<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>Le 13-févr.-09 ā 11:04, Alexander Sjögren a écrit :</div><br class="Apple-interchange-newline"><blockquote type="cite">Hi,<div><br></div><div>I'm pretty new to GMSH and my problem may be due to a basic mistake, nevertheless I'm really stuck. I'm trying to make a mesh of the volume around a spacecraft. The spacecraft consists of an almost cubic body, large solar panels and two booms. The most interesting volumes for my simulations are around the two booms, so the mesh around the booms need to be in good quality. The program I'm doing my simulation in needs the quite large simulation box (ellipsoidal in the pictures).</div> <div><br></div><div>The problem is that when I make a 3D mesh of the volume around the spacecraft, the mesh around the two booms consists largely of straight lines to the booms, not of a mesh in all (random) directions. I've tried using different characteristic lengths for the booms, both making it larger and smaller than the characteristic length for the ellipsoid and rest of the spacecraft. I've also tried using the two different meshing algorithms (Tetgen+Delaunay and Netgen), the result looks maybe a little bit better with Netgen but the problem is still there. The result of the mesh-problem is that when I run simulations you can tell from the results that the mesh affects the result, too much, in a bad way.</div> <div><br></div><div>Does anyone have an idea of what I'm do</div></blockquote><div><br></div><div><br></div><div>You shoud define a size field. By default, Gmsh interpolates mesh sizes from boundaries :</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>-) in 1D mesh, we take mesh sizes at vertices and interpolate linearly</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>-) in 2D, we use edge sizes at boundaries and interpolate using baricentric coordinates</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>-) in 3D, we use triangle sizes and interpolate using baricentric coordinates</div><div><br></div><div>If you have huge sizes in your outside box, this causes gmsh to believe that the initial</div><div>3D mesh is ok.</div><div><br></div><div>JF</div><div><br></div><blockquote type="cite"><div>ing wrong and what I can do to make my mesh better? I've attached three pictures:</div><div><br></div><div>1.jpg: This is the spacecraft inside the ellipsoid I'm using for the calculations.</div> <div>2.jpg: A close-up of one of the booms.</div><div>3.jpg: Same as 2.jpg, now with the mesh that I'm not happy with. </div><div><br></div><div>Thanks in advance for your help and your time!</div><div><br></div><div> Best regards</div><div>Alexander Sjögren, Uppsala, Sweden</div><div><a href="mailto:alex.ph.sjogren@gmail.com">alex.ph.sjogren@gmail.com</a></div> <span><1.jpg></span><span><2.jpg></span><span><3.jpg></span>_______________________________________________<br>gmsh mailing list<br><a href="mailto:gmsh@geuz.org">gmsh@geuz.org</a><br>http://www.geuz.org/mailman/listinfo/gmsh<br></blockquote></div><br><div> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>----------------</div><div>Prof. Jean-Francois Remacle</div><div>Universite catholique de Louvain (UCL)</div><div>Tel : +32-10-472082 -- Mobile : +32-473-909930 </div><div><br></div></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"> </div><br></body></html>