1. Every time a single mesh generation command is issued, the entire part must be rebuilt.
2. The resolution of the geometry can slow the projection algorithm.
3. The command insprt command causes an increased load every time the session file is re-run.
4. Smoothing commands (relax, unifrm, esm, tme) can be very slow, depending on the number of iterations selected.
5. Edges or vertices projected to the intersection of tangent surfaces are problematic. The iterative Newton method cannot work in this case and TrueGrid resorts to a primitive search algorithm to find the intersection.
6. Edges in a part are the most expensive calculation, except for smoothing.
7. If there is not enough RAM, TrueGrid, like any program,TrueGrid will have to swap memory which will have a dramatic effect on performance.
Here are some suggestions to improve the speed of TrueGrid®
1. Build smaller parts and use the BB command liberally to glue parts together.
2. Reduce the mesh size while building the part and then increase the mesh density after everything is completed and run the model in batch mode for the last time. You can use several strategies to reduce the mesh density. Use parameters for all mesh density issues (block, cylinder, mseq, insprt). Keep these numbers as low as possible while building the mesh. Alternatively, design the mesh density so that it is a half or a third the required mesh density. Then use meshscal of 2 or 3, respectively, to increase the mesh density in your final rerun.
3. Issue multiple commands before having TrueGrid draw (and consequently rebuild) the mesh. This can be done in a number of ways. A good method is to type the command in the text window, click on the F1 function key to automatically enter either the region or progression into the text window. Then use other function keys or type the remaining arguments to the command. Repeat this many times without typing the Enter key. This buffers the commands and submits them all at once. You can stack about 10 commands at a time, so you reduce the wait time by a factor of 10. It is not always possible to type a command in because you may not remember the sequence of arguments to a command. But this certainly will help with commands like pb, mb, and bb. Also, use index progressions with multiple regions as often as is practical, reducing the number of commands, thus reducing the number of redraws.
Alternatively, when a command is completed in a dialogue, click on the exec/quit button with the left mouse button and do not redraw. This has limitations, because sometimes you cannot continue until you see the results of the command. When the rebuild takes too long, avoid using the attach button, since it always causes a rebuild.
One can also use a text editor, such as notepad or vi (actually gvim on the PC which is great) to form the commands. This has a drawback that you have to know the syntax of the command to be effective. This is most effective if you have a large number of commands with a pattern that is easily reproduced with a text editor. Then you can copy and paste this list of commands generated in the text editor directly into the text window of TrueGrid.
A combination of these methods can have a profound effect on the efficiency of TrueGrid.
4. Never issue one of the smoothing commands while in the initial stages of positioning the vertices, attaching edges, projecting faces, or other routine steps to shape the mesh. This is the single biggest mistake in using TrueGrid. If you issue a smoothing command, then every time you enter a new command, the smoothing is recalculated. Save the smoothing for the last step in the development of the part.
5. The insprt command is not re-executed every time you issue a new command, so you only have to pay the price once every time you rerun. But this too can become a problem. You can avoid this by planning your part out in advance, removing the need for many insprt commands. Alternatively, once you have run the part with insprt commands, you can recreate a cleaned up version without the insprt commands by using the tghist file that is automatically generated.
6. The intersection of tangent surfaces must be avoided at all cost. The primary way to avoid this is to make a composite surface (sds option of the sd command) and project both faces that share the edge to the composite surface. If you need the edge to be on the intersection of the two tangent surfaces, create a 3D curve and attach the edge to the curve. This avoids the calculation of the intersection of two tangent surfaces. If it is not possible to combine the two tangent surfaces because they are not trimmed where they meet, use the curf command (instead of the default curs command) to permanently attach the edge to the curve, again avoiding the costly calculation of intersecting tangent surfaces. This discussion also applies to vertices in the part.
7. The positioning of nodes along an edge is the second most expensive calculation in TrueGrid. Only smoothing is more expensive. Usually you cannot reduce the number of edges in a part. But if you are not aware of this fact, you may inadvertently generate a part with many more edges than are needed, decreasing the efficiency.
8. It is usually an easy matter to increase the RAM. You should get approximately 120 bytes per nodes (32 bit system).
9. If you can, use the getol command with perhaps 30 for 50 to reduce the number of polygons used to approximate the surface geometry from a CAD model. Keep in mind that once you build and use a binary IGES file (saveiges and useiges), changing the getol will not effect the existing IGES binary file. If this low resolution affects the projection quality, increase the accuracy to 3. This keeps the number of polygons that are searched for the initial projection to a minimum and then kicks in the highly accurate Newton method on the algebraic surface. This trade off of number of polygons and algebraic surface evaluations can be significant.
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www.truegrid.com/FAQ/efficiency.html April. 4, 2008