. Thus, I present how the body learns the cultural enactments in fighting and how these forces shape the fighters’ gender, habitus, and way of resisting the discourse of critical opinions on MMA practice. Moreover, in trying to grasp the inner sense of MMA, I argue that the physical phenomenon of MMA is dependent on an intersubjective engagement and on the control of one’s inner coordination, which teaches a fighter how to deal with power, pain, suffering, aggression, and adrenaline flows. Keywords: abject, adrenaline, anthropology, athletes, autoethnography, body, combat arts, culture, desire, embodied, enculturation, ethnology, fieldwork, field-making, flow, fighting, full-contact, gender, harm, homosociality, intercultural, interobject, intersubjectivity, martial arts, materiality, masculinity, MMA, method, pain, personal, performance, performativity, phenomenology, pleasure, posthuman, postmodern, power, ritual, risk-taking, rush, self-reflexive, sportive, sport, stained, struggle, suffering, thrill, UFC, violence.
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Stewart, Ian. "Experimental verification and comparison of non-intrusive methods for detecting laminar-turbulent transition on a natural laminar flow axisymmetric body." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245394.
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Qin, Lihai. "Vorticity Modeling for the Flow Over Surface-Mounted Prisms." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31859.
Full textAbstract:
Vorticity modeling is used to simulate the flow around a surface-mounted prism. The objective is
to examine whether vorticity modeling can give satisfactory information about surface pressure
fluctuations which are mostly due to the outer or inviscid flow. Differences between results
obtained with vorticity modeling and what one should expect from DNS and LES are pointed
out. These include the difference between the governing equations, the shortcomings of having a
2-D simulation and the realization of introducing and convecting vorticity to simulate some
turbulence aspects. All necessary details needed for the setup of vorticity modeling for complex
flows, such as the one considered here are given. These details include choice of elements, the
calculation of velocities, the application of boundary conditions and calculation of pressure. The
numerical procedure and our use of parallelization in the code are explained. The results
presented on velocity magnitude, vorticity and pressure show important characteristics of the
flow field in terms of interaction of positive and negative vorticities and their effects on the
surface pressure. The calculated peak and mean values for the pressure coefficients at the leading
edge are close to those measured in separating flows over prisms.Master of Science
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Jerram, Neil. "The effect of a group of obstacles on flow and dispersion over a surface." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/244799.
Full textAbstract:
In this thesis we develop analytical models for boundary layer flow through a two dimensional group of obstacles , based on the "distributed force" model. An array of obstacles is represented as a region without solid obstructions but with distributed body forces resisting the flow. Linear analyses are presented of inviscid, laminar (or constant eddy viscosity) and turbulent flow through such force distributions. For any group of obstacles, we show how to calculate the model force distribution which becomes the input for the linear analyses. The entire procedure can be iterated to take account of non-linear upstream sheltering effects. In general the model distributed force integrates to equal the actual force exerted by obstacles on the flow divided by the fraction of the array volume not occupied by solid obstacles. Turbulent stresses are modelled using a mixing length that is uniform up to a specified height and increases linearly above. Our physical arguments for a displaced mixing length above the obstacles provide an explanation for the observed coincidence between displacement height and the level of mean momentum absorption. Comparisons of the turbulent analysis results with numerical simulations and experimental data show very encouraging agreement and so support both the distributed force model and the assumptions of the mathematical analysis. From the results of the turbulent flow analysis, effective roughness and displacement heights can be calculated for the flow above the obstacles. When the displacement of the turbulent mixing length is correctly taken into account, the calculated parameters are comparable with those obtained experimentally. An analysis of plume dispersion through a group of obstacles shows how the flow field results can be applied to practical situations, and highlights the dominant effect of enhanced perturbation shear stress, especially in the obstacle roof top layer, on changes to the downstream evolution of the plume.
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Shao, Yan-Lin. "Numerical Potential-Flow Studies on Weakly-Nonlinear Wave-Body Interactions with/without Small Forward Speeds." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11529.
Full textAbstract:
A two-dimensional Quadratic Boundary Element Method (QBEM) and a three-dimensional cubic Higher-order Boundary Element Method (HOBEM) are developed to study respectively the twodimensional and three-dimensional weakly-nonlinear wave-body interactions with/without forward speed within potential flow theory of an incompressible liquid. A direct method based on a triangular polar-coordinate system transformation for the evaluation of the Cauchy Principle Value (CPV) integrals for the diagonal terms of the influence matrix in the 3D HOBEM is presented. A numerical module based on the Fast Multipole Method (FMM) is developed, which can be used as an option to speed up the present 3D HOBEM solver. Both the operation count and the required memory of a FMM accelerated BEM is asymptotically O(N), where N is the total number of the unknowns. Suggestion on the selection of a proper matrix solver for a specific problem is given. A new approach based on domain decomposition using body-fixed coordinate system in the inner domain and the inertial reference frame in the outer domain is proposed for the weakly-nonlinear wave-body analysis. Consistent theoretical description of the new method based on second-order theory is presented. The new method does not require any derivatives on the right-hand sides of the body boundary conditions and thus avoid the mj -like terms and their derivatives. Furthermore, because the body boundary condition is formulated on the instantaneous position of the body, the resulting integral equations are valid for both smooth bodies and bodies with sharp corners. In order to improve the convergence of the second-order forces/moments on a body with sharp corners in the near-field approach, a re-formulation of the quadratic force is suggested. This re-formulation transfers the integrals on the body into the sum of two groups of integrals. The first group contains integrals on body surface with integrands whose singularities are weaker than that of the velocity square. The second group consists of regular integrals on the inner free surface and the control surface in the inner domain. A two-dimensional third-order numerical wave tank (NWT) is developed. The effect of the Stokes drift in the second-order solution is discussed. A two-time scale approach is proposed as a secularity (solvability) condition in order to avoid unphysical third-order results. The numerical results for the second-order diffraction/radiation of a horizontal semi-submerged circular cylinder are verified by some other analytical and numerical results. Comparisons with the experimental results are also made. The second-order wave-body interaction with/without the presence of a small forward speed for a three-dimensional floating body is studied by both the traditional method (if applicable) with a formulation in the inertial coordinate system and the new method with a formulation in the body-fixed coordinate system near the body. Both bodies without sharp corners and a truncated vertical circular cylinder with sharp corners are studied. Comparisons between the present numerical results with some other analytical and numerical results (if any) show good agreement. The influences of a small forward speed on the second-order wave loads on floating bodies are investigated. The complete third-order wave diffraction of a stationary three-dimensional body is studied by the time-domain HOBEM, which means that the solution contains not only the triple-harmonic effect but also the third-order contribution with fundamental frequencies of the incident waves. Careful convergence studies and alternative way of calculating the force have been made with very satisfactory results.
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Kim, Sangho. "Observation and measurements of flow structures in the stagnation region of a wing-body junction." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08222008-063435/.
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Mulcahey, Thomas Ian. "Convective instability of oscillatory flow in pulse tube cryocoolers due to asymmetric gravitational body force." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51808.
Full textAbstract:
Pulse tube cryocoolers (PTCs) are among the most attractive choices of refrigerators for applications requiring up to 1 kW of cooling in the temperature range of 4-123 K as a result of the high relative efficiency of the Stirling cycle, the reliability of linear compressors, and the lack of cryogenic moving parts resulting in long life and low vibration signature. Recently, PTCs have been successfully used in applications in the 150 K range, extending the useful range of the device beyond the traditional cryogenic regime. A carefully designed cylindrical cavity referred to as the pulse tube replaces the mechanical expander piston found in a Stirling machine. A network consisting of the pulse tube, inertance tube, and surge volume invoke out-of-phase pressure and mass flow oscillations while eliminating all moving parts in the cold region of the device, significantly improving reliability over Stirling cryocoolers. Terrestrial applications of PTCs expose a fundamental flaw. Many PTCs only function properly in a narrow range of orientations, with the cold end of the pulse tube pointed downward with respect to gravity. Unfavorable orientation of the cold head often leads to a catastrophic loss of cooling, rendering the entire cryocooler system inoperable. Previous research indicates that cooling loss is most likely attributed to secondary flow patterns in the pulse tube caused by free convection. Convective instability is initiated as a result of non-uniform density gradients within the pulse tube. The ensuing secondary flow mixes the cryogen and causes enhanced thermal transport between the warm and cold heat exchangers of the cryocooler.
This study investigates the nonlinear stabilizing effect of fluid oscillation on Rayleigh-Bénard instability in a cryogenic gas subject to misalignment between gravitational body force and the primary flow direction. The results are directly applicable to the flow conditions frequently experienced in PTCs. Research has shown that the convective component can be minimized by parametrically driven fluid oscillation as a result of sinusoidal pressure excitation; however, a reliable method of predicting the influence of operating parameters has not been reported. In this dissertation, the entire PTC domain is first fully simulated in three dimensions at various angles of inclination using a hybrid method of finite volume and finite element techniques in order to incorporate conjugate heat transfer between fluid domains and their solid containment structures. The results of this method identify the pulse tube as the sole contributor to convective instability, and also illustrate the importance of pulse tube design by incorporating a comparison between two pulse tubes with constant volume but varying aspect ratio. A reduced domain that isolates the pulse tube and its adjacent components is then developed and simulated to improve computational efficiency, facilitating the model’s use for parametric study of the driving variables. A parametric computational study is then carried out and analyzed for pulse tubes with cold end temperatures ranging from 4 K to 80 K, frequencies between 25-60 Hz, mass flow - pressure phase relationships of -30◦ and +30◦, and Stokes thickness-based Reynolds numbers in the range of 43-350, where the turbulent transition occurs at 500.
In order to validate the computational models reported and therefore justify their suitability to perform parametric exploration, the CFD codes are applied to a commercially developed single stage PTR design. The results of the CFD model are compared to laboratory-measured values of refrigeration power at temperatures ranging from 60 K to 120 K at inclination angles of 0◦ and 91◦. The modeled results are shown to agree with experimental values with less than 8.5% error for simulation times of approximately six days using high performance computing (HPC) resources through Georgia Tech’s Partnership for Advanced Computing (PACE) cluster resource, and 10 days on a common quad-core desktop computer. The results of the computational parametric study as well as the commercial cryocooler data sets are compiled in a common analysis of the body of data as a whole. The results are compared to the current leading pulse tube convective stability model to improve the reliability of the predictions and bracket the range of losses expected as a function of pulse tube convection number. Results can be used to bracket the normalized cooling loss as a function of the pulse tube convection number NPTC. Experimental data and simulated results indicate that a value of NPTC greater than 10 will yield a loss no greater than 10% of the net pulse tube energy flow at any angle. A value of NPTC greater than 40 is shown to yield a loss no greater than 1% of the net pulse tube energy flow at all angles investigated.
The computational and experimental study completed in this dissertation addresses static angles of inclination. Recent interest in the application of PTCs to mobile terrestrial platforms such as ships, aircraft, and military vehicles introduces a separate regime wherein the angle of inclination is dynamically varying. To address this research need, the development of a single axis rotating cryogenic vacuum facility is documented. A separate effects apparatus with interchangeable pulse tube components has also been built in a modular fashion to accommodate future research needs.
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House, James R. "An investigation into the use of the limbs as sites for body cooling and the influence of skin blood flow on body cooling rates." Thesis, University of Portsmouth, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438815.
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Ma, Ye, and 马烨. "Lagrangian mass transport induced by wave motions in biological systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hdl.handle.net/10722/205828.
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