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Active structural acoustic radiation control of a piezolaminated arbitrary thick rectangular plate with a mixed-norm H_2/H_∞ robust controller is developed. The structure is made of a transversely isotropic host layer with a distributed piezoelectric sensor layer as well as a matched piezoelectric actuator layer, facing high frequency uncertainties and random external disturbances. The elasto-acoustic formulation, based on the exact linear 3D piezo-elasticity theory, is developed for problem of fully coupled structure and acoustic mediums. Identification of the fluid/structure interaction system with subspace algorithm is implemented on actuator/sensor data sets. A multi-objective controller with regional pole placement, formulated in LMI framework, is synthesized while unmodeled dynamics are treated as multiplicative uncertainties. Numerical simulations confirm effectiveness of the implemented multi-objective robust active control scheme for reduction of radiated acoustic power from a piezocomposite plate, without stimulating any instability. Also, better tracking performance and disturbance rejection of mixed-norm controller is observed in comparison to that of H_2 and H_∞ controllers. Finally, validity of the elasto-acoustic model is proved by results obtained from a finite element software, as well as with the data available in the literature.

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Drop vortex is utilized to convey sewage across elevation change in steep catchments. This structure is generally used when the elevation difference is more than 5 m. Since the air and water flow are extensively combined in these structures and the sewage flow might contain detergent and foam producing materials, foam could produce in some parts of drop vortex. This phenomenon could affect vortex airflow and reduce drop vortex hydraulic performance. In this investigation, the effects of Foam Producing Flow (FPF) on vortex air discharge were studied by a scaled model and statistical Design of Experiment (DoE) methodology. Effects of Concentration Number, detergent type, and Froude Number on the dependent variable, air discharge to water discharge ratio, were studied by 33 full-factorial design and 63 runs. Analysis of the results revealed that all design factors had meaningful effects on vortex air discharge and it decreases by the increase of Concentration and Froude Number. Moreover, it was illuminated that foam formation could boost air discharge by 82% and in some conditions could reduce it more than 64%.