DESCRIPTION:
Function used to calculate Wave Bed Shear Stress, tauw, from the
bottom orbital velocity (Ubot) and the bottom wave period (TmBot).
This function is currently set up to extract these values from SWAN
output. Currently temperature, salinity and z0 are set to be constant
accross the domain. Using actual data could improve accuaracy.
REQUIRES FVCOM_TOOLBOX to be in your MATLAB path
INPUT
z0 = bed roughness length (z0=d50/12) [mm]
<=={possibly use constant value 0.05 Soulsby pg. 49}==>
ncfile = netcdf file containing Ubot & TmBot
that was created from swan2netcdf.m
writenetcdf = accepts either true or false
if 'True' write tauw and fw to netcdf
OUTPUT:
tauw = array containing values of tauw at all time for each node in
model domain
EXAMPLE USAGE
tauw = calc_tauw(z0,'skg4.3.nc',true);
Author(s):
Eric Holmes (University of Massachusetts Dartmouth)
Revision history
Initially created 09-24-2010
==============================================================================0001 function [tauw] = calc_tauw(z0,ncfile,writenetcdf) 0002 0003 % DESCRIPTION: 0004 % Function used to calculate Wave Bed Shear Stress, tauw, from the 0005 % bottom orbital velocity (Ubot) and the bottom wave period (TmBot). 0006 % This function is currently set up to extract these values from SWAN 0007 % output. Currently temperature, salinity and z0 are set to be constant 0008 % accross the domain. Using actual data could improve accuaracy. 0009 % 0010 % REQUIRES FVCOM_TOOLBOX to be in your MATLAB path 0011 % 0012 % 0013 % INPUT 0014 % z0 = bed roughness length (z0=d50/12) [mm] 0015 % <=={possibly use constant value 0.05 Soulsby pg. 49}==> 0016 % 0017 % ncfile = netcdf file containing Ubot & TmBot 0018 % that was created from swan2netcdf.m 0019 % 0020 % writenetcdf = accepts either true or false 0021 % if 'True' write tauw and fw to netcdf 0022 % 0023 % 0024 % 0025 % 0026 % OUTPUT: 0027 % tauw = array containing values of tauw at all time for each node in 0028 % model domain 0029 % 0030 % EXAMPLE USAGE 0031 % tauw = calc_tauw(z0,'skg4.3.nc',true); 0032 % 0033 % 0034 % Author(s): 0035 % Eric Holmes (University of Massachusetts Dartmouth) 0036 % 0037 % Revision history 0038 % Initially created 09-24-2010 0039 % 0040 %============================================================================== 0041 0042 %------------------------------------------------------------------------------ 0043 % Convert z0 to meters 0044 %------------------------------------------------------------------------------ 0045 z0 = z0/1000; 0046 0047 %------------------------------------------------------------------------------ 0048 % Set Ubot & TmBot from netCDF file 0049 %------------------------------------------------------------------------------ 0050 nc = netcdf(ncfile,'w'); 0051 0052 nctime=ncdim('time',nc); 0053 nctime = size(nctime); 0054 nctime=nctime(1,1); 0055 ncnode=ncdim('node',nc); 0056 node = size(ncnode); 0057 node = node(1,1); 0058 Ubot = ncvar('Ubot',nc); 0059 Ubot = Ubot.*ones(nctime,node); 0060 TmBot = ncvar('TmBot',nc); 0061 TmBot = TmBot.*ones(nctime,node); 0062 0063 0064 0065 %------------------------------------------------------------------------------ 0066 % Set Generic Values to Salinity and Temperature 0067 % This is temporary, it would be better to use actual salinity and 0068 % temperature data. 0069 %------------------------------------------------------------------------------ 0070 vectorsize=size(Ubot); 0071 T=zeros(vectorsize); 0072 S=zeros(vectorsize); 0073 0074 T(:,:)=15; 0075 S(:,:)=30; 0076 0077 %------------------------------------------------------------------------------ 0078 % Call Kinematic Viscosity Routine and Density Routine 0079 %------------------------------------------------------------------------------ 0080 nu = SW_Kviscosity(T,S); % 0081 rho = SW_Density(T,S); % 0082 0083 0084 %------------------------------------------------------------------------------ 0085 % Calculate fwr & fws according to Soulsby pg. 77-79 0086 %------------------------------------------------------------------------------ 0087 0088 %----CONSTANTS----------------------------------------------------------------- 0089 %ks = z0*30.; % Nikuradse roughness 0090 A = Ubot.*TmBot/(2.*pi); % semi-orbital excursion 0091 % r = A/ks; % relative roughness 0092 Rw = Ubot.*A./nu; % wave Reynolds 0093 %------------------------------------------------------------------------------ 0094 fwr = 1.39*(A/z0).^(-0.52); % case in which flow is rough turbulent 0095 % Soulsby (62a) 0096 0097 % Smooth Cases 0098 for i = 1:vectorsize(1,1) 0099 for j = 1:vectorsize(1,2) 0100 if(Rw(i,j) > 5e5) 0101 B=0.0521; N=0.187; % case in which flow is smooth turbulent 0102 else 0103 B=2; N=0.5; % case in which flow is laminar 0104 end; 0105 end 0106 end 0107 0108 fws = B*Rw.^(-N); % smooth bed friction factor Soulsby (63) 0109 0110 %------------------------------------------------------------------------------ 0111 % Choose wave friction factor for current conditions 0112 %------------------------------------------------------------------------------ 0113 fw = zeros(vectorsize); 0114 0115 for i = 1:vectorsize(1,1) 0116 for j = 1:vectorsize(1,2) 0117 fw(i,j) = max(fwr(i,j),fws(i,j)); 0118 % wave friction factor 0119 end; 0120 end; 0121 0122 tauw = 0.5*rho.*fw.*Ubot.*Ubot; % wave shear stress 0123 %tauw(isnan(tauw)) = 0; 0124 0125 %------------------------------------------------------------------------------ 0126 % Write Values of tauw to ncfile 0127 %------------------------------------------------------------------------------ 0128 if (writenetcdf == true) 0129 0130 nc = netcdf(ncfile,'w'); 0131 0132 nc{'tauw'} = ncfloat('time','node'); 0133 nc{'tauw'}.long_name = 'Bed Shear Stress'; 0134 nc{'tauw'}.units = 'N/m^2'; 0135 0136 for i=1:vectorsize(1,1) 0137 nc{'tauw'}(i,1:vectorsize(1,2)) = tauw(i,1:vectorsize(1,2)); 0138 end 0139 0140 close(nc); 0141 0142 end; 0143 0144 0145 0146 0147 0148 0149 0150 0151 0152 end