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Unintended plot while using the cylinder function

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Kevin Hanekom
Kevin Hanekom on 17 Oct 2021
Commented: Kevin Hanekom on 18 Oct 2021
Hello!
I have been attempting to create a 3d object by rotating a 2d plot utilizing the cylinder function. But for some reason my plot comes out with this funnel attached to the bottom. Could you possibly bring some insight on how I may be able to create the shape located above the funnel? To be clear the shape above is exactly what we would expect.
Heres the code.
Yieldstr = 1000; % KPa, Sets the str for all following 2d Plots
minValue = -4*Yieldstr;
maxValue = 4*Yieldstr;
fidelity = Yieldstr/125; %able to use much higher fidelity in 2d
sigx = minValue:fidelity:maxValue;
sigy = sigx.';
VM = (1/(sqrt(2)) .* sqrt((sigx-sigy).^2 + (sigy).^2 +(-sigx).^2));
[x,y,~] = find(VM<Yieldstr);
PStress = [sigx(y).' sigy(x)];
A = boundary(PStress,0);
plot(PStress(A,1),PStress(A,2),'LineWidth',1.75);
view(0,90);
colormap jet
[X,Y,Z] = cylinder(PStress);
mesh(X,Y,Z)
view([-32.636 3.808])
Please let me know if you can think of a better way to achieve this 3d shape.
Thank you,
Kevin.

Accepted Answer

Robert U
Robert U on 18 Oct 2021
Hi Kevin Hanekom,
it seems your vector PStress has two colums which are both interpreted as radius by the function cylinder and merged accordingly. If just one column is of interest, you would have to call it explicitely.
Yieldstr = 1000; % KPa, Sets the str for all following 2d Plots
minValue = -4*Yieldstr;
maxValue = 4*Yieldstr;
fidelity = Yieldstr/125; %able to use much higher fidelity in 2d
sigx = minValue:fidelity:maxValue;
sigy = sigx.';
VM = (1/(sqrt(2)) .* sqrt((sigx-sigy).^2 + (sigy).^2 +(-sigx).^2));
[x,y,~] = find(VM<Yieldstr);
PStress = [sigx(y).' sigy(x)];
A = boundary(PStress,0);
plot(PStress(A,1),PStress(A,2),'LineWidth',1.75);
view(0,90);
colormap jet
[X,Y,Z] = cylinder(PStress(:,2));
mesh(X,Y,Z)
view([-32.636 3.808])
Kind regards,
Robert

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