Wind

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[WIND]

The reference manual in pdf can be found here.

[BODY#]

Each vessel has its own characteristics with regards to wind, that's why a few records are added to the BODY section:

Keyword Unit Description Options Version
Lpp
[m] Length between perpendicular (compulsory) aNySIM_V8.0
Beam [m] Breadth of body (compulsory) aNySIM_V8.0
CoG [m] Cog's coordinates (compulsory) aNySIM_V8.0
WindFrontArea [m2] Surface of front area (compulsory) aNySIM_V8.0
WindSideArea [m2] Surface of side area (compulsory) aNySIM_V8.0
WindCoefFile [-] Wind coefficient file (compulsory) aNySIM_V8.0

[WIND]

Keyword Unit Description Options Version
WindType [-] 3 choices:
Constant
Spectrum
Timetrace
(compulsory) aNySIM_V8.0
MeanSpeed [m/s] Mean wind speed (compulsory for constant wind and spectrum) aNySIM_V8.0
MeanDirection [deg] Mean wind direction ('going to' direction in global EF referential) (compulsory) aNySIM_V8.0
WindSpeedSpectrum [-] 8 choices:
Harris
API
Ochi
Wills
NPD
Davenport
UserDef
None
(compulsory for wind-spectrum) aNySIM_V8.0
WindDirectionSpectrum [-] 3 choices:
White noise
UserDef
None
(optional) aNySIM_V8.0
WindDirectionStDev [deg] White noise parameter (compulsory for White noise) aNySIM_V8.0
UserDefSpeedSpectrumFile [-] File path and name of wind-speed-spectrum (compulsory for UserDef) aNySIM_V8.0
UserDefDirSpectrumFile [-] File path and name of wind-direction-spectrum (compulsory for UserDef direction spectrum) aNySIM_V8.0
SeedNumberSpeed [-] Seed number (compulsory for any wind-spectrum) aNySIM_V8.0
SeedNumberDir [-] Seed number (compulsory for any direction spectrum) aNySIM_V8.0
WindTimeseriesFile [-] File path and name of wind-speed-timetrace (compulsory if WindType is Timetrace) aNySIM_V8.0
ApplyShielding [-] Boolean switch (optional)
UpstreamBodyNr [-] Index of upstream body in shielding model (compulsory if ApplyShielding is true) aNySIM_V8.0
DownstreamBodyNr [-] Index of downstream body in shielding model (compulsory if ApplyShielding is true) aNySIM_V8.0
WindWakeFile [-] File path and name of wind-speed-timetrace (compulsory if ApplyShielding is true) aNySIM_V8.0

[Output]

The following signals can be written in the output files.

Alias Index1 Index2 Description Version
WindSp - - Absolute wind speed ([m/s]) aNySIM_V8.0
WindDr - - Absolute wind direction in engineering referential ([deg]) aNySIM_V8.0
Fwind iBody iMode Forces at cog in the local referential of the body with index iBody (6 modes, [kN],[kN.m]) aNySIM_V8.0

The format of the user supplied files

User supplied wind speed spectrum

The wind speed spectrum file is a free-format file. The first line contains the reference height to which the spectrum applies. The second line gives the units of the frequencies, which are either "Hz" or "rad/s". Next two columns follow, the first column with the wind gust frequencies and the second column with the wind speed spectral densities in (m/s)^2^s. The frequencies need not be equidistant, but must be in increasing order. There is no limit to the number of frequencies. An example is shown below:


ReferenceHeight = 10.0
FrequencyUnits = Hz
0.01 15.0
0.02 12.0
0.03 8.0
0.06 3.0
0.08 1.0
0.10 0.2

User supplied wind direction spectrum

The wind direction spectrum file is a free-format file. The first line contains the reference height to which the spectrum applies. The second line gives the units of the frequencies, which are either "Hz" or "rad/s". Next two columns follow, the first column with the wind gust frequencies and the second column with the wind direction spectral densities in deg2s. The frequencies need not be equidistant, but must be in increasing order. There is no limit to the number of frequencies. An example is shown below:


ReferenceHeight = 10.0
FrequencyUnits = rad/s
0.01 15.0
0.5 0.2

User supplied wind timetraces

The wind timetraces file is a free-format file. The first line contains the reference height to which the timetraces apply. Next three columns follow, the first column with the time in s, the second column with the wind speed in m/s and the third column with the wind direction in deg. The timesteps need not be equidistant, but must be in increasing order. There is no limit to the number of timesteps.

Please note that the aNySIM simulation should not exceed the last timestep of the user supplied timetraces, otherwise the simulation will be stopped premature.

An example is shown below:


ReferenceHeight = 10.0
0     0  180
30   12  175
60   24  170
90   25  160
120  26  150
200  25  150
1200 24  150
1800 12  180

User supplied wind coefficients

The wind coefficients may be given for one or more segments of a body. Dividing a body into several segments is only useful when the wind speed and direction are position dependent, i.e. in case of wind shielding.

The user supplied wind coefficients are defined with respect to xmoment (relative to the centre of the segment, i.e. st. 10 if only one segment is defined), the CL and waterplane area in x,y and z-direction. Anysim will translate the forces and moments of all segments to one Fx, Fy and Mz at CoG.

The number of segments and the number of directions, for which the coefficients are given, are not limited. Because there are no symmetry options the coefficients must be given for all directions, starting at 0 degrees upto 360 degrees. The directions need not be equidistant, but must be in increasing order. The wind module interpolates linearly between directions to determine the coefficients.

The directions are defined in a vessel-fixed, right-handed system of axes: 0 degrees denotes a direction from stern to bow (along the positive X-axis), 90 degrees from starboard to port side (along the positive Y-axis), and so on. The positive rotation is counter-clockwise.

Below an example is given of a file with wind coefficients for a vessel divided into three segments. The format of the file is equal to the format of the SHUTTLE coefficients file, with the exception that for aNySIM three columns are added because aNySIM calculates the wind forces for six degrees of freedom instead of three. Note that a dot (.) has to be used as decimal separator.


Nsegments 3
ReferenceLength 300
ReferenceHeight 10
segment 1
segmentheight 46.75
xmin -150
xmax -50
xmoment 0.0
Ndirections 9
  0.0    0.5457  -0.0000   0.0  0.0  0.0   0.0000
 45.0    0.3936   0.5168   0.0  0.0  0.0  -0.2104
 90.0    0.3918   0.4548   0.0  0.0  0.0  -0.1698
135.0   -0.3196   0.2970   0.0  0.0  0.0  -0.1128
180.0   -0.8704  -0.0036   0.0  0.0  0.0   0.0012
225.0   -0.3198  -0.2964   0.0  0.0  0.0   0.1120
270.0    0.3260  -0.4512   0.0  0.0  0.0   0.1682
315.0    0.3496  -0.5098   0.0  0.0  0.0   0.2066
360.0    0.5457  -0.0000   0.0  0.0  0.0   0.0000
segment 2
segmentheight 21.0
xmin -50.
xmax 50.
xmoment 0.0
Ndirections 9
  0.0   0.0156   0.0000  0.0  0.0  0.0   0.0000
 45.0   0.0769   0.1303  0.0  0.0  0.0   0.0006
 90.0  -0.0148   0.3033  0.0  0.0  0.0  -0.0034
135.0  -0.0079   0.1428  0.0  0.0  0.0  -0.0017
180.0  -0.0570   0.0071  0.0  0.0  0.0  -0.0005
225.0  -0.0149  -0.1500  0.0  0.0  0.0   0.0009
270.0   0.0412  -0.3134  0.0  0.0  0.0   0.0034
315.0   0.1358  -0.1140  0.0  0.0  0.0  -0.0001
360.0   0.0156   0.0000  0.0  0.0  0.0   0.0000
segment 3
segmentheight 21.0
xmin 50
xmax 150
xmoment 0.0
Ndirections 9
 0.0     0.0490   0.0000   0.0  0.0  0.0   0.0000
 45.0   -0.0604   0.0547   0.0  0.0  0.0   0.0131
 90.0   -0.1928   0.2566   0.0  0.0  0.0   0.0834
135.0   -0.0025   0.3076   0.0  0.0  0.0   0.1136
180.0   -0.0658   0.0008   0.0  0.0  0.0   0.0006
225.0   -0.0061  -0.3138   0.0  0.0  0.0  -0.1151
270.0   -0.1980  -0.2504   0.0  0.0  0.0  -0.0807
315.0   -0.0474  -0.0510   0.0  0.0  0.0  -0.0115
360.0    0.0490   0.0000   0.0  0.0  0.0   0.0000

The reference length is used to scale the segment length, the segment height and segment "xmoment". When wind shielding is applied the reference length of the upstream body is also used to scale the wind wake field.

The reference height is the height above sealevel at which the wind speed is defined. Because in aNySim it is not possible to define a vertical wind profile the program cannot convert the wind speed from one reference height to another. Therefore, the reference height of the coefficients should be equal to the reference height of the user defined wind spectrum or wind timetraces. With a standard wind spectrum, or constant wind speed, it is assumed that the reference height is 10 m.

The segment height is used in the shielding calculation to determine the average pressure. The height is divided into 10 slices. At each slice the pressure is calculated using the X-, Y- and Z-components of the wind wake field and then the average is calculated of the 10 slice pressures.

The segment "xmin" and "xmax" values define the rear and fore ends of the segment relative to the vessel midship. These values are used to calculate the position of the segment in the wind wake field.

The segment "xmoment" is the location at the segment, relative to its centre (station 10 if only one segment is defined), where the yaw moment coefficients are defined. Anysim will translate the yaw-moments of the different segments to one yaw-moment at CoG.

Please note that the sum of the segment lengths S(xmax - xmin) should be equal to the reference length.