problem in plotting in a nested while loop in a for loop

i want to plot for different values of Vx. but it is only plotting for one value. please guide

clc
clear all

Vx = [0.7383
    1.3266
    1.5226
    1.6058
    1.6388
    1.6482
    1.6486
    1.6494
    1.6552
    1.6663
    1.6787
    1.6847
    1.6727
    1.6240
    1.5007
    1.1878]*1000;
 
  m=.001; 
  
  A=pi*(.007)^2;
  C=.9; 
  rho= 1.2 ;
  D=rho*C*A/2;
  g=9.81; 
          %Initial Conditions
    delta_t= .001; %s
    theta=10; %deg
    count=1;
  for aa=1:16
    nn=1;    
    x(1)=0;
    y(1)=0;
    t(1)=0 ;
    vin=Vx(aa);
    
    
    vx=vin*cosd(theta);
    vy=vin*sind(theta);

    while min(y)> -.001
        v = sqrt(vx^2 + vy^2);
        ax=-(D/m)*vx^2;
        ay=-g-(D/m)*vy^2;
        vx=vx+ax*delta_t;
        vy=vy+ay*delta_t;
        x(nn+1)=x(nn)+vx*delta_t+.5*ax*delta_t^2;
        y(nn+1)=y(nn)+vy*delta_t+.5*ay*delta_t^2;
        t(nn+1)=t(nn)+delta_t;
        nn=nn+1;
    end
    
    count=count+1;
    plot(x,y)
    xlabel('x distance (m)')
    ylabel('y distance (m)')
    title('Projectile Path')
    
    
    hold on
    
  end
 

Answer 1

[Alan Stevens]

Replace the code after count = count+1; with the following to get separate figures (though the curves ae all the same!):

    figure
    plot(x,y)
    xlabel('x distance (m)')
    ylabel('y distance (m)')
    title(['Projectile Path    Vx = ' num2str(Vx(aa))] )
    
    
    %hold on
    

I think your while loop logic needs modifying to the following in order to get different curves:

        flag = true;
    while flag
        v = sqrt(vx^2 + vy^2);
        ax=-(D/m)*vx^2;
        ay=-g-(D/m)*vy^2;
        vx=vx+ax*delta_t;
        vy=vy+ay*delta_t;
        x(nn+1)=x(nn)+vx*delta_t+.5*ax*delta_t^2;
        y(nn+1)=y(nn)+vy*delta_t+.5*ay*delta_t^2;
        t(nn+1)=t(nn)+delta_t;
        nn=nn+1;
        if y(nn)<=0
            x(nn) = NaN; y(nn) = NaN; t(nn) = NaN;
            flag = false;
        end
        
    end
    

If you want all the curves to appear on the same figure then keep your original plot commands.

Also, I suspect your ay term should be:

     ay=-g-(D/m)*vy*abs(vy);
     

as the drag will oppose gravity when the projectile is coming down (i.e. when vy is negative).

[Haris Hameed]

thanks but i want in a single plot. it is plotting separate files for them

[Alan Stevens]

See my edited comments above.

[Haris Hameed]

got it, bundle of thanks

[Alan Stevens]

Looking at your equations again, I notice an error in the physics. You need to caculate the drag force using the veocity v, then resolve this onto the x and y directions, not resolve the velocity first and then apply the drag to the separate x and y velocities. The end result is that your acceleration equations should look like the following;

        ax=-(D/m)*vx*v;
        ay=-g-(D/m)*vy*v;

[Haris Hameed]

yes thank you , got it