1,108 research outputs found
The resolution bias: low resolution feedback simulations are better at destroying galaxies
Feedback from super-massive black holes (SMBHs) is thought to play a key role
in regulating the growth of host galaxies. Cosmological and galaxy formation
simulations using smoothed particle hydrodynamics (SPH), which usually use a
fixed mass for SPH particles, often employ the same sub-grid Active galactic
nuclei (AGN) feedback prescription across a range of resolutions. It is thus
important to ask how the impact of the simulated AGN feedback on a galaxy
changes when only the numerical resolution (the SPH particle mass) changes. We
present a suite of simulations modelling the interaction of an AGN outflow with
the ambient turbulent and clumpy interstellar medium (ISM) in the inner part of
the host galaxy at a range of mass resolutions. We find that, with other things
being equal, degrading the resolution leads to feedback becoming more efficient
at clearing out all gas in its path. For the simulations presented here, the
difference in the mass of the gas ejected by AGN feedback varies by more than a
factor of ten between our highest and lowest resolution simulations. This
happens because feedback-resistant high density clumps are washed out at low
effective resolutions. We also find that changes in numerical resolution lead
to undesirable artifacts in how the AGN feedback affects the AGN immediate
environment.Comment: 15 pages, 12 figures, accepted for publication in MNRA
A Comparative Study on the Optimal Modeling of Laminated Glass
This study addresses the challenging task of modeling laminated glass responses to extreme loading scenarios for the design and analysis of protective structures. The primary objective is to seek an optimal modeling approach that balances accuracy and computational efficiency. To achieve this, the failure modeling of laminated glass layups comprising thin and thick panels with three and eleven layers is investigated under blast loading conditions. Various simulation techniques are employed, including the finite element method (FEM) with element erosion/deletion, smoothed particle hydrodynamics (SPH), and a hybrid approach involving the conversion of elements into particles. The feasibility and limitations of each technique are examined, considering both accuracy and computational cost. Experimental results from arena and shock tube testing scenarios assess the deployed modeling techniques and the presented comparisons. Emphasis is placed on mesh sensitivity and the significance of adaptive meshing in capturing fracture patterns. The present paper suggests that utilizing hybrid techniques results in optimal modeling outcomes. Furthermore, the stability of the modeling results under diverse blast conditions is confirmed. This article contributes to the field by offering insights into modeling laminated glass responses to extreme loading, emphasizing the use of hybrid techniques to strike a balance between accuracy and computational efficiency. This research enhances the understanding of protective structure design and analysis, highlighting the critical importance of computational methods in this context. Doi: 10.28991/CEJ-2023-09-11-018 Full Text: PD
Enhancing the iterative smoothed particle hydrodynamics method
Motivated by recent research on the iterative approach proposed for the smoothed particle hydrodynamics (ISPH) method, some ideas to improve the process are introduced. The standard procedure is enhanced iterating on the residuals preserving the matrix-free nature of the process. The method is appealing providing reasonable results with disordered data distribution too and no kernel variations are needed in the approximation. This work moves forward with a novel formulation requiring a lower number of iterations to reach a desired accuracy. The computational procedure is described and some results are introduced to appreciate the proposed formulation
Constrained simulations of the Antennae Galaxies: Comparison with Herschel-PACS observations
We present a set of hydro-dynamical numerical simulations of the Antennae
galaxies in order to understand the origin of the central overlap starburst.
Our dynamical model provides a good match to the observed nuclear and overlap
star formation, especially when using a range of rather inefficient stellar
feedback efficiencies (0.01 < q_EoS < 0.1). In this case a simple conversion of
local star formation to molecular hydrogen surface density motivated by
observations accounts well for the observed distribution of CO. Using radiative
transfer post-processing we model synthetic far-infrared spectral energy
distributions (SEDs) and two-dimensional emission maps for direct comparison
with Herschel-PACS observations. For a gas-to-dust ratio of 62:1 and the best
matching range of stellar feedback efficiencies the synthetic far-infrared SEDs
of the central star forming region peak at values of ~65 - 81 Jy at 99 - 116
um, similar to a three-component modified black body fit to infrared
observations. Also the spatial distribution of the far-infrared emission at 70
um, 100 um, and 160 um compares well with the observations: >50% (> 35%) of the
emission in each band is concentrated in the overlap region while only < 30% (<
15%) is distributed to the combined emission from the two galactic nuclei in
the simulations (observations). As a proof of principle we show that parameter
variations in the feedback model result in unambiguous changes both in the
global and in the spatially resolved observable far-infrared properties of
Antennae galaxy models. Our results strengthen the importance of direct,
spatially resolved comparative studies of matched galaxy merger simulations as
a valuable tool to constrain the fundamental star formation and feedback
physics.Comment: 17 pages, 8 figures, 4 tables, submitted to MNRAS, including
revisions after first referee report, comments welcom
A CUDA-based implementation of an improved SPH method on GPU
We present a CUDA-based parallel implementation on GPU architecture of a modified version of the Smoothed Particle Hydrodynamics (SPH) method. This modified formulation exploits a strategy based on the Taylor series expansion, which simultaneously improves the approximation of a function and its derivatives with respect to the standard formulation. The improvement in accuracy comes at the cost of an additional computational effort. The computational demand becomes increasingly crucial as problem size increases but can be addressed by employing fast summations in a parallel computational scheme.
The experimental analysis showed that our parallel implementation significantly reduces the runtime, with speed-ups of up to 90,when compared to the CPU-based implementation
Numerical Simulations of the Dark Universe: State of the Art and the Next Decade
We present a review of the current state of the art of cosmological dark
matter simulations, with particular emphasis on the implications for dark
matter detection efforts and studies of dark energy. This review is intended
both for particle physicists, who may find the cosmological simulation
literature opaque or confusing, and for astro-physicists, who may not be
familiar with the role of simulations for observational and experimental probes
of dark matter and dark energy. Our work is complementary to the contribution
by M. Baldi in this issue, which focuses on the treatment of dark energy and
cosmic acceleration in dedicated N-body simulations. Truly massive dark
matter-only simulations are being conducted on national supercomputing centers,
employing from several billion to over half a trillion particles to simulate
the formation and evolution of cosmologically representative volumes (cosmic
scale) or to zoom in on individual halos (cluster and galactic scale). These
simulations cost millions of core-hours, require tens to hundreds of terabytes
of memory, and use up to petabytes of disk storage. The field is quite
internationally diverse, with top simulations having been run in China, France,
Germany, Korea, Spain, and the USA. Predictions from such simulations touch on
almost every aspect of dark matter and dark energy studies, and we give a
comprehensive overview of this connection. We also discuss the limitations of
the cold and collisionless DM-only approach, and describe in some detail
efforts to include different particle physics as well as baryonic physics in
cosmological galaxy formation simulations, including a discussion of recent
results highlighting how the distribution of dark matter in halos may be
altered. We end with an outlook for the next decade, presenting our view of how
the field can be expected to progress. (abridged)Comment: 54 pages, 4 figures, 3 tables; invited contribution to the special
issue "The next decade in Dark Matter and Dark Energy" of the new Open Access
journal "Physics of the Dark Universe". Replaced with accepted versio
Hydrodynamical simulations of cluster formation with central AGN heating
We analyse a hydrodynamical simulation model for the recurrent heating of the
central intracluster medium (ICM) by active galactic nuclei (AGN). Besides the
self-gravity of the dark matter and gas components, our approach includes the
radiative cooling and photoheating of the gas, as well as a subresolution
multiphase model for star formation and supernova feedback. Additionally, we
incorporate a periodic heating mechanism in the form of hot, buoyant bubbles,
injected into the intragalactic medium (IGM) during the active phases of the
accreting central AGN. We use simulations of isolated cluster halos of
different masses to study the bubble dynamics and the heat transport into the
IGM. We also apply our model to self-consistent cosmological simulations of the
formation of galaxy clusters with a range of masses. Our numerical schemes
explore a variety of different assumptions for the spatial configuration of
AGN-driven bubbles, for their duty cycles and for the energy injection
mechanism, in order to obtain better constraints on the underlying physical
picture. We argue that AGN heating can substantially affect the properties of
both the stellar and gaseous components of clusters of galaxies. Most
importantly, it alters the properties of the central dominant (cD) galaxy by
reducing the mass deposition rate of freshly cooled gas out of the ICM, thereby
offering an energetically plausible solution to the cooling flow problem. At
the same time, this leads to reduced or eliminated star formation in the
central cD galaxy, giving it red stellar colours as observed.Comment: 22 pages, 15 figures, minor revisions, MNRAS accepte
Smoothed Particle Hydrodynamics Physically Reconsidered -- The Relation to Explicit Large Eddy Simulation and the Issue of Particle Duality
In this work we will identify a novel relation between Smoothed Particle
Hydrodynamics (SPH) and explicit Large Eddy Simulation (LES) using a
coarse-graining method from Non-Equilibrium Molecular Dynamics (NEMD). While
the current literature points at the conclusion that characteristic SPH issues
become restrictive for subsonic turbulent flows, we see the potential to
mitigate these SPH issues by explicit subfilter stress (SFS) modelling. We
verify our theory by various simulations of homogeneous, isotropic turbulence
(HIT) at and compare the results to a Direct Numerical Simulation
(DNS) reported by Dairay et al. (2017). Although the simulations substantiate
our theory, we see another issue arising, which is conceptually rooted in the
particle itself, termed as Particle Duality. Finally, we conclude our work by
acknowledging SPH as coarse-graining method for turbulent flows, highlighting
its capabilities and limitations.Comment: Added Journal Reference & DO
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