I have setup the components that will be used in this simulation. The figures show the mesh and the boundary of the outflow.

In this simulation, we are going to use static-mesh-refinement. Adaptive-mesh-refinement can be applied when needed. This is because we know where need to be resolved.

The solid sphere in the center of the figures is the outflow boundary. Its radius is roughly 160R_sun.

The next question will be:

1. What outflow do we need? (velocity, gravity, temperature, density)

2. Which machine should we use to carry out this simulation? It is a huge simulation. I estimated that to generate 1 year of simulation, we need roughly 1000 CPU hours.

Feedback

Almost ready to start pulling out my feedback development branch and finalize testing/development for that. At this point we are at a crossroads — where we can either

a) improve the algorithm to simultaneously inject the target amount of linear and angular momentum into the outflow codes (currently the code has trouble with getting the right amount of angular momentum into the cones),

b) ignore angular momentum injection altogether (would limit accurate simulation of outflows on small scales, I suppose),

c) leave the code as is, which can introduce some potential wonky behavior of the outflows under certain circumstances (such as a counter rotating accretion disk/star system)

Reorientation Paper

The referee had a few comments for the paper before it could be accepted for publication. Namely, he thought there should be a convergence study in the paper (sims are currently running for this), suggested adding a infinite cooling case to the paper (which we are making a counter argument against, see attached draft of referee responses), and remaking some of the plots so that they have larger text (currently working on this now, should be finished by the end of the day).

The referee responses are due no later than May 9th, but would like to get them in by the *end of the week*. Since the report is so short, thought I would definitely run it by Jonathan at the very least before submitting.

Thesis Defense

I still need to finalize the last person on my committee and to check with Segev again about the scheduled defense date of August 4th.

In order to defend my thesis by August 4th, I need to have a copy of my finished thesis to the committee by *June 26* (almost two months away). How long do these things typically take to write? If it takes 3 weeks, then that leaves me a little over a month to get the feedback sims up and running for the next paper (before I have to hunker down and write my thesis).

Thermal Instability Presentation

I recently read Koyama & Inutsuka 2004 on the "Field Condition" (convergence condition for the thermal instability), and really enjoyed it. Put together a short presentation on this paper to share with you all (see link here: ​https://docs.google.com/presentation/d/1uaQ5ukZL6sNtdwxfubdH_EHZIQfWY8EESwC1P0QtV9I/pub?start=false&loop=false&delayms=60000).

• CIRC poster Session
  1. Deadline for registering: Next Friday 04/28
  2. Link for registering ​https://registration.circ.rochester.edu/postersession
  3. Will do a poster for Wire Turbulence
  4. I will register some of our old posters next Monday. If you have a poster or will do a poster and need help, please let me know.

• Bluehive space under afrank name and will be charged (97$ per TB)

Shall we move Eddie's account to his current group instead?

• Code & Users
  1. One user asking for code of mass transfer between binaries are putting on hold.

• XSEDE Machine usage
  1. TG-AST160054, expired date 2017-9-21: Stampede (-3517 out of 50000 SUs, 0% remaining); Comet (43427 out of 50000 SUs, 86% remaining)
  2. TG-AST120060, expired date 2017-12-31: Stampede (960802 out of 980222 SUs, 98% remaining); Comet (858187 out of 980222 SUs, 86% remaining)

• Wire Turbulence
  1. Velocity Spectra — supersonic for solenoidal and subsonic for compressive turbulence

2. Redid Mach number vs b

3. Hydro pressure histogram

frame 199
On Visit

• Wrote Godunov solver for linear advection, inviscid Burgers equations, as well as Godunov solver for Euler equations (see here). Need to write up and comment Euler solver still, though not much is different. Also looking at a quick parallelization - need to check shared and private variables in loops. See ​here for test results.

• Implemented (but haven't tested) charge exchange - see changelog​.

• Working on higher mass loss rate planet. Think I was trying to change too much at once, so upped the stellar wind density a bit (bow shock radius is now at ~0.3). Currently having trouble reloading grids on restart - MPI errors.

The past few weeks I've been trying to make progress on obtaining a stable giant. Details are available ​here but a summary is presented below.

I) Boundary conditions

• I changed the Poisson BCs from (a) periodic to (b) multipole expansion and performed some tests. This prevents the star from oscillating. It is worth noting that Ohlmann et al. 2017 used periodic BCs and obtained oscillations.

Comparison with (a-periodic) on left and (b-multipole expansion) on right
​2d density ​2d density and velocity

• Note that without periodic gravity, inflows from the centres of the boundary walls tend to produce "boxiness" of the star. In the hope of reducing this boxiness, I tried several variations on the hydro BCs. In the end, none of these efforts resulted in a large improvement and it seems that simply putting reflecting hydro BCs works as well or better than anything (slightly better than extrapolating, at least for a fixed grid).

Comparison with (a-extrapolating) on left and (b-reflecting) on right
​2d density ​2d density and velocity

II) Damping

• I implemented velocity damping (see also last blog post), with a constant damping time \tau=10^5s (about 0.2 dynamical times) or, in a few cases, 10^4s. The latter value can prevent the boxiness, even in a small box with only moderate resolution. I performed some tests with larger boxes and found the results to be basically consistent with those of the smaller box runs.

Extrapolated BCs, multipole expansion Poisson BCs \tau=10^4 s
​2d density ​2d density and velocity ​2d pressure ​1d density ​1d pressure

Extrapolated BCs, multipole expansion Poisson BCs \tau=10^5 s
​2d density ​2d density and velocity ​2d pressure ​1d density ​1d pressure

Reflecting hydro BCs, Multipole expansion Poisson BCs, Velocity damping with \tau=1\times10^5 s
​2d density ​2d density and velocity

Comparison with (a-large box extrapolating) on left and (b-large box reflecting) on right, \tau=10^5 s
(i) Constant ambient pressure and density
​2d density ​2d density and velocity

III) Hydrostatic atmosphere

• With a hydrostatic atmosphere (rather than a constant pressure and density ambient medium), we might expect it to be easier to obtain a steady state. Long story short, the low densities and sharp gradients at the boundaries lead to large spurious velocities that tend to increase the computation time (or cause the code to crash).

Reflecting hydro BCs, Multipole expansion Poisson BCs, Velocity damping with \tau=1\times10^5 s
​2d density ​2d density and velocity ​2d density (extended color bar) ​2d density and velocity (extended color bar)

IV) AMR

• I performed two AMR runs (with \tau=10^5 s velocity damping and either extrapolated hydro BCs or reflecting hydro BCs).

• Inside of 3.5\times10^{12} cm, the refinement level was forced by hand to be equal to the highest level.

a) Extrapolating hydro BCs, Multipole expansion Poisson BCs, Velocity damping with \tau=1\times10^5s, 64^3, maxlevel=4
(i) Constant ambient pressure and density (Damp047, 27 hrs on comet compute, 576 cores)
​2d density ​2d density and velocity

b) Reflecting hydro BCs, Multipole expansion Poisson BCs, Velocity damping with \tau=1\times10^5s, 64^3, maxlevel=4
(NOTE THAT THIS HAS ONLY RUN FOR 2/3 OF THE TIME AS (a))
(i) Constant ambient pressure and density (Damp044)
​2d density ​2d density and velocity

Conclusions

• "Boxiness" of the star owing to inflows from the centres of the boundaries has been a problem both because a cubical star is unphysical and because it eventually leads to instabilities at the star "corners."

• Small improvements can be made by varying the BCs. For Poisson, we may choose periodic or multipole expansion. For hydro, either extrapolating or reflecting.

• More complicated hydro BCs (e.g. fixing the ghost zones or the region exterior to some pre-defined sphere to be equal to the initial ambient values) probably do not generate enough improvement (sometimes not any) to be worth the extra computational cost.

• From past blog posts, we know that reducing the ambient pressure by a factor of a few may also help to reduce the boxiness (though the pressure scale-height at the surface will be smaller, thus not as resolved).

• What works best against boxiness and instability at the surface is velocity damping, which has now been implemented successfully. Using \tau=10^4s keeps the star completely stable (at least for a uniform fixed grid), while \tau=10^5s leads to a significant reduction in boxiness.

• The boxiness/inflow problem becomes worse with AMR, but the star remains remarkably stable after a few dynamical times with \tau=10^5 s damping.

• Using a hydrostatic envelope (instead of a constant density-pressure ambient medium) reduces the boxiness, but causes instabilities to develop at the corners of the grid, which then propagate inward. The code tends to crash, and I could not get it to run at all in AMR.

Next steps

• Given the above conclusions, it is probably best to stick with a constant density and pressure ambient medium.

• The logical next step is to try the prescription outlined in Ohlmann et al. 2017 which starts with a small \tau and gradually ramps it up to \infty.

• This should be done concurrently for 1) a fixed uniform grid 256^3 simulation, 2) AMR simulation.

​Three-dimensional hydrodynamical models of wind and outburst-related accretion in symbiotic systems

​Playlist

3AU, 0 degree and 90 degree

4AU, 0 degree and 90 degree

6AU, 0 degree and 45 degree

8AU, 0 degree and 45 degree