Give a brief explanation to a Why are 48 Hz whole body vibra

Give a brief explanation to: a) Why are 4-8 Hz whole body vibrations of particular concern? b) Why or why not are vibrations at all frequencies treated equally when using ISO standards?

Solution

A)In normal locomotion, such as walking, the human musculo-skeletal system dampens the effects of extraneous body motion from the head. The legs, torso, and neck all absorb shock and limit the amount of motion passed on to the head. However, when in a vibrating environment, these same body parts may resonate and amplify vibration. The components of the body of principal interest in vibration research are the head, torso, and arms. While other body parts may also resonate at given frequencies, their effects are not central to the performance of visual or manual tasks. More specific modeling of resonant frequencies for body parts can be predicted by computer simulation of given environments. For example, for a operator of given size, and a given seat and posture, the Biodyne-78 computer model estimates that there will be maximum task disruption due to head resonance when the body is exposed to vibration at 4 Hz. So at this range resonace chances in head torso and arm is more. And resonce cause of death so to avoid this situation this frequency is important.

B) Not, beacause Vibration Magnitude is defined as the maximum value of the broadband rms velocity in the specified frequency range (typically from 10 to 1,000 Hz), as evaluated on the structure at prescribed points. Note that other quantities such as displacement or acceleration and peak values instead of rms values are permitted, but may not easily correlate to criteria based on rms values. Evaluation criteria to assess vibration severity include both vibration magnitude and changes in vibration magnitude.