1. Specification of boundary conditions, stressfree configuration and static equilibrium configuration
Coordinates of all supernodes must be specified to define the initial stressfree configuration as well as the final static configuration. If the distance between supernodes in stressfree configuration do not correspond to the line length as specified in Type and location of contact point, NCNODE input lines, the length of the last segment in the line is adjusted, and a warning is written.
Boundary conditions and coordinates for supernodes with at least one fixed or prescribed degree of freedom
The following two or three input lines must be given in blocks for each
of the NSNFIX
supernodes.
Boundary conditions:
SNOD_ID IPOS IX IY IZ IRX IRY IRZ CHCOO CHUPRO

SNOD_ID: character(8)
: Supernode identifier 
IPOS: integer, default: 0
: Boundary condition type
IPOS = 0
: The supernode is not connected to a support vessel 
IPOS = IVES
: The supernode is connected to support vessel numberIVES
,1 <= IVES <= NVES
.


IX: integer, default: 1
: Boundary condition code for translation in Xdirection
IX = 0
: Free 
IX = 1
: Fixed or prescribed


IY: integer, default: 1
: Boundary condition code for translation in Ydirection (same interpretation as forIX
) 
IZ: integer, default: 1
: Boundary condition code for translation in Zdirection (same interpretation as forIX
) 
IRX: integer, default: 1
: Boundary condition code for rotation about Xaxis (same interpretation as forIX
) 
IRY: integer, default: 1
: Boundary condition code for rotation about Yaxis (same interpretation as forIX
) 
IRZ: integer, default: 1
: Boundary condition code for rotation about Zaxis (same interpretation as forIX
) 
CHCOO: character(6)
: Identifier for boundary condition reference coordinate system
CHCOO = GLOBAL
: Boundary conditions are referenced to global coordinate system. 
CHCOO = SKEWG
: Boundary conditions are referenced to a skew coordinate system. 
CHCOO = VESSEL
: Boundary conditions are referenced to vessel coordinate system. 
CHCOO = SKEWV
: Boundary conditions are referenced to a skew vessel coordinate system.


CHUPRO: character(3), default: NO
: Computational parameter. Boundaries rotate with specified rotation
CHUPRO = YES

CHUPRO = NO

A supernode with prescribed motions during dynamic analysis must have
IPOS>0
.
Possible hinges at riser ends connected to fixed supports or to a support vessel may be modelled by either choosing the correct boundary condition code (see above) or using balljoint connectors. Be careful not to use both these modelling options at the same time for a given supernode. This will lead to program abortion.
Note that if some of the translations are not prescribed, rotationinduced translations may cause driftoff if used in combination with global boundary conditions at a node attached to a vessel.
Coordinates for stress free and static equilibrium position:
X0 Y0 Z0 X1 Y1 Z1 ROT DIR

X0: real
: Coordinates for stress free configuration specified so that the line between any two supernodes are straight and with zero tension. \([\mathrm {L}]\) 
Y0: real
: As forX0

Z0: real
: As forX0

X1: real, default: X0
: 
Y1: real, default: Y0
: Coordinates for static equilibrium position \([\mathrm {L}]\) 
Z1: real, default: Z0

ROT: real, default: 0
: Specified rotation of supernode from stress free position to static equilibrium position \(\mathrm {[deg]}\) 
DIR: real, default: 0
: Direction of axis for specified rotation \(\mathrm {[deg]}\)
ROT
is the specified rotation in degrees from stress free position to
equilibrium position and is analogous to ALFL
/ALFU
parameters used
for the standard systems. The rotation ROT
will be around the local
YREF
axis as shown in the figure below. DIR
is the rotation in
degrees from global Xaxis to XREF
axis. The local ZREF
axis is
parallel to global Zaxis. DIR=0
signifies that the rotation ROT
will be around the global Yaxis. If the line end is allowed to rotate
freely around the local YREF
axis, ROT
will be dummy. Free rotation
around global Yaxis is obtained with IRY = 0
and DIR = 0
.
Definition of rotation axis YREF versus global coordinate system, X, Y. The supernode is located in the origin
Definition of skew coordinate system One input line only if CHCOO
=
`SKEWG' OR `SKEWV'
XX XY XZ XP YP ZP

XX: real
: Components of the skew Xaxis referred to the global system. \([\mathrm {L}]\). See figure below. 
XY: real
: As forXX
. 
XZ: real
: As forXX
. 
XP: real
: Components of a reference vector from the supernode to a point in the skew XYplane, referred to global system \([\mathrm {L}]\) 
YP: real
: As forXP

ZP: real
: As forXP
The skew Zaxis is found by the cross product between the skew Xaxis and the reference vector. The skew Yaxis is found by the cross product between the skew Zaxis and the skew Xaxis
Coordinates for completely free supernodes
This input group consists of NSNFRE
input lines, where
NSNFRE=NSNODNSNFIX
gives the number of supernodes where all degrees
of freedom are free. Skip this group if NSNFRE=0
.
SNODID X0 Y0 Z0

SNODID: character(8)
: Supernode identifier 
X0: real
: Nodal coordinate in stress free configuration \([\mathrm {L}]\) 
Y0: real
: Nodal coordinate in stress free configuration \([\mathrm {L}]\) 
Z0: real
: Nodal coordinate in stress free configuration \([\mathrm {L}]\)