Program Zero Up Crossing

Coming back to the blog and i got a good news for ya'll:  I'm a master student now!! *YAY!* majoring Ocean Engineering in ITB. hahaha! I'm soo excited that finally i can sit in class again working on assignments and worrying the mid test :))  *Ewh~ such a beautiful pain!* 

so today i'm going to post something, that related to my course in ITB. this is my first assignment in my master course: A Zero up crossing program in matlab! . for those who doesn't know what the f* is zero up crossing here's the definition :

 

zero up crossing is one common method that use to define one wave from wave records statistically. in this method a 'wave' is defined as the portion of a record between two successive zero up crossings.

still don't get it? here's the illustration taken from Mandly Hydraulics Laboratory:

zero up crossing wave illustration
image taken from this

so here's the program and the explaination:

1. Loading wave data from excell file:

clc; clear all; close all;

%--------------------------------------------------

% ZERO UP CROSSING PROGRAM

% MEIRITA RAMDHANI

% 25511301

% 2ND ASSIGNMENT OF ADVANCE RANDOM WAVES SUBJECT

% -------------------------------------------------

% 1. LOADING WAVE DATA

filename ='Wave elevation_wt_ meter_ Meulaboh_Feb4.xls';

sheet = 'RawData Wave';

range = 'D4:DP409';    

PAR = xlsread(filename, sheet, range);

dt=0.4;

2. Calculating wave average 

% 2. CALCULATING WAVE AVERAGE

Araw=PAR(:,1);

Abar=sum(Araw)/length(Araw);

Azero=Araw-Abar;

resulting:

the wave data minus its average.

3. Determining the zero up crossing index.

The zero up crossing index is determined by looking at the wave records value sign. after you subtracted your  wave record with its average, you'll get your data reference in y=0. so that, you'll have data which values is negative and positive. from here, you can determine the zero up crossing index. 

in your data, whenever negative values meets positive values then you'll get one zero up crossing wave. the 'one zero up crossing wave'  is define between one 'negative-meet-positiv' and 'next negative-meet-positive'

*ewh.. i'm not really good in explaining this* anyway here's the matlab scipt:

% 3. CALCULATING ZERO UP CROSSING

I1=Azero(1:end-1);

I2=Azero(2:end);

indx=zeros(size(I1));

for i=1:length(indx);

    indx(i)=I1(i)*I2(i); %negativ ketemu positiv

end   

indz=find(indx < 0); %index ZUC & ZDC

indc=zeros(length(indz),1);

indzuc= find(Azero < 0);

zuc=intersect(indz,indzuc);  %index zeroup crossing

izuc=zeros(length(zuc),1);

result:

the wave data and it's zero up crossing index

1.       4. Calculating the Wave height;

     After you got your index, now, its time calculating the wave height between 2 index of zero up crossing that we define in previous. to calculate the wave height, we must subtracting the maximum and minimum values which happen in between 2 zero up crossing index. then you'll get list of wave height. 

     if you sort the wave height from the larger value to the smaller value then you can calculate other waves parameter such as: H1/3, H1/10, Hrms. etc.

%4. CALCULATING WAVE HEIGHT

   w1=zuc(1:end-1)+1;

   w2=zuc(2:end);

  for i=1:length(w1);

    A=max(max(Azero(w1(i):w2(i)))) % maximum wave

    B=min(min(Azero(w1(i):w2(i)))) % minimum wave

    H(i)=A-B   ; % maximum wave height – minimum wave height

  end

%5. SORTING WAVE HEIGHT

nwave=length(H);

swave=sort(H)'; % mengurutkan tinggi gelombang dari yg tinggi ke rendah

swave=flipud(swave);

  Results:

Upper picture is the wave height that is calculated from the zero up crossing .
and the lower picture is after we sort the wave height.

  Oke that's it for today. hope the program will usefull for anyone who need it. next post will be arround FFT something.

  SEE YA!