no data plots on graph (plot (x,y))

Question

Jocelyn 2020-11-8

0
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评论： Rafael Hernandez-Walls 2020-11-8

Hello,

Thank you for your assistance.

When I run my code, the 'Figure' graph box pop up however there is no data/lines on the graph. I am trying to plot the acceleration, velocity, and altitude of a paratrooper falling out of a plane as a function of time.

Below is my code:

d = 32000;

H = 8000;

Re = 6370000;

%c2 = 0.5*exp(-d/H);

g = 9.8*((1+(d/Re))^2);

Dt = 0;

t = 0;

%Vt = sqrt(g*m/(0.5*exp(-d/H));

dt = 0.0001;

while d > Dt

v = (sqrt((9.8*((1+(d/Re))^2))*m/(0.5*exp(-d/H))))*tanh((9.8*((1+(d/Re))^2))*t/(sqrt((9.8*((1+(d/Re))^2))*m/(0.5*exp(-d/H)))));

d = d + (v*dt);

if d == Dt

break

else

t = t+dt;

d = d + (v*dt);

end

disp('time until ground impact (seconds): ')

disp(t)

plot(d,t)

plot(v,t)

plot((v/t),t)

Full question that I was trying to get the above code to solve was: calculate the time of fall until the ground impact, given c2 scales with atmospheric density as c2 =0.5exp(-d/H), where H= 8km is the scale height of the atmosphere and d is the height above the ground. Furthermore, assume that g is no longer constant but is given by g = 9.8/(1+(d/Re))^2 where Re = 6370km is the radius of the earth. Plot the acceleration, velocity, and altitude of the paratrooper as a function of time.

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Rafael Hernandez-Walls 2020-11-8

m?

Jocelyn 2020-11-8

Thank you. This value was previously saved (it's 70) in the command window, so my code was running even though I did not program it on this script.

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Answer 1

Rafael Hernandez-Walls 2020-11-8

0
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在 MATLAB Online 中打开

David is correct. Why don't you try something like that in your code...

d(1) = 32000;
H = 8000;
Re = 6370000;
%c2 = 0.5*exp(-d/H);
Dt = 0;
t(1) = 0;
%Vt = sqrt(g*m/(0.5*exp(-d/H));
dt = 0.0001;
 m=70;
 indice=1;
while d(indice) > Dt
    g = 9.8*((1+(d(indice)/Re)).^2);
    v(indice) = (sqrt((9.8*((1+(d(indice)/Re))^2))*m/(0.5*exp(-d(indice)/H))))*tanh((9.8*((1+(d(indice)/Re))^2))*t(indice)/(sqrt((9.8*((1+(d(indice)/Re))^2))*m/(0.5*exp(-d(indice)/H)))));
    d(indice+1) = d(indice) + (v(indice)*dt);
    
    if d(indice+1) == Dt
        break
    else 
        t(indice+1) = t(indice)+dt;
        d(indice+1) = d(indice) + (v(indice)*dt);
    end
    indice=indice+1;
    end
 disp('time until ground impact (seconds): ')
 disp(t(indice))
 v(indice)=[];
 plot(d,t)
 figure
 plot(v,t)
 figure
 plot((v./t),t)