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====== Bad Bursters Logbook ======

===== Goal =====
We have decided to analyze the accretion onto a neutron star just up until the hydrogen burning begins. We'll first attempt this as an adaptation to the Bondi accretion problem with a solid sphere near the origin (also relevant to the problem of infall onto the proto-neutron star during core collapse). If we're successful, we'll try an accretion disk in 2D with polar geometry.

===== Log Book =====
===Input: Sarah Schwartz===
    * [X] X-ray bursts
      * [X] Accretion rate ~ 10^-8 Solar Mass / yr
      * [X] Radius ~ 10-15 km
      * [X] Mass ~ 1 Solar Mass
    * [X] Novae
      * [X] Accretion rate ~ 10^-9 Solar Mass / yr
      * [X] Radius ~ 10^4 km
      * [X] Mass ~ 1 Solar Mass
    * [ ] Density of in falling material
    * [X] Alpha parameter = 0<alpha<1
  ===Code: Justin Brown===
[[https://github.com/brownjustinmichael/VH1|Link to Code on GitHub]]
    * 2D
      * [X] Get the VH-1 polar model working.
        * Set ngeomx = 1 (radial cylindrical), ngeomy = 3 (theta), nlefty = 3, nrighty = 3 (periodic)
      * [X] Set up accretion
        * Set nrightx = 2 (constant inflow), uotflo * rotflo * outer area of simulation (2 * pi * xmas) = 1
        * Set votflo to be the desired velocity at the boundary edge
      * [X] Implement gravity
        * In forces, set grav (n) under sweep "x", cylindrical to be -GM/xao(n)**2
      * [X] Implement a viscosity model.
        * We're choosing to use the derivative in the radial direction of only the tangential coordinate
          * alpha*1/r(dv/dr)+alpha*d2v/dr2
        * In forces, set grav (n) under sweep "y", cylindrical angle to the above expression 
      * [X] Run Models
        * [X] Non-dimensionalize
          * The length unit is the radius of the neutron star, R_ns
          * The time unit is sqrt (R_ns^3/GM_ns)
          * The mass unit is M'sqrt (R_ns^3/GM_ns), where M' is the mass infall rate
        * [X] Determine free parameters
          * Outer radius of simulation, xmax
          * Infall velocity, uotflo
          * Viscosity, alpha
          * Tangential initial velocity, votflo
        * [X] Run models with uotflo = -0.1, votflo = 0.2, xmax = 10.0
          * [X] Viscid (alpha = 1.0)
          * [X] Semi-Viscid (alpha = 0.1)
          * [X] Inviscid (alpha = 0.0)
        * [] Run models with uotflo = -1.0, votflo = 0.2, xmax = 10.0
  ===Analysis: Amber Lauer===
    * [x] Get visualization working 
      * [x] Install NetCDF
        * visit on ubuntu/linux was a quagmire, went with windows virtualbox installation :(
    * [x] Gathering the initial conditions for novae and X-ray bursts
      * have average values for NS and WD, time permitting will constrain to single case and derive
    *[x] PRESENTATION
    * [x] Outline concepts and highlight theory for presentation
    * [x] Encode .cdf data to video for presentation
    * [x] Compile references for presentation
    * [x] Compile images for presentation


Determined to be outside scope of project.
<del>
* [ ] Determine the input abundances
   * [ ] Build the nuclear network for the problem
    * [ ] Take output from the codes
      * [ ]determine when hydrogen burning begins
      * [ ]analyze data values to optimize scale(linear vs log) and ranges(0-?) for visualization
</del>

=====RESULTS=====
1D on a solid surface was successful so the 2D case was the bulk of the project work. The solid case was unstable and resulted in an non-physical explosion. Both the infall and reflective cases were attempted, we found the [] to be optimal. We were able to model a non-viscous and viscous case using hydronamic force and energy equation. Terms for the extremely large B field (10^7-8 T) were not included. Both accreted around the central mass with a large high pressure/empty barrier for the non-viscous case, as the angular momentum is not dissipated. The viscous case correctly accreted on to the surface.

[[https://docmgmt.nscl.msu.edu/share/proxy/alfresco/api/node/content/workspace/SpacesStore/8e4a7857-347b-4603-9f64-bf2422ff5e7e/Simulating%20Accretion%20on%20Degenerate%20Matter%20to%20Model%20Surface.pdf|Presentation PDF]]

[[https://docmgmt.nscl.msu.edu/share/proxy/alfresco/api/node/content/workspace/SpacesStore/e6353d93-8726-45d6-bcf4-d2e3366fdb46/inviscid.mpg|video of non viscous accretion]]

[[https://docmgmt.nscl.msu.edu/share/proxy/alfresco/api/node/content/workspace/SpacesStore/507d83f6-8cc2-46c4-a1ee-34fc6e3e3889/viscous.mpg|video of viscous accretion]]

[[https://docmgmt.nscl.msu.edu/share/proxy/alfresco/api/node/content/workspace/SpacesStore/d4a5588e-c2ce-4136-bb49-78cbf8b1e959/zero%20pressure.mpg|video of accidental zero pressure accretion]]


References: 
  *Accretion Power in Astrophysics - Frank, King, Raine
  *Accretion Disk for Beginners : [[http://www.astronomy.ohio-state.edu/~ryden/ast825/ | External Link]] (Notes PDF)
 (further resources in presentation)



~~DISCUSSION|Comments~~