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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>Guidelines for Optimization of Structures with Nonlinear Behavior</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 presents guidelines to build a stable optimization setup for sizing
            optimization. These guidelines can help the user to address the issues during the
            optimization run. </span>
 
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<p>This page discusses: </p><ul><li><a href = "#tso-c-usr-sizing-NonLin-Guidelines__tso-c-usr-sizing-NonLin-Guidelines-GeneralGuidelines" id = "toc_rg" title = "">Sizing Optimization in the Context of Nonlinear <span class = "ph">Structural Analysis</span>
</a></li><li><a href = "#tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-ManuConstr" id = "toc_rg" title = "">Manufacturing Constraints in the Model</a></li><li><a href = "#tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-Thermal" id = "toc_rg" title = "">Thermal Expansion in the Model</a></li><li><a href = "#tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-Contact" id = "toc_rg" title = "">Contact in the Model</a></li><li><a href = "#tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-StressObj" id = "toc_rg" title = "">Minimize Stress as Objective</a></li></ul>
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<div class = "section" id = "tso-c-usr-sizing-NonLin-Guidelines__tso-c-usr-sizing-NonLin-Guidelines-GeneralGuidelines"><h2 class = "title sectiontitle">Sizing Optimization in the Context of Nonlinear <span class = "ph">Structural Analysis</span>
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<p>The above setup is considered to be stable for running sizing optimization of structures with
   nonlinear behavior. Even though the settings consume more time for convergence, the
   optimization can converge in the first attempt. A recommendation for the settings:
   small initial time increment, <code class = "ph codeph">THICKNESS_MOVE = 0.1</code>,
   <code class = "ph codeph">THICKNESS_UPDATE = CONSERVATIVE</code>. If there are still convergence
   issues on the solver side, look for the above mentioned warnings in the
   <span class = "ph">Abaqus</span> 
   *.msg and *.dat files. One of the trivial methods of stabilizing a nonlinear
   optimization task is by increasing the frozen domain. If convergence issues remain,
   impose additional constraints on displacement or structural stiffness to further
   stabilize the optimization procedure. </p> 
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<div class = "section" id = "tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-ManuConstr"><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">Manufacturing Constraints in the Model</h2>

<p> In cases where the model contains
          manufacturing restrictions:<ul class = "ul">
          <li class = "li"> It is crucial to set the correct origin of the co system and the axis corresponding
            to the restrictions in the parameter file.</li>
          <li class = "li"> In the case of nonlinear problems, if the optimization ends in the solver convergence
            issues, the recommendation to remove the manufacturing constraints and solve the
            convergence issues. After obtaining a converged result, impose the restrictions one
            after the other. </li>
          </ul></p>
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<div class = "section" id = "tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-Thermal"><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">Thermal Expansion in the Model</h2>

<p> For thermal expansion problems, the
          recommendation is to use the <code class = "ph codeph">ENERGY_STIFF_MEASURE</code> design response instead
          of the <code class = "ph codeph">STRAIN_ENERGY</code> design response.</p>
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<div class = "section" id = "tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-Contact"><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">Contact in the Model</h2>

<p> For highly nonlinear contact problems,
          the automatic stabilization technique offered by the <span class = "ph">Abaqus</span> solver is the recommendation. This option helps automatically control rigid body motion
          before the contact closure restrains such motion, which can be activated by
          <code class = "ph codeph">*CONTACT CONTROLS, STABILIZE</code> command. By default, the auto-frozen option
          is activated in <span class = "ph">Tosca Structure</span>, which affects regions with contact, load, and displacement boundary conditions. Hence,
          it is important to deactivate the Auto frozen option <code class = "ph codeph">AUTO_FROZEN=OFF</code> to
          acquire the contact regions as design domain in cases where it is required. Note, this
          setting can lead to solver convergence issues.</p>
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<div class = "section" id = "tso-c-usr-sizing-NonLin-Guidelines__tso-c-user-TopOpt-NonLin-Guidelines-StressObj"><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">Minimize Stress as Objective</h2>

<p> In cases where stress design
          responses are used to define the objective function, the recommendation is to give
          reference values for the corresponding design responses. If stress design responses are
          used in the model, the recommendation is to use sensitivities calculated by the <span class = "ph">Abaqus</span> solver.</p>
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