Please my Simulink result graph fluctuates but it always ends up constant at 1 with or without an actuator force or even when I change some parameters. What can I do?

Answer 1

[Sam Chak]

Hi @Tobechukwu

The response is most likely caused by the two factors:

• the Unit Step function, generated by the Step block.
• the steady-state output of a system to its constant input

The default value of the Step time in the Step block is '1' second, that is when the step output jumps from the Initial value '0' to the Final value '1'. This seems to be consistent with the transient response that you showed us.

On the steady-state output, you can evaluate if the dcgain command returns 1. See the example:

w = 2e1;
G = tf(w^2, [1 2*0.25*w w^2]);
ssOut = dcgain(G)

ssOut = 1

If the Step block produces the Unit Step function and the dcgain of a system is also 1, then final value of system response at steady state will also be 1.

[Tobechukwu]

I think I get what you said. But hiw I can edit my paramters to give a different graph result?

[Tobechukwu]

I changed the final value of both my Fa and -Fa in the screenshot attached below to 10 and 8 yet it still gave the same graph result. The simulink model is attached below.

[Sam Chak]

Hey @Tobechukwu, you didn't tell the "whole picture" that it is a coupled system. From the beginning, you just gave a piece of image of the Scope, without whatsover numerical information, letting the community to mentally guess what might be causing the observed system response.

More critically, I don't know what the parameters stand for, but if you have changed and , and when all dynamical excitations die down, then I suspect that the Step block is the reason behind this.

[Tobechukwu]

Thank you so much Sam Chak.

[Sam Chak]

Don't mention it, @Tobechukwu. If my analytical deductions from the Answer and Comments have helped you, consider accepting ✔ and voting 👍 the Answer as a closure to this. Thanks!