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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>Review of Available Options and Possibilities</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">This section reviews useful options and possibilities to get a more robust
               optimization.</span>
 
</p>
<p>This page discusses: </p><ul><li><a href = "#tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-usr-sizing-NonLin-ReviewOptions-General" id = "toc_rg" title = "">General Information for Sizing Optimization</a></li><li><a href = "#tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca" id = "toc_rg" title = ""><span class = "ph">Tosca Structure</span> Options</a></li><li><a href = "#tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Solver" id = "toc_rg" title = "">Solver Settings: <span class = "ph">Abaqus</span></a></li></ul>
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<div class = "section" id = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-usr-sizing-NonLin-ReviewOptions-General"><h2 class = "title sectiontitle">General Information for Sizing Optimization</h2>

<ul class = "ul">
<li class = "li"> Since the design variables for sizing optimization are the elemental thicknesses, the elemental
                         stiffness changes during the optimization process. This can lead to larger
                         deformations and strains compared to the initial simulation. Therefore, the
                         material laws need to be defined for all material states, especially
                         plasticity laws. Continuous material laws such as Johnson-Cook are
                         preferred for nonlinear optimizations since they are defined for all strain
                         values.</li>
<li class = "li"> As the structure softens during the optimization, the recommendation is to adapt applied loads
                         in such a manner that they are reasonable for the final, softer structure
                         with less material, for example 20% of the original material. Otherwise,
                         too much plastic deformation occurs.</li>
<li class = "li"> If possible, convert loading to prescribed displacements to improve the robustness of the optimization. </li>
<li class = "li"> For shell elements, it is possible that elements form new contacts over the course of the
                         sizing optimization when they are initially not in contact and vice versa,
                         because their shell thickness changes during the process.</li>
</ul>
</div>

  
<div class = "section" id = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca"><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"><span class = "ph">Tosca Structure</span> Options</h2> 
 
<p>In <span class = "ph">Tosca Structure</span>, all the following described options are set in the
                    <code class = "ph codeph">OPT_PARAM</code> block of the <code class = "ph codeph">*.par</code> file. </p> 
<table class = "table"><caption/><colgroup><col style = "width:50%"/><col style = "width:50%"/></colgroup><thead class = "thead"> 
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<th class = "entry" id = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__1"> Option: </th> 
<th class = "entry" id = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__2"> Description: </th> 
</tr> 
</thead><tbody class = "tbody"> 
<tr class = "row"> 
<td class = "entry" headers = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__1"> <code class = "ph codeph">THICKNESS_MOVE</code> </td> 
<td class = "entry" headers = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__2"> This option sets the maximum possible move limit on design variables per
                                        optimization iteration. Smaller values of this parameter
                                        help to overcome optimization convergence issues, but tend
                                        to slow down the convergence rate. This is a relative value
                                        of the difference between the minimum and maximum thickness.
                                        The default value is <code class = "ph codeph">THICKNESS_MOVE=0.25</code>,
                                        meaning that the maximum change in thickness per iteration
                                        is 25%. In cases where it is observed that either the
                                        objective function or some of the constraint functions are
                                        oscillating during the optimization, setting
                                        <code class = "ph codeph">THICKNESS_MOVE=0.1</code> is the
                                        recommendation.</td> 
</tr> 
<tr class = "row"> 
<td class = "entry" headers = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__1"> <code class = "ph codeph">THICKNESS_UPDATE</code> </td> 
<td class = "entry" headers = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__2"> This option affects the thickness update behavior of CSA (Algorithm based on
                                        Convex Separable Approximations). There are three settings
                                        available: <code class = "ph codeph">CONSERVATIVE</code>,
                                        <code class = "ph codeph">NORMAL</code>, and <code class = "ph codeph">AGGRESSIVE</code>.
                                        The default setting is
                                        <code class = "ph codeph">THICKNESS_UPDATE=NORMAL</code>, whereas
                                        <code class = "ph codeph">CONSERVATIVE</code> and
                                        <code class = "ph codeph">AGGRESSIVE</code> are used for complex and
                                        unstable or simple and stable problems, respectively. In
                                        cases where it is observed that either the objective
                                        function or some of the constraint functions are oscillating
                                        during the optimization, the recommendation is to set
                                        <code class = "ph codeph">THICKNESS_UPDATE=CONSERVATIVE</code>. </td> 
</tr> 
<tr class = "row"> 
<td class = "entry" headers = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__1"> <code class = "ph codeph">AUTO_FROZEN</code> </td> 
<td class = "entry" headers = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Tosca__entry__2"> This option keeps elements with loaded nodes and boundary conditions from
                                        being optimized, respectively. There are four settings
                                        available: <code class = "ph codeph">LOAD</code>, <code class = "ph codeph">SPC</code>,
                                        <code class = "ph codeph">BOTH</code>, and <code class = "ph codeph">OFF</code>.
                                        <code class = "ph codeph">LOAD</code> and <code class = "ph codeph">SPC</code> constrain
                                        elements with loaded nodes or boundary conditions,
                                        respectively, from being optimized, while
                                        <code class = "ph codeph">BOTH</code> simultaneously freezes all elements
                                        with either load and boundary condition. The default setting
                                        is <code class = "ph codeph">AUTO_FROZEN=LOAD</code>. </td> 
</tr> 
</tbody></table> 
</div>
 
  
<div class = "section" id = "tso-c-usr-sizing-NonLin-ReviewOptions__tso-c-user-TopOpt-NonLin-ReviewOptions-Solver"><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">Solver Settings: <span class = "ph">Abaqus</span></h2>

The <span class = "ph">Abaqus</span> 
solver gives the possibility to define settings to improve the convergence for nonlinear models. 
See <a class = "xref" href = "tso-c-usr-solver-abaqus-nonlinguide.htm" title = "Features that are supported by Tosca are considered within this section.">Guide for Nonlinear Models</a>.
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