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Frequently Asked Questions (FAQ)
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AnswerThe nonlinear material models are only available in the 3D environment. Please make sure that the model type is set to "3D" (see Figure 02).
Since there are only the directions x- and y- in the plane for surfaces, it is first necessary to define which should be the hoop stress and which the axial stress. In the following example, sigma_x should be the axial stress and sigma_y the hoop stress.
The example consists of an inclined circular container (Figure 01). After the modeling, the program tries to align the local axis systems on the global axis system (Figure 02). However, the x‑axis should run along the container for all surfaces in this case. This orientation can be achieved as follows.
First, the z‑axis of all surfaces must point inwards or outwards. In the example, the outside direction has been selected. If this is not the case for the surface, you can right-click the surface and use the "Reverse Local Axis System" feature to move the z‑axis to the other surface side. Then, select all surfaces and open the Axes tab in the Edit Surface dialog box. Figure 03 shows the dialog box. In this case, one of the boundary lines oriented axially has been selected. Figure 04 shows the aligned local axis systems now. All x-axes are axial and all y-axes run in the circumferential (hoop) direction.
Figure 05 shows the results of the membrane stresses axial (sigma‑x,m) and along the circumference (sigma‑y,m).
AnswerRFEM provides a perfect basis for the calculation and design of piping systems. The add-on modules RF‑PIPING and RF‑PIPING Design provide you with a support for modeling and design.
Since it is also possible to model supporting structures and other components of the entire model, an analysis and design close to reality is possible.
Main Program RFEMThe main program RFEM is used to define structures, materials, and actions.
Modeling of pipelines including specific piping components, such as valves, flanges or fittings.
- RF-PIPING Design
Comparison of existing and allowable stresses of piping systems
- EN 13480-3
- ASME B31.1
- ASME B31.3
Dynamic AnalysisIf it is necessary to perform seismic analysis or vibration designs of a building, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, for an analysis of forced vibrations, a generation of equivalent loads, or for a nonlinear time history analysis.If you have any question about the Dlubal Software programs, please do not hesitate to contact the sales department.
AnswerUsing RFEM or RSTAB, the structures of process manufacturing plants can be calculated very well. The modular structure allows you to configure the software individually.
Main Programs RFEM or RSTABThe main programs are used to define structures, materials, and loads.RSTAB allows you to edit and analyze beam, frame, or truss structures. RFEM also provides plate, wall, shell, and solid elements.Add-on modules
Dynamic AnalysisIn case a seismic analysis or vibration designs are required, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, for an analysis of forced vibrations, a generation of equivalent loads, or for a nonlinear time history analysis.If you have any question about the Dlubal Software programs, please do not hesitate to contact the sales department.
Yes, it is; the RWIND Simulation program is designed universally and can implement any model of RFEM or RSTAB.
Figure 03 - RFEM Model
For a steel structure consisting of pure member elements, the program creates a coherent, voluminous envelope of member surfaces for the numerical wind tunnel. The result of this modeling for the simulation depends on the available cross-sections and the mesh settings. Due to the wind flow, the corresponding surface pressures result on this surface layer.
Figure 02 - Surface Pressure on OpenFOAM Mesh
After the wind flow analysis, the program summarizes the surface pressures of the member units, and gives back the corresponding equivalent load (single, uniform, or trapezoidal) for each member axis.
Figure 04 - Options for Member Load Distribution
These loads are applied in RFEM or RSTAB for the further calculation of internal forces.
Figure 05 - Equivalent Load from RWIND Simulation
The "Simulate and Generate Wind Loads" interface application allows you to exchange member, surface, and solid elements in RFEM, and member elements in RSTAB.
To avoid too fine mesh and thus too long calculation time, the program simulates all members with a rectangular cross-section by default. In this case, the size of the rectangular cross-section is selected in such a way that it barely includes the real cross-section geometry.
By deactivating the "Export optimized member topology" option, you can avoid this additional optimization of the model and allow consideration of the real cross-section geometry within the existing cross-section settings.
If the exact display of the cross-section geometry requires more than 1,000,000 elements, the interface automatically switches to the simplified rectangular cross-section display.
AnswerIn the RWIND Simulation program, a stationary flow analysis of incompressible gases is implemented. The principles and formulations used for this do not change over time. Thus, the calculation gives a result set without temporal variation. The effect of a "Kármán vortex street," in which counter-rotating vortices develop behind a body around which flows, results in a temporal change of the flow effect. Therefore, this fluid-mechanical effect cannot be simulated in RWIND Simulation.
AnswerThe option to enter a taper on a beam can be activated in the Arrangement section of Window 1.4 Geometry. Here you can model the taper on the bottom or top side of the beam.The plate thicknesses as well as the height of the taper are defined by selecting the cross-section of the taper, since the cut rolled cross-sections are often used, for example. If user-defined plates are used, you can select a parametric T‑section. The length of the taper as well as the material are entered in the same section. The weld thicknesses for connecting the taper to the beam can be defined in the Welds section.If there is a tapered member already used as a beam (entered in the "Nodes and Members" section by specifying different cross-sections and lengths), it is not possible to model an additional taper.
AnswerIf the stiffeners are welded into the crane runway, it is necessary to consider the corresponding detail category for the fatigue design in compliance with EN 1993‑1‑9, Table 8.4, Detail 7. This is implemented in CRANEWAY by creating additional stress points at the connection point of the stiffeners to the cross-section. They can be adjusted manually in the settings for the detail categories, depending on the stiffener geometry.During the fatigue design of the craneway girder, the design of the axial stress range is additionally performed in the newly created stress points for the x‑locations where is the stiffener.
AnswerIn the case of long crane runways and many cranes, the large number of load combinations can lead to a long calculation time. The following settings affect the calculation time significantly:
Calculation Method for Determining Internal Forces
The fast calculation type may therefore be useful for preliminary design.
- Fast calculation (a calculation of all load combinations according to the linear static analysis, then a calculation of the governing load combinations according to the second-order torsional buckling analysis)
- Detailed calculation (a calculation of all load combinations according to the second-order torsional buckling analysis)
Maximum Target Length of Finite ElementsThe maximum length of the finite elements generated for the calculation according to the second-order torsional buckling analysis can be entered within the range of 100 mm to 2,500 mm. The calculation time can be increased significantly by the finer division of finite elements.Thus, you should select a reasonable length of the finite elements for an optimized calculation time, depending on the structural system. Usually, 8 elements for each girder span are enough to calculate the deformations with a deviation of less than 5% with regard to a precise solution.
Number of Load CombinationsYou can use a reasonable setting of the load increment to control the number of generated load combinations. When entering the load increment, the generated number of crane load positions and load combinations is already displayed in a preview. A small load increment may result in many load combinations that take more time in the calculation accordingly.
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Wind Simulation & Wind Load Generation
With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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