Finding Damped Frequency of a State Space Matrix Equation with MATLAB

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Discussion Overview

The discussion revolves around finding the damped frequency of a state space matrix equation using MATLAB, specifically in the context of a vibration problem related to tyre mechanics. Participants explore the relationship between state space representations and the parameters necessary for calculating damped frequency.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant seeks assistance in calculating the damped frequency from a state space equation represented by a known 2x2 matrix [A] and a 1x2 matrix [B].
  • Another participant suggests that if the states are defined correctly, mass, stiffness, and damping ratio can be extracted from the [A] matrix to calculate the damped frequency using basic vibration equations.
  • A participant notes that the system is likely a second order system, which is confirmed by the original poster.
  • The original poster acknowledges the need to derive the mass, stiffness, and damping matrices (M, K, C) from [A] to proceed with the calculations.
  • One participant advises that deriving the transfer function from the state space equation could provide the necessary information to find the damped frequency, while also noting the potential for multiple state-space representations for the same system.

Areas of Agreement / Disagreement

Participants generally agree on the nature of the system being a second order system and the importance of deriving the transfer function. However, there is no consensus on how to extract the necessary matrices from [A] or on the specific steps to calculate the damped frequency.

Contextual Notes

Participants express uncertainty regarding the extraction of the mass, stiffness, and damping matrices from the state space representation, indicating a potential limitation in the information provided by the [A] matrix.

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Matlab, how to find damped frequency of a sate space matrix euqation?

Hello:

I am working on a tyre mechanic problem basically it just a vibration problem so far I have dervied the the state space equation which is in the form

x'=[A]x+u

[A] is 2x2 matrix, is a 1X2 matrix (u could be treated as 0) and they are both known

but I don't know how to calculate the damped frequency. Anybody could help please?
 
Last edited:
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How did you define your states? If you know (or can extract from your A matrix, based on how you defined your states) your mass, stiffness, and damping ratio you can calculate it using some basic vibration equations. Try googling "damped natural frequency." The wikipedia article shows how to calculate it based on the undamped natural frequency and damping ratio.

-Kerry
 
By the way - it sounds like you've probably got a second order system :wink:
 
KLoux said:
By the way - it sounds like you've probably got a second order system :wink:

Ya you are right it is a second order. Thanks dude. I know that if I have the mass, stffness and damping matrix can work out the natural frequncy and damping ratio so it is the damped frequency but the problem is I couldn't extract the M,K,C matrix from [A]. I have seen the damp function in matlab. I think what I need to do it is to derive the transfer function of the state space equation.
 
If you can derive the transfer function yourself, that should give you what you need. Be aware that there can be multiple state-space representations for the same system depending on how you construct your state vector.

-Kerry
 

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