index.rst 3.04 KB
 Matthieu Schaller committed Dec 20, 2018 1 2 3 4 5 6 7 .. GEAR sub-grid model Matthieu Schaller, 20th December 2018 GEAR model ===========  Loic Hausammann committed Aug 09, 2019 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Pressure Floor ~~~~~~~~~~~~~~ In order to avoid the artificial collapse of unresolved clumps, a minimum in pressure is applied to the particles. This additional pressure can be seen as the pressure due to unresolved hydrodynamics turbulence and is given by: .. math:: P_\textrm{Jeans} = \frac{\rho}{\gamma} \left( \frac{4}{\pi} G h^2 \rho N_\textrm{Jeans}^{2/3} - \sigma^2 \right) where :math:\rho is the density, :math:\gamma the adiabatic index, :math:G is the gravitational constant, :math:h the smoothing length, :math:N_\textrm{Jeans} is the number of particle required in order to resolve a clump and :math:\sigma the velocity dispersion.  Loic Hausammann committed Jan 22, 2020 22 This must be directly implemented into the hydro schemes, therefore only a subset of schemes (Gadget-2, SPHENIX and Pressure-Energy) have the floor available.  Loic Hausammann committed Aug 09, 2019 23 24 25 26 27 28 29 30 In order to implement it, you need equation 12 in Hopkins 2013 _: .. math:: m_i \frac{\mathrm{d}v_i}{\mathrm{d}t} = - \sum_j x_i x_j \left[ \frac{P_i}{y_i^2} f_{ij} \nabla_i W_{ij}(h_i) + \frac{P_j}{y_j^2} f_{ji} \nabla_j W_{ji}(h_j) \right] and simply replace the :math:P_i, P_j by the pressure with the floor. Here the :math:x, y are simple weights that should never have the pressure floor included even if they are related to the pressure (e.g. pressure-entropy).  Matthieu Schaller committed Dec 20, 2018 31 32 33 34 35 36 37 38 39  Cooling: Grackle ~~~~~~~~~~~~~~~~ Grackle is a chemistry and cooling library presented in B. Smith et al. 2016 _ (do not forget to cite if used). Four different modes are available: equilibrium, 6 species network (H, H\$$^+ \$$, e\$$^- \$$, He, He\$$^+ \$$ and He\$$^{++} \$$), 9 species network (adds H\$$^-\$$, H\$$_2\$$ and H\$$_2^+\$$) and 12 species (adds D, D\$$^+\$$ and HD). Following the same  Loic Hausammann committed Dec 10, 2019 40 41 order, the swift cooling options are grackle_0, grackle_1, grackle_2 and grackle_3 (the numbers correspond to the value of  Matthieu Schaller committed Dec 20, 2018 42 43 44 45 46 47 48 primordial_chemistry in Grackle). It also includes some self-shielding methods and UV background. In order to use the Grackle cooling, you will need to provide an HDF5 table computed by Cloudy. When starting a simulation without providing the different fractions, the code supposes an equilibrium and computes the fractions automatically.  Loic Hausammann committed Dec 10, 2019 49 50 In order to compile SWIFT with Grackle, you need to provide the options with-chemistry=GEAR and with-grackle=$GRACKLE_ROOT where $GRACKLE_ROOT is the root of the install directory (not the lib).  Matthieu Schaller committed Dec 20, 2018 51 52 53 54 55 56 57 58 59 60  You will need a Grackle version later than 3.1. To compile it, run the following commands from the root directory of Grackle: ./configure; cd src/clib. Update the variables LOCAL_HDF5_INSTALL and MACH_INSTALL_PREFIX in the file src/clib/Make.mach.linux-gnu. Finish with make machine-linux-gnu; make && make install. If you encounter any problem, you can look at the Grackle documentation _ You can now provide the path given for MACH_INSTALL_PREFIX to with-grackle.