directionalpsdetauv#
[Syy2d, f2d, theta] = directionalpsdetauv(Eta, Ux, Uy, fs, h, UVheightfrombed, dtheta, coordinatesys, fKuvmin, fcL, fcH, KuvafterfKuvmin, kCalcMethod, nfft, SegmentSize, OverlapSize, dispout)
Description#
Calculate wave directional spectrum using water surface elevation and horizontal orbital velocity
Inputs#
- Eta
Water surface elevation time series data in (m)
- Ux
Wave horizontal orbital velocity data in x direction in (m/s)
- Uy
Wave horizontal orbital velocity data in y direction in (m/s)
- fs
Sampling frequency that data collected at in (Hz)
- h
Water depth in (m)
- UVheightfrombed=0;
Velocity sensor height from bed that data collected at in (m)
- dtheta=15;
Direction interval at which directional spectrum calculated between 0 and 360 (Degree)
- coordinatesys=’xyz’;
- Define the coordinate system‘xyz’: XYZ coordinate system, ‘enu’: ENU (East North Up) coordinate systemIf coordinatesys=’enu’, then x is East and y is NorthIf coordinatesys=’enu’, results are reported with respect to true northIn true north coordinate system, wave comes from as:0 degree: from north, 90 degree: from east, 180 degree: from south, 270 degree: from west
- fKuvmin=fs/2;
Frequency that a velocity conversion factor (Kuv) at that frequency is considered as a minimum limit for Kuv
- 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)
- KuvafterfKuvmin=’constant’;
- Define conversion factor, Kuv, value for frequency larger than fKuvmin‘nochange’: Kuv is not changed for frequency larger than fKuvmin‘one’: Kuv=1 for frequency larger than fKuvmin‘constant’: Kuv for f larger than fKuvmin stays equal to Kuv at fKuvmin (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
- 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 overlaped with data in previous segments
- dispout=’no’;
- Define to display outputs or not‘2d’: 2 dimensional plot, ‘surface’: Surface plot, ‘polar’: Polar plot, ‘no’: not display
Outputs#
- Syy2d
Directional wave power spectral density (m^2/Hz/Degree)
- f2d
Directional frequency (Hz)
- theta
Direction (Degree)
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;
Ux=(pi/5).*(2.*Eta).*(cosh(k*hfrombed)/sinh(k*h));
Uy=0.2.*Ux;
[Syy2d,f2d,theta]=directionalpsdetauv(Eta,Ux,Uy,fs,h,4,15,'xyz',0.7,0,fs/2,'constant','beji',N,256,128,'polar');
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.