Performance analysis of active control systems based on the source-sink flow relationship of the structural intensity

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.

Imaging the Tectonic Grain of the Northern Cordillera Orogen Using Transportable Array Receiver Functions

Azimuthal variations in receiver function conversions can image lithospheric structural contrasts and anisotropic fabrics that together compose tectonic grain. We apply this method to data from EarthScope Transportable Array in Alaska and additional stations across the northern Cordillera. The best-resolved quantities are the strike and depth of dipping fabric contrasts or interfaces. We find a strong geographic gradient in such anomalies, with large amplitudes extending inboard from the present-day subduction margin, the Aleutian arc, and an influence of flat-slab subduction of the Yakutat microplate north of the Denali fault. An east–west band across interior Alaska shows low-amplitude crustal anomalies. Anomaly amplitudes correlate with structural intensity (density of aligned geological elements), but are the highest in areas of strong Cenozoic deformation, raising the question of an influence of current stress state. Imaged subsurface strikes show alignment with surface structures. We see concentric strikes around arc volcanoes implying dipping magmatic structures and fabric into the middle crust. Regions with present-day weaker deformation show lower anomaly amplitudes but structurally aligned strikes, suggesting pre-Cenozoic fabrics may have been overprinted or otherwise modified. We observe general coherence of the signal across the brittle-plastic transition. Imaged crustal fabrics are aligned with major faults and shear zones, whereas intrafault blocks show imaged strikes both parallel to and at high angles to major block-bounding faults. High-angle strikes are subparallel to neotectonic deformation, seismicity, fault lineaments, and prominent metallogenic belts, possibly due to overprinting and/or co-evolution with fault-parallel fabrics. We suggest that the underlying tectonic grain in the northern Cordillera is broadly distributed rather than strongly localized. Receiver functions thus reveal key information about the nature and continuity of tectonic fabrics at depth and can provide unique insights into the deformation history and distribution of regional strain in complex orogenic belts.