USER MANUAL SWAN Cycle III version 40.72A
USER MANUAL SWAN Cycle III version 40.72A USER MANUAL SWAN Cycle III version 40.72A
30 Chapter 4 [yexc] CIRCLE SECTOR [dir1] [dir2] [mdc] [flow] [fhigh] [msc] x−coordinate considered in the file of the x−coordinates, see command READGRID COOR). Required if this option EXCEPTION is used. Default: [xexc] = 0.0. the value which the user uses to indicate that a grid point is to be ignored in the computations (this value is provided by the user at the location of the y−coordinate considered in the file of the y−coordinates, see command READGRID COOR). Required if this option EXCEPTION is used. Default: [yexc] = [xexc]. this option indicates that the spectral directions cover the full circle. This option is default. this option means that only spectral wave directions in a limited directional sector are considered; the range of this sector is given by [dir1] and [dir2]. It must be noted that if the quadruplet interactions are to be computed (see command GEN3), then the SECTOR should be 30 o wider on each side than the directional sector occupied by the spectrum (everywhere in the computational grid). If not, then these computations are inaccurate. If the directional distribution of the spectrum is symmetric around the centre of the SECTOR, then the computed quadruplet wave-wave interactions are effectively zero in the 30 o range on either end of the SECTOR. The problem can be avoided by not activating the quadruplet wave-wave interactions (use command GEN1 or GEN2) or, if activated (with command GEN3), by subsequently de-activating them with command OFF QUAD. the direction of the right-hand boundary of the sector when looking outward from the sector (required for option SECTOR) in degrees. the direction of the left-hand boundary of the sector when looking outward from the sector (required for option SECTOR) in degrees. number of meshes in θ−space. In the case of CIRCLE, this is the number of subdivisions of the 360 degrees of a circle, so ∆θ = [360 o ]/[mdc] is the spectral directional resolution. In the case of SECTOR, ∆θ = ([dir2] - [dir1])/[mdc]. The minimum number of directional bins is 3 per directional quadrant. lowest discrete frequency that is used in the calculation (in Hz). highest discrete frequency that is used in the calculation (in Hz). one less than the number of frequencies. This defines the grid resolution in frequency-space between the lowest discrete frequency [flow] and the highest discrete frequency [fhigh]. This resolution is not constant, since the frequencies are distributed logarithmical: f i+1 = γf i with γ is a constant. The minimum number of frequencies is 4. The value of [msc] depends on the frequency resolution ∆f that the user requires. Since, the frequency distribution on the frequency axis is logarithmic, the relationship is:
⎛ ∆f = ⎝−1 + Description of commands 31 [ ] ⎞ [fhigh] 1/[msc] ⎠ [flow] f Vice versa, if the user chooses the value of ∆f/f (= γ − 1.), then the value of [msc] is given by: [msc] = log([fhigh]/[flow])/ log(1 + ∆f/f) In this respect, it must be observed that the DIA approximation of the quadruplet interactions (see command GEN3) is based on a frequency resolution of ∆f/f = 0.1 and hence, γ = 1.1. The actual resolution in the computations should therefore not deviate too much from this. Alternatively, the user may only specifies one of the following possibilities: • [flow] and [msc]; SWAN will compute [fhigh], such that γ = 1.1, and write it to the PRINT file. • [fhigh] and [msc]; SWAN will compute [flow], such that γ = 1.1, and write it to the PRINT file. • [flow] and [fhigh]; SWAN will compute [msc], such that γ = 1.1, and write it to the PRINT file. For illustration of a regular grid with its dimensions, see Figure 4.1. problem coordinates yp−axis (mxc,myc) yc−axis (0,myc) computational grid (mxc,0) xc−axis ypc (0,0) alpc xpc problem coordinates xp−axis Figure 4.1: Coordinates of the origin [xpc] and [ypc], the orientation [alpc] and the grid point numbering of the computational grid with respect to the problem coordinates system. Note that in case of spherical coordinates the xc− and xp−axes both point East.
- Page 1: SWAN USER MANUAL SWAN Cycle III ver
- Page 5 and 6: Contents 1 Introduction 1 2 General
- Page 7 and 8: TABLE . . . . . . . . . . . . . . .
- Page 9 and 10: Chapter 1 Introduction The informat
- Page 11 and 12: Chapter 2 General definitions and r
- Page 13 and 14: General definitions and remarks 5 r
- Page 15 and 16: General definitions and remarks 7 I
- Page 17 and 18: which SWAN performs the computation
- Page 19 and 20: General definitions and remarks 11
- Page 21 and 22: General definitions and remarks 13
- Page 23 and 24: General definitions and remarks 15
- Page 25 and 26: General definitions and remarks 17
- Page 27 and 28: Chapter 3 Input and output files 3.
- Page 29 and 30: Chapter 4 Description of commands 4
- Page 31 and 32: (h) Commands to write or plot outpu
- Page 33 and 34: Description of commands 25 ’name
- Page 35 and 36: Description of commands 27 Default:
- Page 37: Description of commands 29 mesh. Th
- Page 41 and 42: Description of commands 33 • Easy
- Page 43 and 44: Description of commands 35 grids ca
- Page 45 and 46: Description of commands 37 y ′
- Page 47 and 48: Description of commands 39 [fac]
- Page 49 and 50: Description of commands 41 ’(10X,
- Page 51 and 52: Description of commands 43 | | East
- Page 53 and 54: Description of commands 45 CONSTANT
- Page 55 and 56: Description of commands 47 points o
- Page 57 and 58: Description of commands 49 CRAY WKS
- Page 59 and 60: Description of commands 51 This com
- Page 61 and 62: Description of commands 53 | JANSse
- Page 63 and 64: Description of commands 55 [Csh3] c
- Page 65 and 66: Description of commands 57 [ursell]
- Page 67 and 68: Description of commands 59 [slope]
- Page 69 and 70: Description of commands 61 [cgmod]
- Page 71 and 72: Description of commands 63 < > [lim
- Page 73 and 74: Description of commands 65 SIGIMPL
- Page 75 and 76: Description of commands 67 ’sname
- Page 77 and 78: Description of commands 69 (see bel
- Page 79 and 80: Description of commands 71 [alpn] d
- Page 81 and 82: Description of commands 73 ‘long
- Page 83 and 84: | HSign | | | | HSWEll | | | | DIR
- Page 85 and 86: Description of commands 77 | WLENgt
- Page 87 and 88: Description of commands 79 QP DEPTH
30 Chapter 4<br />
[yexc]<br />
CIRCLE<br />
SECTOR<br />
[dir1]<br />
[dir2]<br />
[mdc]<br />
[flow]<br />
[fhigh]<br />
[msc]<br />
x−coordinate considered in the file of the x−coordinates, see command<br />
READGRID COOR). Required if this option EXCEPTION is used.<br />
Default: [xexc] = 0.0.<br />
the value which the user uses to indicate that a grid point is to be ignored<br />
in the computations (this value is provided by the user at the location of the<br />
y−coordinate considered in the file of the y−coordinates, see command<br />
READGRID COOR). Required if this option EXCEPTION is used.<br />
Default: [yexc] = [xexc].<br />
this option indicates that the spectral directions cover the full circle.<br />
This option is default.<br />
this option means that only spectral wave directions in a limited directional sector<br />
are considered; the range of this sector is given by [dir1] and [dir2].<br />
It must be noted that if the quadruplet interactions are to be computed (see<br />
command GEN3), then the SECTOR should be 30 o wider on each side than the<br />
directional sector occupied by the spectrum (everywhere in the computational grid).<br />
If not, then these computations are inaccurate. If the directional distribution of the<br />
spectrum is symmetric around the centre of the SECTOR, then the computed<br />
quadruplet wave-wave interactions are effectively zero in the 30 o range on<br />
either end of the SECTOR. The problem can be avoided by not activating<br />
the quadruplet wave-wave interactions (use command GEN1 or GEN2) or, if<br />
activated (with command GEN3), by subsequently de-activating them with<br />
command OFF QUAD.<br />
the direction of the right-hand boundary of the sector when looking outward from<br />
the sector (required for option SECTOR) in degrees.<br />
the direction of the left-hand boundary of the sector when looking outward from<br />
the sector (required for option SECTOR) in degrees.<br />
number of meshes in θ−space. In the case of CIRCLE, this is the number of<br />
subdivisions of the 360 degrees of a circle, so ∆θ = [360 o ]/[mdc] is the spectral<br />
directional resolution. In the case of SECTOR, ∆θ = ([dir2] - [dir1])/[mdc].<br />
The minimum number of directional bins is 3 per directional quadrant.<br />
lowest discrete frequency that is used in the calculation (in Hz).<br />
highest discrete frequency that is used in the calculation (in Hz).<br />
one less than the number of frequencies. This defines the grid resolution<br />
in frequency-space between the lowest discrete frequency [flow] and the highest<br />
discrete frequency [fhigh]. This resolution is not constant, since the frequencies<br />
are distributed logarithmical: f i+1 = γf i with γ is a constant. The minimum<br />
number of frequencies is 4.<br />
The value of [msc] depends on the frequency resolution ∆f that the user requires.<br />
Since, the frequency distribution on the frequency axis is logarithmic, the<br />
relationship is:
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