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modified doc to include mdr damping model

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This commit is contained in:
William Zunker
2025-03-31 22:55:42 -04:00
parent 3c1ed34753
commit b8aaa8d60f
1 changed files with 27 additions and 9 deletions
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36
doc/src/pair_granular.rst
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@ -44,7 +44,7 @@ Examples
pair_coeff * * hertz 1000.0 50.0 tangential mindlin 1000.0 1.0 0.4 heat area 0.1
pair_style granular
pair_coeff * * mdr 5e6 0.4 1.9e5 2.0 0.5 0.5 tangential linear_history 940.0 0.0 0.7 rolling sds 2.7e5 0.0 0.6 damping none
pair_coeff * * mdr 5e6 0.4 1.9e5 2.0 0.5 0.5 tangential linear_history 940.0 0.0 0.7 rolling sds 2.7e5 0.0 0.6 damping mdr
Description
"""""""""""
@ -88,7 +88,8 @@ and their required arguments are:
3. *hertz/material* : E, :math:`\eta_{n0}` (or :math:`e`), :math:`\nu`
4. *dmt* : E, :math:`\eta_{n0}` (or :math:`e`), :math:`\nu`, :math:`\gamma`
5. *jkr* : E, :math:`\eta_{n0}` (or :math:`e`), :math:`\nu`, :math:`\gamma`
6. *mdr* : :math:`E`, :math:`\nu`, :math:`Y`, :math:`\Delta\gamma`, :math:`\psi_b`, :math:`e`
6. *mdr* : :math:`E`, :math:`\nu`, :math:`Y`, :math:`\Delta\gamma`,
:math:`\psi_b`, :math:`\eta_{n0}`
Here, :math:`k_n` is spring stiffness (with units that depend on model
choice, see below); :math:`\eta_{n0}` is a damping prefactor (or, in its
@ -253,13 +254,6 @@ algorithm see :ref:`Zunker et al. <Zunker2025>`.
newton off
The damping model must be set to *none*. The *mdr* model already has a built
in damping model.
.. code-block:: LAMMPS
pair_coeff * * mdr 5e6 0.4 1.9e5 2 0.5 0.5 damping none
The definition of multiple *mdr* models in the *pair_style* is currently not
supported. Similarly, the *mdr* model cannot be combined with a different normal
model in the *pair_style*. Physically this means that only one homogeneous
@ -336,6 +330,12 @@ for the damping model currently supported are:
3. *viscoelastic*
4. *tsuji*
5. *coeff_restitution*
6. *mdr*
.. note::
It is suggested to use the *mdr* damping model with when the normal
*mdr* contact model is defined.
If the *damping* keyword is not specified, the *viscoelastic* model is
used by default.
@ -425,6 +425,24 @@ the damping coefficient, it accurately reproduces the specified coefficient of
restitution for both monodisperse and polydisperse particle pairs. This damping
model is not compatible with cohesive normal models such as *JKR* or *DMT*.
The *mdr* damping model is only compatible with the normal *mdr* contact model.
It takes into account the contact stiffness :math:`k_{mdr}` calulated
by the normal *mdr* contact model to determine the damping coefficent:
.. math::
\eta_n = \eta_{n0} (m_{eff}k_{mdr})^{1/2},
where :math:`k_{mdr}` is proportional to contact radius :math:`a_{mdr}` tracked by the
normal *mdr* contact model:
.. math::
k_{mdr} = 2 E_{eff} a_{mdr}.
In this case, :math:`\eta_{n0}` is simply a dimensionless coefficent that scales the
the overall damping coefficent.
The total normal force is computed as the sum of the elastic and
damping components: