# A 2nd Order ODE

1. Jul 31, 2006

### amir99civil

Dear All,

I have a Problem about a 2nd order ode. I dont know how it can be solved with Matlab. If someone know about it then please let me know. I need to get the values of x & y. All other values are known.

The equation is:

[ M + mf mf
mf mf ][ ¨x
¨y ]+
[ C 0
0 cf ][ x˙
y˙ ]+[ K 0
0 kf][ x
y ] = [ Fe(t)
0 ]

Thanks Alot

2. Jul 31, 2006

### Data

you are going to have to make the equation more clear. What are all the 0s? Try to put it up in tex.

3. Jul 31, 2006

### Mute

I think this is how it's supposed to look:
$$\left( \begin{array}{cc} M + m_f & m_f \\ m_f & m_f \end{array} \right) \left( \begin{array}{cc} \ddot{x} \\ \ddot{y} \end{array} \right) + \left( \begin{array}{cc} C & 0 \\ 0 & c_f \end{array} \right) \left( \begin{array}{cc} x\\ y \end{array} \right) + \left( \begin{array}{cc} K & 0 \\ 0 & k_f \end{array} \right) = \left( \begin{array}{cc} F_{e}(t)\\ 0 \end{array} \right)$$

I don't know how to use MATLAB to solve it, though.

Last edited: Jul 31, 2006
4. Aug 1, 2006

### J77

There should be an $$\dot{x}$$ after the damping terms (c's) and an $$x$$ after the stiffness terms (k's)...

For the simulation, first write it in first-order form.

It's quite simple to solve this forced msk system as an IVP in Matlab, check the help files on odes...

5. Aug 1, 2006

### amir99civil

yes. This is an equation of motion for a Tuned Liquid Column Damper with (xdot & ydot) after damping terms and (x & y) after the stiffness matrix.I dont know how i can handle the matrics if i change it to first order. If you know something then please explain a little more about the problem. How to handle the matrics to get a first order system.

The zeros 0s are 0.There is no entry where there is zero.

6. Aug 2, 2006

### J77

Write:

$$u=\dot{x}$$ and $$v=\dot{y}$$

then...

$$\dot{u}=\ddot{x}$$ and $$\dot{v}=\ddot{y}$$

ie. you now have 4 first-order equations.