function [taucr] = ST_taucr(d,varargin) % Calculate critical shear stress in Pascals % % function [wset] = ST_taucr(d,varargin) % % DESCRIPTION: % Calculate critical shear stress for threshold of motion in Pa % % INPUT: % d: sediment grain size in m % [optional] 'temperature' = temperature of the seawater in C [default=10] % [optional] 'salinity' = salinity of seawater in PSU [default=35] % [optional] 'sdens' = sediment density in kg/m^3 [default=2650] % % OUTPUT: % taucr: critical shear stress in N/m^2 % % EXAMPLE USAGE % TCR = ST_taucr(.0005,'temperature',10,'salinity',35,'sdens',2650) % % Author(s): % Geoff Cowles (University of Massachusetts Dartmouth) % % References % Soulsby Dynamics of Marine Sands (SC77) % % Revision history % %============================================================================== subname = 'ST_taucr'; %fprintf('\n') %fprintf(['begin : ' subname '\n']) % constants grav = 9.8106; %g T = 10; %T (C) S = 35; %S (PSU) sdens = 2650; %sediment density in kg/m^3 % parse arguments for i=1:2:length(varargin)-1 keyword = lower(varargin{i}); if( ~ischar(keyword) ) error('incorrect usage of ST_wset') end; switch(keyword(1:3)) case 'tem' T = varargin{i+1}; case 'sal' S = varargin{i+1}; case 'sde' sdens = varargin{i+1}; otherwise error(['Can''t understand value for:' keyword]); end; %switch keyword end; % calculate rho dens = SW_Density(T,S); % calculate dstar dstar = ST_Dstar(d,'temp',T,'sal',S,'sdens',sdens); % calculate theta_cr theta_cr = (0.30/(1+1.2*dstar)) + 0.055*[1 - exp(-.020*dstar)]; % calculate taucr taucr = theta_cr*grav*(sdens-dens)*d; %fprintf(['end : ' subname '\n'])