<p>keyword = <ahref="#id1"><spanclass="problematic"id="id2">**</span></a>DENSITY_SUMMATION* or <ahref="#id3"><spanclass="problematic"id="id4">**</span></a>DENSITY_CONTINUITY* and <ahref="#id5"><spanclass="problematic"id="id6">**</span></a>VELOCITY_GRADIENT* or <ahref="#id7"><spanclass="problematic"id="id8">**</span></a>NO_VELOCITY_GRADIENT* and <ahref="#id9"><spanclass="problematic"id="id10">**</span></a>GRADIENT_CORRECTION* or <ahref="#id11"><spanclass="problematic"id="id12">**</span></a>NO_GRADIENT_CORRECTION*</p>
<p>The <em>smd/ulsph</em> style computes particle interactions according to continuum mechanics constitutive laws and an updated Lagrangian Smooth-Particle Hydrodynamics algorithm.</p>
<p>This pair style is invoked similar to the following command:</p>
<p>Here, <em>i</em> and <em>j</em> denote the <em>LAMMPS</em> particle types for which this pair style is
defined. Note that <em>i</em> and <em>j</em> can be different, i.e., <em>ulsph</em> cross interactions
between different particle types are allowed. However, <em>i</em>–<em>i</em> respectively <em>j</em>–<em>j</em> pair_coeff lines have to preceed a cross interaction.
In contrast to the usual <em>LAMMPS</em><em>pair coeff</em> definitions, which are given solely a
number of floats and integers, the <em>ulsph</em><em>pair coeff</em> definition is organised using
keywords. These keywords mark the beginning of different sets of parameters for particle properties,
material constitutive models, and damage models. The <em>pair coeff</em> line must be terminated with
the <ahref="#id29"><spanclass="problematic"id="id30">**</span></a>END* keyword. The use the line continuation operator <em>&</em> is recommended. A typical
invocation of the <em>ulsph</em> for a solid body would consist of an equation of state for computing
the pressure (the diagonal components of the stress tensor), and a material model to compute shear
stresses (the off-diagonal components of the stress tensor).</p>
<p>Note that the use of <ahref="#id31"><spanclass="problematic"id="id32">*</span></a>GRADIENT_CORRECTION can lead to severe numerical instabilities. For a general fluid simulation, <ahref="#id33"><spanclass="problematic"id="id34">*</span></a>NO_GRADIENT_CORRECTION is recommended.</p>
<p>Please see the <aclass="reference external"href="USER/smd/SMD_LAMMPS_userguide.pdf">SMD user guide</a> for a complete listing of the possible keywords and material models.</p>
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