Support Vessel Data - File Format

The file format is described in the following sections. An example of a support vessel data file is given at the end of this section.

If the vessel transfer function frequency range does not cover the entire frequency range of the analysis, the vessel response will be calculated using the transfer function in the covered frequency range and extrapolated beyond it.

For wave frequencies below the lowest frequency, the transfer function is held constant at its lowest-frequency value. For wave frequencies above the highest frequency, the transfer function is set to zero.

1. File format

1.1. Identification

1.1.1. Data group identifier, one input line

SUPPort VESSel IDENtification

1.1.2. Heading, one input line

Heading

Text describing the transfer functions.

Always one input line, which may be blank. The line may contain up to 60 characters.

1.1.3. Identifier, one input line

IDWFTR

  • IDWFTR: character(6): Identifier for transfer functions. The value NONE is not allowed.

1.2. Transfer function reference position

This data group is used as control parameter and compared with vessel position specified in Single Riser Data.

1.2.1. Data group identifier, one input line

HFTRan REFErence POSItion

1.2.2. 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.

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

um ii fig164
Figure 1. Location of support vessel coordinate system

1.3. Dimension parameter and input type code

1.3.1. Data group identifier, one input line

HFTRansfer CONTrol DATA

1.3.2. Dimension parameters, one input line

NDHFTR NWHFTR ISYMHF ITYPIN

  • NDHFTR: integer: No. of directions for which transfer functions are given

    • NDHFTR=1 or NDHFTR>=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 XV-ZV plane

    • ISYMHF=2: Symmetry about XV-ZV and YV-ZV planes

  • ITYPIN: integer: Code for which format the HF-transfer function are given

    • ITYPIN=1: Non-dimensional complex form

    • ITYPIN=2: Non-dimensional amplitude ratio and phase, where phase is given in degrees

    • ITYPIN=3: Non-dimensional amplitude ratio and phase, where phase is given in radians

The complex form and the amplitude ratio are to be given as non-dimensional. 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.

1.4. Specifications of wave directions

Wave directions given in vessel coordinate system for input of motion transfer functions.

1.4.1. Data group identifier, one input line

WAVE DIREctions

1.4.2. Directions, NDHFTR input lines

IHEAD HEAD

  • IHEAD: integer: Direction number

  • HEAD: real: Direction. The angle HEAD 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).

1.5. Specification of wave frequencies

1.5.1. Data group identifier, one input line

WAVE FREQuencies

1.5.2. Frequencies, NWHFTR input lines

IFREQ WHFTR

  • IFREQ: integer: Frequency number

  • WHFTR: real: Frequency \(\mathrm {[rad/T]}\)

Frequencies must be given in increasing order.

1.6. Transfer function input

1.6.1. Data group identifier, one input line

HFTRansfer FUNCtion "DOF"

dof is either SURGE, SWAY, HEAVE, ROLL, PITCH or YAW

1.6.2. 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 of ITYPIN

    • ITYPIN=1: A - Real part

    • ITYPIN=2: A - Amplitude ratio

    • ITYPIN=3: A - Amplitude ratio

  • B: real: Interpretation according to value of ITYPIN

    • ITYPIN=1: B - Imaginary part

    • ITYPIN=2: B - Phase (degrees)

    • ITYPIN=3: B - Phase (radians)

HFTRansfer FUNCtion "Dof" 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.

1.7. Termination of input data

END

2. Example

Download example file.