jnwalther
commented
2 years ago This is a fairly legthy issue, so I will need to take some time to get through to all the details. What I can already say, is that im pretty decidedly against removing the "obsolete" options for bulkhead reinforcements, since those provide as imple as possible parametrizations of established bulkhead designs, and I know of several tools, that use them. So the way I see it, we should rather consider the eta-ksi way you propose as an additional option for more complex designs.
Another point, since eta-ksi-coordinates are a known concept from the wing, where it is in the interval of [0,1], it might be confusing to have it in the interval [-0.5, 0.5] here (incidentally, I think your coordinate system origin in the sketches might be wrong). Anyway, for the walls, which are not subject to configuration symmetry like bulkheads the (0, 0) coordinate would be pretty meaningless.
sdeinert
In reality large planar structural components such as fuselage walls or pressure bulkheads need to be reinforced to increase stiffness and prevent stability issues such as buckling. Such reinforcements are quite similar to wing stringers. Depending on the specific design, these reinforcements can have quite complex geometries as they need to consider other intersecting structures and cutouts. Therefore, a logic similar to wing spars or explicit wing stringers is proposed using a list of positions and segments connecting these positions.
CPACS extension proposal:
To allow modelling this in CPACS, the following extensions to the types
pressureBulkheadAssemblyPositionTypeandwallSegmentTypeare proposed:pressureBulkheadAssemblyPositionTypethe following optional element needs to be added:The
pressureBulkheadReinforcementsTypelooks like this:The
wallSegmentTypeis extended with a similar optional element:with
The
pressureBulkheadReinforcementsTypeandwallReinforcementsTypeeach contain a list of positions and a list of segments similar to the wing spar logic:Reinforcement positions are defined using relative coordinates (
eta/xsi) inside the shape of the parent component (wall/pressure bulkhead). For walls an additionalsubSegmentIndexis required as they can consist of several segments. ThesubSegmentIndexselects the wall segment relative to which theeta/xsicoordinates shall be evaluated. An alternative placement option toeta/xsiis the direct reference of another structural component intersecting the parent component (i.e. other walls, pressure bulkheads, reinforcements of other walls/pressure bulkheads, frames, stringers). In case this intersection with the parent component yields a wire, therelPosparameter is applied to select a point along the intersection wire. In case of a point as result to this intersectionrelPosis not required.The
fuselageStructureReinforcementSegmentTypeis defined as follows:structuralElementUID: References a profileBasedStructuralElement to assign physical properties to the segmentoffsetSide: Defines on which side of the parent geometry face the reinforcement shall be located using an offsetsinglePosition: Referencing only one position + an angle and a flag to which side the reinforcement shall extendpositionUIDs: A list of position references connecting at least two positions with straight linesAnd some additional types used by the definitions above:
Geometric construction
With this definition the geometry for pressure bulkhead reinforcements can be realized like this:
The eta/xsi space is defined by the bounding box (grey dashed box) of the pressure bulkhead so that also positions outside the actual geometry could be defined. The geometry construction must be robust enough to support this.
Two options are shown above, a straight reinforcement segment with a single position definition plus an angle, and a multi-position reinforcement segment based on four positions with the last one placed outside the actual loft.
Etaruns from -0.5 (left border) to +0.5 (right border), whilexsiranges between -0.5 (lower border) and 0.5 (upper border).A similar geometry construction logic is applied for wall reinforcements:
Eta/xsilocations are always relative to the bounding boxes of the respective wall (sub-)segment that contains them. The example in the figure above shows a reinforcement segment with three positions, where the last position lies in wall sub-segment 2. For each wall sub-segmentetaranges between 0 (start position border of wall subsegment) to 1 (end position border of wall subsegment) andxsifrom 0 ("left" border of wall subsegment) to 1 ("right" border of wall subsegment) depending on the orientation with which the wall was defined. Also in this case the geometry construction must be robust enough to support positions lying outside the shape of the wall segment but inside its bounding box.As reinforcement segments may reference common position definitions, fixed intersections between reinforcements can be defined explicitly.
An example for a pressure bulkhead reinforcement definition created with a TiGL prototype can be seen here:
Obsolete CPACS definitions
With the new definitions detailed above the following CPACS definitions become obsolete:
structuralWallElementType: RemovelongitudinalReinforcementandlateralReinforcementdefinitionspressureBulkheadType: Remove choice for horizontal/vertical or radial reinforcements: