Hydrodynamic Interaction Between Bodies

This option enables the user to include hydrodynamic interaction effects between an arbitrary number of bodies. These effects may be significant when the distance between the floating bodies is small.

Two groups of data are considered to enable this functionality:

  • Coupled added mass (at infinite frequency)

  • Coupled retardation function

Other load terms affected by hydrodynamic interaction are specified together with body forces (section A2).

The input specification makes use of the symmetric properties:

  • Coupled added mass: \(\mathrm {(\boldsymbol{A}_\infty)_{i,j}=(\boldsymbol{A}_\infty)_{j,i}^T}\)

  • Retardation function: \(\mathrm {\boldsymbol{h}(t-\tau)_{i,j}=\boldsymbol{h}(t-\tau)_{j,i}^T}\)

where the indices i and j refers to body i and body j and superscript T denoted matrix transpose.

Hydrodynamic coupling between several bodies has to be specified as coupling between pairs of bodies.

This data group has to be specified once for each hydrodynamic coupling between two bodies.

1 input line

HYDRodynamic COUPling DATA

1 input line

CHCPL

  • CHCPL: character(8): Hydrodynamic coupling identifier, must be unique

2 input lines

TEXT

  • TEXT: character(60): Character string

1 input line

CHBDY_A

  • CHBDY_A: character(8): Body identification for body A

1 input line

CHBDY_B

  • CHBDY_B: character(8): Body identification for body B

Note that the body data for CHBDY_A and CHBDY_B must precede the hydrodynamic coupling data for the two bodies.

1. Coupled added mass data

1 input line

COUPled ADDEd MASS

6 input lines

AMi1  AMi2  AMi3  AMi4  AMi5  AMi6

  • AMij: real: An acceleration of body A in dof i will be multiplied with AMij to give a force on body B in dof j, and an acceleration of body B in dof j will be multiplied with AMij to give a force on body A in dof i \(\mathrm {[M,ML,ML^2]}\)

2. Coupled retardation function

1 input line

COUPled RETArdation FUNCtion

1 input line

TIMDEL

  • TIMDEL: real: Time step in retardation function

1 input line

RETArdation ELEment DATA

1 input line

NRETij  IDOF_A  IDOF_B

  • NRETij: integer: Number of time delays for which function is given for element (IELEM, JELEM)

  • IDOF_A: integer: Degree of freedom body A

  • IDOF_B: integer: Degree of freedom body B

The velocity of body A degree of freedom IDOF_A will be convoluted with the retardation function to give a force/moment at body B in degree of freedom IDOF_B and

the velocity of body B degree of freedom IDOF_B will be convoluted with the retardation function to give a force/moment at body A in degree of freedom IDOF_A.

1 input line (continue by continuation mark &)

RETij(1)........RETij(NRETij)

  • RETij(k): real: Retardation function value \(\mathrm {[F/L,FT,FL]}\)