297 research outputs found
A TVD Scheme using Roe's Flux and the Ambient Boundary Condition
Details of a second-order accurate TVD scheme using the Roe's Riemann solver is described for the three-dimensional Euler equation. The differential equations are discretized using a finite volume formulation. The ambient boundary condition proposed by us is also explained
An Idea on Normal Flow Discharge of a Small Sized River Draining a Low Laying Area - In Case of the Shinbori River, A Tributary of the Nagara River in Gifu City
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Two-dimensional hydrodynamic simulation of an accretion flow with radiative cooling in a close binary system
Two-dimensional numerical simulations of an accretion flow in a close binary
system are performed by solving the Euler equations with radiative transfer. In
the present study, the specific heat ratio is assumed to be constant while
radiative cooling effect is included as a non-adiabatic process. The cooling
effect of the disc is considered by discharging energy in the vertical
directions from the top and bottom surfaces of the disc. We use the
flux-limited diffusion approximation to calculate the radiative heat flux
values. Our calculations show that a disc structure appears and the spiral
shocks are formed on the disc. These features are similar to that observed in
the case of an adiabatic gas with a lower specific heat ratio, .
It is found that when radiative cooling effect is accounted for, the mass of
the disc becomes larger than that assuming , and smaller than that
assuming . It is concluded that employing an adiabatic gas with a
lower specific heat ratio is almost a valid assumption for simulating accretion
disc with radiative cooling effect.Comment: 9 pages, 5 figures. Accepted for NMRA
Three-Dimensional Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae
We have studied non-axisymmetric standing accretion shock instability, or
SASI, by 3D hydrodynamical simulations. This is an extention of our previous
study on axisymmetric SASI. We have prepared a spherically symmetric and steady
accretion flow through a standing shock wave onto a proto-neutron star, taking
into account a realistic equation of state and neutrino heating and cooling.
This unperturbed model is supposed to represent approximately the typical
post-bounce phase of core-collapse supernovae. We then have added a small
perturbation (~1%) to the radial velocity and computed the ensuing evolutions.
Not only axisymmetric but non-axisymmetric perturbations have been also
imposed. We have applied mode analysis to the non-spherical deformation of the
shock surface, using the spherical harmonics. We have found that (1) the growth
rates of SASI are degenerate with respect to the azimuthal index m of the
spherical harmonics Y_l^m, just as expected for a spherically symmetric
background, (2) nonlinear mode couplings produce only m=0 modes for the
axisymmetric perturbations, whereas m=!0 modes are also generated in the
non-axisymmetric cases according to the selection rule for the quadratic
couplings, (3) the nonlinear saturation level of each mode is lower in general
for 3D than for 2D because a larger number of modes are contributing to
turbulence in 3D, (4) low l modes are dominant in the nonlinear phase, (5) the
equi-partition is nearly established among different m modes in the nonlinear
phase, (6) the spectra with respect to l obey power laws with a slope slightly
steeper for 3D, and (7) although these features are common to the models with
and without a shock revival at the end of simulation, the dominance of low l
modes is more remarkable in the models with a shock revival.Comment: 37 pages, 16 figures, and 1 table, submitted to Ap
Noble gases and K-Ar ages of five Rumuruti chondrites Yamato(Y)-75302, Y-791827, Y-793575, Y-82002, and Asuka-881988
Noble gases and K concentrations have been determined for aliquot samples prepared from the five Antarctic R-chondrites Yamato (Y)-75302,Y-791827,Y-793575,Y-82002,and Asuka (A)-881988. K-Ar ages of about 4.2Ga were obtained for Y-75302,Y-791827,Y-793575 and A-881988,while Y-82002 showed a slightly younger age of 3.9Ga. The Y-75302,Y-791827 and Y-82002 are enriched in solar light noble gases. Four meteorites Y-75302,Y-791827,Y-82002 and A-881988 have cosmic-ray exposure ages of about 20Ma, while the age of Y-793575 is about 7Ma. Based on the noble gas compositions and K-Ar ages, Y-75302 and Y-791827 are probably paired and Y-82002 may belong to this pair. Relatively high and variable ^Xe/^Xe ratios between 2-3.7 as well as enrichments of heavier Xe isotopes were observed in all R-chondrites
The Osher Upwind Scheme and its Application to Cosmic Gas Dynamics
Details of the second order Osher scheme for the multi-dimensional Euler equation are presented. The adopted method to attain the second order of accuracy differs from the existing second order formulation by Osher. The present method is easy to be implemented and can be applied to other first order upwind schemes. Two types of numerical integration forms are coded. One is written in the integral form (cell method), and the other is the usual finite-difference form. Both forms work well and can capture strong shocks without any auxiliary artificial damping. The integration form strictly satisfies the flux conservation even on geometrical singular coordinate lines, which inevitably appear in three dimensional calculations with bodies embedded. Hydrodynamic calculations of the interaction between a stellar wind and an accretion flow are performed to demonstrate the ability of the present method
- …