how coding drag coefficient?

2016 8 2
2 个回答
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更新时间：2021 4 14
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Hi all, I need kindly help to write a code to calculate drag coefficient as the attached figure.
thank you in advance

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Bob Thompson
Bob Thompson 2016-8-2
Could you expand a little bit more on what you're looking for exactly? All I can determine from the information in the pic is that Cd = 0.0012.
Lilya
Lilya 2016-8-3
The equation is in the first line, this is what I actually want. The wind speed values are in matrix which in form of u, v.

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Star Strider
Star Strider 2016-8-3

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See if this does what you want:
tau = @(U10) 1.22.*[1.2E-3.*((4 < U10) & (U10 < 11)) + 1E-3*(0.49 + 0.065*U10).*((11 <= U10) & (U10 < 25))].*U10.^2;
x = linspace(0, 24.9);
figure(1)
plot(x, tau(x))
xlabel('\itU_{10}\rm')
ylabel('\bf\tau\rm')
grid

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Lilya
Lilya 2016-8-3
编辑：Lilya 2016-8-3
thank you Strider for your answer. tau has to components regarding the two wind components (u, v). the output should be taux and tauy. the wind speed magnitude is given by the following equation: U=sqrt(u^2+v^2). thus, tau will be taux and tauy . taux=rho*CD*U*u, tauy=rho*CD*U*v Kindly find the attached figure for more explanation.
thank you again .
Star Strider
Star Strider 2016-8-3
That image doesn’t tell me anything useful. I have absolutely no idea what ‘u’ and ‘v’ are.
If they are directions, you need to separate them as, for example, sin and cos (or sind and cosd for degree measure) functions.
Lilya
Lilya 2016-8-3
编辑：Lilya 2016-8-3
I did it already when I calculated the two components of wind speed u and v. It gave these wind speeds to calculate the wind stress (i.e. tau).
Star Strider
Star Strider 2016-8-3
I’m still lost. If you’ve already used ‘u’ and ‘v’ to calculate ‘U10’, what is the problem?
What do you want to do with ‘u’ and ‘v’?
Lilya
Lilya 2016-8-3
I apologize. u and v to calculate tau. But in form of those two components. Taux by using u. Tauy by using v.
I really appreciate your help.
Star Strider
Star Strider 2016-8-3
My pleasure.
I believe I understand now.
See if this works:
tau = @(U10) 1.22.*[1.2E-3.*((4 < U10) & (U10 < 11)) + 1E-3*(0.49 + 0.065*U10).*((11 <= U10) & (U10 < 25))].*U10.^2;
taux = tau(u);
tauy = tau(v);
Note that the ‘tau’ function has not changed. I included it here for convenience.
Lilya
Lilya 2016-8-3
Thank you very much for your help. I greatly appreciate it.

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YATIK SHAH
YATIK SHAH 2021-4-14

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tau = @(U10) 1.22.*[1.2E-3.*((4 < U10) & (U10 < 11)) + 1E-3*(0.49 + 0.065*U10).*((11 <= U10) & (U10 < 25))].*U10.^2;
x = linspace(0, 24.9);
figure(1)
plot(x, tau(x))
xlabel('\itU_{10}\rm')
ylabel('\bf\tau\rm')
grid

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