Theoretical Manual for SEALOADS Version 1.1: A Computer Program for Prediction of Nonlinear Ship Motions, Sea Loads, and Pressure Distribution in the time Domain


  1. Qui, W.
  2. Peng, H.
  3. Hsiung, C.C.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN);MARTEC Ltd, Halifax NS (CAN)
This report outlines the theoretical background in the FORTRAN program SEALOADS version 1.1 for computing nonlinear ship motions, bending moments and shear forces on the hull, and hydrodynamic pressure distributions over the wetted hull surface. The computation is carried out in the time domain by using the three-dimensional panel method. A pseudo-nonlinear module is introduced to account for the instantaneous wetted surface. In SEALOADS, the external forces acting on the ship hull include the linearized radiation and diffraction forces, nonlinear Froude-Krylov force, viscous roll ramping force, bow-flare slamming force and forces from rudder, maneuvering and propeller. The linearized radiation and diffraction forces are obtained from the impulse response functions, which are solved by using the time-domain Green function and applying a non-impulsive input to the ship. The nonlinear Froude-Krylov force is computed at the instantaneous wetted surface of the hull. A two-dimensional wedge model is applied to compute the bow-flare slamming force. The nonlinear equations of ship motion are solved by the fourth-order Runge-Kutta technique or by the extrapolation method. Effects of position-dependent hydrodynamic coefficients are considered. An automatic panel generator based on NURBS surfaces is also included in this version.

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Sea loads;Time domain;Hydrodynamic pressures;Nonlinear forces
Report Number
DREA-CR-2001-176 — Contractor Report
Date of publication
01 Aug 2001
Number of Pages
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