1. Seafloor support conditions
Seafloor contact specification
IBTANG ZBOT IBOT3D

IBTANG: integer, default: 0
: Bottom tangent option.
IBTANG = 0
: No seafloor contact 
IBTANG = 1
: Seafloor contact forces on all nodes that are belowZ < ZBOT + R_EXTCNT
. The modified 3D seafloor formulation is used. Friction contribution to torsional loading is possible. 
IBTANG = 3
: Seafloor contact elements will be added according to the specification given in the data group SEAFLOOR CONTACT SPECIFICATION.


ZBOT: real
: Zcoordinate of seafloor (ZBOT < 0
). \(\mathrm {[L]}\)
Dummy variable if
IBTANG = 0
orIBOT3D = 1
.


IBOT3D: integer, default: 0
: Code for 3D bottom
IBOT3D = 0
: flat bottom at depthZBOT

IBOT3D = 1
: 3D topology, file to be specified in input to STAMOD

Note that flat bottom topology based on original Fortran code is planned to be removed and substituted by the general 3D seafloor contact formulation FORTRAN code. The old code will be kept for debugging purposes.
Seafloor stiffness, friction and damping
The following input line must only be given if IBTANG=1
STFBOT STFAXI STFLAT FRIAXI FRILAT DAMBOT DAMAXI DAMLAT ILTOR

STFBOT: real > 0
: Seafloor stiffness normal to the seafloor \([\mathrm {F/L^2}]\) 
STFAXI: real >= 0, default: 0
: Inplane seafloor stiffness for friction in axial direction \([\mathrm {F/L^2}]\) 
STFLAT: real >= 0, default: 0
: Inplane seafloor stiffness for friction in lateral direction \([\mathrm {F/L^2}]\) 
FRIAXI: real >= 0, default: 0
: Inplane seafloor friction coefficient in axial direction [1] 
FRILAT: real >= 0, default: 0
: Inplane seafloor friction coefficient in lateral direction [1] 
DAMBOT: real >= 0, default: 0
: seafloor damping coefficient normal to the seafloor \([\mathrm {F\times T/L^2}]\) 
DAMAXI: real >= 0, default: 0
: Inplane seafloor damping coefficient in axial direction \([\mathrm {F\times T/L^2}]\) 
DAMLAT: real >= 0, default: 0
: Inplane seafloor damping coefficient in lateral direction \([\mathrm {F\times T/L^2}]\) 
ILTOR: integer, default: 0
: Option for applying lateral contact forces at the external contact radius, giving a torsional moment
= 0
: Lateral loads are applied at the node 
= 1
: Lateral loads are applied at the external contact radius if it is specified for the associated beam crosssection.

STFBOT
is used for computing the vertical spring stiffness,
\(\mathrm {k_V}\) , for seafloor contact.
\(\mathrm {k_V}\) = STFBOT
\(\mathrm {\times L}\)
where \(\mathrm {L}\) is the element length.
Horizontal contact with the seafloor is modelled independently in the axial and lateral directions. Contact is initially modelled with linear springs. Sliding will occur when an axial or lateral spring force reaches the friction force value. Springs will be reinstated if the line starts sliding in the opposite direction, or if the friction force increases and is greater than the spring force. The spring stiffness is calculated as \(k_h=\mathrm {Stalks}\times L_h\), where \(\mathrm {L_h}\) is the length of the element’s horizontal projection. The seafloor friction forces are calculated as \(F=\mathrm {FRIxxx}\times F_{vert}\) and are directed against the axial or lateral displacements, where \(\mathrm {F_{vert}}\) is the vertical contact force between the pipe and the bottom.
2. Line, line type and supernode connectivity
This data group defines the connectivity between lines and supernodes. If the line identifier is missing the line number implicitly defined by the order in which the lines are specified, will be used as the line identifier. References to line type IDs and supernode IDs are mandatory.
NLIN
input lines.
LINEID LINTYPID SNODID1 SNOD_ID2

LINEID: character(8)
: Line identifier 
LINTYPID: character(8)
: Reference to line type identifier 
SNODID1: character(8)
: Reference to supernode identifier at end 1 
SNODID2: character(8)
: Reference to supernode identifier at end 2
If only 3 alphanumeric strings are specified, the first string is taken
as LINTYPID
, the second as SNODID1
and the third as SNODID2
:
LINTYPID SNODID1 SNODID2
The LINEID
is taken as the line
number as implicitly defined by the order in which the lines are given.
The local element y and zaxes are found from local xaxis and a reference vector.
The local element xaxis goes from end 1 to end 2 of the element. The local element y and zaxes are found from local xaxis and a reference vector. The local element x, y and zaxes will form a righthanded coordinate system.
The reference vector may be specified using the option LOCAL ELEMENT AXIS.
If the line is a blade in a wind turbine and LOCAL ELEMENT AXIS
is not
specified, the reference vector will be found as the cross product
between the local xaxis of the shaft and the local xaxis of the blade
element.
If the reference vector is not given by either of these two methods, the default method will be used to determine the local element axis.
Default method

If the element is not vertical, the reference vector is found as the cross product between the global zaxis and the local xaxis.

If the element is vertical, the positive or negative global yaxis will be used as the reference vector; positive if completely vertical or tilted in the positive global xdirection and negative otherwise.

This will give a horizontal yaxis and, if possible, a local zaxis oriented upwards.
Once the reference vector is found by one of these methods, then

The local zaxis is found as the cross product between the local xaxis and the reference vector.

The local yaxis is found as the cross product between the local zaxis and the local xaxis.
For beam elements, the element axes are found at the stressfree configuration and will subsequently follow the element.
Examples:

If the element is in the global xzplane and the local xaxis is completely vertical or tilted in the positive global xdirection, the global yaxis will be used as the reference vector.

If the local xaxis is tilted in the negative global xdirection, the negative global yaxis will be used as the reference vector.

If local xaxis is tilted 45 deg wrt to global zaxis, the reference vector will point in the positive global ydirection.

If the local xaxis is along the global xaxis, the reference vector will point in the global ydirection. The initial local element axes will be aligned with the corresponding global axes.

If the local xaxis is along the global yaxis, the reference vector will point in the negative xdirection. The local zaxis will point in the positive global zdirection and the local element yaxes in the negative global xdirection.

If the local xaxis points in the direction (1,2,3), the reference vector will point in the direction (2,1,0). The local zaxis will point in the direction (3,6,5) and the local yaxis will coincide with the reference vector.

If the local xaxis points in the direction (1,2,3), the reference vector will point in the direction (2,1,0). The local zaxis will point in the direction (3,6,5) and the local yaxis will coincide with the reference vector.
3. 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 \([\mathrm {L}]\)
4. Support vessel reference
Identification and location of support vessel, NVES
input lines
IVES IDWFTR XG YG ZG DIRX

IVES: integer, default: 1
: Vessel number,1 ⇐ IVES ⇐ NVES
. 
IDWFTR: character(6), default: 'NONE'
: Identifier for support vessel motion transfer function
IDWFTR = 'NONE'
means no transfer function specified


XG: real
: X position of vessel coordinate system referred in global system \([\mathrm {L}]\) 
YG: real
: Y position of vessel coordinate system referred in global system \([\mathrm {L}]\) 
ZG: real
: Z position of vessel coordinate system referred in global system \([\mathrm {L}]\) 
DIRX: real
: Direction of vessel Xaxis.
5. Description of global springs
To be specified if NSPR>0
The input lines below (`Spring localization
and properties' and `Nonlinear spring stiffness') must be given in one
block for each global spring.
Spring location and properties
LINEID ISEG INOD ILDOF STIFF/NPAIR DAMP A2

LINEID: character (8)
: Line identifier 
ISEG: integer
: Local segment number within line 
INOD: integer
: Local node number within actual segment 
ILDOF: integer
: Local degree of freedom
=1 global Xdirection

=2 global Ydirection

=3 global Zdirection

=4 rotation around global Xaxis

=5 rotation around global Yaxis

=6 rotation around global Zaxis

= 12 or 21 translation in global XYplane

= 13 or 31 translation in global XZplane

= 23 or 32 translation in global YZplane


STIFF/NPAIR

STIFF: real >= 0
: Constant spring stiffness \([\mathrm {F/L}]\) or \([\mathrm {FL/deg}]\) 
NPAIR: integer ⇐ 2
:NPAIR
is number of forcedisplacement or momentrotation relations in spring specification


DAMP: real, default: 0
: Linear damping coefficient \([\mathrm {FT/L}]\) or \([\mathrm {FLT/deg}]\) 
A2: real, default: 0
: Stiffness proportional damping factor
Nonlinear spring stiffness
The following input line is to be given if NPAIR
>= 2
PON(1) DISPL(1)...............PON(NPAIR) DISPL(NPAIR)

PON(1): real
: Spring force \([\mathrm {F}]\) or moment \([\mathrm {FL}]\) corresponding to 
DISPL(1): real
: Spring displacement \([\mathrm {L}]\) or \([\mathrm {deg}]\)
All NPAIR
pairs of PON
and DISPL
values are given on a single
input line. The values of PON
and DISPL
must be monotonically
increasing; PON(1) < PON(2) < … < PON(NPAIR)
and
DISPL(1) < DISPL(2) < … < DISPL(NPAIR)
.
For ILDOF > 6
, the first pair of values must both be zero;
i.e. \(\mathrm {\:}\) PON(1) = DISPL(1) = 0.0
.
6. Description of kill and choke lines (deprecated functionality)
NAKC input lines.
IKCTYP DIAAKC MASAKC FLUAKC TENAKC NLINKC LINEID(1) ... LINEID(nlinkc)

IKCTYP: integer
: Type of kill and choke line
IKCTYP = 1
: Internal line 
IKCTYP = 2
: External line


DIAAKC: real, default: 0
: Outer diameter of kill and choke line \([\mathrm {L}]\) 
MASAKC: real, default: 0
: Mass per unit length of kill and choke line excluding contents \([\mathrm {M/L}]\) 
FLUAKC: real, default: 0
: Mass per unit length of fluid contents of kill and choke line \([\mathrm {M/L}]\) 
TENAKC: real, default: 0
: Tension of kill and choke line \([\mathrm {F}]\) 
NLINKC: integer, default: 1
: Number of riser lines this kill and choke line is attached to 
LINEID(1): character(8)
: Reference to line identifiers (Adjacent lines) 
.

.

.

LINEID(nlinkc)
:
LINEIDs must be given in correct order from lower end to upper end.
Tension will be applied at the supernode at the second end of line
LINEID(nlinkc)
If tension is zero, an internal line will be fixed at the upper end.
7. Rigid supernode connections
In present version only to be applied for static and nonlinear dynamic analysis.
This option enables the user to model rigid connections between supernodes. A rigid connection is modelled by specifying a master  and a slave node. Both the master and the slave have initially to be defined as free nodes. The theoretical formulation is a special application of linear constraints between degrees of freedom.
NRICON input lines.
CHMAST CHSLAV

CHMAST: character
: Reference to supernode identifier,SNODID
, specified as the master node 
CHSLAV: character
: Reference to supernode identifier,SNODID
, specified as the slave node
Note that:

Both the master and the slave node have initially to be defined as free nodes.

A master node can not be slave of another master node.

A slave node can only be slave of one master node.

An arbitrary number of slave nodes can have the same master node.

The number of DOFs at the slave node must not exceed the number of DOFs at the master node.
8. Seafloor contact specification
This data group must be given for Arbitrary Systems ARsytems with
IBTANG = 3
.
8.2. Seafloor contact specification
NSPEC

NSPEC: integer > 0
: Number of input lines to be given with seafloor contact specification
NSPEC input lines
CMPTYPID LINEID ISEG1 ISEG2 … ISEGn

CMPTYPID: character(8)
: Reference to a seafloor contact component identifier. Must be of typeSPRI
orSOIL
. 
LINEID: character(8)
: Reference to a line identifier 
ISEG1: integer >= 0, default: 0
: Segment for which seafloor contact of typeCMPTYPID
is possible.
ISEG1 = 0
: Seafloor contact is possible for all segments in lineLINEID

ISEG1 > 0
: First segment for which seafloor contact is possible.


ISEG2: integer != 0
: Segment for which seafloor contact of typeCMPTYPID
is possible.
ISEG2 > 0
: Second segment for which seafloor contact is possible. 
ISEG2 < 0
: Seafloor contact is possible for all segments from ISEG1 to ABS(ISEG2).


ISEGn: integer !=0
: Last segment for which seafloor contact of typeCMPTYPID
is possible.
ISEGn > 0
: Last segment for which seafloor contact is possible. 
ISEGn < 0
: Seafloor contact is possible for all segments from the previous specified segment to ABS(ISEGn).

Pairs of a positive and a negative segment number may be given anywhere in the sequence.
Note that a segment may only have one seafloor contact.
9. Elastic contact surface
This data group is optional and is available as additional information for Arbitrary Systems only. It enables the user to model contact effects between lines. For normal riser systems this data group should not be considered.
The main intention of this data group is to enable modelling of pipelines during laying operations. This includes contact forces between the pipe and rollers on the lay barge/stinger and applied tension from a tensioner.
Contact between roller and pipe is modelled by a bilinear or nonlinear spring and a bilinear dash pot damper. The contact force acts normal to the pipe and the roller. It is treated as a discrete element load acting on the pipe, while the contact load acting on the roller is transferred as a nodal force to the stinger. The last includes possible torsional moment.
The term contact surface is introduced to cover stinger modelling. The stinger may be fixed or hinged to the vessel. Generally it is curved and may consist of a rigid part following the vessel motions and a flexible part.
The term contact point is defined as the location of rollers or tensioner on the stinger.
9.1. Contact surface modelling
A complete model of an elastic contact surface includes the following information:

Number of lines describing the surface The surface may consist of several adjacent lines. By introducing several adjacent lines it is possible to model a contact surface which has a curved stressfree initial configuration. In addition boundary conditions for the supernodes at the line intersections can be specified. This is necessary to model prescribed displacements due to vessel motions.

Type and location of contact points Contact points can be of roller and/or tensioner type and have to be located at ends of line segments.

Identification of lines which may experience contact with the contact surface. The line identification is used to limit the number of elements that have to be checked for contact during program execution.
Supplementary information is specified in the following data groups: