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*Added Mass

Purpose

To define added mass for a floating body.

Theory

Refer to Wave Radiation Loads and Added Mass 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 added mass definition. For frequency independent added mass, a 6x6 matrix is defined by a single block preceded by a TYPE=CONSTANT line. For frequency dependent added mass, 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 added mass over a range of frequencies. Finally, an optional final block of data defining the added mass at the cut-off frequency, preceded by TYPE=CUTOFF, may be included. The entire block of data can then be repeated to specify added mass 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 added mass 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 Added Mass

Purpose

To define constant (frequency-independent) added mass for a floating body.

Keyword Format

Line to define floating body name:

FLOATING BODY=Floating Body Name

Block of lines defining frequency independent added mass:

TYPE=CONSTANT

A11, A12, A13, A14, A15, A16

A21, A22, A23, A24, A25, A26

A31, A32, A33, A34, A35, A36

A41, A42, A43, A44, A45, A46

A51, A52, A53, A54, A55, A56

A61, A62, A63, A64, A65, A66

 

Table Input

Notes

(b)Refer to Added Mass Coefficients for further information on the layout of the added mass terms.

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

Reference Matrices

Purpose

To reference frequency dependent and cut-off added mass 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 Added Mass and Body – Cut-Off Added Mass.

Frequency Dependent Added Mass

Purpose

To define frequency-dependent added mass for a floating body.

Keyword Format

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

TYPE=FREQUENCY

FREQ=Frequency

A11, A12, A13, A14, A15, A16

A21, A22, A23, A24, A25, A26

A31, A32, A33, A34, A35, A36

A41, A42, A43, A44, A45, A46

A51, A52, A53, A54, A55, A56

A61, A62, A63, A64, A65, A66

 

Table Input

Notes

(a)Refer to Added Mass Coefficients for further information on the layout of the added mass terms

(b)This table is used in conjunction with the Body – Cut-Off Added Mass table, in which added mass at the cut-off frequency is specified. Added mass 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 added mass corresponds to the added mass at the cut-off frequency. If no cut-off frequency is specified, the added mass is assumed to be zero below the range of user-specified frequencies.

(d)For frequencies above the range of user-specified frequencies, the added mass 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 added mass.

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

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

Cut-Off Added Mass

Purpose

To define cut-off added mass for a floating body.

Keyword Format

Block of lines defining added mass at the cut-off frequency:

TYPE=CUTOFF

A11, A12, A13, A14, A15, A16

A21, A22, A23, A24, A25, A26

A31, A32, A33, A34, A35, A36

A41, A42, A43, A44, A45, A46

A51, A52, A53, A54, A55, A56

A61, A62, A63, A64, A65, A66

Table Input

Notes

(a)Refer to Added Mass Coefficients for further information on the layout of the added mass terms.

(b)This table is used in conjunction with the Body - Frequency Dependent Added Mass table, in which frequency-dependent added mass is specified. The cut-off frequency itself is specified in the Body – Frequency table.

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