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1 
The theory and numerical simulation of nonlocal mixinglength convection.Grossman, Scott Alan January 1992 (has links)
Local convection theory makes the unphysical prediction that turbulent mixing terminates at the Schwarzschild stability boundary, and existing nonlocal convection theories have been criticized by Renzini (1987). Since the size of convecting cores bears upon stellar structure and evolution, a selfconsistent treatment of nonlocal convection is needed. We have developed a theory of nonlocal mixinglength convection based upon a Boltzman transport theory for subsonic, turbulent fluid elements. The momentum and thermal energy excesses of fluid elements are dissipated on the scale of a mixing length. The distribution function, f(t,z,v,T), which is the mass density per velocitytemperature phase space volume, evolves according to the Boltzmann equation. The minimal nonlocal theory is obtained by taking moments of the Boltzmann equation, up to third order. The local limit of the moment equations reduces to standard mixinglength theory. We extend this moment method to local convection in a composition stratified fluid by considering the evolution of the distribution function, f(t,z,v,T,μ), in velocitytemperaturemolecular weight phase space. The stability criteria for convection, semiconvection, and saltfinger instability are derived. To determine closure approximations and evaluate the validity of the moment theory, we have developed an algorithm called Generalized Smooth Particle Hydrodynamics (GSPH) that numerically simulates convection. The vertical structure of the background fluid is calculated by SPH averaging of particles on a grid. Forces on particles are calculated from the background grid and from the local deviations between particles and grid. Particles move vertically only, but the local deviation forces, which account for turbulent losses of momentum and energy, arise from horizontal interactions. GSPH simulations show that the fourth moments are approximately proportional to squares of the second moments in unstable regions, with a proportionality constant between 2 and 4. With this closure approximation, we show that solutions of the moment equations agree well with GSPH results. The closure relations lead to nearly correct second moments, even in overshooting regions where the closure approximations are poor. GSPH simulations of convective overshooting in plane parallel and spherical geometry typically give overshooting distances in the range dₒᵥₑᵣ ≈ 1  2ℓ(M). We discuss improvements that we would like to make to the GSPH code and to the analytic work to obtain more precise answers that are directly relevant to realistic stars.

2 
Numerical analysis of critical field functions for thermal convection in vertical or quasivertical Darcy flow slabsShyu, Chuen Tien 26 April 1979 (has links)
The numerical analysis of thermal convection in porous media,
heated from below, and assuming Darcy flow conditions, involves the
solving of a set of nonlinear equations for the temperature and flow
fields. The condition of criticality determining the onset of convection
is obtained by linearization and the solving of an eigenvalue problem
of the fourth order. The smallest eigenvalue represents the
critical Rayleigh number. The shape of the critical temperature and
flow fields is then obtained from the linear set. In most practical
cases, the problem setting is such that closed analytical solutions
cannot be derived.
The difficulties of solving the convection equations can be
overcome by using the Galerkin finiteelement method. The method
allows the solution of both the linear set and also the more complete
nonlinear set of equations at various boundary conditions and taking
variations in the material parameters into account.
In this thesis, the Galerkin method is used to solve the
convection equations for infinitely long porous vertical or semivertical
slabs with prescribed temperatures at the top and bottom surfaces.
The first set of models investigated involve boundary walls
that are impermeable to the fluid but perfectly conducting to heat.
The critical Rayleigh numbers and critical temperature and
flow fields are obtained for such slabs with various aspect ratios. The
results show that the critical number is raised by 200 to 400% as
compared with published data for similar slabs with thermally nonconducting
walls.
The results are generalized by investigating cases of slabs with
(1) three types of vertically varying permeability, (2) by taking the
temperature dependence of the fluid properties into account, (3) by
including nonlinear terms, and finally, (4) a few cases of slabs with
boundary walls of finite thermal conductivity are investigated.
The results are applicable to a number of situations in
geothermal areas. A brief discussion of two such cases is given,
that is, (1) the estimating of the critical permeability profile for the
East geothermal field in the Imperial Valley and (2) the computation
of a temperature cross section in the Cumali geothermal field in
Turkey. / Graduation date: 1979

3 
The QBO's influence on lightning production and deep convection in the tropicsHernandez, Celina Anne 15 May 2009 (has links)
Variations in characteristics of tropical deep convection are examined for an association with the stratospheric quasibiennial oscillation (QBO). Eight years (19982005) of Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) flash densities and ten years (19982007) of TRMM Precipitation Radar (PR) deep convective and stratiform rainfall and convective echo top heights are analyzed. The QBO can be linked to deep convection through two hypothesized mechanisms: 1) modulation of tropopause height, which may affect the altitude that convection can penetrate; and 2) modulation of crosstropopause shear, which may affect the vertical development of convection via shearing of cloud tops. Tropopause height and crosstropopause shear is measured by National Centers for Environmental Prediction (NCEP) reanalysis 100 hPa temperatures and 50200 hPa zonal wind shear, respectively.
When partitioned by QBO east and west phases, zonal monthly mean anomalies and anomalous monthly mean difference maps illustrate a QBO signal in lightning flash rates, convective and stratiform rain amounts, and the number of convective echo tops > 12 km. QBO modulation of crosstropopause shear causes 50200 hPa shear east (west) phase anomalies to decrease (increase) about the equator and increase (decrease) in offequator regions. QBO modulation of tropopause height induces a higher/colder (lower/warmer) tropopause near the equator during the east (west) phase. While the expectation was that decreases in crosstropopause shear and tropopause temperatures at monthly time scales during the QBO would result in an increase of deep convective properties near the equator, observations suggest that deep convective properties may increase or decrease depending on the location and season. Similar to the QBO results, the increase or decrease of deep convective properties with general variations in crosstropopause shear and tropopause temperatures depends on the location and season.

4 
Phytokonvektion im offenen Ozean : Feldexperimente und numerische Prozessstudien /Wehde, Henning. January 2001 (has links)
DissertationFachbereich GeowissenschaftenUniversität Hamburg, 2001. / Bibliogr. p. 113123.

5 
Measurement of convective fluid flow in centrifugal fieldsStockett, Lawrence Edward, 1929 January 1965 (has links)
No description available.

6 
Convective and boiling heat transfer from a vibrating surface.Nangia, Krishan Kumar. January 1968 (has links)
No description available.

7 
An investigation into the development of laminar natural convection in heated vertical ductsDyer, James Ross January 1971 (has links)
ix, 174 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)University of Adelaide, Dept. of Mechanical Engineering, 1972

8 
The evolution and properties of deep convection within an African wave on day 245 of GATEMower, R. Neil. January 1981 (has links)
Thesis (Ph. D.)University of WisconsinMadison, 1981. / Typescript. Vita. eContent providerneutral record in process. Description based on print version record. Includes bibliographical references (leaves 7275).

9 
Dynamic destabilization and the evolution of deep convection a case study /Hoerling, Martin Paul. January 1982 (has links)
Thesis (M.S.)University of WisconsinMadison, 1982. / Typescript. eContent providerneutral record in process. Description based on print version record. Includes bibliographical references (leaves 6869).

10 
Measurement of upper convective boundary layer parameters by means of lidarKunkel, Kenneth Edward, January 1978 (has links)
ThesisWisconsin. / Vita. Includes bibliographical references (leaves 125129).

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