Numerical Hydrodynamics of Estuaries

1980 ◽  
pp. 115-146 ◽  
Author(s):  
John Eric Edinger ◽  
Edward M. Buchak
Keyword(s):  
Numerical Hydrodynamics

Relativistic Numerical Hydrodynamics

2003 ◽  
Author(s):  
James R. Wilson ◽  
Grant J. Mathews
Keyword(s):  
Numerical Hydrodynamics

scholarly journals A Dynamical Systems Approach to Nonlinear Stellar Pulsations

1993 ◽  
Vol 134 ◽  
pp. 9-31
Author(s):  
J. R. Buchler
Keyword(s):  
Dynamical Systems ◽  
Ad Hoc ◽  
Systems Approach ◽  
Chaotic Behavior ◽  
Theoretical Explanation ◽  
Modal Interactions ◽  
Reduction Techniques ◽  
Numerical Hydrodynamics ◽  
Stellar Pulsations ◽  
The One

AbstractOver the last decade we have seen the application of novel techniques to the old problem of nonlinear stellar pulsations. Together with numerical hydrodynamics this approach provides a more fundamental understanding of the systematics of the pulsational behavior. For weakly nonadiabatic pulsations, whether regular or multi-periodic, dimensional reduction techniques lead to amplitude equations and to a description in terms of modal interactions and resonances. In particular they shed new light on the bump progression in the classical Cepheids. In more dissipative stars numerical hydrodynamical modelling has uncovered the existence of irregular variability, both in radiative and in convective models. An application of modern dynamical systems techniques has shown that this behavior occurs according to well understood routes from regular to chaotic behavior. The mechanism is very robust and represents the first non ad hoc theoretical explanation of irregular stellar variability. Finally, we discuss how a comparison with observations of irregular variability shows the need for more suitable observations, on the one hand, and of better techniques of signal processing, on the other.

Why Ultrarelativistic Numerical Hydrodynamics is Difficult

1986 ◽  
pp. 449-475 ◽  
Author(s):  
Michael L. Norman ◽  
Karl-Heinz A. Winkler
Keyword(s):  
Numerical Hydrodynamics

Implicit Large-Eddy Simulation of Transition and Turbulence Decay

2019 ◽  
Author(s):  
Fernando F. Grinstein
Keyword(s):  
Large Eddy Simulation ◽  
Isotropic Turbulence ◽  
Navier Stokes ◽  
Homogeneous Isotropic Turbulence ◽  
Eddy Simulation ◽  
Numerical Hydrodynamics ◽  
Geometrical Complexity ◽  
Turbulence Decay ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

Abstract Accurate predictions with quantifiable uncertainties are essential to many practical turbulent flow applications exhibiting extreme geometrical complexity and broad ranges of length and time scales. Under-resolved computer simulations are typically unavoidable in such applications, and implicit large-eddy simulation (ILES) often becomes the effective strategy. We focus on ILES initialized with well-characterized 2563 homogeneous isotropic turbulence datasets generated with direct numerical simulation (DNS). ILES is based on the LANL xRAGE code, and solutions are examined as function of resolution for 643, 1283, 2563, and 5123 grids. The ILES performance of new directionally-unsplit high-order numerical hydrodynamics algorithms in xRAGE is examined. Compared to the initial 2563 DNS, we find longer inertial subranges and higher turbulence Re for directional-split 2563 & 5123 xRAGE — attributed to having linked DNS (Navier-Stokes based) solutions to nominally inviscid (higher Re) Euler based ILES solutions. Alternatively — for fixed resolution, we find that significantly higher simulated turbulence Re can be achieved with unsplit (vs. split) discretizations.

scholarly journals Numerical Hydrodynamics: SPH versus AMR

2001 ◽  
Vol 200 ◽  
pp. 563-566
Author(s):  
Tomek Plewa
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Computational Hydrodynamics ◽  
Advantages And Disadvantages ◽  
Numerical Hydrodynamics ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

The advantages and disadvantages of two approaches to astrophysical hydrodynamics, Smoothed Particle Hydrodynamics (SPH) and Adaptive Mesh Refinement (AMR), are briefly discussed together with some current problems of computational hydrodynamics.

scholarly journals GRAVITATIONAL COLLAPSE AND WEAK INTERACTIONS

1966 ◽  
Vol 44 (11) ◽  
pp. 2553-2594 ◽  
Author(s):  
W. David Arnett
Keyword(s):  
General Relativity ◽  
Energy Transfer ◽  
Equation Of State ◽  
Gravitational Collapse ◽  
Massive Star ◽  
Weak Interactions ◽  
Approximation Procedure ◽  
The Core ◽  
Numerical Hydrodynamics ◽  
Subsequent Behavior

The behavior of a massive star during its final catastrophic stages of evolution has been investigated theoretically, with particular emphasis upon the effect of electron-type neutrino interactions. The methods of numerical hydrodynamics, with coupled energy transfer in the diffusion approximation, were used. In this respect, this investigation differs from the work of Colgate and White (1964) in which a "neutrino deposition" approximation procedure was used. Gravitational collapse initiated by electron capture and by thermal disintegration of nuclei in the stellar center is examined, and the subsequent behavior does not depend sensitively upon which process causes the collapse.As the density and temperature of the collapsing stellar core increase, the material becomes opaque to electron-type neutrinos and energy is transferred by these neutrinos to regions of the star less tightly bound by gravity. Ejection of the outer layers of the star can result. This phenomenon has been identified with supernovae.Uncertainty concerning the equation of state of a hot, dense nucleon gas causes uncertainty in the temperature of the collapsing matter. This affects the rate of energy transfer by electron-type neutrinos and the rate of energy lost to the star by muon-type neutrinos.The effects of general relativity do not appear to become important in the core until after the ejection of the outer layers.

First step toward numerical hydrodynamics: SPH and Finite Differences with artificial dissipative terms

2010 ◽  
Author(s):  
J. P. Cruz-Pérez ◽  
J. A. González ◽  
F. S. Guzmán ◽  
F. D. Lora-Clavijo ◽  
H. A. Morales-Tecotl ◽  
...  
Keyword(s):  
Finite Differences ◽  
Numerical Hydrodynamics ◽  
Dissipative Terms

scholarly journals Early evolution of viscous and self-gravitating circumstellar disks with a dust component

2018 ◽  
Vol 614 ◽  
pp. A98 ◽  
Author(s):  
Eduard I. Vorobyov ◽  
Vitaly Akimkin ◽  
Olga Stoyanovskaya ◽  
Yaroslav Pavlyuchenkov ◽  
Hauyu Baobab Liu
Keyword(s):  
Radial Distance ◽  
Circumstellar Disks ◽  
Growth Efficiency ◽  
Azimuthal Velocity ◽  
Narrow Region ◽  
Numerical Hydrodynamics ◽  
T Tauri ◽  
Dust Component ◽  
Disk Evolution ◽  
Self Gravity

Context. Aims. The long-term evolution of a circumstellar disk starting from its formation and ending in the T Tauri phase was simulated numerically with the purpose of studying the evolution of dust in the disk with distinct values of the viscous α-parameter and dust fragmentation velocity vfrag. Methods. We solved numerical hydrodynamics equations in the thin-disk limit, which were modified to include a dust component consisting of two parts: sub-micron-sized dust, and grown dust with a maximum radius ar. The former is strictly coupled to the gas, while the latter interacts with the gas through friction. Dust growth, dust self-gravity, and the conversion of small to grown dust were also considered. Results. We found that the process of dust growth that is known for the older protoplanetary phase also holds for the embedded phase of the disk evolution. The dust growth efficiency depends on the radial distance from the star – ar is largest in the inner disk and gradually declines with radial distance. In the inner disk, ar is limited by the dust fragmentation barrier. The process of small-to-grown dust conversion is very fast once the disk is formed. The total mass of the grown dust in the disk (beyond 1 AU) reaches tens or even hundreds of Earth masses as soon as in the embedded phase of star formation, and an even greater amount of grown dust drifts in the inner, unresolved 1 AU of the disk. Dust does not usually grow to radii greater than a few cm. A notable exception are models with α ≤ 10−3, in which case a zone with reduced mass transport develops in the inner disk and dust can grow to meter-sized boulders in the inner 10 AU. Grown dust drifts inward and accumulates in the inner disk regions. This effect is most pronounced in the α ≤ 10−3 models, where several hundreds of Earth masses can be accumulated in a narrow region of several AU from the star by the end of embedded phase. The efficiency of grown dust accumulation in spiral arms is stronger near corotation where the azimuthal velocity of dust grains is closest to the local velocity of the spiral pattern. In the framework of the adopted dust growth model, the efficiency of small-to-grown dust conversion was found to increase for lower values of α and vfrag.

scholarly journals Partial Stellar Explosions - Ejected Mass and Minimal Energy

2021 ◽  
Author(s):  
Itai Linial ◽  
Jim Fuller ◽  
Re’em Sari
Keyword(s):  
Compact Stars ◽  
Polytropic Index ◽  
Minimal Energy ◽  
Stellar Radius ◽  
Numerical Hydrodynamics ◽  
Wide Range ◽  
Wave Heating ◽  
Red Supergiants ◽  
Minimal Mass ◽  
Late Stages

Abstract Many massive stars appear to undergo enhanced mass loss during late stages of their evolution. In some cases, the ejected mass likely originates from non-terminal explosive outbursts, rather than continuous winds. Here we study the dependence of the ejecta mass, mej, on the energy budget E of an explosion deep within the star, using both analytical arguments and numerical hydrodynamics simulations. Focusing on polytropic stellar models, we find that for explosion energies smaller than the stellar binding energy, the ejected mass scales as $m_{\rm ej} \propto E^{\varepsilon _{m}}$, where ϵm = 2.4 − 3.0 depending on the polytropic index. The loss of energy due to shock breakout emission near the stellar edge leads to the existence of a minimal mass-shedding explosion energy, corresponding to a minimal ejecta mass. For a wide range of progenitors, from Wolf-Rayet stars to red supergiants, we find a similar limiting energy of $E_{\rm min} \approx 10^{46}-10^{47} \rm \, erg$, almost independent of the stellar radius. The corresponding minimal ejecta mass varies considerably across different progenitors, ranging from $\sim \! 10^{-8} \, \rm M_\odot$ in compact stars, up to $\sim \! 10^{-2} \, \rm M_\odot$ in red supergiants. We discuss implications of our results for pre-supernova outbursts driven by wave heating, and complications caused by the non-constant opacity and adiabatic index of realistic stars.

scholarly journals Thermal evolution of protoplanetary disks: from β-cooling to decoupled gas and dust temperatures

2020 ◽  
Vol 638 ◽  
pp. A102 ◽  
Author(s):  
Eduard I. Vorobyov ◽  
Ryoki Matsukoba ◽  
Kazuyuki Omukai ◽  
Manuel Guedel
Keyword(s):  
Thermal Evolution ◽  
Thermal Structure ◽  
Protoplanetary Disks ◽  
Gas Temperature ◽  
Numerical Hydrodynamics ◽  
Variable Nature ◽  
Dynamical Time ◽  
Envelope Material ◽  
Disk Evolution ◽  
Dust Evolution

Aims. We explore the long-term evolution of young protoplanetary disks with different approaches to computing the thermal structure determined by various cooling and heating processes in the disk and its surroundings. Methods. Numerical hydrodynamics simulations in the thin-disk limit were complemented with three thermal evolution schemes: a simplified β-cooling approach with and without irradiation, where the rate of disk cooling is proportional to the local dynamical time; a fiducial model with equal dust and gas temperatures calculated taking viscous heating, irradiation, and radiative cooling into account; and a more sophisticated approach allowing decoupled dust and gas temperatures. Results. We found that the gas temperature may significantly exceed that of dust in the outer regions of young disks thanks to additional compressional heating caused by the infalling envelope material in the early stages of disk evolution and slow collisional exchange of energy between gas and dust in low-density disk regions. However, the outer envelope shows an inverse trend, with the gas temperatures dropping below that of dust. The global disk evolution is only weakly sensitive to temperature decoupling. Nevertheless, separate dust and gas temperatures may affect the chemical composition, dust evolution, and disk mass estimates. Constant-β models without stellar and background irradiation fail to reproduce the disk evolution with more sophisticated thermal schemes because of the intrinsically variable nature of the β-parameter. Constant-β models with irradiation more closely match the dynamical and thermal evolution, but the agreement is still incomplete. Conclusions. Models allowing separate dust and gas temperatures are needed when emphasis is placed on the chemical or dust evolution in protoplanetary disks, particularly in subsolar metallicity environments.

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