Specification of polygon points of pipeline configuration through coordinate differences and height levels (Input Table)
Through the input data table POLYDIF the pipeline configuration is described by means of successive polygon points, each defined relative to the preceding polygon point, starting with the first polygon point as defined in the input data table ORIGIN. The height level is defined as an absolute Z-value. The number of data lines in the table equals the number of polygon lines of the pipeline configuration.
Over each polygon line the division in elements is defined by means of a nominal pipe element length PIPE.EL and at each polygon bend by means of a nominal bend element length BEND.EL The bend element length can be extended at both ends of the bend at the straight pipe through the parameter EXT. Bend elements may be specified as elastic through ETYP. If ETYP is set to ODD elements, the number of elements generated in the bend will be odd. In this way it is possible to obtain for instance stresses in the middle of the bend being the decisive point in most cases. The calculated elements in the pipeline configuration may differ from the specified element lengths in order to fit into the available bend and straight lengths. The bend extension elements have a length equal to the calculated length of the bend elements. In case there are no bend elements the elements are taken equal to the specified bend element length.
The maximum element length shall be taken in accordance with the required analysis accuracy.
It is advised to prevent adjacent elements with a length ratio greater than about 20. The pipeline configuration is defined as a set of continuous polygon lines even in case of a branched pipeline. In that case (virtual) polygon lines must be specified as WEAK elements through ETYP. A WEAK element is a polygon line without axial and flexural stiffness providing the possibility to specify branched connections. It may have any length.
As from version 4.3.1 the polygon points can also be entered as absolute values. In the table menu bar of table POLYDIF an extra option is available to switch from relative coordinates to absolute coordinates and back. This switch only affects the X- and Y-coordinates, the Z-coordinate remains only absolute. The rest of the columns also is not affected, their parameter values remain unchanged. The resulting node positions are independent of the switch mode.
When the Polydif table contains X- and Y-coordinate values switching will result in a 'translation': relative coordinates will be translated into absolute coordinates and vice versa.
Switching to 'Absolute' mode (see above) Polydif will have absolute coordinates as shown below.
Be aware that changing the coordinates of the ORIGIN the configuration as shape will remain unchanged when POLYDIF is in relative mode, but the shape of the configuration will change when POLYIF is in absolute mode:
IMPORTANT NOTE: Switching between relative and absolute be aware the TESTED data of table ORIGIN is used. When table ORIGIN is not tested, the origin is unknown and assumed to be: X-S = 0 and Y-S = 0.
Take care when importing absolute values into POLYDIF, the table should be in absolute mode as well. Importing data does not perform any check. So when absolute values are imported into a relative mode POLYDIF the data will be treated as relative values. This also counts for importing relative values; POLYDIF should be in relative mode.
H200122, last changed: 14/09/2016