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Gridgen Version 13 FAQ

1
Q: What is Pointwise?
A: Pointwise develops, distributes, and supports grid generation software tools and serves the computational analysis community as the premier supplier of these products. Gridgen, the primary product of Pointwise, is used by scientists and engineers around the world as a preprocessor primarily to engineering analysis and simulation of fluid flows. Pointwise has been in business since 1994, but personnel at Pointwise have been working on Gridgen and grid generation research since 1984. For more information check out our Corporate Profile page.

2
Q: What is Gridgen?
A: Gridgen is a interactive, graphical software package used to create 2D and 3D quadrilateral, hexahedral, triangular, and tetrahedral grid meshes and finite element models. Gridgen is employed in the construction of hybrid meshes as well, through the use of prisms and pyramids. In this regard, it serves as a preprocessor to Computational Fluid Dynamics and Finite Element Analysis. Gridgen also has a user friendly and intuitive graphical user interface and runs on UNIX/LINUX or PC platforms. The UNIX/LINUX platforms supported are SGI®, Hewlett Packard®, IBM®, Compaq®, and Sun®. For the PC platform only Intel®-based architectures are supported. For more information check out our Products and Services page.

3
Q: What is CFD?
A: CFD is an acronym that stands for Computational Fluid Dynamics. "Computational" refers to the use of computers. "Fluid" refers to gases or liquids. And "Dynamics" refers to motion. Putting it all together, CFD is the computer simulation of the motion of gases or liquids. Who's interested in the flow of gases or liquids?

  • NASA uses CFD to predict the aerodynamic forces acting on the Space Shuttle during launches.
  • Chrysler uses CFD to study how the airflow through your car's grill keeps the engine compartment cool.
  • The Navy uses the results of CFD simulations to shape submarine hulls so that the ships can move silently through the oceans.
  • Food and beverage manufacturers model the flow and mixing of liquids in pipes and tanks using CFD.

A good introduction to CFD is provided by this link.

4
Q: What is grid generation?
A: Grid generation goes by many other names including finite element modeling (FEM), and meshing. Regardless of what you call it, grid generation refers to the discretization of the domain on which a CFD or FEA solution is to be computed. For example, in the previous question about CFD the simulation of the aerodynamics of the Space Shuttle was mentioned. In this case, the air surrounding the shuttle is discretized. If you were to apply FEA to compute the stress in a bracket, the bracket itself would be discretized.

Discretization simply refers to the process of replacing a continuous medium like air, water, or metal with a finite (discrete) number of pieces. These pieces, called cells, can be any shape but are usually bricks (hexahedra) or tetrahedra. It's a lot easier to solve CFD and FEA problems by dividing the domain into these small cells. There may be hundreds of thousands or even millions of cells.

Therefore, you can envision grid generation as the process of replacing the air around a vehicle by a large number of small bricks that fit together with each other and the car's exterior like a 3D jigsaw puzzle.

Besides having to conform to the body being gridded, the grid cells must also obey certain rules regarding the total number of cells that can be used, the cell sizes, and cell shapes. That's where expertise comes in to play; knowing how to put together this 3D jigsaw puzzle when you don't even know what the pieces look like.



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6
Q: Do I need to be logged in as root on my system to be able to install Gridgen and the Elan License Manager?
A: If you follow our suggested Installation procedure, you may need to be root to install in "/usr/local". However, any user can install Gridgen and the Elan License Manager and can also generate a license key and start the Elan License Manager daemon.

7
Q: I'm having trouble transferring my new Gridgen software from the tape. I've been getting a message
appears to be a byte swapped archive.
Is there some other way to get the data?
A: This doesn't come up that often any more since Gridgen is delivered on CD-ROM. However, if you've somehow ended up with a tape try using the "dd" file copy/convert command available in the Unix environment. Enter
dd if=/dev/tape conv=swab | tar xvf -.
Also try this when getting the message
directory checksum error.
For detailed usage information check your online man pages.

8
Q: I'm running Gridgen from a remote server. I haven't specified a port yet. How can I find out which one Gridgen is using?
A: When the server is started up, it lists the port in the log. The log can generally found in the same location as the license key. The port listed is typically tcp-27000.

9
Q: Gridgen seems to start up OK on my machine, but the text on the menus is red and other colors seem to be different as well. It seems to be working, but is difficult to use with the colors as they are. Is there a problem with my installation?
A: This problem is related to question 8 above. The phenomenon you are seeing is a result of the fact that your workstation does not support Native OpenGL and is trying to implement a runtime conversion. In this case you should use the IRIX 5 executable as described in the answer to question 8. The IRIX 5 executable will implement IrisGL instead of OpenGL.

10
Q: We have just installed Gridgen. When I try to run it, it does not start, and I get the message: "cannot write file". Why will it not run?
A: This message indicates that the license daemon was not executed under the same user privilege as that which owns the license key file and the elm.log file. Be sure the same user installs these files and executes the daemon since the files are updated by the daemon each time a seat is released to a new process. Because the license daemon cannot update these files, it will not release a seat to allow you to start Gridgen.

11
Q: Our local network over which we run Gridgen was recently altered. Why can't I get Gridgen to obtain a license from the license server, even when I try to run it on the machine running the license manager? I keep getting the message
License authorization failure.
A: If the IP address of the machine running the Elan License Manager has changed for any reason, the license key you currently have will no longer be valid, even if the name of the machine has not changed. Also, incorporating subnets and subnet masks will cause communication problems between Gridgen and the workstation running the Elan License Manager daemon elmd. You must use the environment variable GRIDGEN_ELMHOST in the case of subnets. If your host's IP address has changed, please call Pointwise to update your license key.

12
Q: When I press the Help button I get the message
Can't open help file.
What's up?
A: This means that Gridgen cannot find the gridgen.hlp file in the default location set by the environment variable GRIDGEN_HOME. For proper Gridgen execution this variable must be set to the path to where the Gridgen executable and the gridgen.hlp and other related files reside. If for some reason the gridgen.hlp file is not in this location, there is a file browser option in the Help menu marked (Re)Load Help Library.

13
Q: We are running the Elan License Manager daemon elmd on more than one workstation on our network. Can I force my Gridgen session to obtain its license from a particular server?

A: Yes, just set the environment variable GRIDGEN_ELMHOST to the name of the server host using the "@" symbol. For example, setenv GRIDGEN_ELMHOST @hostname.
Generally under these circumstances it would be best to combine all licenses into a single server and use the Elan License Manager's reserved license feature. Call Pointwise for details.

14
Q: I can't get Gridgen to display on my X-terminal. Why?
A: Gridgen does not support the X-terminal display. Its display output must be sent only to the main display of your workstation.

15
Q: When I try to run Gridgen I get the message
No Licenses Available.
What does this mean?
A: This simply means that all available licenses are currently being used. If for some reason a Gridgen session was ended without exiting the software in a normal manner, it will take the license manager a few minutes to recognize that that particular session has ended and make that license seat available. To obtain a list of all current users and outstanding licenses available for all license managers on the network enter elmadmin -l.

16
Q: When I try to run Gridgen I get the message
License server is down.
What does this mean?
A:This message means that the host on which the Elan license Manager is running is not currently online or for some reason the Elan License Manager daemon elmd was killed. Check with your system administrator or the host's primary user to get the server back online or to get the license manager restarted.



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17
Q: I have some grids stored in PLOT3D format files. Can I use Gridgen to work on them?
A: Yes, Gridgen can actually read in existing grid edges, surfaces, and volumes as connectors, domains, and blocks by going to the Import Grid Pts (hot key 7) option in the Input/Output Commands menu. Upon reading in your file, Gridgen will automatically create the connectors, domains, and blocks for you.

18
Q: I'm not using Analysis Software that Gridgen supports with direct grid and BC output. How do I get my grid out?
A: Your grid can easily be exported using the Export Grid Pts (hot key 8) option in the Input/Output Commands menu. Just follow Gridgen's directions for specifying a file name and format.

19
Q: I'm trying to import an IGES file and I keep getting the error message:
empty GLOBAL section.
What's wrong with my file and can I fix it?
A: This error usually occurs when an IGES file has been transferred from a PC platform to a Unix workstation without specifying binary transfer. As a result, the IGES file will contain ^m (control m) at the end of each line and the IGES file reader in Gridgen does not like them. Deleting all of these characters from your file should allow you to import into Gridgen with no more errors.



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20
Q: Do I have to keep the display of all my database entities turned on?
A: No, that is not necessary. In fact, Gridgen will be able to render your grid more quickly if only the database entities you currently need for construction are active. You can disable database entities (in a similar fashion to domains and blocks) using En/Disable (hot key t) in the Database Commands menu. En/Disable is also available in the Display Commands menu. Disabled database entities default to being completely non-rendered. A toggle button is available in the Display Commands menu to have disabled database entities rendered as faint hashed lines.

21
Q: Why is my zoom box not working?
A: The zoom box feature works best in orthonormal viewing mode. To toggle between orthonormal and perspective viewing modes use the v hot key while in any menu. There is also a toggle button for this in the Display Commands menu.

22
Q: I've run another application while in a Gridgen session and when I returned to Gridgen, its colors were messed up. Can I fix the colors?
A: Gridgen's color map can be reset easily from the Display Commands menu by pressing the Set Colors (hot key ^c) button.



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23
Q: I created two sets of database entities inside Gridgen in two different sessions which were saved in two different Gridgen Composite database files. When I read both files in and create a grid on the database entities, then save a Gridgen file and try to read it back in later, my connectors are being associated to the wrong entities. What is causing this?
A: It is likely that since your database entities were created in separate sessions you have entities in each file which have the same name. Therefore when a Gridgen file that was created on these entities is imported, Gridgen has no way to distinguish which entity to associate to, so it picks the first one with the correct name that it comes to. To get around this problem, read in both of your database files, use the Name option in the Database menu to ensure all entities have a unique name, and then make sure you save all the entities in a new Grigen Composite database file. You will then always use the new comprehensive database file for all your grid work.

24
Q: I don't have my geometry in an IGES file. Can I still use Gridgen?
A: You don't need to have a database in order to start building grids in Gridgen. You can also import database geometry as Gridgen networks, segments, or Patran neutral files. Refer to the appendices in your Gridgen manual for file format information.

25
Q: I intersected two surfaces and the intersection curve looks like a dashed line. Why?
A: Gridgen has actually produced a set of intersection segments. This means that the surfaces you are intersecting are probably bilinear surfaces. Slope continuous surfaces always provide a continuous intersection curve.


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26
Q: Do I want to "Maintain Linkage" or not?
A: Generally yes...Answering this question will take some discussion. As you may have already observed, there are many instances when it does not seem to matter whether you pick Unlink or Maintain Linkage. In all operations Gridgen will strive to maintain the connectivity of your connector nodes, domain edges, and block faces. If you are modifying an entity which is already a component of the next higher construction level, you will not be allowed to unlink that entity. This applies to connectors that are used as components of domains and domains that are part of blocks.

There is no higher level above blocks so they can always be either Unlinked or not. In many cases the question may be irrelevant like when you have not actually changed the physical location of the entity you are modifying. For instance, when you have just modified a group of connectors and only redimensioned them. Linkage is therefore most important in cases where you are moving the entity's physical location.

Sometimes you really do want to alter an entity and unlink it. For instance you have decided to make some major connector changes in an area of your grid or you have some domains you would like to swap around. In these cases you must delete the highe level entities (the domains the connectors are part of or the blocks the domains are part of) so that when you complete your modifications, Gridgen will allow you to unlink them. Keep in mind that in all cases when linkage is maintained whether by choice or not, if the modified entity has been physically moved, Gridgen will alter the connecting components however necessary to maintain linkage.

27
Q: How do I make a complete 360 degree circle?
A: Gridgen will only create a half circle connector. A full circle could be created by joining two half circle connectors, although this type of connector would only be necessary for fairly unusual grid topologies. Full circle database curves would be created in a similar manner.


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28
Q: During domain creation sometimes my new domains are green and sometimes they are purple. Why?
A: A newly created domain that is rendered in purple has been computed using Parametric or Parametric Fit TFI. A newly created domain rendered in green has been initialized using Standard TFI.

29
Q: During domain creation I can't pick the next connector. Why?
A: This means that the common nodes of your current connector and the next connector you wish to add do not occupy the same point to within Gridgen's preset node tolerance. In this case you have three options. You can zoom in and modify the end of one of the two connectors, you can change the default node tolerance in the Defaults menu which is accessed from Gridgen's main menu, or you can use the new Pick Unlinked Connector feature and Gridgen will dynamically update the node tolerance as necessary. Be aware that changing the node tolerance affects the whole grid, not just the current node.

30
Q: When I projected one of my domains, why were some of my edge connectors changed?
A: All of the domain projection types (spherical, cylindrical, linear, and closest pt) default to projecting the domain edge connectors as well. If you wish to only project the interior, each type has radio buttons in the last menu prior to actual projection -- select the button marked Int Pts (hot key k) to prevent your connectors from also being projected.



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31
Q: When creating a block I get the message
The six faces don't make an understandable blocking topology.
What the heck does that mean?
A: This means that the six faces you have chosen for some reason do not make a regular six sided block with all faces having appropriate dimension and sharing edge connectors with their adjacent faces. You may have inadvertently omitted a very small domain from a particular face, accidentally selected the same domain twice for one or more block faces, or two adjacent faces don't share all the same edge connectors (duplicate connectors lying on top of each other).

If you suspect that you have duplicate connectors, just go to the Connector Commands menu and select Examine. Then select Pick (hot key 1) and while placing the cursor over the suspected connectors, use the x key to toggle among any coincident connectors.

32
Q: I need to replace a connector that is part of a domain already in a block. Can I do this without having to delete and recreate my whole block?
A: Yes you can. First you need to keep your existing system as it is and create your new connector and the new domains that the connector will be a part of. Once this is done you can go into Block Commands and Modify the affected block. Remove the affected face(s) and then rebuild those faces with the newly created domains. After saving the new block you can delete the unwanted domains and connectors.


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33
Q: Why can't I set Analysis Software BC's on my 2D grid?
A: To set BC's on a 2D grid, you must follow the same procedure as you would for a 3D grid. First pick 2D and your flow solver using the Set Analysis S/W option in the Analysis S/W Commands menu, then using the Block Commands menu to generate and save 2D blocks from your domains, and then return to the Analysis S/W Commands menu and use the Set BCs option to set all your BC's.


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35
Q: How can I make sure I'm running the latest version of
Gridgen?
A: All you need to do is check our Release Notes page to see what the latest release version is. If you're not up-to-date, refer to Downloading a New Executable on the Installation page. Your current Elan License Manager key will remain valid for the new executable as long as the major version number that you are running is the same for the version you are installing.

36
Q: I have files created in an older version of Gridgen. Can the latest version read my files?
A: Yes, Gridgen is backwards compatible with the two following exceptions. Version 8 will require database editing to remove group entities for a smooth read-in, and Version 6 files will only produce connectors in the current version.

37
Q: I'm using an older version of Gridgen. Can I still get trained at your class?
A: Yes, anyone can attend Gridgen training classes, even individuals who currently do not use it or have a license. This is an excellent way for prospective buyers to check out Gridgen. Just keep in mind that we only support our current version and therefore the training will be geared to the current software. However many of the same concepts used to build grids in our latest version have their heritage and usefulness in earlier Gridgen versions. If you are interested in learning more about training or want pricing information please check out our Training page.