0 个投票

Hi there
I have the following code:
tf = 1;
t = linspace(0,3);
Ft = zeros(length(t),1);
% Here I generate the force values at different time intervals.
for i = 1:length(t)
if t(i) <= tf
Ft(i) = Fo*sin(2*pi*t(i)/tf);
elseif t(i) > tf
Ft(i) = 0;
end
end
ic = [0, 0]; % Initial conditions
dXdt = @(t, x) [x(2);
Ft * 1/(m1+m2)];
[t, x] = ode23(dXdt, [0, 3], ic);
I'm struggling to incorportate this time varying force F(t) into the ode23 function.
Any help as to how I can maybe get this done?
Thanks in advance!

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darova
darova 2020-4-25

0 个投票

Use function handle
Ft = @(t) (t<=tf)*Fo*sin(2*pi*t/tf);
dXdt = @(t, x) [x(2);
Ft(t) * 1/(m1+m2)];

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Walter Roberson
Walter Roberson 2020-4-25
That would work if the driving force was not discontinuous.
It seems to work though.
Walter I'll try your method now, because what you're saying makes sense.
Thanks for the help!

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Walter Roberson
Walter Roberson 2020-4-25

1 个投票

You cannot do that the way you want. The ode* routines cannot handle discontinuities in the driving functions. You need to break it up into two time periods, one with the force and one without the force.
tf = 1;
dXdt_F = @(t, x) [x(2); Fo*sin(2*pi*t/tf) / (m1+m2)];
dXdt_NF = @(t, x) [x(2); 0];
ic = [0, 0]; % Initial conditions
[t1, x1] = ode23(dXdt_F, [0, tf], ic);
ic2 = x1(end,:);
[t2, x2] = ode23(dXdt_NF, [tf, 3], ic2);
t = [t1; t2(2:end)];
x = [x1; x2(2:end,:)];

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