This doctoral thesis by Rostislav Lang deals with the design and analysis of membrane structures using FEA software.
RF-CUTTING-PATTERN Add-on Module for RFEM
Cutting Patterns for Tensile Membrane Structures
"RFEM is the best I have used. I have experience with RISA, STAAD, ETABS, Visual Analysis, and others. In the tensile/fabric structure world, I've tried NDN, Forten, etc. Once you get used to RFEM's interface, it has no comparison to the others. Even with typical structures, it's much easier."
Doctoral Thesis on Membrane Structure Design According to FEA
The RF-CUTTING-PATTERN add-on module generates and organizes cutting patterns for membrane structures. Boundary conditions of the cutting patterns on curved geometry are determined by boundary lines and independent planar cutting lines or geodesic cutting lines. The flattening process is performed according to the minimum energy theory.
For each pattern, compensation can be applied in the warp and weft direction. It is possible to set a special compensation value for each boundary line as well as overlaps for manufacturing processes.
- 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")
- Graphic display of cutting patterns
- Statistical information about each cutting pattern (width, length, size)
- Option to automatically generate cutting patterns from cells
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 by 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
The nonlinear calculation adopts the real mesh geometry of planar, buckled, simple curved, or double curved surface components from the selected cutting pattern and flattens this surface component in compliance with the minimization of distortion energy, assuming defined material behaviour.
Basically, this method attempts to compress the mesh geometry in a press assuming frictionless contact and to find such a state where the stresses due to flattening the component in the plane are in equilibrium. In this way, the minimum energy and the optimum accuracy of the cutting pattern are achieved. Compensation for warp and weft as well as compensation for boundary lines are considered. Then, the defined allowances on boundary lines are applied to the resulting planar surface geometry.Features:
- Minimization of distortion energy in the flattening process for very accurate cutting patterns
- Application for almost all mesh arrangements
- Recognition of adjacent cutting pattern definitions to keep the same length
- Mesh application for main calculation
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
- Results in the global printout report
- Results of strains after flattening for the evaluation of patterns
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