wavefrompressurepsd#
[Hm0, fp, Tp, Tm01, Tm02, f, Syy, m0, ftail] = wavefrompressurepsd(P, fs, h, heightfrombed, fmaxpcorr, fminpcorr, fcL, fcH, fmaxpcorrCalcMethod, Kpafterfmaxpcorr, kCalcMethod, Rho, nfft, SegmentSize, OverlapSize, dispout)
Description#
Calculate wave properties from water pressure by converting it to water surface elevation power spectral density
Inputs#
- P
Water pressure time series data in (N/m^2)
- fs
Sampling frequency that data collected at in (Hz)
- h
Water depth in (m)
- heightfrombed=0;
Height from bed that data collected at in (m)
- fmaxpcorr=fs/2;
- Maximum frequency that a pressure attenuation factor applies up on that (Hz)If fmaxpcorrCalcMethod=’user’, then the smaller of calculated and user defined fmaxpcorr will be chosen
- fminpcorr=0;
- Minimum frequency that is used for defining fmaxpcorr if fmaxpcorrCalcMethod=’auto’ (Hz)fminpcorr should be smaller than fpIf swell energy exists, fminpcorr should be smaller than fp of wind sea (fpsea) and larger than fp of swell (fpswell) if there swell
- fcL=0;
Low cut-off frequency, between 0*fs to 0.5*fs (Hz)
- fcH=fs/2;
High cut-off frequency, between 0*fs to 0.5*fs (Hz)
- fmaxpcorrCalcMethod=’auto’;
- Define if to calculate fmaxpcorr and ftail or to use user defined‘user’: use user defined value for fmaxpcorr‘auto’: automatically define value for fmaxpcorr
- Kpafterfmaxpcorr=’constant’;
- Define a apressure response factor, Kp, value for frequency larger than fmaxpcorr‘nochange’: Kp is not changed for frequency larger than fKuvmin‘one’: Kp=1 for frequency larger than fmaxpcorr‘constant’: Kp for f larger than fmaxpcorr stays equal to Kp at fmaxpcorr (constant)
- kCalcMethod=’beji’;
- Wave number calculation method‘hunt’: Hunt (1979), ‘beji’: Beji (2013), ‘vatankhah’: Vatankhah and Aghashariatmadari (2013)‘goda’: Goda (2010), ‘exact’: calculate exact value
- Rho=1000;
Water density (kg/m^3)
- nfft=length(Eta);
Total number of points between 0 and fs that spectrum reports at is (nfft+1)
- SegmentSize=256;
Segment size, data are divided into the segments each has a total element equal to SegmentSize
- OverlapSize=128;
Number of data points that are overlapped with data in previous segments
- dispout=’no’;
Define to display outputs or not (‘yes’: display, ‘no’: not display)
Outputs#
- Hm0
Zero-Moment Wave Height (m)
- fp
Peak wave frequency (Hz)
- Tp
Peak wave period (second)
- Tm01
Wave Period from m01 (second), Mean Wave Period
- Tm02
Wave Period from m02 (second), Mean Zero Crossing Period
- f
Frequency (Hz)
- Syy
Power spectral density (m^2/Hz)
- m0
Zero-Moment of the power spectral density (m^2)
- ftail
Frequency that diagnostic tail apply after that (typically: ftail=2.5fm where fm=1/Tm01)
Examples#
fs=2; %Sampling frequency
duration=1024; %Duration of the data
N=fs*duration; %Total number of points
df=fs/N; %Frequency difference
dt=1/fs; %Time difference, dt=1/fs
t(:,1)=linspace(0,duration-dt,N); %Time
Eta(:,1)=detrend(0.5.*cos(2*pi*0.2*t)+(-0.1+(0.1-(-0.1))).*rand(N,1));
hfrombed=4;
h=5;
k=0.2;
P=Eta.*9.81.*1000.*(cosh(k*hfrombed)/cosh(k*h));
[Hm0,fp,Tp,Tm01,Tm02,f,Syy,m0,ftail]=wavefrompressurepsd(P,fs,5,4,0.7,0.15,0,fs/2,'auto','constant','beji',1025,N,256,128,'yes');
References#
Beji, S. (2013). Improved explicit approximation of linear dispersion relationship for gravity waves. Coastal Engineering, 73, 11-12.
Goda, Y. (2010). Random seas and design of maritime structures. World scientific.
Hunt, J. N. (1979). Direct solution of wave dispersion equation. Journal of the Waterway Port Coastal and Ocean Division, 105(4), 457-459.
Vatankhah, A. R., & Aghashariatmadari, Z. (2013). Improved explicit approximation of linear dispersion relationship for gravity waves: A discussion. Coastal engineering, 78, 21-22.
Welch, P. (1967). The use of fast Fourier transform for the estimation of power spectra: a method based on time averaging over short, modified periodograms. IEEE Transactions on audio and electroacoustics, 15(2), 70-73.