Theory vibration and shock insulation

Below you will find some information about what vibration isolation is, with active and passive isolation, what a response of a vibration entails and finally what SRS is. If you would like more detailed information about the theory with regards to shock, vibration or sound, please contact us and we will help you further.

Vibration isolation

Vibrations always occur, as an example during transport of a (packaged) product, due to environmental conditions (equipment on board an aircraft, ship or train, wind, etc.) or vibrations are created by the equipment itself like an engine.

The actual vibration level can sometimes be low but can increase strongly due to resonance or an imbalance in the device. The level can increase up to 10-20x from the original vibration level.

Vibrations can cause damage to adjacent machinery, increase wear and tear and can interfere with measuring equipment. Moreover, they can create unacceptably high levels of noise and vibration in an environment.

Vibration isolation by application of springs should prevent the vibrations from being transmitted to the environment, this is called passive isolation. The springs are also used to protect sensitive equipment against vibrations from the environment, this is called active isolation. In order to minimize vibrations, it is necessary to optimally align the mass-spring systems.

The response of a product to a vibration

A mass-spring system has the characteristic that the vibration speed (frequency) is always the same. If nothing has changed in the mass or spring, this combination will remain at the same natural frequency. If a mass-spring system is forced into motion, three extreme states can occur:

·         the mass moves with the impulse

·         the mass moves faster than the impulse

·         the mass moves less than the impulse

If the impulse is gradually increased from a low frequency to a high frequency whilst the response of the mass is measured, the transfer can be calculated. The transfer is the quotient of the response and the impulse by dividing the response by the impulse. For example, if the mass moves twice as fast as the impulse (2/1), the transfer is 2. The point where the increase is at its highest is also called resonance frequency. Vibration isolation only occurs at that point when the ratio is greater than √2.

Shock Response Spectrum (SRS)

A Shock Response Spectrum (SRS) is a graphical presentation of a transient acceleration pulse's potential to damage a structure. It plots the peak acceleration responses of a bank of single degree-of-freedom (SDOF) spring, mass damper systems all experiencing the same base-excitation as if on a rigid massless base.

The diagram shows the SRS of the shock input (red line) and the response of a spring (green line). The natural frequency of the maximum response, such as travel, speed and acceleration, can be read directly from the diagrams.

Note that the Wire Rope Mounts have a non-linear force road diagram in all directions. Therefore, the springs can only be used to a limited extent in a response spectrum.