Here is shown a run up transient with a certain constant acceleration. As you can see the vibration level goes up and then goes down again. Here we are interested in the envelope, which is the maximum vibration level which is reached during this transient. This is for instance a transient, which was calculated with a constant acceleration. In a real machine a constant acceleration is not so common because you have limited power in the machine and you generally have a very high acceleration at low speed.

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