scholarly journals How to Simulate the Universe in a Computer

2005 ◽  
Vol 22 (3) ◽  
pp. 184-189 ◽  
Author(s):  
Alexander Knebe
Keyword(s):  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Adaptive Mesh ◽  
General Idea ◽  
Short Introduction ◽  
Set Up ◽  
Self Gravity ◽  
Tree Codes ◽  
The Universe ◽  
Broad Overview

AbstractIn this contribution a broad overview of the methodologies of cosmological N-body simulations and a short introduction explaining the general idea behind such simulations is presented. After explaining how to set up the initial conditions using a set of N particles two (diverse) techniques are presented for evolving these particles forward in time under the influence of their self-gravity. One technique (tree codes) is solely based upon a sophistication of the direct particle–particle summation whereas the other method relies on the continuous (de-)construction of arbitrarily shaped grids and is realized in adaptive mesh refinement codes.

scholarly journals Insights into the physics when modelling cold gas clouds in a hot plasma

2019 ◽  
Vol 490 (1) ◽  
pp. L52-L56
Author(s):  
Bastian Sander ◽  
Gerhard Hensler
Keyword(s):  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Careful Consideration ◽  
Necessary Condition ◽  
Interstellar Clouds ◽  
Hot Plasma ◽  
Magnetic Dipole Field ◽  
Set Up ◽  
Self Gravity ◽  
Cold Gas

ABSTRACT This paper aims at studying the reliability of a few frequently raised, but not proven, arguments for the modelling of cold gas clouds embedded in or moving through a hot plasma and at sensitizing modellers to a more careful consideration of unavoidable acting physical processes and their relevance. At first, by numerical simulations we demonstrate the growing effect of self-gravity on interstellar clouds and, by this, moreover argue against their initial set-up as homogeneous. We apply the adaptive-mesh refinement code flash with extensions to metal-dependent radiative cooling and external heating of the gas, self-gravity, mass diffusion, and semi-analytic dissociation of molecules, and ionization of atoms. We show that the criterion of Jeans mass or Bonnor–Ebert mass, respectively, provides only a sufficient but not a necessary condition for self-gravity to be effective, because even low-mass clouds are affected on reasonable dynamical time-scales. The second part of this paper is dedicated to analytically study the reduction of heat conduction by a magnetic dipole field. We demonstrate that in this configuration, the effective heat flow, i.e. integrated over the cloud surface, is suppressed by only 32 per cent by magnetic fields in energy equipartition and still insignificantly for even higher field strengths.

scholarly journals Striations, integrals, hourglasses, and collapse – thermal instability driven magnetic simulations of molecular clouds

2020 ◽  
Vol 500 (3) ◽  
pp. 2831-2849
Author(s):  
C J Wareing ◽  
J M Pittard ◽  
S A E G Falle
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Adaptive Mesh Refinement ◽  
Thermal Instability ◽  
Initial Conditions ◽  
Power Spectra ◽  
Adaptive Mesh ◽  
Spherical Cloud ◽  
Field Lines ◽  
Self Gravity

ABSTRACT The MHD version of the adaptive mesh refinement (AMR) code, MG, has been employed to study the interaction of thermal instability, magnetic fields, and gravity through 3D simulations of the formation of collapsing cold clumps on the scale of a few parsecs, inside a larger molecular cloud. The diffuse atomic initial condition consists of a stationary, thermally unstable, spherical cloud in pressure equilibrium with lower density surroundings and threaded by a uniform magnetic field. This cloud was seeded with 10 per cent density perturbations at the finest initial grid level around n = 1.1 cm−3 and evolved with self-gravity included from the outset. Several cloud diameters were considered (100, 200, and 400 pc) equating to several cloud masses (17 000, 136 000, and 1.1 × 106 M⊙). Low-density magnetic-field-aligned striations were observed as the clouds collapse along the field lines into disc-like structures. The induced flow along field lines leads to oscillations of the sheet about the gravitational minimum and an integral-shaped appearance. When magnetically supercritical, the clouds then collapse and generate hourglass magnetic field configurations with strongly intensified magnetic fields, reproducing observational behaviour. Resimulation of a region of the highest mass cloud at higher resolution forms gravitationally bound collapsing clumps within the sheet that contain clump-frame supersonic (M ∼ 5) and super-Alfvénic (MA ∼ 4) velocities. Observationally realistic density and velocity power spectra of the cloud and densest clump are obtained. Future work will use these realistic initial conditions to study individual star and cluster feedback.

scholarly journals EDGE: a new approach to suppressing numerical diffusion in adaptive mesh simulations of galaxy formation

2020 ◽  
Vol 501 (2) ◽  
pp. 1755-1765
Author(s):  
Andrew Pontzen ◽  
Martin P Rey ◽  
Corentin Cadiou ◽  
Oscar Agertz ◽  
Romain Teyssier ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Adaptive Mesh Refinement ◽  
Large Scale ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Morphological Structure ◽  
Adaptive Mesh ◽  
Numerical Diffusion

ABSTRACT We introduce a new method to mitigate numerical diffusion in adaptive mesh refinement (AMR) simulations of cosmological galaxy formation, and study its impact on a simulated dwarf galaxy as part of the ‘EDGE’ project. The target galaxy has a maximum circular velocity of $21\, \mathrm{km}\, \mathrm{s}^{-1}$ but evolves in a region that is moving at up to $90\, \mathrm{km}\, \mathrm{s}^{-1}$ relative to the hydrodynamic grid. In the absence of any mitigation, diffusion softens the filaments feeding our galaxy. As a result, gas is unphysically held in the circumgalactic medium around the galaxy for $320\, \mathrm{Myr}$, delaying the onset of star formation until cooling and collapse eventually triggers an initial starburst at z = 9. Using genetic modification, we produce ‘velocity-zeroed’ initial conditions in which the grid-relative streaming is strongly suppressed; by design, the change does not significantly modify the large-scale structure or dark matter accretion history. The resulting simulation recovers a more physical, gradual onset of star formation starting at z = 17. While the final stellar masses are nearly consistent ($4.8 \times 10^6\, \mathrm{M}_{\odot }$ and $4.4\times 10^6\, \mathrm{M}_{\odot }$ for unmodified and velocity-zeroed, respectively), the dynamical and morphological structure of the z = 0 dwarf galaxies are markedly different due to the contrasting histories. Our approach to diffusion suppression is suitable for any AMR zoom cosmological galaxy formation simulations, and is especially recommended for those of small galaxies at high redshift.

scholarly journals Turbulent structure and star formation in a stratified, supernova-driven, interstellar medium

2006 ◽  
Vol 2 (S237) ◽  
pp. 358-362
Author(s):  
M. K. Ryan Joung ◽  
Mordecai-Mark Mac Low
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Adaptive Mesh Refinement ◽  
Formation Rate ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Mass Function ◽  
Initial Mass Function ◽  
Interstellar Turbulence ◽  
Self Gravity

AbstractWe report on a study of interstellar turbulence driven by both correlated and isolated supernova explosions. We use three-dimensional hydrodynamic models of a vertically stratified interstellar medium run with the adaptive mesh refinement code Flash at a maximum resolution of 2 pc, with a grid size of 0.5 × 0.5 × 10 kpc. Cold dense clouds form even in the absence of self-gravity due to the collective action of thermal instability and supersonic turbulence. Studying these clouds, we show that it can be misleading to predict physical properties such as the star formation rate or the stellar initial mass function using numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. The amount of mass available for collapse depends on scale, suggesting a simple translation from the density PDF to the stellar IMF may be questionable. Even though the supernova-driven turbulence does produce compressed clouds, it also opposes global collapse. The net effect of supernova-driven turbulence is to inhibit star formation globally by decreasing the amount of mass unstable to gravitational collapse.

scholarly journals Global simulations of galactic discs: violent feedback from clustered supernovae during bursts of star formation

2019 ◽  
Vol 492 (1) ◽  
pp. 79-95 ◽  
Author(s):  
Davide Martizzi
Keyword(s):  
Adaptive Mesh Refinement ◽  
Gravitational Instability ◽  
Adaptive Mesh ◽  
Dark Matter Halo ◽  
Time Variability ◽  
Mass Loading ◽  
Star Forming ◽  
Galactic Winds ◽  
Self Gravity ◽  
Supernova Feedback

ABSTRACT A suite of idealized, global, gravitationally unstable, star-forming galactic disc simulations with 2 pc spatial resolution, performed with the adaptive mesh refinement code ramses, is used in this paper to predict the emergent effects of supernova feedback. The simulations include a simplified prescription for the formation of single stellar populations of mass $\sim 100 \, {\rm M}_{\odot }$, radiative cooling, photoelectric heating, an external gravitational potential for a dark matter halo and an old stellar disc, self-gravity, and a novel implementation of supernova feedback. The results of these simulations show that gravitationally unstable discs can generate violent supersonic winds with mass-loading factors η ≳ 10, followed by a galactic fountain phase. These violent winds are generated by highly clustered supernovae exploding in dense environments created by gravitational instability, and they are not produced in simulation without self-gravity. The violent winds significantly perturb the vertical structure of the disc, which is later re-established during the galactic fountain phase. Gas resettles into a quasi-steady, highly turbulent disc with volume-weighted velocity dispersion $\sigma \gt 50 \, {\rm km\, s}^{-1}$. The new configuration drives weaker galactic winds with a mass-loading factor η ≤ 0.1. The whole cycle takes place in ≤10 dynamical times. Such high time variability needs to be taken into account when interpreting observations of galactic winds from starburst and post-starburst galaxies.

The NEMO (Nucleus for European Modelling of the Ocean) numerical ocean platform

2020 ◽  
Author(s):  
Guillaume Samson ◽  
Claire Levy ◽  
Nemo System Team
Keyword(s):  
Adaptive Mesh Refinement ◽  
State Of The Art ◽  
Adaptive Mesh ◽  
Ocean Model ◽  
Ocean Dynamics ◽  
Ice Shelves ◽  
Model Code ◽  
Set Up ◽  
Climate Studies

<p>The Nucleus for European Modelling of the Ocean (NEMO) is a state-of-the art modelling platform for oceanographic research, operational oceanography, sesonnal forecasts and climate studies. NEMO includes three major components; the blue ocean (dynamics), the white ocean (sea-ice), the green ocean (ocean biogeochemistry). It also allows coupling through interfaces with atmosphere (through OASIS software), waves, ice-shelves, so as nesting through the adaptive mesh refinement software AGRIF. Some reference configurations and test cases allowing to explore, to set-up and to validate the applications, and a set of tools to use the platform are also available to the community. The whole platform and its documentation are available under free licence.</p><p>The evolution and reliability of NEMO are organised and controlled by a European Consortium between CMCC (Italy), CNRS (France), MOI France), NOC (UK), UKMO (UK).</p><p>Consortium members agree on long term strategy and yearly plans, sharing expertise and efforts within the NEMO System Team: the core team of NEMO developers in order to ensure the successful and sustainable development of the NEMO System as a well-organised, state-of-the-art ocean model code system suitable for both research and operational work</p>

scholarly journals What determines the formation and characteristics of protoplanetary discs?

2020 ◽  
Vol 635 ◽  
pp. A67 ◽  
Author(s):  
Patrick Hennebelle ◽  
Benoit Commerçon ◽  
Yueh-Ning Lee ◽  
Sébastien Charnoz
Keyword(s):  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Adaptive Mesh ◽  
Small Scale ◽  
Initial Structure ◽  
Solar Mass ◽  
Central Object ◽  
The Impact ◽  
Protoplanetary Discs

Context. Planets form in protoplanetary discs. Their masses, distribution, and orbits sensitively depend on the structure of the protoplanetary discs. However, what sets the initial structure of the discs in terms of mass, radius and accretion rate is still unknown. Aims. It is therefore of great importance to understand exactly how protoplanetary discs form and what determines their physical properties. We aim to quantify the role of the initial dense core magnetisation, rotation, turbulence, and misalignment between rotation and magnetic field axis as well as the role of the accretion scheme onto the central object. Methods. We performed non-ideal magnetohydrodynamics numerical simulations using the adaptive mesh refinement code Ramses of a collapsing, one solar mass molecular core to study the disc formation and early, up to 100 kyr, evolution. We paid particular attention to the impact of numerical resolution and accretion scheme. Results. We found that the mass of the central object is almost independent of the numerical parameters such as the resolution and the accretion scheme onto the sink particle. The disc mass and to a lower extent its size, however heavily depend on the accretion scheme, which we found is itself resolution dependent. This implies that the accretion onto the star and through the disc are largely decoupled. For a relatively large domain of initial conditions (except at low magnetisation), we found that the properties of the disc do not change too significantly. In particular both the level of initial rotation and turbulence do not influence the disc properties provide the core is sufficiently magnetised. After a short relaxation phase, the disc settles in a stationary state. It then slowly grows in size but not in mass. The disc itself is weakly magnetised but its immediate surrounding on the contrary is highly magnetised. Conclusions. Our results show that the disc properties directly depend on the inner boundary condition, i.e. the accretion scheme onto the central object. This suggests that the disc mass is eventually controlled by a small-scale accretion process, possibly the star-disc interaction. Because of ambipolar diffusion and its significant resistivity, the disc diversity remains limited and except for low magnetisation, their properties are weakly sensitive to initial conditions such as rotation and turbulence.

The Initial Condition of Cosmological High-Resolution Simulations

2005 ◽  
Vol 201 ◽  
pp. 499-500
Author(s):  
Tomoya. Ogawa ◽  
Shuuichi. Ebi ◽  
Kazuyuki. Yamashita ◽  
Mitsue. Den
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Mesh Refinement ◽  
Computational Cost ◽  
Adaptive Mesh ◽  
Initial Condition ◽  
Cosmological Simulations ◽  
Frequency Components

Recently, High-resolution algorithms such as the adaptive mesh refinement (AMR) method have been applied to cosmological simulations by several authors. However, the resolution of their INITIAL conditions is not high. We argue the need for cosmological high-resolution simulations to use a high-resolution initial condition or an initial condition including high-frequency components. Then we present the method of creating such initial condition, and estimate its computational cost.

scholarly journals Bipolar planetary nebulae from outflow collimation by common envelope evolution

2020 ◽  
Vol 497 (3) ◽  
pp. 2855-2869 ◽  
Author(s):  
Yangyuxin Zou ◽  
Adam Frank ◽  
Zhuo Chen ◽  
Thomas Reichardt ◽  
Orsola De Marco ◽  
...  
Keyword(s):  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Planetary Nebulae ◽  
Adaptive Mesh ◽  
Cooling Curve ◽  
Radiative Cooling ◽  
Inertial Confinement ◽  
Common Envelope ◽  
Fast Wind ◽  
Particle Hydrodynamics

ABSTRACT The morphology of bipolar planetary nebulae (PNe) can be attributed to interactions between a fast wind from the central engine and the dense toroidal-shaped ejecta left over from common envelope (CE) evolution. Here we use the 3D hydrodynamic adaptive mesh refinement (AMR) code AstroBEAR to study the possibility that bipolar PN outflows can emerge collimated even from an uncollimated spherical wind in the aftermath of a CE event. The output of a single CE simulation via the smoothed particle hydrodynamics (SPH) code phantom serves as the initial conditions. Four cases of winds, all with high enough momenta to account for observed high momenta pre-PN outflows, are injected spherically from the region of the CE binary remnant into the ejecta. We compare cases with two different momenta and cases with no radiative cooling versus application of optically thin emission via a cooling curve to the outflow. Our simulations show that in all cases highly collimated bipolar outflows result from deflection of the spherical wind via the interaction with the CE ejecta. Significant asymmetries between the top and bottom lobes are seen in all cases. The asymmetry is strongest for the lower momentum case with radiative cooling. While real post-CE winds may be aspherical, our models show that collimation via ‘inertial confinement’ will be strong enough to create jet-like outflows even beginning with maximally uncollimated drivers. Our simulations reveal detailed shock structures in the shock-focused inertial confinement (SFIC) model and develop a lens-shaped inner shock that is a new feature of SFIC-driven bipolar lobes.

scholarly journals Achieving Extreme Resolution in Numerical Cosmology Using Adaptive Mesh Refinement: Resolving Primordial Star Formation

2002 ◽  
Vol 10 (4) ◽  
pp. 291-302
Author(s):  
Greg L. Bryan ◽  
Tom Abel ◽  
Michael L. Norman
Keyword(s):  
Star Formation ◽  
Adaptive Mesh Refinement ◽  
Dynamic Range ◽  
Parallel Implementation ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Local Refinement ◽  
First Stars ◽  
Standard Cosmological Model ◽  
The Universe

As an entry for the 2001 Gordon Bell Award in the "special" category, we describe our 3-d, hybrid, adaptive mesh refinement (AMR) codeEnzodesigned for high-resolution, multiphysics, cosmological structure formation simulations. Our parallel implementation places no limit on the depth or complexity of the adaptive grid hierarchy, allowing us to achieve unprecedented spatial and temporal dynamic range. We report on a simulation of primordial star formation which develops over 8000 subgrids at 34 levels of refinement to achieve a local refinement of a factor of 1012in space and time. This allows us to resolve the properties of the first stars which form in the universe assuming standard physics and a standard cosmological model. Achievingextreme resolutionrequires the use of 128-bit extended precision arithmetic (EPA) to accurately specify the subgrid positions. We describe our EPA AMR implementation on the IBM SP2 Blue Horizon system at the San Diego Supercomputer Center.

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