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Frequently Asked Questions (FAQ)
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The perimeter of membrane cutting patterns is described by boundary lines. These boundary lines can be as follows:
Figure 01 - Boundary Lines of Cutting Patterns
- Globally defined boundary lines of the assigned membrane surfaces, or
- Cutting lines applied subsequently for the distribution of cutting patterns on the membrane surfaces
The global boundary lines are untouchable due to their fixed geometry description (arc, circle, spline, and so on), and are also implemented in the design of planar cutting patterns in this way.
On the other hand, the subsequently applied cutting lines are based on the FE mesh of the surfaces assigned in the cutting line specification and have no influence on the mesh itself.The cutting units encircled by the boundary lines and cutting lines take over the FE mesh of the assigned surfaces for flattening. Since the cutting lines run through the FE elements themselves, with no regard to the global mesh in the edge area, the edges of the original FE elements cannot be used to describe the cutting pattern limitation. In this case, the affected FE elements within the cutting line area are divided by the cutting lines.
Depending on the orientation of the cutting line, the FE elements are cut in the middle or almost on the edge. Since the FE elements on the edge can cause some problems with the geometry, a certain tolerance limit has been entered for the decision. This limit controls the critical length ratio between the FE edge length specified by the cutting line and the original FE edge length. If the ratio is smaller than the given limiting value, the cutting line refers to the original FE node.Figure 03 - SmoothingThis fact may lead to an "Irritation" of the cutting line if the cutting lines are close to the FE element edges. This situation can be optimized by reducing the given tolerance limit.
The integral flattening process in RF-CUTTING-PATTERN does not flatten each cutting pattern individually, but rather the complete model geometry in one step. In this case, the line type of the respective cutting pattern units also has an effect on the adjacent cutting patterns.If there is a welding line between two cutting patterns, the program ensures that the lines in the connecting area are equal. The geometry of the cutting patterns is determined in the way that the relevant edge lengths of the cutting patterns are identical.The line type of "boundary line" allows for an independent examination of the adjacent cutting pattern units. The length of the boundary lines in the adjacent area may be different.Basically, the cutting pattern units meet the following conditions:
Thus, the program is close to the optimum solution. The affected cutting patterns are particularly noticeable due to their curvature in relation to the uncompensated solution. Due to the greater degree of modification, these cutting patterns also differ slightly from the defined compensation specifications, but are in equilibrium with all other cutting patterns because of the overall calculation.
- Surface compensation,
- Boundary line compensation, and
- Boundary line type.
AnswerThis requires the RF‑CUTTING‑PATTERN add-on module. This calculates and organizes cutting patterns for membrane structures. The boundary conditions of cutting patterns on the curved geometry are determined by means of boundary lines or by independent planar or geodesic cutting lines. For detailed information, see the links below and the videos.
The flattening process in the RF‑CUTTING‑PATTERN add-on module is an iterative process that flattens the respective areas of a cutting pattern by minimizing the distortion energy assuming the assigned material behavior.
In simplified terms, the method compresses the initial geometry in a press assuming a frictionless contact until the stresses due to flattening are in equilibrium with each other.
→ See the video
Since this process covers the complete mechanics of the curved structural component, you it is possible to additionally consider the compensation directly as an applied strain load.
Figure 01 - Compensation
Since the strains from the compensation specification interact with the strains from the flattening in the algorithm of RF‑CUTTING‑PATTERN, this kind of compensation consideration cannot be compared with the usual, flat scaling of the non-compensated cutting patterns. The consideration of the complete "cutting pattern mechanics" with all strain terms provides very high-quality geometry of the cutting pattern.Before the flattening itself, the integral flattening process determines a coordinate system (warp and weft direction) from the mean orientation of FE elements, and uses the initially defined coordinate system with no regard to the respective position of the FE elements in the coordinate system orientation in order to describe the compensation strain and stiffness. Thus, the comparison shown in the video is only valid for an isotropic linear elastic membrane model.
AnswerThe direction change results from the 0% line compensation in the "Different Compensation by Line" tab for the boundary line in the support area.This setting requires that the boundary line in the support area keeps the line length, regardless of the compensation set in plane. Since the weld lines adjoining the adjacent cutting patterns are allowed to change their lengths due to the compensation set in plane, the algorithm seeks the geometrically poor but energetically balanced solution.You can avoid the abrupt change if the relevant boundary lines are allowed to relax freely in the flattening process.
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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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