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The effects of subgrid-scale (SGS) condensation and transport become more important as the grid spacings increase from those typically used in large-eddy simulation (LES) to those typically used in cloudresolving models (CRMs). In...
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The effects of subgrid-scale (SGS) condensation and transport become more important as the grid spacings increase from those typically used in large-eddy simulation (LES) to those typically used in cloudresolving models (CRMs). Incorporation of these SGS effects can be achieved by a joint probability density function approach that utilizes higher-order moments of thermodynamic and dynamic variables. This study examines how well shallow cumulus and stratocumulus clouds are simulated by two versions of a CRM implemented with low-order (1.5-order) and third-order turbulence closures (LOC and TOC). Resolution sensitivities of the closure are studied by refining the grid spacing from control simulation (with standard CRM grids of 4 km) to simulations with much finer meshes in the horizontal. In our simulations cumulus clouds are mostly produced through SGS transport processes while stratocumulus clouds are produced through both SGS and resolved-scale processes in the TOC version of the CRM at standard resolution. In contrast, the LOC version of the CRM requires resolved-scale circulations to produce both cumulus and stratocumulus clouds, as SGS transports within cloud layer remain small in this model. The mean profiles of thermodynamic variables, cloud fraction and liquid water content exhibit significant differences between the two versions of the CRM, with the TOC results agreeing better with the LES than the LOC results. The characteristics, temporal evolution and mean profiles of shallow cumulus and stratocumulus clouds are weakly dependent upon the horizontal grid spacing used in the TOC CRM. However, the ratio of the SGS to resolved-scale fluxes becomes smaller as the horizontal grid spacing decreases. The subcloud-layer fluxes are mostly due to the resolved scales when horizontal grid spacings approach the depth of this layer. The overall results of the TOC simulations suggest that the 1-km grid spacing is a good choice for CRM simulation of shallow cumulus and stratocumulus.
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Shallow turbulent flows occurring in wide rivers, estuaries, lakes or coastal regions, as well as the atmosphere, are readily susceptible to transverse disturbances that lead to two-dimensional coherent structures. The shallow jet...
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Shallow turbulent flows occurring in wide rivers, estuaries, lakes or coastal regions, as well as the atmosphere, are readily susceptible to transverse disturbances that lead to two-dimensional coherent structures. The shallow jet. the shallow wake, and the shallow mixing layer are examples of such flow patterns. A linear stability analysis incorporating the effects of bottom friction and viscosity is applied to these flows to determine the criteria for absolute and convective instability and for stabilization of the flow. All three flow types exhibit instabilities within the range of natural flows. Three mechanisms for large-scale instability generation, namely topographic forcing, transverse velocity shear, and secondary instabilities of the base flow, are compared to the stability calculations. Based on the results, topographic forcing, and to a lesser extent, transverse shear are expected to have both absolute and convective instabilities; whereas, secondary instabilities of the base flow are expected to generate primarily convective instabilities. The resulting large-scale coherent structures greatly influence the mixing and transport of pollutants and momentum that are released into such flows.
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Vibrational seismic sources frequently provide a higher-frequency seismic wavelet (and therefore better resolution) than other sources, and can provide a superior signal-to-noise ratio in many settings. However, they are often pro...
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Vibrational seismic sources frequently provide a higher-frequency seismic wavelet (and therefore better resolution) than other sources, and can provide a superior signal-to-noise ratio in many settings. However, they are often prohibitively expensive for lower-budget shallow surveys. In order to address this problem, I designed and built a simple but effective vibrator source for about one thousand dollars. ne "EMvibe" is an inexpensive electromagnetic vibrator that can be built with easy-to-machine parts and off-the-shelf electronics. It can repeatably produce pulse and frequency-sweep signals in the range of 5 to 650 Hz, and provides sufficient energy for recording at offsets up to 20 in. Analysis of frequency spectra show that the EMvibe provides a broader frequency range than the sledgehammer at offsets up to similar to 10 in in data collected at a site with soft sediments in the upper several meters. The EMvibe offers a high-resolution alternative to the sledgehammer for shallow surveys. It is well-suited to teaching applications, and to surveys requiring a precisely-repeatable source signature.
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This note examines the linear response of thin, shallow curved beams to an axially-directed compressive load. The response is tracked with a rise parameter drawn from related work on linear arches through which it is shown that th...
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This note examines the linear response of thin, shallow curved beams to an axially-directed compressive load. The response is tracked with a rise parameter drawn from related work on linear arches through which it is shown that the curved beam behaves like an axially compressed bar for small values of the rise parameter, whereas it responds as a beam in bending for large values of the parameter. This is totally opposite to that of laterally-loaded arches.
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This paper discusses the ability of the two-dimensional (2D) shallow water equations to model meandering flows in shallow rectangular reservoirs. Four meandering flows of various shallowness were modeled using an academic flow mod...
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This paper discusses the ability of the two-dimensional (2D) shallow water equations to model meandering flows in shallow rectangular reservoirs. Four meandering flows of various shallowness were modeled using an academic flow model that includes a depth-averaged k-E model accounting for the horizontal and vertical turbulent length-scales. Different roughness heights were considered for modeling the bottom friction. A proper orthogonal decomposition (POD) was applied to the simulation results to extract the behavior of the main structures responsible for the meandering flow. The same POD analysis was also performed for the reference experimental flow fields, obtained by large-scale particle image velocimetry. The first two POD modes obtained from the numerical simulations assuming a smooth bottom are in good agreement with the experimental modes in terms of energy, as well as temporal and spatial variations, whatever the shallowness. In contrast, the remaining simulated modes are not well rendered. The effect of an increased roughness height in the simulations is finally discussed. It leads to an improved reproduction of the first two modes and of the following modes, except when significant viscous effects govern in the flow.
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A novel focused-source electromagnetic (FSEM) method focuses the EM field in the vertical direction to provide deep-reading resistivity data. FSEM offers better spatial resolution and greater depth of investigation than the conven...
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A novel focused-source electromagnetic (FSEM) method focuses the EM field in the vertical direction to provide deep-reading resistivity data. FSEM offers better spatial resolution and greater depth of investigation than the conventional controlled-source electromagnetic (CSEM) method for land and marine EM surveys. We have proven the high efficiency of FSEM by analyzing 3D models of various complex geologic formations in the presence of seafloor bathymetry, shallow resistive gas-hydrate overburdens, and secondary gas reservoirs formed above deeper oil reservoirs. Combining the power of our focusing technique with the power of our 3D numerical modeling method, we have developed exceptionally challenging test cases to conclude that FSEM automatically cancels unwanted shallow effects and allows simple visual interpretation of deep reservoir responses. In addition, FSEM is insensitive to imperfections in the setup geometry. We achieve these advantages using a proper combination of measurements acquired in the receiver excited by transmitters situated at different space points. The method is promising in anisotropic formations as well.
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A finite element analysis for the free vibration behaviour of doubly curved shells is presented in which eight-noded curved quadrilateral isoparametric finite elements are used. The first order shear deformation theory for thin an...
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A finite element analysis for the free vibration behaviour of doubly curved shells is presented in which eight-noded curved quadrilateral isoparametric finite elements are used. The first order shear deformation theory for thin and shallow shells is used in the formulation. Results are obtained for comparison with those in the existing literature and to investigate the effects of various composite parameters relevant to doubly curved shells, such as fibre orientations and lamination schemes and several geometrical parameters like aspect ratio, smaller height to greater height ratio (for conoids), thickness to radius ratio (for hyperbolic and elliptic paraboloids), and radii of curvature ratio (for elliptic paraboloids). (C) 1996 Academic Press Limited [References: 9]
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A finite element analysis for the free vibration behaviour of point supported laminated composite cylindrical shells is presented. Eight-noded curved quadrilateral isoparametric elements are used. The formulation is based on the a...
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A finite element analysis for the free vibration behaviour of point supported laminated composite cylindrical shells is presented. Eight-noded curved quadrilateral isoparametric elements are used. The formulation is based on the assumptions of the first order shear deformation theory for thin, shallow shells. Some of the results obtained in the analysis are compared with those present in the existing literature. Several numerical results are also presented for selected material parameters, shell geometry and support spacing to study the free vibration characteristics of various point supported laminated composite cylindrical shells. [References: 10]
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Relationships between ciliates and the presence of emergent and submerged vegetation were studied in a shallow lake in eastern Poland. Samples were collected in zones of Phragmites, Typha, Batrachium, Elodea, Stratiotes and from t...
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Relationships between ciliates and the presence of emergent and submerged vegetation were studied in a shallow lake in eastern Poland. Samples were collected in zones of Phragmites, Typha, Batrachium, Elodea, Stratiotes and from the open water zone. The abundance and biomass of ciliates were significantly higher at sites with structurally most complex plants than in the open water or sparsely vegetated sites. The redundancy analysis indicated that bacterial abundance and total organic carbon were the most influential variables that determine the distribution of ciliates. However, chlorophyll a and Ptot have a lesser influence on the distribution of these microorganisms. Based on differences in macrophyte structure, two groups of habitats with similar patterns of size-related ciliate distribution were distinguished. The first group consisted of three vegetation zones of sparse stem structure and the open water zone, the second group comprised submerged macrophyte species, which were more complex.
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In this paper, we present the results of numerical simulations matched to laboratory experiments of tidal, starting-jet vortices forming at idealized, barotropic inlets. The laboratory experiments are for sinusoidally varying infl...
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In this paper, we present the results of numerical simulations matched to laboratory experiments of tidal, starting-jet vortices forming at idealized, barotropic inlets. The laboratory experiments are for sinusoidally varying inflow/outflow along a wide, flat basin. Inlet configurations include simple inlets with negligible channel length as well as a longer inlet channels through a long barrier island and jettied inlet. Laboratory observations are made using particle image velocimetry, and we analyze the laboratory and numerical model velocity fields to compare starting-jet trajectory, diameter, and total circulation. The numerical simulations use the Fine Resolution Environmental Hydrodynamic model, solving the three-dimensional, hydrostatic, barotropic equations of motion. Our goal is to identify the minimum model attributes necessary to match the vortex properties. This is accomplished using a third-order upwind scheme for advection, a constant bottom friction drag coefficient, and a one-equation turbulence model for transport of turbulent kinetic energy. The optimal value of the bottom drag coefficient matches the time-average value at the basin inflow/outflow boundaries, and the optimal dissipation coefficient, , was an order of magnitude smaller than literature values for a steady open-channel flow. We show that the drag coefficient mainly affects the advection speeds of the outer coastal waters, which control the penetration of the tidal vortices away from the inlet, and the lower turbulence dissipation rate results from the low turbulent dissipation in the large, shallow starting-jet vortices.
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