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1
Kim, K. C., and R. J. Adrian. "Very large-scale motion in the outer layer." Physics of Fluids 11, no. 2 (February 1999): 417–22. http://dx.doi.org/10.1063/1.869889.
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Baltzer, J. R., R. J. Adrian, and Xiaohua Wu. "Structural organization of large and very large scales in turbulent pipe flow simulation." Journal of Fluid Mechanics 720 (February 27, 2013): 236–79. http://dx.doi.org/10.1017/jfm.2012.642.
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AbstractThe physical structures of velocity are examined from a recent direct numerical simulation of fully developed incompressible turbulent pipe flow (Wu, Baltzer & Adrian, J. Fluid Mech., vol. 698, 2012, pp. 235–281) at a Reynolds number of ${\mathit{Re}}_{D} = 24\hspace{0.167em} 580$ (based on bulk velocity) and a Kármán number of ${R}^{+ } = 685$. In that work, the periodic domain length of $30$ pipe radii $R$ was found to be sufficient to examine long motions of negative streamwise velocity fluctuation that are commonly observed in wall-bounded turbulent flows and correspond to the large fractions of energy present at very long streamwise wavelengths (${\geq }3R$). In this paper we study how long motions are composed of smaller motions. We characterize the spatial arrangements of very large-scale motions (VLSMs) extending through the logarithmic layer and above, and we find that they possess dominant helix angles (azimuthal inclinations relative to streamwise) that are revealed by two- and three-dimensional two-point spatial correlations of velocity. The correlations also reveal that the shorter, large-scale motions (LSMs) that concatenate to comprise the VLSMs are themselves more streamwise aligned. We show that the largest VLSMs possess a form similar to roll cells centred above the logarithmic layer and that they appear to play an important role in organizing the flow, while themselves contributing only a minor fraction of the flow turbulent kinetic energy. The roll cell motions play an important role with the smaller scales of motion that are necessary to create the strong streamwise streaks of low-velocity fluctuation that characterize the flow.
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GUALA, M., S. E. HOMMEMA, and R. J. ADRIAN. "Large-scale and very-large-scale motions in turbulent pipe flow." Journal of Fluid Mechanics 554, no. -1 (April 24, 2006): 521. http://dx.doi.org/10.1017/s0022112006008871.
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Cameron, Stuart, Vladimir Nikora, Mark Stewart, and Andrea Zampiron. "Large and very large scale motions in roughbed open-channel flow." E3S Web of Conferences 40 (2018): 05061. http://dx.doi.org/10.1051/e3sconf/20184005061.
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Long duration PIV measurements in rough-bed (glass beads) open-channel flow (OCF) reveal that the pre-multiplied spectra of the streamwise velocity has a bimodal distribution due to the presence of large and very large scale motions (LSMs and VLSMs, respectively). The existence of VLSMs in boundary layers, pipes and closed channels has been acknowledged for some time, but strong supporting evidence for their presence in OCF has been lacking. Length scales of the large and very large scale motions in OCF exhibit different scaling properties; whereas the streamwise length of the LSM scales with the flow depth, the VLSM streamwise length does not scale purely with flow depth and may additionally depend on other scales such as the channel width, roughness height, or viscous length. Supplementary data for flows over self-affine fractal rough beds support these findings and additionally indicate that the length of VLSMs may grow along the extensive distance from the channel entrance. The origin and nature of LSMs and VLSMs are still to be resolved, but differences in their scaling suggest that VLSMs in rough-bed open-channel flows form independently rather than as a spatial alignment of LSMs.
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Hsia, Shih‐Chang, and Lung‐Sen Chen. "Parallel very large‐scale integration chip implementation of optimal fractional motion estimation." IET Circuits, Devices & Systems 8, no. 6 (November 2014): 499–508. http://dx.doi.org/10.1049/iet-cds.2013.0465.
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Martǐn-Mirones, J. M., and L. J. Goicoechea. "Can Very Large-Scale Structures Exist in the Universe?" Symposium - International Astronomical Union 139 (1990): 422–23. http://dx.doi.org/10.1017/s007418090024120x.
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The controversy about the position of the matter accumulation that causes our peculiar motion with respect to the cosmic background radiation (CBR) has very recently acquired great interest. So, the very local attractor suggested by Lynden-Bell et al. (1988) and Dressler (1988) begins to be questioned. The histogram done by Melnick and Moles (1987) shows that the dominant structure may be at ~140 h−1 Mpc. Similar results have been obtained by Scaramella et al. (1989). On the other hand, the analysis of the very local candidate in the X-ray band shows that this does not have rich clusters of galaxies (Jahoda and Mushotzky 1989). Moreover, Lahav et al. (1989) have studied a sample of 53 clusters emitting X-rays (E ≈ 2–20 keV, LX ≈ 5 × 1042–7 × 1044h−2 erg s−1); they have observed a great concentration of clusters in the direction of the attractor suggested by Lynden-Bell et al., but at a distance of ~100 h−1–150 h−1 Mpc. The detections of nonlocal structures (further than 300 h−1 Mpc) are very few. However, the study done by Shaver (1987) using catalogs of quasars showed that a superstructure with a radius of ~200 h−1 Mpc and with a density in excess of δ ≈ 1 may exist at a distance of ~800 h−1 Mpc.
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MAROTO, ANTONIO L. "DARK ENERGY IN MOTION." International Journal of Modern Physics D 15, no. 12 (December 2006): 2165–70. http://dx.doi.org/10.1142/s0218271806009492.
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Recent large-scale peculiar velocity surveys suggest that large matter volumes could be moving with appreciable velocity with respect to the CMB rest frame. If confirmed, such results could conflict with the Cosmological Principle according to which the matter and CMB rest frames should converge on very large scales. In this work, we explore the possibility that such large-scale bulk flows are due, not to the motion of matter with respect to the CMB, but to the flow of dark energy with respect to matter. Indeed, when dark energy is moving, the usual definition of the CMB rest frame as that in which the CMB dipole vanishes is not appropriate. We find instead that the dipole vanishes for observers at rest with respect to the cosmic center of mass, i.e. in motion with respect to the background radiation.
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Yücesan, Sencer, Daniel Wildt, Philipp Gmeiner, Johannes Schobesberger, Christoph Hauer, Christine Sindelar, Helmut Habersack, and Michael Tritthart. "Interaction of Very Large Scale Motion of Coherent Structures with Sediment Particle Exposure." Water 13, no. 3 (January 20, 2021): 248. http://dx.doi.org/10.3390/w13030248.
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A systematic variation of the exposure level of a spherical particle in an array of multiple spheres in a high Reynolds number turbulent open-channel flow regime was investigated while using the Large Eddy Simulation method. Our numerical study analysed hydrodynamic conditions of a sediment particle based on three different channel configurations, from full exposure to zero exposure level. Premultiplied spectrum analysis revealed that the effect of very-large-scale motion of coherent structures on the lift force on a fully exposed particle resulted in a bi-modal distribution with a weak low wave number and a local maximum of a high wave number. Lower exposure levels were found to exhibit a uni-modal distribution.
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Balakumar, B. J., and R. J. Adrian. "Large- and very-large-scale motions in channel and boundary-layer flows." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 365, no. 1852 (January 22, 2007): 665–81. http://dx.doi.org/10.1098/rsta.2006.1940.
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Large-scale motions (LSMs; having wavelengths up to 2–3 pipe radii) and very-LSMs (having wavelengths more than 3 pipe radii) have been shown to carry more than half of the kinetic energy and Reynolds shear stress in a fully developed pipe flow. Studies using essentially the same methods of measurement and analysis have been extended to channel and zero-pressure-gradient boundary-layer flows to determine whether large structures appear in these canonical wall flows and how their properties compare with that of the pipe flow. The very large scales, especially those of the boundary layer, are shorter than the corresponding scales in the pipe flow, but otherwise share a common behaviour, suggesting that they arise from similar mechanism(s) aside from the modifying influences of the outer geometries. Spectra of the net force due to the Reynolds shear stress in the channel and boundary layer flows are similar to those in the pipe flow. They show that the very-large-scale and main turbulent motions act to decelerate the flow in the region above the maximum of the Reynolds shear stress.
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Katul, G. G. "The anatomy of large-scale motion in atmospheric boundary layers." Journal of Fluid Mechanics 858 (October 31, 2018): 1–4. http://dx.doi.org/10.1017/jfm.2018.731.
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The atmospheric boundary layer is the level of the atmosphere where all human activities occur. It is a layer characterized by its turbulent flow state, meaning that the velocity, temperature and scalar concentrations fluctuate over scales that range from less than a millimetre to several kilometres. It is those fluctuations that make dispersion of pollutants and transport of heat, momentum as well as scalars such as carbon dioxide or cloud-condensation nuclei efficient. It is also the layer where a ‘hand-shake’ occurs between activities on the land surface and the climate system, primarily due to the action of large energetic swirling motions or eddies. The atmospheric boundary layer experiences dramatic transitions depending on whether the underlying surface is being heated or cooled. The existing paradigm describing the size and energetics of large-scale and very large-scale eddies in turbulent flows has been shaped by decades of experiments and simulations on smooth pipes and channels with no surface heating or cooling. The emerging picture, initiated by A. A. Townsend in 1951, is that large- and very large-scale motions appear to be approximated by a collection of hairpin-shaped vortices whose population density scales inversely with distance from the boundary. How does surface heating, quintessential to the atmospheric boundary layer, alter this canonical picture? What are the implications of such a buoyancy force on the geometry and energy distribution across velocity components in those large eddies? How do these large eddies modulate small eddies near the ground? Answering these questions and tracking their consequences to existing theories used today to describe the flow statistics in the atmospheric boundary layer are addressed in the work of Salesky & Anderson (J. Fluid Mech., vol. 856, 2018, pp. 135–168). The findings are both provocative and surprisingly simple.
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Cameron, S. M., V. I. Nikora, and M. T. Stewart. "Very-large-scale motions in rough-bed open-channel flow." Journal of Fluid Mechanics 814 (February 9, 2017): 416–29. http://dx.doi.org/10.1017/jfm.2017.24.
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Long-duration particle image velocimetry measurements in rough-bed open-channel flows (OCFs) reveal that the pre-multiplied spectra of the streamwise velocity have a bimodal distribution due to the presence of large- and very-large-scale motions (LSMs and VLSMs, respectively). The existence of VLSMs in boundary layers, pipes and closed channels has been acknowledged for some time, but strong supporting evidence for their presence in OCF has been lacking. The data reported in this paper fill this gap. Length scales of the LSMs and VLSMs in OCF exhibit different scaling properties; whereas the streamwise length of the LSM scales with the flow depth, the VLSM streamwise length does not scale purely with flow depth and may additionally depend on other scales such as the channel width, roughness height or viscous length. The transverse extent of the LSMs was found to increase with increasing elevation, but the VLSM transverse scale is anchored around two flow depths. The origin and nature of LSMs and VLSMs are still to be resolved, but differences in their scaling suggest that VLSMs in rough-bed OCFs form independently rather than as a spatial alignment of LSMs.
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Hmoudou, K., W. Allan, K. Goni Boulama, and X. Wu. "Very large-scale computation of very small-scale motions in a fully developed pipe flow." International Journal for Numerical Methods in Fluids 67, no. 11 (October 6, 2010): 1437–55. http://dx.doi.org/10.1002/fld.2425.
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de Giovanetti, Matteo, Hyung Jin Sung, and Yongyun Hwang. "Streak instability in turbulent channel flow: the seeding mechanism of large-scale motions." Journal of Fluid Mechanics 832 (October 26, 2017): 483–513. http://dx.doi.org/10.1017/jfm.2017.697.
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It has often been proposed that the formation of large-scale motion (or bulges) is a consequence of successive mergers and/or growth of near-wall hairpin vortices. In the present study, we report our direct observation that large-scale motion is generated by an instability of an ‘amplified’ streaky motion in the outer region (i.e. very-large-scale motion). We design a numerical experiment in turbulent channel flow up to $Re_{\unicode[STIX]{x1D70F}}\simeq 2000$ where a streamwise-uniform streaky motion is artificially driven by body forcing in the outer region computed from the previous linear theory (Hwang & Cossu, J. Fluid Mech., vol. 664, 2015, pp. 51–73). As the forcing amplitude is increased, it is found that an energetic streamwise vortical structure emerges at a streamwise wavelength of $\unicode[STIX]{x1D706}_{x}/h\simeq 1{-}5$ ($h$ is the half-height of the channel). The application of dynamic mode decomposition and the examination of turbulence statistics reveal that this structure is a consequence of the sinuous-mode instability of the streak, a subprocess of the self-sustaining mechanism of the large-scale outer structures. It is also found that the statistical features of the vortical structure are remarkably similar to those of the large-scale motion in the outer region. Finally, it is proposed that the largest streamwise length of the streak instability determines the streamwise length scale of very-large-scale motion.
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BAILEY, SEAN C. C., and ALEXANDER J. SMITS. "Experimental investigation of the structure of large- and very-large-scale motions in turbulent pipe flow." Journal of Fluid Mechanics 651 (March 24, 2010): 339–56. http://dx.doi.org/10.1017/s0022112009993983.
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Multi-point velocity measurements have been performed in turbulent pipe flow at ReD = 1.5 × 105 and combined with cross-spectral and proper orthogonal decomposition analysis to elucidate information on the structure of the large- and very-large-scale motions in the outer layer of wall-bounded flows. The results indicate that in the outer layer the large-scale motions (LSM) may be composed of detached eddies with a wide range of azimuthal scales, whereas in the logarithmic layer they are attached. The very-large-scale motions (VLSM) have large radial scales, are concentrated around a single azimuthal mode and make a smaller angle with the wall compared to the LSM. The results support a hypothesis that only the detached LSM in the outer layer align to form the VLSM.
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Karri, Sirisha S. "Toward an analog very large scale integration system for perceiving depth through motion parallax." Optical Engineering 44, no. 6 (June 1, 2005): 066402. http://dx.doi.org/10.1117/1.1930947.
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LEE, JAE HWA, and HYUNG JIN SUNG. "Very-large-scale motions in a turbulent boundary layer." Journal of Fluid Mechanics 673 (February 17, 2011): 80–120. http://dx.doi.org/10.1017/s002211201000621x.
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Direct numerical simulation of a turbulent boundary layer was performed to investigate the spatially coherent structures associated with very-large-scale motions (VLSMs). The Reynolds number was varied in the range Reθ = 570–2560. The main simulation was conducted by using a computational box greater than 50δo in the streamwise domain, where δo is the boundary layer thickness at the inlet, and inflow data was obtained from a separate inflow simulation based on Lund's method. Inspection of the three-dimensional instantaneous fields showed that groups of hairpin vortices are coherently arranged in the streamwise direction and that these groups create significantly elongated low- and high-momentum regions with large amounts of Reynolds shear stress. Adjacent packet-type structures combine to form the VLSMs; this formation process is attributed to continuous stretching of the hairpins coupled with lifting-up and backward curling of the vortices. The growth of the spanwise scale of the hairpin packets occurs continuously, so it increases rapidly to double that of the original width of the packets. We employed the modified feature extraction algorithm developed by Ganapathisubramani, Longmire & Marusic (J. Fluid Mech., vol. 478, 2003, p. 35) to identify the properties of the VLSMs of hairpin vortices. In the log layer, patches with the length greater than 3δ–4δ account for more than 40% of all the patches and these VLSMs contribute approximately 45% of the total Reynolds shear stress included in all the patches. The VLSMs have a statistical streamwise coherence of the order of ~6δ; the spatial organization and coherence decrease away from the wall, but the spanwise width increases monotonically with the wall-normal distance. Finally, the application of linear stochastic estimation demonstrated the presence of packet organization in the form of a train of packets in the log layer.
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Agnew, Tom A., Hao Le, and Tom Hirose. "Estimation of large-scale sea-ice motion from SSM/I 85.5 GHz imagery." Annals of Glaciology 25 (1997): 305–11. http://dx.doi.org/10.3189/s0260305500014191.
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This paper describes the application of an automated cross-correlation technique to pairs of 85.5 GHz Special Sensor Microwave Imager (SSM/I) images to obtain ice motion over the entire Arctic Basin for a contiguous two month period between December 1993 and January 1994. Although the surface ice information in the imagery is coarse and noisy, the area cross-correlation method is quite successful in picking up ice-motion information. The accuracy of 85.5 GHz SSM/I derived ice motions is evaluated by comparing results with Arctic buoy drift. Over 390 comparisons with buoy-drift estimates of ice displacement were made with an overall correlation of 0.75 and an average vector magnitude error in ice velocity of 3.5 km d−1. The main difficulty with the automated technique is the tendency to overestimate ice displacement compared to buoy data by about 14%. Two detailed examples of ice motion are presented. The first occurred in December 1993, when a major westward shift in the ice pack took place in the Canada Basin and opened up a very large lead off Banks and Prince Patrick Islands. The second example occurred in January 1994, when an intense anticyclone over the Canada Basin produced a strong Beaufort Gyre.
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Agnew, Tom A., Hao Le, and Tom Hirose. "Estimation of Large-Scale Sea-Ice Motion from SSM/I 85.5 GHz Imagery." Annals of Glaciology 25 (1997): 305–11. http://dx.doi.org/10.1017/s0260305500014191.
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This paper describes the application of an automated cross-correlation technique to pairs of 85.5 GHz Special Sensor Microwave Imager (SSM/I) images to obtain Ice motion over the entire Arctic Basin for a contiguous two month period between December 1993 and January 1994. Although the surface ice information in the imagery is coarse and noisy, the area cross-correlation method is quite successful in picking up ice-motion information. The accuracy of 85.5 GHz SSM/I derived ice motions is evaluated by comparing results with Arctic buoy drift. Over 390 comparisons with buoy-drift estimates of ice displacement were made with an overall correlation of 0.75 and an average vector magnitude error in ice velocity of 3.5 km d−1. The main difficulty with the automated technique is the tendency to overestimate ice displacement compared to buoy data by about 14%. Two detailed examples of ice motion are presented. The first occurred in December 1993, when a major westward shift in the ice pack took place in the Canada Basin and opened up a very large lead off Banks and Prince Patrick Islands. The second example occurred in January 1994, when an intense anticyclone over the Canada Basin produced a strong Beaufort Gyre.
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Elsey, Matt, Selim Esedoḡlu, and Peter Smereka. "Large-scale simulation of normal grain growth via diffusion-generated motion." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, no. 2126 (July 21, 2010): 381–401. http://dx.doi.org/10.1098/rspa.2010.0194.
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Diffusion-generated motion is used to perform a very large-scale simulation of normal grain growth in three dimensions with high accuracy. The method is based on the diffusion of signed distance functions and shares similarities with level-set methods. The Herring-angle condition at junctions and topological transitions are naturally captured with this formulation. This approach offers significant advantages over existing numerical methods and allows for accurate computations on scales not previously possible. A fully resolved simulation of normal grain growth, initially containing over 130 000 grains in three dimensions, is presented and analysed. It is shown that the average grain radius grows as the square root of time and the grain-size distribution is self-similar. Good agreement with other theoretical predictions, experimental results and simulation results via other techniques is also demonstrated.
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Lee, Jae-Hwa, and Hyung-Jin Sung. "A Direct Numerical Simulation Study on the very Large-Scale Motion in Turbulent Boundary Layer." Transactions of the Korean Society of Mechanical Engineers B 33, no. 12 (December 1, 2009): 977–82. http://dx.doi.org/10.3795/ksme-b.2009.33.12.977.
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Michalewicz, Marek T., and Per Nyberg. "Equation-of-Motion O(N) Electronic Structure Studies of Very Large Systems (N ~ 10 7 )." Australian Journal of Physics 52, no. 5 (1999): 919. http://dx.doi.org/10.1071/ph99002.
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Extremely fast parallel implementation of the equation-of-motion method for electronic structure computations is presented. The method can be applied to non-periodic, disordered nanocrystalline samples, transition metal oxides and other systems. It scales linearly, O(N), runs with a speed of up to 43 GFLOPS on a NEC SX-4 vector-parallel supercomputer with 32 processors and computes electronic densities of states (DOS) for multi-million atom samples in mere minutes. The largest test computation performed was for the electronic DOS for a TiO2 sample consisting of 7,623,000 atoms. Mathematically, this is equivalent to obtaining the spectrum of an n × n Hermitian operator (Hamiltonian) where n = 38;115; 000. We briefly discuss the practical implications of being able to perform electronic structure computations of this great speed and scale.
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Hellström, Leo H. O., Aman Sinha, and Alexander J. Smits. "Visualizing the very-large-scale motions in turbulent pipe flow." Physics of Fluids 23, no. 1 (January 2011): 011703. http://dx.doi.org/10.1063/1.3533016.
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Bothun, G. "The motion of test particles and cosmological interpretations: the role of MOND." Canadian Journal of Physics 93, no. 2 (February 2015): 139–50. http://dx.doi.org/10.1139/cjp-2014-0165.
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Throughout history, observations of the motions of objects in the Universe have provided the foundation for various cosmological models. In many cases, the invoked causes of the observed motion appeal to mysterious elements. Indeed, the very first test motion was that of the retrograde motion of Mars, which lead to a required epicycle to save the model (e.g., Ptolemy’s unmoving Earth). By the early 1840s, from approximately 50 years of orbital data (since its 1789 discovery) it was apparent that Uranus was disobeying the Newtonian rules in its orbit and speculation mounted that a “large unseen mass” was perturbing the orbit. Using Uranus as a test particle then yields the first notion of dark matter (DM). Alas, it was not DM but merely Neptune, discovered in September 1846. By 1859 enough data had been gathered to reveal that Mercury is also not obeying Newtonian physics but rather revealing curved space–time. The continuation of this history is now set in scales larger than the Solar System. Observations suggest two basic choices: (i) gravity is fully understood and Newton’s second law is invariant (except in very strong gravity) and observed motions on galactic scales require the existence of DM (a currently unproven “epicycle”) or (ii) Newton’s second law can be modified (e.g., MOND) in certain low acceleration scale environments. In this contribution we discuss the case for and against MOND on various scales and conclude that neither MOND nor our current cosmology (ΛCDM) consistently explain all observed phenomena. In general, MOND works much better on small scales than ΛCDM but encounters difficulties on large scales. Moreover, the nature of the acoustic power spectrum of the CMB now pretty clearly shows that a fully baryonic Universe is ruled out, thus necessitating some DM component. But this should not diminish the consideration of MOND as its introduced acceleration scale; ao is fully consistent with the observed structural properties of galaxies in a way that the DM halo paradigm cannot match. Indeed, despite many attempts to falsify MOND, it has always come back from its proclaimed death to provide unique insights into the gravitational nature of galaxies, consistently raising the specter that our current understanding of gravity acting over large spatial scales may be flawed.
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Huai, J., Y. Zhang, and A. Yilmaz. "REAL-TIME LARGE SCALE 3D RECONSTRUCTION BY FUSING KINECT AND IMU DATA." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences II-3/W5 (August 20, 2015): 491–96. http://dx.doi.org/10.5194/isprsannals-ii-3-w5-491-2015.
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Kinect-style RGB-D cameras have been used to build large scale dense 3D maps for indoor environments. These maps can serve many purposes such as robot navigation, and augmented reality. However, to generate dense 3D maps of large scale environments is still very challenging. In this paper, we present a mapping system for 3D reconstruction that fuses measurements from a Kinect and an inertial measurement unit (IMU) to estimate motion. Our major achievements include: (i) Large scale consistent 3D reconstruction is realized by volume shifting and loop closure; (ii) The coarse-to-fine iterative closest point (ICP) algorithm, the SIFT odometry, and IMU odometry are combined to robustly and precisely estimate pose. In particular, ICP runs routinely to track the Kinect motion. If ICP fails in planar areas, the SIFT odometry provides incremental motion estimate. If both ICP and the SIFT odometry fail, e.g., upon abrupt motion or inadequate features, the incremental motion is estimated by the IMU. Additionally, the IMU also observes the roll and pitch angles which can reduce long-term drift of the sensor assembly. In experiments on a consumer laptop, our system estimates motion at 8Hz on average while integrating color images to the local map and saving volumes of meshes concurrently. Moreover, it is immune to tracking failures, and has smaller drift than the state-of-the-art systems in large scale reconstruction.
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Bahcall, Neta A. "Superclustering and Motion of Galaxy Clusters*." Symposium - International Astronomical Union 130 (1988): 229–38. http://dx.doi.org/10.1017/s0074180900136083.
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The evidence for the existence of very large scale structures, ∼ 100h−1 Mpc in size, as derived from the spatial distribution of clusters of galaxies is summarized. A “shell model” of galaxy clustering is described in which clusters of galaxies are located at shell intersections; the model yields results consistent with cluster observations. Detection of a ∼ 2000 km s−1 elongation in the redshift direction in the distribution of the clusters is also described. Possible causes of the effect are peculiar velocities of clusters on scales of 10–100h−1 Mpc and geometrical elongation of superclusters. If the effect is entirely due to the peculiar velocities of clusters, then superclusters have masses of order 1016,5M⊙ and may contain a larger amount of dark matter than previously anticipated.
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Naka, Yoshitsugu, Michel Stanislas, Jean-Marc Foucaut, Sebastien Coudert, Jean-Philippe Laval, and Shinnosuke Obi. "Space–time pressure–velocity correlations in a turbulent boundary layer." Journal of Fluid Mechanics 771 (April 22, 2015): 624–75. http://dx.doi.org/10.1017/jfm.2015.158.
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The spatio-temporal pressure–velocity correlation in a turbulent boundary layer is investigated so as to understand the link between pressure fluctuations and turbulent coherent structures. A new experimental set-up is developed to measure the pressure fluctuations at the wall and in the field and, simultaneously, the velocity field by stereoscopic particle image velocimetry. The present measurement area covers the whole boundary layer thickness, and the spatial resolution of the measurement is good enough to assess the representative length scales of the flow. The Reynolds number effect is quantified from the data at $\mathit{Re}_{{\it\theta}}=7300$, 10 000, 18 000. The spatio-temporal three-dimensional structures of the pressure–velocity correlations, $\boldsymbol{R}_{pu}$, $\boldsymbol{R}_{pv}$ and $\boldsymbol{R}_{pw}$, are evaluated. The wall pressure fluctuations are closely coupled with coherent structures which occupy a large region of the boundary layer in the wall-normal and spanwise directions and up to $10{\it\delta}/U_{e}$ in time, where ${\it\delta}$ and $U_{e}$ denote the boundary layer thickness and the free stream velocity. Reynolds number effects are mainly observed on the size and intensity of the pressure–velocity correlations. Conditioning the correlations on the pressure signal sign shows different types of flow phenomena linked to the positive and negative pressure events. For the wall pressure, positive pressure fluctuations appear to be correlated with the leading edge of a large sweeping motion of splatting type followed by a large ejection. The negative pressure fluctuations are linked to a localized ejection upstream, followed by a large sweeping motion downstream. For the pressure fluctuations in the field, in addition to the structures observed with the wall pressure, the pressure–velocity correlations exhibit a significant correlation in a region very extended in time. Such long structures appear to be independent of the one observed at the wall and to grow significantly in time with the Reynolds number when scaling with external variables. When conditioned by the pressure sign, clear ejection and sweeping motions are observed with associated streamwise vortical structures at a scale of the order of $0.2{\it\delta}$. These structures can be linked to the large-scale motion and very-large-scale motion previously observed by different authors and seem to organize in a scheme analogous to the near-wall cycle, but at a much larger scale.
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Li, Yun Hua, Li Man Yang, and Gui Lin Yang. "Coordinated Motion Control of Large-Scale Transporter for Conveying Heavy Frame Components in Ship-Manufacturing." Materials Science Forum 505-507 (January 2006): 1159–64. http://dx.doi.org/10.4028/www.scientific.net/msf.505-507.1159.
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A large-scale elevating transporter that has multi-wheels to be steered independently is a very complex mechatronic system. Aiming at its real-time coordinated motion control, a multi-mode steering system based on Networked Control System (NCS) is proposed to tackle the problem in the paper. Through motion synthesis, such as kinematics and dynamics modeling and analysis, and using the inherent real-time data sharing of the NCS, a cross-coupled control algorithm for improving contour accuracy is developed. This control methodology is then applied to the coordinated motion control of a practical product with multi-steering modes successfully.
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Puthenpurayil, Shiju Padmanabhan, Indrajit Chakrabarti, Rishi Virdi, and Harsh Kaushik. "Very large scale integration architecture for block‐matching motion estimation using adaptive rood pattern search algorithm." IET Circuits, Devices & Systems 10, no. 4 (July 2016): 309–16. http://dx.doi.org/10.1049/iet-cds.2015.0108.
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Lee, Jin, Junsun Ahn, and Hyung Jin Sung. "Comparison of large- and very-large-scale motions in turbulent pipe and channel flows." Physics of Fluids 27, no. 2 (February 2015): 025101. http://dx.doi.org/10.1063/1.4906805.
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Lee, Jin, Jae Hwa Lee, Jung-Il Choi, and Hyung Jin Sung. "Spatial organization of large- and very-large-scale motions in a turbulent channel flow." Journal of Fluid Mechanics 749 (May 23, 2014): 818–40. http://dx.doi.org/10.1017/jfm.2014.249.
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AbstractDirect numerical simulations were carried out to investigate the spatial features of large- and very-large-scale motions (LSMs and VLSMs) in a turbulent channel flow ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Re}_{\tau }=930$). A streak detection method based on the streamwise velocity fluctuations was used to individually trace the cores of LSMs and VLSMs. We found that both the LSM and VLSM populations were large. Several of the wall-attached LSMs stretched toward the outer regions of the channel. The VLSMs consisted of inclined outer LSMs and near-wall streaks. The number of outer LSMs increased linearly with the streamwise length of the VLSMs. The temporal features of the low-speed streaks in the outer region revealed that growing and merging events dominated the large-scale (1–$3\delta $) structures. The VLSMs $({>}3\delta )$ were primarily created by merging events, and the statistical analysis of these events supported that the merging of large-scale upstream structures contributed to the formation of VLSMs. Because the local convection velocity is proportional to the streamwise velocity fluctuations, the streamwise-aligned structures of the positive- and negative-$u$ patches suggested a primary mechanism underlying the merging events. The alignment of the positive- and negative-$u$ structures may be an essential prerequisite for the formation of VLSMs.
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Ren, Hehe, and Shujin Laima. "Very-large-scale motions in typhoons and one possible original mechanism." Ocean Engineering 246 (February 2022): 110568. http://dx.doi.org/10.1016/j.oceaneng.2022.110568.
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Discetti, Stefano, Gabriele Bellani, Ramis Örlü, Jacopo Serpieri, Carlos Sanmiguel Vila, Marco Raiola, Xiaobo Zheng, Lucia Mascotelli, Alessandro Talamelli, and Andrea Ianiro. "Characterization of very-large-scale motions in high-Re pipe flows." Experimental Thermal and Fluid Science 104 (June 2019): 1–8. http://dx.doi.org/10.1016/j.expthermflusci.2019.02.001.
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Yan, Zili, Dejun Zhu, and Danxun Li. "The vitality of very-large-scale motions upstream of an overflow structure." AIP Advances 13, no. 3 (March 1, 2023): 035217. http://dx.doi.org/10.1063/5.0141728.
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The flows upstream of a run-of-river dam, commonly utilized as an overflow structure on rivers, are complex due to heterogeneities in both streamwise and spanwise directions. In particular, very-large-scale motions (VLSMs) are greatly influenced by the overflow structure, yet relevant understandings remain limited. Reported as novel coherent structures in turbulent flows, VLSMs are recognized with the scale up to several and tens of the outer-scaled unit, and they contribute significantly to turbulent transport and mixing. To fill the gap, experiments with particle image velocimetry were conducted to investigate the vitality of VLSMs upstream of a model dam. Measurements were designed to cover broad hydraulic scope with flow heterogeneities. The results reveal that VLSMs in the present flow scenario show noticeable characteristics in both streamwise and spanwise directions. Compared to those in uniform flows, the VLSMs in present flows are found to be more energetic and stress-active.
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Papalukopoulos, C., and S. Natsiavas. "Dynamics of Large Scale Mechanical Models Using Multilevel Substructuring." Journal of Computational and Nonlinear Dynamics 2, no. 1 (July 4, 2006): 40–51. http://dx.doi.org/10.1115/1.2389043.
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An appropriate substructuring methodology is applied in order to study the dynamic response of very large scale mechanical systems. The emphasis is put on enabling a systematic study of dynamical systems with nonlinear characteristics, but the method is equally applicable to systems possessing linear properties. The accuracy and effectiveness of the methodology are illustrated by numerical results obtained for example vehicle models, having a total number of degrees of freedom lying in the order of a million or even bigger. First, the equations of motion of each component are set up by applying the finite element method. The order of the resulting models is so high that the classical substructuring methodologies become numerically ineffective or practically impossible to apply. However, the method developed overcomes these difficulties by imposing a further, multilevel substructuring of each component, based on the sparsity pattern of the stiffness matrix. In this way, the number of the equations of motion of the complete system is substantially reduced. Consequently, the numerical results presented demonstrate that besides the direct computational savings, this reduction in the dimensions enables the application of numerical codes, which capture response characteristics of dynamical systems sufficiently accurate up to a prespecified level of forcing frequencies. The study concludes by investigating biodynamic response of passenger-seat subsystem models coupled with complex mechanical models of ground vehicles resulting from deterministic or random road excitation.
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Rotunno, R., and C. Snyder. "A Generalization of Lorenz’s Model for the Predictability of Flows with Many Scales of Motion." Journal of the Atmospheric Sciences 65, no. 3 (March 1, 2008): 1063–76. http://dx.doi.org/10.1175/2007jas2449.1.
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Abstract In a seminal paper, E. N. Lorenz proposed that flows with many scales of motion in which smaller-scale error spreads to larger scales and in which the error-doubling time decreases with decreasing scale have a finite range of predictability. Although the Lorenz theory of limited predictability is widely understood and accepted, the model upon which the theory is based is less so. The primary objection to the model is that it is based on the two-dimensional vorticity equation (2DV) while simultaneously emphasizing results using a basic turbulent flow with a “−5/3” energy spectrum in the atmospheric synoptic scale instead of those using a more theoretically and observationally consistent “−3” spectrum. The present work generalizes the Lorenz model so that it may apply to the surface quasigeostrophic equations (SQGs), which are mathematically very similar to 2DV but are known to have a −5/3 kinetic energy spectrum downscale from a large-scale forcing. This generalized Lorenz model is applied here to both 2DV (with a −3 spectrum) and SQG (with a −5/3 spectrum), producing examples of flows with unlimited and limited predictability, respectively. Comparative analysis of the two models allows for the identification of the distinctive attributes of a many-scaled flow with limited predictability.
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Bui, Hien Xuan, Jia-Yuh Yu, and Chia Chou. "Impacts of Vertical Structure of Large-Scale Vertical Motion in Tropical Climate: Moist Static Energy Framework." Journal of the Atmospheric Sciences 73, no. 11 (October 20, 2016): 4427–37. http://dx.doi.org/10.1175/jas-d-16-0031.1.
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Abstract Interactions between cumulus convection and its large-scale environment have been recognized as crucial to the understanding of tropical climate and its variability. In this study, the moist static energy (MSE) budget is employed to investigate the potential impact of the vertical structure of large-scale vertical motion in tropical climate based on results from both reanalysis data and model simulation. Two domains are selected over the western and eastern Pacific with vertical motion profiles that are dominated by top-heavy and bottom-heavy structures, respectively. The bottom-heavy structure is climatologically associated with more shallow convection, while the top-heavy structure is related to more deep convection. The column-integrated vertical MSE advection of top-heavy vertical motion is positive, while that of bottom-heavy vertical motion tends to be negative. Controlling factors responsible for the above vertical MSE advection contrast are discussed based on a simple decomposition of the MSE budget equation. It was found that the sign of vertical MSE advection is determined mainly by the vertical moisture transport, the magnitude of which is very sensitive to the structure of vertical motion. A top-heavy (bottom heavy) structure of vertical motion favors an export (import) of MSE and a positive (negative) value of the vertical MSE advection.
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Wang, Guohua, Tianli Bo, Jinghong Zhang, Wei Zhu, and Xiaojing Zheng. "Transition region where the large-scale and very large scale motions coexist in atmospheric surface layer: wind tunnel investigation." Journal of Turbulence 15, no. 3 (February 28, 2014): 172–85. http://dx.doi.org/10.1080/14685248.2014.887849.
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Yuan, Jian, Dennis L. Hartmann, and Robert Wood. "Dynamic Effects on the Tropical Cloud Radiative Forcing and Radiation Budget." Journal of Climate 21, no. 11 (June 1, 2008): 2337–51. http://dx.doi.org/10.1175/2007jcli1857.1.
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Abstract Vertical velocity is used to isolate the effect of large-scale dynamics on the observed radiation budget and cloud properties in the tropics, using the methodology suggested by Bony et al. Cloud and radiation budget quantities in the tropics show well-defined responses to the large-scale vertical motion at 500 hPa. For the tropics as a whole, the ratio of shortwave to longwave cloud forcing (hereafter N) is about 1.2 in regions of upward motion, and increases to about 1.9 in regions of strong subsidence. If the analysis is restricted to oceanic regions with SST > 28°C, N does not increase as much for subsiding motions, because the stratocumulus regions are eliminated, and the net cloud forcing decreases linearly from about near zero for zero vertical velocity to about −15 W m−2 for strongly subsiding motion. Increasingly negative cloud forcing with increasing upward motion is mostly related to an increasing abundance of high, thick clouds. Although a consistent dynamical effect on the annual cycle of about 1 W m−2 can be identified, the effect of the probability density function (PDF) of the large-scale vertical velocity on long-term trends in the tropical mean radiation budget is very small compared to the observed variations. Observed tropical mean changes can be as large as ±3 W m−2, while the dynamical components are generally smaller than ±0.5 W m−2. For relatively small regions in the east and west Pacific, changes in the relative magnitude of longwave and shortwave cloud forcing can be related to the PDF of vertical velocity. The east Pacific in 1987 and 1998 showed large reductions of N in association with an increase in the fraction of the area in the domain with upward motion, and concomitant increases in high cloud. For the west Pacific in 1998, a large increase in N was caused not so much by a change in the mean vertical motion, but rather by a shift from top- to bottom-heavy upward motion.
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Fang, Jiannong, and Fernando Porté-Agel. "Large-Eddy Simulation of Very-Large-Scale Motions in the Neutrally Stratified Atmospheric Boundary Layer." Boundary-Layer Meteorology 155, no. 3 (February 20, 2015): 397–416. http://dx.doi.org/10.1007/s10546-015-0006-z.
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Lee, Jae Hwa, Hyung Jin Sung, and Ronald J. Adrian. "Space–time formation of very-large-scale motions in turbulent pipe flow." Journal of Fluid Mechanics 881 (October 25, 2019): 1010–47. http://dx.doi.org/10.1017/jfm.2019.786.
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We examine the origin of very-large-scale motions (VLSMs) in fully developed turbulent pipe flow at friction Reynolds number, $\mathit{Re}_{\unicode[STIX]{x1D70F}}=934$, using data from a direct numerical simulation. The VLSMs and the packet-like large-scale motions (LSMs) found in this study are very similar to those found in earlier studies. Three-dimensional time-evolving instantaneous fields show that one component of the process leading to the large streamwise length of VLSMs is the concatenation of adjacent streamwise LSMs caused by the continuous elongation of LSMs due to the strain component of the mean shear. Spatial organization patterns of the VLSMs and LSMs and their properties are studied by separating auto-correlation of the streamwise velocity fluctuations into the components of the VLSM and the LSM defined by low-pass/high-pass filtering in the streamwise direction. The structures of the two-point spatial correlations of the streamwise velocity component of the VLSMs and the LSMs in the streamwise-azimuthal plane are characterized by multiple maxima and complex patterns that beg explanation in terms of patterned coherent arrangements of the LSMs. Using proper orthogonal decomposition (POD), it is found that the X-shape correlation pattern of the VLSMs results from the superposition of very long helically inclined structures and streamwise-aligned structures. Further explanation of the patterns in the correlations of the VLSMs and LSMs is provided through the study of synthetically constructed arrangements of simple hairpin packet models of the LSM. Head-to-tail alignment of the model packets along streamwise and helical directions suggested by the eigenvalues of the POD creates a pair of long roll-cells centred above the logarithmic layer, and bracketing the LSMs. These roll-cells are pure kinematic consequences of the induction within the LSM packets, but they may also serve to organize smaller packets.
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Wang, Guohua, and Xiaojing Zheng. "Very large scale motions in the atmospheric surface layer: a field investigation." Journal of Fluid Mechanics 802 (August 4, 2016): 464–89. http://dx.doi.org/10.1017/jfm.2016.439.
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A field observation array for the atmospheric surface layer (ASL) was built on a dry flat bed of Qingtu Lake in Minqin (China) as the Qingtu Lake Observation Array (QLOA) site, which is similar to the Surface Layer Turbulence and Environmental Science Test (SLTEST) site in the Utah (USA) Western desert. The present observation array can synchronously perform multi-point measurements of wind velocity and temperature at different vertical and streamwise positions. In other words, three-dimensional turbulent ASL flows can be measured at the QLOA station and Reynolds numbers as high as $Re_{\unicode[STIX]{x1D70F}}\sim O(10^{6})$ can be achieved with steady wind conditions. By careful selection and pretreatment for measured data of more than 1200 h, the QLOA data have been validated to be reliable for high Reynolds number turbulent boundary layer research. Results from correlation and spectral analysis confirm that very large scale motions (VLSMs) exist in the ASL at a Reynolds number up to $Re_{\unicode[STIX]{x1D70F}}\approx 4\times 10^{6}$. Through premultiplied spectral analysis, it is revealed that the spectral energy in the high-wavenumber region decreases with height, similar to turbulent boundary layers at low or moderate Reynolds numbers, while it increases with height in the low-wavenumber region resulting in a log–linear increase of VLSMs energy with height, which is different from turbulent boundary layers at low or moderate Reynolds numbers. The present analyses support the view that the evolution of the VLSMs cannot be fully attributed to a ‘bottom-up’ mechanism alone, and probably other mechanisms, including a ‘top-down’ mechanism, also play a role.
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Shen, Ying, Shengfa Yang, and Jie Liu. "Characteristics of Very Large-Scale Motions in Rough-Bed Open-Channel Flows." Water 15, no. 7 (April 6, 2023): 1433. http://dx.doi.org/10.3390/w15071433.
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Rough-bed open-channel flows (OCFs) are ubiquitous in rivers and canals. However, the scaling and energy contents of very-large-scale motions (VLSMs) in such flows remain unclear. In this study, the above characteristics of VLSMs are experimentally investigated with the measurement of particle imaging velocimetry (PIV). VLSM wavelengths obtained via premultiplied spectra analysis were consistent with previously reported values. Comparisons with these studies ruled out the role of relative submergence, and suggested that the channel aspect ratio is key to controlling the VLSM wavelengths in OCFs. VLSMs carry approximately 60% of the turbulence kinetic energy (TKE) and 38–50% of the Reynolds stress in rough-bed OCFs. The VLSM-related TKE fraction in the 0.1–0.5H range increased with increasing friction Reynolds number, while variation in the Reynolds shear stress did not exhibit any explicit trend.
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Hwang, Yongyun. "Statistical structure of self-sustaining attached eddies in turbulent channel flow." Journal of Fluid Mechanics 767 (February 12, 2015): 254–89. http://dx.doi.org/10.1017/jfm.2015.24.
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AbstractThe linear growth of the spanwise correlation length scale with the distance from the wall in the logarithmic region of wall-bounded turbulent flows has been understood as a reflection of Townsend’s attached eddies. Based on this observation, in the present study, we perform a numerical experiment, which simulates energy-containing motions only at a given spanwise length scale in the logarithmic region, using their self-sustaining nature found recently. The self-sustaining energy-containing motions at each of the spanwise length scales are found to be self-similar with respect to the given spanwise length. Furthermore, their statistical structures are consistent with those of the attached eddies in the original theory, providing direct evidence on the existence of Townsend’s attached eddies. It is shown that a single self-sustaining attached eddy is composed of two distinct elements, one of which is a long streaky motion reaching the near-wall region, and the other is a relatively short vortical structure carrying all the velocity components. For the given spanwise length ${\it\lambda}_{z}$ between ${\it\lambda}_{z}^{+}=100$ and ${\it\lambda}_{z}\simeq 1.5h$, where $h$ is half the height of the channel, the former is found to be self-similar along $y\simeq 0.1{\it\lambda}_{z}$ and ${\it\lambda}_{x}\simeq 10{\it\lambda}_{z}$, while the latter is self-similar along $y\simeq 0.5{\it\lambda}_{z}\sim 0.7{\it\lambda}_{z}$ and ${\it\lambda}_{x}\simeq 2{\it\lambda}_{z}\sim 3{\it\lambda}_{z}$ where $y$ is the wall-normal direction. The scaling suggests that the smallest attached eddy would be a near-wall coherent motion in the form of a streak and quasi-streamwise vortices aligned to that, whereas the largest one would be an outer motion with a very-large-scale motion (VLSM) and large-scale motions (LSMs) aligned to that. The attached eddies in between, the size of which is proportional to their distance from the wall, contribute to the logarithmic region and fill the space caused by the length scale separation. The scaling is also found to yield behaviour consistent with the emergence of $k_{x}^{-1}$ spectra in a number of previous studies. Finally, a further discussion is provided, in particular on Townsend’s inactive motion and several recent theoretical findings.
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Hanjalić, K., and S. Kenjereš. "RANS-Based Very Large Eddy Simulation of Thermal and Magnetic Convection at Extreme Conditions." Journal of Applied Mechanics 73, no. 3 (October 2, 2005): 430–40. http://dx.doi.org/10.1115/1.2150499.
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For thermal and magnetic convection at very high Rayleigh and Hartman numbers, which are inaccessible to the conventional large eddy simulation, we propose a time-dependent Reynolds-average-Navier-Stokes (T-RANS) approach in which the large-scale deterministic motion is fully resolved by time and space solution, whereas the unresolved stochastic motion is modeled by a “subscale” model for which an one-point RANS closure is used. The resolved and modeled contributions to the turbulence moments are of the same order of magnitude and in the near-wall regions the modeled heat transport becomes dominant, emphasizing the role of the subscale model. This T-RANS approach, with an algebraic stress/flux subscale model, verified earlier in comparison with direct numerical simulation and experiments in classic Rayleigh-Bénard convection, is now expanded to simulate Rayleigh-Bénard (RB) convection at very high Ra numbers—at present up to O(1016)—and to magnetic convection in strong uniform magnetic fields. The simulations reproduce the convective cell structure and its reorganization caused by an increase in Ra number and effects of the magnetic field. The T-RANS simulations of classic RB indicate expected thinning of both the thermal and hydraulic wall boundary layer with an increase in the Ra number and an increase in the exponent of the Nu∝Ran correlation in accord with recent experimental findings and Kraichnan asymptotic theory.
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Lee, Jae Hwa, and Hyung Jin Sung. "Comparison of very-large-scale motions of turbulent pipe and boundary layer simulations." Physics of Fluids 25, no. 4 (April 2013): 045103. http://dx.doi.org/10.1063/1.4802048.
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Wang, Guohua, Xiaojing Zheng, and Jianjun Tao. "Very large scale motions and PM10 concentration in a high-Re boundary layer." Physics of Fluids 29, no. 6 (June 2017): 061701. http://dx.doi.org/10.1063/1.4990087.
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Rybka, Harald, Ulrike Burkhardt, Martin Köhler, Ioanna Arka, Luca Bugliaro, Ulrich Görsdorf, Ákos Horváth, et al. "The behavior of high-CAPE (convective available potential energy) summer convection in large-domain large-eddy simulations with ICON." Atmospheric Chemistry and Physics 21, no. 6 (March 22, 2021): 4285–318. http://dx.doi.org/10.5194/acp-21-4285-2021.
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Abstract. Current state-of-the-art regional numerical weather prediction (NWP) models employ kilometer-scale horizontal grid resolutions, thereby simulating convection within the grey zone. Increasing resolution leads to resolving the 3D motion field and has been shown to improve the representation of clouds and precipitation. Using a hectometer-scale model in forecasting mode on a large domain therefore offers a chance to study processes that require the simulation of the 3D motion field at small horizontal scales, such as deep summertime moist convection, a notorious problem in NWP. We use the ICOsahedral Nonhydrostatic weather and climate model in large-eddy simulation mode (ICON-LEM) to simulate deep moist convection and distinguish between scattered, large-scale dynamically forced, and frontal convection. We use different ground- and satellite-based observational data sets, which supply information on ice water content and path, ice cloud cover, and cloud-top height on a similar scale as the simulations, in order to evaluate and constrain our model simulations. We find that the timing and geometric extent of the convectively generated cloud shield agree well with observations, while the lifetime of the convective anvil was, at least in one case, significantly overestimated. Given the large uncertainties of individual ice water path observations, we use a suite of observations in order to better constrain the simulations. ICON-LEM simulates a cloud ice water path that lies between the different observational data sets, but simulations appear to be biased towards a large frozen water path (all frozen hydrometeors). Modifications of parameters within the microphysical scheme have little effect on the bias in the frozen water path and the longevity of the anvil. In particular, one of our convective days appeared to be very sensitive to the initial and boundary conditions, which had a large impact on the convective triggering but little impact on the high frozen water path and long anvil lifetime bias. Based on this limited set of sensitivity experiments, the evolution of locally forced convection appears to depend more on the uncertainty of the large-scale dynamical state based on data assimilation than of microphysical parameters. Overall, we judge ICON-LEM simulations of deep moist convection to be very close to observations regarding the timing, geometrical structure, and cloud ice water path of the convective anvil, but other frozen hydrometeors, in particular graupel, are likely overestimated. Therefore, ICON-LEM supplies important information for weather forecasting and forms a good basis for parameterization development based on physical processes or machine learning.
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Wang, G., and D. H. Richter. "Two mechanisms of modulation of very-large-scale motions by inertial particles in open channel flow." Journal of Fluid Mechanics 868 (April 15, 2019): 538–59. http://dx.doi.org/10.1017/jfm.2019.210.
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Very-large-scale motions (VLSMs) and large-scale motions (LSMs) coexist at moderate Reynolds numbers in a very long open channel flow. Direct numerical simulations two-way coupled with inertial particles are analysed using spectral information to investigate the modulation of VLSMs. In the wall-normal direction, particle distributions (mean/preferential concentration) exhibit two distinct behaviours in the inner flow and outer flow, corresponding to two highly anisotropic turbulent structures, LSMs and VLSMs. This results in particle inertia’s non-monotonic effects on the VLSMs: low inertia (based on the inner scale) and high inertia (based on the outer scale) both strengthen the VLSMs, whereas moderate and very high inertia have little influence. Through conditional tests, low- and high-inertia particles enhance VLSMs following two distinct routes. Low-inertia particles promote VLSMs indirectly through the enhancement of the regeneration cycle (the self-sustaining mechanism of LSMs) in the inner region, whereas high-inertia particles enhance the VLSM directly through contribution to the Reynolds shear stress at similar temporal scales in the outer region. This understanding also provides more general insight into inner–outer interaction in high-Reynolds-number, wall-bounded flows.
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Hsia, S. C., and P. Y. Hong. "Very large scale integration (VLSI) implementation of low-complexity variable block size motion estimation for H.264/AVC coding." IET Circuits, Devices & Systems 4, no. 5 (2010): 414. http://dx.doi.org/10.1049/iet-cds.2009.0200.
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Wu, Xiaohua, J. R. Baltzer, and R. J. Adrian. "Direct numerical simulation of a 30R long turbulent pipe flow at R+ = 685: large- and very large-scale motions." Journal of Fluid Mechanics 698 (April 5, 2012): 235–81. http://dx.doi.org/10.1017/jfm.2012.81.
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AbstractFully developed incompressible turbulent pipe flow at Reynolds number ${\mathit{Re}}_{D} = 24\hspace{0.167em} 580$ (based on bulk velocity) and Kármán number ${R}^{+ } = 684. 8$ is simulated in a periodic domain with a length of $30$ pipe radii $R$. While single-point statistics match closely with experimental measurements, questions have been raised of whether streamwise energy spectra calculated from spatial data agree with the well-known bimodal spectrum shape in premultiplied spectra produced by experiments using Taylor’s hypothesis. The simulation supports the importance of large- and very large-scale motions (VLSMs, with streamwise wavelengths exceeding $3R$). Wavenumber spectral analysis shows evidence of a weak peak or flat region associated with VLSMs, independent of Taylor’s hypothesis, and comparisons with experimental spectra are consistent with recent findings (del Álamo & Jiménez, J. Fluid Mech., vol. 640, 2009, pp. 5–26) that the long-wavelength streamwise velocity energy peak is overestimated when Taylor’s hypothesis is used. Yet, the spectrum behaviour retains otherwise similar properties to those documented based on experiment. The spectra also reveal the importance of motions of long streamwise length to the $uu$ energy and $uv$ Reynolds stress and support the general conclusions regarding these quantities formed using experimental measurements. Space–time correlations demonstrate that low-level correlations involving very large scales persist over $40R/ {U}_{\mathit{bulk}} $ in time and indicate that these motions convect at approximately the bulk velocity, including within the region approaching the wall. These very large streamwise motions are also observed to accelerate the flow near the wall based on force spectra, whereas smaller scales tend to decelerate the mean streamwise flow profile, in accordance with the behaviour observed in net force spectra of prior experiments. Net force spectra are resolved for the first time in the buffer layer and reveal an unexpectedly complex structure.