The mechanisms of feedforward and feedback methods were analyzed for active vibration control. A feedforward controller was designed in the frequency domain using optimal control theory. The feedback control uses the direct velocity feedback method. The two control methods were applied
to a plate, and the mechanisms were analyzed by examining the structural intensity map. In the case of the feedback system, the disturbance acting on the structure serves as a source, and the control force acts as a sink to reduce the vibration energy of the structure. On the other hand, in
the feedforward system, the energy is reduced by the destructive interference of the intensity generated by the disturbance and control force. In this case, when analyzing the vibration intensity of the structure, component by component, the intensity generated by the control force is interfered
with mainly the mutual power terms. They are the product of the force due to disturbance and the velocity due to control force, vice versa. Based on this analysis under the source-sink relationship of the feedback system, we confirmed that a higher control performance can be obtained by the
control force at a point where the structural intensity is in a more easily flow position.
many clinical studies done on the changes of heart rate variability (HRV) during anesthesia have analysed and reported their results using only absolute values without any problems, 1-4 and some have even suggested that the normalisation of spectral powers does not reveal any additional information compared to the low frequency/high frequency (LF/HF) index. 5 LabChart v7 software (ADInstruments, Co., Sydney, NSW, Australia) was used for analysis of HRV in our study, and the LF/HF ratio offered by this program is not different when calculated with both absolute and normalised units. Our primary outcome was the change in the LF/HF ratio in each group during controlled hypotension induced with different agents, and we feel that although not perfect, our method was sufficient enough to explain and support our results and discussion. We appreciate the opinion of Dr. Kurtoglu et al., and plan to analyse and present HRV results in normalised units as well in future studies.
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