Large-scale structure generation by anisotropic small-scale flows

1987 ◽  
Vol 30 (5) ◽  
pp. 1272 ◽  
Author(s):  
Victor Yakhot ◽  
Richard Pelz
Keyword(s):  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Small Scale ◽  
Structure Generation

scholarly journals Heterogeneity, Permeability Patterns, and Permeability Upscaling: Physical Characterization of a Block of Massillon Sandstone Exhibiting Nested Scales of Heterogeneity

2000 ◽  
Vol 3 (04) ◽  
pp. 283-291 ◽  
Author(s):  
V.C. Tidwell ◽  
J.L. Wilson
Keyword(s):  
Predictive Models ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Small Scale ◽  
Small Scale Structure ◽  
Permeability Upscaling ◽  
Block Face ◽  
The Cross ◽  
Permeability Data

Summary Over 75,000 permeability measurements were collected from a meter-scale block of Massillon sandstone, characterized by conspicuous crossbedding that forms two distinct nested scales of heterogeneity. With the aid of a gas minipermeameter, spatially exhaustive fields of permeability data were acquired at each of five different sample supports (i.e., sample volumes) from each block face. These data provide a unique opportunity to physically investigate the relationship between the multiscale cross-stratified attributes of the sandstone and the corresponding statistical characteristics of the permeability. These data also provide quantitative physical information concerning the permeability upscaling of a complex heterogeneous medium. Here, a portion of the data taken from a single block face cut normal to stratification is analyzed. The results indicate a strong relationship between the calculated summary statistics and the cross-stratified structural features visibly evident in the sandstone sample. Specifically, the permeability fields and semivariograms are characterized by two nested scales of heterogeneity, including a large-scale structure defined by the cross-stratified sets (delineated by distinct bounding surfaces) and a small-scale structure defined by the low-angle cross-stratification within each set. The permeability data also provide clear evidence of upscaling. That is, each calculated summary statistic exhibits distinct and consistent trends with increasing sample support. Among these trends are an increasing mean, decreasing variance, and an increasing semivariogram range. The results also clearly indicate that the different scales of heterogeneity upscale differently, with the small-scale structure being preferentially filtered from the data while the large-scale structure is preserved. Finally, the statistical and upscaling characteristics of individual cross-stratified sets were found to be very similar because of their shared depositional environment; however, some differences were noted that are likely the result of minor variations in the sediment load and/or flow conditions between depositional events. Introduction Geologic materials are inherently heterogeneous because of the depositional and diagenetic processes responsible for their formation. These heterogeneities often impose considerable influence on the performance of hydrocarbon bearing reservoirs. Unfortunately, quantitative characterization and integration of reservoir heterogeneity into predictive models are complicated by two challenging problems. First, the quantity of porous media observed and/or sampled is generally a minute faction of the reservoir under investigation. This gives rise to the need for models to predict material characteristics at unsampled locations. The second problem stems from technological constraints that often limit the measurement of material properties to sample supports (i.e., sample volumes) much smaller than can be accommodated in current predictive models. This disparity in support requires measured data be averaged or upscaled to yield effective properties at the desired scale of analysis. The concept of using "soft" geologic information to supplement often sparse "hard" physical data has received considerable attention.1,2 Successful application of this approach requires that some relationship be established between the difficult to measure material property (e.g., permeability) and that of a more easily observable feature of the geologic material. For example, Davis et al.3 correlated architectural-element mapping with the geostatistical characteristics of a fluvial/interfluvial formation in central New Mexico; Jordan and Pryor4 related permeability controls and reservoir productivity to six hierarchical levels of sand heterogeneity in a fluvial meander belt system; while Istok et al.5 found a strong correlation between hydraulic property measurements and visual trends in the degree of welding of ash flow tuffs at Yucca Mountain, Nevada. Phillips and Wilson6 mapped regions where the permeability exceeds some specified cutoff value and related their dimensions to the correlation length scale by means of threshold-crossing theory. Also, Journel and Alabert7 proposed a spatial connectivity model based on an indicator formalism and conditioned on geologic maps of observable, spatially connected, high-permeability features. The description and quantification of heterogeneity is necessarily related to the issue of scale. It is often assumed that geologic heterogeneity is structured according to a discrete and disparate hierarchy of scales. For example, the hierarchical models proposed by Dagan8 and by Haldorsen9 conveniently classify heterogeneities according to the pore, laboratory, formation, and regional scales. This assumed disparity in scales allows parameter variations occurring at scales smaller than the modeled flow/transport process to be spatially averaged to form effective media properties,10–14 while large-scale variations are treated as a simple deterministic trend.2,15 However, natural media are not always characterized by a large disparity in scales as assumed above;16 but rather, an infinite number of scales may coexist,17–20 leading to a fractal geometry or continuous hierarchy of scales.21

Flame Area Fluctuation Measurements in Velocity-Forced Premixed Gas Turbine Flames

2015 ◽  
Author(s):  
Alexander J. De Rosa ◽  
Janith Samarasinghe ◽  
Stephen J. Peluso ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Heat Release Rate ◽  
Release Rate ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Small Scale ◽  
Flame Velocity ◽  
Unstable Combustion

Fluctuations in the heat release rate that occur during unstable combustion in lean premixed gas turbine combustors can be attributed to velocity and equivalence ratio fluctuations. For a fully premixed flame, velocity fluctuations affect the heat release rate primarily by inducing changes in the flame area. In this paper, a technique to analyze changes in flame area using chemiluminescence-based flame images is presented. The technique decomposes the flame area into separate components which characterize the relative contributions of area fluctuations in the large scale structure and the small scale wrinkling of the flame. The fluctuation in the wrinkled area of the flame which forms the flame brush is seen to dominate its response in the majority of cases tested. Analysis of the flame area associated with the large scale structure of the flame resolves convective perturbations that move along the mean flame position. Results are presented that demonstrate the application of this technique to both single-nozzle and multi-nozzle flames.

scholarly journals Theories of Small-Scale Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 457-474 ◽  
Author(s):  
P. A. Sweet
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Solar Flares ◽  
Large Scale ◽  
Large Scale Structure ◽  
Energetic Particles ◽  
Scale Structure ◽  
Small Scale ◽  
Solar Chromosphere

This review is concerned with the origin of the fine structure of the fields and their relationship to the heating of the solar chromosphere and corona, the structure of prominences and the production of energetic particles in solar flares. The dynamics of sunspot formation, and the large-scale structure of individual sunspots have not been dealt with, although the evolution of AR fields has been considered insofar as it affects the flare problem.

scholarly journals Spatial Distribution of Quasars

1987 ◽  
Vol 124 ◽  
pp. 627-638
Author(s):  
Yaoquan Chu ◽  
LiZhi Fang
Keyword(s):  
Spatial Distribution ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Observational Cosmology ◽  
Small Scale ◽  
Large Scale Systems ◽  
Isothermal Case ◽  
The Universe ◽  
Adiabatic Case

The distribution of quasars has become one of the most interesting problems in observational cosmology. This is due mainly to the development of theory of the formation of large scale structure in the universe. In recent years, several scenarios of clustering have been proposed. In the adiabatic case, the clustering process is from larger scales to smaller ones, i.e., the first systems to form out would be on the scale of superclusters, then these systems fragment to form smaller scale systems such as galaxies. In the isothermal case, the clustering is from smaller scales to larger ones, namely, galaxies condense out at first and larger scale systems, such as clusters and superclusters, then form later via hierachical build-up processes. In the universe contain two components, the scenario of clustering might be different from both standard adiabatic and isothermal cases(1). According to this new scenario, there should be two kinds of small scale objects, one is formed due to fragment of larger scale systems, another is formed before large scale systems form.

A physical mechanism of large-scale structure generation in turbulent convection

1996 ◽  
Vol 31 (5) ◽  
pp. 647-654
Author(s):  
V. D. Zimin ◽  
G. V. Levina ◽  
S. S. Moiseev ◽  
S. E. Startsev ◽  
K. G. Shvarts
Keyword(s):  
Large Scale ◽  
Physical Mechanism ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Turbulent Convection ◽  
Structure Generation

scholarly journals Autochthonous granodiorites north-west of Frederikshåbs Isblink, Fiskenæsset region

1973 ◽  
Vol 51 ◽  
pp. 23-27
Author(s):  
A.M Hopgood
Keyword(s):  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Amphibolite Facies ◽  
Small Scale ◽  
North West ◽  
Gneiss Complex ◽  
Lithological Unit

The gneiss complex immediately north-west of Frederikshåbs Isblink is composed mostly of amphibolite facies, grey, streaky, quartzo-feldspathic, biotite and hornblende gneisses. Subordinate amphibolites, homblendites, thin anorthosites, peridotite lenses up to 200 m across, rare concordant marble bands and associated calc-silicate gneisses and kyanite and sillimanite gneisses make up the bulk of the remainder, and the whole has been complexly deformed. Occupying the higher ground within the complex, and comprising the largest single lithological unit there is a considerable volume of massive weathering, porphyroblastic granodiorite and granodiorite gneiss. Field relationships show this to be unquestionably autochthonous and almost certainly of palingenetic origin and while on a small scale the 'contact' with the surrounding gneisses may be locally discordant, overall it follows closely the large scale structure and this suggests its control by preexisting lithology.

scholarly journals Lyman-α Forest and Cosmic Weak Lensing in a Warm Dark Matter Universe

2014 ◽  
Vol 31 ◽  
Author(s):  
Katarina Markovič ◽  
Matteo Viel
Keyword(s):  
Dark Matter ◽  
Large Scale ◽  
Theoretical Models ◽  
Large Scale Structure ◽  
Mass Function ◽  
Scale Structure ◽  
Small Scale ◽  
Current State ◽  
Upper Limits ◽  
Order Of Magnitude

AbstractWe review the current state of the theory of large-scale structure in a warm dark matter (WDM) cosmological model. In particular, we focus on the non-linear modelling of the matter power spectrum and on the mass function of dark matter haloes. We describe the results of N-body simulations with WDM and mention the effects that could be induced by baryonic physics. We also examine the halo model of large-scale structure and its recently suggested modifications for a WDM cosmology, which account for the small-scale smoothness of the initial matter density field and better fit the results of N-body simulations. Having described the theoretical models, we discuss the current lower limits on the WDM particle mass, mwdm, which correspond to upper limits on the WDM temperature under the assumption that the particles are thermal relics. The best such constraints come from the Lyα forest and exclude all masses below 3.3 keV at the 2σ confidence level. We finally review the forecasts for future lensing surveys, which will be of the same order of magnitude as the already existing constraints from the Lyα forest data but explore a different redshift regime.

scholarly journals The HASHTAG Project: The First Submillimeter Images of the Andromeda Galaxy from the Ground

2021 ◽  
Vol 257 (2) ◽  
pp. 52
Author(s):  
Matthew W. L. Smith ◽  
Stephen A. Eales ◽  
Thomas G. Williams ◽  
Bumhyun Lee ◽  
Zongnan Li ◽  
...  
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Dust Emission ◽  
Angular Size ◽  
Line Emission ◽  
Large Scale Structure ◽  
Spatial Filter ◽  
Scale Structure ◽  
Small Scale ◽  
Andromeda Galaxy

Abstract Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy’s large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850 μm. We also have created a method to predict the CO(J = 3–2) line flux across M31, which contaminates the 850 μm band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed.

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