Vibrations 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 in depth.
- 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.