×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

vibrataion isolation

vibrataion isolation

vibrataion isolation

(OP)
Hi guys

I would very much appreciate if someone can help me answer this question. In sdof vibration isolation system with very stiff spring does the system still resonate at the resonant frequency region even if the disturbance force is very small

Many Thanks
Tim

RE: vibrataion isolation

(OP)
Mnany Thanks, your help is very much appreciated. I thought before the disturbance force must be large enough if the stiff is very stiff

Kind Regards
Hatim

RE: vibrataion isolation

(OP)
sorry I ment in my previous message if the spring is very stiff

RE: vibrataion isolation

I agree with the above. You should look into damping fundamentals.
A force that can oppose the external forcing function at resonance is proportional to the first time derivative of the displacement.
This is completely regardless of the stiffness of the 'spring' as the others point out.
cheers

peace
Fe

RE: vibrataion isolation

(OP)
Many thanks guys for your help and sorry about my late reply.To start with  my system is a sdof system isoalton system with mass supported by srpring in parallel with an MR damper (see the attached).

The magnitude of disturbance fore  applied at the top of the system (i.e mass) is about 100N and spring stiffness is 1.4212e+005N.s/m which means my resonance  is at 12Hz. Not sure whether this force is enough to make the mass moves buy few mms at 12Hz (i.e. displacement of mass).

Kind Regards
Tim

RE: vibrataion isolation

(OP)
No it is for a job where it is required to design an experimental vibration rig  

RE: vibrataion isolation

You need to know the damping, since that controls the amplitude at resonance.

F=x*2*pi*f*d  where d is the damping and x is the maximum displacement, for lightly damped systems at resonance, at a guess. The proper equation is in the book you took the picture from, no  doubt.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: vibrataion isolation

Presumably, if you are using a MR damper, then you can control the damping over quite a wide range by adjusting the magnetic field strength to suit your purpose.

M

--
Dr Michael F Platten

RE: vibrataion isolation

"Presumably, if you are using a MR damper, then you can control the damping over quite a wide range by adjusting the magnetic field strength to suit your purpose."
I agree. This is a great suggestion.
To the OP:
This is known as semi-active vibration isolation.
A nonlinear stiffness is also sometimes designed to take advantage good properties in certain regions.
To date, best results (research and practice) have been from a combination of passive and active.  

peace
Fe

RE: vibrataion isolation

Also about your sdof question. That force is it constant? What is the frequency of excitation? (if there is one)
Without this info you don't have much.  

peace
Fe

RE: vibrataion isolation

(OP)
First of all, I would like to thank everyone for the input. The thing I am concerned about is the system might be over-damped even with no current applied to MR damper.Because MR dampers are known to have a pre-loading damping force.  Regarding the excitation, I am using an inertial shaker so I can excite the system at any frequencies within the range of 6HZ to 100Hz frequencies and with magnitude of 100N.

Kind Regards
Tim

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources