Post-processing

A program named HOS-Ocean-PostProcessing is provided for the post-processing of HOS-Ocean outputs. It should be run with an input file named input_post_process.dat containing necessary informations and described hereafter.

Input file

The input file has the following form and is assumed to be named input_post_process.dat

--- Choice of post-processing options
Wave-by-wave analysis        :: i_ana            :: 0
Wave-by-wave analysis probes :: i_ana_probes     :: 1
VP-card output               :: i_card           :: 0
Starting time analysis       :: T_start          :: 34.0
Stoping time analysis        :: T_stop           :: 64.0
--- Velocities/pressure cards
Minimum x in VP-card         :: x_min            :: 0.0
Maximum x in VP-card         :: x_max            :: 500.0
Minimum y in VP-card         :: y_min            :: 0.0
Maximum y in VP-card         :: y_max            :: 100.0
Minimum z in VP-card         :: z_min            :: -35.0
Maximum z in VP-card         :: z_max            :: 5.0
Number of points in z        :: i_zvect          :: 20
--- Input files
Tecplot version              :: tecplot          :: 11
Name of free-surface file    :: file_3d          :: 3d.dat
Name of probes file          :: file_probes      :: probes.dat
Name of modal description    :: file_mod         :: modes_HOS_SWENSE.dat

Choice of post-processing options

  • i_ana defines the wavefield analysis to perform (i_ana /= 0)

    • i_ana = 1 : computation of the moments of the free surface elevation η

    • i_ana = 2 : computation of the moments and wave-by-wave analysis along x-direction (for 2D or 3D wavefields)

    • i_ana = 3 : computation of the moments and wave-by-wave analysis along x and y direction (for 3D wavefields with sufficient directional spreading and domain size)

  • i_ana_probes specifies the computation of the moments and wave-by-wave analysis of wave probes signals (i_ana_probes = 1)

  • i_card defines the output of velocity and pressure cards (i_card /= 0)

    • i_card = 1 : Mesh is defined with constant z and (x,y) from HOS-ocean simulation. This is the most efficient way to generate cards or for coupling since it allows use of FFTs

    • i_card = 2 : Mesh is defined with boundary (free-surface) fitted z and (x,y) from HOS-ocean simulation.

  • T_start gives the time (in s) of the beginning of the post-processing (wavefield analysis and/or cards)

  • T_stop gives the time (in s) of the end of the post-processing (wavefield analysis and/or cards)

Velocities/pressure cards

This section of input file describes the mesh of the output of velocity and pressure card:

  • x_min is the minimum (in m) of the x-mesh

  • x_max is the maximum (in m) of the x-mesh

  • y_min is the minimum (in m) of the y-mesh (for 3D simulation)

  • y_max is the maximum (in m) of the y-mesh (for 3D simulation)

  • z_min is the minimum (in m) of the z-mesh

  • z_max is the maximum (in m) of the z-mesh (for i_card = 1)

  • i_zvect is the number of points to describe z vector

Input files

  • tecplot gives the tecplot version of output files

  • file_3d gives the name of file describing the free surface elevation (with possible relative path)

  • file_probes gives the name of file describing the probes signals (with possible relative path)

  • file_mod gives the name of file of modal amplitudes of volumic informations (with possible relative path)

Analysis of wavefield i_ana ≠ 0

The main idea of the different wavefield analysis provided in postprocessing of HOS-ocean is summarized hereafter

  • Moments of free surface elevation η are always computed: mean, standard deviation, skewness, kurtosis. These are basic informations useful for analysis

    • Analysis.dat file is created with these informations

  • Wave-by-wave analysis along x-direction (i_ana = 2)

    • 2D wave fields: compute H1/3 , Hmax , Amax and detect freak waves (i.e. waves with H>2Hs )

    • 3D wave fields: same as 2D wave fields with analysis done on eta(1:n1,1) (i.e. y=0)

    • Analysis.dat contains those informations

    • freak_waves.dat gives the free surface profile of each detected freak wave

    • Caract_freak_waves.dat gives the characteristics of detected freak waves (size, amplitude…)

  • Wave-by-wave analysis along x and y direction (i_ana = 3)

    • Available for 3D wavefields with sufficient directional spreading and domain size

    • 3D waves are detected assuming they are propagating along x direction and that their transverse direction is along y

    • Compute H1/3 , Hmax , Amax and detect freak waves (i.e. waves with H>2Hs )

    • Analysis.dat contains those informations

    • freak_waves.dat gives the 3D free surface profile of each detected freak wave

    • Caract_freak_waves.dat gives the characteristics of detected freak waves (size, amplitude…)

Analysis of probe signals i_ana_probes = 1

The analysis of the probe signals consists in evaluating the moments of the temporal signal, the maximum wave height, the maximum crest height, as well as the significant wave height and H1/3 . The informations are written in the file Probes_ana.dat

Description of kinematics inside fluid domain i_card ≠ 0

HOS-ocean is able to create a modal description of some volumic informations in the fluids. All necessary informations to compute velocities, pressure, acceleration (or whatever derivatives of these quantities) are included in this file usually named modes_HOS_SWENSE.dat

We give as an example of treatment of this file the possibility to create representation of velocities and pressure field (i_card /= 0). Depending on the choice of user following files are created:

  • data_VP_card.dat gives useful informations about the card created in VP_card.dat. This is used at ECN as coupling informations file. (i_card=1)

  • VP_card.dat contains the velocities and pressure card in the case i_card=1, i.e. when the mesh is at constant z. This file is adapted to Tecplot visualization.

  • VP_card_fitted.dat contains the velocities and pressure card in the case i_card=2, i.e. when a boundary fitted (free surface) mesh is used. This file is adapted to Tecplot visualization.

Note that the process used to create those cards is similar to the one used for coupling between HOS and CFD solver (see the dedicated package for coupling Grid2Grid).

We refer to Ferrant et al. [2003], Luquet et al. [2004], Kim et al. [2024] for details about the coupling strategy.