Previous in Forum: P1 Material Spec   Next in Forum: Something Cool.
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
6 comments
Rate Comments: Nested
zhulianwei
Participant

Join Date: Mar 2011
Posts: 3

The Dominant Poles Of The Third Order System

03/11/2011 5:29 PM

how can i determine the step response characteristics of the third order system. the lecturer told me first find dominant poles. my equation is 180/(s^3+152.7s^2+135s+180), after i calculate, the equation changed to 180/(s+2.13)(s^2+150.57s+84.2859), but i if use this equation, i can not solve damping ratio and natural frequency. how can i solve this problem. i use calculator got the poles are s1=-150,s2=0.56,s3=-2.13. also can not get zeta and omegan
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
nick name
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3943
Good Answers: 183
#1

Re: The dominant poles of the third order system

03/12/2011 4:22 AM

You have ALL in front of your eyes! One 1st degree equation and an other of the second degree so that you have as I said ALL in front of your eyes!
Register to Reply
zhulianwei
Participant

Join Date: Mar 2011
Posts: 3
#2
In reply to #1

Re: The dominant poles of the third order system

03/12/2011 4:45 AM

no, i cannot find the damping ratio,because the damping ratio should less than 1,if i use that equation calculate, this should further more than one.
Register to Reply
nick name
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3943
Good Answers: 183
#3
In reply to #2

Re: The dominant poles of the third order system

03/12/2011 12:55 PM

According to my computations the damping is 0.44 ! so that it is <1. When i say that you have all in front of your eyes it was not a joke. You do not use the right approach. Try as follows: assume you replace the 3rd degree with a 1st degree +a second degree fraction and assume that the second has the symbolic values as usual then proceed to the equivalence of coefficients and you obtain 6 equations for 6 unknown = a system which is determined (number of equations = number of unknown) and gives you all values you need to write the transfer function in the canonic form.
Register to Reply
zhulianwei
Participant

Join Date: Mar 2011
Posts: 3
#4
In reply to #3

Re: The dominant poles of the third order system

03/12/2011 8:59 PM

i use Matlab command, got the zeta=1, it is critically damped if the damping ratio=1. how can u got damping ratio = 0.44? can u tell me?
Register to Reply
nick name
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3943
Good Answers: 183
#5
In reply to #4

Re: The dominant poles of the third order system

03/13/2011 5:24 AM

That is the problem you use a "command" but do not know how to use the basic algebraic solutions. Unfortunately using soft leads to less knowledge when you are out of the soft. Have a look at classical methods they did not lose their value. You have in previous explanations every thing you need to solve your problem.
Register to Reply
Wicked
Participant

Join Date: Jun 2016
Posts: 1
#6
In reply to #4

Re: The dominant poles of the third order system

06/15/2016 1:32 AM

I followed the steps and got 6 equations and I still got zeta = 1. The one with 0.44 is damping frequency. How do you get zeta = 0.44?
Register to Reply
Register to Reply
Have a Different Question?
6 comments
Copy to Clipboard

Users who posted comments:

nick name (3); Wicked (1); zhulianwei (2)

Previous in Forum: P1 Material Spec   Next in Forum: Something Cool.

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Mechanical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (53 right now)
Show Members
Advertisement