Smoothed Particle Hydrodynamics: Numerical Techniques and Applications to Accretion Disks in Close Binaries.

Details Smoothed Particle Hydrodynamics: Numerical Techniques and Applications to Accretion Disks in Close Binaries. Smoothed Particle Hydrodynamics: Numerical Techniques and Applications to Accretion Disks in Close Binaries.

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........11s&link_type=abstract

Thesis (PH.D.)--FLORIDA INSTITUTE OF TECHNOLOGY, 1995.Source: Dissertation Abstracts International, Volume: 56-05, Section: B, p

Statistics

Computation

4

Scientific paper

Numerical techniques for the method of smoothed particle hydrodynamics (SPH) are described for three dimensional systems in the absence of self-gravity. These include a method for locating neighboring particles using an Eulerian grid that conserves memory by partitioning the computational space into manageable layers. Further savings in memory and computational time are achieved using interparticle distances that are discretized with respect to integral increments of the smoothing length. We also present a time integration algorithm using multiple time steps which guarantees that all particles maintain phase space synchronicity to at least first order accuracy with respect to the time steps. These techniques are used to compare currently available SPH artificial viscosities in accretion disks in low mass ratio systems (q = {M_2 }over{M_1} = 0.02) using the ideal gas law and low adiabatic gamma (gamma = 1.01): radiation effects and magnetic fields are excluded. The standard artificial viscosity given by Monaghan (1992) consistently gives results which agree qualitatively with the Shukura-Sunyaev alpha -disk model. The radial temperature profile is overestimated by a factor of about 10, indicating that radiation effects must be included for a complete model. This viscosity is also used to compare accretion disks in systems with the four different extreme mass ratios: q = 0.01, 0.02, 0.03, and 0.05. These simulated disks are stable with high mass transfer rates. The outer disk edges do not extend into the regions of the low order corotation resonances, consequently no precession is observed. The disks are slightly asymmetric with spiral density waves that appear stationary in the corotating frame. These may be responsible for the double humped pulses in the light curves of these systems. Finally, the free expansion of an ideal gas into a vacuum is simulated using elastic collisions between SPH particles and impenetrable flat surfaces. After _sp{~}<100 interparticle collisions the velocity distribution closely matches the exact Maxwell-Boltzmann distribution. The simulated mean free path agrees with the predicted value.

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