Running HOS-NWT

HOS-NWT has been developed for command-line run with an input file containing all specifications needed (name can be arbitrary but will be referred to input_HOS-NWT.dat in the following for clarity). The following commands can be executed:

  • Linux environment (in a terminal):

./HOS-NWT input_HOS-NWT.dat

  • Windows environment (using the standard command prompt cmd):

HOS-NWT.exe input_HOS-NWT.dat

Note

All output files will be created in a directory Results that has to be created before the run by the user.

Input file

The input file has the following form and is usually named input_HOS-NWT.dat. This subsection describes in details the content of the file.

---------------------- Tank dimensions -----------------------
Length(m) of the wavetank    :: xlen             :: 120.0d0
Beam(m) of the wavetank      :: ylen             :: 100.d0
Depth(m) of the wavetank     :: h                :: 5.d0
------------------------ Select case --------------------------
Choice of computed case      :: icase            :: 3
------------------ Sloshing case (icase = 1) ------------------
Number of the natural mode   :: islosh           :: 3
Amplitude (m) of the mode    :: aslosh           :: 0.2d0
--------------- Monochromatic case (icase = 2) ----------------
Amplitude (m) of wave train  :: amp_mono         :: 0.1d0
Frequency (Hz) of wave train :: nu_mono          :: 0.5588d0
Angle (deg) from x-axis      :: theta_mono       :: 0.d0
Phasis (rad) of wave train   :: ph_mono          :: 0.d0
Directional wmk type         :: ibat             :: 2
Wave target distance (ibat=3):: xd_mono          :: 18.d0
-------------------- File case (icase = 3) --------------------
Name of frequency file       :: file_name        :: Hs4_Tp10
Frequency cut-off            :: i_cut            :: 0
Low cut_off frequency (Hz)   :: nuc_low          :: 0.3d0
High cut_off frequency (Hz)  :: nuc_high         :: 3.d0
------------------ Irregular wave (icase=4) -------------------
Significant wave height (m)  :: Hs               :: 0.05d0
Peak period (s)              :: Tp               :: 1.d0
Shape factor (Jonswap)       :: gamma            :: 3.3d0
Seed number for random numb. :: iseed            :: 513
-------------------- Wavemaker definition ---------------------
Nonlinear order of wavemaker :: i_wmk            :: 2
Type (1: piston, 2: hinged)  :: igeom            :: 2
Rotation axis distance       :: d_hinge          :: 1.d0
Time ramp                    :: iramp            :: 0
Time ramp duration (s)       :: Tramp            :: 5.0d0
----------------------- Numerical beach -----------------------
Absorption numerical beach   :: iabsnb           :: 1
Beginning front num. beach   :: xabsf            :: 0.8d0
Absorption strength front    :: coeffabsf        :: 1.d0
------------- Elevation/Velocity-Pressure probes --------------
Use of probes                :: iprobes          :: 1
Filename of probe positions  :: pro_file         :: prob.inp
---------------------- Time-integration -----------------------
Duration of the simulation   :: T_stop           :: 50.0d0
Time tolerance: RK 4(5)      :: toler            :: 1.e-4
Output frequency             :: f_out            :: 30.d0
--------------------------- Output ----------------------------
Output: 1-dim. ; 0-nondim.   :: idim             :: 1
free surface plot            :: i3d              :: 0
modes plot                   :: imodes           :: 0
wavemaker motion plot        :: iwmk             :: 0
Swense output 1='yes',0='no' :: i_sw             :: 0
HDF5 output 1='yes',0='no'   :: is_hdf5          :: 0
----------------------- Discretization ------------------------
Number of points in x-dir.   :: n1               :: 512
Number of points in y-dir.   :: n2               :: 1
Number of points in y-dir.   :: n3               :: 17
HOS nonlinearity order       :: mHOS             :: 3
Dealiasing parameters in x   :: p1               :: 3
Dealiasing parameters in y   :: p2               :: 1
Filtering in x-direction     :: coeffiltx        :: 1.d0
Filtering in y-direction     :: coeffilty        :: 1.d0
Filtering in z-direction     :: coeffiltz        :: 1.d0
--------------------- Wave breaking type ---------------------
Breaking model type          :: ibrk             :: 0
---------- Tian model characteristics (ibrk=1 or 3) ----------
Breaking threshold           :: threshold        :: 0.85d0
alpha eddy_viscosity         :: alpha_eddy_vis   :: 0.02d0
Length ramp visc. (wrt Lc)   :: ramp_eddy        :: 0.25d0
Change of breaking length    :: fact_Lbr         :: 1.d0
Change of breaking duration  :: fact_Tbr         :: 1.d0
cubic spline interpolant     :: numspl           :: 5
Additional constant visc.    :: eqv_vis          :: 0.d0
-------- Chalikov model characteristics (ibrk=2 or 3) --------
Filter order                 :: order_filt       :: 1
Filter param                 :: r_filt           :: 0.75d0
Filter coefficient           :: coeffilt_chalikov:: 0.9d0
Diffusion strength           :: Cb               :: 0.03d0
Diffusion threshold          :: threshold_s      :: 75.d0

Tank dimension

  • xlen is the length (in m) of the wave tank (Lx in Fig. 2)

  • ylen is the beam (in m) of the wave tank (Ly in Fig. 2, useful only in 3D)

  • h is the depth (in m) of the wave tank (constant)

_images/HOS_NWT_1.png

Fig. 2 Wave tank and coordinate system

Description of initial conditions

  • icase = 1 : Sloshing case

    • Computation starts with a normal mode of the tank (in x-direction) of a given amplitude. It is defined by islosh (mode number) and aslosh (amplitude in m)

  • icase = 2 : Monochromatic case

    • Regular wave is generated in the NWT

    • User defines amplitude (amp_mono in m), frequency (nu_mono in Hz), phase (ph_mono in rad)

    • 3D simulations uses in addition

      • theta_mono: the angle of propagation (in deg)

      • ibat: the method used for directional wave generation. ibat=2 uses snake’s principle and ibat=3 uses Dalrymple’s method

      • xd_mono: uses the wave target distance (in m) for Dalrymple’s method (ibat=3)

  • icase = 3 and 31 and 32 and 33 : File case

    • Wavemaker movement is deduced from input file named ‘file_name’

    • Fine description wavemaker motion description in input files may be found in the Wavemaker motion from file section:

      • icase=3: file_name.dat describes the frequency components of wavemaker movement and file_name.cfg describes the configuration of wavemaker

      • icase=31: file_name.txt is an output of control software used in ECN Wave Basin

      • icase=32: file_name.txt is an output of control software used in ECN Towing Tank

      • icase=33: file_name.txt is an output of control software used in other tanks

    • i_cut specifies if a frequency cut off is used (i_cut=1) or not. Latter is defined by low nuc_low and high nuc_high cut-off frequencies (in Hz)

  • icase = 4 and 41 : Irregular wave

    • Wavemaker movement creates an irregular wave field with a given Hs and Tp

      • icase = 4: JONSWAP spectrum with gammashape factor

      • icase = 41: Bretschneider spectrum

    • iseed defines the number used for random wave generation

Wavemaker definition

  • i_wmk defines the order of non-linearity used for the wavemaker (recommended value is i_wmk=2 but it may be 1,2 or 3)

  • igeom defines the wavemaker vertical shape (1: piston, 2: hinged, see Fig. 3)

  • d_hinge defines for hinged wavemaker the rotation axis distance (from bottom in m, d_hinge >= 0, see d in Fig. 3)

  • iramp specifies the possible use of a time ramp on the wavemaker movement at the beginning of the simulation (iramp /= 0) and its shape (1: linear, 2: 2nd order polynom, 4: 4th order polynom)

  • Tramp is the duration (in s) of the time ramp on the wavemaker movement at the beginning of the simulation

_images/HOS_NWT_2.png

Fig. 3 Wavemaker shape: piston (igeom=1, left) and hinged (igeom=2, right)

Numerical beach

  • iabsnb defines the use (iabsnb=1) or not (iabsnb=0) of numerical beach at the end of the tank

  • xabsf defines the location of the beginning of the numerical beach (ratio to the total length of wave tank xlen). The absorbing beach starts at x=xabsf*xlen.

  • coeffabsf defines the absorption strength of the previously defined numerical beach

Elevation/Velocity-pressure probes

  • iprobes defines the possible use (iprobes /= 0) of probes

    • iprobes=1: free-surface probes, each line gives location x (and y in 3D)

    • iprobes=2: pressure probes, each line gives location x z (or x y z in 3D)

  • pro_file defines the file name of probes position. In the input file example provided in Input file, it is named prob.inp

_images/HOS_NWT_4.png

Fig. 4 Probe signals obtained for 3D focused wave

Time-integration

  • T_stop is the duration (in s) of the simulation (and of the wavemaker movement)

  • toler gives the tolerance of the adaptative Runge-Kutta scheme

  • f_out gives the output frequency (in Hz) of the output files described in the following paragraph

Output files

Depending on the choices (0 to disable output) made in the input file (see Input file), different output files are created. They are created in a specific folder Results with a specific format dedicated to Tecplot visualization. Those are ASCII files that can be easily read with Python, Matlab, etc.

The parameter idim specifies if output are dimensional(=1) or nondimensional(=0).

  • 3d.dat gives the 3D free surface quantities (elevation η and surface velocity potential φs ) as function of time: i3d=1

  • HOS_modes.dat gives the modal amplitudes of free surface quantities (η and φs ) as function of time: imodes=1

  • vol_energy.dat gives the temporal evolution of volume and energy

  • wmk_motion.dat gives the wavemaker motion as function of time: iwmk=1

  • probes.dat gives the free surface elevation at specific locations given in the file specified in pro_file: i_prob=1

  • modes_HOS_SWENSE.dat gives the file containing modal information of volumic HOS field for visualization, physical interpretation of wavefield, or possible coupling between HOS and wave-structure interactions model (see the dedicated package for coupling Grid2Grid): see post-processing section: i_sw=1

Those are standard outputs in ASCII format. The parameter is_hdf5 allows the use of HDF5 format instead of ASCII (for instance for data size concerns).

Note

HDF5 outputs requires the code to be compiled with the dedicated option (see corresponding section)

Note

MPI outputs are slightly modified for the files describing 3D spatial or modal quantities. Each computational core will output the spatial/modal part it has in memory. For instance the output file 3d.dat will be replaced in the case of HOS-NWT compiled with MPI and executed with 4 processes by 3d_000.dat, 3d_001.dat, 3d_002.dat, and 3d_003.dat files

Numerical parameters

  • n1 is the number of spatial points (or equivalently modes) used in the x-direction

  • n2 is the number of spatial points (or equivalently modes) used in the y-direction. For a 2D simulation, choose n2=1

  • n3 is the number of spatial points (or equivalently modes) used in the z-direction, to describe the wave maker motion

  • mHOS is the HOS order of nonlinearity

  • p1 describes the methodology used for dealiasing in x-direction. For total dealiasing p1=mHOS should be used while for partial dealiasing, one should use p1<mHOS

  • p2 describes the methodology used for dealiasing in y-direction. For total dealiasing p2=mHOS should be used while for partial dealiasing, one should use p2<mHOS. For a 2D simulation, choose p2=1

  • coeffiltx parameterizes a possible filtering along x-direction. The mode numbers in the range [coeffiltx;1]*n1 are set to zero

  • coeffilty parameterizes a possible filtering along y-direction. The mode numbers in the range [coeffilty;1]*n2 are set to zero

  • coeffiltz parameterizes a possible filtering along x-direction. The mode numbers in the range [coeffiltz;1]*n3 are set to zero

Note

The user needs to choose the numerical parameters wisely to achieve accurate numerical solution. Some elements are provided in corresponding section

Wave breaking model

The end of the input file is dedicated to the parametrization of the wave breaking models.

Warning

The breaking models are only implemented for unidirectional waves for now (n2=1)

  • ibrk defines the use of the wave breaking models in HOS-NWT

    • ibrk=0: no model for wave breaking (original HOS-NWT solver)

    • ibrk=1: Barthelemy’s model for breaking onset and Tian’s model for the dissipation, see [Seiffert et al., 2017, Seiffert and Ducrozet, 2018]:

    • ibrk=2: Chalikov’s breaking model for the breaking onset and dissipation, see [Seiffert and Ducrozet, 2017]:

    • ibrk=3: Combined use of previous models (ibrk=1 and ibrk=2)

  • Barthelemy-Tian model parameters are the following (ibrk=1 and ibrk=3)

    • threshold stands for the threshold used in Barthelemy breaking onset, which is the ratio of fluid velocity on phase velocity (default is 0.85)

    • alpha_eddy_vis stands for the eddy viscosity used in Tian’s dissipation model (default is 0.02)

    • ramp_eddy stands for the length (with respect to crest length) of the spatial ramp used to apply eddy viscosity (default is 0.25)

    • fact_Lbr can be used to increase the dissipation length parameterized in Tian’s model (default is 1.0)

    • fact_Tbr can be used to increase the dissipation duration parameterized in Tian’s model (default is 1.0)

    • numspl stands for the spline interpolant used to refine the HOS grid for better estimate of crest speed (default is 5)

    • eqv_vis stands for a constant additional viscosity added to the whole spatial domain (default is 0.0)

  • Chalikov model parameters are the following (ibrk=2 and ibrk=3)

    • order_filt stands for the exponent applied to the maximum wavenumber in hyperviscous filter continuously applied in Chalikov’s model (default 1.0)

    • r_filt defines the constant parameter of the hyperviscous filter continuously applied in Chalikov’s model (default 0.25)

    • coeffilt_chalikov defines the application of the hyperviscous filter. The latter starts is applied on mode numbers in [coeffilt_chalikov,1]*n1

    • Cb stands for the strength of the dissipation applied in Chalikov’s model (default 0.05). This multiplies the curvature of the free surface

    • threshold_s stands for the threshold used in Chalikov’s model for breaking onset, based on the curvature of the free surface (default 10.0)

Examples

Some input files examples are available in the Benchmark directory. See Benchmark cases for details.

Important notice

For irregular wave motion (i.e. icase=3, 31, 32, 33, 4 or 41), the description of wavemaker motion is filtered above a cut-off limit of 4 Hz. In usual test cases, this is not a problem since HOS-NWT is dedicated to the generation and propagation of gravity waves (no capillary effects taken into account): waves with frequencies higher than 4 Hz could not be considered pure gravity waves. However, this may be changed in wavemaking_HOS.f90file for specific purpose.