forked from lijiext/lammps
317 lines
14 KiB
HTML
317 lines
14 KiB
HTML
|
|
|
|
<!DOCTYPE html>
|
|
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
|
|
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
|
|
<head>
|
|
<meta charset="utf-8">
|
|
|
|
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
|
|
|
<title>fix gravity command — LAMMPS 15 May 2015 version documentation</title>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<link rel="stylesheet" href="_static/css/theme.css" type="text/css" />
|
|
|
|
|
|
|
|
<link rel="stylesheet" href="_static/sphinxcontrib-images/LightBox2/lightbox2/css/lightbox.css" type="text/css" />
|
|
|
|
|
|
|
|
<link rel="top" title="LAMMPS 15 May 2015 version documentation" href="index.html"/>
|
|
|
|
|
|
<script src="_static/js/modernizr.min.js"></script>
|
|
|
|
</head>
|
|
|
|
<body class="wy-body-for-nav" role="document">
|
|
|
|
<div class="wy-grid-for-nav">
|
|
|
|
|
|
<nav data-toggle="wy-nav-shift" class="wy-nav-side">
|
|
<div class="wy-side-nav-search">
|
|
|
|
|
|
|
|
<a href="Manual.html" class="icon icon-home"> LAMMPS
|
|
|
|
|
|
|
|
</a>
|
|
|
|
|
|
<div role="search">
|
|
<form id="rtd-search-form" class="wy-form" action="search.html" method="get">
|
|
<input type="text" name="q" placeholder="Search docs" />
|
|
<input type="hidden" name="check_keywords" value="yes" />
|
|
<input type="hidden" name="area" value="default" />
|
|
</form>
|
|
</div>
|
|
|
|
|
|
</div>
|
|
|
|
<div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
|
|
|
|
|
|
|
|
<ul>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_start.html">2. Getting Started</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_commands.html">3. Commands</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_packages.html">4. Packages</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_howto.html">6. How-to discussions</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_example.html">7. Example problems</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_perf.html">8. Performance & scalability</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_tools.html">9. Additional tools</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_modify.html">10. Modifying & extending LAMMPS</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_python.html">11. Python interface to LAMMPS</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_errors.html">12. Errors</a></li>
|
|
<li class="toctree-l1"><a class="reference internal" href="Section_history.html">13. Future and history</a></li>
|
|
</ul>
|
|
|
|
|
|
|
|
</div>
|
|
|
|
</nav>
|
|
|
|
<section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
|
|
|
|
|
|
<nav class="wy-nav-top" role="navigation" aria-label="top navigation">
|
|
<i data-toggle="wy-nav-top" class="fa fa-bars"></i>
|
|
<a href="Manual.html">LAMMPS</a>
|
|
</nav>
|
|
|
|
|
|
|
|
<div class="wy-nav-content">
|
|
<div class="rst-content">
|
|
<div role="navigation" aria-label="breadcrumbs navigation">
|
|
<ul class="wy-breadcrumbs">
|
|
<li><a href="Manual.html">Docs</a> »</li>
|
|
|
|
<li>fix gravity command</li>
|
|
<li class="wy-breadcrumbs-aside">
|
|
|
|
|
|
<a href="http://lammps.sandia.gov">Website</a>
|
|
<a href="Section_commands.html#comm">Commands</a>
|
|
|
|
</li>
|
|
</ul>
|
|
<hr/>
|
|
|
|
</div>
|
|
<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
|
|
<div itemprop="articleBody">
|
|
|
|
<div class="section" id="fix-gravity-command">
|
|
<span id="index-0"></span><h1>fix gravity command<a class="headerlink" href="#fix-gravity-command" title="Permalink to this headline">¶</a></h1>
|
|
</div>
|
|
<div class="section" id="fix-gravity-cuda-command">
|
|
<h1>fix gravity/cuda command<a class="headerlink" href="#fix-gravity-cuda-command" title="Permalink to this headline">¶</a></h1>
|
|
</div>
|
|
<div class="section" id="fix-gravity-omp-command">
|
|
<h1>fix gravity/omp command<a class="headerlink" href="#fix-gravity-omp-command" title="Permalink to this headline">¶</a></h1>
|
|
<div class="section" id="syntax">
|
|
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
|
|
<div class="highlight-python"><div class="highlight"><pre>fix ID group gravity magnitude style args
|
|
</pre></div>
|
|
</div>
|
|
<ul class="simple">
|
|
<li>ID, group are documented in <a class="reference internal" href="fix.html"><em>fix</em></a> command</li>
|
|
<li>gravity = style name of this fix command</li>
|
|
<li>magnitude = size of acceleration (force/mass units)</li>
|
|
<li>magnitude can be a variable (see below)</li>
|
|
<li>style = <em>chute</em> or <em>spherical</em> or <em>gradient</em> or <em>vector</em></li>
|
|
</ul>
|
|
<pre class="literal-block">
|
|
<em>chute</em> args = angle
|
|
angle = angle in +x away from -z or -y axis in 3d/2d (in degrees)
|
|
angle can be a variable (see below)
|
|
<em>spherical</em> args = phi theta
|
|
phi = azimuthal angle from +x axis (in degrees)
|
|
theta = angle from +z or +y axis in 3d/2d (in degrees)
|
|
phi or theta can be a variable (see below)
|
|
<em>vector</em> args = x y z
|
|
x y z = vector direction to apply the acceleration
|
|
x or y or z can be a variable (see below)
|
|
</pre>
|
|
</div>
|
|
<div class="section" id="examples">
|
|
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
|
|
<div class="highlight-python"><div class="highlight"><pre>fix 1 all gravity 1.0 chute 24.0
|
|
fix 1 all gravity v_increase chute 24.0
|
|
fix 1 all gravity 1.0 spherical 0.0 -180.0
|
|
fix 1 all gravity 10.0 spherical v_phi v_theta
|
|
fix 1 all gravity 100.0 vector 1 1 0
|
|
</pre></div>
|
|
</div>
|
|
</div>
|
|
<div class="section" id="description">
|
|
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
|
|
<p>Impose an additional acceleration on each particle in the group. This
|
|
fix is typically used with granular systems to include a “gravity”
|
|
term acting on the macroscopic particles. More generally, it can
|
|
represent any kind of driving field, e.g. a pressure gradient inducing
|
|
a Poiseuille flow in a fluid. Note that this fix operates differently
|
|
than the <a class="reference internal" href="fix_addforce.html"><em>fix addforce</em></a> command. The addforce fix
|
|
adds the same force to each atom, independent of its mass. This
|
|
command imparts the same acceleration to each atom (force/mass).</p>
|
|
<p>The <em>magnitude</em> of the acceleration is specified in force/mass units.
|
|
For granular systems (LJ units) this is typically 1.0. See the
|
|
<a class="reference internal" href="units.html"><em>units</em></a> command for details.</p>
|
|
<p>Style <em>chute</em> is typically used for simulations of chute flow where
|
|
the specified <em>angle</em> is the chute angle, with flow occurring in the +x
|
|
direction. For 3d systems, the tilt is away from the z axis; for 2d
|
|
systems, the tilt is away from the y axis.</p>
|
|
<p>Style <em>spherical</em> allows an arbitrary 3d direction to be specified for
|
|
the acceleration vector. <em>Phi</em> and <em>theta</em> are defined in the usual
|
|
spherical coordinates. Thus for acceleration acting in the -z
|
|
direction, <em>theta</em> would be 180.0 (or -180.0). <em>Theta</em> = 90.0 and
|
|
<em>phi</em> = -90.0 would mean acceleration acts in the -y direction. For
|
|
2d systems, <em>phi</em> is ignored and <em>theta</em> is an angle in the xy plane
|
|
where <em>theta</em> = 0.0 is the y-axis.</p>
|
|
<p>Style <em>vector</em> imposes an acceleration in the vector direction given
|
|
by (x,y,z). Only the direction of the vector is important; it’s
|
|
length is ignored. For 2d systems, the <em>z</em> component is ignored.</p>
|
|
<p>Any of the quantities <em>magnitude</em>, <em>angle</em>, <em>phi</em>, <em>theta</em>, <em>x</em>, <em>y</em>,
|
|
<em>z</em> which define the gravitational magnitude and direction, can be
|
|
specified as an equal-style <a class="reference internal" href="variable.html"><em>variable</em></a>. If the value is
|
|
a variable, it should be specified as v_name, where name is the
|
|
variable name. In this case, the variable will be evaluated each
|
|
timestep, and its value used to determine the quantity. You should
|
|
insure that the variable calculates a result in the approriate units,
|
|
e.g. force/mass or degrees.</p>
|
|
<p>Equal-style variables can specify formulas with various mathematical
|
|
functions, and include <a class="reference internal" href="thermo_style.html"><em>thermo_style</em></a> command
|
|
keywords for the simulation box parameters and timestep and elapsed
|
|
time. Thus it is easy to specify a time-dependent gravitational
|
|
field.</p>
|
|
<hr class="docutils" />
|
|
<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
|
|
functionally the same as the corresponding style without the suffix.
|
|
They have been optimized to run faster, depending on your available
|
|
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a>
|
|
of the manual. The accelerated styles take the same arguments and
|
|
should produce the same results, except for round-off and precision
|
|
issues.</p>
|
|
<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
|
|
KOKKOS, USER-OMP and OPT packages, respectively. They are only
|
|
enabled if LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
|
|
<p>You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
|
|
use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
|
|
<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
|
|
more instructions on how to use the accelerated styles effectively.</p>
|
|
</div>
|
|
<hr class="docutils" />
|
|
<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
|
|
<h2>Restart, fix_modify, output, run start/stop, minimize info<a class="headerlink" href="#restart-fix-modify-output-run-start-stop-minimize-info" title="Permalink to this headline">¶</a></h2>
|
|
<p>No information about this fix is written to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>.</p>
|
|
<p>The <a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a> <em>energy</em> option is supported by this
|
|
fix to add the gravitational potential energy of the system to the
|
|
system’s potential energy as part of <a class="reference internal" href="thermo_style.html"><em>thermodynamic output</em></a>.</p>
|
|
<p>This fix computes a global scalar which can be accessed by various
|
|
<a class="reference internal" href="Section_howto.html#howto-15"><span>output commands</span></a>. This scalar is the
|
|
gravitational potential energy of the particles in the defined field,
|
|
namely mass * (g dot x) for each particles, where x and mass are the
|
|
particles position and mass, and g is the gravitational field. The
|
|
scalar value calculated by this fix is “extensive”.</p>
|
|
<p>No parameter of this fix can be used with the <em>start/stop</em> keywords of
|
|
the <a class="reference internal" href="run.html"><em>run</em></a> command. This fix is not invoked during <a class="reference internal" href="minimize.html"><em>energy minimization</em></a>.</p>
|
|
</div>
|
|
<div class="section" id="restrictions">
|
|
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
|
|
<blockquote>
|
|
<div>none</div></blockquote>
|
|
</div>
|
|
<div class="section" id="related-commands">
|
|
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
|
|
<p><a class="reference internal" href="atom_style.html"><em>atom_style sphere</em></a>, <a class="reference internal" href="fix_addforce.html"><em>fix addforce</em></a></p>
|
|
<p><strong>Default:</strong> none</p>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
</div>
|
|
</div>
|
|
<footer>
|
|
|
|
|
|
<hr/>
|
|
|
|
<div role="contentinfo">
|
|
<p>
|
|
© Copyright .
|
|
</p>
|
|
</div>
|
|
Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>.
|
|
|
|
</footer>
|
|
|
|
</div>
|
|
</div>
|
|
|
|
</section>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
<script type="text/javascript">
|
|
var DOCUMENTATION_OPTIONS = {
|
|
URL_ROOT:'./',
|
|
VERSION:'15 May 2015 version',
|
|
COLLAPSE_INDEX:false,
|
|
FILE_SUFFIX:'.html',
|
|
HAS_SOURCE: true
|
|
};
|
|
</script>
|
|
<script type="text/javascript" src="_static/jquery.js"></script>
|
|
<script type="text/javascript" src="_static/underscore.js"></script>
|
|
<script type="text/javascript" src="_static/doctools.js"></script>
|
|
<script type="text/javascript" src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
|
|
<script type="text/javascript" src="_static/sphinxcontrib-images/LightBox2/lightbox2/js/jquery-1.11.0.min.js"></script>
|
|
<script type="text/javascript" src="_static/sphinxcontrib-images/LightBox2/lightbox2/js/lightbox.min.js"></script>
|
|
<script type="text/javascript" src="_static/sphinxcontrib-images/LightBox2/lightbox2-customize/jquery-noconflict.js"></script>
|
|
|
|
|
|
|
|
|
|
|
|
<script type="text/javascript" src="_static/js/theme.js"></script>
|
|
|
|
|
|
|
|
|
|
<script type="text/javascript">
|
|
jQuery(function () {
|
|
SphinxRtdTheme.StickyNav.enable();
|
|
});
|
|
</script>
|
|
|
|
|
|
</body>
|
|
</html> |