Graph Not Plotting All Values??

Question

Kevin 2014-7-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/141259-graph-not-plotting-all-values

评论： dpb 2014-7-10

Hi,

I am trying to output a graph from my programme which will plot TSR against CP for values of TSR ranging from 4 to 10. This is my code:

filename = 'book2.xlsx';
Input = xlsread(filename);
N = xlsread(filename,'C7:C15')
r = xlsread(filename,'D7:D15')
C = xlsread(filename,'E7:E15')
S = xlsread(filename,'F7:F15')
Non = xlsread(filename,'G7:G15')
% Inputs
R=0.4;                                          % Radius of Rotor
B=3;                                            % Number of blades
V=2;                                            % Fluid velocity
Rho=998;                                        % Fluid Density
N=9;                                            % Number of Blade Elements
Cp_estimate=0.5;                                % Estimate power coefficient
Alpha_design=4;                                 % Design alpha
Cl_design=1.04;                                 % Design lift coefficient
% Variables
TSR=4;                                          % Initial tip speed ratio
Cp=0;                                           % Initial power coefficient
i=1;                                            % Counter
alpha_new=0;                                    % Initial value for alpha new
axial_induction=0;                              % Initial axial induction factor
tolerance=0.01;                                  % Tolerance Value
Check=1;                                        % Initial check value
axial_induction_old=0;                          % Initial value for old axial induction factor
r_local=[(R./N)*1; (R./N)*2; (R./N)*3; (R./N)*4; (R./N)*5; (R./N)*6; (R./N)*7; (R./N)*8; (R./N)*9];
r_over_R=r_local./R;
TSR_local=r_over_R.*TSR;
Phi=(2/3)*atan(1./TSR_local);
C=((8.*pi.*r_local)./(B.*Cl_design)).*(1-cos(Phi));
sigma=(B*C)./(pi.*r_local.*2);
Cl=[1.3; 1.1; 1; 0.9; 0.86; 0.83; 0.8; 0.75; 0.5];                                  % Lift Coefficients
Cd=[0.027; 0.024; 0.02; 0.019; 0.018; 0.016; 0.013; 0.012; 0.01];                   % Drag Coefficients
F=(2/pi).*acos(exp(-(((B/2).*(1-(r_over_R)))./((r_over_R).*sin(Phi)))));
axial_induction=1./(((4.*(sin(Phi).^2))./(sigma.*Cl_design.*cos(Phi)))+1);
angular_induction=(1-(3*axial_induction))./((4.*axial_induction)-1);
for TSR=4:10,disp(TSR),                                                             % TSR from 4 to 10
     while abs(Check)>=tolerance
axial_induction_old=axial_induction;        
TSR_local=TSR*(r_local./R);                                                         % Local Tip Speed Ratio
Phi=(2/3)*atan(1./TSR_local);                                                       % Angle of Relative Fluid
relative_wind=(1-axial_induction)./((1+axial_induction).*TSR);
F=(2/pi).*acos(exp(-(((B/2).*(1-(r_over_R)))./((r_over_R).*sin(relative_wind)))));          % Tip Loss Factor
C_T=(sigma.*((1-axial_induction).^2).*((Cl.*cos(relative_wind))+(Cd.*sin(relative_wind))))./((sin(relative_wind)).^2);
if C_T(TSR,:)<0.96
    axial_induction=1./(1+(4.*F.*(sin(relative_wind).^2))./(sigma.*Cl.*cos(relative_wind)));  
else
    axial_induction=1./(((4.*F.*cos(relative_wind))./(sigma.*Cl))-1); 
end
D=(8./(TSR.*N)).*(F.*(sin(Phi).^2).*(cos(Phi)-((TSR_local).*(sin(Phi)))).*(sin(Phi)+((TSR_local).*(cos(Phi)))).*(1-(Cd./Cl).*atan(Phi)).*(TSR_local.^2));
Cp=sum(D);
Diff=axial_induction-axial_induction_old;
Check=max(Diff(:));
TSR=TSR+1;disp(TSR);
store_Phi(:,TSR)=Phi;
store_TSR_local(:,TSR)=TSR_local;
store_axial_induction(:,TSR)=axial_induction;
store_angular_induction(:,TSR)=angular_induction;
store_relative_wind(:,TSR)=relative_wind;
store_Check(:,TSR)=Check;
store_Diff(:,TSR)=Diff;
store_Cp(:,TSR)=Cp;
store_TSR(:,TSR)=TSR;
     end
end
figure(1)
plot(store_Cp,store_TSR)
hold all
title('Cp vs Tip Speed Ratio')
xlabel('TSR')
ylabel('Cp')

However, when I run the programme I get the following graph. It is clear that the programme is not plotting all TSR values. Could anybody please help with this?

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dpb 2014-7-10

在 MATLAB Online 中打开

We've been over this plowed ground once before -- until you fix up the loop indices and quit trying to modify the loop index internally in the loop you're going to continue to struggle.

It's not possible to tell what it is you want for the final dimensions from the code alone and you've not helped by explaining the desire when trying to help in the previous thread but in the following section

for  TSR=4:10
  ...
  TSR=TSR+1;disp(TSR);
  store_Phi(:,TSR)=Phi;
  store_TSR_local(:,TSR)=TSR_local;
  store_axial_induction(:,TSR)=axial_induction;
  store_angular_induction(:,TSR)=angular_induction;
  store_relative_wind(:,TSR)=relative_wind;
  store_Check(:,TSR)=Check;
  store_Diff(:,TSR)=Diff;
  store_Cp(:,TSR)=Cp;
  store_TSR(:,TSR)=TSR;
  ...

GET RID OF THE LINE

TSR=TSR+1;

entirely. If you're trying to build an array by column, what columns to you want the values to go into? As is, you're putting them into 5 and up since the first TSR value is four and you inexplicably increment it by one before using it; that leaves the first four columns empty and it's not surprising you're subsequently confused with what you're plotting.

Kevin 2014-7-10

Hi,

Thanks for the reply. I have removed the TSR=TSR+1 line from my code so now it appears to iterate as expected. I want the final values to go from a TSR value of 4 to 10. I have attached the graph which I have now outputted. However, instead of the desired power curve with all 6 points, the graph appears to only have the highest (or initial) value. Do you have any idea of how I might fix this problem?

Thanks, Kevin

dpb 2014-7-10

...TSR value of 4 to 10.

Well, you guaranteed that by the loop index.

...instead of the desired power curve with all 6 points, ...

The sequence 4:10 includes 7 values, not 6.

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Answer 1

Star Strider 2014-7-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/141259-graph-not-plotting-all-values#answer_144487

在 MATLAB Online 中打开

It’s difficult to follow your code, and I can’t run it. You probably need to display the incremental value of store_TSR to see what its value is in the loop.

If you want to plot Cp as a function of TSR, your plot statement should be:

plot(store_TSR,store_Cp)

I don’t know what you’re doing with this statement:

TSR=TSR+1;disp(TSR);

Since you’re using TSR as a loop counter, it will have no effect, so delete it. You can’t redefine the loop counter inside the loop.

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dpb 2014-7-10

Well, tho, he can (and does) create/modify a local variable of the same name in the loop and he's (stubbornly) refused to take the previous advice given in that regard at

http://www.mathworks.com/matlabcentral/answers/141112-for-loop-not-working

The loop index TSR variable does revert and alias the other local TSR at the beginning of the next iteration but he then mungs it up again.

I gave several demos in the other thread; unfortunately, while thanking for the advice it seems to have not had any effect.

@Kevin -- I gave several hints at otherwise simplifying your code in the previous thread. I again suggest you look at those. If the idea is to build an array from 1:someN columns; keep a secondary variable, say iCol and initialize it then increment it in the loop instead of munging on the loop index variable.

Also, if that's the idea, preallocate and fill the arrays instead of dynamically "growing" them each pass thru the loop.

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