scholarly journals Visual Simulation of Detailed Turbulent Water by Preserving the Thin Sheets of Fluid

Symmetry ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 502 ◽  
Author(s):  
Jong-Hyun Kim ◽  
Wook Kim ◽  
Young Kim ◽  
Jung Lee
Keyword(s):  
Turbulent Flows ◽  
Visual Simulation ◽  
Numerical Dissipation ◽  
Small Scale ◽  
Thin Sheets ◽  
Global Flow ◽  
Low Mass ◽  
The Difference ◽  
Water Simulation ◽  
Turbulent Water

When we perform particle-based water simulation, water particles are often increased dramatically because of particle splitting around breaking holes to maintain the thin fluid sheets. Because most of the existing approaches do not consider the volume of the water particles, the water particles must have a very low mass to satisfy the law of the conservation of mass. This phenomenon smears the motion of the water, which would otherwise result in splashing, thereby resulting in artifacts such as numerical dissipation. Thus, we propose a new fluid-implicit, particle-based framework for maintaining and representing the thin sheets and turbulent flows of water. After splitting the water particles, the proposed method uses the ghost density and ghost mass to redistribute the difference in mass based on the volume of the water particles. Next, small-scale turbulent flows are formed in local regions and transferred in a smooth manner to the global flow field. Our results show us the turbulence details as well as the thin sheets of water, thereby obtaining an aesthetically pleasing improvement compared with existing methods.

Lattice Boltzmann Shallow Water Simulation With Surface Pressure

2018 ◽  
pp. 293-336
Author(s):  
Iñaki Zabala ◽  
Jesús M. Blanco
Keyword(s):  
Shallow Water ◽  
Surface Pressure ◽  
Scale Effects ◽  
Small Scale ◽  
Pressure Gradients ◽  
Simulation Domain ◽  
Consistent Manner ◽  
The Difference ◽  
Water Simulation ◽  
3D Problem

Shallow water conditions are produced in coastal and river areas and allow the simplification of fluid solving by integrating in height to the fluid equations, discarding vertical flow so a 3D problem is solved with a set of 2D equations. Usually the boundary conditions defined by the surface pressure are discarded, as it is considered that the difference in atmospheric pressure in simulation domain is irrelevant in most hydraulic and coastal engineering scenarios. However, anticyclones and depressions produce noticeable pressure gradients that may affect the consequences of phenomena like tides and tsunamis. This chapter demonstrates how to remove this weakness from the LBM-SW by incorporating pressure into the LBM for this kind of scenario in a consistent manner. Other small-scale effects like buoyancy may be solved using this approach.

scholarly journals QPOs in compact binaries from small scale eruptions in an inner magnetized disk

2020 ◽  
Author(s):  
Nicolas Scepi ◽  
Mitchell C Begelman ◽  
Jason Dexter
Keyword(s):  
Rapid Heating ◽  
Small Scale ◽  
Type B ◽  
Periodic Oscillations ◽  
X Ray ◽  
Compact Binaries ◽  
Heating And Cooling ◽  
Low Mass ◽  
X Ray Binaries ◽  
Standard Disk

Abstract Dwarf novæ (DNe) and low mass X-ray binaries (LMXBs) are compact binaries showing variability on time scales from years to less than seconds. Here, we focus on explaining part of the rapid fluctuations in DNe, following the framework of recent studies on the monthly eruptions of DNe that use a hybrid disk composed of an outer standard disk and an inner magnetized disk. We show that the ionization instability, that is responsible for the monthly eruptions of DNe, is also able to operate in the inner magnetized disk. Given the low density and the fast accretion time scale of the inner magnetized disk, the ionization instability generates small, rapid heating and cooling fronts propagating back and forth in the inner disk. This leads to quasi-periodic oscillations (QPOs) with a period of the order of 1000 s. A strong prediction of our model is that these QPOs can only develop in quiescence or at the beginning/end of an outburst. We propose that these rapid fluctuations might explain a subclass of already observed QPOs in DNe as well as a, still to observe, subclass of QPOs in LMXBs. We also extrapolate to the possibility that the radiation pressure instability might be related to Type B QPOs in LMXBs.

Feedback Control of Turbulence

1994 ◽  
Vol 47 (6S) ◽  
pp. S3-S13 ◽  
Author(s):  
Parviz Moin ◽  
Thomas Bewley
Keyword(s):  
Feedback Control ◽  
Turbulent Flows ◽  
Systems Approach ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Small Scale ◽  
Flow Equations ◽  
Active Feedback ◽  
Active Feedback Control ◽  
Mathematical Techniques

A brief review of current approaches to active feedback control of the fluctuations arising in turbulent flows is presented, emphasizing the mathematical techniques involved. Active feedback control schemes are categorized and compared by examining the extent to which they are based on the governing flow equations. These schemes are broken down into the following categories: adaptive schemes, schemes based on heuristic physical arguments, schemes based on a dynamical systems approach, and schemes based on optimal control theory applied directly to the Navier-Stokes equations. Recent advances in methods of implementing small scale flow control ideas are also reviewed.

scholarly journals Analysis of livestock breeders’ perceptions and their adaptation measures to climate change in Morocco‘s arid rangelands

2020 ◽  
Vol 6 (1) ◽  
pp. 1-25
Author(s):  
Wadii Snaibi
Keyword(s):  
Climate Change ◽  
Local Level ◽  
Small Scale ◽  
Climate Data ◽  
Chi Square ◽  
Adaptation Measures ◽  
Significant Difference ◽  
The Difference ◽  
Eastern Morocco ◽  
Climate Analysis

AbstractThe high plateaus of eastern Morocco are already suffering from the adverse impacts of climate change (CC), as the local populations’ livelihoods depend mainly on extensive sheep farming and therefore on natural resources. This research identifies breeders’ perceptions about CC, examines whether they correspond to the recorded climate data and analyses endogenous adaptation practices taking into account the agroecological characteristics of the studied sites and the difference between breeders’ categories based on the size of owned sheep herd. Data on perceptions and adaptation were analyzed using the Chi-square independence and Kruskal-Wallis tests. Climate data were investigated through Mann-Kendall, Pettitt and Buishand tests.Herders’ perceptions are in line with the climate analysis in term of nature and direction of observed climate variations (downward trend in rainfall and upward in temperature). In addition, there is a significant difference in the adoption frequency of adaptive strategies between the studied agroecological sub-zones (χ2 = 14.525, p <.05) due to their contrasting biophysical and socioeconomic conditions, as well as among breeders’ categories (χ2 = 10.568, p < .05) which attributed mainly to the size of sheep flock. Policy options aimed to enhance local-level adaptation should formulate site-specific adaptation programs and prioritise the small-scale herders.

Fluid Flow and Heat Transfer of Liquid Sodium in Small-Scale Heat Sinks With Different Geometries

2021 ◽  
Author(s):  
Mahyar Pourghasemi ◽  
Nima Fathi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Sections ◽  
Heat Sink ◽  
Volume Ratio ◽  
Heat Sinks ◽  
Liquid Sodium ◽  
Small Scale ◽  
Nusselt Numbers ◽  
The Difference

Abstract 3-D numerical simulations are performed to investigate liquid sodium (Na) flow and the heat transfer within miniature heat sinks with different geometries and hydraulic diameters of less than 5 mm. Two different straight small-scale heat sinks with rectangular and triangular cross-sections are studied in the laminar flow with the Reynolds number up to 1900. The local and average Nusselt numbers are obtained and compared against eachother. At the same surface area to volume ratio, rectangular minichannel heat sink leads to almost 280% higher convective heat transfer rate in comparison with triangular heat sink. It is observed that the difference between thermal efficiencies of rectangular and triangular minichannel heat sinks was independent of flow Reynolds number.

scholarly journals Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis

2018 ◽  
Vol 857 ◽  
pp. 270-290 ◽  
Author(s):  
Josef Hasslberger ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Small Scale ◽  
Flow Topology ◽  
Two Phase ◽  
Local Flow ◽  
Interface Curvature

This paper presents a detailed investigation of flow topologies in bubble-induced two-phase turbulence. Two freely moving and deforming air bubbles that have been suspended in liquid water under counterflow conditions have been considered for this analysis. The direct numerical simulation data considered here are based on the one-fluid formulation of the two-phase flow governing equations. To study the development of coherent structures, a local flow topology analysis is performed. Using the invariants of the velocity gradient tensor, all possible small-scale flow structures can be categorized into two nodal and two focal topologies for incompressible turbulent flows. The volume fraction of focal topologies in the gaseous phase is consistently higher than in the surrounding liquid phase. This observation has been argued to be linked to a strong vorticity production at the regions of simultaneous high fluid velocity and high interface curvature. Depending on the regime (steady/laminar or unsteady/turbulent), additional effects related to the density and viscosity jump at the interface influence the behaviour. The analysis also points to a specific term of the vorticity transport equation as being responsible for the induction of vortical motion at the interface. Besides the known mechanisms, this term, related to surface tension and gradients of interface curvature, represents another potential source of turbulence production that lends itself to further investigation.

Dust discs around low-mass main-sequence stars

1988 ◽  
Vol 325 (1587) ◽  
pp. 423-437 ◽  
Keyword(s):  
Thermal Emission ◽  
Orbital Evolution ◽  
Prima Facie ◽  
Mass Star ◽  
Orbital Inclination ◽  
Sources And Sinks ◽  
Central Regions ◽  
Low Mass ◽  
The Difference ◽  
Two Sides

Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars a Lyr, a PsA, P Pic and 8 Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The discs have outer radii that range between about 250 and 800 AU and have dust masses that are unlikely to exceed about 300 Earth masses. Assuming a gas: dust ratio of 100:1 for the pre-mainsequence disc this corresponds to a mass of ca. 0.1 M Q comparable to that of the premain-sequence star HL Tau. The colour, diameter and thickness of the optical image of P Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. Although replenishment of these discs may be occurring, for example by grains ejected from comets, discs of initial radius ca. 1000 AU can survive Poynting-Robertson depletion over the stellar age and there is no prima facie evidence as yet in favour of a balance between sources and sinks of dust.

scholarly journals DEVELOPMENT OF VERSATILE MOBILE MAPPING SYSTEM ON A SMALL SCALE

2020 ◽  
Vol XLIII-B1-2020 ◽  
pp. 271-275
Author(s):  
T. Tachi ◽  
Y. Wang ◽  
R. Abe ◽  
T. Kato ◽  
N. Maebashi ◽  
...  
Keyword(s):  
Small Scale ◽  
Road Maintenance ◽  
Data Utilization ◽  
Mobile Mapping ◽  
The Road ◽  
Map Generation ◽  
Mapping Technology ◽  
Light Vehicle ◽  
The Difference ◽  
Asset Inventory

Abstract. Mobile mapping technology is an effective method to collect geospatial data with high point density and accuracy. It is mainly used for asset inventory and map generation, as well as road maintenance (detecting road cracks and ruts, and measuring flatness). Equipment of former mobile mapping systems (MMS) is large in size and usually installed (hard-mounted) onto dedicated vehicle. Cost-effectiveness and flexibility of MMS have not been regarded as important until Leica Pegasus series, a much smaller system with integrated and configurable components, come out. In this paper, we show you how we realize a versatile MMS with a Pegasus II loaded on a remodelled Japanese light vehicle (small size and less than a cubic capacity of 660 cc). Besides Pegasus II and data-processing PC, we equip this system with a small crane to bring the sensor onto a different platform, an electric cart to survey narrow roads or pedestrian walkway, and a boat attachment so that the sensor can be fixed on a boat. Thus, one Pegasus II can collect data from various platforms. This paper also discusses the precision and accuracy of the Pegasus II working on various platforms. When mounted on a light vehicle, we verified the accuracy of the difference with GCP and evaluated the accuracy of the road maintenance (detecting road cracks and ruts, and measuring flatness). When mounted on an electric cart, we verified the accuracy of the difference with GCP on a pedestrian road and generated road hazard map as a data utilization. When mounted on a boat, we verified the accuracy of the difference with GCP on a dam slope and created slope shading map of landslide area as a data utilization. It turns out that Pegasus II can totally achieve to required surveying-grade.

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