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getjonswappeakedness

PURPOSE ^

Peakedness factor Gamma given Hm0 and Tp for JONSWAP

SYNOPSIS ^

gam = getjonswappeakedness(Hm0,Tp)

DESCRIPTION ^

 GETJONSWAPPEAKEDNESS Peakedness factor Gamma given Hm0 and Tp for JONSWAP 
  
   CALL: Gamma =  getJonswapPeakedness(Hm0,Tp); 
  
  Hm0   = significant wave height [m]. 
  Tp    = peak period [s] 
  gamma = Peakedness parameter of the JONSWAP spectrum 
  
   GETJONSWAPPEAKEDNESS relate GAMMA to Hm0 and Tp. 
   A standard value for GAMMA is 3.3. However, a more correct approach is  
   to relate GAMMA to Hm0 and Tp: 
         D = 0.036-0.0056*Tp/sqrt(Hm0); 
         gamma = exp(3.484*(1-0.1975*D*Tp^4/(Hm0^2))); 
   This parameterization is based on qualitative considerations of deep water 
   wave data from the North Sea, see Torsethaugen et. al. (1984) 
   Here GAMMA is limited to 1..7. 
   
   NOTE: The size of GAMMA is the common size of Hm0 and Tp. 
    
  Example 
  Hm0 = linspace(1,20); 
  Tp = Hm0; 
  [T,H] = meshgrid(Tp,Hm0); 
  gam = getjonswappeakedness(H,T); 
  contourf(Tp,Hm0,gam,1:7),fcolorbar(1:7) 
  
  Hm0 = 1:10;   
  Tp  = linspace(2,16); 
  [T,H] = meshgrid(Tp,Hm0); 
  gam =  getjonswappeakedness(H,T);  
  plot(Tp,gam) 
  xlabel('Tp [s]')   
  ylabel('Peakedness parameter') 
    
  See also jonswap

CROSS-REFERENCE INFORMATION ^

This function calls: This function is called by:

SOURCE CODE ^

001 function gam = getjonswappeakedness(Hm0,Tp) 
002 %GETJONSWAPPEAKEDNESS Peakedness factor Gamma given Hm0 and Tp for JONSWAP 
003 % 
004 %  CALL: Gamma =  getJonswapPeakedness(Hm0,Tp); 
005 % 
006 % Hm0   = significant wave height [m]. 
007 % Tp    = peak period [s] 
008 % gamma = Peakedness parameter of the JONSWAP spectrum 
009 % 
010 %  GETJONSWAPPEAKEDNESS relate GAMMA to Hm0 and Tp. 
011 %  A standard value for GAMMA is 3.3. However, a more correct approach is  
012 %  to relate GAMMA to Hm0 and Tp: 
013 %        D = 0.036-0.0056*Tp/sqrt(Hm0); 
014 %        gamma = exp(3.484*(1-0.1975*D*Tp^4/(Hm0^2))); 
015 %  This parameterization is based on qualitative considerations of deep water 
016 %  wave data from the North Sea, see Torsethaugen et. al. (1984) 
017 %  Here GAMMA is limited to 1..7. 
018 %  
019 %  NOTE: The size of GAMMA is the common size of Hm0 and Tp. 
020 %   
021 % Example 
022 % Hm0 = linspace(1,20); 
023 % Tp = Hm0; 
024 % [T,H] = meshgrid(Tp,Hm0); 
025 % gam = getjonswappeakedness(H,T); 
026 % contourf(Tp,Hm0,gam,1:7),fcolorbar(1:7) 
027 % 
028 % Hm0 = 1:10;   
029 % Tp  = linspace(2,16); 
030 % [T,H] = meshgrid(Tp,Hm0); 
031 % gam =  getjonswappeakedness(H,T);  
032 % plot(Tp,gam) 
033 % xlabel('Tp [s]')   
034 % ylabel('Peakedness parameter') 
035 %   
036 % See also jonswap   
037    
038 % Tested on matlab 6.1 
039 %History 
040 % revised pab 13april2004 
041 % -made sure gamma is 1 if Tp/sqrt(Hm0) > 5.1429 
042 % by pab 11Jan2004   
043    
044   error(nargchk(2,2,nargin)) 
045   [errorcode,Hm0,Tp] = comnsize(Hm0,Tp); 
046   if errorcode > 0 
047     error('Requires non-scalar arguments to match in size.'); 
048   end 
049   x   = Tp./sqrt(Hm0); 
050    
051   gam = ones(size(x)); 
052    
053   k1 = find(x<=5.14285714285714); 
054   if any(k1), %limiting gamma to [1 7] 
055     D       = 0.036-0.0056*x(k1); % approx 5.061*Hm0^2/Tp^4*(1-0.287*log(gam)); 
056     gam(k1) = min(exp(3.484*( 1-0.1975*D.*x(k1).^4 ) ),7); % gamma  
057   end 
058   return

Mathematical Statistics
Centre for Mathematical Sciences
Lund University with Lund Institute of Technology

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