Wave Loading |
 
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Wave Loading |
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Flexcom presents a wide range of wave specification options. There are three regular wave options as follows:
•Regular Airy describes linear Airy wave theory.
•Stokes V describes Stokes V wave theory, and presents the various options for the calculation of vessel response.
•Dean’s Stream describes Dean’s Stream wave theory, and presents the various options for the calculation of vessel response.
There are five options for defining a random seastate in terms of a wave spectrum, as follows:
•Pierson-Moskowitz describes the Pierson-Moskowitz wave spectum model, and presents the various formats for input data specification.
•Jonswap describes the Jonswap wave spectum model, and presents the various formats for input data specification.
•Ochi-Hubble outlines the Ochi-Hubble wave spectum model.
•Torsethaugen outlines the Torsethaugen wave spectum model.
•User-defined describes a facility whereby you can input an arbitrary wave spectrum directly in terms of a series of data pairs.
You may also define a random seastate in terms of a time history of water surface elevation; the name of the file containing the time is the actual program input in the case. When this option is invoked, Flexcom first calculates a wave spectrum from the time history. The output from this process is then treated as a series of regular waves, each with its individual period, amplitude and phase.
Waves can be specified in various combinations in a time domain dynamic analysis as follows:
(i)One Stokes V wave.
(ii)One Dean’s Stream wave.
(iii)One or multiple regular Airy waves.
(iv)One or multiple random seas (characterised by Pierson-Moskowitz, Jonswap, Ochi-Hubble, Torsethaugen or User-Defined spectra).
(v)One wave elevation time history.
(vi)One or multiple random seas of any type combined with one or more regular Airy waves.
The full range of inputs is available to you to define a spectrum for the above combinations. For example, each spectrum can have a separate dominant direction, and may be uni- or multi-directional, regardless of combination.
A narrower range of combinations is available in the frequency domain:
(i)One regular Airy wave.
(ii)Multiple regular Airy waves. This option consists of a series of regular wave analyses over a range of periods, each wave having the same amplitude. The solution for each wave period is performed independently. The only use of this option is to generate RAOs of the response. These are calculated by dividing the amplitude of the response by the wave amplitude, so it is often the case that the wave is of unit amplitude.
(iii)One random sea, characterised by a Pierson-Moskowitz, Jonswap, Ochi-Hubble, Torsethaugen or user-defined wave spectrum. Flexcom first discretises the spectrum into component harmonics, before assembling and solving the equations of motion at each harmonic. However, the solutions at each harmonic are not independent, but are in fact coupled through the drag linearisation process. Further details are provided in Frequency Domain Analysis, where the frequency domain theory is described in detail.
Flexcom provides a helpful Wave Spectrum Plot option in the user interface. If there is random sea data defined in the analysis, it displays a plot of the resultant wave spectrum. There may be more than one wave spectrum defined, in which case the various spectra are combined. Another helpful feature is the Water Elevation Plot option. This affords you an instantaneous preview of results, by producing a time history of the water surface elevation at the origin. This option is particularly useful if you are interested in performing a random sea analysis in the time domain – you can verify the relevant input data is correct before undertaking a full 3-hour simulation.
•*WAVE-REGULAR is used to specify regular Airy wave loading.
•*WAVE-STOKES is used to specify Stokes V regular wave loading.
•*WAVE-DEANS is used to specify Dean’s Stream regular wave loading.
•*WAVE-PIERSON-MOSKOWITZ is used to specify a Pierson-Moskowitz random sea wave spectrum or spectra.
•*WAVE-JONSWAP is used to specify a JONSWAP random sea wave spectrum or spectra.
•*WAVE-OCHI-HUBBLE is used to specify an Ochi-Hubble random sea wave spectrum or spectra.
•*WAVE-TORSETHAUGEN is used to specify a Torsethaugen random sea wave spectrum or spectra.
•*WAVE-TIME-HISTORY is used to specify a random seastate in terms of a time history of water surface elevation.
•*WAVE-USER-DEFINED is used to specify a User-Defined random sea wave spectrum or spectra.
•*WAVE-GENERAL is used to specify miscellaneous parameters to wave loading.