ABSTRACT Eddy Current Test (ET) is one of the widely-used method in the nondestructive testing (NDT). It is used to examine thinner sheet metal. According to the theory of electromagnetic induction, the researcher used a coil to make the surface of the metal pipe bring much eddy current. In addition, he investigated the variations of the coil impendence by the interaction between the coil magnetic field and the eddy current magnetic field. By observing the variations of the phase angle and the impendence plane diagram, the researcher also found factors for different defects. The purpose of this study is to research the influence of the diversity of the geometry when examining metal pipe. According to Eddy Current Test, the magnetic field is a major factor in testing. So the researcher generalized a 3-D electromagnetic model with software and analyzed the results of the magnetic field by the finite element method. By drawing the impendence plane diagram, evaluating curves and by observing the variations of the influence by diversity of the geometry, the researcher found the possibility of preventing the inaccuracy and errors in testing with a 3-D electromagnetic model. Later on, he found some influential factors, confirmed the tendency, and then increased the accuracy in examining thin sheet metal.

No description available.

<p>The aim of the present study is to develop subgrid-scale models that are relevant for complex flows and combustion. A stochastic model based on a stochastic Smagorinsky constant with adjustable variance and time scale is proposed. The stochastic model is shown to provide for backscatter of both kinetic energy and scalar variance without causing numerical instabilities. A new subgrid-scale scalar flux model is developed using the same kind of methodology that leads to the explicit algebraic scalar flux model, EASFM, for RANS. The new model predicts the anisotropy of the subgrid-scales in a more realistic way than the eddy diffusion model. Both new models were tested in rotating homogeneous shear flow with a passive scalar. Rogallo’s method of moving the frame with the mean flow to enable periodic boundary conditions was used to simulate homogeneous shear flow.</p>

Optimal large eddy simulation (OLES) is an approach to LES sub-grid modeling that requires multi-point correlation data as input. Until now, this has been obtained by analyzing DNS statistics. In the finite-volume OLES formulation studied here, under the assumption of small-scale homogeneity and isotropy, these correlations can be theoretically determined from Kolmogorov inertial-range theory, small-scale isotropy, along with the quasi-normal approximation. These models are expressed as generalized quadratic and linear finite volume operators that represent the convective momentum flux. These finite volume operators have been analyzed to determine their characteristics as numerical approximation operators and as models of small-scale effects. In addition, the dependence of the model operators on the anisotropy of the grid and on the size of the stencils is analyzed to develop idealized general operators that can be used on general grids. The finite volume turbulence operators developed here will be applicable in a wide range of LES problems. / text

Accurate models for the mixing of fuel and oxidizer at small, unresolved flow length scales are critical to the predictive skill of large eddy simulation (LES) of turbulent combustion. Subfilter scalar variance and subfilter scalar dissipation rate are important parameters in combustion modeling approaches based on a conserved scalar, but are prone to numerical and modeling errors due to the nature of practical LES computations. This work examines the errors incurred in these models using a novel method that couples LES scalar modeling with direct numerical simulation (DNS) of homogeneous isotropic turbulence and offers modeling and numerical techniques to address these errors. In the coupled DNS-LES method, DNS velocity fields are evolved simultaneously with LES scalar fields. The filtered DNS velocities are supplied to the LES scalar equations, instead of solving the LES momentum equations. This removes the effect of errors in the filtered scalar evolution from the scalar modeling analysis. Results obtained using the coupled DNS-LES approach, which permits detailed study of physics-related and numerical errors in scalar modeling, show that widely used algebraic dynamic models for subfilter scalar variance lack accuracy due to faulty equilibrium modeling assumptions and sensitivity to numerical error. Transport equation models for variance show superior performance, provided that the scalar dissipation rate model coefficient is set appropriately. For this purpose, a new dynamic approach for nonequilibrium modeling of subfilter scalar dissipation rate is developed and validated through a priori tests in an inhomogeneous jet flow and using the coupled DNS-LES method for assessment of numerical error effects. Explicit filtering is assessed as means to control numerical error in LES scalar modeling and the scalar equations are reformulated to account for the explicit filtering technique. Numerical convergence of the mean subfilter scalar variance prediction with increasing grid resolution is demonstrated. / text

A fast response vertical anemometer and wet and dry bulb thermocouples were used to measure the turbulence within a forest canopy. Five trials of ten minutes duration were run in each of a sixty-five foot high pine forest and a fifteen foot high lodgepole pine forest. [...]

Circulation and associated variability in the Intra-Americas Sea (IAS) are examined using observations and numerical models. Vertically integrated transport variations through the Yucatan Channel in the model are found to be related to the intrusion of the Loop Current into the Gulf of Mexico. We argue that the transport variations are part of a “compensation effect” by which transport variations through the Yucatan Channel are at least partly compensated by flow around Cuba. Numerical experiments show that the transport variations result from the interaction between the density anomalies associated with the Loop Current intrusion and the variable bottom topography. The compensation effect is found to be associated with baroclinic (2-layer) flow through the Yucatan Channel at timescales longer than a month, while at shorter timescales (less than a month) the vertical structure of the flow is barotropic. An index, that can be computed from satellite data, is proposed for measuring the impact of the Loop Current intrusion on the transport variability through the Yucatan Channel. This index is shown to be significantly correlated at low frequencies (cutoff 120 days) with the cable estimates of transport between Florida and the Bahamas. We argue that it is the geometric connectivity between the Yucatan Channel and the Straits of Florida between Florida and the Bahamas that accounts for the relationship. A three-dimensional, data-assimilative, ocean circulation model is developed in order to simulate circulation, hydrography and associated variability in the IAS from 1999 to 2002. The model performance is assessed by comparing model results with various observations made in the IAS during this period. Model results are used to study the role played by Caribbean eddies in the dynamics of monthly to seasonal (with timescales of 30-120 days) circulation variability in the IAS. It is shown that the variations in vertically integrated transport between Nicaragua and Jamaica are linked to the interaction of Caribbean eddies with the Nicaraguan Rise. The mechanism can be explained in terms of the form drag effect acting across the Nicaraguan Rise.

In this thesis, large-eddy simulation (LES) is used to simulate both Newtonian and non-Newtonian physiological pulsatile flows in constricted channels to gain insights into the physical phenomenon of laminar-turbulent flow transition due to the presence of an artificial arterial stenosis. The advanced dynamic nonlinear subgrid-scale stress (SGS) model of Wang and Bergstrom (DNM) was utilized to conduct numerical simulations and its predictive performance was examined in comparison with that of the conventional dynamic model (DM) of Lilly. An in-house LES code has been modified to conduct the unsteady numerical simulations, and the results obtained have been validated against available experimental and direct numerical simulation (DNS) results. The physical characteristics of the flow field have been thoroughly studied in terms of the resolved mean velocity, turbulence kinetic energy, viscous wall shear stress, and turbulence energy spectra along the central streamline of the domain.

Sequestering atmospheric carbon in soil is an attractive option for mitigation of rising atmospheric carbon dioxide concentrations through agriculture. Perennial crops are more likely to gain carbon while annual crops are more likely to lose carbon. A pair of eddy covariance towers were set up near Winnipeg Manitoba, Canada to measure carbon flux over adjacent fertilized long-term perennial grass hay fields with high soil organic carbon. In 2009 the forage stand of one field (Treatment) was sprayed with herbicide, cut and bailed; following which cattle manure was applied and the land was tilled. The forage stand in the other field (Control) continued to be cut and bailed. Differences between net ecosystem productivity of the fields were mainly due to gross primary productivity; ecosystem respiration was similar for both fields. When biomass removals and manure applications are included in the carbon balance, the Treatment conversion lost 149 g C m^(-2) and whereas the Control sequestered 96 g C m^(-2), for a net loss of 245 g C m^(-2) over the June to December period (210 days). This suggests that perennial grass converted for annual cropping can lose more carbon than perennial grasses can sequester in a season.

Sequestering atmospheric carbon in soil is an attractive option for mitigation of rising atmospheric carbon dioxide concentrations through agriculture. Perennial crops are more likely to gain carbon while annual crops are more likely to lose carbon. A pair of eddy covariance towers were set up near Winnipeg Manitoba, Canada to measure carbon flux over adjacent fertilized long-term perennial grass hay fields with high soil organic carbon. In 2009 the forage stand of one field (Treatment) was sprayed with herbicide, cut and bailed; following which cattle manure was applied and the land was tilled. The forage stand in the other field (Control) continued to be cut and bailed. Differences between net ecosystem productivity of the fields were mainly due to gross primary productivity; ecosystem respiration was similar for both fields. When biomass removals and manure applications are included in the carbon balance, the Treatment conversion lost 149 g C m^(-2) and whereas the Control sequestered 96 g C m^(-2), for a net loss of 245 g C m^(-2) over the June to December period (210 days). This suggests that perennial grass converted for annual cropping can lose more carbon than perennial grasses can sequester in a season.