84 lines
2.2 KiB
Markdown
84 lines
2.2 KiB
Markdown
# Sink particle
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The document aims to describe how the sink particle is calculated.
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For referfence see Lee et al. (2014) Apj, 783, 50.
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## Stage 1: Initialization
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Create datatype `sink` with coordinate and location for the particle.
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```c
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sink.x
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sink.y
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sink.z
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sink.mass
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```
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Either we start with an initial particle, or we can assume it to form later
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(e.g. based on Truelove criterion.)
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## Stage 2: Communication (host to device)
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Values of `sink` need to be communicated from Host to Device.
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## Stage 3: Gravitation
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Based on `sink` gravitational force effect is added to the momentun equation (via DSL).
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## Stage 4: Accretion
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This part of the process is most complicated, and will require special
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attention. The starting point should be the Truelove criterion, but we migh
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need additional subgrid model assumptions.
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Jeans length
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\begin{equation}
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\lambda_\mathrm{J} = \Big( \frac{\pi c_s^2}{G \rho} \Big)^{1/2}
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\end{equation}
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Truelove-Jeans density.
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\begin{equation}
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\rho_\mathrm{TJ} = \frac{\pi J^2 c_s^2}{G \Delta x^2}
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\end{equation}
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where $J = \Delta x / \lambda_\mathrm{J}$. Lee et al. (2014) set $J=1/8$.
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Magnetic Truelove criterion
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\begin{equation}
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\rho_\mathrm{TJ, mag} = \rho_\mathrm{TJ} (1 + 0.74/\beta)
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\end{equation}
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Accreted mass
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\begin{equation}
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(\rho - \rho_\mathrm{TJ, mag})\Delta x^3
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\end{equation}
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## Stage 5: Data gathering (device to host)
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After accretion we will need to gather all data to `sink.mass`. This might need gathering from multiple GPUs, i.e. like in
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Depends on the stencils size and shape used for at the accretion stage. Currently the method is not clear.
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## Plan
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### 1. Add gravitating particle
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Add a particle with specific mass and location. No accretion included.
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### 2. Add simple accretion
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Add an accretion property of the particle. Use just a basic form.
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### 3. Add Complicated accretion
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Add accretion properties which might be useful for the sake of physical correctness and/or numerical stability.
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### 4. Add particle movement. (OPTIONAL)
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Make is possible for the particle to accrete momentum in addition to mass, and therefore influence its movement.
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### 5. Multiple particles. (VERY OPTIONAL)
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Create sink particles dynamically and allow the presence of multiple sinks.
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