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Frequently Asked Questions (FAQ)
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AnswerBasically, the surfaces of the model have the FE size that was preset in the general FE mesh settings.You can add "FE Mesh Refinements" locally to a surface model.This has the effect that the general finite size can be retained in the FE mesh settings, but the mesh is locally refined so that more accurate results can be expected from the calculation.In this case, the FE mesh refinement can be performed on nodes, lines, and surfaces. The setting can be found in the "Edit" dialog boxes of the node, line, or surface.By using the local FE mesh refinement, it is possible to keep or even increase the general FE mesh size. Thus, it is possible to keep the total number of elements in the model relatively low.
Yes, this is also possible.If you want to edit a graphic retroactively in the printout report, right-click the graphic and click the 'Edit' command.Then, you can adjust the configuration in the Display Navigator in this graphic where you can clear the checkbox in ‘FE Mesh Refinement’ and return to the report by clicking the ‘Return to Printout Report’.Thus, the representation of the FE mesh refinement in existing graphics can also be edited.
AnswerThe consideration of curved elements depends on the FE mesh refinement.
An FE element always has straight outer edges.
If the FE mesh is selected too roughly, the result is a very inaccurate mapping of the curved elements with straight lines.
If the global setting of the target length of the finite elements is specified with sufficient accuracy in 'Calculation' → 'FE Mesh Settings', you can also perform a local FE mesh refinement on the nodes, lines, or surfaces.
AnswerYou can find the setting for this as 'Model' and 'FE Mesh Refinement' in the Display Navigator.If you switch off the checkbox, the symbol for the FE mesh refinement will not be displayed in the structure anymore.
AnswerIt is not possible to globally answer this question because it depends on the system. There are several divisions to be considered in RFEM.
1. Member divisions for results tablesYou can create member divisions for result values by using the menu 'Insert > Model Data > 'Member Divisions'. This division ensures that - e.g. in the RFEM results tables - the internal forces of members can also be displayed at intermediate points. The graphical output remains unaffected.
2. Member divisionsThe divisions for the graphical result diagram and the determination of the extreme value can be viewed and influenced in the FE mesh settings (see Figure 1).For cable, foundation, and tapered members or members with plastic properties, you can specify the number of internal divisions. They lead to a real division of the member by intermediate nodes. However, if a member is arranged on the boundary line of a surface or if the definition line has an FE mesh refinement, the specification has no effect.Select the 'Activate Internal Member Divisions for Large Deformation Analysis' option to divide also beams by intermediate nodes for the calculation according to large deformation analysis so that these members are calculated with higher accuracy. The number of member divisions is taken over into the input field above.If using the division even for straight members, which are not integrated into surfaces, FE nodes are generated on all free members and considered for calculations according to the linear static and second-order analysis. The length of the finite elements is either determined by the global target length l FE set in the General dialog section or entered manually.With the option 'Use Division for Members with Nodes Lying on Them', RFEM generates FE nodes on those locations of the member where end nodes of other members are lying, without having any connection existing between these members.
AnswerWith the FE mesh refinement, it is also possible to create an aligned FE mesh in the program. Thus, the automatic FE mesh generator can be controlled to a certain extent. However, it is not possible to use it for setting of a specified mesh geometry.
The smoothing is an interpolation of the existing internal forces. This is explained in the corresponding technical article. The internal forces as such are displayed in the post-processing. The COM interface always shows all internal forces on each FE node. Use the Results example from the SDK (FAQ) to analyze these settings.However, it is possible to distinguish between grid points and FE mesh nodes in the results output.
AnswerThe tolerance epsilon can be found in the FE mesh settings in the "General" window section. It controls the behavior of the FE mesh generator when nodes are very close to lines. Figure 3 shows the difference. If the tolerance is greater than the distance of the node to the line, this small local difference in the mesh generation is neglected. In the case shown, the mesh of the line is deflected towards the node. In this case, the line is no longer ideally straight. If the tolerance is smaller than the distance, a separate FE node is generated for the node.The error message appears if the distance between two adjacent nodes is smaller than epsilon and they are connected by a line (see Figure 3). In most cases, this is due to an inaccuracy in the modeling. Since the error message contains no information about node numbers, you can use the model check "Identical Nodes". The program searches for nodes whose distance meets the tolerance delta. Now set the Tolerance value to the value of epsilon. Then, the nodes are listed in the upper part of the dialog box.As described below, the descriptions differ depending on the case. If there is an inaccuracy in the modeling, it can be adjusted. In other cases, it is, of course, possible to further reduce the tolerance of epsilon.
After the calculation is aborted due to the instability, there will be shown a window with "Calculation Errors and Messages". For each displayed message, you can see a yellow arrow on the screen which will guide you to the location of the instability.
In most cases, the error message contains also a FE mesh node number.
FE mesh nodes can be found also by using the menu "Edit" → "Find via Number".
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