Trying to find a value at a specific point in an array.

Question

Chett Manly 2021-10-24

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1570433-trying-to-find-a-value-at-a-specific-point-in-an-array

评论： Chett Manly 2021-10-24

采纳的回答： Scott MacKenzie

在 MATLAB Online 中打开

What I am trying to do is find the value of Hmax @ Tmax.

Tmax is a product of Vmax.

clear; close all; clc
G = 9.80665;  %gravity            
D = 0.1;              
v0 = 0; %Start velocity
h0 = 38969; %start height
t0 = 0; %start time
T = 0.01;
A = 0.7; %area pre parachute
m = 118; %mass
%p = 1.2; %rho
C = 1; %drag
%% part a
v(1) = v0;     
H(1) = h0; 
t(1) = T;
n = 1;
  
% 
% vc = sqrt(2*m*g/(p*C*A))
% tc = vc/g
% hc = vc*tc
while 1                                   
    if H(n) < 1043 %break when ground is reached                     
        break 
    end
    Hkm = H(end)/1000;
    g = G*6356.766.^2/(6356.766+Hkm).^2;
    p = 1.2241*exp(-(Hkm/11.661)-(Hkm/18.192)^2+(Hkm/29.235)^3);
   vc = sqrt(2*m*g/(p*C*A));
   tc = vc/g;
   hc = vc*tc;
    
    
    
    
    if n > 26000 %50 sec parachute Drag increase                   
        A = 50;
        C = 3.17;
        
    end
   
    %a(n) = -g - D*v(n)*abs(v(n));  
    a(n) = -g*(1-v(n)^2/((vc^2)));
    %a(n) = g*(vc^2-v(n)^2)/(vc*cosh(t-t0/tc))+v0*sinh(t-t0/tc);
    
    v(n+1) = v(n) + a(n)*T;    
    %v(n+1) = vc*(v0/vc)+tanh(t-t0/tc)/(1+v0/vc*tanh(t-t0/tc)); 
    
    H(n+1) = H(n) + v(n)*T;                
    n = n+1;
    
    t(n) = n/100;
end
 
ng = n-1;           
tg = (n-1)*T;  
a(end+1)=0;
vneg = -v;
aneg = -a;
plot(t,H,'r-');
xlabel('T')
ylabel('H')
title('H(t)')
legend('height')
grid on
[Vmax,Tmax] = max(vneg);
% Hmax??? neet to find the value of H @ Tmax 