FAQ 003216 | How does the flattening process account for compensation when determining...

Compliance with building codes, such as Eurocode, is essential to ensure the safety, structural integrity, and sustainability of buildings and structures. Computational Fluid Dynamics (CFD) plays a vital role in this process by simulating fluid behavior, optimizing designs, and helping architects and engineers meet Eurocode requirements related to wind load analysis, natural ventilation, fire safety, and energy efficiency. By integrating CFD into the design process, professionals can create safer, more efficient, and compliant buildings that meet the highest standards of construction and design in Europe.

In computational fluid dynamics (CFD), complex surfaces that are not completely solid can be modeled using porous or permeability media. In the actual world, examples of such things include windbreak fabric structures, wire meshes, perforated facades and claddings, louvers, tube banks (stacks of horizontal cylinders), and so on.

Windbreak structures are special types of fabric structures which protect the environment from harmful chemical particles, abate wind erosion, and help to maintain valuable sources. RFEM and RWIND are used for wind-structure analysis as one-way fluid-structure interaction (FSI). This article demonstrates how to structural design windbreak structures using RFEM and RWIND.

RF-CUTTING-PATTERN is activated by selecting the respective option in the Options tab in General Data of any RFEM model. After activating the add‑on module, a new object, "Cutting Patterns", is displayed under Model Data. If the membrane surface distribution for cutting in the basic position is too large, you can divide the surface by cutting lines (line types "Cut via Two Lines" or "Cut via Section") in the corresponding partial strips.

Then you can define the individual entries for each cutting pattern using the "Cutting Pattern" object. Here you can set boundary lines, compensations, and allowances.

Steps of the working sequence:

• Creation of cutting lines
• Creation of the pattern by selecting its boundary lines or using a semi‑automatic generator
• Free selection of warp and weft orientation by entering an angle
• Application of compensation values
• Optional definition of different compensations for boundary lines
• Different allowances (welding, boundary line)
• Preliminary representation of the cutting pattern in the graphic window at the side without starting the main nonlinear calculation

• Planar and geodesic cutting lines
• Flattening of double-curved surface parts of tensioned membranes or pneumatic cushions
• Definition of cutting patterns by using boundary lines which are not required to be connected
• Sophisticated flattening based on the minimum energy theory
• Welding and boundary allowances
• Uniform or linear compensation in warp and weft direction
• Possibility of different compensations for boundary lines
• Adaptable data organisation (any additional modification of input data is considered up to the final "weld")
• Graphical display of cutting patterns
• Statistical information about each cutting pattern (width, length, size)
• Option to automatically generate cutting patterns from cells

After the calculation, the "Point Coordinates" tab appears in the cutting pattern dialog box. In this tab, the result is displayed in the form of a table with coordinates and a surface in the graphical window. The coordinate table presents new flattened coordinates relative to the centroid of the cutting pattern for each mesh node. Furthermore, the cutting pattern with the coordinate system at the centroid is represented in the graphical window. When selecting a table cell, the respective node is displayed with an arrow in the graphic. In addition, the area of the cutting pattern is displayed below the node table.

Moreover, standard stress/strain results for each pattern are displayed in the RF‑CUTTING‑PATTERN load case in RFEM.
Features:

• Results in a table, including information about the cutting pattern
• Smart table relating to the graphic
• Results of flattened geometry in a DXF file
• Output of strains after flattening in order to evaluate the cutting patterns
• Results of strains after flattening for the evaluation of patterns