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Copy file name to clipboardExpand all lines: doc/src/physics.rst
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@@ -673,10 +673,7 @@ Specifically, |code|, adds the body force,
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.. math::
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\rho\frac{D \mathbf{v}}{D t} = \rho\mathbf{g}
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To activate external gravity, there must be a ``<gravity>`` node and ``gravity = true`` under the ``<physics>`` node.
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The ``<gravity>`` requires setting the parameter ``gm``, typically this is set to ``gm = 1.0``.
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In addition to ``gm``, the ``tstart`` and ``tstop`` parameters control when gravity is active.
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To activate external gravity, there must be a subnode of ``<gravity>`` (e.g., ``<gravity/point>``) and ``gravity = true`` under the ``<physics>`` node.
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The specific model for the gravitational acceleration, :math:`\mathbf{g}`, is controlled by adding the appropriate subnode.
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Available options are:
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@@ -687,8 +684,6 @@ Available options are:
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::
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<gravity>
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gm = 1.0
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<gravity/constant>
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gx1 = 0.0
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gx2 = 0.0
@@ -703,9 +698,8 @@ Available options are:
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::
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<gravity>
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gm = 1.0
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<gravity/point>
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mass = 1.0
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x = 0.0
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y = 0.0
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z = 0.0
@@ -721,9 +715,8 @@ Available options are:
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::
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<gravity>
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gm = 1.0 # Binary total GM
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<gravity/binary>
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mass = 1.0 # Total binary mass
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x = 0.0 # Binary x center of mass
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y = 0.0 # Binary y center of mass
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z = 0.0 # Binary z center of mass
@@ -745,14 +738,11 @@ Available options are:
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* ``<gravity/nbody>``
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This indicates that the gravitational force will be calculated by the N-body system defined in the ``<nbody>`` input block.
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The only parameter required is the ``gm`` parameter.
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Note that the total mass of the system defined in the ``<nbody>`` block will be rescaled to ``gm``.
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An example input block would thus read:
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Unlike the other gravity nodes, ``<gravity/nbody>`` has no parameters. Instead, all parameters live under the ``<nbody>`` node.
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To activate nbody gravity, simply add:
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::
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<gravity>
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gm = 1.0
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<gravity/nbody>
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See `N-Body Dynamics`_ for a description of how to set up the N-body system.
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