Regular Analysis

1. Analysis Parameters

  • Periods : Number of periods for regular wave analysis

  • Time steps : Number of integration time steps per period

  • Wave acting : Wave acting or not.

  • Support vessel motion: Options are

    • Generated motions: Support vessel motions calculated from wave period, wave amplitude and motion transfer function

    • No motions : Switch off vessel motion. Body motions will be included if the model contains bodies.

    • Specified motions : Support vessel motions specified directly using motion amplitude and phase angles, see Regular Vessel motion.

No motions must be specified if the model does not contain a support vessel.

Model without bodies:

  • The wave period specified in the environment will be used.

  • The simulation time step will be the wave period divided by the number of time steps per period.

Model with bodies:

The specified regular wave will be replaced by a wave spectrum with a single FFT frequency. The FFT parameters are given in the Irregular Analysis section.

  • The wave period will be approximated by the closest FFT frequency.

  • Increasing Requested Time series Length will give a finer frequency resolution and can thus give a more accurate wave period.

  • The simulation time step is then chosen as a fraction of the irregular time increment and as close to the specified number of time steps per period as possible.

2. Wave calculation method

2.1. Wave theory and kinematics

Wave theory :

  • Airy linear : Airy linear wave theory

  • Stoke 5th order: Stoke 5th order wave theory. Not available if the model contains bodies.

Kinematics in the wave zone:

  • Mean water level: Wave kinematics and wave loads calculated to the mean water level

  • Stretching and compression of wave potential

  • Moving the potential to actual surface

  • Keeping the potential constant from mean water level to wave surface when the surface is above the mean water level

  • Second order wave with integration of wave forces to wave surface

See illustration of wave kinematics in in Wave kinematics and the wave surface- 1: to mean water level, 2: profile stretched / compressed, 3: profile moved .

The options for kinematics in the wave zone are only relevant for Airy linear wave theory.
The combination of integration of wave forces to the wave surface and MacCamy-Fuchs or Potential hydrodynamic loads is not consistent. MacCamy-Fuchs / Potential loads are calculated to the mean water level at the static position. Additional loads (e.g. drag) will be applied up to the wave surface.

Kinematics position: Choice of position and method for calculation of wave kinematics. Options are

  • Dynamic position: Kinematics are calculated at the dynamic position during the simulation.

  • Static position: Kinematics are calculated at the static position during the simulation.

2.2. Regular Vessel motion

Regular vessel motion is specified of the option Specified motion is chosen.

  • Support vessel :

  • Xamp : Motion amplitude, global x-direction

  • Yamp : Motion amplitude, global ydirection

  • Zamp : Motion amplitude, global zdirection

  • Zramp : Motion amplitude, global x-rotation

  • YRamp : Motion amplitude, global y-rotation

  • ZRamp: Motion amplitude, global z-rotation

  • Xpha : Phase angle, x-motion

  • YPha : Phase angle, y-motion

  • Zpha : Phase angle, z-motion

  • ZRpha: Phase angle, x-rotation

  • TRpha : Phase angle, y-rotation

  • ZRpha : Phase angle, z-rotation