1.1 Program RWIND Simulation

RWIND Simulation is an outstanding tool for creating wind-induced loads on general structures. RWIND Simulation is a separate program which is used externally to determine load cases and wind loads for RFEM or RSTAB models. As for RFEM, the model may consist of beams, surfaces, and/or solids in any composition. For RSTAB models, loads can be created for models that fully conform to the structural system, such as lattice towers or braced girders without cladding. RWIND Simulation uses a numerical CFD (Computational Fluid Dynamics) model to apply a fluid-mechanics simulation of the flow around objects in a wind tunnel. As a result of the simulation process, specific wind loads are created for RFEM or RSTAB.

For the simulation, a 3D mesh of finite volumes is used. RWIND Simulation performs an automatic meshing, while the overall mesh density as well as the local mesh refinement near the model can be easily set using just a few parameters. For the calculation of the air flow and the surface pressure on the model, a finite volume numerical solver for incompressible turbulent flow is applied. The results are then extrapolated on the model. RWIND Simulation has been designed to work with various numerical solvers. Currently we recommend using the OpenFOAM® software package, which according to our tests gives very good results and is a widely used tool for CFD simulations. Alternative numerical solvers are under development.

RWIND Simulation is able to read the topology from RFEM or RSTAB models or from *.stl, *.ifc, *.obj and *.vtp files (importing *.stp and *.igs files is in preparation). Minor corrections of the model that may be required for corners or joints are applied automatically. The data relevant to the loading can be defined either in RWIND Simulation or in RFEM/RSTAB where a separate window is available. The latter option is recommended: It enables you to create load cases at equidistant angles and apply velocity profiles according to specific standards. Effects of turbulence can be included optionally. The dimensions of the wind tunnel are set to the size of the model but can be modified, if necessary.

The results of the simulation include the pressure and velocity fields around the model, the streamlines, as well as the surface pressure and the member forces. They represent the results of a stationary analysis. All results are illustrated by means of color maps (isobands) or isolines on the model or by slicer planes within the wind tunnel, respectively. The streamlines can be displayed in an animated view, which makes it easy to evaluate the effects of laminar and turbulent flow. As an essential result of the simulation, loads are created for the RFEM/RSTAB model. They are exported to the respective load cases where they are applied as FE nodal loads or member loads. To check the surface loads resulting from the velocity profile, a special feature is available to display the load distribution in one of the global or local directions.

The common procedure for creating wind loads with RWIND Simulation is as follows:

• Define the model data in RFEM or RSTAB.
• Open the Simulate and Generate Wind Loads window in RFEM/RSTAB. Define the wind directions to create the corresponding load cases and specify the wind load parameters to be applied.
• Use the [Open in RWIND Simulation] function to export the model data relating to one of the load cases to the RWIND Simulation program.

• In RWIND Simulation, you can review the settings of the wind tunnel, mesh, simplification of the model, etc. Adjust the parameters, if necessary.
• Start the calculation in RWIND Simulation.
• Check the results.
• Quit RWIND Simulation and return to RFEM/RSTAB.
• Calculate the remaining load cases, if applicable.
• Close the Simulate and Generate Wind Loads window. Then set the load case containing the wind loads created by RWIND Simulation.
• Inspect the imported loads in the work window and tables.
• Combine the wind load case(s) with other load cases in load and result combinations, if applicable.
• Finally, start the calculation of the deformations and internal forces.

Apart from the interactive application with RFEM or RSTAB, RWIND Simulation can be used as a stand-alone program for universal CFD analyses. Simply import the model that you have created in your CAD application and perform the analysis in RWIND Simulation. The flow fields, surface pressures, drag forces, etc. can be utilised for various fields of application, such as an analysis of closely spaced buildings or a pedestrian wind comfort simulation in a city.

We wish you a pleasant and successful time working with RWIND Simulation.

Your Dlubal Software team