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    Hi,<br>
    it seems that the gmsh readin in moab only supports linear elements,
    am I right?  I saw that in the newest version of moab, there is a
    spectral Hex module, but I don't know if this is already supported
    in Nek, and if moab is able to read / write spectral elements...?<br>
    best<br>
    Florian<br>
    <br>
    <br>
    <br>
    <div class="moz-cite-prefix">Am 28.04.2014 15:13, schrieb
      <a class="moz-txt-link-abbreviated" href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>:<br>
    </div>
    <blockquote
      cite="mid:mailman.7284.1398690804.3880.nek5000-users@lists.mcs.anl.gov"
      type="cite">
      <div dir="ltr">Dear all
        <div>I have read on the list that you can read 3d gmsh meshes
          into nek via moab. Gmsh can generate higher order elements.
          Last time I checked, it was not possible to read 2d gmsh
          grids, only 3d. This would be a great option if the 2d case
          worked with gmsh.</div>
        <div>Best</div>
        <div>praveen</div>
      </div>
      <div class="gmail_extra"><br>
        <br>
        <div class="gmail_quote">On Mon, Apr 28, 2014 at 3:50 PM, <span
            dir="ltr"><<a moz-do-not-send="true"
              href="mailto:nek5000-users@lists.mcs.anl.gov"
              target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span>
          wrote:<br>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">
            <div bgcolor="#FFFFFF" text="#000000"> Hi Wei,<br>
              I don't think genbox is the right tool to mesh airfoils,
              just because you need the curved elements for high order
              computations. We are using high order meshes for
              discontinuous Galerkin schemes. One technique is to 
              construct them from agglomeration of fine structured grids
              (ICEM, Poitwise, Gridgen...), leading to coarse grids with
              the intermediate points used for the curved element
              mapping. <br>
              <br>
              But then I really don't know how this fits into the nek
              mesh format, since I think there is no possibility to
              define intermediate interpolation points for the elements.
              The only thing I saw is to prescribe a curvature of an
              edge, but I think this is restricted to 2D meshes and
              circular geometries, no?<br>
              <br>
              Our workaround for an airfoil computation was more or less
              a hack directly in Nek, where we read  Gauss-Lobatto high
              order points of the elements from file (we produced
              ourselves, together with the Nek format with linear edges)
              and replaced (overwrote) the linear elements with the
              curved ones during grid setup. Maybe somebody knows a
              better way to do this...<br>
              <br>
              regards<br>
              <br>
              Florian<br>
              <br>
              <br>
              <br>
              <div>Am 28.04.2014 10:38, schrieb <a
                  moz-do-not-send="true"
                  href="mailto:nek5000-users@lists.mcs.anl.gov"
                  target="_blank">nek5000-users@lists.mcs.anl.gov</a>:<br>
              </div>
              <div>
                <div class="h5">
                  <blockquote type="cite">Hi Florian,
                    <div><br>
                    </div>
                    <div>For the 2D airfoil profile, I guess, the
                      profile in nek5000 is connected by small straight
                      lines not the curved lines. But even this, I have
                      no idea to make a mesh for 2d airfoil flow. in the
                      Genbox introduction there is something words on
                      segments mesh without a sample</div>
                    <div><span
                        style="font-size:13px;line-height:19px;font-family:sans-serif">
                        <h3
                          style="border-bottom-width:initial;padding-top:0.5em;width:auto;background-color:initial;margin-bottom:0.3em;font-weight:bold;padding-bottom:0.17em;border-bottom-color:initial;border-bottom-style:none;margin-right:0px;overflow-x:hidden;overflow-y:hidden;font-size:17px;margin-left:0px;margin-top:0px;background-repeat:initial
                          initial;background-image:none">
                          <span>For Multiple Segmented Geometries</span></h3>
                        <ul
style="line-height:1.5em;list-style-type:square;margin-top:0.3em;margin-right:0px;margin-bottom:0px;margin-left:1.6em;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px">
                          <li style="margin-bottom:0.1em">This feature
                            allows users to enter a complex sequence of
                            segments for each of the x,y,z directions.</li>
                          <li style="margin-bottom:0.1em">Each segment
                            set is defined in x,y,z sections. So, Lines
                            6-8 would all pertain to x-dimension, 9-12
                            to y-dimension, ect.</li>
                        </ul>
                        <div
style="margin-top:0.4em;margin-right:0px;margin-bottom:0.5em;margin-left:0px;line-height:1.5em"><b>Line
                            5:</b> The line following the string name,
                          is the number of segments, <i>nsegs</i>, in
                          the x_direction</div>
                        <div
style="margin-top:0.4em;margin-right:0px;margin-bottom:0.5em;margin-left:0px;line-height:1.5em"><b>Line
                            6:</b> The next line is the number of
                          elements in each segment, so there should be <i>nsegs</i> numbers.

                          (nelx_1,nelx_2...)</div>
                        <div
style="margin-top:0.4em;margin-right:0px;margin-bottom:0.5em;margin-left:0px;line-height:1.5em"><b>Line
                            7:</b> The next line is the start(and end)
                          coordinates for each segment in this
                          direction. There should be <i>nsegs</i>+1.
                          (x(0),x(1)...x(nsegs))</div>
                        <div
style="margin-top:0.4em;margin-right:0px;margin-bottom:0.5em;margin-left:0px;line-height:1.5em"><b>Line
                            8:</b> The following line is the
                          distribution of each segment, uniform spacing
                          corresponds to 1, otherwise a geometric
                          sequence is generated.</div>
                        <dl style="margin-top:0.2em;margin-bottom:0.5em">
                          <dd
style="line-height:1.5em;margin-left:1.6em;margin-bottom:0.1em;margin-right:0px">-In
                            conclusion, a segment between x(e-1) and
                            x(e) is filled with nelx_e elements
                            determined by the geometric ratio given for
                            that segment.</dd>
                        </dl>
                        <ul
style="line-height:1.5em;list-style-type:square;margin-top:0.3em;margin-right:0px;margin-bottom:0px;margin-left:1.6em;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px">
                          <li style="margin-bottom:0.1em">Repeat (Lines
                            5-8) for dimensions 2 and, if applicable, 3.</li>
                        </ul>
                      </span>
                      <div><br>
                      </div>
                      <div>can anyone give us a sample?</div>
                      <div><br>
                      </div>
                      <div>regards</div>
                      <div><br>
                      </div>
                      <div>Wei</div>
                      <div>
                        <div>On Apr 25, 2014, at 10:17 PM, <a
                            moz-do-not-send="true"
                            href="mailto:nek5000-users@lists.mcs.anl.gov"
                            target="_blank">nek5000-users@lists.mcs.anl.gov</a>
                          wrote:</div>
                        <br>
                        <blockquote type="cite">
                          <div dir="auto">
                            <div>Hi matt,</div>
                            <div>Sorry that I cannot fully answer your
                              question, I know that at least the
                              smallest edge length  in the mesh is a
                              measure for the stiffness of the full
                              problem, so maybe you should avoid too
                              small element heights in the boundary
                              layer. </div>
                            <div>However, I also would like to know  how
                              you are generating the airfoil mesh, since
                              the mesh has to be coarser than a standard
                              meshes and the boundary layer elements
                              need to have curved boundaries, no? Which
                              mesh generator you use and how do you
                              convert the mesh to Nek format? </div>
                            <div>The 3d problem should boil down to a 2d
                              problem, since I assume that you want
                              simulate a small part of the wing with
                              periodic boundary conditions in spanwise
                              direction... But wei, for the 2d mesh, did
                              you resolve the issue to curve the
                              boundary layer elements?</div>
                            <div><br>
                            </div>
                            <div>Florian</div>
                            <div><br>
                              Am 25.04.2014 um 18:02 schrieb <a
                                moz-do-not-send="true"
                                href="mailto:nek5000-users@lists.mcs.anl.gov"
                                target="_blank">nek5000-users@lists.mcs.anl.gov</a>:<br>
                              <br>
                            </div>
                            <blockquote type="cite">
                              <div>
                                <div dir="ltr">·HI Matt,
                                  <div><br>
                                  </div>
                                  <div>Till now I have no experiments on
                                    3D problem, what I am interested in
                                    is how you generate the 3D or 2D
                                    airfoil mesh for nek5000? I spend 2
                                    weeks in generated a 2d airfoil flow
                                    mesh without any good results. would
                                    you like tell me some informations?
                                    thank you a lot!</div>
                                  <div><br>
                                  </div>
                                  <div>Wei<br>
                                    <div class="gmail_extra"><br>
                                      <br>
                                      <div class="gmail_quote">2014-04-25
                                        17:00 GMT+02:00 <span dir="ltr"><<a
                                            moz-do-not-send="true"
                                            href="mailto:nek5000-users@lists.mcs.anl.gov"
                                            target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span>:<br>
                                        <blockquote class="gmail_quote"
                                          style="margin:0 0 0
                                          .8ex;border-left:1px #ccc
                                          solid;padding-left:1ex">
                                          <div dir="ltr">
                                            <div>
                                              <div>
                                                <div>
                                                  <div>Hello,<br>
                                                    <br>
                                                    I am looking to do
                                                    simulations of flow
                                                    past a wing in 3D
                                                    using nek5000 and I
                                                    have been thinking
                                                    more about potential
                                                    issues with high
                                                    aspect ratio
                                                    elements. In general
                                                    we have very fine
                                                    resolution near the
                                                    wing and then as we
                                                    get further away the
                                                    wall normal and wall
                                                    parallel spacing
                                                    increases. As a
                                                    first try we will
                                                    extend the domain in
                                                    the cross stream
                                                    direction which will
                                                    result in small dz
                                                    values. I know that
                                                    in general the best
                                                    performance is
                                                    obtained with
                                                    elements having
                                                    dx=dy=dz and that as
                                                    the aspect ratio
                                                    increases the
                                                    performance will
                                                    degrade. <br>
                                                    <br>
                                                    I'm wondering if
                                                    there are general
                                                    rules of thumb for
                                                    the performance
                                                    degradation with
                                                    increased aspect
                                                    ratio. For example,
                                                    is an aspect ratio
                                                    of 10 ok but an
                                                    aspect ratio of 100
                                                    unacceptable? Is
                                                    this even something
                                                    we can estimate in
                                                    general or does it
                                                    vary so much problem
                                                    to problem that no
                                                    general estimate is
                                                    possible?<br>
                                                    <br>
                                                  </div>
                                                  I saw an earlier post
                                                  that referred to the
                                                  paper "An Overlapping
                                                  Schwarz Method for
                                                  Spectral Element
                                                  Solution of the
                                                  Incompressible
                                                  Navier-Stokes
                                                  Equations", P. Fischer
                                                  JCP 1997. From the
                                                  paper I see two
                                                  general strategies. <br>
                                                </div>
                                                1. limit the maximum
                                                aspect ratio to a
                                                critical value<br>
                                              </div>
                                              2. design a grid for our
                                              case, run it for a short
                                              time and then iteratively
                                              add more grid points to
                                              decrease the aspect ratio
                                              until optimal performance
                                              is achieved. <br>
                                              <br>
                                            </div>
                                            Does anyone have a general
                                            or specific suggestion
                                            regarding how we should
                                            handle the grid generation
                                            in terms of selecting the
                                            largest aspect ratio
                                            possible with low
                                            computational cost?<br>
                                            <br>
                                            Thanks,<br>
                                            <br>
                                            Matt<br>
                                          </div>
                                          <br>
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                                          <br>
                                        </blockquote>
                                      </div>
                                      <br>
                                      <br>
                                    </div>
                                  </div>
                                </div>
                              </div>
                            </blockquote>
                            <blockquote type="cite">
                              <div><span>_______________________________________________</span><br>
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                    <br>
                    <pre>_______________________________________________
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</pre>
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              <span class="HOEnZb"><font color="#888888">
                  <pre cols="72">-- 
-----------------------------------------------------------------------------
Dipl. Ing. Florian Hindenlang
Institut fuer Aerodynamik und Gasdynamik 
Phone: 0049 (0)711-685 63413
office 1.14
Pfaffenwaldring 21
70569 Stuttgart 
E-Mail: <a moz-do-not-send="true" href="mailto:hindenlang@iag.uni-stuttgart.de" target="_blank">hindenlang@iag.uni-stuttgart.de</a>
---------------------------------------------------------------------------
</pre>
                </font></span></div>
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      <br>
      <pre wrap="">_______________________________________________
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    <br>
    <pre class="moz-signature" cols="72">-- 
-----------------------------------------------------------------------------
Dipl. Ing. Florian Hindenlang
Institut fuer Aerodynamik und Gasdynamik 
Phone: 0049 (0)711-685 63413
office 1.14
Pfaffenwaldring 21
70569 Stuttgart 
E-Mail: <a class="moz-txt-link-abbreviated" href="mailto:hindenlang@iag.uni-stuttgart.de">hindenlang@iag.uni-stuttgart.de</a>
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