Frequency response of a hydraulic system in simulink

I'm now modeling a hydraulic system and trying to study its frequency response. I use the linearization manager app to specify the input perturbation and output, however the bode plot is always blank with a vertical line. I'm not sure if it's a hydraulic system so that the linearization failed?

[Mathieu NOE]

hello

have you made some basic tests to make sure your model is working fine

• response for a fixed static value (stable ?)
• step response (stable ?)
• chirp excitation

....

[Paul]

that looks like the plot that would be obtained if linsys1 is 0 with either an undefined sample time or a sample time of 1 sec. The vertical line indicates the Nyquist frequency.

bode(tf(0,1,-1))

Answer 1

[Sahas]

Hi @Shijun CHEN,

As per my understanding, you are using the “Linearization Manager” to linearize the provided Simulink model by adding input and output perturbation points. The “bode” plot for the same appears blank.

I was able to reproduce the issue and see the vertical line in the bode plot. This indicates that the linearization might not have been performed correctly. I used the “Linearization Advisor” to collect diagnostic information from all the blocks of the model and identify potential issues.

I found six possible blocks listed in the image below that could be potential reasons for failed linearization of the model:

Additionally, executing “linmod” command in the MATLAB Command Window provided reasoning behind the failed linearization of the model. Review the warnings below and make the necessary adjustments to the model.

Refer to the following MathWorks documentation for further details on using “Linearization Advisor” and the “linmod” command:

• https://www.mathworks.com/help/slcontrol/ug/identify-and-fix-common-linearization-issues.html
• https://www.mathworks.com/help/simulink/slref/linmod.html#mw_dc636ffe-cf82-4540-bde3-867f459fdbb3

Hope this is beneficial!