OrcaFlex Manual - Orcina

System Modelling: Data and Results, All Objects Data Form
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On the other hand, the Object Relative Position data are the Cartesian coordinates of the connection relative to the
frame of reference of the object to which it is connected.
OrcaFlex keeps the two sets of coordinates synchronised, so if you change one then the other is automatically
updated to match. If you change any other data then the Cartesian Object Relative Position coordinates are taken to
be the master data and so left unchanged, and the polar coordinates are updated to match.
You have a quite a lot of flexibility to choose what reference frame you want for the polar coordinates. The reference
frame has its origin at your chosen Reference Origin and has its axes are parallel to those of your chosen
Reference Axes.
For the reference origin you can choose between:
� The global origin.
� The point on the seabed that is directly below the global origin. This is only available if a connection point is
anchored.
� The origin of the frame of reference of any connected object.
� The position of the other end of the object – available for Lines and Links only.
And for the reference axes directions you can choose between:
� The global axes directions.
� The axes directions of the frame of reference of any connected object.
Example of Using Polar Coordinates
The choices of reference frame for the polar coordinates may seem complex at first sight, but they allow various
useful coordinate transformations to be done easily and accurately. Here is an example.
Consider mooring a spar with an array of 4 lines, each of which has End A connected to the spar and End B
anchored. Suppose you want to place the A ends of the lines so that they are evenly spaced circumferentially around
the spar, all at radius 5m from the spar axis and all 3m below the spar origin. To do this easily, first sort into
Connection order so that all the End A connections are grouped together. Then, for the first line, set the reference
frame origin and axes to be the spar origin and spar axes and set its polar coordinates to be R=5, and Z=-3. You can
now use copy/paste or fill down to set all the other A ends to the same reference origin, axes and R and Z
coordinates. Finally you can set the θ coordinates for the A ends to 0°, 90°, 180° and 270°.
Similarly, suppose you want the End B connections to be anchored to the seabed, with the anchors again evenly
spaced circumferentially, and with each line spanning 200m horizontally. The easiest reference frame for this is
with the reference origin being End A and the reference axes being the spar axes. The θ coordinates should again be
set to 0°, 90°, 180° and 270° and the R coordinates set to 200m. But this time, to set the vertical positions of the B
ends, it is easier (especially if the seabed is sloping) to go to the Connections page and set Connect To Object to be
Anchored and then go to the Positions page and set the Object Relative Position z coordinate to zero.
Other data
The Other data mode presents tables of data for Vessels, Lines, 6D Buoys, 3D Buoys, Links, Winches and Shapes.
The tables are laid out with each row containing related data for a single object. The notable exception is the Line
sections page in which each row contains data for a single section of a Line.
This tabulation allows data for multiple objects to be set in an efficient and coordinated way. The copy/paste or fill
down keyboard shortcuts are particularly useful here. Another useful technique is to build a table of data in Excel
with identical layout of columns and rows. This allows you to make use of Excel's formulae and data handling
facilities to prepare data, and then to paste it into OrcaFlex in a single operation.