The force on a cylinder near a wall in viscous potential flows

[Myo Gyi]

How can i plot to get this figure. This is the page number 92 of POTENTIAL FLOWS OF VISCOUS AND VISCOELASTIC FLUIDS, Daniel Joseph, somebody help me please!

[John D'Errico]

How is this a question about MATLAB?

[Myo Gyi]

I am sorry sir... I want to plot this kind of figure sir. But I have no idea to plot sir, Thanks

[John D'Errico]

So then you need to learn MATLAB. Do the free MATLAB OnRamp course. Read the help docs for functions like plot. Look at the examples in the documentation. Try things out. If you don't know how to plot something, then try to plot something simple. TRY IT.

You won't learn unless you make an effort to learn, and there is much available online already to teach you how to plot a simple function of one variable. That is all this is: a simple function of one variable, thus (b/a).

[Myo Gyi]

Thank you very much sir.

Answer 1

[Alan Stevens]

Here is Cx for you:

>> bovera = 1.001:0.2:10;
>> Cx = 1./(sqrt(bovera.^2-1)*2*pi);
>> plot(bovera,Cx,'o'),grid

(Note that Cx is infinite at x = 1).

I'll leave you to try Cy.

[Myo Gyi]

Thank you very much sir.... Please give me some suggestions.

[Alan Stevens]

If you are unable to understand my reply above enough to have a go at calculating and plotting Cy, then it strongly suggests that you should do the Matlab Online course before tackling any other Matlab activities.

[Myo Gyi]

Yes sir.. Thanks your suggestion.

[Myo Gyi]

Can I plot just only Cy ? Sir

[Alan Stevens]

Yes, just use the Cy formula.

[Myo Gyi]

Its not working Sir... Help me please

bovera = 1.001:0.2:10;
Re = 1 ;
Cy = -(4/Re).*1./(sqrt(bovera.^2-1)).*(1-exp^(-2.*cosh^(-1)*((bovera))));
plot(bovera,Cy,'r-o'),grid on

[Alan Stevens]

Replace

Cy = -(4/Re).*1./(sqrt(bovera.^2-1)).*(1-exp^(-2.*cosh^(-1)*((bovera))));

with

Cy = -(4/Re).*1./(sqrt(bovera.^2-1)).*(1-exp(-2.*cosh(bovera).^-1));

(Also, plot the absolute value of Cy).

[David Goodmanson]

I think it's more likely that what was intended is

Cy = -(4/Re).*1./(sqrt(bovera.^2-1)).*(1-exp(-2.*acosh(bovera)));

[Alan Stevens]

@David Goodman. Yes, I think you are probably right, though niether version quite agrees with Myo's plot!

[Myo Gyi]

Thank you very much Sir David Goodmanson and Sir Alan Stevens. Can I combine Cx and Cy? If not, no problem sir.

[David Goodmanson]

HI Alan,

I didn't list the acos version as a for-sure answer because for whatever reason it differs from the plot by a factor of 2.

Also if you were to spell my name correctly I would appreciate it. Thanks.

[Alan Stevens]

@David. Apologies for misspelling your name - I'll try to be more careful in future!

[Myo Gyi]

Yes Sir. How can I label /Cx/ or /Cy/ ? Which code shell i uses?