netsse.model.ship.rollCF

netsse.model.ship.rollCF(om0, beta_deg, U, L, B0, T, C_B, C_WP, GM_T, kappa, mu, T_N=0)

Computes the roll transfer function amplitude, using the closed-form expressions presented in Jensen et al. (2004).

Parameters:

• om0 (array_like of shape (Nom0,)) – Vector of absolute wave frequencies [rad/s].

• beta_deg (array_like of shape (Nbeta,)) – Vector of heading angles [deg].

• U (float) – Vessel forward speed [m/s].

• L (float) – Length of the ship [m].

• B0 (float) – Breadth of the ship [m].

• T (float) – Draft of the ship [m].

• C_B (float) – Block coefficient of the ship [-].

• C_WP (float) – Waterplane area coefficient of the ship [-].

• GM_T (float) – Transverse metacentric height [m].

• kappa (float) – Custom parameter (chosen between 0 and C_WP) representing the ratio between the length of the aft beam and the whole ship length in the simplified ship model for roll.

• mu (float, default 0) – Ratio between added viscous damping and critical damping.

• T_N (float, optional) –

  Roll natural period [s].

  Note

  If not specified as input, T_N is calculated using empirical formulas from ADA147598.

Returns:

roll – Coefficients of the roll transfer function amplitude [rad/m].

Return type:

numpy.ndarray of shape (Nom0,Nbeta)

See also

heaveCF, pitchCF

References

1. Jensen, J. J., Mansour, A. E., & Olsen, A. S. (2004). Estimation of ship motions using closed-form expressions. Ocean Engineering, 31(1), 61–85. https://doi.org/10.1016/S0029-8018(03)00108-2

2. ADA147598, 1973. Code of Safety for Fishermen and Fishing Vessels. Part B. Safety and Health Requirements for the Construction and Equipment of Fishing Vessels. Inter-Governmental Maritime Consultative Organization, London, England.

Example

>>> roll = rollCF(om0,beta_deg,U,L,B0,T,C_B,C_WP,GM_T,kappa,mu,T_N=0)