# Indexing into a matrix to create a plot

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Justin Hayes il 29 Mar 2020
Commentato: Justin Hayes il 30 Mar 2020
I would like to store Tskin for all t values and then use indexing to create a plot. How do I accomplish this?
Tambient = 20; % C
Tfilm = (T + Tambient)/2;
T = 29;
for t = 1:1:10
k_air_2 = 0 * (2.4131 + 0.0078 * T) * 10^-2; % W/m*C = 0
k_cotton = 0; % because long sleeve
rho_air = 1.2893 - 0.004 * Tfilm; % kg/m^3
mu_air = (0.0047 * Tfilm + 1.7164) * 10^-5; % kg/m*s
k_air_ambient= (2.4131 + 0.0078 * Tfilm) * 10^-2; % W/m*C
Re = Diameter_forearm * V * rho_air / mu_air;
h_air = (k_air_ambient/Diameter_forearm) * (0.3 + ((0.62 * Re.^.5 * Pr.^.333)/((1 + (0.4 * Pr)^.667).^.25))*(1 + ((Re/282000).^(5/8))).^.8) % J/s*K*m^2
Uskin = (k_air_2/thickness_air) + (k_cotton/thickness_shirt) + (h_air) % J/s*K*m^2
Uambient = (k_air_ambient/thickness_air) + (k_cotton/thickness_shirt) + (h_air)
old_Tskin = T
Tskin = [(T * Area * Cp_air * rho_air)/(t-(t-1)) + Qgen + (Uambient * Area * Tambient)]/((Area * Cp_air * rho_air / ((t-(t-1)))) + Uskin * Area);
T = Tskin
Tfilm = (T + Tambient)/2;
fprintf('Your frontal forearm temperature is %.2f C after %d seconds ' ,Tskin,t)
dT = old_Tskin - Tskin
if dT > 0.007
elseif dT < -0.005
display('Your forearm probably is probably feeling hot')
else
end
end
##### 2 CommentiMostra 1 commento meno recenteNascondi 1 commento meno recente
Justin Hayes il 30 Mar 2020
T = 29; % %C
% Constants
Area = .1/2; % m^2 divide by 2 for the "frontal area", I assume this is 50% of the SA of arm
Qgen = 4.5/2; %J/s divide by 2 for the "frontal area"
thickness_shirt = 0.002286; % m
thickness_air = 0.01 % m thickness of air layer in shirt
k_cotton = 0.04; % W/m*C
Diameter_forearm = 0.07; % m
Tambient = 20; % C
% Properties of ambient air
Pr = 0.71;
V = 5; %m/s
Cp_air = 1006; %J/kg*K
Tfilm = (T + Tambient)/2;
p = input('long-sleeve, short-sleeve, tank, or none: ','s')
for t = 1:1:100
k_air_2 = 0 * (2.4131 + 0.0078 * T) * 10^-2; % W/m*C = 0
k_cotton = 0;
rho_air = 1.2893 - 0.004 * Tfilm; % kg/m^3
mu_air = (0.0047 * Tfilm + 1.7164) * 10^-5; % kg/m*s
k_air_ambient= (2.4131 + 0.0078 * Tfilm) * 10^-2; % W/m*C
Re = Diameter_forearm * V * rho_air / mu_air;
h_air = (k_air_ambient/Diameter_forearm) .* (0.3 + ((0.62 * Re.^.5 * Pr.^.333)/((1 + (0.4 * Pr).^.667).^.25)).*(1 + ((Re/282000).^(5/8))).^.8) % J/s*K*m^2
Uskin = (k_air_2/thickness_air) + (k_cotton/thickness_shirt) + (h_air) % J/s*K*m^2
Uambient = (k_air_ambient/thickness_air) + (k_cotton/thickness_shirt) + (h_air)
Tskin = [(T * Area * Cp_air * rho_air)/(t-(t-1)) + Qgen + (Uambient * Area * Tambient)]/((Area * Cp_air * rho_air / ((t-(t-1)))) + Uskin * Area);
T = Tskin
Tfilm = (T + Tambient)/2
end

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### Risposte (1)

MaryD il 29 Mar 2020
you can just try
T_skin(t)= [(T * Area * Cp_air * rho_air)/(t-(t-1)) + Qgen + (Uambient * Area * Tambient)]/((Area * Cp_air * rho_air / ((t-(t-1)))) + Uskin * Area);
inside the loop.
then outside the loop
t=1:1:10
plot(t,T_skin)
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Justin Hayes il 30 Mar 2020
When I use this method to plot it produces an empty plot

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