1. Data Group E: Support Vessel Data
Observe that the motion transfer function definition is related to the
wave field definition. See Motion Transfer Functions
in the Theory
Manual for the definition of wave field and motion transfer functions.
Transfer functions based on other definitions must be converted by
appropriate phase shift operations before they are used as input to this
program.
This data group needs not be given for systems with no vessel attachment
points. Note that either Support vessel data on file
or
Identification
through Transfer function input
is to be given.
1.1. Support vessel data on file
1.1.2. File name
CHFTRA

CHFTRA: character(80)
: File name with transfer functions data
File with transfer function data given in RIFLEX format terminated with
an END
statement.
This group replaces the rest of group E if given. Either Support vessel
data on file
or Identification
through Transfer function input
should be given. If Support vessel data on file
is given, the content
on the file should be Identification
to Transfer function input
with
an END
termination.
1.2. Identification
1.3. Transfer function reference position
This data group is used as control parameter and compared with vessel position specified in Single Riser Data.
1.3.2. Reference position, one input line
ZG

ZG: real
: Vertical position of the support vessel coordinate system. \(\mathrm {[L]}\)
(The global Z coordinate for which the vessel motion transfer function is calculated.)

Confer the figure Location of support vessel coordinate system (below).

This parameter is used as control parameter and compared with
ZG
in data groups.

1.4. Dimension parameter and input type code
1.4.2. Dimension parameters, one input line
NDHFTR NWHFTR ISYMHF ITYPIN

NDHFTR: integer
: No. of directions for which transfer functions are given
NDHFTR=1
orNDHFTR>=4


NWHFTR: integer
: No of frequencies for which transfer functions are given
NWHFTR>=4


ISYMHF: integer
: Symmetry code related to transfer functions
ISYMHF=0
: No symmetry 
ISYMHF=1
: Symmetry about XVZV plane 
ISYMHF=2
: Symmetry about XVZV and YVZV planes


ITYPIN: integer
: Code for which format the HFtransfer function are given
ITYPIN=1
: Nondimensional complex form 
ITYPIN=2
: Nondimensional amplitude ratio and phase, where phase is given in degrees 
ITYPIN=3
: Nondimensional amplitude ratio and phase, where phase is given in radians

The complex form and the amplitude ratio are to be given as nondimensional. This means:

L/L for freedoms surge, sway and heave

radian/radians or degrees/degrees for freedoms roll, pitch and yaw, giving motion angle/surface wave slope amplitude. The wave slope amplitude is defined by \(\mathrm {\gamma _a=k\zeta_a}\) where \(\mathrm {k}\) is the wave number and \(\mathrm {\zeta_a}\) is the wave amplitude.
If NDHFTR=1
, ISYMHF
is dummy (set to zero by the program). In this
case the specified transfer function is used, regardless of the wave
direction. Note that the specified motions are applied in the local
vessel coordinate system regardless of the wave direction; e.g. surge
motions are applied in the local vessel xdirection. In practice, the
wave direction will not have any effect on the vessel motions in this
case. To rotate the motions with the wave direction, update the vessel
heading when the wave direction is changed. This method must however be
used with care, if the model is not symmetric and connected to the
vessel in the local vessel origo, it may not give the desired effect.
1.5. Specifications of wave directions
Wave directions given in vessel coordinate system for input of motion transfer functions.
1.5.2. Directions, NDHFTR input lines
IHEAD HEAD

IHEAD: integer
: Direction number 
HEAD: real
: Direction. The angleHEAD
is measured in degrees from the XV axis counter clockwise to the wave propagation vector
IHEAD
and HEAD
must be given in ascending order
If NDHFTR=1
, HEAD
is dummy.
If the directions do not cover a full circle, the transfer functions for
the first direction will be repeated for the direction HEAD(1) + 360
.
For ISYMHF
> 0, the last direction after mirroring is 360  HEAD(1)
.
1.7. Transfer function input
1.7.1. Data group identifier, one input line
HFTRansfer FUNCtion "DOF"
dof
is either SURGE, SWAY, HEAVE, ROLL, PITCH
or YAW
1.7.2. Transfer function for HF dof
motion, NDHFTR x NWHFTR input lines
IDIR IFREQ A B

IDIR: integer
: Direction number 
IFREQ: integer
: Frequency number 
A: real
: Interpretation according to value ofITYPIN
(given in the data group Data Group E: Support Vessel Data_transfer_reference_reference)
ITYPIN=1:
A  Real part 
ITYPIN=2:
A  Amplitude ratio 
ITYPIN=3:
A  Amplitude ratio


B: real
: Interpretation according to value ofITYPIN
(given in the data group Data Group E: Support Vessel Data_transfer_reference_reference)
ITYPIN=1:
B  Imaginary part 
ITYPIN=2:
B  Phase (degrees) 
ITYPIN=3:
B  Phase (radians)

Data Group E: Support Vessel Data_transfer_input_data is repeated for each degree of freedom included in motion description. If one (or more) degrees of freedom are omitted, they are set equal to zero.
For phase and sign convention, see Motion Transfer Functions
in the
Theory Manual.
If only one direction is specified (NDHFTR=1
), the transfer function
is used independent of incoming wave direction.
Amplitudes and phase angles at required frequencies are calculated by linear interpolation/extrapolation in the dynamic analysis. Transfer functions will therefore be extrapolated for spectral components outside the frequency range defined for the transfer function. Ensure that the amplitude values given for the two highest/lowest frequencies give physical realistic values when extrapolated. Add two zero amplitude components at both ends of the frequency range if no extrapolation is wanted.
Linear interpolation is also used for wave direction.
1.8. Termination of input data
Do not forget the END
input line if this is the last
data group
given in this INPMOD
run. See also
Termination of input data.
END