| JinshiC |
February 8, 2022 16:17 |
Meaning of "amplitude" for spectra under waveProperties
Hi all,
This can be a very stupid question...but I am having trouble understanding the output of "amplitude" of the wave spectra under ./constant/waveProperties after the wavefield is set up.
Prior to setting up wave field. I edited the wave properties as follows:
Code:
inletCoeffs
{
waveType irregular;
N 50; //Number of sampling frequencies
Tsoft 30; //Ramp time
// Define the phases
phaseMethod randomPhase;
// Define the spectrum
spectrum JONSWAP;
Hs 0.6; // Significant wave height
Tp 10; // Peak wave period
gamma 3.3; // Peak enhancement factor
depth 4.5; // Water depth
direction (1 0 0);
frequencyAxis
{
discretisation equidistantFrequencyAxis;
lowerFrequencyCutoff 0.06;
upperFrequencyCutoff 0.3;
writeSpectrum false;
}
This means that I want to have a JONSWAP spectrum with peak frequency at 0.1Hz, 0.6m significant waveheight, and cutoff frequency at 0.06Hz and 0.3Hz respectively. After I setup the wave field, the waveproperties changes to
Code:
...
amplitude nonuniform List<scalar>
50
(
0.00535889
0.0114397
0.019171
0.0272411
0.0350467
0.0440764
0.0575423
0.073119
0.0793958
0.0722352
0.059356
0.0485175
0.0418549
0.0379943
0.0353735
0.0331837
0.0311556
0.029235
0.027421
0.0257176
0.0241254
0.0226421
0.0212633
0.0199834
0.0187963
0.0176958
0.0166754
0.0157291
0.0148512
0.0140361
0.0132789
0.0125749
0.0119197
0.0113094
0.0107404
0.0102093
0.00971319
0.00924923
0.00881492
0.00840796
0.00802626
0.0076679
0.00733114
0.00701436
0.00671613
0.00643508
0.00617
0.00591977
0.00568335
0.00545979
);
frequency nonuniform List<scalar>
50
(
0.0624
0.0672
0.072
0.0768
0.0816
0.0864
0.0912
0.096
0.1008
0.1056
0.1104
0.1152
0.12
0.1248
0.1296
0.1344
0.1392
0.144
0.1488
0.1536
0.1584
0.1632
0.168
0.1728
0.1776
0.1824
0.1872
0.192
0.1968
0.2016
0.2064
0.2112
0.216
0.2208
0.2256
0.2304
0.2352
0.24
0.2448
0.2496
0.2544
0.2592
0.264
0.2688
0.2736
0.2784
0.2832
0.288
0.2928
0.2976
);
...
Here I ignored some other information since I already knew what those are about.
Now I got confused by the "amplitude" when I want to check the significant waveheight from the amplitude. Denote those "amplitude" as g(f) where f is frequency, what I learned is:
Hs=4*sum(g(f)*df)^0.5
where df is the width of frequency band. Yet what I get is about 0.297 from this method.
I tried 4*sum(g(f)^0.5*df)^0.5 and it gives me 0.736.
I am wondering that how can I get Hs (0.6) from those amplitudes? Thank you so much!
Best,
Peter |
