MATLAB: Help with Colebrook equation and f zero command.

colebrookcolebrook equationfzerofzero commandroot

I am trying to do a problem with the colebrook equation in which I have to find the roots of the equation to find "f". I am trying to use the fzero command along with a function file, but it is not working. How do I do this?

function f = fricfactor(f) Re = linspace(10e4,10e7,31); f = (1/sqrt(f))-2*log10(Re*sqrt(f))-0.8; end

 fcw = fzero(@fricfactor,[0 1]);

Best Answer

f=@(x)(1/sqrt(x)-2*log10(Re*sqrt(x))-0.8);

Re=10000;

Delta_Re=200;

for i=1:20

fcw(i)=fzero(f,[1e-8 1]);

Reynolds(i)=Re;

Re=Re+Delta_Re;

end

Best wishes

Torsten.

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MATLAB will plot in the same open axes object unless it to create a new one.

Do this:

figure(1)
plot(Re1, FCW, Re1, fSJ, Re1, fB)
   ... CODE ...
figure(2)
plot(fB,FCW,fSJ,FCW)
   ... CODE ...

and they should both be visible (although you will probably have to toggle between them or offset them from one another to see them both).

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You should be able to use the function fzero() to solve for f in your implicit equation.

>> doc fzero

for details.

I think this will do it, but definitely check:

darbyFormula = @(x) 1/sqrt(x)+2*log10(eoverD/3.7 + 2.51/Re/sqrt(x));
f = fzero(darbyFormula,1)

Best Answer

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