Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

Principles of Vibrations Control - Notes, Videos, MCQs & PPT

Civil Engineering (CE) : Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

The document Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev is a part of the Civil Engineering (CE) Course Principles of Vibrations Control - Notes, Videos, MCQs & PPT.
All you need of Civil Engineering (CE) at this link: Civil Engineering (CE)

Elements of Vibration Isolation
Vibration Isolation is ususlly required in two cases:
a. Isolating a noisy machine - Here, the focus us on design of a suitable foundation which can absorb the vibrational energy and stop propagation.
Example: Machine foundation for P.A and F.D fan in a power plant, vibration isolation of washing machine.

b. Isolating a sensitive instrument - Here, the focus is on developing a supporting structure that can isolate a precision system from severe ambient excitation.
Example: vibration isolation of satellite structure from the Launching Vehicle

To reduce the transmitted excitation isolators in the form of springs and dampers are used. These are grouped into several catagories as shown below:
Important Isolating Elements
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

Use of elasto-damping materials 

  • Springs
  • Dampers
  •  
  • Complex damping/stiffness

In this lecture, we will discuss about various industrially applied springs and dampers.


Springs 
Various springs are used for vibration isolation. A few of them are discussed here.

Helical spring 
Helical steel springs are often used in earthquake/vibration prone areas below the superstructure. These springs offer high load bearing capacity and effective low frequency isolation. The spring constant is given as follows:
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
Performance of such springs in compression may vary significantly if the ends are not properly secured.

Transversely loaded spring 
The transversely loaded arrangement as shown below offer higher load carrying capacity (due to smaller deflection). This also offers increased damping due to the friction between the spring surface and the support.
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
   Figure 20.1: Transversely loaded spring

Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

where,
a - Helix angle
E - elastic modulus
d - wire dia
n - no. of coils
D - coil dia
 

Springs 
Slotted Spring 
This type of springs can be fabricated by machining tubular blanks.
High stiffness ( load carrying capacity ) with high accuracy in a small outline is obtainable with such springs. The spring constant is given by.
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev                     b/a             an
                                                    0.1           0.1
                                                    0.25         0.1
                                                    0.5           0.11
                                                    0.66         0.11
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
Figure 20.2: Passive vibration isolator

 Springs

Statically nonlinear coil spring 
Nonlinear coil springs of different types as shown below are used such that the springs show constant natural frequency isolation. Such system may have undesirable effects like sub or super harmonic Vibration. Isolators with high damping may alleviate this problem.

Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
     Figure 20.3: Different non linear springs

 Belleville Springs 

Beleville springs are also used to provide high load carrying capacity in a small volume similar to slotted springs.
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
               Figure 20.4: Beleville springs 

The load - deflection characteristic is given by the following non-linear relationship.
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
 
As has been shown in the next figure, by varying the h0/t ratio one can obtain a drastic change in the load deflection behaviour of this system.
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
       Figure 20.5: Load deflection curve


 Wire mesh material 

Use of stainless cold drawn wire (0.1-0.6 mm) diameter; knit into bands and wrapped into round packs has been used widely as vibration isolator. The stiffness of the system is given by:
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev               a - ratio of the vibration amplitude to element height
                                                                      A - material parameter
  
The material is strongly hardening for static loading and strongly softening for dynamic loading.


Felt 
Same like wiremesh but developed using nylon or rubber fibre. The dynamic stiffness is given by
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev                        where, N,M, A - material parameter

The next figure shows an approximate guideline for choosing an isolator material based on the level of development.
Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev
Figure 20.6: Different non linear springs
 

Offer running on EduRev: Apply code STAYHOME200 to get INR 200 off on our premium plan EduRev Infinity!

Dynamic Test

Content Category

Related Searches

MCQs

,

Viva Questions

,

Objective type Questions

,

shortcuts and tricks

,

Summary

,

Sample Paper

,

Extra Questions

,

Previous Year Questions with Solutions

,

Semester Notes

,

pdf

,

Exam

,

Free

,

practice quizzes

,

past year papers

,

Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

,

ppt

,

mock tests for examination

,

study material

,

video lectures

,

Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

,

Elements of Vibration Isolation Civil Engineering (CE) Notes | EduRev

,

Important questions

;