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Frequently Asked Questions (FAQ)
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Since surfaces only have the directions x- and y- in the plane, it is necessary to define which should be the hoop stress and 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 modeling, the program tries to align the local axis systems on the global axis system (Figure 02). In the present case, however, the x-axis should run along the container for all surfaces. This orientation can be achieved as follows.
First, the z-axis of all surfaces must point inwards or outwards. In the example, the outward direction has been selected. If this is not the case for a surface, you can right-click the surface and use the function "Reverse Local Axis System" to move the z-axis to the other surface side. Then, select all surfaces and select the Axes tab in the surface dialog box. Figure 03 shows the dialog box. In this case, one of the axially extending boundary lines has been selected for the orientation. Figure 04 shows the now aligned local axis systems. All x-axes are axial and all y-axes are circumferential.
Figure 05 shows the results of the membrane stresses axial (sigma-x, m) and over the circumference (sigma-y, m).
AnswerIt is possible because RFEM provides the perfect basis for the calculation and design of piping systems. The RF-PIPING and RF-PIPING Design add-on modules provide support for modeling and design.
Since support structures and other components of the entire model can also be represented, a realistic analysis and design is possible.
Main Programs of RFEMThe RFEM basic programs are used to define structures, materials, and actions.
Modeling of pipelines including typical fittings such as valves, flanges or reducers.
- RF-PIPING Design
Comparison of existing and allowable stresses of piping systems
- EN 13480-3
- ASME B31.1
- ASME B31.3
Dynamic AnalysisIf earthquake calculations or vibration analyzes are necessary on the building, the RF-/DYNAM Pro add-on modules provide suitable tools for determining natural frequencies and shapes, analysis of forced vibrations, for generating equivalent loads, or for nonlinear time history analysis.If you have any further questions on the Dlubal programs, please do not hesitate to contact the sales department.
AnswerWith RFEM or RSTAB, structures in industrial and plant engineering can be calculated very well. The modular structure allows you to configure the software individually.
Main Programs RFEM or RSTABUsing the main programs, the structures and materials, and the effects can be definedWith RSTAB you can process and calculate framework or frame-like constructions. RFEM enables also the processing of plates, panes, shells, and solid elements.Add-on Modules
Dynamic AnalysisIf seismic calculations or vibration analyzes are necessary, the RF-/DYNAM Pro add-on modules provide suitable tools for the determination of natural frequencies and shapes, the analysis of forced vibrations, the generation of equivalent loads, or for the nonlinear time history analysis.In case of having any further questions about the Dlubal programs, please do not hesitate to contact the sales department.
Yes, the RWIND Simulation program is generally designed 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 the 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 current, corresponding surface pressures result on this surface layer.
Figure 02 - Surface Pressure on OpenFOAM Mesh
After having calculated the wind flow, the program sums the surface pressures of the member units and returns a 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
In RFEM, the interface application 'Simulate and Generate Wind Loads' makes it possible to exchange member, surface, and solid elements, and in RSTAB to exchange the bar elements.
To avoid generating a too fine mesh along with a corresponding long calculation time, the program simulates all members with a rectangular cross-section as standard. The size of the rectangular cross-section is selected in such a way that the real cross-section geometry is barely included.
By deactivating the option 'Export Optimized Member Topology', you can avoid this additional optimization of the model and allow consideration of the real cross-section geometry within existing cross-section settings.
If the exact representation of the cross-section geometry requires more than 1000000 elements, the interface automatically changes to the simplified rectangular section display of the cross-sections.
AnswerThe program RWIND Simulation implements a stationary flow calculation for non-compressible gases. The laws and wording used in this way do not change over time. Thus, the calculation outputs 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.
AnswerTo enter a taper on a beam, it is necessary to select the Layout dialog section. A taper can be modeled either on the bottom side or on the top side of the beam.The plate thicknesses, as well as the height of the taper, are defined by selecting a tapered cross-section, since, for example, repeatedly cut rolled cross-sections are used. If any plates are used, a parametric T-profile can be selected. The length of the taper, as well as the material, are entered in the same dialog section. The weld thicknesses for connecting the taper to the beam can be defined in the Welds dialog section.If a tapered member is already used as a beam (entered in the 'Nodes and Members via Different Cross-Sections and Lengths' section), it is not possible to model an additional taper.
AnswerIf stiffeners are welded into the crane runway, the corresponding notch category according to EN 1993-1-9, Table 8.4, detail 7 has to be considered for the fatigue design. This is implemented in CRANEWAY by creating additional stress points at the connection point of the stiffeners to the section. They can be adjusted manually in the settings for the detail categories depending on the geometry of the stiffener.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 on which a stiffener is provided.
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 the internal forces
The fast calculation type may therefore be useful for the preliminary design.
- Fast calculation (calculation of all load combinations according to the 1st-order analysis, then calculation of the governing load combinations according to second-order analysis for torsional buckling)
- Detailed calculation (calculation of all load combinations according to second-order analysis for torsional buckling)
Maximum target length of the finite elementsThe maximum length of the finite elements generated for the calculation according to the second-order analysis for torsional buckling can be entered within a range of 100 mm to 2500 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% relative to the 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 accordingly more time in the calculation.
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.
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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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