Troubleshooting my code ( ~15 lines)

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Vidhan Malik 2016-3-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/275162-troubleshooting-my-code-15-lines

评论： Vidhan Malik 2016-3-24

采纳的回答： Star Strider

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I am using the following code:

syms B1 B2 SWR Cv 
i = 1;
Cv(1,2) = 0.39;
B1(1,2) = 55;
B2(1,2) = 29;
while i<61
    i = i + 1;
      Cv(i,2)= Cv(i-1) + 0.01;
      R = 0.5 == Cv(i,2)./2*(tan(B1*pi/180) + tan(B2*pi/180));
      Cp = 0.5 == 1- (1+tan(B2*pi/180).^2)/(1+tan(B1*pi/180).^2); 
      [B1(i,2),B2(i,2)] = vpasolve([R, Cp], [B1,B2]); 
      SWR = Cv(i,2)*(tan(B1(i,2)*pi/180) - tan(B2(i,2)*pi/180)); 
      X(i,2) = Cv(i,2);
      Y(i,2) = SWR;
end

And it is giving me the following errors:

Warning: The system is inconsistent. Solution does not
exist. 
> In symengine
  In sym/privBinaryOp (line 908)
  In  /  (line 309)
  In gasturbine_hw7_try2 (line 16) 
Error using sym.getEqnsVars>checkVariables (line 92)
The second argument must be a vector of symbolic
variables.
Error in sym.getEqnsVars (line 54)
    checkVariables(vars);
Error in sym/vpasolve (line 132)
    [eqns,vars] = sym.getEqnsVars(varargin{1:N});
Error in gasturbine_hw7_try2 (line 18)
    [B1(i,2),B2(i,2)] = vpasolve([R, Cp], [B1,B2]);

I am having trouble understanding why the errors are occurring. What I am trying to do is solve equation R and Cp for increasing values of Cv. So I am simply making an array for the variables B1, B2 and Cv and using the values in each index to solve for a specific value of SWR. I know you can do this using anonymous functions, but I am having trouble doing it that way and so am doing it this way. I seek help in this method, not the other.

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Walter Roberson 2016-3-24

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Why do you sometimes access Cv with one index and sometimes access it with two indices?

Cv(i,2) = Cv(i-1) + 0.01;

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采纳的回答

Star Strider 2016-3-23

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此回答的直接链接

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What was the problem with my fsolve approach? Using fsolve is much more efficient than using the Symbolic Math Toolbox for iterative problems.

Note that:

R = 0.5 == Cv(i,2)./2*(tan(B1*pi/180) + tan(B2*pi/180));

is equivalent to:

R = 0.5 == Cv(i,2)*(tan(B1*pi/180) + tan(B2*pi/180))./2;

You need to be sure your parentheses are nested correctly.

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Vidhan Malik 2016-3-24

编辑：Vidhan Malik 2016-3-24

This is what a singular compressor stage looks like where the blade between 1 and 2 is the rotor blade which revolves. The blade between 2 and 3 is the stator blade which remains stationary and corrects the flow coming out of the stator blade and gets the flow of air it ready to go into the next stage.

This is a crude drawing of the velocity triangle for the air entering the compressor stage (like wise you will have an additional triangle for the air leaving the blade). In the triangle, W represents the speed of air relative to the blade, C is the absolute velocity of the air, and U is the speed at which the rotor blades revolve!

Finally, this is the velocity triangle that you get for just the rotor blade (The triangle on the bottom, triangle1 is the velocity triangle of the air entering the rotor blade. The triangle on the top, triangle2 is the velocity triangle of the air leaving the rotor blade. Like wise, Beta1 is the angle at which the air enters the rotor stage, and Beta2 is the angle at which the air leaves the rotor stage, the angles being relative to the rotor blade)! Cz simply represents the horizontal component of the velocity of air (axial velocity). The flow coefficient with applied assumptions and simplification turns out to be Cv=Cz/u. As you guess, this is the parameter I was changing in my equations! As the value of Cv is changed, you can see that the geometry of the triangles would change too, giving you new Beta1 and Beta2 values so that is exactly what I am finding out using this code! Fun stuff right? :)

Star Strider 2016-3-24

It’s relatively esoteric physiology and biochemistry, likely on par with the detailed fluid dynamics of jet engines. The point is that there are a lot of components to physiological regulatory systems, not all of which are even known, and most of which are important but are both uncontrollable and unobservable, at least in real time.

Vidhan Malik 2016-3-24

Only until you figure it out! :)

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