LQR control of wind induced motion of a benchmark building is considered. The building is fitted with a semiactive variable stiffness tuned mass damper adapted from the literature. The nominal stiffness of the device corresponds to the fundamental frequency of the building and is included in the system matrix. This results in a linear time-invariant system, for which the desired control force is computed using LQR control. The control force thus computed is then realized by varying the device stiffness around its nominal value by using a simple control law. A nonlinear static analysis is performed in order to establish the range of linearity, in terms of the device (configuration) angle, for which the control law is valid. Results are obtained for the cases of zero and nonzero structural stiffness variation. The performance criteria evaluated show that the present method provides displacement control that is comparable with that of two existing controllers. The acceleration control, while not as good as that obtained with the existing active controller, is comparable or better than that obtained with the existing semiactive controller. By using substantially less power as well as control force, the present control yields comparable displacement control and reasonable acceleration control.
Effective thermal conductivity and Young's modulus of periodic unit cell geometries are widely studied in the literature. This paper compares and contrasts strut-based unit cells against surface-based unit cells obtained by subtraction of sphere from solid cube. In order to understand the reason for the difference in the behavior of effective thermal conductivity of surface-based and strut-based unit cell geometries and the difference in the behavior of Young's modulus of surface-based and strut-based unit cell geometries, the effect of material distribution on effective thermal conductivity and Young's modulus is studied here. The material in the unit cell is varied in two ways, i.e., by changing the material distribution on the cell wall (partially closed unit cell) and changing the material distribution across the strut of unit cell geometry. It is found that the distribution of material on the wall of the unit cell improves the effective thermal conductivity and Young's modulus. In contrast, a narrow cross-section area reduces the effective thermal conductivity and Young's modulus. Using the studied effect of material distribution, the reason for the difference in properties of surface-based and strut-based unit cell geometry is explained. Partially closed unit cell geometries introduced here for studying the effect of material distribution on cell walls give a wide range of effective thermal conductivity and Young's modulus for the same porosity with a change in pore opening ratio.
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