Simulating a free fall-project with ode45

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Hallo everyone, I'm trying to simulate a free fall-project, from the stratosphere (about 50 km) to the ground. So, in order to conclude an appropriate solution, drag must be put in consideration. I've allready found a proper solution for the Euler-method, but not for the ode45-method. Furthermore I need to put the [vector-]solutions of the acceleration (the differnecial) for every single calculation-step, in the velocity terms, I mean you could realize this one easy, by putting a while-slope in the code, that the steps would repeat itself until completion. But now to my issue, I've tried many approches with the ode45-method, but non of those have worked out.
Here my code:
function [a] = Test2
start=[0];
tspan=[0 100];
[t,A] = ode45(@Beschleunigung, tspan, start);
%a(end+1) = - g + 1/(2*m)* c_w * A * rho(end)* (v(end))^2;
plot(t,A(:,1));
end
function dv = Beschleunigung(t, v)
g = 9.81;
m = 120;
c_w = 0.28;
A = 2.7;
rho = 1.2041;
dt = 0.5;
hi = 40000;
vi = 0;
t = [0]; % Deklaration des Zeit-Arrays
h = [hi]; % Deklaration des Höhe-Arrays
v = [vi]; % Deklaration des Geschwindigkeits-Arrays
a = [0]; % Deklaration des Beschleunigungs-Arrays
dv = zeros(2,1);
a=dv(1,end);
dv(1,end+1) = g-(1/2*m)*c_w*A*rho*v^2;
v(end+1)=v(end)+dv(1,end)*dt;
h(end+1)=h(end)+v(end)*dt;
t(end+1)=t(end)+dt;
end
  1 个评论
Lukas Menzel
Lukas Menzel 2020-12-22
And here are the errors of my programm
>> Test2
Error using odearguments (line 93)
BESCHLEUNIGUNG must return a column vector.
Error in ode45 (line 115)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options,
varargin);
Error in Test2 (line 10)
[t,A] = ode45(@Beschleunigung, tspan, start);

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采纳的回答

Alan Stevens
Alan Stevens 2020-12-22
More like this perhaps:
hi = 40000; % Initial height
start=[hi 0]; % [Initial height, initial velocity]
tspan=[0 100];
[t,A] = ode45(@Beschleunigung, tspan, start);
%a(end+1) = - g + 1/(2*m)* c_w * A * rho(end)* (v(end))^2;
subplot(2,1,1)
plot(t,A(:,1)),grid
xlabel('t'),ylabel('height')
subplot(2,1,2)
plot(t,A(:,2)),grid
xlabel('t'),ylabel('velocity')
function dv = Beschleunigung(~, hv)
g = 9.81;
m = 120;
c_w = 0.28;
A = 2.7;
rho = 1.2041;
v = hv(2); % velocity, positive downwards
dv = [-v; % dh/dt
g-1/(2*m)*c_w*A*rho*v^2]; % dv/dt
end
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