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*Wave-User-Defined |
 
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*Wave-User-Defined
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*Wave-User-Defined |
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To specify a User-Defined random sea wave spectrum or spectra.
Refer to User-Defined Wave Spectrum for further information on this feature.
Blocks of lines which define the wave loading parameters.
Block defining a user-specified spectrum with equal area discretisation. The third line can be repeated as often as necessary:
FREQUENCY=AREA
Max Freq. Increment, No. of Harmonics, Wave Directions [, Dominant Direction] [, Wave Spreading Exponent]
Frequency, Spectral Value
Block defining a user-specified spectrum with geometric progression discretisation. The third line can be repeated as often as necessary:
FREQUENCY=GP
Geometric Progression Factor, Wave Directions [, Dominant Direction] [, Wave Spreading Exponent]
Frequency, Spectral Value
The Wave Spreading Exponent for random sea analyses must be an even integer and defaults to 2. The Wave Spreading Exponent is omitted for frequency domain analyses and should not be specified for this type of analysis.
To define general wave spectra as a series of frequency/spectral ordinate pairs.
Input: |
Description |
Spectrum Name: |
The name of the user-defined spectrum. See Note (b). |
Frequency: |
A frequency value in Hz. |
Spectral Value: |
The corresponding value of the wave spectrum. |
To define a number of parameters relating to the specification of a general wave spectrum to be discretised using equal areas.
Input: |
Description |
Spectrum Name: |
The name of the user-defined spectrum. See Note (b). |
Max Frequency Increment: |
The maximum frequency increment in Hz. to be used in the spectral discretisation. See Note (c). This parameter defaults to a value of 0.05 Hz. |
No. of Harmonics: |
The number of harmonics to be used in the spectral discretisation. |
Wave Directions: |
The number of wave directions. The default of 1 gives a uni-directional random sea, greater than 1 gives a multi-directional sea. See Note (d). |
Dominant Direction: |
The wave direction in a uni-directional sea, or the dominant wave direction in a multi-directional random sea, measured in degrees anticlockwise from the global Y direction. The default is 0°. |
Wave Spreading Exponent: |
The exponent used in distributing wave energy between directions in a multi-directional random sea. This entry defaults to 2. See Note (d). |
To define a number of parameters relating to the specification of a general wave spectrum to be discretised using a geometric progression of frequencies.
Input: |
Description |
Spectrum Name: |
The name of the user-defined spectrum. See Note (b). |
Geometric Progression Factor: |
The geometric progression factor for the spectral discretisation. See Note (c). This parameter defaults to a value of 0.02. |
No. of Wave Directions: |
The number of wave directions. The default of 1 gives a uni-directional random sea, greater than 1 gives a multi-directional sea. See Note (d). |
Dominant Direction: |
The wave direction in a uni-directional sea, or the dominant wave direction in a multi-directional random sea, measured in degrees anticlockwise from the global Y direction. The default is 0°. |
Wave Spreading Exponent: |
The exponent used in distributing wave energy between directions in a multi-directional random sea. This entry defaults to 2. See Note (d). |
(a)A random sea analysis can consider combinations of wave spectra and/or regular waves. Refer to Wave Loading for a description of the available wave specification combinations.
(b)The specification of data when you want to input a wave spectrum directly, that is as a series of (frequency, spectral ordinate) data pairs, is in two parts. Naturally the most important part is the actual series of values. You input this using the User Spectrum table. The second part of the data for a user-specified spectrum comprises general parameters relating to the spectrum discretisation. This data is input using either the User Spectrum – Equal Area or User Spectrum – Geometric Progression table. Note that the Spectrum Name inputs are used to link each spectrum with its associated discretisation parameters.
(c)The wave spectrum may be discretised into segments based an equal area approach (which divides the area under the spectrum into segments of equal area) or a geometric progression approach (based on frequency increments that form a geometric progression). Refer to Spectrum Discretisation for a detailed discussion of this discretisation procedure.
(d)A multi-directional random sea is defined in terms of a dominant wave direction and the number of wave directions. Refer to Wave Energy Spreading for further information on this feature.