The COMP data record describes a composite mooring line consisting of one or more elastic catenaries. Internally Aqwa converts all composite mooring lines to a multi-dimensional load/extension database. You are strongly advised to read this section before using this facility.

     2   5  7    11    16    21          31        41        51
    - --- -- ---- ----- ----- ----- ----- --------- --------- -----------
   |X|   |  |COMP|    3|   10|11112|    2|         |         |          |
    - --- -- ---- ----- ----- ----- ----- --------- --------- -----------
       |  |   |     |     |     |     |      |       |             |_(7) Sea bed slope (F10.0)
       |  |   |     |     |     |     |      |       |
       |  |   |     |     |     |     |      |       |_(6) Z Maximum Value of 1st attachment (F10.0)
       |  |   |     |     |     |     |      |
       |  |   |     |     |     |     |      |_(5) Z Minimum Value of 1st attachment (F10.0)
       |  |   |     |     |     |     |
       |  |   |     |     |     |     |_(4) Number of lines in the cable
       |  |   |     |     |     |           composite (I5) (NO DEFAULT) (Max=10)
       |  |   |     |     |     |
       |  |   |     |     |     |_(3) Warning flags and Symmetry forcing (I5)
       |  |   |     |     |          (Def = all warnings issued)
       |  |   |     |     |
       |  |   |     |     |_(2) Number of X coordinates (I5) (Def =40,Max = 40) or 600 divided by (1), whichever is less
       |  |   |     |
       |  |   |     |_(1) Number of Z coordinates (I5) (Def =15, Max = 20) or 600 divided by (2), whichever is less
       |  |   |
       |  |   |_Compulsory Data Record Keyword (A4)
       |  |
       |  |_Optional User Identifier (A2)
       |
       |_Compulsory END on last data record in Data Category (A3)

(1) The number of Z values to be used in creating the multi-dimensional load extension database for this composite mooring line

(2) The number of X values to be used in creating the multi-dimensional load/extension database for this composite mooring line.

For composite catenaries linking two structures in deep water (configuration type 2), it is strongly recommended that the full two-dimensional database size (600 points) be used. The default numbers, when these fields are left blank, for Z and X are 15 and 40 respectively. Also the Z becomes the angular coordinate and the X the radial coordinate, and the program will ignore user specifications for the Z range and use the default values (-90 to + 90 degrees). The seabed slope will also be ignored for catenaries between structures as they are not allowed to touch the seabed.

(3) This parameter indicates whether warnings should be issued when the position of the attachment point of the mooring line relative to the anchor point is outside the range of the database created for this mooring line characteristic. Warnings about the degree of symmetry are not issued, as the stiffness matrix is automatically symmetric for composite cables. See The LE2D Data Record for further details on stiffness matrix asymmetry.

It is used for configuration types 1-2 only.

This parameter should be thought of as five separate flags, which indicate the following:

If a value is set to non-zero then the corresponding warning will be suppressed.

The Z range warnings during the analysis correspond directly to the relative Z position of the attachment point on the vessel in the database axis system being outside the values specified in (5)(6).

The X range (horizontal distance between the attachment point on the vessel and the anchor) will depend on the position of the anchor and the maximum tension specified on the ECAT data record. Warnings during the analysis relating to values below the X range correspond to slack condition when the mooring line is hanging vertically. Warnings during the analysis relating to values exceeding the X range correspond to tensions in excess of the lowest value of maximum tension specified on the ECAT data records following this data record.

The 5th number (column 25) relates to the symmetry forcing. The calculation of the stiffness matrix from the database is not exact and normally leads to small errors (in the order of 1 or 2%). The exact solution is always symmetrical. In theory symmetry forcing should therefore give a slightly more accurate stiffness matrix. The database of 600 values minimises this error. A value of 1 should be used to switch off the warning of asymmetry and a value of 2 should be entered to make the matrix symmetrical.

(4) The number of lines of different properties in the composite cable i.e. for a line made from one section of wire and one of chain, the value would be 2, indicating that two ECAT data records will follow the COMP data record.

(5)-(6) These values have different meanings for a line between a structure and the seabed or between two structures.

Configuration Types 1 and 3: Structure-Anchor Line

These values define the expected range of the vertical distance between the anchor and the attachment point on the structure. These values will normally be the Z distance between the attachment point on the vessel and the anchor plus or minus the expected amplitude of motion of the attachment point. For example:

if the sea bed is at Z = -100;

the Z position of the attachment point when the vessel is in equilibrium is at -10;

the expected amplitude of the vessel motion is 10;

ZMIN and ZMAX would be 80 and 100 respectively.

ZMAX must be greater than ZMIN.

Configuration Type 2: Structure-Structure Line in Deep Water

These values are not used for a line between two structures. However, at the point when the COMP data record is read it is not known if the line will be connected to an anchor or not. Therefore two positive values must be input, with ZMAX > ZMIN. The local seabed slope is ignored for catenaries between structures, as they are not allowed to touch the seabed.

Configuration Types 4 and 5: Structure-Structure Line with Seabed Effect

These values define the expected range of the vertical position of the first attachment point in the fixed reference axis (FRA).

(7) This value is the seabed slope (in degrees) for this COMP mooring line if the global seabed definition (SBED) is not provided (database type 1). A positive slope is for the seabed to slope up from the anchor towards the attachment point, and a negative slope is for the seabed to slope down from the anchor towards the attachment point. Seabed slope is ignored if cable dynamics is being used for this line (or lines).

This data is ignored if the global seabed is defined by the SBED data record.