How can I model a delay differential equation in simulink?

Hi I'm looking to model the following non linear delay differential equation modelling a single point turning situation in Simulink in order to then be able to apply a control to the process. However I'm having difficulty doing so and was hoping someone would help me out?

xddot= -a*xdot - b*(x+x^3 )- c*x(t-1)

Where: xddot is the second derivative of x;

xdot is the first derivate of x;

a, b and c are constants;

Answer 1

[Shashank Prasanna]

You can use the delay block:

http://www.mathworks.com/help/simulink/slref/delay.html

For the rest you just need integrator blocks and gain blocks.

[James Fraser]

Hi Shashank,

I was hoping you could be a bit more specific? I've attempted to produce a model of the equation using these blocks in a similar way as to (<http://blogs.mathworks.com/seth/2008/05/23/how-to-draw-odes-in-simulink/>) but for some reason the value of x goes to infinity after a short period of time and the solution breaks down.

I've already used the dde23 solver in matlab to produce a solution for the motion of the cutting tool. However, as it is easier to apply a control in simulink i'm attempting to remodel it.

Thanks

[Shashank Prasanna]

Can you share what you have already?

[James Fraser]

Infact, problem solved - it was down to the solver that was being used in simulink causing singularities. Changed to the ode45 solver and its working great.