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Frequently Asked Questions (FAQ)
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Usually, you only need it once in the self-weight load case, not in any other load cases. Each additional load case should be considered in load combinations that are usually governing for determining internal forces.
The program allows you to activate the self-weight for each load case. It is up to the user to decide which case this might be. For the reason mentioned above, the self-weight is only activated for the first load case by default (see Figure 01).
The fastest way is to use a result beam. For the sake of convenience, you can place it directly next to the building.
The function of the result beam is to transfer all internal forces of members, surfaces, and solids to a beam element in order to obtain the internal forces for the entire structure referred to a beam. The result beam allows you to display the resulting shear force for each floor in the X- and Y-direction.
After defining the result beam, you can view the internal forces integrated into the result beam. The internal forces Vz and Vy are important for the evaluation. The maximum of the shear force is visible on the bottom side of the result element which takes into account the entire structure.
The shear force for each floor is always determined by the difference between the upper and lower value. It is necessary to use a sufficiently fine division of the result beam (Calculation Parameters → Global Calculation Parameters → Number of divisions of members for - Result diagrams), and to define a sufficiently fine FE mesh as this can sometimes have a strong impact on the result accuracy.
AnswerProject Navigator - Results provides a special option to evaluate the results of the RWIND Simulation loads: Activate the results of "Distribution of load" and then select the "Wind load using RWIND Simulation" option.
The default path for the RWIND Simulation projects created by RFEM/RSTAB is C:\Users\Public\Documents\Dlubal\RWIND Simulation 1.x\ProjectsRX.
You can adjust this path in the "Program Options" dialog box.
This setting can be found in the menu "Options" → "Program Options," tab "Files and Directories," category "RWIND Simulation projects created by RFEM/RSTAB."
RWIND Simulation is exclusively compatible with RFEM due to the CFD modeling, which requires a finite element calculation. The model created in RSTAB can be opened in RFEM. The wind load parameters can be defined in the Simulate and Generate Wind Loads dialog box of RFEM.
At the bottom of the Wind load tab, it is possible to remain and automatically generate loads for the corresponding load cases the CFD calculation has been performed in the background.
If you would rather perform the wind simulation in RWIND, click the Open in RWIND Simulation button in the Load Cases tab.
To obtain the trial version of RWIND Simulation, proceed as described in this FAQ.
A user-defined wind load distribution is not provided in the Eurocode. In order to implement a user-defined wind load distribution in the RF‑/TOWER Loading add-on module, this can only be done after conversion to DIN, for example, DIN 4131:1993‑11, see Figure 01, Window "1.3 Wind Load - Part 1."
Then, you can select the user-defined distribution in Window 1.4 "Wind Load - Part 2," and define it in the adjacent table, see Figure 02.
AnswerThe "Simulate and Generate Wind Loads" feature for exporting models to RWIND Simulation is available in RFEM or RSTAB as of the version x.21.01 from 22.10.2019.With a valid service contract, you can download the current program version from your Dlubal account. Simply log in on this page:If you do not have a service contract, you can download the program version that you have purchased on the following page:
AnswerThe internal pressure coefficients do not need to be considered with in the RWIND Simulation program.RWIND Simulation always outputs the net pressure on the surfaces in RFEM. When it comes to a simulation with a building that has open windows in RWIND Simulation, there is an internal pressure acting on the inside of the building. The program uses this information to determine the resulting pressure based on the external and internal surfaces. This can be seen in Figure 1.A comparison cannot be made between this coefficient in the standard and a CFD calculation because there is no direct correlation.
For the calculation, the program creates a solid mesh between the model and the outer sides of the wind tunnel. In this case, the solid mesh does not connect directly to the model geometry, but to a separate model wrapping mesh situated around the model geometry. This model wrapping mesh has a certain distance to the exact model geometry, depending on the model mesh setting (Simplified Model - Shrink-Wrapping-Mesh). Similar to the surrounding model wrapping mesh, the exact model geometry itself is also represented from a wrapping mesh, but on the exact model shape.
Figure 01 - Mesh Types
With the OpenFOAM calculation, a print result is obtained on each solid element. These values are extrapolated to the respective edge nodes at the transition to the model. To determine the final surface pressures on the model geometry, the pressures at the edge nodes of the solid mesh are transformed into the exact model wrapping mesh in a further step. In case the triangular meshing of the exact model mesh geometry is too rough, the last transformation process initiates a partial refinement of the exact model wrapping mesh.
Figure 02 - Difference Between Wrapping Mesh Geometry and Exact Model Geometry
There is no load distribution displayed between the external facade elements in the example shown in Figure 01. The unstressed cells are not displayed according to the color scale for the load distribution, but remain empty. Thus, the value on these elements is 0. This has the advantage that it is recognized immediately that the FE elements are not subjected to a load.The cause of the problem can be visualized directly in RWIND Simulation. By default, the calculations are based on a simplified model there. Depending on the setting, the shell of the model can be refined or coarsened. An FE mesh is placed over the structure and depending on the level of the detail, this FE mesh clings to the model. Figure 02 shows the extent of the level of detail that is too small. The surfaces standing on the façade are not displayed well enough and no wind flows between the cantilevered surfaces in the simulation, which is why these internal surfaces are not subjected to any wind pressure.The level of detail can be adjusted in RWIND Simulation via "Edit Model" or directly in RFEM in the settings for the wind load simulation (see Figure 03). Optionally, the simplified model can also be deactivated completely in RWIND Simulation.In the case of a higher level of detail (corresponds to a finer FE mesh), the cantilevered surfaces are displayed cleanly and the FE elements are stressed accordingly (see Figure 04 and Figure 05).
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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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