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VibeMeasLab

VibeMeasLab - Vibration Measurements Part 1 Sine Sweep Test...

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1 Vibration Measurements Part 1 Sine Sweep Test of a Cantilever Beam Objectives: The objects of this experiment are to: 1. Find the first natural frequency of a cantilever beam using both theoretical and experimental techniques and to estimate the first mode’s damping. 2. Find the second natural frequency of a cantilever beam by locating its 180° phase shift. Introduction: Every physical bony has an infinite number of resonant or natural frequencies. The body will vibrate with a different vibration envelope for each of these resonant frequencies. We refer to the vibration envelope as the mode of vibration, hence we refer to the resonant frequencies as modal frequencies. You can see the vibration envelope of a meter stick by holding it horizontally by its end and moving it rapidly up and down. The first mode will look like a wedge with the apex at your hand. When the meter stick reaches the edge of the vibration envelope, it must come to a stop so it can reverse its direction. Your eye can see the stick when it briefly stops moving, but when it passes through the midpoint it is going very fast and appears as a blur. If you shake the stick even faster you will see the second vibration mode. No one has been able to shake it fast enough to see the third mode The first three vibration modes of a cantilever beam are shown in Figure 1. Notice that each mode adds one vibration node to the mode shape. The natural (or resonant or modal) frequency associated with each of these vibration envelopes s greater than that associated with the previous envelopes. That is 1 2 3 ...

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