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*Radiation Damping

Purpose

To define radiation damping for a floating body.

Theory

Refer to Wave Radiation Loads and Radiation Damping Coefficients for further information on this feature.

Keyword Overview

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.

Block of data consisting of the floating body name followed by the radiation damping definition. For frequency independent radiation damping, a 6x6 matrix is defined by a single block preceded by a TYPE=CONSTANT line. For frequency dependent radiation damping, multiple 6x6 matrices are defined by several blocks of data, each one preceded by a FREQ= line for the different frequencies, with a TYPE=FREQUENCY line at the beginning. This block is repeated as often as necessary to define the radiation damping over a range of frequencies. Finally, an optional final block of data defining the radiation damping at the cut-off frequency, preceded by TYPE=CUTOFF, may be included. The entire block of data can then be repeated to specify radiation damping for second and subsequent floating bodies.

Data Specified in External File

Keyword Format

Line defining floating body name:

FLOATING BODY=Floating Body Name

Line defining name of external file which contains radiation damping data.

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.

Table Input

Notes

(a)Refer to the following sections for further information regarding the required format of data within the external file.

Constant Radiation Damping

Purpose

To define constant (frequency-independent) radiation damping for a floating body.

Keyword Format

Line to define floating body name:

FLOATING BODY=Floating Body Name

Block of lines defining frequency independent radiation damping:

TYPE=CONSTANT

C11, C12, C13, C14, C15, C16

C21, C22, C23, C24, C25, C26

C31, C32, C33, C34, C35, C36

C41, C42, C43, C44, C45, C46

C51, C52, C53, C54, C55, C56

C61, C62, C63, C64, C65, C66

Table Input

Notes

(a)Refer to Radiation Damping Coefficients for further information on the layout of the radiation damping terms.

(b)The type of radiation damping specified for a particular floating body, either Constant or Frequency Dependent, should be consistent with the type of added mass specified for the same floating body.

radiation damping - Reference Matrices

Purpose

To reference frequency dependent and cut-off radiation damping matrices for use with a floating body.

Keyword Format

Line to define floating body name:

FLOATING BODY=Floating Body Name

Table Input

Notes

(a)Any properties which you refer to for a particular floating body must be defined in other tables – i.e. Body - Frequency Dependent Radiation Damping and Body – Cut-Off Radiation Damping.

Frequency Dependent Radiation Damping

Purpose

To define frequency-dependent radiation damping for with a floating body.

Keyword Format

Block of lines defining frequency dependent radiation damping, preceded by a single TYPE=FREQUENCY line:

TYPE=FREQUENCY

FREQ=Frequency

C11, C12, C13, C14, C15, C16

C21, C22, C23, C24, C25, C26

C31, C32, C33, C34, C35, C36

C41, C42, C43, C44, C45, C46

C51, C52, C53, C54, C55, C56

C61, C62, C63, C64, C65, C66

Table Input

Notes

(a)Refer to Radiation Damping Coefficients for further information on the layout of the radiation damping terms.

(b)This table is used in conjunction with the Body – Cut-Off Radiation Damping table, in which radiation damping at the cut-off frequency is specified. Radiation damping at the cut-off frequency is completely defined by a single 6x6 matrix. The cut-off frequency itself is specified in the Body – Frequency table

(c)For frequencies below the cut-off frequency, the radiation damping corresponds to the radiation damping at the cut-off frequency. If no cut-off frequency is specified, the radiation damping is assumed to be zero below the range of user-specified frequencies.

(d)For frequencies above the range of user-specified frequencies, the radiation damping is assumed to be zero.

(e)For frequencies that do not exactly match one of the frequencies specified, Flexcom linearly interpolates between the nearest frequencies to find the relevant values of radiation damping.

(f)You do not need to specify the frequencies in any particular order; ascending order is not necessary.

(g)The type of radiation damping specified for a particular floating body, either Constant or Frequency Dependent, should be consistent with the type of added mass specified for the same floating body.

Cut-Off Radiation Damping

Purpose

To define cut-off radiation damping for a floating body.

Keyword Format

Block of lines defining radiation damping at the cut-off frequency:

TYPE=CUTOFF

C11, C12, C13, C14, C15, C16

C21, C22, C23, C24, C25, C26

C31, C32, C33, C34, C35, C36

C41, C42, C43, C44, C45, C46

C51, C52, C53, C54, C55, C56

C61, C62, C63, C64, C65, C66

Table Input

Notes

(a)Refer to Radiation Damping Coefficients for further information on the layout of the radiation damping terms.

(b)This table is used in conjunction with the Body - Frequency Dependent Radiation Damping table, in which frequency-dependent radiation damping is specified. The cut-off frequency itself is specified in the Body – Frequency table.

(c)For frequencies below the cut-off frequency, the radiation damping corresponds to the radiation damping at the cut-off frequency. If no cut-off frequency is specified, the radiation damping is assumed to be zero below the range of user-specified frequencies.