Impact excitation is one of the most widely used forms of excitation in modal analysis.
This is advantageous when the excitation is compared with the classical impact excitation illustrated in Figure 2.
Figure 7 shows the results for the impact excitation. The response of the system in the time domain reveals heavy damping in the simulated system; the envelope amplitude decays relatively quickly.
The random impact excitation consists of repeated impacts in order to introduce more energy into the system.
The results for the repeated impact excitation are given in Figure 13.
Base resonant frequencies of the supporting system with the inertial shaker mounted on the frame for different impact excitations Direction of impact excitation Investigated system case [P.sub.x] [P.sub.y] [P.sub.z] Horizontally, Horizontally, Vertically along the laterally frame Position 1 (Shaker mounted above 27,4Hz 18,8Hz 63,3Hz the two dynamometers) Position 2 (Shaker mounted in the 29,3Hz 12,4Hz 42,3Hz middle of the frame) Position 3 (Shaker mounted above 27,5Hz 6,6Hz 36,1Hz the single dynamometer)
The supporting frame was exposed to impact excitations in three directions, while the free vibration of the shaker placed in three positions on the frame were measured (Fig.
For the impact excitations put lengthwise the frame the lowest resonant frequencies stayed almost steady irrespectively of the shaker's placement and they were approximately equal to 27Hz.