illogical graph values when plotting shear diagram

Question

Ali Ramadan 2020-3-29

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513669-illogical-graph-values-when-plotting-shear-diagram

评论： Image Analyst 2020-3-29

I am trying to solve the following problem where i need to plot the shear diagram but in deed when ever i try to plot my graph it comes with illogical values

i am forced to use the function calc with no change to it (thats the only condition ) i can only change my script and in what context do i call my function

am getting the following graph

My script :

clc;
clear all;
w=2;
EI=1e6;
L=10;
x=linspace(0,L,1000)
a1=1;
an=4;
UDL=an-a1;
a=linspace(a1,an,1000);
dis=linspace(1,L,1000);
for i=1:length(a)
 res=calc(dis(i),L,[w a(i)],EI);
    v(i)=res(1);
    m(i)=res(2);
    y(i)=res(3);
end
plot(x,v);

the function calc :(should not change anyhting in it)

function [ res ] = calc( x,L,Load,EI )
%it is used to find the shear moment and deflection
%for a simply supported beam in 2 cases
% UDL, point load
if length(Load)==1 %UDL
    P=Load;
    res(1) = P*L/2-P*x;
        res(2) = P*L/2*x-P*x ^2/2;
        res(3) = -P*x/(24*EI)*(L^3-2*L*x^2+x^3);
elseif length(Load)==2 %Point load
    F=Load(1);
    a=Load(2);
     b=L-a;R1=F*b/L;R2=F*a/L;
        if x <= a
            res(1) = R1;
            res(2) = R1*x;
            res(3) = -F*b*x/(6*L*EI)*(L^2-x^2-b^2);
        else
            res(1) = -R2;
            res(2) = R1*x -F*(x-a);
            res(3) = -F*b/(6*L*EI)*(L/b*(x-a)^3+(L^2-b^2)*x-x^3);
        end
else
    res=[];
end
end

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Answer 1

Image Analyst 2020-3-29

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513669-illogical-graph-values-when-plotting-shear-diagram#answer_422613

在 MATLAB Online 中打开

Your x is just a single value, not a list of every x location for each v location. But you can leave it out and just plot x as the index number:

plot(v, 'b-');

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Ali Ramadan 2020-3-29

i updated it the code and inserted the graph that am getting but in deeed its illogical , the shear diagram should be a staright line then a decrease of y=ax+b form then continue as a straight line and it should decrease by 2 overall , which is not happening any ideas?

Image Analyst 2020-3-29

It IS a line, followed by a decrease/drop of about 2, then another line. At around x = 1.2, the y goes from about 1.75 to -0.25, which is a drop of 2. I have no idea about the physics of that program - it just looks like an uncommented, alphabet soup to me. You maybe can take it up with your professor.

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