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Frequently Asked Questions (FAQ)
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AnswerThe 'Simulate and Generate Wind Loads' function for exporting models to RWIND Simulation is available in RFEM or RSTAB from version x.21.01 of 22.10.2019.With a valid service contract you can download the current program version from your Dlubal account. It is enough to log in here:If you do not have a service contract, you can download the program version 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 placed 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 mesh wrapping in a further step. In the event that the triangular meshing of the exact model mesh geometry is too rough, the last transformation process initiates a partial refinement of the exact model mesh wrapping.
Figure 02 - Difference Between Wrapping Mesh Geometry and Exact Model Geometry
There is no load distribution displayed between the external facade elements at the example shown in Figure 01. Unstressed cells are not displayed according to the color scale during 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 stressed.The cause of the problem can be visualized directly in RWIND Simulation. By default, calculations are based on a simplified model. Depending on the setting, the shell of the model can be refined or coarsened. An FE mesh is placed over the structure, so to speak, and depending on the level of 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 do not experience any wind pressure.The level of detail can be adjusted in RWIND Simulation by 'Edit Model' or directly in RFEM in the settings for the wind load simulation (see Figure 03). Optionally, the simplified model can also be completely deactivated in RWIND Simulation.In the case of a greater 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).
The RWIND Simulation is a program for numerical flow simulation . It is a tool for describing a wind flow problem around an object consisting of a system of partial differential equations with the output of an approximate solution on the basis of the finite-volume method. Such a mathematical model provides similar to a simplified model in a real wind tunnel information about the wind velocity field and the pressures acting on the surfaces of the wind flow object.
The standards describing wind effects on buildings and structural components (e.g. EN 1991-1-4, ASCE/SEI 7, etc.) are based on different principles. The rules and measures specify corresponding instructions for determining the wind loads for specific situations and applications. These formulas are undoubtedly correct for the assigned situations and the resulting values have been confirmed in practice.
However, these guidelines do not describe all situations that occur in the real world of engineers. Here, infinitely different model shapes in the wind flow are processed, whereby each shape has its own high-grade influence on the resulting surface pressures caused by the wind load. However, for all model shapes not mentioned in the respective directives, the equivalent load from wind effects remains unclear.
RWIND Simulation can help here in its role as an auxiliary tool for determining the resulting forces from the wind action. However, despite the use of RWIND Simulation, all requirements of the valid standardization must be ensured. The technology used in the simulation program may also provide further useful insights for sufficiently controlled object shapes.
Figure 01 - Wind Flow Around Complex Antenna System
Figure 02 - Surface Pressures on Complex Antenna Installation due to Wind Load
AnswerThe new standalone program RWIND Simulation provides you with the options for wind simulation and for generating wind loads. The options can be optimally utilized in conjunction with the FEM structural analysis software RFEM or the structural frame analysis software RSTAB.
InputThe direct adoption of models from RFEM or RSTAB makes it possible to determine relevant parameters of the wind directions to be analyzed with height-dependent wind profiles on the basis of a wind standard. This results in the corresponding load cases with globally defined parameters.
The RWIND Simulation can also be run manually if there is no RFEM or RSTAB. For this reason, the data can be imported from STL vector graphics.
The import of terrain and buildings of the environment into the simulation is also possible from STL files.
By exchanging data between RFEM or RSTAB and RWIND Simulation , you can easily use the wind analysis results as load cases in your usual RFEM or RSTAB work environment.
Services of RWIND Simulation
- 3D incompressible wind flow analysis with OpenFoam solvers
- Direct model import of RFEM or RSTAB or STL files
- Simple model changes using Drag and Drop and graphical adjustment assistance
- Automatic corrections of the model topology with shrink wrap networks
- Option to add objects from the environment (buildings, terrain, ...)
- Height-dependent velocity profiles according to the standard
- K-epsilon and K-omega turbulence models
- Automatic mesh generating adjusted to the selected depth of detail
- Parallel calculation with optimal utilization of the capacity of multicore computers
- Results in just minutes for low-resolution simulations (up to 1 million cells)
- Results within a few hours for simulations with medium/high resolution (1-10 million cells)
- Graphical display of results on the Clipper/Slicer planes (scalar and vector fields)
- Graphical representation of streamlines as well as streamline animation
AnswerIn addition to the manual operation, the website provides a web service (API) for the connection to external programs.The following packages are available for this. The same conditions apply as for manual operation.
- Geo-Zone Tool | 500 queries
- Geo-Zone Tool | 5000 queries
AnswerThe Dlubal online service geo-zone tool for load determination contains zone maps for a quick determination of snow load zones, wind load zones and earthquake zones.
The following packages are available.
- Geo-Zone Tool | 500 Requests
- Geo-Zone Tool | 5000 Requests
This contingent can be used by all employees of your company without any restrictions for all supported maps or load standards.
The Geo-Zone Tool for load determination is continuously extended and supplemented.
AnswerNo, they are not included by default. The wind load generation using surface loads always determines the wind load that is orthogonal to the spanned surface.For the attached example, however, Figure 02 shows that the loading in the wind load surface amounting 0.5 kN/m² is relatively easy to convert.It is also possible to generate the wind load for any building geometry with the new stand-alone program RWIND Simulation. This provides you with the possibilities for wind simulations and generating wind loads.In conjunction with the structural FEA software RFEM or the structural frame analysis software RSTAB.InputThe direct import of models from RFEM or RSTAB allows you to define the relevant parameters for the analyzed wind directions with the height-dependent wind profiles, based on the wind standard. This results in the corresponding load cases with globally defined parameters.Without RFEM or RSTAB, RWIND Simulation can also be run manually. Furthermore, you can import the data from the STL vector graphics.It is also possible to import terrain and buildings of the environment into the simulation from the STL files.By exchanging the data between RFEM or RSTAB and RWIND Simulation, you can easily use the results of the wind analysis as load cases in your usual RFEM or RSTAB work environment.Features of RWIND Simulation3D incompressible wind flow analysis with OpenFoam solversDirect model import from RFEM/RSTAB or STL filesSimple model changes using drag & drop and graphical adjustment assistanceAutomatic corrections of the model topology with shrink wrap networksOption to add objects from the environment (buildings, terrain, ...)Height-dependent velocity profiles according to the standardK-epsilon and K-omega turbulence modelsAutomatic mesh generating adjusted to the selected depth of detailParallel calculation with optimal utilization of the capacity of multicore computersResults within a few minutes for low-resolution simulations (up to 1 million cells)Results within a few hours for simulations with the medium/high resolution (1‑10 million cells)Graphically display of results on the Clipper/Slicer planes (scalar and vector fields)Graphical display of streamlines and streamline animation
If the internal pressure is considered in the wind load generator (see Figure 1), the wind pressure on the inner area of the building and the wind pressure on the outer area of the building is added (see Figure 2).If the internal pressure has a positive effect when determining the reaction size (we + wi), it is usually set to zero. It can be done by means of the “Consider Only Increasing Loads” function in the load generator (see Figure 3).
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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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