*TIMEDRIFT

Data format:

A single line with 10 parameters, as follows:

ITYP_DRIFT NODE DURATION HMHS TIME_DRIFT PERCENTAGE_UP PERCENTAGE_DOWN IOP HMR TMR

Status :

Optional

Purpose :

To define the criterion on which the selection of time window will be based when an irregular wave simulation is performed

Details :

Parameter	Description
ITYP_DRIFT	ITYP_DRIFT = 0 : (Default) criterion based on the ratio of the maximum wave height over the significant wave height. ITYP_DRIFT = 1 : The criterion is based on the maximum downward speed. ITYP_DRIFT = 2 : The user defined the wave and not shift is performed but the wave phais is written in file wave2.out with a phase shift based on NODE position with respect to origin. ITYP_DRIFT = 3 : A shift of time TIME_DRIFT is performed, this can be used to play a specific window and can also be used in conjunction with *GMOVE3 if floater motion is not recomputed but imposed.
NODE	Reference node where the calculations are performed
DURATION	Duration expressed in hours on which the calculations are performed.
HMHS	Max/Hs ratio (Default = 1.7) If HMHS = 0, no maximum wave height is looked for. When specified, this value is considered instead of the HMHS value specified in the *WAVJON keyword.
TIME_DRIFT	New reference time to generate the wave elevation. This option is useful when a time series of motions is applied as well as the wave spectrum but only a time window not starting at t=0s is selected to run the simulation.
PERCENTAGE_UP	If PERCENTAGE_UP=5, that means that the wave height should be at most 5% higher than the requested value. By default, PERCENTAGE_UP is such that the maximum wave height is 10*Hs. Actually, that means that no upper limit is imposed so the achieved maximum wave height may be much greater than the requested value.
PERCENTAGE_DOWN	If PERCENTAGE_DOWN=1, that means that the wave height should be at most 1% lower than the requested value. By default, PERCENTAGE_DOWN=1/0.75 which means that the maximum wave height may be 1.333% lower than the requested one.
IOP	IOP = -1 : The maximum height is based on trough to crest instead of crest to trough elevation IOP = 0 (default) IOP = 1: if a maximum ratio is provided for a given location in space, the sum of airy waves is replaced by a stream function of order IOP over two periods centered on the time the maximum wave height is obtained at the given location. For half period there is a smooth transition from the wave generated by the spectrum to the stream function wave, then one period of pure stream function then back over half a period to the spectrum. By default, the wave height is the one that the spectrum would have produced, and the period is the period also obtained from the spectrum. With the next two parameters, those values can be overridden. IOP = -2: the maximum height is based on trough to crest and crest to trough. Furthermore, it is checked that there is no higher maximum on the simulation times. For low Hm/Hs ratio, a solution might not be found.
HMR	If not 0, provides the wave height used for generating the stream function with IOP>0
TMR	If not 0, provides the wave period used for generating the stream function with IOP>0

Note

By default, the duration automatically chosen is as follows :

Duration = 12500*MAX(Tsimulation, Tauto)

Where Tsimulation is the duration of the simulation and Tauto is eight times the wave peak period.

If double peaks spectra are defined, the first peak period is selected.
If several spectra are defined, the highest peak period is chosen.