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<a name = "hj-top"> </a><table class = "table1" id = "table11"><tr><td><table class = "DocHeader"><tr><td class = "DocHeader1" colspan = "2"><h1>Frequency Spectrum</h1></td></tr><tr><td class = "DocHeader4" colspan = "2"/></tr><tr><td class = "DocHeader3" colspan = "2"><table class = "DocThemeIntro" id = "table12"><tr><td class = "Intro1Only"><p class = "header"><p class = "abstract">
<span class = "shortdesc">Within this section, frequency design responses are discussed.
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<p>This page discusses: </p><ul><li><a href = "#tso-c-usr-solver-mscNastran-freq__tso-c-usr-solver-mscNastran-freq-limitations" id = "toc_rg" title = "">Limitations</a></li><li><a href = "#tso-c-usr-solver-mscNastran-freq__tso-c-usr-solver-mscNastran-freq-Options" id = "toc_rg" title = "">Options in Context of Frequency Response</a></li></ul>
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<div class = "section" id = "tso-c-usr-solver-mscNastran-freq__tso-c-usr-solver-mscNastran-freq-limitations"><h2 class = "title sectiontitle">Limitations</h2>

<p>Currently frequency responses are allowed only for sizing optimization.</p>
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<div class = "section" id = "tso-c-usr-solver-mscNastran-freq__tso-c-usr-solver-mscNastran-freq-Options"><p><map name = "FPMap1"><area href = "#hj-top" title = "Back to Top" shape = "rect" coords = "416, 0, 435, 10"/></map><span class = "itemsprite"/></p><h2 class = "title sectiontitle">Options in Context of Frequency Response</h2>

<p>The <code class = "ph codeph">SOL108</code> (direct frequency response) and
<code class = "ph codeph">SOL111</code> (modal frequency response) are supported for
<span class = "ph">MSC Nastran®</span>.
Gravity loading and temperature loadings are not allowed in finite element modeling.</p>
<p>Solution excitation frequencies defined using
<code class = "ph codeph">FREQ</code>, <code class = "ph codeph">FREQ1</code>, and
<code class = "ph codeph">FREQ2</code> are allowed in the finite element input file.
The solution excitation frequencies defined using
<code class = "ph codeph">FREQ3</code>, <code class = "ph codeph">FREQ4</code>, and
<code class = "ph codeph">FREQ5</code> should be used with care because the eigenvalues
usually change a lot during optimization.
</p>
<p>In frequency response, structural damping <code class = "ph codeph">PARAM</code>,
<code class = "ph codeph">G</code>, and <code class = "ph codeph">GE</code> on the
<code class = "ph codeph">MATi</code> are allowed for all design elements. The
structural damping should be the same for all design elements, and the
structural damping for the design elements should also be defined using
<code class = "ph codeph">OPT_PARAM</code> yielding,</p>
<pre class = "codeblock">
<code class = "ph codeph">
OPT_PARAM
  ...
  DAMP_STRUCTURAL_STIFF = G or GE
  ...
END_
</code>
</pre>
<p>where <code class = "ph codeph">G</code> or <code class = "ph codeph">GE</code> is the structural damping of the design elements.</p>
<table class = "Remark" id = "table132"><tr><td class = "Remark"><span class = "run-in.important">Important:
				</span><span class = "notecontent"><p>
All kinds of discrete damping elements and other kind of damping are
allowed outside the design domain if they are not a function of the
eigenfrequencies or eigenmodes. That is, modal damping (for example, defined using
<code class = "ph codeph">SDAMPING</code>) is prohibited.
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