The Advent of Cosmological Gas Dynamic Simulations

The next move forward in simulations of cosmological structure is to include the hydrodynamics and thermal history of a gaseous component. The task is not an easy one. The dynamic range is wide in all interesting quantities (density, temperature, length-scales, time-scales, etc.). Generic initial mass distributions sampled from Gaussian random fields will, for many interesting power spectra, lead to a high degree of substructure present at all stages of the evolution. Grid-based hydrodynamic techniques currently lack the resolution necessary to evolve several levels of a clustering hierarchy simultaneously. A particle-based method known as SPH (Smoothed Particle Hydrodynamics, see Monoghan (1985) for a review) appears best suited for cosmological application. I have recently imbedded the technique into the P3M N-body code, described by Efstathiou et al. (1985) and used extensively by Efstathiou and collaborators, most recently in investigations of the cold dark matter scenario.

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Origin of the galaxy morphology

Symposium - International Astronomical Union ◽

10.1017/s0074180900207614 ◽

2003 ◽

Vol 208 ◽

pp. 431-432

Author(s):

N. Nakasato

Keyword(s):

Dark Matter ◽

Star Formation ◽

High Resolution ◽

Cold Dark Matter ◽

Star Formation History ◽

The Galaxy ◽

Particle Hydrodynamics ◽

History Of ◽

Analytic Models ◽

Galaxy Morphology

In the current most plausible Cold Dark Matter (CDM) cosmology, larger halos increase their mass by the progressive mergers of smaller clumps. Due to these progressive merger events, galaxies have formed and evolved. Such merger events could trigger star bursts depending on mass of a merging object. In other words, star formation history reflects the strength of the interaction between a galaxy and merging objects. Also, a several merger events strongly affect the development of the morphology of galaxies as assumed in semi-analytic models. In the most advanced semi-analytic models, N-body simulations of dark matter particles are used to obtain the merging history of halos. By combining the description of radiative cooling, hydrodynamics and star formation with the obtained merging history, such models successfully have explained the various qualitative predictions. Here, we show the results of similar approach but using a fullly numerical model. In contrast to the semi-analytic models, we use our high resolution Smoothed Particle Hydrodynamics (SPH) models. With our SPH code, we try to tackle the problem of the galaxy morphology. We have done a several handful high-resolution SPH simulations and analyzed the merging history of such models. Accordingly, we can see the relation between the obtained morphology and the merging history or other physical properties of the model.

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Assessing the influence of metallicity on fragmentation of proto-galactic gas

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307010514 ◽

2006 ◽

Vol 2 (14) ◽

pp. 268-268

Author(s):

Anne-Katharina Jappsen ◽

Simon C. O. Glover ◽

Ralf S. Klessen ◽

Mordecai-Mark Mac Low

Keyword(s):

Smoothed Particle Hydrodynamics ◽

Cold Dark Matter ◽

Three Dimensional ◽

Metal Enrichment ◽

Ionized Gas ◽

First Stars ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

Low Levels ◽

Do So

AbstractIn cold dark matter cosmological models, the first stars to form are believed to do so within small protogalaxies. We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in these protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations.

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Towards the Comprehensive Modeling of Multiphase Fluid Flow Pumping Systems Using Smoothed Particle Hydrodynamics (SPH)

Volume 2: Structures, Safety and Reliability; Petroleum Technology Symposium ◽

10.1115/omae2007-29592 ◽

2007 ◽

Author(s):

M. S. Zaman ◽

S. Hossein Mousavizadegan ◽

M. G. Satish ◽

M. Rafiqul Islam

Keyword(s):

Smoothed Particle Hydrodynamics ◽

Dynamic Range ◽

Flow Patterns ◽

Boost Pressure ◽

Horizontal Pipe ◽

Pump System ◽

Economic Dimension ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

Multiphase Fluid

Multiphase pumping is a viable option in hydrocarbon production at different conditions and especially in more challenging environments. A multiphase pump system can boost pressure without the need to separate the phases and occupies less space and weight, which is valuable for offshore applications. Sub-sea multiphase pumping in deepwater will be reliable, bringing a new economic dimension to the development of satellite oil fields. It is necessary to study the different scenarios that may happen during the transferring of a multiphase fluid through the piping systems. The flow patterns transition in horizontal pipes has been studied theoretically using the smoothed particle hydrodynamics (SPH). SPH is a Lagrangian approach, with the particles themselves being the framework on which the fluid equations are solved, and so there is no grid to constrain the dynamic range or geometry of the system being modeled. In the Lagrangian formulation, the mesh follows the fluid motion and this automatically guarantees the accurate treatment of interfaces that is really a disadvantage of the Eulerian approach. Therefore, for multi-material (oil, water, gas and also sand) problems, Lagrangian method is the most accurate tool for tracking the material interfaces. In addition, geometrically complex and/or dynamic boundaries can be handled without undue difficulty. The simultaneous flow of air and water as two representing fluids are studied through a horizontal pipe using SPH method. The mathematical model is represented and the position of the fluids particles is obtained at different time steps. The objective is to simulate the flow patterns that will help us to design multiphase fluid pumping systems and to identify the variables of interest for instrumentation.

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Incompressible SPH Model for Simulating Violent Free-Surface Fluid Flows

Archives of Hydro-Engineering and Environmental Mechanics ◽

10.1515/heem-2015-0004 ◽

2014 ◽

Vol 61 (1-2) ◽

pp. 61-83

Author(s):

Ryszard Staroszczyk

Keyword(s):

Free Surface ◽

Vertical Wall ◽

Fluid Motion ◽

Time History ◽

Particle Hydrodynamics ◽

Sph Model ◽

History Of ◽

Smoothed Particle ◽

Incompressibility Constraint ◽

The Impact

Abstract In this paper the problem of transient gravitational wave propagation in a viscous incompressible fluid is considered, with a focus on flows with fast-moving free surfaces. The governing equations of the problem are solved by the smoothed particle hydrodynamics method (SPH). In order to impose the incompressibility constraint on the fluid motion, the so-called projection method is applied in which the discrete SPH equations are integrated in time by using a fractional-step technique. Numerical performance of the proposed model has been assessed by comparing its results with experimental data and with results obtained by a standard (weakly compressible) version of the SPH approach. For this purpose, a plane dam-break flow problem is simulated, in order to investigate the formation and propagation of a wave generated by a sudden collapse of a water column initially contained in a rectangular tank, as well as the impact of such a wave on a rigid vertical wall. The results of simulations show the evolution of the free surface of water, the variation of velocity and pressure fields in the fluid, and the time history of pressures exerted by an impacting wave on a wall.

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Damped Lyman-α Absorbers in Cosmological SPH Simulations: the “Metallicity Problem”

Symposium - International Astronomical Union ◽

10.1017/s0074180900196706 ◽

2005 ◽

Vol 216 ◽

pp. 266-273

Author(s):

Kentaro Nagamine ◽

Volker Springel ◽

Lars Hernquist

Keyword(s):

Star Formation ◽

Cold Dark Matter ◽

Mass Density ◽

Formation Rate ◽

Neutral Hydrogen ◽

Galactic Winds ◽

Particle Hydrodynamics ◽

Order Of Magnitude ◽

Smoothed Particle ◽

Hydrogen Mass

We study the distribution of star formation rate (SFR) and metallicity of damped Lyman-α absorbers (DLAs) using cosmological smoothed particle hydrodynamics (SPH) simulations of the Λ cold dark matter (CDM) model. Our simulations include a phenomenological model for feedback by galactic winds which allows us to examine the effect of galactic outflows on the distribution of SFR and metallicity of DLAs. For models with strong galactic winds, we obtain good agreement with recent observations with respect to total neutral hydrogen mass density, NHI column-density distribution, abundance of DLAs, and for the distribution of SFR in DLAs. However, we also find that the median metallicity of simulated DLAs is higher than the values typically observed by nearly an order of magnitude. This discrepancy with observations could be due to shortcomings in the treatment of the supernova feedback or the multiphase structure of the gas in our current simulations. Recent observations by Wolfe et al. (2003a,b) seem to point to the same problem; i.e. the observed DLA metallicities are much lower than those expected from the (either observed or simulated) DLA star formation rates, a puzzle that has been known as the “missing metals”-problem for the globally averaged quantities.

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A Local Semi-Fixed Ghost Particles Boundary Method for WCSPH

Journal of Marine Science and Engineering ◽

10.3390/jmse9040416 ◽

2021 ◽

Vol 9 (4) ◽

pp. 416

Author(s):

Kaidong Tao ◽

Xueqian Zhou ◽

Huilong Ren

Keyword(s):

Smoothed Particle Hydrodynamics ◽

Numerical Solutions ◽

Kernel Functions ◽

Numerical Accuracy ◽

Dynamic Simulations ◽

Boundary Method ◽

Weakly Compressible ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

New Generation

Due to the convenience and flexibility in modeling complex geometries and deformable objects, local ghost particles methods are becoming more and more popular. In the present study, a novel local semi-fixed ghost particles method is proposed for weakly compressible smoothed particle hydrodynamics (WCSPH). In comparison with the previous local ghost particles methods, the new boundary method can effectively reduce spurious pressure oscillations and smooth the flow field. Besides, the new generation mechanism of fictitious particles is simple and robust, which is suitable for all kinds of kernel functions with different sizes of the support domain. The numerical accuracy and stability of the new smoothed particle hydrodynamics (SPH) scheme are validated for several typical benchmark cases. A detailed investigation into the pressure on solid walls and the surface elevation in dynamic simulations is also conducted. A comparison of numerical results shows that the new boundary method helps reduce the oscillations in the numerical solutions and improves the numerical accuracy of the pressure field.

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Numerical convergence of hydrodynamical simulations of galaxy formation: the abundance and internal structure of galaxies and their cold dark matter haloes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa316 ◽

2020 ◽

Vol 493 (2) ◽

pp. 2926-2951 ◽

Cited By ~ 2

Author(s):

Aaron D Ludlow ◽

Joop Schaye ◽

Matthieu Schaller ◽

Richard Bower

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Numerical Convergence ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

Hydrodynamical Simulations ◽

Galaxy Populations ◽

Force Resolution ◽

Star Formation Histories

ABSTRACT We address the issue of numerical convergence in cosmological smoothed particle hydrodynamics simulations using a suite of runs drawn from the eagle project. Our simulations adopt subgrid models that produce realistic galaxy populations at a fiducial mass and force resolution, but systematically vary the latter in order to study their impact on galaxy properties. We provide several analytic criteria that help guide the selection of gravitational softening for hydrodynamical simulations, and present results from runs that both adhere to and deviate from them. Unlike dark matter-only simulations, hydrodynamical simulations exhibit a strong sensitivity to gravitational softening, and care must be taken when selecting numerical parameters. Our results – which focus mainly on star formation histories, galaxy stellar mass functions and sizes – illuminate three main considerations. First, softening imposes a minimum resolved escape speed, vϵ, due to the binding energy between gas particles. Runs that adopt such small softening lengths that $v_\epsilon \gtrsim 10\, {\rm km\, s^{-1}}$ (the sound speed in ionized ${\sim }10^4\, {\rm K}$ gas) suffer from reduced effects of photoheating. Secondly, feedback from stars or active galactic nuclei may suffer from numerical overcooling if the gravitational softening length is chosen below a critical value, ϵeFB. Thirdly, we note that small softening lengths exacerbate the segregation of stars and dark matter particles in halo centres, often leading to the counterintuitive result that galaxy sizes increase as softening is reduced. The structure of dark matter haloes in hydrodynamical runs respond to softening in a way that reflects the sensitivity of their galaxy populations to numerical parameters.

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