netsse.model.ship ================= .. py:module:: netsse.model.ship .. autoapi-nested-parse:: Hydrodynamic models for the linear wave-to-motion **transfer functions of ship responses**. .. dropdown:: Copyright (C) 2023-2026 Technical University of Denmark, R.E.G. Mounet :color: primary :icon: law *This code is part of the NetSSE software.* NetSSE is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. NetSSE is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/. To credit the author, users are encouraged to use below reference: .. code-block:: text Mounet, R. E. G., & Nielsen, U. D. NetSSE: An open-source Python package for network-based sea state estimation from ships, buoys, and other observation platforms (version 2.3). Technical University of Denmark, GitLab. July 2026. https://doi.org/10.11583/DTU.26379811. *Last updated on 05-06-2026 by R.E.G. Mounet* Functions --------- .. autoapisummary:: netsse.model.ship.Lewis_param netsse.model.ship.format_ANN_input_data netsse.model.ship.heaveCF netsse.model.ship.heaveST netsse.model.ship.pitchCF netsse.model.ship.pitchST netsse.model.ship.rollCF netsse.model.ship.vbmST Module Contents --------------- .. py:function:: Lewis_param(C_B) Computes the Lewis form parameter for a ship, based on its block coefficient. :param C_B: Block coefficient of the ship [-]. :type C_B: float :returns: **gamma** -- Lewis form parameter for the ship [-]. :rtype: float .. seealso:: :py:obj:`format_ANN_input_data` Prepares the input data for the ANN models based on the ship parameters and wave conditions. .. rubric:: References Takami, T., Nielsen, U. D., Mounet, R. E. G., Jensen, J. J., Mori, R., Komoriyama, Y. (2026). Blind identification of incident waves and response transfer functions of a marine vessel based on measured responses. Expert Systems With Applications, 296, 129236. https://doi.org/10.1016/j.eswa.2025.129236. .. rubric:: Example >>> gamma = Lewis_param(C_B) .. py:function:: format_ANN_input_data(om0, beta_deg, U, L, B0, T, C_B) Prepares the input data for the ANN models based on the ship parameters and wave conditions. :param om0: Vector of absolute wave frequencies [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of relative wave heading angles [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float :returns: **ANN_input_data** -- Normalized input data for the ANN models, including ship parameters and wave conditions. :rtype: numpy.ndarray of shape (Nom0*Nbeta*Nkappas, 7) :raises warnings.warn: If any of the input parameters are outside the valid ranges for the ANN model. .. seealso:: :py:obj:`Lewis_param` Computes the Lewis form parameter for a ship, based on its block coefficient. .. rubric:: References Takami, T., Nielsen, U. D., Mounet, R. E. G., Jensen, J. J., Mori, R., Komoriyama, Y. (2026). Blind identification of incident waves and response transfer functions of a marine vessel based on measured responses. Expert Systems With Applications, 296, 129236. https://doi.org/10.1016/j.eswa.2025.129236. .. rubric:: Example >>> ANN_input_data = format_ANN_input_data(om0, beta_deg, U, L, B0, T, C_B) .. py:function:: heaveCF(om0, beta_deg, U, L, B0, T, C_B=1, gravity=None) Computes the heave transfer function amplitude, using the closed-form expressions proposed by Jensen et al. (2004), for a box-shaped uniformly-loaded **monohull ship**. :param om0: Vector of absolute wave frequencies [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of heading angles [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float, default 1 :param gravity: Gravitational acceleration [m/s^2]. If None, the default value from the NetSSE configuration is used. :type gravity: float, optional :returns: **heave** -- Coefficients of the heave transfer function amplitude [m/m]. :rtype: numpy.ndarray of shape (Nom0,Nbeta) .. seealso:: :py:obj:`pitchCF`, :py:obj:`rollCF` .. rubric:: References 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 .. rubric:: Example >>> heave = heaveCF(om0,beta_deg,U,L,B0,T,C_B=1) .. py:function:: heaveST(om0, beta_deg, U, L, B0, T, C_B) Computes the heave transfer function amplitude and phase, using an ANN-based surrogate model of a strip theory code. The ANN was trained on data from a linear strip theory solver, the so-called New Strip Method (Takagi and Ganno, 1967), in which the Lewis form approximation of ship cross-sections is adopted. Further details of the implementation can be found in Takami et al. (2026). :param om0: Vector of absolute wave frequencies [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of relative wave heading angles [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float, default 1 :returns: * **heave_amp** (*numpy.ndarray of shape (Nom0,Nbeta)*) -- Coefficients of the heave transfer function amplitude [m/m]. * **heave_phase** (*numpy.ndarray of shape (Nom0,Nbeta)*) -- Coefficients of the heave transfer function phase [rad]. :raises warnings.warn: If any of the input parameters are outside the valid ranges for the ANN model. .. seealso:: :py:obj:`pitchST`, :py:obj:`vbmST` :py:obj:`format_ANN_input_data` Prepares the input data for the ANN models based on the ship parameters and wave conditions. .. rubric:: References Takagi, M. & Ganno, M. (1967). On the Accuracy of the Strip Theory, Used for a Calculation of Ship Motions in Waves. Journal of Zosen Kiokai, 121, pp. 48–61. https://doi.org/10.2534/jjasnaoe1952.1967.48. Takami, T., Nielsen, U. D., Mounet, R. E. G., Jensen, J. J., Mori, R., & Komoriyama, Y. (2026). Blind identification of incident waves and response transfer functions of a marine vessel based on measured responses. Expert Systems With Applications, 296, 129236. https://doi.org/10.1016/j.eswa.2025.129236. .. rubric:: Example >>> heave_amp, heave_phase = heaveST(om0, beta_deg, U, L, B0, T, C_B) .. py:function:: pitchCF(om0, beta_deg, U, L, B0, T, C_B=1, gravity=None) Computes the pitch transfer function amplitude, using the closed-form expressions proposed by Jensen et al. (2004), for a box-shaped uniformly-loaded **monohull ship**. :param om0: Vector of absolute wave frequency [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of heading angle [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float, default 1 :param gravity: Gravitational acceleration [m/s^2]. If None, the default value from the NetSSE configuration is used. :type gravity: float, optional :returns: **pitch** -- Coefficients of the pitch transfer function amplitude [rad/m]. :rtype: numpy.ndarray of shape (Nom0,Nbeta) .. seealso:: :py:obj:`heaveCF`, :py:obj:`rollCF` .. rubric:: References 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 .. rubric:: Example >>> pitch = pitchCF(om0,beta_deg,U,L,B0,T,C_B=1) .. py:function:: pitchST(om0, beta_deg, U, L, B0, T, C_B) Computes the pitch transfer function amplitude and phase, using an ANN-based surrogate model of a strip theory code. The ANN was trained on data from a linear strip theory solver, the so-called New Strip Method (Takagi and Ganno, 1967), in which the Lewis form approximation of ship cross-sections is adopted. Further details of the implementation can be found in Takami et al. (2026). :param om0: Vector of absolute wave frequencies [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of relative wave heading angles [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float, default 1 :returns: * **pitch_amp** (*numpy.ndarray of shape (Nom0,Nbeta)*) -- Coefficients of the pitch transfer function amplitude [deg/m]. * **pitch_phase** (*numpy.ndarray of shape (Nom0,Nbeta)*) -- Coefficients of the pitch transfer function phase [rad]. :raises warnings.warn: If any of the input parameters are outside the valid ranges for the ANN model. .. seealso:: :py:obj:`heaveST`, :py:obj:`vbmST` :py:obj:`format_ANN_input_data` Prepares the input data for the ANN models based on the ship parameters and wave conditions. .. rubric:: References Takagi, M. & Ganno, M. (1967). On the Accuracy of the Strip Theory, Used for a Calculation of Ship Motions in Waves. Journal of Zosen Kiokai, 121, pp. 48–61. https://doi.org/10.2534/jjasnaoe1952.1967.48. Takami, T., Nielsen, U. D., Mounet, R. E. G., Jensen, J. J., Mori, R., & Komoriyama, Y. (2026). Blind identification of incident waves and response transfer functions of a marine vessel based on measured responses. Expert Systems With Applications, 296, 129236. https://doi.org/10.1016/j.eswa.2025.129236. .. rubric:: Example >>> pitch_amp, pitch_phase = pitchST(om0, beta_deg, U, L, B0, T, C_B) .. py:function:: rollCF(om0, beta_deg, U, L, B0, T, C_B, C_WP, GM_T, kappa, mu, T_N=0, gravity=None, rho=None) Computes the roll transfer function amplitude, using the closed-form expressions proposed by Jensen et al. (2004), for a **monohull ship**. :param om0: Vector of absolute wave frequencies [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of heading angles [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float :param C_WP: Waterplane area coefficient of the ship [-]. :type C_WP: float :param GM_T: Transverse metacentric height [m]. :type GM_T: float :param kappa: 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. :type kappa: float :param mu: Ratio between added viscous damping and critical damping. :type mu: float, default 0 :param T_N: Roll natural period [s]. .. note:: If not specified as input, ``T_N`` is calculated using empirical formulas from ADA147598. :type T_N: float, optional :param gravity: Gravitational acceleration [m/s^2]. If None, the default value from the NetSSE configuration is used. :type gravity: float, optional :param rho: Density of seawater [kg/m^3]. If None, the default value from the NetSSE configuration is used. :type rho: float, optional :returns: **roll** -- Coefficients of the roll transfer function amplitude [rad/m]. :rtype: numpy.ndarray of shape (Nom0,Nbeta) .. seealso:: :py:obj:`heaveCF`, :py:obj:`pitchCF` .. rubric:: 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. .. rubric:: Example >>> roll = rollCF(om0,beta_deg,U,L,B0,T,C_B,C_WP,GM_T,kappa,mu,T_N=0) .. py:function:: vbmST(om0, beta_deg, U, L, B0, T, C_B, gravity=None) Computes the Vertical Bending Moment (VBM) transfer function amplitude and phase, using an ANN-based surrogate model of a strip theory code. The ANN was trained on data from a linear strip theory solver, the so-called New Strip Method (Takagi and Ganno, 1967), in which the Lewis form approximation of ship cross-sections is adopted. Further details of the implementation can be found in Takami et al. (2026). :param om0: Vector of absolute wave frequencies [rad/s]. :type om0: array_like of shape (Nom0,) :param beta_deg: Vector of relative wave heading angles [deg]. :type beta_deg: array_like of shape (Nbeta,) :param U: Vessel forward speed [m/s]. :type U: float :param L: Length of the ship [m]. :type L: float :param B0: Breadth of the ship [m]. :type B0: float :param T: Draft of the ship [m]. :type T: float :param C_B: Block coefficient of the ship [-]. :type C_B: float, default 1 :param gravity: Gravitational acceleration [m/s^2]. If None, the default value from the NetSSE configuration is used. :type gravity: float, optional :returns: * **vbm_amp** (*numpy.ndarray of shape (Nom0,Nbeta)*) -- Coefficients of the VBM transfer function amplitude [kNm/m]. * **vbm_phase** (*numpy.ndarray of shape (Nom0,Nbeta)*) -- Coefficients of the VBM transfer function phase [rad]. :raises warnings.warn: If any of the input parameters are outside the valid ranges for the ANN model. .. seealso:: :py:obj:`heaveST`, :py:obj:`pitchST` :py:obj:`format_ANN_input_data` Prepares the input data for the ANN models based on the ship parameters and wave conditions. .. rubric:: References Takagi, M. & Ganno, M. (1967). On the Accuracy of the Strip Theory, Used for a Calculation of Ship Motions in Waves. Journal of Zosen Kiokai, 121, pp. 48–61. https://doi.org/10.2534/jjasnaoe1952.1967.48. Takami, T., Nielsen, U. D., Mounet, R. E. G., Jensen, J. J., Mori, R., & Komoriyama, Y. (2026). Blind identification of incident waves and response transfer functions of a marine vessel based on measured responses. Expert Systems With Applications, 296, 129236. https://doi.org/10.1016/j.eswa.2025.129236. .. rubric:: Example >>> vbm_amp, vbm_phase = vbmST(om0, beta_deg, U, L, B0, T, C_B)