General Questions

Where can I get the support concerning AutoFEM?
What versions of AutoCAD does AutoFEM Analysis work?
I'm working with another CAD system (Inventor,Mechanical Desktop, Solidworks). Can I use AutoFEM?
How do I install AutoFEM on Windows 7?
I have installed AutoFEM, but it seems, that Fema Tool does not work. What may be wrong?
I have started the AutoCAD after AutoFEM Analysis installation but I don’t see menu or ribbon of the AutoFEM Analysis, what is wrong?
I have typed FEMAABOUT but I don't see the dialogue "About AutoFEM". What can I do now?
How do I install AutoFEM on AutoCAD 2007, 2008?
To restore the original AutoCAD menu after removing AutoFEM Analysis...
Could AutoFEM Lite version be installed simultaneously with AutoFEM Commercial (Trial) on one computer?
What are the system requirements are recommended for work with AutoFEM Analysis?
Does AutoFEM work with AutoCAD 2011?
Does AutoFEM Analysis work with AutoCAD Lite?
Is the AutoFEM license perpetual?

Around FEA modeling

Requirements for the three-dimensional model for finite element analysis
I have a study but I couldn't create FE mesh. What can I do?
Should direct or iterative method be used for solving?
What do "incorrect" and "error" elements mean in the mesh?
I have created a report on my study and I see a blank image or an error message. What is this?
How can I apply a force (or pressure) to a certain area of the part?

Where can I get the support concerning AutoFEM?

If you encounter difficulties installing or using AutoFEM, the best way to try to resolve them is to go directly to our technical support email: Esta dirección electrónica esta protegida contra spambots. Es necesario activar Javascript para visualizarla .
Please be clear in describing your problem and tell us the version of Windows, AutoCAD and AutoFEM, that you are using.

What versions of AutoCAD does AutoFEM Analysis work?

The system of finite element analysis "AutoFEM Analysis" is working with AutoCAD (x86) 2007, 2008, 2009, 2010, 2012 for Windows based operational systems on 32-bit platform x86 and with  AutoCAD x64 2008, 2009, 2010, 2012 for Windows based operational systems on 64-bit platform.

I'm working with another CAD system (Inventor,Mechanical Desktop, Solidworks). Can I use AutoFEM?

AutoFEM Analysis works only in AutoCAD's 3D environment, it does not work directly with Inventor, Mechanical Desktop, SolidWorks etc. However, if you have the possibility to use AutoCAD, you can export your 3D model from CAD system into AutoCAD via SAT file format (ACIS exchange file format) and then you can try to provide finite-element analysis of your model using AutoFEM.

How do I install AutoFEM on Windows 7?

You should have the administrative rights to install AutoFEM on Windows 7 properly. Sometimes it is necessary to use Fema Tool program to register AutoFEM in AutoCAD (usually if you have installed via *.msi file).

Then select desirable version of AutoCAD and launch AutoCAD.

I have installed AutoFEM, but it seems, that Fema Tool does not work. What may be wrong?

Sometimes, you should install the Microsoft Visual C++ 2008 SP1 Redistributable Package x86 or the Microsoft Visual C++ 2008 SP1 Redistributable Package (x64) before AutoFEM installation. Also you can find these packages in the AutoFEM distribution package or you can download them from our site: vcredistx86_2008 or vcredistx64_2008.

I have started the AutoCAD after AutoFEM Analysis installation but I don’t see menu or ribbon of the AutoFEM Analysis, what is wrong?

The first, it is necessary to check, was AutoFEM loaded or no. Type the command FEMAABOUT in the AutoCAD command line. If you see the dialogue as it is shown below it means that AutoFEM is loaded and you don't see the Ribbon. In such case, usually, it is sufficient to reload 3D Environment of AutoCAD and the AutoFEM Ribbon and menu will appear.

If the dialogue "About AutoFEM" appears this means that AutoFEM is loaded successfully

Using the command APPLOAD of AutoCAD

Adding AutoFEM ARX file in startup list

• Windows version;
• Specify Windows bit capacity (x32 or 64-bit);
• Language pack of Windows;
  
• AutoCAD version;
• AutoCAD bit capacity (x32 or 64-bit);
• Language pack of AutoCAD.

To restore the original AutoCAD menu after removing AutoFEM Analysis...

To restore the original AutoCAD menu after removing AutoFEM Analysis one must call the commands AutoCAD "cui" and "reset" as shown in the figure.

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Does AutoFEM work with AutoCAD 2011?

No, it doesn't at this moment.
We were forced turn off AutoFEM loading in AutoCAD 2011 x86 because there are some problems of compatibility.
Therefore AutoFEM 1.3 does not work with AutoCAD 2011 x86 at this moment. Only AutoCAD 2007-2010 are fully supported.

Does AutoFEM Analysis work with AutoCAD Lite?

No, it doesn't. AutoFEM Analysis and AutoFEM Analysis Lite can be used only with full version of AutoCAD because the 3D modelling workspace is necessary for finite-element analysis.

Is the AutoFEM license perpetual?

Yes, it is.
Each customer gets perpetual license. All updates within the main version number (1.1, 1.2, 1.3...) are absolutely free of charge.
Licensing is provided by the electronic key which customer obtains upon confirmation of his/her payment.
The license can be moved to the other computer system through deactivation process (10 deactivations are provided).

The buyer of the full AutoFEM Analysis package has some additional advantages:

• two activations
• discount for the next purchase
• all new modules of AutoFEM Analysis within basic version number. Absolutely free!

If you have any difficulties with managing your license, please contact our support team.

Requirements for the three-dimensional model for finite element analysis

The quality and possibility of constructing a finite element mesh is strongly dependent on the quality of volume models, so when building 3D models imposed more stringent requirements than conventional modeling in AutoCAD. You should consider the following requirements to create three-dimensional models of your products in terms of finite-element analysis.

• Mutual or self-intersection bodies are not allowed. It is impossible to construct a finite element mesh for intersecting bodies. Before you create a study, you always should test your model on the intersections by special AutoCAD command INTERFERE. This command shows intersections between bodies if they are. One advice is how intersections may be removed from the assembly if intersecting bodies consist of the same material. You can use the command of AutoCAD: UNION and unite intersecting bodies in a whole body.

There are lots of intersections. Creating a finite element study impossible.

• Between the bodies must be no gap, except when there are no actual gaps between the bodies. All bodies, which are included in a study, must have a contact by a face, or edge, or vertex, with any other body of the study. So in the study, a totally unengaged body should not exist as it is like freely “hovering” in space.

The models with gaps are not allowed.

• 3D body should be singly closed volume. Volume finite element mesh can be built only for a limited volume.
• In AutoCAD one can create a solid 3D model which consists of multiple separate volumes. For instance if you have extruded multiple profile (see at the picture). Meshing of the such 3D body is impossible. So the 3D solid which consists of multiple separate volumes is not allowed in the FEA study. If you have such 3D solid you need use the AutoCAD's command SOLIDEDIT|SEPARATE before creating the FEA study to separate the single solid on multiple independent volumes.

The 3D solid consists of multiple volumes.

That solid after using SOLIDEDIT|SEPARATE command.

• It is recommended to avoid to do rounding, chamfering, holes and decorative elements if they are not important for the strength of design . They can complicate the construction of the finite element grid and increase the dimension of the problem (time to find a solution). But items which are bearing influence on strength of design, e.g., fillets, ribs, etc., can be presented in the model.
• The bodies, united in a block, are treated as one solid body which is obtained using a Boolean union of all bodies in the block. The bodies in the block may intersect with each other. No gap should exist between the bodies as this will generate an error of grid generation.

I have a study but I couldn't create FE mesh. What can I do?

You have constructed 3D model of your design, created a Study, and you are trying to create FE mesh, but you faill.
Why does it happen and how one can avoid it?

First, it is necessary to check the model according to the Requirements for 3D model.

Second, if the model has no intersections or gaps, but mesh is still not created, it is recommended to change mesh parameters which control the meshing process. In many cases changing parameters of meshing will provide success.

Meshing parameters.

The follows sequence of the varying meshing parameters varying can be put forward:

Unfortunately there are cases when creation of FE mesh is impossible despite changing the mesh parameters. Sometimes this happens because of an erroneous PLC model for the transfer of models from AutoCAD in Preprocessor of AutoFEM. This is the most difficult case, because for this there is not any solution via AutoFEM tools. In this case, it is necessary to modify the 3D model in AutoCAD in such a way as to eliminate errors in the creation of the PLC-model.

Our experience shows that if the mesh is not created, this usually means that a drawback presences in the model. This is especially true for assembly models.
If you cannot find the cause of which meshing failed, please contact with our Support Service (support@autofemsoft. com). Send us your model in .dwg with short description of the problem. We will try to help you.

Remember: meshing of strictly performed models usually is successful.

Should direct or iterative method be used for solving?

Generally, there are two main methods of equation systems solving. They are direct and iterative methods. The default mode of automatically choosing one of these methods is turned on in AutoFEM Analysis. If the number of equations is more than the number, specified in Processor settings (which equals 100,000 on default), the iterative method is used for solving. If the system is smaller, the direct method is used. You can set your own criterion for choosing a method of solving that is determined by parameters of your computer system. Also you can manually set whether the direct or iterative method should be used for solving the equation system, choosing the desirable mode directly before solving.

General recommendations of choosing and using these methods are as follows. The first criterion is power of your computer system. The iterative method has fewer requirements for the amount of memory (RAM) than the direct method. The next criteria are the quality of finite-element mesh and "thickness" of a problem.

The direct method is based on the Gauss method and its modifications. Full inversion of matrix occurs. This means that the large amount of memory is needed for storing the inverse matrix. In addition the time of calculation increases as N³ with number of equations N.

Usually the direct method works well and it is preferred when you have:

• relatively small equation system or a powerful computer system, based on x64-platform, and sufficient memory (RAM) amount (at least 4-8GB), which allows to place the inverse matrix fully in RAM. If you have such a computer system, you can efficiently solve problems up tol 1.5 -3 million degrees by the direct method in the "thin" 3D model.
• mesh has many "stretched" elements
• study has contact restrictions

The iterative method. The main advantage of iterative method is its posing ow demands on the RAM amount in comparison with the direct method. For the iterative method, the amount of necessary additional RAM is comparable with the amount of RAM for initial stiffness matrix location. Therefore, even relatively weak computer system (such as an office computer with Windows 32-bit operational system and no more than 3GB RAM) is able to solve up tol 1 million equations. But there is a certain drawback. Its performance depends on such property of tetrahedral finite elements as aspect ratio. When aspect ratio grows, the number of iterations increases and time of solving may significantly increase too. Therefore, if the mesh has many stretched elements (this often occurs if your model is slim and thin) or even "incorrect" ones, you may face the slowdown of the solving rate. Usually the iterative method works well and is preferred when you have:

• good mesh with total aspect ratio less than 8-4 and small number of stretched elements.
• "thick" model, meaning that you have several layers of tetrahedral elements per section.
• study has no contact restrictions.

A "thick" finite element model. There are several layers of the finite elements. The Iterative method works better in comparison with the direct method in the medium and large models.

A "thin" finite element model. Mesh consists of one or two layers of finite elements. The direct method works well, and the iterative method may be down if quality of the mesh is poor.

What do "incorrect" and "error" elements mean in the mesh?

The dialog of the mesh generator displays special messages, featuring the mesh quality.

Message "Mesh contains elements with incorrect geometry (N)" means that there are N elements with the aspect ratio over 20. The Aspect Ratio of a tetrahedral element is the ratio of the maximum side length to the minimum altitude of the element.
The optimal aspect ratio is about two but this ratio is not possible for all elements of the mesh without exception. If the aspect ratio of a tetrahedron is more larger than 2 this means that the tetrahedron is stretched. Stretched tetrahedrons have a big error in stress calculation, therefore they are not desirable. When there are many elements of this type in the mesh, the result of the stress calculation may be inaccurate. Sometimes stress peaks may occur at the nodes of stretched tetrahedrons. Another drawback of the mesh with a large amount of such tetrahedrons is that the iterative method rate may go down because the number of iterations may greatly increase.

The message "Mesh contains error elements (N)" means that there are N elements with the aspect ratio over 1,000,000. These elements are removed from the mesh because they critically influence the convergence of the iterative solver. Presence of these elements in the mesh is not desirable and may significantly decrease the accuracy of calculations.

I have created a report on my study and I see a blank image or an error message. What is this?

On default AutoFEM Study's report contains 3D image of the result saved in VRML format. To see and operate with the VRML presentation of the result, you must install the special plug-in for your Web-browser. We use and test this functionality of the AutoFEM report system using Cortona3D Vrml viewer which can be freely downloaded by the link: http://www.cortona3d.com/install.aspx
Also you can turn off the creation of 3D Vrml-model of the result using a special check box in the dialog box of the Report settings.

Vrml viewer is not installed

Vrml viewer is available

Dialog box of the Report settings

How can I apply a force (or pressure) to a certain area of the part?

Often the loads are applied at some area of the part which you want to study. Use the AutoCAD's command IMPRINT to create an area of load applying on the facet of the 3D model. Firstly (before creating the study!), you shoud draw the geometry, which describes the area of loading, using AutoCAD's drawing commands. Then use IMPRINT to create a new facet on the existing face of the 3D model. See the screen-shots, illustrating these steps, below.

Drawing the contour of load aplying

Use the command IMPRINT

Selecting the body

Selecting the contour

Deleting the contour

Creating the Study and applying the force