How can I change the response to forced excitation?

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sam plant 2019-8-27

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https://ww2.mathworks.cn/matlabcentral/answers/477757-how-can-i-change-the-response-to-forced-excitation

评论： Anmol Dhiman 2019-9-5

function Structural_drift
% Define initial conditions x(0) & x'(0)
x0 = [0 1];
% Time interval
t = [0 120];
% Solve equation of motion
[T, X] = ode45(@EOM, t, x0);
plot(T, X(:,1), T, X(:,2));
% EOM function & variables
function dx = EOM(t, x)
% Define initial conditions x(0) & x'(0)
% Time interval
M =87500;             % Mass (kg)
k = 20000; % Stiffness value
c = 170;  % Damping constant of structure
Cd = 5000;
Fd = Cd*x(2); %damping force
f=5; %forcing frequency in Hz
w=2*pi*f; %forcing frequency
F = 500000*sin(w*t) ;   %excitation force
term1 = F;
term2 = k*x(1);
term3 = c*x(2);
term4 = Fd;
term5 = M;
dx = [x(2); ((term1 - term2 - term3 - term4)/(term5))]; % Equation of motion
end
end

When using ODE45 for an equation of motion. The forcing amplitude is F. When i change this value the peak value of displacement from the solver isn't changing, it's always the same value regardless of the force size?

any help would be seriously appreciated

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Anmol Dhiman 2019-9-5

I am unable to reproduce the above issue as I am getting different peak value of displacement as shown in the figures below. Can you provide an example with plots explaining the issue.