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*QTF

Purpose

To specify Quadratic Transfer Functions (QTFs) that allow the slow drift loads on a floating body or moored vessel to be determined.

Theory

Refer to Wave Drift Loads, QTF Coefficients and QTF Calibration Coefficients for further information on this feature.

Keyword Format

Data may defined explicitly within the keyword file itself, or defined separately in an external file which is simply referenced using a FILE= entry. The latter approach is highly recommended as it reduces unnecessary clutter in the keyword file, and also helps to improve user interface performance and enhanced user experience.

Floating Body

A block of data consisting of floating body name followed by a single line defining the name of an external file which contains QTF data.

FLOATING BODY=Floating Body Name

FILE=File Name

File Name should include the entire path of the file including its extension. If a file name or any part of its path contains spaces then it should be enclosed in double quotation marks.

A block of data consisting of floating body name, followed by a frequency value, followed by the QTFs for that frequency, with the QTF line repeated as necessary. The block is then itself repeated as necessary for further frequencies. The whole block may then be repeated to specify QTFs for different floating bodies.

FLOATING BODY=Floating Body Name

FREQ=Frequency

Floating Body/QTF Heading, Surge QTF Value, Sway QTF Value, Yaw QTF Value

 

Moored Vessel

A block of data consisting of a moored vessel tag line followed by a single line defining the name of an external file which contains current coefficient data.

MOORED VESSEL

FILE=File Name

File Name should include the entire path of the file including its extension. If a file name or any part of its path contains spaces then it should be enclosed in double quotation marks.

A block of data consisting of a moored vessel tag line, followed by a frequency value, followed by the QTFs for that frequency, with the QTF line repeated as necessary. The block is then itself repeated as necessary for further frequencies.

MOORED VESSEL

FREQ=Frequency

Floating Body/QTF Heading, Surge QTF Value, Sway QTF Value, Yaw QTF Value

 

Table Input

Floating Body (External File)

Floating Body

Moored Vessel (External File)

Moored Vessel

Notes

(a)To determine the relevant values of the QTFs for a given wave in a seastate, Flexcom first determines the relative heading for that wave. If the frequency of the wave matches any of the user-specified frequencies, the program then linearly interpolates between the closest user-specified headings for that frequency to find the relevant QTF data.

(b)If the frequency of the wave does not match any of the user-specified frequencies, Flexcom linearly interpolates between the closest user-specified headings and the closest user-specified frequencies to find QTF data for the particular wave heading and frequency.

(c)If either the frequency or heading of the particular wave falls outside the range of user-specified frequencies and headings, the value of the QTFs is assumed to be zero. Again, it is recommended that a sufficiently large range of frequencies and headings is specified to avoid this occurrence. The sign of the QTF values for a particular wave heading should reflect the direction of the force that a wave in that direction would exert on the body.