plotting for loop answers with changing variables

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Muamin Sulaiman 2021-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/814195-plotting-for-loop-answers-with-changing-variables

评论： DGM 2021-4-28

Hello

I am running into an issue with some code I am writing for a class, I have defined the mathematical aspect of the code, which gives me the answer I need for on simulation, but how would I go about plotting the same code but variables changing in step intervals? I am new to indexing and I believe that may be the answer to my question but I am unsure how to execute it in this example.

I want to re run the code for KC to start from 2 to 20 in 2 step intervals to compare results and overlay them for my power plot, and run another simulation where I keep KC constant but change one of my other constants to an interval in the same fashion and overlay results etc, the problem is I do not know if I need to have multiple for loops or just an indexing line?

%% Variables
KC = 2
pi = acos(-1);
Um = 1.6;
T = 1.8 %(KC*D)/Um;
D = 0.16;
L = 1;
m = 50;
rho = 1024;
K = 200;
c = 100;
CA = 1;
CD = 1.8;
omega = 2*pi/T;
md = 1;
Ap = D*L;
dt = T/40;
ndt = T/dt*5;
X(1:ndt+1) = 0;
V(1:ndt+1) = 0;
%% Governing equations
time(1:ndt+1) = (0:ndt)*dt;
P(1:ndt+1)= 0;
Pavg=0;
Kc=(Um*T)/D;
for n=1:ndt,
    %for KC = 2:2:20,
    % Calculation of kx1 and kv1
    ta= time(n);
    aw= omega*Um*cos(omega*ta)-(2*Um*omega*cos(omega*ta))/3;
    Vw= Um*sin(omega*ta)- (Um/3)*sin(2*omega*ta);
    Va= V(n);
    Xa= X(n);
    t1= CA*md*aw;
    t2= 0.5*rho*CD*Ap*abs(Vw-Va)*(Vw-Va);
    t3= -K*Xa-c*Va;
    kx1= V(n);
    kv1= (t1+t2+t3)/(m+CA*md);
    
    %% Calculation of kx2 and kv2
    ta= time(n)+dt/2;
    aw= omega*Um*cos(omega*ta)-(2*Um*omega*cos(omega*ta))/3;
    Vw= Um*sin(omega*ta)- (Um/3)*sin(2*omega*ta)
    Va= V(n)+0.5*dt*kv1;
    Xa= X(n)+0.5*dt*kx1;
    t1= CA*md*aw;
    t2= 0.5*rho*CD*Ap*abs(Vw-Va)*(Vw-Va);
    t3= -K*Xa-c*Va;
    kx2= V(n)+0.5*dt*kv1;
    kv2= (t1+t2+t3)/(m+CA*md);
    
    %% Calculation of kx3 and kv3
    ta= time(n)+dt/2;
    aw= omega*Um*cos(omega*ta)-(2*Um*omega*cos(omega*ta))/3;
    Vw= Um*sin(omega*ta)-(Um/3)*sin(2*omega*ta);
    Va= V(n)+0.5*dt*kv2;
    Xa= X(n)+0.5*dt*kx2;
    t1= CA*md*aw;
    t2= 0.5*rho*CD*Ap*abs(Vw-Va)*(Vw-Va);
    t3= -K*Xa-c*Va;
    kx3= V(n)+0.5*dt*kv2;
    kv3= (t1+t2+t3)/(m+CA*md);
    
    %% Calculation of kx4 and kv4
    ta= time(n)+dt;
    aw= omega*Um*cos(omega*ta)-(2*Um*omega*cos(omega*ta))/3; % acceleration of the fluid
    Vw= Um*sin(omega*ta)- (Um/3)*sin(2*omega*ta); % velocity of the fluid
    Va= V(n)+0.5*dt*kv3;
    Xa= X(n)+0.5*dt*kx3;
    t1= CA*md*aw;
    t2= 0.5*rho*CD*Ap*abs(Vw-Va)*(Vw-Va);
    t3= -K*Xa-c*Va;
    kx4= V(n)+dt*kv3;
    kv4= (t1+t2+t3)/(m+CA*md);
    
    %% Step Equations
    X(n+1)= X(n)+(dt/6)*(kx1+2*kx2+2*kx3+kx4);
    V(n+1)= V(n)+(dt/6)*(kv1+2*kv2+2*kv3+kv4);
    P(n+1)= c*(V(n)^2);
    Pavg= P(n)+(1/ndt)*P(n);
end %end
%% Plot of cylinder displacement, velocity and power output
% X Displacement plot
figure (1);
plot(time(1:ndt),X(1:ndt),'-g');
xlabel('time (s)');
ylabel('X (m)');
title('X displacment');
legend ('RK method');
% V Velocity plot
figure (2);
plot(time(1:ndt),V(1:ndt),'-b');
xlabel('time (s)');
ylabel('V (m/s)');
title('V Velocity');
legend ('RK method');
% P Power plot
figure (3);
plot (time(1:ndt),P(1:ndt),'-b');
xlabel('time (s)');
ylabel('P (W)');
title('P Power');
legend ('R-K method');
hold;

After writing the code I am now confused on what to do since the second for loop I have implemented doesnt seeem to do anything and the results are the same so I am confused as to why or how to actually get it to do what I want it to?

note: I took out the second loop and replaced the variable KC with a constant to get one answer.

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Muamin Sulaiman 2021-4-28

I renamed Kc to KC, and i am receiving different results everytime I change the variable in line 2 now.

Could I maybe vector the KC value to acheive what I want? or maybe start a for loop at line 2 and end it at the end of the original for loop?

Thanks for bringing my attention to the parameters being named differently, that helped me :)

I will have to research storing array results and plotting them, I dont believe I have done that before.

DGM 2021-4-28

Your results are already vectors, so if they're all the same length each time, just concatenate them into a 2D array.

If they're not the same length, you'd have to use a cell array or take a different approach.

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plotting for loop answers with changing variables

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