Errors trying to get the right plots

I'm trying to get the plots shown in the enclosed image. Not sure how to fix the code. Attached the .txt data file. Any help will be appreciated. Thanks
close all
clear all
clc
% Inputs
A = 10;
m = 0.06;
L = 1;
nu = 2e-5; % Kinematic viscosity of the fluid
rho = 10; % Fluid density
x_start = 0.2;
x_end = 1;
dx = 0.001;
y_start = 0;
VelN = load('posm_profiles.txt');
y_high = round(max(VelN(:,1)),2);
y_end = y_high;
dy = 0.0001;
N = (x_end - x_start) / dx + 1
N = 801
M = (y_end - y_start) / dy + 1
M = 501
Re_x = A * L / nu;
% Initialize arrays
U = zeros(M, N);
Ue = zeros(1, N);
Theta = zeros(1, N);
cf = zeros(1, N);
y = linspace(y_start, y_end, M);
x = linspace(x_start, x_end, N);
%Inital Data Interpolation
Uef = @(XX)A*(XX/L).^m;
u = interp1(VelN(:,1),VelN(:,2),y)*Uef(x_start);
% Boundary conditions
U(1, :) = 0;
U(M, :) = 1;
% Solve for velocity profile using an explicit finite method
for i = 1:N
Ue(i) = (x(i) / L)^m * A;
theta = zeros(1, M);
for j = 2:M-1
F = [U(j-1, i), U(j, i), U(j+1, i)];
Uy = (F(3) - F(1)) / (2 * dy);
Uyy = (F(3) - 2 * F(2) + F(1)) / dy^2;
theta(j) = theta(j-1) + U(j, i) * dy / Ue(i);
cf(i) = 2 * nu * Uy / Ue(i)^2;
U(j, i+1) = U(j, i) + (U(j, i) * (F(3) - F(1)) - U(j, i)^2 * theta(j) + nu * Uyy) * dx / Ue(i)^2;
end
Theta(i) = trapz(y, 1 - U(:, i));
end
% Plot results
figure
plot(x, Theta,'o-')
title('Momentum thickness as a function of x')
xlabel('x')
ylabel('\theta')
figure
semilogy(x, cf,'o-')
title('Skin friction coefficient as a function of x')
xlabel('x')
ylabel('C_f')
% figure
% plot(y,u)
%
% title('Velocity Profile')
% xlabel('u [m/s]')
% ylabel('y [mm]')
%axis([-.001 .05 0 y_end])
figure
for i = 1:100:N
plot(U(:, i), y,'-')
hold on
end
title('Velocity profiles')
xlabel('u [m/s]')
ylabel('y [mm]')
%axis([-.001 .05 0 y_end])
legend('x = 0.2 m', 'x = 0.3 m', 'x = 0.4 m', 'x = 0.5 m', 'x = 0.6 m', 'x = 0.7 m', 'x = 0.8 m', 'x = 0.9 m', 'x = 1.0 m')
figure
for i = 1:100:N
U_over_Ue = U(:, i) / Ue(i);
y_over_theta = y / Theta(i);
plot(U_over_Ue, y_over_theta,'o-')
hold on
end
title('Velocity profiles normalized by momentum thickness')
xlabel('u/U_e')
ylabel('y/\theta')
axis([-0.001 .125 0 1.01])
legend('x = 0.2 m', 'x = 0.3 m', 'x = 0.4 m', 'x = 0.5 m', 'x = 0.6 m', 'x = 0.7 m', 'x = 0.8 m', 'x = 0.9 m', 'x = 1.0 m')

5 commentaires

Steven Lord
Steven Lord le 29 Mar 2023
The full and exact text of any warning and/or error messages you receive (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warnings and/or errors.
Cesar Cardenas
Cesar Cardenas le 29 Mar 2023
This is all I'm getting text orange, nothing in red.
Line 2: Using 'clear' with the 'all' option usually decreases code performance and is often unnecessary.
Line 22: Add a semicolon
Cris LaPierre
Cris LaPierre le 29 Mar 2023
These are not errors, they are code analyzer wardnings, which are giving you suggestions on how to improve your code.
Cesar Cardenas
Cesar Cardenas le 29 Mar 2023
Ok thank you, however, I have not been able to get the plots as shown in the image attached, so not sure how to fix it.?
When vector U are all zeros, its less likely, that velocity profile can be evaluated correctly,
There needs to be a condition where the vector U needs to be updated with right values
theta(j) = theta(j-1) + U(j, i) * dy / Ue(i);
% ------------------->>> theta vector are all zeros, conisder u(j) or some
% input taken from VelN variable or combination of both u(j) & VelN
% Recheck whether this equation is correctly formulated
U(j, i+1) = U(j, i) + (U(j, i) * (F(3) - F(1)) - U(j, i)^2 * theta(j) + nu * Uyy) * dx / Ue(i)^2;

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le 30 Mar 2023

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