Transient Problem in Simulink

I am trying to solve a problem in simulink of the form u' = a + bu + cu^n. ANy suggestions? I'm still new to this, but this has me stuck...

Answer 1

[Arnaud Miege]

I suggest you go through the Getting Started section of the documentation to familiarise yourself with Simulink. Also have a look at the Simulink tutorial section of the web site. There are various demos in the product as well, which you can find in the help browser under Simulink -> Demos.

For your particular problem, you will need the following blocks to compute du/dt as a function of u:

• Constant
• Gain
• Math Function (select "pow")

One you have computed du/dt, you can get u(t) using an Integrator block, and close the loop by feeding the output of the integrator (i.e. u(t)) to the blocks above, that compute du/dt as a function of u(t).

HTH,

Arnaud

[Arnaud Miege]

I forgot the sum block (http://www.mathworks.com/access/helpdesk/help/toolbox/simulink/slref/add.html).

[Brendan]

Thank you Amaud. I have indeed looked at those sections, and thought that the power function should be used. I am a little unsure how they go together. In a simple transient u'= a + bu you would hook together using the sum to add the constant and the return from an integrator, with the gain as an intermediary. But an integrator takes into account the u and the u' component. I am unsure how to hook in the second u to the second power (or more exactly in the case I was looking at, the fourth power) and its multiplier. I would guess its pretty simple, and I am just missing something. I am actually planning to put together a series of different u functions (u1, u2, etc) connected together. But I am still unclear as to how that power component goes in.

Again, I appreciate your help.

[Brendan]

I looked through some of the university sites. I found this...

http://www.engin.umich.edu/group/ctm/working/mac/first_order/linearize/index.htm

It discuses a problem similar enough to mine. I see I was putting the power in the wrong location. THanks