ODE45: IF/loop function
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Komal Rajana
il 9 Gen 2020
Risposto: Jyothis Gireesh
il 12 Feb 2020
Hello,
I would like to know if its correct to write my differential equations as follow in the 'if' command in the function file. If not, please advice. I am trying to model a simple damper.
Thanks.
function [dy] = SDOF2(t, u);
dy = zeros(2,1);
m=1000; %Mass (lb.sec^2/in.)
k =100000; %Stiffness (lb/in.)
omega = sqrt(k/m); %Natural Frequency
c=2000;%Damping coefficient (lb.sec/in.)
g =386;%Acceleration of gravity (in./sec^2)
c_cr=2*m*omega; %Critical damping coefficient
xi = c/c_cr;%Damping ratio
%%Define the forcing function
% if t<=0.5
% F = sin(4*pi*t);
% else
% F =0;
F = 0;
% b=1*m*(((-omega*omega*u(1)-2*xi*omega*u(2)+F))/u(2)>0);
% end %%%%-ESTIMATION-%%%%
if ((((-omega*omega*u(1))-(2*xi*omega*u(2))+F/m)/u(2))>0)
dy(1) = u(2);
dy(2)= -omega*omega*u(1)-2*xi*omega*u(2)+F/m-0.5*m*((-omega*omega*u(1))-(2*xi*omega*u(2))+F/m);
else
dy(1) = u(2);
dy(2)= -omega*omega*u(1)-2*xi*omega*u(2)+F/m;
end
% dy(2)= -omega*omega*u(1)-2*xi*omega*u(2)+F/m;
end
7 Commenti
Meg Noah
il 10 Gen 2020
There's a solution here on the web:
Also, I've implemented a Runge-Kutta to solve baseball motion under atmosphere drag and lift:
It's a 3-D version.
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Jyothis Gireesh
il 12 Feb 2020
It is my understanding that the differential equation is a function of “u(1)” and “u(2)”. So it is safe to assume that “u(1)” and “u(2)” are symbolic variables (or can be defined as symbolic). In this case, it may be better to use the “piecewise” function which allows conditionally defined expressions or functions.
Please refer to the following documentation link to get information on “piecewise” function
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