scholarly journals Spiral Shocks in Accretion Disks with SPH

1997 ◽  
Vol 163 ◽  
pp. 770-770
Author(s):  
James Rhys Murray
Keyword(s):  
Accretion Disks ◽  
Equations Of Motion ◽  
Fixed Ratio ◽  
Artificial Viscosity ◽  
Spiral Density Waves ◽  
Viscosity Term ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass ◽  
Continued Use

AbstractSmoothed Particle Hydrodynamics (SPH) is now seen as a numerical scheme well suited to the study of accretion disks. SPH simulations have been conducted of cataclysmic variable disks (Lubow 1991, Murray 1996, Armitage and Livio 1996), galactic disks (Artymowicz and Lubow 1989), and protostellar disks (Artymowicz and Lubow 1994). It is therefore important to test the technique against theory and other numerical results to obtain an estimate of the accuracy and reliability of SPH in this context. Previously SPH has been tested against standard stationary and time-dependent results of viscous thin disk theory (Murray 1996). Strictly these tests relate to disks where ‘viscous’ terms dominate pressure terms in the equations of motion.In this paper we describe tests of the code more appropriate for hot disks where pressure forces are relatively more important than viscosity. Specifically we consider the form of the spiral density waves that can be excited in a disk by a perturbing gravitational potential. Very low mass perturbing bodies excite linear spiral waves which redistribute angular momentum in the disk. For increasingly massive perturbers, the disk response becomes nonlinear and eventually shocks form. In the standard formulation of SPH, an artificial viscosity term is added to the SPH equations to improve shock capture. This is equivalent to introducing a fixed ratio of shear to bulk viscosity into the equations of motion. In Eulerian schemes, artificial viscosity has been discarded in favour of other more accurate, less dissipative schemes for resolving shocks. The continued use of artificial viscosity in SPH has become a source of ‘friction’ between numericists. The simulations described here demonstrate the scheme’s ability to resolve spiral shocks, and show that SPH is a valuable tool for probing the structure of tidally perturbed accretion disks.

scholarly journals Accretion Effects on Disks Around Non-Magnetic Compact Objects

2012 ◽  
Vol 8 (S290) ◽  
pp. 279-280
Author(s):  
Michele M. Montgomery
Keyword(s):  
Accretion Disks ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
Compact Objects ◽  
Additional Time ◽  
Compact Binaries ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass ◽  
Magnetic Cataclysmic Variables

AbstractAccretion disks in compact binaries are thought to sometimes tilt and precess in the retrograde direction as indicated by modulations in light curves and/or signals. Using 3D Smoothed Particle Hydrodynamics and a low mass transfer rate, Montgomery (2012) shows the disk in non-magnetic Cataclysmic Variables tilts naturally after enough time has passed. In that work, twice the fundamental negative superhump signal 2ν_ is associated with disk tilt around the line of nodes, gas stream overflow approximately twice per orbital period, and retrograde precession. In this work, we show that after enough additional time has passed in the same simulation, the 4ν_ harmonic appears. The decrease in the 2ν_ amplitude approximately equals the amplitude of the 4ν_ harmonic. We discuss the implications.

scholarly journals The Role of Discs in the Collapse and Fragmentation of Prestellar Cores

2016 ◽  
Vol 33 ◽  
Author(s):  
O. Lomax ◽  
A. P. Whitworth ◽  
D. A. Hubber
Keyword(s):  
Kinetic Energy ◽  
Smoothed Particle Hydrodynamics ◽  
Low Mass Stars ◽  
Gravitational Instabilities ◽  
Disc Material ◽  
Prestellar Cores ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass

AbstractDisc fragmentation provides an important mechanism for producing low-mass stars in prestellar cores. Here, we describe smoothed particle hydrodynamics simulations which show how populations of prestellar cores evolve into stars. We find the observed masses and multiplicities of stars can be recovered under certain conditions.First, protostellar feedback from a star must be episodic. The continuous accretion of disc material on to a central protostar results in local temperatures which are too high for disc fragmentation. If, however, the accretion occurs in intense outbursts, separated by a downtime of ~ 104yr, gravitational instabilities can develop and the disc can fragment.Second, a significant amount of the cores’ internal kinetic energy should be in solenoidal turbulent modes. Cores with less than a third of their kinetic energy in solenoidal modes have insufficient angular momentum to form fragmenting discs. In the absence of discs, cores can fragment but results in a top-heavy distribution of masses with very few low-mass objects.

scholarly journals The Kelvin–Helmholtz instability and smoothed particle hydrodynamics

2019 ◽  
Vol 488 (4) ◽  
pp. 5210-5224 ◽  
Author(s):  
Terrence S Tricco
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Initial Conditions ◽  
Initial Density ◽  
Artificial Viscosity ◽  
Numerical Dissipation ◽  
Reference Solution ◽  
Helmholtz Instability ◽  
Non Linear ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

ABSTRACT We perform simulations of the Kelvin–Helmholtz instability using smoothed particle hydrodynamics (SPH). The instability is studied both in the linear and strongly non-linear regimes. The smooth, well-posed initial conditions of Lecoanet et al. (2016) are used, along with an explicit Navier–Stokes viscosity and thermal conductivity to enforce the evolution in the non-linear regime. We demonstrate convergence to the reference solution using SPH. The evolution of the vortex structures and the degree of mixing, as measured by a passive scalar ‘colour’ field, match the reference solution. Tests with an initial density contrast produce the correct qualitative behaviour. The $\mathcal {L}_2$ error of the SPH calculations decreases as the resolution is increased. The primary source of error is numerical dissipation arising from artificial viscosity, and tests with reduced artificial viscosity have reduced $\mathcal {L}_2$ error. A high-order smoothing kernel is needed in order to resolve the initial velocity amplitude of the seeded mode and inhibit excitation of spurious modes. We find that standard SPH with an artificial viscosity has no difficulty in correctly modelling the Kelvin–Helmholtz instability and yields convergent solutions.

scholarly journals SPH Simulations of Early and Late Superhumps

2004 ◽  
Vol 194 ◽  
pp. 130-131
Author(s):  
S. Kunze
Keyword(s):  
Accretion Disk ◽  
Early Stage ◽  
Hot Spot ◽  
Type Systems ◽  
Tidal Dissipation ◽  
Tidal Forces ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass ◽  
Low Mass Ratio

AbstractSmoothed particle hydrodynamics is a Lagrangian method for the solution of the hydrodynamic equations. Here this method is used to simulate the accretion disk in dwarf novae with very low mass ratio, q < 0.25, typical for SU UMa-type systems where the accretion disk can become eccentric and precessing during a superoutburst, leading to periodic brightness variations, so-called superhumps. Two phenomena are examined. First the late superhumps, i.e., the occasional persistence of superhumps well after the return to quiescence, seen e.g. in OY Car and IY UMa. This is due to a varying brightness of the hot spot region, as the eccentric disk continues to precess in quisecence. Second, the occurence of early superhumps in the superoutburst of WZ Sge. Tidal forces compress the rim of the disk, the tidal dissipation leads to a double-peaked strucure in the orbital light curve during the early stage of the superoutburst.

Artificial viscosity in smoothed particle hydrodynamics simulation of sound interference

2014 ◽  
Vol 136 (4) ◽  
pp. 2224-2224 ◽  
Author(s):  
Xu Li ◽  
Tao Zhang ◽  
YongOu Zhang ◽  
Huajiang Ouyang ◽  
GuoQing Liu
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Artificial Viscosity ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

scholarly journals Planet migration in self-gravitating discs: survival of planets

2020 ◽  
Vol 496 (2) ◽  
pp. 1598-1609 ◽  
Author(s):  
Sahl Rowther ◽  
Farzana Meru
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Three Dimensional ◽  
Cooling Time ◽  
Early Stages ◽  
Simplified Method ◽  
Planet Migration ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass ◽  
Protoplanetary Discs

ABSTRACT We carry out three-dimensional smoothed particle hydrodynamics simulations to study whether planets can survive in self-gravitating protoplanetary discs. The discs modelled here use a cooling prescription that mimics a real disc, which is only gravitationally unstable in the outer regions. We do this by modelling the cooling using a simplified method such that the cooling time in the outer parts of the disc is shorter than in the inner regions, as expected in real discs. We find that both giant (&gt;MSat) and low-mass (&lt;MNep) planets initially migrate inwards very rapidly, but are able to slow down in the inner gravitationally stable regions of the disc without needing to open up a gap. This is in contrast to previous studies where the cooling was modelled in a more simplified manner where, regardless of mass, the planets were unable to slow down their inward migration. This shows the important effect the thermodynamics has on planet migration. In a broader context, these results show that planets that form in the early stages of the discs’ evolution, when they are still quite massive and self-gravitating, can survive.

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