are responsible for causing harmful effects to the adjoining structures,
foundation and machines leading to devastating damages. Additionally, the
dynamic vibrations also cause annoyance or distraction to the people working or
accessing near the machine operation area. However, if the frequency ratio is
managed to remain outside the critical range of 0.4 and 1.5 and if the amplitude
lies within the allowance limits then damaging/harmful effects may be
successfully eliminated, especially when the system us damped.Transfer or
transmission of vibration may be controlled and damaging effects can be
successfully reduced to considerable amounts by isolation of the source called
active isolation or by protecting absorber or receiver called passive isolation.
The measures employed are as follows;
- By placement or location of machine foundation far away from adjoining
structures, the process is called as geometric isolation. Mechanism is that
with the increase in distance between machine foundation and adjoining
structure the amplitude of surface waves (R-waves) gets reduced. For this
follow the ratio of foundation mass to engine mass. The specific
decreasement in the amplitude can be achieved by placing the foundation to a
greater depth since the R-waves tends to reduce successfully due to increase
- Extra masses called as dampers may be attached/added to the foundation
encountering higher frequency machines in order to form a multiple degree
freedom system plus for altering the natural frequency.
- In case of reciprocating machines, considerable amount of vibrations can be
reduced by counterbalancing the exciting forces through means of attachment
of counterweights at the crank sides.
- The placement or use of absorbers helps to reduce the vibrations
considerably. Absorbers may be rubber mountings, felts and corks applied
amid the base and machine.
- Another technique can be by attaching an auxiliary mass along with a spring
to the machine foundation such that the system gets transformed to
two-degree-freedom system. Usable when the system is at resonance.
- The strength of soil may be improved via chemical or cement stabilization
technique, which enhances the natural frequency of system. This technique
is preferable in machines with operating frequencies.
- The propagation or fluctuation of waves can also be lowered by use of sheet
piles, screens and trenches.